Constitutively active protein kinase that acts as a negative regulator in the hormonal control of glucose homeostasis, Wnt signaling and regulation of transcription factors and microtubules, by phosphorylating and inactivating glycogen synthase (GYS1 or GYS2), EIF2B, CTNNB1/beta-catenin, APC, AXIN1, DPYSL2/CRMP2, JUN, NFATC1/NFATC, MAPT/TAU and MACF1. Requires primed phosphorylation of the majority of its substrates. In skeletal muscle, contributes to insulin regulation of glycogen synthesis by phosphorylating and inhibiting GYS1 activity and hence glycogen synthesis. May also mediate the development of insulin resistance by regulating activation of transcription factors. Regulates protein synthesis by controlling the activity of initiation factor 2B (EIF2BE/EIF2B5) in the same manner as glycogen synthase. In Wnt signaling, GSK3B forms a multimeric complex with APC, AXIN1 and CTNNB1/beta-catenin and phosphorylates the N-terminus of CTNNB1 leading to its degradation mediated by ubiquitin/proteasomes. Phosphorylates JUN at sites proximal to its DNA-binding domain, thereby reducing its affinity for DNA. Phosphorylates NFATC1/NFATC on conserved serine residues promoting NFATC1/NFATC nuclear export, shutting off NFATC1/NFATC gene regulation, and thereby opposing the action of calcineurin. Phosphorylates MAPT/TAU on 'Thr-548', decreasing significantly MAPT/TAU ability to bind and stabilize microtubules. MAPT/TAU is the principal component of neurofibrillary tangles in Alzheimer disease. Plays an important role in ERBB2-dependent stabilization of microtubules at the cell cortex. Phosphorylates MACF1, inhibiting its binding to microtubules which is critical for its role in bulge stem cell migration and skin wound repair. Probably regulates NF-kappa-B (NFKB1) at the transcriptional level and is required for the NF-kappa-B-mediated anti-apoptotic response to TNF-alpha (TNF/TNFA). Negatively regulates replication in pancreatic beta-cells, resulting in apoptosis, loss of beta-cells and diabetes. Phosphorylates MUC1 in breast cancer cells, decreasing the interaction of MUC1 with CTNNB1/beta-catenin. Is necessary for the establishment of neuronal polarity and axon outgrowth. Phosphorylates MARK2, leading to inhibit its activity. Phosphorylates SIK1 at 'Thr-182', leading to sustain its activity. Phosphorylates ZC3HAV1 which enhances its antiviral activity. Phosphorylates SFPQ at 'Thr-687' upon T-cell activation.
In resting human epithelial and fibroblastic cells, c-Jun is phosphorylated on serine and threonine at five sites, three of which are phosphorylated in vitro by glycogen synthase kinase 3 (GSK-3). These three sites are nested within a single tryptic peptide located just upstream of the basic region of the c-Jun DNA-binding domain (residues 227-252). Activation of protein kinase C results in rapid, site-specific dephosphorylation of c-Jun at one or more of these three sites and is coincident with increased AP-1-binding activity. Phosphorylation of recombinant human c-Jun proteins in vitro by GSK-3 decreases their DNA-binding activity. Mutation of serine 243 to phenylalanine blocks phosphorylation of all three sites in vivo and increases the inherent trans-activation ability of c-Jun at least 10-fold. We propose that c-Jun is present in resting cells in a latent, phosphorylated form that can be activated by site-specific dephosphorylation in response to protein kinase C activation.
Site-specific phosphorylation of tau negatively regulates its ability to bind and stabilize microtubule structure. Although tau is a substrate of glycogen synthase kinase 3beta (GSK3beta), the exact sites on tau that are phosphorylated by this kinase in situ have not yet been established, and the effect of these phosphorylation events on tau-microtubule interactions have not been fully elucidated. GSK3beta phosphorylates both primed and unprimed sites on tau, but only primed phosphorylation events significantly decrease the ability of tau to bind microtubules. The focus of the present study is on determining the importance of the GSK3beta-mediated phosphorylation of a specific primed site, Thr231, in regulating tau's function. Pre-phosphorylation of Ser235 primes tau for phosphorylation by GSK3beta at Thr231. Phosphorylation by GSK3beta of wild-type tau or tau with Ser235 mutated to Ala decreases tau-microtubule interactions. However, when Thr231 alone or Thr231 and Ser235 in tau were mutated to Ala, phosphorylation by GSK3beta did not decrease the association of tau with the cytoskeleton. Further, T231A tau was still able to efficiently bind microtubules after phosphorylation by GSK3beta. Expression of each tau construct alone increased tubulin acetylation, a marker of microtubule stability. However, when cells were cotransfected with wild-type tau and GSK3beta, the level of tubulin acetylation was decreased to vector-transfected levels. In contrast, coexpression of GSK3beta with mutated tau (T231A/S235A) did not significantly decrease the levels of acetylated tubulin. These results strongly indicate that phosphorylation of Thr231 in tau by GSK3beta plays a critical role in regulating tau's ability to bind and stabilize microtubules.
Autophosphorylation is an important mechanism by which protein kinases regulate their own biological activities. Salt inducible kinase 1 (SIK1) is a regulator in the feedback cascades of cAMP-mediated gene expression, while its kinase domain also features autophosphorylation activity. We provide evidence that Ser186 in the activation loop is the site of autophosphorylation and essential for the kinase activity. Ser186 is located at the +4 position of the critical Thr residue Thr182, which is phosphorylated by upstream kinases such as LKB1. The relationship between phosphorylation at Ser186 and at Thr182 in COS-7 cells indicates that the former is a prerequisite for the latter. Glycogen synthase kinase-3beta (GSK-3beta) phosphorylates Ser/Thr residues located at the fourth position ahead of the pre-phosphorylated Ser/Thr residues, and inhibitors of GSK-3beta reduce the phosphorylation at Thr182. The results of an in vitro reconstitution assay also indicate that GSK-3beta could be the SIK1 kinase. However, overexpression and knockdown of GSK-3beta in LKB1-defective HeLa cells suggests that GSK-3beta alone may not be able to phosphorylate or activate SIK1, indicating that LKB1 may play a crucial role by phosphorylating SIK1 at Thr182, possibly as an initiator of the autophosphorylation cascade, and GSK-3beta may phosphorylate SIK1 at Thr182 by recognizing the priming-autophosphorylation at Ser186 in cultured cells. This may also be the case for the other isoform SIK2, but not for SIK3.
Microtubules (MTs) contribute to key processes during cell motility, including the regulation of focal adhesion turnover and the establishment and maintenance of cell orientation. It was previously demonstrated that the ErbB2 receptor tyrosine kinase regulated MT outgrowth to the cell cortex via a complex including Memo, the GTPase RhoA, and the formin mDia1. But the mechanism that linked this signaling module to MTs remained undefined. We report that ErbB2-induced repression of glycogen synthase kinase-3 (GSK3) activity, mediated by Memo and mDia1, is required for MT capture and stabilization. Memo-dependent inhibition of GSK3 allows the relocalization of APC (adenomatous polyposis coli) and cytoplasmic linker-associated protein 2 (CLASP2), known MT-associated proteins, to the plasma membrane and ruffles. Peripheral microtubule extension also requires expression of the plus-end binding protein EB1 and its recently described interactor, the spectraplakin ACF7. In fact, in migrating cells, ACF7 localizes to the plasma membrane and ruffles, in a Memo-, GSK3-, and APC-dependent manner. Finally, we demonstrate that ACF7 targeting to the plasma membrane is both required and sufficient for MT capture downstream of ErbB2. This function of ACF7 does not require its recently described ATPase activity. By defining the signaling pathway by which ErbB2 allows MT capture and stabilization at the cell leading edge, we provide insights into the mechanism underlying cell motility and steering.
Signal-induced alternative splicing of the CD45 gene in human T cells is essential for proper immune function. Skipping of the CD45 variable exons is controlled, in large part, by the recruitment of PSF to the pre-mRNA substrate upon T cell activation; however, the signaling cascade leading to exon exclusion has remained elusive. Here we demonstrate that in resting T cells PSF is directly phosphorylated by GSK3, thus promoting interaction of PSF with TRAP150, which prevents PSF from binding CD45 pre-mRNA. Upon T cell activation, reduced GSK3 activity leads to reduced PSF phosphorylation, releasing PSF from TRAP150 and allowing it to bind CD45 splicing regulatory elements and repress exon inclusion. Our data place two players, GSK3 and TRAP150, in the complex network that regulates CD45 alternative splicing and demonstrate a paradigm for signal transduction from the cell surface to the RNA processing machinery through the multifunctional protein PSF.
The transcription factor NF-AT responds to Ca2+-calcineurin signals by translocating to the nucleus, where it participates in the activation of early immune response genes. Calcineurin dephosphorylates conserved serine residues in the amino terminus of NF-AT, resulting in nuclear import. Purification of the NF-AT kinase revealed that it is composed of a priming kinase activity and glycogen synthase kinase-3 (GSK-3). GSK-3 phosphorylates conserved serines necessary for nuclear export, promotes nuclear exit, and thereby opposes Ca2+-calcineurin signaling. Because GSK-3 responds to signals initiated by Wnt and other ligands, NF-AT family members could be effectors of these pathways.
Biochem. J. 294 ( Pt 3), 625-629 (1993)[PubMed:8397507]
We have studied the control of insulin-regulated protein kinases in Chinese hamster ovary cells transfected with the human insulin receptor (CHO.T cells). Among these enzymes is one that is obtained after chromatography of cell extracts on Mono-S, whose activity is decreased (7.3 +/- 1.9-fold) within 10 min of insulin treatment. This enzyme phosphorylates glycogen synthase and the largest subunit of protein synthesis eukaryotic initiation factor (eIF)-2B (the guanine nucleotide exchange factor). The kinase appears to be glycogen synthase kinase-3 (GSK-3), on the basis of: (1) its ability to phosphorylate a peptide based on the phosphorylation sites for GSK-3 in glycogen synthase, and (2) the finding that the fractions possessing this activity contain immunoreactive GSK-3, whose peak is coincident with that of kinase activity, as judged by immunoblotting using antibodies specific for the alpha- and beta-isoforms of GSK-3. The decrease in kinase activity induced by insulin was reversed by treatment of the column fractions with protein phosphatase-2A. These data indicate that insulin rapidly causes inactivation of GSK-3 and that this is due to phosphorylation of GSK-3. The implications of these findings for the control of glycogen and protein metabolism are discussed.
Glycogen synthase kinase 3beta (GSK3beta) is a serine/threonine kinase involved in insulin, growth factor and Wnt signalling. In Wnt signalling, GSK3beta is recruited to a multiprotein complex via interaction with axin, where it hyperphosphorylates beta-catenin, marking it for ubiquitylation and destruction. We have now determined the crystal structure of GSK3beta in complex with a minimal GSK3beta-binding segment of axin, at 2.4 A resolution. The structure confirms the co-localization of the binding sites for axin and FRAT in the C-terminal domain of GSK3beta, but reveals significant differences in the interactions made by axin and FRAT, mediated by conformational plasticity of the 285-299 loop in GSK3beta. Detailed comparison of the axin and FRAT GSK3beta complexes allows the generation of highly specific mutations, which abrogate binding of one or the other. Quantitative analysis suggests that the interaction of GSK3beta with the axin scaffold enhances phosphorylation of beta-catenin by >20 000-fold.
The DF3/MUC1 mucin-like glycoprotein is highly overexpressed in human carcinomas. Recent studies have demonstrated that the cytoplasmic domain of MUC1 interacts with beta-catenin. Here we show that MUC1 associates with glycogen synthase kinase 3beta (GSK3beta). GSK3beta binds directly to an STDRSPYE site in MUC1 and phosphorylates the serine adjacent to proline. Phosphorylation of MUC1 by GSK3beta decreases binding of MUC1 to beta-catenin in vitro and in vivo. GSK3beta-mediated phosphorylation of MUC1 had no apparent effect on beta-catenin levels or the transcriptional coactivation function of beta-catenin. The results, however, demonstrate that MUC1 expression decreases binding of beta-catenin to the E-cadherin cell adhesion molecule. Negative regulation of the beta-catenin-MUC1 interaction by GSK3beta is associated with restoration of the complex between beta-catenin and E-cadherin. These findings indicate that GSK3beta decreases the interaction of MUC1 with beta-catenin and that overexpression of MUC1 in the absence of GSK3beta activity inhibits formation of the E-cadherin-beta-catenin complex.
The inhibition of GSK3 is required for the stimulation of glycogen and protein synthesis by insulin and the specification of cell fate during development. Here, we demonstrate that the insulin-induced inhibition of GSK3 and its unique substrate specificity are explained by the existence of a phosphate binding site in which Arg-96 is critical. Thus, mutation of Arg-96 abolishes the phosphorylation of "primed" glycogen synthase as well as inhibition by PKB-mediated phosphorylation of Ser-9. Hence, the phosphorylated N terminus acts as a pseudosubstrate, occupying the same phosphate binding site used by primed substrates. Significantly, this mutation does not affect phosphorylation of "nonprimed" substrates in the Wnt-signaling pathway (Axin and beta-catenin), suggesting new approaches to design more selective GSK3 inhibitors for the treatment of diabetes.
Zinc-finger antiviral protein (ZAP) is a host factor that specifically inhibits the replication of certain viruses, including HIV-1, Ebola virus, and Sindbis virus. ZAP binds directly to specific viral mRNAs and recruits cellular mRNA degradation machinery to degrade the target RNA. ZAP has also been suggested to repress translation of the target mRNA. In this study, we report that ZAP is phosphorylated by glycogen synthase kinase 3β (GSK3β). GSK3β sequentially phosphorylated Ser-270, Ser-266, Ser-262, and Ser-257 of rat ZAP. Inhibition of GSK3β by inhibitor SB216763 or down-regulation of GSK3β by RNAi reduced the antiviral activity of ZAP. These results indicate that phosphorylation of ZAP by GSK3β modulates ZAP activity.
The phenotypic changes of increased motility and invasiveness of cancer cells are reminiscent of the epithelial-mesenchymal transition (EMT) that occurs during embryonic development. Snail, a zinc-finger transcription factor, triggers this process by repressing E-cadherin expression; however, the mechanisms that regulate Snail remain elusive. Here we find that Snail is highly unstable, with a short half-life about 25 min. We show that GSK-3beta binds to and phosphorylates Snail at two consensus motifs to dually regulate the function of this protein. Phosphorylation of the first motif regulates its beta-Trcp-mediated ubiquitination, whereas phosphorylation of the second motif controls its subcellular localization. A variant of Snail (Snail-6SA), which abolishes these phosphorylations, is much more stable and resides exclusively in the nucleus to induce EMT. Furthermore, inhibition of GSK-3beta results in the upregulation of Snail and downregulation of E-cadherin in vivo. Thus, Snail and GSK-3beta together function as a molecular switch for many signalling pathways that lead to EMT.
The adenomatous polyposis coli gene (APC) is mutated in most colon cancers. The APC protein binds to the cellular adhesion molecule beta-catenin, which is a mammalian homolog of ARMADILLO, a component of the WINGLESS signaling pathway in Drosophila development. Here it is shown that when beta-catenin is present in excess, APC binds to another component of the WINGLESS pathway, glycogen synthase kinase 3beta (GSK3beta), a mammalian homolog of Drosophila ZESTE WHITE 3. APC was a good substrate for GSK3 beta in vitro, and the phosphorylation sites were mapped to the central region of APC. Binding of beta-catenin to this region was dependent on phosphorylation by GSK3 beta.
Interacting selectively and non-covalently with an ionotropic glutamate receptor. Ionotropic glutamate receptors bind glutamate and exert an effect through the regulation of ion channels.
The phenotypic changes of increased motility and invasiveness of cancer cells are reminiscent of the epithelial-mesenchymal transition (EMT) that occurs during embryonic development. Snail, a zinc-finger transcription factor, triggers this process by repressing E-cadherin expression; however, the mechanisms that regulate Snail remain elusive. Here we find that Snail is highly unstable, with a short half-life about 25 min. We show that GSK-3beta binds to and phosphorylates Snail at two consensus motifs to dually regulate the function of this protein. Phosphorylation of the first motif regulates its beta-Trcp-mediated ubiquitination, whereas phosphorylation of the second motif controls its subcellular localization. A variant of Snail (Snail-6SA), which abolishes these phosphorylations, is much more stable and resides exclusively in the nucleus to induce EMT. Furthermore, inhibition of GSK-3beta results in the upregulation of Snail and downregulation of E-cadherin in vivo. Thus, Snail and GSK-3beta together function as a molecular switch for many signalling pathways that lead to EMT.
The activity of NF-kappaB is controlled at several levels including the phosphorylation of the strongly transactivating p65 (RelA) subunit. However, the overall number of phosphorylation sites, the signaling pathways and protein kinases that target p65 NF-kappaB and the functional role of these phosphorylations are still being uncovered. Using a combination of peptide arrays with in vitro kinase assays we identify serine 468 as a novel phosphorylation site of p65 NF-kappaB. Serine 468 lies within a GSK-3beta consensus site, and recombinant GSK-3beta specifically phosphorylates a GST-p65-(354-551) fusion protein at Ser(468) in vitro. In intact cells, phosphorylation of endogenous Ser(468) of p65 is induced by the PP1/PP2A phosphatase inhibitor calyculin A and this effect is inhibited by the GSK-3beta inhibitor LiCl. Reconstitution of p65-deficient cells with a p65 protein where serine 468 was mutated to alanine revealed a negative regulatory role of serine 468 for NF-kappaB activation. Collectively our results suggest that a GSK-3beta-PP1-dependent mechanism regulates phosphorylation of p65 NF-kappaB at Ser(468) in unstimulated cells and thereby controls the basal activity of NF-kappaB.
The tumor suppressor p53, a sensor of multiple forms of cellular stress, is regulated by post-translational mechanisms to induce cell-cycle arrest, senescence, or apoptosis. We demonstrate that endoplasmic reticulum (ER) stress inhibits p53-mediated apoptosis. The mechanism of inhibition involves the increased cytoplasmic localization of p53 due to phosphorylation at serine 315 and serine 376, which is mediated by glycogen synthase kinase-3 beta (GSK-3beta). ER stress induces GSK-3beta binding to p53 in the nucleus and enhances the cytoplasmic localization of the tumor suppressor. Inhibition of apoptosis caused by ER stress requires GSK-3beta and does not occur in cells expressing p53 with mutation(s) of serine 315 and/or serine 376 to alanine(s). As a result of the increased cytoplasmic localization, ER stress prevents p53 stabilization and p53-mediated apoptosis upon DNA damage. It is concluded that inactivation of p53 is a protective mechanism utilized by cells to adapt to ER stress.
Interacting selectively and non-covalently with any protein or protein complex (a complex of two or more proteins that may include other nonprotein molecules).
Evidence
1:
Inferred from Physical InteractionIntAct
The stability of the Wnt pathway transcription factor beta-catenin is tightly regulated by the multi-subunit destruction complex. Deregulated Wnt pathway activity has been implicated in many cancers, making this pathway an attractive target for anticancer therapies. However, the development of targeted Wnt pathway inhibitors has been hampered by the limited number of pathway components that are amenable to small molecule inhibition. Here, we used a chemical genetic screen to identify a small molecule, XAV939, which selectively inhibits beta-catenin-mediated transcription. XAV939 stimulates beta-catenin degradation by stabilizing axin, the concentration-limiting component of the destruction complex. Using a quantitative chemical proteomic approach, we discovered that XAV939 stabilizes axin by inhibiting the poly-ADP-ribosylating enzymes tankyrase 1 and tankyrase 2. Both tankyrase isoforms interact with a highly conserved domain of axin and stimulate its degradation through the ubiquitin-proteasome pathway. Thus, our study provides new mechanistic insights into the regulation of axin protein homeostasis and presents new avenues for targeted Wnt pathway therapies.
Evidence
2:
Inferred from Physical InteractionIntAct
Degradation of cytosolic β-catenin by the APC/Axin1 destruction complex represents the key regulated step of the Wnt pathway. It is incompletely understood how the Axin1 complex exerts its Wnt-regulated function. Here, we examine the mechanism of Wnt signaling under endogenous levels of the Axin1 complex. Our results demonstrate that β-catenin is not only phosphorylated inside the Axin1 complex, but also ubiquinated and degraded via the proteasome, all within an intact Axin1 complex. In disagreement with current views, we find neither a disassembly of the complex nor an inhibition of phosphorylation of Axin1-bound β-catenin upon Wnt signaling. Similar observations are made in primary intestinal epithelium and in colorectal cancer cell lines carrying activating Wnt pathway mutations. Wnt signaling suppresses β-catenin ubiquitination normally occurring within the complex, leading to complex saturation by accumulated phospho-β-catenin. Subsequently, newly synthesized β-catenin can accumulate in a free cytosolic form and engage nuclear TCF transcription factors.
Evidence
3:
Inferred from Physical InteractionIntAct
Axin is a central component of the canonical Wnt signaling pathway that interacts with the adenomatous polyposis coli protein APC and the kinase GSK3beta to downregulate the effector beta-catenin. In the nematode Caenorhabditis elegans, canonical Wnt signaling is negatively regulated by the highly divergent Axin ortholog PRY-1. Mutation of pry-1 leads to constitutive activation of BAR-1/beta-catenin-dependent Wnt signaling and results in a range of developmental defects. The pry-1 null phenotype is however not fully penetrant, indicating that additional factors may partially compensate for PRY-1 function. Here, we report the cloning and functional analysis of a second Axin-like protein, which we named AXL-1. We show that despite considerable sequence divergence with PRY-1 and other Axin family members, AXL-1 is a functional Axin ortholog. AXL-1 functions redundantly with PRY-1 in negatively regulating BAR-1/beta-catenin signaling in the developing vulva and the Q neuroblast lineage. In addition, AXL-1 functions independently of PRY-1 in negatively regulating canonical Wnt signaling during excretory cell development. In contrast to vertebrate Axin and the related protein Conductin, AXL-1 and PRY-1 are not functionally equivalent. We conclude that Axin function in C. elegans is divided over two different Axin orthologs that have specific functions in negatively regulating canonical Wnt signaling.
Evidence
4:
Inferred from Physical InteractionIntAct
The Wnt/β-catenin signaling pathway plays important roles in the progression of colon cancer. DACT1 has been identified as a modulator of Wnt signaling through its interaction with Dishevelled (Dvl), a central mediator of both the canonical and noncanonical Wnt pathways. However, the functions of DACT1 in the WNT/β-catenin signaling pathway remain unclear. Here, we present evidence that DACT1 is an important positive regulator in colon cancer through regulating the stability and sublocation of β-catenin. We have shown that DACT1 promotes cancer cell proliferation in vitro and tumor growth in vivo and enhances the migratory and invasive potential of colon cancer cells. Furthermore, the higher expression of DACT1 not only increases the nuclear and cytoplasmic fractions of β-catenin, but also increases its membrane-associated fraction. The overexpression of DACT1 leads to the increased accumulation of nonphosphorylated β-catenin in the cytoplasm and particularly in the nuclei. We have demonstrated that DACT1 interacts with GSK-3β and β-catenin. DACT1 stabilizes β-catenin via DACT1-induced effects on GSK-3β and directly interacts with β-catenin proteins. The level of phosphorylated GSK-3β at Ser9 is significantly increased following the elevated expression of DACT1. DACT1 mediates the subcellular localization of β-catenin via increasing the level of phosphorylated GSK-3β at Ser9 to inhibit the activity of GSK-3β. Taken together, our study identifies DACT1 as an important positive regulator in colon cancer and suggests a potential strategy for the therapeutic control of the β-catenin-dependent pathway.
Evidence
5:
Inferred from Physical InteractionBHF-UCL
beta-catenin-mediated Wnt signaling is critical in animal development and tumor progression. The single-span transmembrane Wnt receptor, low-density lipoprotein receptor-related protein 6 (LRP6), interacts with Axin to promote the Wnt-dependent accumulation of beta-catenin. However, the molecular mechanism of receptor internalization and its impact on signaling are unclear. Here, we present evidence that LRP6 is internalized with caveolin and that the components of this endocytic pathway are required not only for Wnt-3a-induced internalization of LRP6 but also for accumulation of beta-catenin. Overall, our data suggest that Wnt-3a triggers the interaction of LRP6 with caveolin and promotes recruitment of Axin to LRP6 phosphorylated by glycogen synthase kinase-3beta and that caveolin thereby inhibits the binding of beta-catenin to Axin. Thus, caveolin plays critical roles in inducing the internalization of LRP6 and activating the Wnt/beta-catenin pathway. We also discuss the idea that distinct endocytic pathways correlate with the specificity of Wnt signaling events.
Evidence
6:
Inferred from Physical InteractionBHF-UCL
A single nucleotide polymorphism in the DAB2IP gene is associated with risk of aggressive prostate cancer (PCa), and loss of DAB2IP expression is frequently detected in metastatic PCa. However, the functional role of DAB2IP in PCa remains unknown. Here, we show that the loss of DAB2IP expression initiates epithelial-to-mesenchymal transition (EMT), which is visualized by repression of E-cadherin and up-regulation of vimentin in both human normal prostate epithelial and prostate carcinoma cells as well as in clinical prostate-cancer specimens. Conversely, restoring DAB2IP in metastatic PCa cells reversed EMT. In DAB2IP knockout mice, prostate epithelial cells exhibited elevated mesenchymal markers, which is characteristic of EMT. Using a human prostate xenograft-mouse model, we observed that knocking down endogenous DAB2IP in human carcinoma cells led to the development of multiple lymph node and distant organ metastases. Moreover, we showed that DAB2IP functions as a scaffold protein in regulating EMT by modulating nuclear beta-catenin/T-cell factor activity. These results show the mechanism of DAB2IP in EMT and suggest that assessment of DAB2IP may provide a prognostic biomarker and potential therapeutic target for PCa metastasis.
Evidence
7:
Inferred from Physical InteractionIntAct
The increased motility and invasiveness of tumor cells are reminiscent of epithelial-mesenchymal transition (EMT), which occurs during embryonic development, wound healing, and metastasis. In this study, we found that Snail is stabilized by the inflammatory cytokine TNFalpha through the activation of the NF-kappaB pathway. We demonstrated that NF-kappaB is required for the induction of COP9 signalosome 2 (CSN2), which, in turn, blocks the ubiquitination and degradation of Snail. Furthermore, we showed that the expression of Snail correlated with the activation of NF-kappaB in cancer cell lines and metastatic tumor samples. Knockdown of Snail expression inhibited cell migration and invasion induced by inflammatory cytokines and suppressed inflammation-mediated breast cancer metastasis. Our study provides a plausible mechanism for inflammation-induced metastasis.
Evidence
8:
Inferred from Physical InteractionUniProtKB
BACKGROUND: Inactivation of the adenomatous polyposis coli (APC) tumor suppressor protein is responsible for both inherited and sporadic forms of colon cancer. Growth control by APC may relate to its ability to downregulate beta-catenin post-translationally. In cancer, mutations in APC ablate its ability to regulate beta-catenin, and mutations in beta-catenin prevent its downregulation by wild-type APC. Moreover, signaling by the protein product of the wnt-1 proto-oncogene upregulates beta-catenin and promotes tumorigenesis in mice. In a Xenopus developmental system, Wnt-1 signaling was inhibited by Axin, the product of the murine fused gene. This suggests a possible link between Axin, the Wnt-1 signaling components beta-catenin and glycogen synthase kinase 3 beta (GSK3 beta), and APC. RESULTS: Human Axin (hAxin) binds directly to beta-catenin, GSK3 beta, and APC in vitro, and the endogenous proteins are found in a complex in cells. Binding sites for Axin were mapped to a region of APC that is typically deleted due to cancer-associated mutations in the APC gene. Overexpression of hAxin strongly promoted the downregulation of wild-type beta-catenin in colon cancer cells, whereas mutant oncogenic beta-catenin was unaffected. The downregulation was increased by deletion of the APC-binding domain from Axin, suggesting that APC may function to derepress Axin activity. In addition, hAxin dramatically facilitated the phosphorylation of APC and beta-catenin by GSK3 beta in vitro. CONCLUSIONS: Axin acts as a scaffold upon which APC, beta-catenin and GSK3 beta assemble to coordinate the regulation of beta-catenin signaling.
Evidence
9:
Inferred from Physical InteractionIntAct
The protein kinase Akt/PKB is stimulated by the phosphorylation of two regulatory residues, Thr 309 of the activation segment and Ser 474 of the hydrophobic motif (HM), that are structurally and functionally conserved within the AGC kinase family. To understand the mechanism of PKB regulation, we determined the crystal structures of activated kinase domains of PKB in complex with a GSK3beta-peptide substrate and an ATP analog. The activated state of the kinase was generated by phosphorylating Thr 309 using PDK1 and mimicking Ser 474 phosphorylation either with the S474D substitution or by replacing the HM of PKB with that of PIFtide, a potent mimic of a phosphorylated HM. Comparison with the inactive PKB structure indicates that the role of Ser 474 phosphorylation is to promote the engagement of the HM with the N-lobe of the kinase domain, promoting a disorder-to-order transition of the alphaC helix. The alphaC helix, by interacting with pThr 309, restructures and orders the activation segment, generating an active kinase conformation. Analysis of the interactions between PKB and the GSK3beta-peptide explains how PKB selects for protein substrates distinct from those of PKA.
Evidence
10:
Inferred from Physical InteractionIntAct
The immediate early transcription factor nuclear factor (IκBs) kappa B (NF-κB) is crucially involved in the regulation of numerous physiological or pathophysiological processes such as inflammation and tumourigenesis. Therefore, the control of NF-κB activity, which is mainly regulated by signal-induced degradation of cytoplasmic inhibitors of NF-κB (IκBs), is of high relevance. One known alternative pathway of NF-κB regulation is the stimulus-induced proteasomal degradation of RelB, a component of the NF-κB dimer. Here, we identified the serine/threonine protein kinase glycogen synthase kinase-3β (GSK-3β) as a critical signalling component leading to RelB degradation. In Jurkat leukaemic T cells as well as in primary human T cells, tetradecanoylphorbolacetate/ionomycin- and CD3/CD28-induced RelB degradation were impaired by a GSK-3β-specific pharmacological inhibitor, an ectopically expressed dominant-negative GSK-3β mutant and by small-interfering RNA-mediated silencing of GSK-3β expression. Furthermore, a physical interaction between RelB and GSK-3β was shown by co-immunoprecipitation, which was already notable in unstimulated cells. Most importantly, as demonstrated by in vitro kinase assays, human RelB is inducibly phosphorylated by GSK-3β, indicating a direct substrate-enzyme relationship. The serine residue 552 is a target of GSK-3β-mediated phosphorylation in vitro and in vivo. We conclude that GSK-3β is a crucial regulator of RelB degradation, stressing the relevant linkage between the NF-κB system and GSK-3β.
Evidence
11:
Inferred from Physical InteractionBHF-UCL
The adenomatous polyposis coli gene (APC) is mutated in most colon cancers. The APC protein binds to the cellular adhesion molecule beta-catenin, which is a mammalian homolog of ARMADILLO, a component of the WINGLESS signaling pathway in Drosophila development. Here it is shown that when beta-catenin is present in excess, APC binds to another component of the WINGLESS pathway, glycogen synthase kinase 3beta (GSK3beta), a mammalian homolog of Drosophila ZESTE WHITE 3. APC was a good substrate for GSK3 beta in vitro, and the phosphorylation sites were mapped to the central region of APC. Binding of beta-catenin to this region was dependent on phosphorylation by GSK3 beta.
Evidence
12:
Inferred from Physical InteractionUniProtKB
Members of the dynamin superfamily are implicated in vesicle trafficking. Using human glycogen synthase kinase 3 beta (Gsk-3 beta) as bait in the yeast two-hybrid system, we identified a novel human dynamin-like protein IV (HdynIV). When the full-length cDNA of HdynIV was sequenced, it showed that HdynIV's carboxyl terminal lacks a proline-rich domain that can bind to Gsk-3 beta. By Northern blot analysis and isoform-specific PCR, we found that HdynIV is expressed ubiquitously in all human tissues examined. Two transcripts of 2.4 and 4.4 kb are shown to be more abundant in heart, brain, and skeletal muscle. Interestingly, the 2.4-kb transcript is expressed more distinctly in the fetal liver than in the adult liver, suggesting that this protein might play a role during development. In the present report, we have demonstrated that HdynIV interacts with the Gsk-3 beta through its carboxyl-terminal region, implying than HdynIV may also be involved in cell signaling.
Evidence
13:
Inferred from Physical InteractionBHF-UCL
Glycogen synthase kinase 3 (GSK3) is a widely expressed Ser/Thr protein kinase that phosphorylates numerous substrates. This large number of substrates requires precise and specific regulation of GSK3 activity, which is achieved by a combination of phosphorylation, localization, and interactions with GSK3-binding proteins. Members of the Wnt canonical pathway have been shown to influence GSK3 activity. Through a yeast two-hybrid screen, we identified the Wnt canonical pathway co-receptor protein low density lipoprotein receptor-related protein 6 (LRP6) as a GSK3-binding protein. The interaction between the C terminus of LRP6 and GSK3 was also confirmed by in vitro GST pull-down assays and in situ coimmunoprecipitation assays. In vitro assays using immunoprecipitated proteins demonstrated that the C terminus of LRP6 significantly attenuated the activity of GSK3beta. In situ, LRP6 significantly decreased GSK3beta-mediated phosphorylation of tau at both primed and unprimed sites. Finally, it was also demonstrated that GSK3beta phosphorylates the PPP(S/T)P motifs in the C terminus of LRP6. This is the first identification of a direct interaction between LRP6 and GSK3, which results in an attenuation of GSK3 activity.
Evidence
14:
Inferred from Physical InteractionIntAct
Microsomal prostaglandin E synthase-1 (mPGES-1) is a key enzyme that couples with cyclooxygenase-2 (COX-2) for the production of PGE(2). Although COX-2 is known to mediate the growth and progression of several human cancers including hepatocellular carcinoma (HCC), the role of mPGES-1 in hepatocarcinogenesis is not well established. This study provides novel evidence for a key role of mPGES-1 in HCC growth and progression. Forced overexpression of mPGES-1 in two HCC cell lines (Hep3B and Huh7) increased tumor cell growth, clonogenic formation, migration and invasion, whereas knockdown of mPGES-1 inhibited these parameters, in vitro. In a mouse tumor xenograft model, mPGES-1-overexpressed cells formed palpable tumors at earlier time points and developed larger tumors when compared with the control (P<0.01); in contrast, mPGES-1 knockdown delayed tumor development and reduced tumor size (P<0.01). Mechanistically, mPGES-1-induced HCC cell proliferation, invasion and migration involve PGE(2) production and activation of early growth response 1 (EGR1) and β-catenin. Specifically, mPGES-1-derived PGE(2) induces the formation of EGR1-β-catenin complex, which interacts with T-cell factor 4/lymphoid enhancer factor 1 transcription factors and activates the expression of β-catenin downstream genes. Our findings depict a novel crosstalk between mPGES-1/PGE(2) and EGR1/β-catenin signaling that is critical for hepatocarcinogenesis.
Evidence
15:
Inferred from Physical InteractionBHF-UCL
Glycogen synthase kinase-3 (GSK-3) mediates epidermal growth factor, insulin and Wnt signals to various downstream events such as glycogen metabolism, gene expression, proliferation and differentiation. We have isolated here a GSK-3beta-interacting protein from a rat brain cDNA library using a yeast two-hybrid method. This protein consists of 832 amino acids and possesses Regulators of G protein Signaling (RGS) and dishevelled (Dsh) homologous domains in its N- and C-terminal regions, respectively. The predicted amino acid sequence of this GSK-3beta-interacting protein shows 94% identity with mouse Axin, which recently has been identified as a negative regulator of the Wnt signaling pathway; therefore, we termed this protein rAxin (rat Axin). rAxin interacted directly with, and was phosphorylated by, GSK-3beta. rAxin also interacted directly with the armadillo repeats of beta-catenin. The binding site of rAxin for GSK-3beta was distinct from the beta-catenin-binding site, and these three proteins formed a ternary complex. Furthermore, rAxin promoted GSK-3beta-dependent phosphorylation of beta-catenin. These results suggest that rAxin negatively regulates the Wnt signaling pathway by interacting with GSK-3beta and beta-catenin and mediating the signal from GSK-3beta to beta-catenin.
Evidence
16:
Inferred from Physical InteractionIntAct
Axin, a negative regulator of Wnt signaling, is a key scaffold protein for the β-catenin destruction complex. It has been previously shown that multiple post-translational modification enzymes regulate the level of Axin. Here, we provide evidence that protein arginine methyltransferase 1 (PRMT1) directly interacts with and methylates the 378th arginine residue of Axin both in vitro and in vivo. We found that the transient expression of PRMT1 led to an increased level of Axin and that knockdown of endogenous PRMT1 by short hairpin RNA reduced the level of Axin. These results suggest that methylation by PRMT1 enhanced the stability of Axin. Methylation of Axin by PRMT1 also seemingly enhanced the interaction between Axin and glycogen synthase kinase 3β, leading to decreased ubiquitination of Axin. Consistent with the role of PRMT1 in the regulation of Axin, knockdown of PRMT1 enhanced the level of cytoplasmic β-catenin as well as β-catenin-dependent transcription activity. In summary, we show that the methylation of Axin occurred in vivo and controlled the stability of Axin. Therefore, methylation of Axin by PRMT1 may serve as a finely tuned regulation mechanism for Wnt/β-catenin signaling.
Evidence
17:
Inferred from Physical InteractionHGNC
The centrosomal protein ninein has been identified as a microtubules minus end capping, centriole position, and anchoring protein, but the true physiological function remains to be determined. In this report, using immunofluorescence analysis and GFP-fusions we show that coiled-coil II domain (CCII domain, 1303-2096) co-localized with gamma-tubulin and centrin at the centrosome. We further narrow down within 83 amino acids and classify a new centrosomal targeting signal. Interestingly, antibodies raised against CCII domain reveal that ninein protein declines from spindle poles during mitosis, but reaccumulates at centrosomes at the end of cell division. Moreover, the data also suggest that fragment 1783-1866 may be attributed to declined signal of ninein. In kinase assay, we show that CCII domain could readily be phosphorylated by AIK and PKA. Taken together, our results suggest that ninein protein contains two distinct subdomains which are required for targeting and regulating asymmetry centrosomes. Importantly, the decline of ninein during mitosis implies that this centrosomal protein may play a role to regulate the process of chromosome segregation without discrimination. The model we propose here will foster a clearer picture of how two asymmetric centrosomes could direct and ensure the correct segregation of chromosomes during the mitotic stage.
Evidence
18:
Inferred from Physical InteractionIntAct
Pancreatic cancer is a deadly disease characterized by late diagnosis and resistance to therapy. Much progress has been made in defining gene defects in pancreatic cancer, but a full accounting of its molecular pathogenesis remains to be provided. Here, we show that expression of the ataxia-telangiectasia group D complementing gene (ATDC), also called TRIM29, is elevated in most invasive pancreatic cancers and pancreatic cancer precursor lesions. ATDC promoted cancer cell proliferation in vitro and enhanced tumor growth and metastasis in vivo. ATDC expression correlated with elevated beta-catenin levels in pancreatic cancer, and beta-catenin function was required for ATDC's oncogenic effects. ATDC was found to stabilize beta-catenin via ATDC-induced effects on the Disheveled-2 protein, a negative regulator of glycogen synthase kinase 3beta in the Wnt/beta-catenin signaling pathway.
Evidence
19:
Inferred from Physical InteractionIntAct
The PI3K/AKT signaling pathway is aberrant in a wide variety of cancers. Downstream effectors of AKT are involved in survival, growth and metabolic-related pathways. In contrast, contradictory data relating to AKT effects on cell motility and invasion, crucial prometastatic processes, have been reported pointing to a potential cell type and isoform type-specific AKT-driven function. By implication, study of AKT signaling should optimally be conducted in an appropriate intracellular environment. Prognosis in soft-tissue sarcoma (STS), the aggressive malignancies of mesenchymal origin, is poor, reflecting our modest ability to control metastasis, an effort hampered by lack of insight into molecular mechanisms driving STS progression and dissemination. We examined the impact of the cancer progression-relevant AKT pathway on the mesenchymal tumor cell internal milieu. We demonstrate that AKT1 activation induces STS cell motility and invasiveness at least partially through a novel interaction with the intermediate filament vimentin (Vim). The binding of AKT (tail region) to Vim (head region) results in Vim Ser39 phosphorylation enhancing the ability of Vim to induce motility and invasion while protecting Vim from caspase-induced proteolysis. Moreover, vimentin phosphorylation was shown to enhance tumor and metastasis growth in vivo. Insights into this mesenchymal-related molecular mechanism may facilitate the development of critically lacking therapeutic options for these devastating malignancies.
Evidence
20:
Inferred from Physical InteractionIntAct
Proteome-scale protein interaction maps are available for many organisms, ranging from bacteria, yeast, worms and flies to humans. These maps provide substantial new insights into systems biology, disease research and drug discovery. However, only a small fraction of the total number of human protein-protein interactions has been identified. In this study, we map the interactions of an unbiased selection of 5026 human liver expression proteins by yeast two-hybrid technology and establish a human liver protein interaction network (HLPN) composed of 3484 interactions among 2582 proteins. The data set has a validation rate of over 72% as determined by three independent biochemical or cellular assays. The network includes metabolic enzymes and liver-specific, liver-phenotype and liver-disease proteins that are individually critical for the maintenance of liver functions. The liver enriched proteins had significantly different topological properties and increased our understanding of the functional relationships among proteins in a liver-specific manner. Our data represent the first comprehensive description of a HLPN, which could be a valuable tool for understanding the functioning of the protein interaction network of the human liver.
Evidence
21:
Inferred from Physical InteractionIntAct
Using human glycogen synthase kinase 3beta (GSK-3beta) as bait in the yeast two-hybrid system, we identified a novel human centrosome associated protein, hNinein. When the full length cDNA of hNinein was sequenced, it showed that an open reading frame encoded a protein consisting of 2047 amino acids with a predicted molecular mass of 239 kDa. The features of this protein include a potential GTP binding site, a large coiled-coil domain together with four leucine zipper domains and a GSK-3beta binding site. Fluorescence microscopy experiment showed that hNinein is localized in the pericentriolar matrix of the centrosome. In addition, hNinein also showed to react with centrosomal autoantibody sera. Our findings suggest that hNinein may be involved in the formation of centrosome matrix and interacts with the GSK-3beta, implying that it may also be regulated by GSK-3beta phosphorylation signaling.
Evidence
22:
Inferred from Physical InteractionIntAct
The phosphatidylinositol 3-kinase-mammalian target of rapamycin (PI3K-mTOR) pathway plays pivotal roles in cell survival, growth, and proliferation downstream of growth factors. Its perturbations are associated with cancer progression, type 2 diabetes, and neurological disorders. To better understand the mechanisms of action and regulation of this pathway, we initiated a large scale yeast two-hybrid screen for 33 components of the PI3K-mTOR pathway. Identification of 67 new interactions was followed by validation by co-affinity purification and exhaustive literature curation of existing information. We provide a nearly complete, functionally annotated interactome of 802 interactions for the PI3K-mTOR pathway. Our screen revealed a predominant place for glycogen synthase kinase-3 (GSK3) A and B and the AMP-activated protein kinase. In particular, we identified the deformed epidermal autoregulatory factor-1 (DEAF1) transcription factor as an interactor and in vitro substrate of GSK3A and GSK3B. Moreover, GSK3 inhibitors increased DEAF1 transcriptional activity on the 5-HT1A serotonin receptor promoter. We propose that DEAF1 may represent a therapeutic target of lithium and other GSK3 inhibitors used in bipolar disease and depression.
Evidence
23:
Inferred from Physical InteractionUniProtKB
The phenotypic changes of increased motility and invasiveness of cancer cells are reminiscent of the epithelial-mesenchymal transition (EMT) that occurs during embryonic development. Snail, a zinc-finger transcription factor, triggers this process by repressing E-cadherin expression; however, the mechanisms that regulate Snail remain elusive. Here we find that Snail is highly unstable, with a short half-life about 25 min. We show that GSK-3beta binds to and phosphorylates Snail at two consensus motifs to dually regulate the function of this protein. Phosphorylation of the first motif regulates its beta-Trcp-mediated ubiquitination, whereas phosphorylation of the second motif controls its subcellular localization. A variant of Snail (Snail-6SA), which abolishes these phosphorylations, is much more stable and resides exclusively in the nucleus to induce EMT. Furthermore, inhibition of GSK-3beta results in the upregulation of Snail and downregulation of E-cadherin in vivo. Thus, Snail and GSK-3beta together function as a molecular switch for many signalling pathways that lead to EMT.
Evidence
24:
Inferred from Physical InteractionIntAct
To explore more hNinein interacting proteins, the yeast two-hybrid screening using ninein C-terminal domain as bait protein was performed. One novel gene, CGI-99, was demonstrated to associate with hNinein in the yeast two-hybrid method and in vitro GST pull-down assay. Molecular characterization also showed that CGI-99 possessed a transcriptional activity at the N-terminal. In addition, CGI-99 formed a dimer with the C-terminal, which overlapped with hNinein binding site. In kinase assay, CGI-99 binds to hNinein and completely blocks the phosphorylation of hNinein by GSK3beta. Moreover, CGI-99 was highly expressed in all brain tumors which is in agreement with the Northern blot analysis. Taken together, we have isolated a novel protein CGI-99, which may be involved in the functional regulation of human ninein in the centrosome structure and may also be important in brain development and tumorigenesis.
Evidence
25:
Inferred from Physical InteractionIntAct
Bim, the Bcl-2 interacting mediator of cell death, is a member of the BH3-only family of pro-apoptotic proteins. Recent studies have demonstrated that the apoptotic activity of Bim can be regulated through a post-translational mechanism whereby ERK phosphorylation serves as a signal for Bim ubiquitination and proteasomal degradation. In this report, we investigated the signaling pathways leading to Bim phosphorylation in Ba/F3 cells, an interleukin-3 (IL-3)-dependent B-cell line. IL-3 stimulation induced phosphorylation of Bim(EL), one of the predominant isoforms of Bim expressed in cells, at multiple sites, as evidenced by the formation of at least three to four bands by Western blotting that were sensitive to phosphatase digestion. The appearance of multiple, phosphorylated species of Bim(EL) correlated with Akt, and not ERK, activation. The PI3K inhibitor, LY294002, blocked IL-3-stimulated Akt activity and partially blocked Bim(EL) phosphorylation. In vitro kinase assays showed that recombinant Akt could directly phosphorylate a GST-Bim(EL) fusion protein and identified the Akt phosphorylation site in the Bim(EL) domain as Ser(87). Further, we demonstrated that cytokine stimulation promotes Bim(EL) binding to 14-3-3 proteins. Finally, we show that mutation of Ser(87) dramatically increases the apoptotic potency of Bim(EL). We propose that Ser(87) of Bim(EL) is an important regulatory site that is targeted by Akt to attenuate the pro-apoptotic function of Bim(EL), thereby promoting cell survival.
Evidence
26:
Inferred from Physical InteractionIntAct
The Disrupted in Schizophrenia 1 (DISC1) gene is disrupted by a balanced chromosomal translocation (1; 11) (q42; q14.3) in a Scottish family with a high incidence of major depression, schizophrenia, and bipolar disorder. Subsequent studies provided indications that DISC1 plays a role in brain development. Here, we demonstrate that suppression of DISC1 expression reduces neural progenitor proliferation, leading to premature cell cycle exit and differentiation. Several lines of evidence suggest that DISC1 mediates this function by regulating GSK3beta. First, DISC1 inhibits GSK3beta activity through direct physical interaction, which reduces beta-catenin phosphorylation and stabilizes beta-catenin. Importantly, expression of stabilized beta-catenin overrides the impairment of progenitor proliferation caused by DISC1 loss of function. Furthermore, GSK3 inhibitors normalize progenitor proliferation and behavioral defects caused by DISC1 loss of function. Together, these results implicate DISC1 in GSK3beta/beta-catenin signaling pathways and provide a framework for understanding how alterations in this pathway may contribute to the etiology of psychiatric disorders.
Evidence
27:
Inferred from Physical InteractionIntAct
BMP receptors determine the intensity of BMP signals via Smad1 C-terminal phosphorylations. Here we show that a finely controlled cell biological pathway terminates this activity. The duration of the activated pSmad1(Cter) signal was regulated by sequential Smad1 linker region phosphorylations at conserved MAPK and GSK3 sites required for its polyubiquitinylation and transport to the centrosome. Proteasomal degradation of activated Smad1 and total polyubiquitinated proteins took place in the centrosome. Inhibitors of the Erk, p38, and JNK MAPKs, as well as GSK3 inhibitors, prolonged the duration of a pulse of BMP7. Wnt signaling decreased pSmad1(GSK3) antigen levels and redistributed it from the centrosome to cytoplasmic LRP6 signalosomes. In Xenopus embryos, it was found that Wnts induce epidermis and that this required an active BMP-Smad pathway. Epistatic experiments suggested that the dorsoventral (BMP) and anteroposterior (Wnt/GSK3) patterning gradients are integrated at the level of Smad1 phosphorylations during embryonic pattern formation.
Glycogen synthase kinase 3 (GSK-3) is implicated in multiple biological processes including metabolism, gene expression, cell fate determination, proliferation, and survival. GSK-3 activity is inhibited through phosphorylation of serine 21 in GSK-3 alpha and serine 9 in GSK-3 beta. These serine residues of GSK-3 have been previously identified as targets of protein kinase B (PKB/Akt), a serine/threonine kinase located downstream of phosphatidylinositol 3-kinase. Here, we show that serine 21 in GSK-3 alpha and serine 9 in GSK-3 beta are also physiological substrates of cAMP-dependent protein kinase A. Protein kinase A physically associates with, phosphorylates, and inactivates both isoforms of GSK-3. The results indicate that depending on the stimulatory context, the activity of GSK-3 can be modulated either by growth factors that work through the phosphatidylinositol 3-kinase-protein kinase B cascade or by hormonal stimulation of G protein-coupled receptors that link to changes in intracellular cAMP levels.
Interacting selectively and non-covalently with a protein kinase, any enzyme that catalyzes the transfer of a phosphate group, usually from ATP, to a protein substrate.
Evidence
1:
Inferred from Physical InteractionUniProtKB
Autophosphorylation is an important mechanism by which protein kinases regulate their own biological activities. Salt inducible kinase 1 (SIK1) is a regulator in the feedback cascades of cAMP-mediated gene expression, while its kinase domain also features autophosphorylation activity. We provide evidence that Ser186 in the activation loop is the site of autophosphorylation and essential for the kinase activity. Ser186 is located at the +4 position of the critical Thr residue Thr182, which is phosphorylated by upstream kinases such as LKB1. The relationship between phosphorylation at Ser186 and at Thr182 in COS-7 cells indicates that the former is a prerequisite for the latter. Glycogen synthase kinase-3beta (GSK-3beta) phosphorylates Ser/Thr residues located at the fourth position ahead of the pre-phosphorylated Ser/Thr residues, and inhibitors of GSK-3beta reduce the phosphorylation at Thr182. The results of an in vitro reconstitution assay also indicate that GSK-3beta could be the SIK1 kinase. However, overexpression and knockdown of GSK-3beta in LKB1-defective HeLa cells suggests that GSK-3beta alone may not be able to phosphorylate or activate SIK1, indicating that LKB1 may play a crucial role by phosphorylating SIK1 at Thr182, possibly as an initiator of the autophosphorylation cascade, and GSK-3beta may phosphorylate SIK1 at Thr182 by recognizing the priming-autophosphorylation at Ser186 in cultured cells. This may also be the case for the other isoform SIK2, but not for SIK3.
The majority of cases with early onset familial Alzheimer's disease have been attributed to mutations in the presenilin 1 (PS1) gene. PS1 protein is a component of a high molecular weight membrane-bound complex that also contains beta-catenin. The physiological relevance of the association between PS1 and beta-catenin remains controversial. In this study, we report the identification and functional characterization of a highly conserved glycogen synthase kinase-3beta consensus phosphorylation site within the hydrophilic loop domain of PS1. Site-directed mutagenesis, together with in vitro and in vivo phosphorylation assays, indicates that PS1 residues Ser(353) and Ser(357) are glycogen synthase kinase-3beta targets. Substitution of one or both of these residues greatly reduces the ability of PS1 to associate with beta-catenin. By disrupting this interaction, we demonstrate that the association between PS1 and beta-catenin has no effect on Abeta peptide production, beta-catenin stability, or cellular susceptibility to apoptosis. Significantly, in the absence of PS1/beta-catenin association, we found no alteration in beta-catenin signaling using induction of this pathway by exogenous expression of Wnt-1 or beta-catenin and a Tcf/Lef transcriptional assay. These results argue against a pathologically relevant role for the association between PS1 and beta-catenin in familial Alzheimer's disease.
The adenomatous polyposis coli gene (APC) is mutated in most colon cancers. The APC protein binds to the cellular adhesion molecule beta-catenin, which is a mammalian homolog of ARMADILLO, a component of the WINGLESS signaling pathway in Drosophila development. Here it is shown that when beta-catenin is present in excess, APC binds to another component of the WINGLESS pathway, glycogen synthase kinase 3beta (GSK3beta), a mammalian homolog of Drosophila ZESTE WHITE 3. APC was a good substrate for GSK3 beta in vitro, and the phosphorylation sites were mapped to the central region of APC. Binding of beta-catenin to this region was dependent on phosphorylation by GSK3 beta.
Autophosphorylation is an important mechanism by which protein kinases regulate their own biological activities. Salt inducible kinase 1 (SIK1) is a regulator in the feedback cascades of cAMP-mediated gene expression, while its kinase domain also features autophosphorylation activity. We provide evidence that Ser186 in the activation loop is the site of autophosphorylation and essential for the kinase activity. Ser186 is located at the +4 position of the critical Thr residue Thr182, which is phosphorylated by upstream kinases such as LKB1. The relationship between phosphorylation at Ser186 and at Thr182 in COS-7 cells indicates that the former is a prerequisite for the latter. Glycogen synthase kinase-3beta (GSK-3beta) phosphorylates Ser/Thr residues located at the fourth position ahead of the pre-phosphorylated Ser/Thr residues, and inhibitors of GSK-3beta reduce the phosphorylation at Thr182. The results of an in vitro reconstitution assay also indicate that GSK-3beta could be the SIK1 kinase. However, overexpression and knockdown of GSK-3beta in LKB1-defective HeLa cells suggests that GSK-3beta alone may not be able to phosphorylate or activate SIK1, indicating that LKB1 may play a crucial role by phosphorylating SIK1 at Thr182, possibly as an initiator of the autophosphorylation cascade, and GSK-3beta may phosphorylate SIK1 at Thr182 by recognizing the priming-autophosphorylation at Ser186 in cultured cells. This may also be the case for the other isoform SIK2, but not for SIK3.
The transcription factor NF-AT responds to Ca2+-calcineurin signals by translocating to the nucleus, where it participates in the activation of early immune response genes. Calcineurin dephosphorylates conserved serine residues in the amino terminus of NF-AT, resulting in nuclear import. Purification of the NF-AT kinase revealed that it is composed of a priming kinase activity and glycogen synthase kinase-3 (GSK-3). GSK-3 phosphorylates conserved serines necessary for nuclear export, promotes nuclear exit, and thereby opposes Ca2+-calcineurin signaling. Because GSK-3 responds to signals initiated by Wnt and other ligands, NF-AT family members could be effectors of these pathways.
Glycogen synthase kinase 3 (GSK-3) is implicated in multiple biological processes including metabolism, gene expression, cell fate determination, proliferation, and survival. GSK-3 activity is inhibited through phosphorylation of serine 21 in GSK-3 alpha and serine 9 in GSK-3 beta. These serine residues of GSK-3 have been previously identified as targets of protein kinase B (PKB/Akt), a serine/threonine kinase located downstream of phosphatidylinositol 3-kinase. Here, we show that serine 21 in GSK-3 alpha and serine 9 in GSK-3 beta are also physiological substrates of cAMP-dependent protein kinase A. Protein kinase A physically associates with, phosphorylates, and inactivates both isoforms of GSK-3. The results indicate that depending on the stimulatory context, the activity of GSK-3 can be modulated either by growth factors that work through the phosphatidylinositol 3-kinase-protein kinase B cascade or by hormonal stimulation of G protein-coupled receptors that link to changes in intracellular cAMP levels.
The tumor suppressor p53, a sensor of multiple forms of cellular stress, is regulated by post-translational mechanisms to induce cell-cycle arrest, senescence, or apoptosis. We demonstrate that endoplasmic reticulum (ER) stress inhibits p53-mediated apoptosis. The mechanism of inhibition involves the increased cytoplasmic localization of p53 due to phosphorylation at serine 315 and serine 376, which is mediated by glycogen synthase kinase-3 beta (GSK-3beta). ER stress induces GSK-3beta binding to p53 in the nucleus and enhances the cytoplasmic localization of the tumor suppressor. Inhibition of apoptosis caused by ER stress requires GSK-3beta and does not occur in cells expressing p53 with mutation(s) of serine 315 and/or serine 376 to alanine(s). As a result of the increased cytoplasmic localization, ER stress prevents p53 stabilization and p53-mediated apoptosis upon DNA damage. It is concluded that inactivation of p53 is a protective mechanism utilized by cells to adapt to ER stress.
Interacting selectively and non-covalently with an RNA polymerase II transcription factor, any protein required to initiate or regulate transcription by RNA polymerase II.
Evidence
1:
Inferred from Physical InteractionUniProtKB
Phosphotase and tensin homolog deleted on chromosome 10 (PTEN) is a potent negative regulator of PI3K/Akt pathway. Here, we tried to elucidate the role of PTEN in the regulation of endothelial adhesion molecules, vascular cell adhesion molecule (VCAM)-1 and intracellular adhesion molecule (ICAM)-1, induced by TNF-α in human endothelial cells (ECs). Transfection with PTEN overexpressing vector resulted in the significant decrease in phosphorylation of Akt in TNF-α-treated ECs. PTEN strongly inhibited VCAM-1 but not ICAM-1, however this inhibitory effect was reversed by co-transfection with constitutively active-Akt (CA-Akt-HA) in TNF-α-stimulated ECs. Additionally, silencing of PTEN with specific siRNA showed significant increase of phosphor-Akt compared with TNF-α alone treated ECs. siPTEN significantly upregulated VCAM-1 but was indifferent to ICAM-1 in TNF-α-treated cells. Further, chromatin immunoprecipitation (ChIP) assay showed that PTEN targets GATA-6 but not IRF-1 binding to VCAM-1 promoter. In addition, GATA-6 is associated with glycogen synthesis kinase-3beta (GSK-3β) which is in turn regulated by PTEN-dependent Akt activity. Finally, PTEN significantly prevented monocyte adhesion to TNF-α-induced ECs probably through VCAM-1 regulation. It is concluded that PTEN selectively inhibits expression of VCAM-1 but not ICAM-1 through modulation of PI3K/Akt/GSK-3β/GATA-6 signaling cascade in TNF-α-treated ECs.
Interacting selectively and non-covalently with tau protein. tau is a microtubule-associated protein, implicated in Alzheimer's disease, Down Syndrome and ALS.
Glycogen synthase kinase 3 (GSK3) is a widely expressed Ser/Thr protein kinase that phosphorylates numerous substrates. This large number of substrates requires precise and specific regulation of GSK3 activity, which is achieved by a combination of phosphorylation, localization, and interactions with GSK3-binding proteins. Members of the Wnt canonical pathway have been shown to influence GSK3 activity. Through a yeast two-hybrid screen, we identified the Wnt canonical pathway co-receptor protein low density lipoprotein receptor-related protein 6 (LRP6) as a GSK3-binding protein. The interaction between the C terminus of LRP6 and GSK3 was also confirmed by in vitro GST pull-down assays and in situ coimmunoprecipitation assays. In vitro assays using immunoprecipitated proteins demonstrated that the C terminus of LRP6 significantly attenuated the activity of GSK3beta. In situ, LRP6 significantly decreased GSK3beta-mediated phosphorylation of tau at both primed and unprimed sites. Finally, it was also demonstrated that GSK3beta phosphorylates the PPP(S/T)P motifs in the C terminus of LRP6. This is the first identification of a direct interaction between LRP6 and GSK3, which results in an attenuation of GSK3 activity.
Site-specific phosphorylation of tau negatively regulates its ability to bind and stabilize microtubule structure. Although tau is a substrate of glycogen synthase kinase 3beta (GSK3beta), the exact sites on tau that are phosphorylated by this kinase in situ have not yet been established, and the effect of these phosphorylation events on tau-microtubule interactions have not been fully elucidated. GSK3beta phosphorylates both primed and unprimed sites on tau, but only primed phosphorylation events significantly decrease the ability of tau to bind microtubules. The focus of the present study is on determining the importance of the GSK3beta-mediated phosphorylation of a specific primed site, Thr231, in regulating tau's function. Pre-phosphorylation of Ser235 primes tau for phosphorylation by GSK3beta at Thr231. Phosphorylation by GSK3beta of wild-type tau or tau with Ser235 mutated to Ala decreases tau-microtubule interactions. However, when Thr231 alone or Thr231 and Ser235 in tau were mutated to Ala, phosphorylation by GSK3beta did not decrease the association of tau with the cytoskeleton. Further, T231A tau was still able to efficiently bind microtubules after phosphorylation by GSK3beta. Expression of each tau construct alone increased tubulin acetylation, a marker of microtubule stability. However, when cells were cotransfected with wild-type tau and GSK3beta, the level of tubulin acetylation was decreased to vector-transfected levels. In contrast, coexpression of GSK3beta with mutated tau (T231A/S235A) did not significantly decrease the levels of acetylated tubulin. These results strongly indicate that phosphorylation of Thr231 in tau by GSK3beta plays a critical role in regulating tau's ability to bind and stabilize microtubules.
Wnt/β-catenin signaling plays a central role in development and is also involved in a diverse array of diseases. β-Catenin activity is tightly regulated via a multiprotein complex that includes the kinase glycogen synthase kinase-3β (GSK-3β). GSK-3β phosphorylates β-catenin, marking it for ubiquitination and degradation via the proteasome. Thus in regulation of the Wnt pathway, the ubiquitin system is known to be involved mostly in mediating the turnover of β-catenin, resulting in reduced Wnt signaling levels. Here we report that an arm of the ubiquitin system increases β-catenin protein levels. We show that GSK-3β directly interacts with the E3 ubiquitin ligase identified by differential display (EDD) that also binds β-catenin. Expression of EDD leads to enhanced nuclear accumulation of both GSK-3β and β-catenin and results in up-regulation of β-catenin expression levels and activity. Importantly, EDD ubiquitinates β-catenin through Lys29- or Lys11-linked ubiquitin chains, leading to enhanced stability of β-catenin. Our results demonstrate a role for the ubiquitin system in up-regulation of the Wnt signaling pathway, suggesting that EDD could function as a colorectal oncogene.
The series of molecular signals initiated by binding of a Wnt protein to a frizzled family receptor on the surface of the target cell, followed by propagation of the signal via beta-catenin, and ending with a change in transcription of target genes. In this pathway, the activated receptor signals via downstream effectors that result in the inhibition of beta-catenin phosphorylation, thereby preventing degradation of beta-catenin. Stabilized beta-catenin can then accumulate and travel to the nucleus to trigger changes in transcription of target genes.
BACKGROUND: Inactivation of the adenomatous polyposis coli (APC) tumor suppressor protein is responsible for both inherited and sporadic forms of colon cancer. Growth control by APC may relate to its ability to downregulate beta-catenin post-translationally. In cancer, mutations in APC ablate its ability to regulate beta-catenin, and mutations in beta-catenin prevent its downregulation by wild-type APC. Moreover, signaling by the protein product of the wnt-1 proto-oncogene upregulates beta-catenin and promotes tumorigenesis in mice. In a Xenopus developmental system, Wnt-1 signaling was inhibited by Axin, the product of the murine fused gene. This suggests a possible link between Axin, the Wnt-1 signaling components beta-catenin and glycogen synthase kinase 3 beta (GSK3 beta), and APC. RESULTS: Human Axin (hAxin) binds directly to beta-catenin, GSK3 beta, and APC in vitro, and the endogenous proteins are found in a complex in cells. Binding sites for Axin were mapped to a region of APC that is typically deleted due to cancer-associated mutations in the APC gene. Overexpression of hAxin strongly promoted the downregulation of wild-type beta-catenin in colon cancer cells, whereas mutant oncogenic beta-catenin was unaffected. The downregulation was increased by deletion of the APC-binding domain from Axin, suggesting that APC may function to derepress Axin activity. In addition, hAxin dramatically facilitated the phosphorylation of APC and beta-catenin by GSK3 beta in vitro. CONCLUSIONS: Axin acts as a scaffold upon which APC, beta-catenin and GSK3 beta assemble to coordinate the regulation of beta-catenin signaling.
Aberrations of the Wnt canonical pathway (WCP) are known to contribute to the pathogenesis of various types of cancer. We hypothesize that these defects may exist in mantle cell lymphoma (MCL). Both the upstream and downstream aspects of WCP were examined in MCL cell lines and tumors. Using WCP-specific oligonucleotide arrays, we found that MCL highly and consistently expressed Wnt3 and Wnt10. beta-catenin, a transcriptional factor that is a downstream target of WCP, is localized to the nucleus and transcriptionally active in all 3 MCL cell lines examined. By immunohistochemistry, 33 (52%) of 64 MCL tumors showed nuclear localization of beta-catenin, which significantly correlated with the expression of the phosphorylated/inactive form of GSK3beta (p-GSK3beta; P = .011, Fisher). GSK3beta inactivation is directly linked to WCP stimulation, since addition of recombinant sFRP proteins (a naturally occurring decoy for the Wnt receptors) resulted in a significant decrease in p-GSK3beta. Down-regulation of DvL-2 (an upstream signaling protein in WCP) by siRNA or selective inhibition of beta-catenin using quercetin significantly decreased cell growth in MCL cell lines. To conclude, WCP is constitutively activated in a subset of MCL and it appears to promote tumorigenesis in MCL.
Canonical Wnt receptor signaling pathway involved in positive regulation of apoptotic processdefinition[GO:0044337]‹silver
The series of molecular signals initiated by binding of a Wnt protein to a frizzled family receptor on the surface of the target cell, followed by propagation of the signal via beta-catenin, and ending with a change in transcription of target genes involved in the positive regulation of apoptotic process.
A transition where an epithelial cell loses apical/basolateral polarity, severs intercellular adhesive junctions, degrades basement membrane components and becomes a migratory mesenchymal cell.
Evidence
1:
Inferred from Mutant PhenotypeUniProtKB
The phenotypic changes of increased motility and invasiveness of cancer cells are reminiscent of the epithelial-mesenchymal transition (EMT) that occurs during embryonic development. Snail, a zinc-finger transcription factor, triggers this process by repressing E-cadherin expression; however, the mechanisms that regulate Snail remain elusive. Here we find that Snail is highly unstable, with a short half-life about 25 min. We show that GSK-3beta binds to and phosphorylates Snail at two consensus motifs to dually regulate the function of this protein. Phosphorylation of the first motif regulates its beta-Trcp-mediated ubiquitination, whereas phosphorylation of the second motif controls its subcellular localization. A variant of Snail (Snail-6SA), which abolishes these phosphorylations, is much more stable and resides exclusively in the nucleus to induce EMT. Furthermore, inhibition of GSK-3beta results in the upregulation of Snail and downregulation of E-cadherin in vivo. Thus, Snail and GSK-3beta together function as a molecular switch for many signalling pathways that lead to EMT.
The series of molecular signals generated by the accumulation of normal or misfolded proteins in the endoplasmic reticulum and leading to activation of transcription by NF-kappaB.
The tumor suppressor p53, a sensor of multiple forms of cellular stress, is regulated by post-translational mechanisms to induce cell-cycle arrest, senescence, or apoptosis. We demonstrate that endoplasmic reticulum (ER) stress inhibits p53-mediated apoptosis. The mechanism of inhibition involves the increased cytoplasmic localization of p53 due to phosphorylation at serine 315 and serine 376, which is mediated by glycogen synthase kinase-3 beta (GSK-3beta). ER stress induces GSK-3beta binding to p53 in the nucleus and enhances the cytoplasmic localization of the tumor suppressor. Inhibition of apoptosis caused by ER stress requires GSK-3beta and does not occur in cells expressing p53 with mutation(s) of serine 315 and/or serine 376 to alanine(s). As a result of the increased cytoplasmic localization, ER stress prevents p53 stabilization and p53-mediated apoptosis upon DNA damage. It is concluded that inactivation of p53 is a protective mechanism utilized by cells to adapt to ER stress.
The process in which a relatively unspecialized cell acquires specialized features of an adipocyte, an animal connective tissue cell specialized for the synthesis and storage of fat.
The chemical reactions and pathways involving glycogen, a polydisperse, highly branched glucan composed of chains of D-glucose residues in alpha-(1->4) glycosidic linkage, joined together by alpha-(1->6) glycosidic linkages.
The adenomatous polyposis coli gene (APC) is mutated in most colon cancers. The APC protein binds to the cellular adhesion molecule beta-catenin, which is a mammalian homolog of ARMADILLO, a component of the WINGLESS signaling pathway in Drosophila development. Here it is shown that when beta-catenin is present in excess, APC binds to another component of the WINGLESS pathway, glycogen synthase kinase 3beta (GSK3beta), a mammalian homolog of Drosophila ZESTE WHITE 3. APC was a good substrate for GSK3 beta in vitro, and the phosphorylation sites were mapped to the central region of APC. Binding of beta-catenin to this region was dependent on phosphorylation by GSK3 beta.
CONTEXT: Indirect evidence suggests that the glycogen synthase kinase-3beta (GSK3beta) gene might be implicated in major depressive disorder (MDD). BACKGROUND: We evaluated 15 GSK3beta single-nucleotide polymorphisms (SNPs) to test for associations with regional gray matter (GM) volume differences in patients with recurrent MDD. We then used the defined regions of interest based on significant associations to test for MDD x genotype interactions by including a matched control group without any psychiatric disorder, including MDD. DESIGN: General linear model with nonstationary cluster-based inference. SETTING: Munich, Germany. PARTICIPANTS: Patients with recurrent MDD (n = 134) and age-, sex-, and ethnicity-matched healthy controls (n = 143). MAIN OUTCOME MEASURES: Associations between GSK3beta polymorphisms and regional GM volume differences. RESULTS: Variation in GM volume was associated with GSK3beta polymorphisms; the most significant associations were found for rs6438552, a putative functional intronic SNP that showed 3 significant GM clusters in the right and left superior temporal gyri and the right hippocampus (P < .001, P = .02, and P = .02, respectively, corrected for multiple comparisons across the whole brain). Similar results were obtained with rs12630592, an SNP in high linkage disequilibrium. A significant SNP x MDD status interaction was observed for the effect on GM volumes in the right hippocampus and superior temporal gyri (P < .001 and P = .01, corrected, respectively). CONCLUSIONS: The GSK3beta gene may have a role in determining regional GM volume differences of the right hippocampus and bilateral superior temporal gyri. The association between genotype and brain structure was specific to the patients with MDD, suggesting that GSK3beta genotypes might interact with MDD status. We speculate that this is a consequence of regional neocortical, glial, or neuronal growth or survival. In considering core cognitive features of MDD, the association of GSK3beta polymorphisms with structural variation in the temporal lobe and hippocampus is of particular interest in the context of other evidence for structural and functional abnormalities in the hippocampi of patients with MDD.
An increase in the epigenetic methylation of cytosine and adenosine residues in a CpG island in DNA. CpG islands are genomic regions that contain a high frequency of the CG dinucleotide and are often associated with the transcription start site of genes.
The process in which a signal is passed on to downstream components within the cell, which become activated themselves to further propagate the signal and finally trigger a change in the function or state of the cell.
The serine/threonine kinase protein kinase B (PKB)/Akt plays a central role in many cellular processes, including cell growth, glucose metabolism, and apoptosis. However, the identification and validation of novel regulators or effectors is key to future advances in understanding the multiple functions of PKB. Here we report the identification of a novel PKB binding protein, called Ft1, from a cDNA library screen using a green fluorescent protein-based protein-fragment complementation assay. We show that the Ft1 protein interacts directly with PKB, enhancing the phosphorylation of both of its regulatory sites by promoting its interaction with the upstream kinase PDK1. Further, the modulation of PKB activity by Ft1 has a strong effect on the apoptosis susceptibility of T lymphocytes treated with glucocorticoids. We demonstrate that this phenomenon occurs via a PDK1/PKB/GSK3/NF-ATc signaling cascade that controls the production of the proapoptotic hormone Fas ligand. The wide distribution of Ft1 in adult tissues suggests that it could be a general regulator of PKB activity in the control of differentiation, proliferation, and apoptosis in many cell types.
A process in which non-proliferating myoblasts fuse to existing fibers or to myotubes to form new fibers. A myoblast is a mononucleate cell type that, by fusion with other myoblasts, gives rise to the myotubes that eventually develop into skeletal muscle fibers.
The tumor suppressor p53, a sensor of multiple forms of cellular stress, is regulated by post-translational mechanisms to induce cell-cycle arrest, senescence, or apoptosis. We demonstrate that endoplasmic reticulum (ER) stress inhibits p53-mediated apoptosis. The mechanism of inhibition involves the increased cytoplasmic localization of p53 due to phosphorylation at serine 315 and serine 376, which is mediated by glycogen synthase kinase-3 beta (GSK-3beta). ER stress induces GSK-3beta binding to p53 in the nucleus and enhances the cytoplasmic localization of the tumor suppressor. Inhibition of apoptosis caused by ER stress requires GSK-3beta and does not occur in cells expressing p53 with mutation(s) of serine 315 and/or serine 376 to alanine(s). As a result of the increased cytoplasmic localization, ER stress prevents p53 stabilization and p53-mediated apoptosis upon DNA damage. It is concluded that inactivation of p53 is a protective mechanism utilized by cells to adapt to ER stress.
Any process that decreases the rate, frequency, or extent of the Wnt receptor signaling pathway through beta-catenin, the series of molecular signals initiated by binding of a Wnt protein to a frizzled family receptor on the surface of the target cell, followed by propagation of the signal via beta-catenin, and ending with a change in transcription of target genes.
Glycogen synthase kinase 3 (GSK3), a constitutively acting multi-functional serine threonine kinase is involved in diverse physiological pathways ranging from metabolism, cell cycle, gene expression, development and oncogenesis to neuroprotection. These diverse multiple functions attributed to GSK3 can be explained by variety of substrates like glycogen synthase, tau protein and beta catenin that are phosphorylated leading to their inactivation. GSK3 has been implicated in various diseases such as diabetes, inflammation, cancer, Alzheimer's and bipolar disorder. GSK3 negatively regulates insulin-mediated glycogen synthesis and glucose homeostasis, and increased expression and activity of GSK3 has been reported in type II diabetics and obese animal models. Consequently, inhibitors of GSK3 have been demonstrated to have anti-diabetic effects in vitro and in animal models. However, inhibition of GSK3 poses a challenge as achieving selectivity of an over achieving kinase involved in various pathways with multiple substrates may lead to side effects and toxicity. The primary concern is developing inhibitors of GSK3 that are anti-diabetic but do not lead to up-regulation of oncogenes. The focus of this review is the recent advances and the challenges surrounding GSK3 as an anti-diabetic therapeutic target.
Glycogen synthase kinase 3 (GSK3), a constitutively acting multi-functional serine threonine kinase is involved in diverse physiological pathways ranging from metabolism, cell cycle, gene expression, development and oncogenesis to neuroprotection. These diverse multiple functions attributed to GSK3 can be explained by variety of substrates like glycogen synthase, tau protein and beta catenin that are phosphorylated leading to their inactivation. GSK3 has been implicated in various diseases such as diabetes, inflammation, cancer, Alzheimer's and bipolar disorder. GSK3 negatively regulates insulin-mediated glycogen synthesis and glucose homeostasis, and increased expression and activity of GSK3 has been reported in type II diabetics and obese animal models. Consequently, inhibitors of GSK3 have been demonstrated to have anti-diabetic effects in vitro and in animal models. However, inhibition of GSK3 poses a challenge as achieving selectivity of an over achieving kinase involved in various pathways with multiple substrates may lead to side effects and toxicity. The primary concern is developing inhibitors of GSK3 that are anti-diabetic but do not lead to up-regulation of oncogenes. The focus of this review is the recent advances and the challenges surrounding GSK3 as an anti-diabetic therapeutic target.
Any process that stops, prevents, or reduces the frequency, rate or extent of the chemical reactions and pathways resulting in the formation of glycogen.
Glycogen synthase kinase 3 (GSK3), a constitutively acting multi-functional serine threonine kinase is involved in diverse physiological pathways ranging from metabolism, cell cycle, gene expression, development and oncogenesis to neuroprotection. These diverse multiple functions attributed to GSK3 can be explained by variety of substrates like glycogen synthase, tau protein and beta catenin that are phosphorylated leading to their inactivation. GSK3 has been implicated in various diseases such as diabetes, inflammation, cancer, Alzheimer's and bipolar disorder. GSK3 negatively regulates insulin-mediated glycogen synthesis and glucose homeostasis, and increased expression and activity of GSK3 has been reported in type II diabetics and obese animal models. Consequently, inhibitors of GSK3 have been demonstrated to have anti-diabetic effects in vitro and in animal models. However, inhibition of GSK3 poses a challenge as achieving selectivity of an over achieving kinase involved in various pathways with multiple substrates may lead to side effects and toxicity. The primary concern is developing inhibitors of GSK3 that are anti-diabetic but do not lead to up-regulation of oncogenes. The focus of this review is the recent advances and the challenges surrounding GSK3 as an anti-diabetic therapeutic target.
The transcription factor NF-AT responds to Ca2+-calcineurin signals by translocating to the nucleus, where it participates in the activation of early immune response genes. Calcineurin dephosphorylates conserved serine residues in the amino terminus of NF-AT, resulting in nuclear import. Purification of the NF-AT kinase revealed that it is composed of a priming kinase activity and glycogen synthase kinase-3 (GSK-3). GSK-3 phosphorylates conserved serines necessary for nuclear export, promotes nuclear exit, and thereby opposes Ca2+-calcineurin signaling. Because GSK-3 responds to signals initiated by Wnt and other ligands, NF-AT family members could be effectors of these pathways.
beta-catenin-mediated Wnt signaling is critical in animal development and tumor progression. The single-span transmembrane Wnt receptor, low-density lipoprotein receptor-related protein 6 (LRP6), interacts with Axin to promote the Wnt-dependent accumulation of beta-catenin. However, the molecular mechanism of receptor internalization and its impact on signaling are unclear. Here, we present evidence that LRP6 is internalized with caveolin and that the components of this endocytic pathway are required not only for Wnt-3a-induced internalization of LRP6 but also for accumulation of beta-catenin. Overall, our data suggest that Wnt-3a triggers the interaction of LRP6 with caveolin and promotes recruitment of Axin to LRP6 phosphorylated by glycogen synthase kinase-3beta and that caveolin thereby inhibits the binding of beta-catenin to Axin. Thus, caveolin plays critical roles in inducing the internalization of LRP6 and activating the Wnt/beta-catenin pathway. We also discuss the idea that distinct endocytic pathways correlate with the specificity of Wnt signaling events.
Mutations resulting in the truncation of the adenomatous polyposis coli (APC) protein are common to most colonic tumours. The APC protein has emerged as a multifunctional protein that contributes to cytoskeletal organisation and is involved in the regulation of beta-catenin. Both, changes in transcription due to increases in beta-catenin, as well as defects in directed cell migration and cell division contribute to cancer when APC is mutated. Little is known about how separate functions of APC are coordinated. In this study, we identified two distinct soluble protein pools containing APC. We found that one of these pools represents the fully assembled beta-catenin-targeting complex. The second pool contained at least two different forms of APC: APC that was bound to partially assembled beta-catenin-targeting complexes and APC that could bind microtubules. Consistent with the previously proposed role for glycogen synthase kinase 3beta (GSK3beta) in modulating the assembly and activity of the beta-catenin-targeting complex, formation of the fully assembled complex was reduced by inhibitors of GSK3beta. Similarly, tumour cells with truncated APC only contained the partially assembly beta-catenin-targeting complex. We also found that highly elevated levels of beta-catenin in tumour cells containing wild-type APC correlated with a decrease in the ability of the endogenous APC protein to bind microtubules. Additionally, APC lacking the direct microtubule binding site was more effective at downregulating beta-catenin. Together, our data suggest that the interaction of APC with microtubules and the beta-catenin-targeting complex are mutually exclusive, and indicate that the distribution of endogenous APC between different pools is dynamic, which allows cells to distribute it as required.
Glycogen synthase kinase 3 (GSK3), a constitutively acting multi-functional serine threonine kinase is involved in diverse physiological pathways ranging from metabolism, cell cycle, gene expression, development and oncogenesis to neuroprotection. These diverse multiple functions attributed to GSK3 can be explained by variety of substrates like glycogen synthase, tau protein and beta catenin that are phosphorylated leading to their inactivation. GSK3 has been implicated in various diseases such as diabetes, inflammation, cancer, Alzheimer's and bipolar disorder. GSK3 negatively regulates insulin-mediated glycogen synthesis and glucose homeostasis, and increased expression and activity of GSK3 has been reported in type II diabetics and obese animal models. Consequently, inhibitors of GSK3 have been demonstrated to have anti-diabetic effects in vitro and in animal models. However, inhibition of GSK3 poses a challenge as achieving selectivity of an over achieving kinase involved in various pathways with multiple substrates may lead to side effects and toxicity. The primary concern is developing inhibitors of GSK3 that are anti-diabetic but do not lead to up-regulation of oncogenes. The focus of this review is the recent advances and the challenges surrounding GSK3 as an anti-diabetic therapeutic target.
Morphogenesis of an organ. An organ is defined as a tissue or set of tissues that work together to perform a specific function or functions. Morphogenesis is the process in which anatomical structures are generated and organized. Organs are commonly observed as visibly distinct structures, but may also exist as loosely associated clusters of cells that work together to perform a specific function or functions.
The majority of cases with early onset familial Alzheimer's disease have been attributed to mutations in the presenilin 1 (PS1) gene. PS1 protein is a component of a high molecular weight membrane-bound complex that also contains beta-catenin. The physiological relevance of the association between PS1 and beta-catenin remains controversial. In this study, we report the identification and functional characterization of a highly conserved glycogen synthase kinase-3beta consensus phosphorylation site within the hydrophilic loop domain of PS1. Site-directed mutagenesis, together with in vitro and in vivo phosphorylation assays, indicates that PS1 residues Ser(353) and Ser(357) are glycogen synthase kinase-3beta targets. Substitution of one or both of these residues greatly reduces the ability of PS1 to associate with beta-catenin. By disrupting this interaction, we demonstrate that the association between PS1 and beta-catenin has no effect on Abeta peptide production, beta-catenin stability, or cellular susceptibility to apoptosis. Significantly, in the absence of PS1/beta-catenin association, we found no alteration in beta-catenin signaling using induction of this pathway by exogenous expression of Wnt-1 or beta-catenin and a Tcf/Lef transcriptional assay. These results argue against a pathologically relevant role for the association between PS1 and beta-catenin in familial Alzheimer's disease.
The tumor suppressor p53, a sensor of multiple forms of cellular stress, is regulated by post-translational mechanisms to induce cell-cycle arrest, senescence, or apoptosis. We demonstrate that endoplasmic reticulum (ER) stress inhibits p53-mediated apoptosis. The mechanism of inhibition involves the increased cytoplasmic localization of p53 due to phosphorylation at serine 315 and serine 376, which is mediated by glycogen synthase kinase-3 beta (GSK-3beta). ER stress induces GSK-3beta binding to p53 in the nucleus and enhances the cytoplasmic localization of the tumor suppressor. Inhibition of apoptosis caused by ER stress requires GSK-3beta and does not occur in cells expressing p53 with mutation(s) of serine 315 and/or serine 376 to alanine(s). As a result of the increased cytoplasmic localization, ER stress prevents p53 stabilization and p53-mediated apoptosis upon DNA damage. It is concluded that inactivation of p53 is a protective mechanism utilized by cells to adapt to ER stress.
The adenomatous polyposis coli gene (APC) is mutated in most colon cancers. The APC protein binds to the cellular adhesion molecule beta-catenin, which is a mammalian homolog of ARMADILLO, a component of the WINGLESS signaling pathway in Drosophila development. Here it is shown that when beta-catenin is present in excess, APC binds to another component of the WINGLESS pathway, glycogen synthase kinase 3beta (GSK3beta), a mammalian homolog of Drosophila ZESTE WHITE 3. APC was a good substrate for GSK3 beta in vitro, and the phosphorylation sites were mapped to the central region of APC. Binding of beta-catenin to this region was dependent on phosphorylation by GSK3 beta.
Consistent with findings of Wnt pathway members involved in vascular cells, a role for Wnt/Frizzled signaling has recently emerged in vascular cell development. Among the few Wnt family members implicated in vessel formation in adult, Wnt7b and Frizzled 4 have been shown as involved in vessel formation in the lung and in the retina, respectively. Our previous work has shown a role for secreted Frizzled-related protein-1 (sFRP-1), a proposed Wnt signaling inhibitor, in neovascularization after an ischemic event and demonstrated its role as a potent angiogenic factor. However the mechanisms involved have not been investigated. Here, we show that sFRP-1 treatment increases endothelial cell spreading on extracellular matrix as revealed by actin stress fiber reorganization in an integrin-dependent manner. We demonstrate that sFRP-1 can interact with Wnt receptors Frizzled 4 and 7 on endothelial cells to transduce downstream to cellular machineries requiring Rac-1 activity in cooperation with GSK-3beta. sFRP-1 overexpression in endothelium specifically reversed the inactivation of GSK-3 beta and increased neovascularization in ischemia-induced angiogenesis in mouse hindlimb. This study illustrates a regulated pathway by sFRP-1 involving GSK-3beta and Rac-1 in endothelial cell cytoskeletal reorganization and in neovessel formation.
Any process that increases the frequency, rate or extent of peptidyl-threonine phosphorylation. Peptidyl-threonine phosphorylation is the phosphorylation of peptidyl-threonine to form peptidyl-O-phospho-L-threonine.
Any process that activates or increases the frequency, rate or extent of the chemical reactions and pathways resulting in the breakdown of a protein by the destruction of the native, active configuration, with or without the hydrolysis of peptide bonds.
Mutations resulting in the truncation of the adenomatous polyposis coli (APC) protein are common to most colonic tumours. The APC protein has emerged as a multifunctional protein that contributes to cytoskeletal organisation and is involved in the regulation of beta-catenin. Both, changes in transcription due to increases in beta-catenin, as well as defects in directed cell migration and cell division contribute to cancer when APC is mutated. Little is known about how separate functions of APC are coordinated. In this study, we identified two distinct soluble protein pools containing APC. We found that one of these pools represents the fully assembled beta-catenin-targeting complex. The second pool contained at least two different forms of APC: APC that was bound to partially assembled beta-catenin-targeting complexes and APC that could bind microtubules. Consistent with the previously proposed role for glycogen synthase kinase 3beta (GSK3beta) in modulating the assembly and activity of the beta-catenin-targeting complex, formation of the fully assembled complex was reduced by inhibitors of GSK3beta. Similarly, tumour cells with truncated APC only contained the partially assembly beta-catenin-targeting complex. We also found that highly elevated levels of beta-catenin in tumour cells containing wild-type APC correlated with a decrease in the ability of the endogenous APC protein to bind microtubules. Additionally, APC lacking the direct microtubule binding site was more effective at downregulating beta-catenin. Together, our data suggest that the interaction of APC with microtubules and the beta-catenin-targeting complex are mutually exclusive, and indicate that the distribution of endogenous APC between different pools is dynamic, which allows cells to distribute it as required.
The adenomatous polyposis coli gene (APC) is mutated in most colon cancers. The APC protein binds to the cellular adhesion molecule beta-catenin, which is a mammalian homolog of ARMADILLO, a component of the WINGLESS signaling pathway in Drosophila development. Here it is shown that when beta-catenin is present in excess, APC binds to another component of the WINGLESS pathway, glycogen synthase kinase 3beta (GSK3beta), a mammalian homolog of Drosophila ZESTE WHITE 3. APC was a good substrate for GSK3 beta in vitro, and the phosphorylation sites were mapped to the central region of APC. Binding of beta-catenin to this region was dependent on phosphorylation by GSK3 beta.
The tumor suppressor p53, a sensor of multiple forms of cellular stress, is regulated by post-translational mechanisms to induce cell-cycle arrest, senescence, or apoptosis. We demonstrate that endoplasmic reticulum (ER) stress inhibits p53-mediated apoptosis. The mechanism of inhibition involves the increased cytoplasmic localization of p53 due to phosphorylation at serine 315 and serine 376, which is mediated by glycogen synthase kinase-3 beta (GSK-3beta). ER stress induces GSK-3beta binding to p53 in the nucleus and enhances the cytoplasmic localization of the tumor suppressor. Inhibition of apoptosis caused by ER stress requires GSK-3beta and does not occur in cells expressing p53 with mutation(s) of serine 315 and/or serine 376 to alanine(s). As a result of the increased cytoplasmic localization, ER stress prevents p53 stabilization and p53-mediated apoptosis upon DNA damage. It is concluded that inactivation of p53 is a protective mechanism utilized by cells to adapt to ER stress.
Consistent with findings of Wnt pathway members involved in vascular cells, a role for Wnt/Frizzled signaling has recently emerged in vascular cell development. Among the few Wnt family members implicated in vessel formation in adult, Wnt7b and Frizzled 4 have been shown as involved in vessel formation in the lung and in the retina, respectively. Our previous work has shown a role for secreted Frizzled-related protein-1 (sFRP-1), a proposed Wnt signaling inhibitor, in neovascularization after an ischemic event and demonstrated its role as a potent angiogenic factor. However the mechanisms involved have not been investigated. Here, we show that sFRP-1 treatment increases endothelial cell spreading on extracellular matrix as revealed by actin stress fiber reorganization in an integrin-dependent manner. We demonstrate that sFRP-1 can interact with Wnt receptors Frizzled 4 and 7 on endothelial cells to transduce downstream to cellular machineries requiring Rac-1 activity in cooperation with GSK-3beta. sFRP-1 overexpression in endothelium specifically reversed the inactivation of GSK-3 beta and increased neovascularization in ischemia-induced angiogenesis in mouse hindlimb. This study illustrates a regulated pathway by sFRP-1 involving GSK-3beta and Rac-1 in endothelial cell cytoskeletal reorganization and in neovessel formation.
Microtubules (MTs) contribute to key processes during cell motility, including the regulation of focal adhesion turnover and the establishment and maintenance of cell orientation. It was previously demonstrated that the ErbB2 receptor tyrosine kinase regulated MT outgrowth to the cell cortex via a complex including Memo, the GTPase RhoA, and the formin mDia1. But the mechanism that linked this signaling module to MTs remained undefined. We report that ErbB2-induced repression of glycogen synthase kinase-3 (GSK3) activity, mediated by Memo and mDia1, is required for MT capture and stabilization. Memo-dependent inhibition of GSK3 allows the relocalization of APC (adenomatous polyposis coli) and cytoplasmic linker-associated protein 2 (CLASP2), known MT-associated proteins, to the plasma membrane and ruffles. Peripheral microtubule extension also requires expression of the plus-end binding protein EB1 and its recently described interactor, the spectraplakin ACF7. In fact, in migrating cells, ACF7 localizes to the plasma membrane and ruffles, in a Memo-, GSK3-, and APC-dependent manner. Finally, we demonstrate that ACF7 targeting to the plasma membrane is both required and sufficient for MT capture downstream of ErbB2. This function of ACF7 does not require its recently described ATPase activity. By defining the signaling pathway by which ErbB2 allows MT capture and stabilization at the cell leading edge, we provide insights into the mechanism underlying cell motility and steering.
Glycogen synthase kinase 3 (GSK-3) is implicated in multiple biological processes including metabolism, gene expression, cell fate determination, proliferation, and survival. GSK-3 activity is inhibited through phosphorylation of serine 21 in GSK-3 alpha and serine 9 in GSK-3 beta. These serine residues of GSK-3 have been previously identified as targets of protein kinase B (PKB/Akt), a serine/threonine kinase located downstream of phosphatidylinositol 3-kinase. Here, we show that serine 21 in GSK-3 alpha and serine 9 in GSK-3 beta are also physiological substrates of cAMP-dependent protein kinase A. Protein kinase A physically associates with, phosphorylates, and inactivates both isoforms of GSK-3. The results indicate that depending on the stimulatory context, the activity of GSK-3 can be modulated either by growth factors that work through the phosphatidylinositol 3-kinase-protein kinase B cascade or by hormonal stimulation of G protein-coupled receptors that link to changes in intracellular cAMP levels.
Heritable alterations in the activity of a gene that depend on whether it passed through the paternal or the maternal germline, but that are not encoded by DNA itself.
Microtubules (MTs) contribute to key processes during cell motility, including the regulation of focal adhesion turnover and the establishment and maintenance of cell orientation. It was previously demonstrated that the ErbB2 receptor tyrosine kinase regulated MT outgrowth to the cell cortex via a complex including Memo, the GTPase RhoA, and the formin mDia1. But the mechanism that linked this signaling module to MTs remained undefined. We report that ErbB2-induced repression of glycogen synthase kinase-3 (GSK3) activity, mediated by Memo and mDia1, is required for MT capture and stabilization. Memo-dependent inhibition of GSK3 allows the relocalization of APC (adenomatous polyposis coli) and cytoplasmic linker-associated protein 2 (CLASP2), known MT-associated proteins, to the plasma membrane and ruffles. Peripheral microtubule extension also requires expression of the plus-end binding protein EB1 and its recently described interactor, the spectraplakin ACF7. In fact, in migrating cells, ACF7 localizes to the plasma membrane and ruffles, in a Memo-, GSK3-, and APC-dependent manner. Finally, we demonstrate that ACF7 targeting to the plasma membrane is both required and sufficient for MT capture downstream of ErbB2. This function of ACF7 does not require its recently described ATPase activity. By defining the signaling pathway by which ErbB2 allows MT capture and stabilization at the cell leading edge, we provide insights into the mechanism underlying cell motility and steering.
A process that modulates neuronal synaptic plasticity, the ability of neuronal synapses to change as circumstances require. They may alter function, such as increasing or decreasing their sensitivity, or they may increase or decrease in actual numbers.
Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a drug stimulus. A drug is a substance used in the diagnosis, treatment or prevention of a disease.
Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a lithium (Li+) ion stimulus.
The process whose specific outcome is the progression of the superior temporal gyrus over time, from its formation to the mature structure. The superior temporal gyrus is a portion of the cerebral cortex that extends from the lateral sulcus to the superior temporal sulcus.
CONTEXT: Indirect evidence suggests that the glycogen synthase kinase-3beta (GSK3beta) gene might be implicated in major depressive disorder (MDD). BACKGROUND: We evaluated 15 GSK3beta single-nucleotide polymorphisms (SNPs) to test for associations with regional gray matter (GM) volume differences in patients with recurrent MDD. We then used the defined regions of interest based on significant associations to test for MDD x genotype interactions by including a matched control group without any psychiatric disorder, including MDD. DESIGN: General linear model with nonstationary cluster-based inference. SETTING: Munich, Germany. PARTICIPANTS: Patients with recurrent MDD (n = 134) and age-, sex-, and ethnicity-matched healthy controls (n = 143). MAIN OUTCOME MEASURES: Associations between GSK3beta polymorphisms and regional GM volume differences. RESULTS: Variation in GM volume was associated with GSK3beta polymorphisms; the most significant associations were found for rs6438552, a putative functional intronic SNP that showed 3 significant GM clusters in the right and left superior temporal gyri and the right hippocampus (P < .001, P = .02, and P = .02, respectively, corrected for multiple comparisons across the whole brain). Similar results were obtained with rs12630592, an SNP in high linkage disequilibrium. A significant SNP x MDD status interaction was observed for the effect on GM volumes in the right hippocampus and superior temporal gyri (P < .001 and P = .01, corrected, respectively). CONCLUSIONS: The GSK3beta gene may have a role in determining regional GM volume differences of the right hippocampus and bilateral superior temporal gyri. The association between genotype and brain structure was specific to the patients with MDD, suggesting that GSK3beta genotypes might interact with MDD status. We speculate that this is a consequence of regional neocortical, glial, or neuronal growth or survival. In considering core cognitive features of MDD, the association of GSK3beta polymorphisms with structural variation in the temporal lobe and hippocampus is of particular interest in the context of other evidence for structural and functional abnormalities in the hippocampi of patients with MDD.
EC 2.7.11.1: ATP + a protein ⇄ ADP + a phosphoprotein.
CuratedUniProtKB
It is regulated in the following manner
Activated by phosphorylation at Tyr-216. In response to insulin, inhibited by phosphorylation at Ser-9 by PKB/AKT1 and RPS6KA3; phosphorylation at this site causes a conformational change, preventing access of substrates to the active site. Inhibited by lithium.
Glycogen synthase kinase 3beta (GSK3beta) is a serine/threonine kinase involved in insulin, growth factor and Wnt signalling. In Wnt signalling, GSK3beta is recruited to a multiprotein complex via interaction with axin, where it hyperphosphorylates beta-catenin, marking it for ubiquitylation and destruction. We have now determined the crystal structure of GSK3beta in complex with a minimal GSK3beta-binding segment of axin, at 2.4 A resolution. The structure confirms the co-localization of the binding sites for axin and FRAT in the C-terminal domain of GSK3beta, but reveals significant differences in the interactions made by axin and FRAT, mediated by conformational plasticity of the 285-299 loop in GSK3beta. Detailed comparison of the axin and FRAT GSK3beta complexes allows the generation of highly specific mutations, which abrogate binding of one or the other. Quantitative analysis suggests that the interaction of GSK3beta with the axin scaffold enhances phosphorylation of beta-catenin by >20 000-fold.
Glycogen synthase kinase-3 (GSK3) is implicated in the regulation of several physiological processes, including the control of glycogen and protein synthesis by insulin, modulation of the transcription factors AP-1 and CREB, the specification of cell fate in Drosophila and dorsoventral patterning in Xenopus embryos. GSK3 is inhibited by serine phosphorylation in response to insulin or growth factors and in vitro by either MAP kinase-activated protein (MAPKAP) kinase-1 (also known as p90rsk) or p70 ribosomal S6 kinase (p70S6k). Here we show, however, that agents which prevent the activation of both MAPKAP kinase-1 and p70S6k by insulin in vivo do not block the phosphorylation and inhibition of GSK3. Another insulin-stimulated protein kinase inactivates GSK3 under these conditions, and we demonstrate that it is the product of the proto-oncogene protein kinase B (PKB, also known as Akt/RAC). Like the inhibition of GSK3 (refs 10, 14), the activation of PKB is prevented by inhibitors of phosphatidylinositol (PI) 3-kinase.
Higher expression and activity of GSK3B are found in the skeletal muscle (vastus lateralis) of patients with type 2 diabetes (PubMed10868943). Several potent GSK3 (GSK3A and GSK3B) inhibitors have been identified and characterized in preclinical models for treatments of type 2 diabetes (PubMed19366350).
Glycogen synthase kinase 3 (GSK3), a constitutively acting multi-functional serine threonine kinase is involved in diverse physiological pathways ranging from metabolism, cell cycle, gene expression, development and oncogenesis to neuroprotection. These diverse multiple functions attributed to GSK3 can be explained by variety of substrates like glycogen synthase, tau protein and beta catenin that are phosphorylated leading to their inactivation. GSK3 has been implicated in various diseases such as diabetes, inflammation, cancer, Alzheimer's and bipolar disorder. GSK3 negatively regulates insulin-mediated glycogen synthesis and glucose homeostasis, and increased expression and activity of GSK3 has been reported in type II diabetics and obese animal models. Consequently, inhibitors of GSK3 have been demonstrated to have anti-diabetic effects in vitro and in animal models. However, inhibition of GSK3 poses a challenge as achieving selectivity of an over achieving kinase involved in various pathways with multiple substrates may lead to side effects and toxicity. The primary concern is developing inhibitors of GSK3 that are anti-diabetic but do not lead to up-regulation of oncogenes. The focus of this review is the recent advances and the challenges surrounding GSK3 as an anti-diabetic therapeutic target.
Glycogen synthase (GS) activity is reduced in skeletal muscle of type 2 diabetes, despite normal protein expression, consistent with altered GS regulation. Glycogen synthase kinase-3 (GSK-3) is involved in regulation (phosphorylation and deactivation) of GS. To access the potential role of GSK-3 in insulin resistance and reduced GS activity in type 2 diabetes, the expression and activity of GSK-3 were studied in biopsies of vastus lateralis from type 2 and nondiabetic subjects before and after 3-h hyperinsulinemic (300 mU x m(-2) x min(-1))-euglycemic clamps. The specific activity of GSK-3alpha did not differ between nondiabetic and diabetic muscle and was decreased similarly after 3-h insulin infusion. However, protein levels of both alpha and beta isoforms of GSK-3 were elevated (approximately 30%) in diabetic muscle compared with lean (P < 0.01) and weight-matched obese nondiabetic subjects (P < 0.05) and were unchanged by insulin infusion. Thus, both basal and insulin-stimulated total GSK-3 activities were elevated by approximately twofold in diabetic muscle. GSK-3 expression was related to in vivo insulin action, as GSK-3 protein was negatively correlated with maximal insulin-stimulated glucose disposal rates. In summary, GSK-3 protein levels and total activities are 1) elevated in type 2 diabetic muscle independent of obesity and 2) inversely correlated with both GS activity and maximally insulin-stimulated glucose disposal. We conclude that increased GSK-3 expression in diabetic muscle may contribute to the impaired GS activity and skeletal muscle insulin resistance present in type 2 diabetes.
Protein participating in biochemical reactions in which carbohydrates are involved. Carbohydrate is a general term for sugars and related compounds with the general formula Cn(H2O)n. The smallest are monosaccharides (e.g. glucose); polysaccharides (e.g. starch, cellulose, glycogen) can be large and vary in length.
Protein involved in differentiation, the developmental process of a multicellular organism by which cells become specialized for particular functions. Differentiation requires selective expression of the genome; the fully differentiated state may be preceded by a stage in which the cell is already programmed for differentiation but is not yet expressing the characteristic phenotype determination. Also used for fungal conidiation proteins, and for some bacteria that present specialization of function in cell types, such as Caulobacter crescentus.
Protein involved in the biochemical reactions with glycogen, a branched polymer of D-glucose (mostly -(1-4) linked, but with some - (1-6) linked residues at branch points). Glycogen is the major short term storage polymer of animal cells and is particularly abundant in liver and to a lesser extent in muscles.
Protein involved in the Wnt signaling pathway. Wnts are a large family of cysteine-rich secreted glycoproteins that control development in organisms ranging from nematodes to mammals. Wnt genes are defined by sequence homology to the original members of the family, Wnt1 in the mouse and wingless (wg) in Drosophila. Wnt signaling is a very complex pathway which includes numerous ligands, receptors and transcriptional effectors. There is a well-characterized canonical pathway as well as diverse, less-characterized noncanonical pathways. Several components of Wnt signaling are implicated in the genesis of human cancer.
Protein involved in development, the process whereby a multicellular organism develops from its early immature forms, e.g., zygote, larva, embryo, into an adult.
Protein which catalyzes the phosphorylation of serine or threonine residues on target proteins by using ATP as phosphate donor. Such phosphorylation may cause changes in the function of the target protein. Protein kinases share a conserved catalytic core common to both serine/ threonine and tyrosine protein kinases.
Protein which inhibits signal transduction, the process by which extracellular signals induce intracellular responses. Usually a hormone or neurotransmitter binds to a cell surface receptor which is coupled to a second messenger system, such as that involving cAMP, or to an ion channel. The final downstream consequence of signal transduction is a change in the cell's function, such as a modification in glucose uptake or in cell division. Such a change may be the result of an activation or an inhibition event.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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