Tumor suppressor. Acts as a dual-specificity protein phosphatase, dephosphorylating tyrosine-, serine- and threonine-phosphorylated proteins. Also acts as a lipid phosphatase, removing the phosphate in the D3 position of the inositol ring from phosphatidylinositol 3,4,5-trisphosphate, phosphatidylinositol 3,4-diphosphate, phosphatidylinositol 3-phosphate and inositol 1,3,4,5-tetrakisphosphate with order of substrate preference in vitro PtdIns(3,4,5)P3 > PtdIns(3,4)P2 > PtdIns3P > Ins(1,3,4,5)P4. The lipid phosphatase activity is critical for its tumor suppressor function. Antagonizes the PI3K-AKT/PKB signaling pathway by dephosphorylating phosphoinositides and thereby modulating cell cycle progression and cell survival. The unphosphorylated form cooperates with AIP1 to suppress AKT1 activation. Dephosphorylates tyrosine-phosphorylated focal adhesion kinase and inhibits cell migration and integrin-mediated cell spreading and focal adhesion formation. Plays a role as a key modulator of the AKT-mTOR signaling pathway controlling the tempo of the process of newborn neurons integration during adult neurogenesis, including correct neuron positioning, dendritic development and synapse formation. May be a negative regulator of insulin signaling and glucose metabolism in adipose tissue. The nuclear monoubiquitinated form possesses greater apoptotic potential, whereas the cytoplasmic nonubiquitinated form induces less tumor suppressive ability.
J. Biol. Chem. 273, 13375-13378 (1998)[PubMed:9593664]
Phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) is a key molecule involved in cell growth signaling. We demonstrated that overexpression of PTEN, a putative tumor suppressor, reduced insulin-induced PtdIns(3,4,5)P3 production in human 293 cells without effecting insulin-induced phosphoinositide 3-kinase activation. Further, transfection of the catalytically inactive mutant of PTEN (C124S) caused PtdIns(3,4,5)P3 accumulation in the absence of insulin stimulation. Purified recombinant PTEN catalyzed dephosphorylation of PtdIns(3,4,5)P3, specifically at position 3 on the inositol ring. PTEN also exhibited 3-phosphatase activity toward inositol 1,3,4,5-tetrakisphosphate. Our results raise the possibility that PTEN acts in vivo as a phosphoinositide 3-phosphatase by regulating PtdIns(3,4,5)P3 levels. As expected, the C124S mutant of PTEN was incapable of catalyzing dephosphorylation of PtdIns(3,4,5)P3 consistent with the mechanism observed in protein-tyrosine phosphatase-catalyzed reactions.
Proc. Natl. Acad. Sci. U.S.A. 94, 9052-9057 (1997)[PubMed:9256433]
Protein tyrosine phosphatases (PTPs) have long been thought to play a role in tumor suppression due to their ability to antagonize the growth promoting protein tyrosine kinases. Recently, a candidate tumor suppressor from 10q23, termed P-TEN, was isolated, and sequence homology was demonstrated with members of the PTP family, as well as the cytoskeletal protein tensin. Here we show that recombinant P-TEN dephosphorylated protein and peptide substrates phosphorylated on serine, threonine, and tyrosine residues, indicating that P-TEN is a dual-specificity phosphatase. In addition, P-TEN exhibited a high degree of substrate specificity, showing selectivity for extremely acidic substrates in vitro. Furthermore, we demonstrate that mutations in P-TEN, identified from primary tumors, tumor cells lines, and a patient with Bannayan-Zonana syndrome, resulted in the ablation of phosphatase activity, demonstrating that enzymatic activity of P-TEN is necessary for its ability to function as a tumor suppressor.
It has long been postulated that protein tyrosine phosphatases may act as tumor suppressors because of their ability to counteract the oncogenic actions of protein tyrosine kinases. Here we report the cloning and characterization of a novel human protein tyrosine phosphatase, TEP1. TEP1 contains the protein tyrosine phosphatase signature motif, and we show that it possesses an intrinsic protein tyrosine phosphatase activity. TEP1 also shares extensive homology with tensin, a cytoskeletal protein localized to focal adhesions, and with auxilin, a protein involved in synaptic vesicle transport. Immunofluorescence studies show that TEP1 is a cytoplasmic protein. The abundance of TEP1 transcription is altered in many transformed cells. In the transforming growth factor beta-sensitive cells, TEP1 expression is rapidly down-regulated by transforming growth factor beta, a cytokine shown to be involved in regulating cell adhesion and cell motility. We have also mapped the gene encoding TEP1 to chromosome 10q23, a locus that is frequently deleted in a variety of human cancers. TEP1 protein is identical to the protein encoded by the candidate tumor suppressor gene PTEN/MMAC1. Our functional studies of the TEP1 protein suggest that its tumor suppressor function may associate with its intrinsic protein tyrosine phosphatase activity and its cytoplasmic localization.
Nuclear exclusion of the PTEN (phosphatase and tensin homologue deleted in chromosome 10) tumour suppressor has been associated with cancer progression. However, the mechanisms leading to this aberrant PTEN localization in human cancers are currently unknown. We have previously reported that ubiquitinylation of PTEN at specific lysine residues regulates its nuclear-cytoplasmic partitioning. Here we show that functional promyelocytic leukaemia protein (PML) nuclear bodies co-ordinate PTEN localization by opposing the action of a previously unknown PTEN-deubiquitinylating enzyme, herpesvirus-associated ubiquitin-specific protease (HAUSP, also known as USP7), and that the integrity of this molecular framework is required for PTEN to be able to enter the nucleus. We find that PTEN is aberrantly localized in acute promyelocytic leukaemia, in which PML function is disrupted by the PML-RARalpha fusion oncoprotein. Remarkably, treatment with drugs that trigger PML-RARalpha degradation, such as all-trans retinoic acid or arsenic trioxide, restore nuclear PTEN. We demonstrate that PML opposes the activity of HAUSP towards PTEN through a mechanism involving the adaptor protein DAXX (death domain-associated protein). In support of this paradigm, we show that HAUSP is overexpressed in human prostate cancer and is associated with PTEN nuclear exclusion. Thus, our results delineate a previously unknown PML-DAXX-HAUSP molecular network controlling PTEN deubiquitinylation and trafficking, which is perturbed by oncogenic cues in human cancer, in turn defining a new deubiquitinylation-dependent model for PTEN subcellular compartmentalization.
Proc. Natl. Acad. Sci. U.S.A. 95, 13513-13518 (1998)[PubMed:9811831]
Since their discovery, protein tyrosine phosphatases have been speculated to play a role in tumor suppression because of their ability to antagonize the growth-promoting protein tyrosine kinases. Recently, a tumor suppressor from human chromosome 10q23, called PTEN or MMAC1, has been identified that shares homology with the protein tyrosine phosphatase family. Germ-line mutations in PTEN give rise to several related neoplastic disorders, including Cowden disease. A key step in understanding the function of PTEN as a tumor suppressor is to identify its physiological substrates. Here we report that a missense mutation in PTEN, PTEN-G129E, which is observed in two Cowden disease kindreds, specifically ablates the ability of PTEN to recognize inositol phospholipids as a substrate, suggesting that loss of the lipid phosphatase activity is responsible for the etiology of the disease. Furthermore, expression of wild-type or substrate-trapping forms of PTEN in HEK293 cells altered the levels of the phospholipid products of phosphatidylinositol 3-kinase and ectopic expression of the phosphatase in PTEN-deficient tumor cell lines resulted in the inhibition of protein kinase (PK) B/Akt and regulation of cell survival.
Proc. Natl. Acad. Sci. U.S.A. 96, 10182-10187 (1999)[PubMed:10468583]
PTEN is a recently identified tumor suppressor inactivated in a variety of cancers such as glioblastoma and endometrial and prostate carcinoma. It contains an amino-terminal phosphatase domain and acts as a phosphatidylinositol 3,4,5-trisphosphate phosphatase antagonizing the activity of the phosphatidylinositol 3-OH kinase. PTEN also contains a carboxyl-terminal domain, and we addressed the role of this region that, analogous to the amino-terminal phosphatase domain, is the target of many mutations identified in tumors. Expression of carboxyl-terminal mutants in PTEN-deficient glioblastoma cells permitted the anchorage-independent growth of the cells that otherwise was suppressed by wild-type PTEN. The stability of these mutants in cells was reduced because of rapid degradation. Although the carboxyl-terminal region contains regulatory PEST sequences and a PDZ-binding motif, these specific elements were dispensable for the tumor-suppressor function. The study of carboxyl-terminal point mutations affecting the stability of PTEN revealed that these were located in strongly predicted beta-strands. Surprisingly, the phosphatase activity of these mutants was affected in correlation with the degree of disruption of these structural elements. We conclude that the carboxyl-terminal region is essential for regulating PTEN stability and enzymatic activity and that mutations in this region are responsible for the reversion of the tumor-suppressor phenotype. We also propose that the molecular conformational changes induced by these mutations constitute the mechanism for PTEN inactivation.
PTEN is a tumor suppressor protein that functions, in large part, by dephosphorylating the lipid second messenger phosphatidylinositol 3,4,5-trisphosphate and by doing so antagonizing the action of phosphoinositide 3-kinase. PTEN structural domains include an N-terminal phosphatase domain, a lipid-binding C2 domain, and a 50-amino acid C-terminal tail that contains a PDZ binding sequence. We showed previously that phosphorylation of the PTEN tail negatively regulates PTEN activity. We now show that phosphorylated PTEN exists in a monomeric "closed" conformation and has low affinity for PDZ domain-containing proteins. Conversely, when unphosphorylated, PTEN is in an "open" conformation, is recruited into a high molecular weight complex (PTEN-associated complex), and strongly interacts with PDZ-containing proteins such as MAGI-2. As a consequence, when compared with wild-type PTEN, the phosphorylation-deficient mutant form of PTEN strongly cooperates with MAGI-2 to block Akt activation. These results indicate that phosphorylation of the PTEN tail causes a conformational change that results in the masking of the PDZ binding domain. Consequently, the ability of PTEN to bind to PDZ domain-containing proteins is reduced dramatically. These data suggest that phosphorylation of the PTEN tail suppresses the activity of PTEN by controlling the recruitment of PTEN into the PTEN-associated complex.
The tumor suppressor PTEN is a phosphatase with sequence similarity to the cytoskeletal protein tensin. Here the cellular roles of PTEN were investigated. Overexpression of PTEN inhibited cell migration, whereas antisense PTEN enhanced migration. Integrin-mediated cell spreading and the formation of focal adhesions were down-regulated by wild-type PTEN but not by PTEN with an inactive phosphatase domain. PTEN interacted with the focal adhesion kinase FAK and reduced its tyrosine phosphorylation. Overexpression of FAK partially antagonized the effects of PTEN. Thus, PTEN phosphatase may function as a tumor suppressor by negatively regulating cell interactions with the extracellular matrix.
Interacting selectively and non-covalently with an anaphase-promoting complex. A ubiquitin ligase complex that degrades mitotic cyclins and anaphase inhibitory protein, thereby triggering sister chromatid separation and exit from mitosis.
Evidence
1:
Inferred from Physical InteractionBHF-UCL
PTEN is a frequently mutated tumor suppressor gene that opposes the PI3K/AKT pathway through dephosphorylation of phosphoinositide-3,4,5-triphosphate. Recently, nuclear compartmentalization of PTEN was found as a key component of its tumor-suppressive activity; however its nuclear function remains poorly defined. Here we show that nuclear PTEN interacts with APC/C, promotes APC/C association with CDH1, and thereby enhances the tumor-suppressive activity of the APC-CDH1 complex. We find that nuclear exclusion but not phosphatase inactivation of PTEN impairs APC-CDH1. This nuclear function of PTEN provides a straightforward mechanistic explanation for the fail-safe cellular senescence response elicited by acute PTEN loss and the tumor-suppressive activity of catalytically inactive PTEN. Importantly, we demonstrate that PTEN mutant and PTEN null states are not synonymous as they are differentially sensitive to pharmacological inhibition of APC-CDH1 targets such as PLK1 and Aurora kinases. This finding identifies a strategy for cancer patient stratification and, thus, optimization of targeted therapies. PAPERCLIP:
The tumour suppressor p53 induces apoptosis or cell-cycle arrest in response to genotoxic and other stresses. In unstressed cells, the anti-proliferative effects of p53 are restrained by mouse double minute 2 (Mdm2), a ubiquitin ligase (E3) that promotes p53 ubiquitination and degradation. Mdm2 also mediates its own degradation through auto-ubiquitination. It is unclear how the cis- and trans-E3 activities of Mdm2, which have opposing effects on cell fate, are differentially regulated. Here, we show that death domain-associated protein (Daxx) is required for Mdm2 stability. Downregulation of Daxx decreases Mdm2 levels, whereas overexpression of Daxx strongly stabilizes Mdm2. Daxx simultaneously binds to Mdm2 and the deubiquitinase Hausp, and it mediates the stabilizing effect of Hausp on Mdm2. In addition, Daxx enhances the intrinsic E3 activity of Mdm2 towards p53. On DNA damage, Daxx dissociates from Mdm2, which correlates with Mdm2 self-degradation. These findings reveal that Daxx modulates the function of Mdm2 at multiple levels and suggest that the disruption of the Mdm2-Daxx interaction may be important for p53 activation in response to DNA damage.
J. Biol. Chem. 273, 13375-13378 (1998)[PubMed:9593664]
Phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) is a key molecule involved in cell growth signaling. We demonstrated that overexpression of PTEN, a putative tumor suppressor, reduced insulin-induced PtdIns(3,4,5)P3 production in human 293 cells without effecting insulin-induced phosphoinositide 3-kinase activation. Further, transfection of the catalytically inactive mutant of PTEN (C124S) caused PtdIns(3,4,5)P3 accumulation in the absence of insulin stimulation. Purified recombinant PTEN catalyzed dephosphorylation of PtdIns(3,4,5)P3, specifically at position 3 on the inositol ring. PTEN also exhibited 3-phosphatase activity toward inositol 1,3,4,5-tetrakisphosphate. Our results raise the possibility that PTEN acts in vivo as a phosphoinositide 3-phosphatase by regulating PtdIns(3,4,5)P3 levels. As expected, the C124S mutant of PTEN was incapable of catalyzing dephosphorylation of PtdIns(3,4,5)P3 consistent with the mechanism observed in protein-tyrosine phosphatase-catalyzed reactions.
Two-hybrid searches with the tumor suppressor MMAC1/PTEN isolated the proteins hDLG and hMAST205. Further two-hybrid analysis and microtiter plate binding assays localized the sites of interaction to PDZ domains from hDLG and hMAST205 and the PDZ binding domain at the COOH terminus of MMAC1/PTEN. A synthetic peptide derived from the MMAC1/PTEN PDZ binding domain (MMAC1/PTEN-PDZBD) was used to coprecipitate proteins from A431 human cell lysate. The recovered proteins were resolved by SDS-PAGE and immobilized on a nitrocellulose membrane. Treatment of this membrane with an anti-hDLG antibody identified a Mr 140,000 band, consistent with the size of hDLG. Treatment of this membrane with the MMAC1/PTEN-PDZBD peptide identified a single prominent band of slightly larger than Mr 200,000 (Mr 200,000 kDa). Threonine phosphorylation of the MMAC1/ PTEN-PDZBD peptide inhibited both microtiter plate binding to the hDLG and hMAST205 PDZ domains and coprecipitation of the Mr 140,000 and > 200,000 proteins, but promoted coprecipitation of proteins of approximately Mr 90,000 and Mr 120,000 from A431 cell lysate. This result suggests phosphorylation of the MMAC1/PTEN PDZ binding domain can both inhibit and promote PDZ interactions.
Evidence
2:
Inferred from Physical InteractionUniProtKB
Proc. Natl. Acad. Sci. U.S.A. 97, 4233-4238 (2000)[PubMed:10760291]
PTEN is a tumor suppressor gene mutated in human cancers. Although many mutations target the phosphatase domain, others create a truncated protein lacking the C-terminal PDZ-binding motif or a protein that extends beyond the PDZ-binding motif. Using the yeast two-hybrid system, we isolated a membrane-associated guanylate kinase family protein with multiple PDZ domains [AIP-1 (atrophin interacting protein 1), renamed MAGI-2 (membrane associated guanylate kinase inverted-2)]. MAGI-2 contains eight potential protein-protein interaction domains and is localized to tight junctions in the membrane of epithelial cells. PTEN binds to MAGI-2 through an interaction between the PDZ-binding motif of PTEN and the second PDZ domain of MAGI-2. MAGI-2 enhances the ability of PTEN to suppress Akt activation. Furthermore, certain PTEN mutants have reduced stability, which is restored by adding the minimal PDZ-binding motif back to the truncated protein. We propose that MAGI-2 improves the efficiency of PTEN signaling through assembly of a multiprotein complex at the cell membrane.
J. Biol. Chem. 273, 13375-13378 (1998)[PubMed:9593664]
Phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) is a key molecule involved in cell growth signaling. We demonstrated that overexpression of PTEN, a putative tumor suppressor, reduced insulin-induced PtdIns(3,4,5)P3 production in human 293 cells without effecting insulin-induced phosphoinositide 3-kinase activation. Further, transfection of the catalytically inactive mutant of PTEN (C124S) caused PtdIns(3,4,5)P3 accumulation in the absence of insulin stimulation. Purified recombinant PTEN catalyzed dephosphorylation of PtdIns(3,4,5)P3, specifically at position 3 on the inositol ring. PTEN also exhibited 3-phosphatase activity toward inositol 1,3,4,5-tetrakisphosphate. Our results raise the possibility that PTEN acts in vivo as a phosphoinositide 3-phosphatase by regulating PtdIns(3,4,5)P3 levels. As expected, the C124S mutant of PTEN was incapable of catalyzing dephosphorylation of PtdIns(3,4,5)P3 consistent with the mechanism observed in protein-tyrosine phosphatase-catalyzed reactions.
Proc. Natl. Acad. Sci. U.S.A. 95, 13513-13518 (1998)[PubMed:9811831]
Since their discovery, protein tyrosine phosphatases have been speculated to play a role in tumor suppression because of their ability to antagonize the growth-promoting protein tyrosine kinases. Recently, a tumor suppressor from human chromosome 10q23, called PTEN or MMAC1, has been identified that shares homology with the protein tyrosine phosphatase family. Germ-line mutations in PTEN give rise to several related neoplastic disorders, including Cowden disease. A key step in understanding the function of PTEN as a tumor suppressor is to identify its physiological substrates. Here we report that a missense mutation in PTEN, PTEN-G129E, which is observed in two Cowden disease kindreds, specifically ablates the ability of PTEN to recognize inositol phospholipids as a substrate, suggesting that loss of the lipid phosphatase activity is responsible for the etiology of the disease. Furthermore, expression of wild-type or substrate-trapping forms of PTEN in HEK293 cells altered the levels of the phospholipid products of phosphatidylinositol 3-kinase and ectopic expression of the phosphatase in PTEN-deficient tumor cell lines resulted in the inhibition of protein kinase (PK) B/Akt and regulation of cell survival.
Proc. Natl. Acad. Sci. U.S.A. 95, 13513-13518 (1998)[PubMed:9811831]
Since their discovery, protein tyrosine phosphatases have been speculated to play a role in tumor suppression because of their ability to antagonize the growth-promoting protein tyrosine kinases. Recently, a tumor suppressor from human chromosome 10q23, called PTEN or MMAC1, has been identified that shares homology with the protein tyrosine phosphatase family. Germ-line mutations in PTEN give rise to several related neoplastic disorders, including Cowden disease. A key step in understanding the function of PTEN as a tumor suppressor is to identify its physiological substrates. Here we report that a missense mutation in PTEN, PTEN-G129E, which is observed in two Cowden disease kindreds, specifically ablates the ability of PTEN to recognize inositol phospholipids as a substrate, suggesting that loss of the lipid phosphatase activity is responsible for the etiology of the disease. Furthermore, expression of wild-type or substrate-trapping forms of PTEN in HEK293 cells altered the levels of the phospholipid products of phosphatidylinositol 3-kinase and ectopic expression of the phosphatase in PTEN-deficient tumor cell lines resulted in the inhibition of protein kinase (PK) B/Akt and regulation of cell survival.
Proc. Natl. Acad. Sci. U.S.A. 95, 13513-13518 (1998)[PubMed:9811831]
Since their discovery, protein tyrosine phosphatases have been speculated to play a role in tumor suppression because of their ability to antagonize the growth-promoting protein tyrosine kinases. Recently, a tumor suppressor from human chromosome 10q23, called PTEN or MMAC1, has been identified that shares homology with the protein tyrosine phosphatase family. Germ-line mutations in PTEN give rise to several related neoplastic disorders, including Cowden disease. A key step in understanding the function of PTEN as a tumor suppressor is to identify its physiological substrates. Here we report that a missense mutation in PTEN, PTEN-G129E, which is observed in two Cowden disease kindreds, specifically ablates the ability of PTEN to recognize inositol phospholipids as a substrate, suggesting that loss of the lipid phosphatase activity is responsible for the etiology of the disease. Furthermore, expression of wild-type or substrate-trapping forms of PTEN in HEK293 cells altered the levels of the phospholipid products of phosphatidylinositol 3-kinase and ectopic expression of the phosphatase in PTEN-deficient tumor cell lines resulted in the inhibition of protein kinase (PK) B/Akt and regulation of cell survival.
Catalysis of the reaction: a phosphoprotein + H2O = a protein + phosphate. Together with protein kinases, these enzymes control the state of phosphorylation of cell proteins and thereby provide an important mechanism for regulating cellular activity.
PTEN is a frequently mutated tumor suppressor gene that opposes the PI3K/AKT pathway through dephosphorylation of phosphoinositide-3,4,5-triphosphate. Recently, nuclear compartmentalization of PTEN was found as a key component of its tumor-suppressive activity; however its nuclear function remains poorly defined. Here we show that nuclear PTEN interacts with APC/C, promotes APC/C association with CDH1, and thereby enhances the tumor-suppressive activity of the APC-CDH1 complex. We find that nuclear exclusion but not phosphatase inactivation of PTEN impairs APC-CDH1. This nuclear function of PTEN provides a straightforward mechanistic explanation for the fail-safe cellular senescence response elicited by acute PTEN loss and the tumor-suppressive activity of catalytically inactive PTEN. Importantly, we demonstrate that PTEN mutant and PTEN null states are not synonymous as they are differentially sensitive to pharmacological inhibition of APC-CDH1 targets such as PLK1 and Aurora kinases. This finding identifies a strategy for cancer patient stratification and, thus, optimization of targeted therapies. PAPERCLIP:
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 tumor suppressor phosphatase PTEN is a key regulator of cell growth and apoptosis that interacts with PDZ domains from regulatory proteins, including MAGI-1/2/3, hDlg, and MAST205. Here we identified novel PTEN-binding PDZ domains within the MAST205-related proteins, syntrophin-associated serine/threonine kinase and MAST3, characterized the regions of PTEN involved in its interaction with distinctive PDZ domains, and analyzed the functional consequences on PTEN of PDZ domain binding. Using a panel of PTEN mutations, as well as PTEN chimeras containing distinct domains of the related protein TPTE, we found that the PTP and C2 domains of PTEN do not affect PDZ domain binding and that the C-terminal tail of PTEN (residues 350-403) provides selectivity to recognize specific PDZ domains from MAGI-2, hDlg, and MAST205. Binding of PTEN to the PDZ-2 domain from MAGI-2 increased PTEN protein stability. Furthermore, binding of PTEN to the PDZ domains from microtubule-associated serine/threonine kinases facilitated PTEN phosphorylation at its C terminus by these kinases. Our results suggest an important role for the C-terminal region of PTEN in the selective association with scaffolding and/or regulatory molecules and provide evidence that PDZ domain binding stabilizes PTEN and targets this tumor suppressor for phosphorylation by microtubule-associated serine/threonine kinases.
Evidence
2:
Inferred from Physical InteractionIntAct
Protein phosphatase 1 (PP1) catalytic subunits typically combine with other proteins that modulate their activity, direct them to distinct substrates, or serve as substrates for PP1. More than 50 PP1-interacting proteins (PIPs) have been identified so far. Given there are approximately 10 000 phosphoproteins in mammals, many PIPs remain to be discovered. We have used arrays containing 100 carefully selected antibodies to identify novel PIPs that are important in cell proliferation and cell survival in murine fetal lung epithelial cells and human A549 lung cancer cells. The antibody arrays identified 31 potential novel PIPs and 11 of 17 well-known PIPs included as controls, suggesting a sensitivity of at least 65%. A majority of the interactions between PP1 and putative PIPs were isoform- or cell type-specific. We confirmed by co-immunoprecipitation that 9 of these proteins associate with PP1: APAF-1, Bax, E-cadherin, HSP-70, Id2, p19Skp1, p53, PCNA, and PTEN. We examined two of these interactions in greater detail in A549 cells. Exposure to nicotine enhanced association of PP1 with Bax (and Bad), but also induced inhibitory phosphorylation of PP1. In addition to p19Skp1, PP1alpha antibodies also coprecipitated cullin 1, suggesting that PP1alpha is associated with the SCF1 complex. This interaction was only detectable during the G1/S transition and S phase. Forced loss of PP1 function decreased the levels of p27Kip1, a well-known SCF1 substrate, suggesting that PP1 may rescue proteins from ubiquitin/proteasome-mediated destruction. Both of these novel interactions are consistent with PP1 facilitating cell cycle arrest and/or apoptosis.
Erratum in:
J Proteome Res. 7(3), 1352 (2008 Mar)
Evidence
3:
Inferred from Physical InteractionUniProtKB
Apoptotic cell death plays a normal role in various physiological processes, and deregulated apoptosis is a hallmark of several diseases, including cancer. Cell fate is dictated by the balance between pro- and antiapoptotic factors. Akt is one of these antiapoptotic factors, which must be activated through phosphorylation. The phosphorylation of Akt has previously been shown to be promoted by X-linked inhibitor of apoptosis protein (XIAP), another antiapoptotic protein dictating the fate of normal and cancer cells. However, the underlying mechanisms are poorly understood. We have observed that XIAP associates with PTEN (phosphatase and tensin homolog deleted on chromosome ten), the best characterized negative regulator of Akt phosphorylation, in vitro and in vivo. XIAP knockdown reduces constitutive mono- and polyubiquitination of PTEN, increases PTEN protein levels, and prevents nuclear accumulation of PTEN. Overexpression of XIAP induces polyubiquitination of PTEN and proteasome-dependent decrease of PTEN protein levels. RNA interference experiments showed that XIAP-induced regulation of Akt phosphorylation is PTEN-dependent. Additional experiments confirmed that XIAP also regulates PTEN in vivo; primary mouse embryonic fibroblasts derived from XIAP(-/-) mice contain higher levels of PTEN protein, less mono- and polyubiquitinated PTEN, and less nuclear PTEN than primary mouse embryonic fibroblasts derived from XIAP(+/+) mice. Finally, we found that XIAP can directly ubiquitinate PTEN in vitro. We thus propose that XIAP acts as an E3 ubiquitin ligase for PTEN and promotes Akt activity by regulating PTEN content and compartmentalization.
Evidence
4:
Inferred from Physical InteractionUniProtKB
Loss of cell polarity is one of the initial alterations in the development of human epithelial cancers. Na(+)/H(+) exchanger regulatory factor (NHERF) homologous adaptors 1 and 2 are membrane-associated proteins composed of two amino (N)-terminal PDZ domains and an ezrin-radixin-moesin (ERM)-binding (EB) carboxyl (C)-terminal region. We describe here an intramolecular conformation of NHERF1/EBP50 (ERM-binding phosphoprotein 50) in which the C-terminal EB region binds to the PDZ2 domain. This novel head-to-tail conformation masked the interaction of both PDZ domains with PDZ domain-specific ligands, such as PTEN and beta-catenin. An EB region composite structure comprising an alpha-helix ending in a PDZ-binding motif imparted opposite effects to NHERF1 associations, mediating binding to ERM proteins and inhibiting binding of PDZ domain ligands. The PDZ domain inhibition was released by prior association of ezrin with the EB region, a condition that occurs in vivo and likely disrupts NHERF1 head-to-tail interaction. In contrast, NHERF2 did not present a regulatory mechanism for protein complex formation. Functionally, NHERF1 is required to organize complexes at the apical membranes of polarized epithelial cells. The regulation of NHERF1 interactions at the apical membrane thus appears to be a dynamic process that is important for maintaining epithelial-tissue integrity.
Evidence
5:
Inferred from Physical InteractionIntAct
PTEN is a frequently mutated tumor suppressor gene that opposes the PI3K/AKT pathway through dephosphorylation of phosphoinositide-3,4,5-triphosphate. Recently, nuclear compartmentalization of PTEN was found as a key component of its tumor-suppressive activity; however its nuclear function remains poorly defined. Here we show that nuclear PTEN interacts with APC/C, promotes APC/C association with CDH1, and thereby enhances the tumor-suppressive activity of the APC-CDH1 complex. We find that nuclear exclusion but not phosphatase inactivation of PTEN impairs APC-CDH1. This nuclear function of PTEN provides a straightforward mechanistic explanation for the fail-safe cellular senescence response elicited by acute PTEN loss and the tumor-suppressive activity of catalytically inactive PTEN. Importantly, we demonstrate that PTEN mutant and PTEN null states are not synonymous as they are differentially sensitive to pharmacological inhibition of APC-CDH1 targets such as PLK1 and Aurora kinases. This finding identifies a strategy for cancer patient stratification and, thus, optimization of targeted therapies. PAPERCLIP:
Evidence
6:
Inferred from Physical InteractionUniProtKB
PTEN, a tumor suppressor frequently inactivated in many human cancers, directly antagonizes the activity of phosphatidylinositol-3-OH kinase (PI3K) by dephosphorylating phosphoinositides. We show here that PTEN interacts directly with the NHERF1 and NHERF2 (Na+/H+ exchanger regulatory factor) homologous adaptor proteins through the PDZ motif of PTEN and the PDZ1 domain of NHERF1 or both PDZ domains of NHERF2. NHERFs were shown to interact directly with platelet-derived growth factor receptor (PDGFR), and we demonstrate the assembly of a ternary complex between PTEN, NHERFs and PDGFR. The activation of the PI3K pathway after PDGFR stimulation was prolonged in NHERF1(-/-) mouse embryonic fibroblasts as compared to wild-type cells, consistent with defective PTEN recruitment to PDGFR in the absence of NHERF1. Depletion of NHERF2 by small interfering RNA similarly increased PI3K signaling. Phenotypically, the loss of NHERF1 enhanced the PDGF-induced cytoskeletal rearrangements and chemotactic migration of the cells. These data indicate that, in normal cells, NHERF proteins recruit PTEN to PDGFR to restrict the activation of the PI3K.
Evidence
7:
Inferred from Physical InteractionUniProtKB
Expression of the PTEN tumor suppressor is frequently lost in breast cancer in the absence of mutation or promoter methylation through as yet undetermined mechanisms. In this study, we demonstrate that the Rak tyrosine kinase physically interacts with PTEN and phosphorylates PTEN on Tyr336. Knockdown of Rak enhanced the binding of PTEN to its E3 ligase NEDD4-1 and promoted PTEN polyubiquitination, leading to PTEN protein degradation. Notably, ectopic expression of Rak effectively suppressed breast cancer cell proliferation, invasion, and colony formation in vitro and tumor growth in vivo. Furthermore, Rak knockdown was sufficient to transform normal mammary epithelial cells. Therefore, Rak acts as a bona fide tumor suppressor gene through the mechanism of regulating PTEN protein stability and function.
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.
Catalysis of the reaction: protein serine phosphate + H2O = protein serine + phosphate, and protein threonine phosphate + H2O = protein threonine + phosphate.
Proc. Natl. Acad. Sci. U.S.A. 94, 9052-9057 (1997)[PubMed:9256433]
Protein tyrosine phosphatases (PTPs) have long been thought to play a role in tumor suppression due to their ability to antagonize the growth promoting protein tyrosine kinases. Recently, a candidate tumor suppressor from 10q23, termed P-TEN, was isolated, and sequence homology was demonstrated with members of the PTP family, as well as the cytoskeletal protein tensin. Here we show that recombinant P-TEN dephosphorylated protein and peptide substrates phosphorylated on serine, threonine, and tyrosine residues, indicating that P-TEN is a dual-specificity phosphatase. In addition, P-TEN exhibited a high degree of substrate specificity, showing selectivity for extremely acidic substrates in vitro. Furthermore, we demonstrate that mutations in P-TEN, identified from primary tumors, tumor cells lines, and a patient with Bannayan-Zonana syndrome, resulted in the ablation of phosphatase activity, demonstrating that enzymatic activity of P-TEN is necessary for its ability to function as a tumor suppressor.
Proc. Natl. Acad. Sci. U.S.A. 94, 9052-9057 (1997)[PubMed:9256433]
Protein tyrosine phosphatases (PTPs) have long been thought to play a role in tumor suppression due to their ability to antagonize the growth promoting protein tyrosine kinases. Recently, a candidate tumor suppressor from 10q23, termed P-TEN, was isolated, and sequence homology was demonstrated with members of the PTP family, as well as the cytoskeletal protein tensin. Here we show that recombinant P-TEN dephosphorylated protein and peptide substrates phosphorylated on serine, threonine, and tyrosine residues, indicating that P-TEN is a dual-specificity phosphatase. In addition, P-TEN exhibited a high degree of substrate specificity, showing selectivity for extremely acidic substrates in vitro. Furthermore, we demonstrate that mutations in P-TEN, identified from primary tumors, tumor cells lines, and a patient with Bannayan-Zonana syndrome, resulted in the ablation of phosphatase activity, demonstrating that enzymatic activity of P-TEN is necessary for its ability to function as a tumor suppressor.
Catalysis of the reactions: protein serine + H2O = protein serine + phosphate; protein threonine phosphate + H2O = protein threonine + phosphate; and protein tyrosine phosphate + H2O = protein tyrosine + phosphate.
PTEN is a frequently mutated tumor suppressor gene that opposes the PI3K/AKT pathway through dephosphorylation of phosphoinositide-3,4,5-triphosphate. Recently, nuclear compartmentalization of PTEN was found as a key component of its tumor-suppressive activity; however its nuclear function remains poorly defined. Here we show that nuclear PTEN interacts with APC/C, promotes APC/C association with CDH1, and thereby enhances the tumor-suppressive activity of the APC-CDH1 complex. We find that nuclear exclusion but not phosphatase inactivation of PTEN impairs APC-CDH1. This nuclear function of PTEN provides a straightforward mechanistic explanation for the fail-safe cellular senescence response elicited by acute PTEN loss and the tumor-suppressive activity of catalytically inactive PTEN. Importantly, we demonstrate that PTEN mutant and PTEN null states are not synonymous as they are differentially sensitive to pharmacological inhibition of APC-CDH1 targets such as PLK1 and Aurora kinases. This finding identifies a strategy for cancer patient stratification and, thus, optimization of targeted therapies. PAPERCLIP:
A programmed cell death process which begins when a cell receives an internal (e.g. DNA damage) or external signal (e.g. an extracellular death ligand), and proceeds through a series of biochemical events (signaling pathways) which typically lead to rounding-up of the cell, retraction of pseudopodes, reduction of cellular volume (pyknosis), chromatin condensation, nuclear fragmentation (karyorrhexis), plasma membrane blebbing and fragmentation of the cell into apoptotic bodies. The process ends when the cell has died. The process is divided into a signaling pathway phase, and an execution phase, which is triggered by the former.
The process in which the anatomical structures of the brain are generated and organized. The brain is one of the two components of the central nervous system and is the center of thought and emotion. It is responsible for the coordination and control of bodily activities and the interpretation of information from the senses (sight, hearing, smell, etc.).
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.
Endothelial cell (EC) migration, cell-cell adhesion, and the formation of branching point structures are considered hallmarks of angiogenesis; however, the underlying mechanisms of these processes are not well understood. Lipid phosphate phosphatase 3 (LPP3) is a recently described p120-catenin-associated integrin ligand localized in adherens junctions (AJs) of ECs. Here, we tested the hypothesis that LPP3 stimulates beta-catenin/lymphoid enhancer binding factor 1 (beta-catenin/LEF-1) to induce EC migration and formation of branching point structures. In subconfluent ECs, LPP3 induced expression of fibronectin via beta-catenin/LEF-1 signaling in a phosphatase and tensin homologue (PTEN)-dependent manner. In confluent ECs, depletion of p120-catenin restored LPP3-mediated beta-catenin/LEF-1 signaling. Depletion of LPP3 resulted in destabilization of beta-catenin, which in turn reduced fibronectin synthesis and deposition, which resulted in inhibition of EC migration. Accordingly, reexpression of beta-catenin but not p120-catenin in LPP3-depleted ECs restored de novo synthesis of fibronectin, which mediated EC migration and formation of branching point structures. In confluent ECs, however, a fraction of p120-catenin associated and colocalized with LPP3 at the plasma membrane, via the C-terminal cytoplasmic domain, thereby limiting the ability of LPP3 to stimulate beta-catenin/LEF-1 signaling. Thus, our study identified a key role for LPP3 in orchestrating PTEN-mediated beta-catenin/LEF-1 signaling in EC migration, cell-cell adhesion, and formation of branching point structures.
The dual-specificity phosphatase PTEN/MMAC1/TEP1 has recently been identified as the tumor suppressor gene most frequently mutated and/or deleted in human tumors. Germline mutations of PTEN give rise to Cowden Disease (CD), an autosomal dominantly-inherited cancer syndrome which predisposes to increased risk of developing breast and thyroid tumors. However, PTEN mutations have rarely been detected in sporadic thyroid carcinomas. In this study, we confirm that PTEN mutations in sporadic thyroid cancer are infrequent as we found one point mutation and one heterozygous deletion of PTEN gene in 26 tumors and eight cell lines screened. However, we report that PTEN expression is reduced both at the mRNA and at the protein level - in five out of eight tumor-derived cell lines and in 24 out of 61 primary tumors. In most cases, decreased PTEN expression is correlated with increased phosphorylation of the PTEN-regulated protein kinase Akt/PKB. Moreover, we demonstrate that PTEN may act as a suppressor of thyroid cancerogenesis as the constitutive re-expression of PTEN into two different thyroid tumor cell lines markedly inhibits cell growth. PTEN-dependent inhibition of BrdU incorporation is accompanied by enhanced expression of the cyclin-dependent kinase inhibitor p27kip1 and can be overcome by simultaneous co-transfection of an excess p27kip1 antisense plasmid. Accordingly, in a subset of thyroid primary carcinomas and tumor-derived cell lines, a striking correlation between PTEN expression and the level of p27kip1 protein was observed. In conclusion, our findings demonstrate that inactivation of PTEN may play a role in the development of sporadic thyroid carcinomas and that one key target of PTEN suppressor activity is represented by the cyclin-dependent kinase inhibitor p27kip1.
The process whose specific outcome is the progression of the central nervous system over time, from its formation to the mature structure. The central nervous system is the core nervous system that serves an integrating and coordinating function. In vertebrates it consists of the brain, spinal cord and spinal nerves. In those invertebrates with a central nervous system it typically consists of a brain, cerebral ganglia and a nerve cord.
Generation of a long process from a neuron whose cell body resides in the central nervous system. The process carries efferent (outgoing) action potentials from the cell body towards target cells.
The process in which the anatomical structures of a dendritic spine are generated and organized. A dendritic spine is a protrusion from a dendrite and a specialized subcellular compartment involved in synaptic transmission.
The process whose specific outcome is the progression of the dentate gyrus over time, from its formation to the mature structure. The dentate gyrus is one of two interlocking gyri of the hippocampus. It contains granule cells, which project to the pyramidal cells and interneurons of the CA3 region of the ammon gyrus.
The process in which the anatomical structures of the forebrain are generated and organized. The forebrain is the anterior of the three primary divisions of the developing chordate brain or the corresponding part of the adult brain (in vertebrates, includes especially the cerebral hemispheres, the thalamus, and the hypothalamus and especially in higher vertebrates is the main control center for sensory and associative information processing, visceral functions, and voluntary motor functions).
The process whose specific outcome is the progression of the heart over time, from its formation to the mature structure. The heart is a hollow, muscular organ, which, by contracting rhythmically, keeps up the circulation of the blood.
J. Biol. Chem. 273, 13375-13378 (1998)[PubMed:9593664]
Phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) is a key molecule involved in cell growth signaling. We demonstrated that overexpression of PTEN, a putative tumor suppressor, reduced insulin-induced PtdIns(3,4,5)P3 production in human 293 cells without effecting insulin-induced phosphoinositide 3-kinase activation. Further, transfection of the catalytically inactive mutant of PTEN (C124S) caused PtdIns(3,4,5)P3 accumulation in the absence of insulin stimulation. Purified recombinant PTEN catalyzed dephosphorylation of PtdIns(3,4,5)P3, specifically at position 3 on the inositol ring. PTEN also exhibited 3-phosphatase activity toward inositol 1,3,4,5-tetrakisphosphate. Our results raise the possibility that PTEN acts in vivo as a phosphoinositide 3-phosphatase by regulating PtdIns(3,4,5)P3 levels. As expected, the C124S mutant of PTEN was incapable of catalyzing dephosphorylation of PtdIns(3,4,5)P3 consistent with the mechanism observed in protein-tyrosine phosphatase-catalyzed reactions.
The specific movement from place to place of an organism in response to external or internal stimuli. Locomotion of a whole organism in a manner dependent upon some combination of that organism's internal state and external conditions.
A process that modulates synaptic plasticity such that synapses are changed resulting in the increase in the rate, or frequency of synaptic transmission at the synapse.
Any process that results in a change in state or activity of a multicellular organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a stimulus indicating the organism is under stress. The stress is usually, but not necessarily, exogenous (e.g. temperature, humidity, ionizing radiation).
Any process that decreases the rate, frequency, or extent of cell aging. Cell aging is the progression of the cell from its inception to the end of its lifespan.
MAGI-2, a multidomain scaffolding protein, contains nine potential protein-protein interaction modules, including a GuK domain, two WW domains and six PDZ domains. In this study, we examined eight human hepatocarcinoma cell lines (HHCCs) and found that MAGI-2 was expressed only in 7721 cells. After 7721, 7404 and 97H cells were transfected with myc-MAGI-2 plasmid, their migration and proliferation was significantly inhibited, which was associated with downregulation of p-FAK and p-Akt. It is known that p-FAK is a substrate of PTEN and p-Akt can be regulated by PTEN via PIP(3). We demonstrated that PTEN was upregulated after myc-MAGI-2 transfection, which was due to the enhancement of PTEN protein stability rather than mRNA levels. Furthermore, MAGI-2-induced inhibition of cell migration and proliferation was attenuated in 7721 cells with PTEN silence or in PTEN-null cell line U87MG, and PTEN transfection could restore the effect of MAGI-2 in U87MG cells. Finally, the molecular association between PTEN and MAGI-2 was confirmed. Our results suggested that PTEN played a critical role in MAGI-2-induced inhibition of cell migration and proliferation in HHCCs.
Evidence
2:
Inferred from Mutant PhenotypeUniProtKB
The tumor suppressor PTEN is a phosphatase with sequence similarity to the cytoskeletal protein tensin. Here the cellular roles of PTEN were investigated. Overexpression of PTEN inhibited cell migration, whereas antisense PTEN enhanced migration. Integrin-mediated cell spreading and the formation of focal adhesions were down-regulated by wild-type PTEN but not by PTEN with an inactive phosphatase domain. PTEN interacted with the focal adhesion kinase FAK and reduced its tyrosine phosphorylation. Overexpression of FAK partially antagonized the effects of PTEN. Thus, PTEN phosphatase may function as a tumor suppressor by negatively regulating cell interactions with the extracellular matrix.
Proc. Natl. Acad. Sci. U.S.A. 96, 10182-10187 (1999)[PubMed:10468583]
PTEN is a recently identified tumor suppressor inactivated in a variety of cancers such as glioblastoma and endometrial and prostate carcinoma. It contains an amino-terminal phosphatase domain and acts as a phosphatidylinositol 3,4,5-trisphosphate phosphatase antagonizing the activity of the phosphatidylinositol 3-OH kinase. PTEN also contains a carboxyl-terminal domain, and we addressed the role of this region that, analogous to the amino-terminal phosphatase domain, is the target of many mutations identified in tumors. Expression of carboxyl-terminal mutants in PTEN-deficient glioblastoma cells permitted the anchorage-independent growth of the cells that otherwise was suppressed by wild-type PTEN. The stability of these mutants in cells was reduced because of rapid degradation. Although the carboxyl-terminal region contains regulatory PEST sequences and a PDZ-binding motif, these specific elements were dispensable for the tumor-suppressor function. The study of carboxyl-terminal point mutations affecting the stability of PTEN revealed that these were located in strongly predicted beta-strands. Surprisingly, the phosphatase activity of these mutants was affected in correlation with the degree of disruption of these structural elements. We conclude that the carboxyl-terminal region is essential for regulating PTEN stability and enzymatic activity and that mutations in this region are responsible for the reversion of the tumor-suppressor phenotype. We also propose that the molecular conformational changes induced by these mutations constitute the mechanism for PTEN inactivation.
Evidence
2:
Inferred from Mutant PhenotypeUniProtKB
MAGI-2, a multidomain scaffolding protein, contains nine potential protein-protein interaction modules, including a GuK domain, two WW domains and six PDZ domains. In this study, we examined eight human hepatocarcinoma cell lines (HHCCs) and found that MAGI-2 was expressed only in 7721 cells. After 7721, 7404 and 97H cells were transfected with myc-MAGI-2 plasmid, their migration and proliferation was significantly inhibited, which was associated with downregulation of p-FAK and p-Akt. It is known that p-FAK is a substrate of PTEN and p-Akt can be regulated by PTEN via PIP(3). We demonstrated that PTEN was upregulated after myc-MAGI-2 transfection, which was due to the enhancement of PTEN protein stability rather than mRNA levels. Furthermore, MAGI-2-induced inhibition of cell migration and proliferation was attenuated in 7721 cells with PTEN silence or in PTEN-null cell line U87MG, and PTEN transfection could restore the effect of MAGI-2 in U87MG cells. Finally, the molecular association between PTEN and MAGI-2 was confirmed. Our results suggested that PTEN played a critical role in MAGI-2-induced inhibition of cell migration and proliferation in HHCCs.
The PTEN tumour suppressor gene is induced by the early growth response 1 (EGR1) transcription factor, which also transactivates p53, p73, and p300/CBP as well as other proapoptotic and anti-cancer genes. Here, we describe a novel Akt-EGR1-alternate reading frame (ARF)-PTEN axis, in which PTEN activation in vivo requires p14ARF-mediated sumoylation of EGR1. This modification is dependent on the phosphorylation of EGR1 at S350 and T309 by Akt, which promotes interaction of EGR1 with ARF at K272 in its repressor domain by the ARF/Ubc9/SUMO system. EGR1 sumoylation is decreased by ARF reduction, and no EGR1 sumoylation is detected in ARF(-/-) mice, which also exhibit reduced amounts of PTEN. Our model predicts that perturbation of any of the clinically important tumour suppressors, PTEN, EGR1, and ARF, will cause some degree of dysfunction of the others. These results also explain the known negative feedback regulation by PTEN on its own synthesis through PI3 kinase inhibition.
PTEN is a frequently mutated tumor suppressor gene that opposes the PI3K/AKT pathway through dephosphorylation of phosphoinositide-3,4,5-triphosphate. Recently, nuclear compartmentalization of PTEN was found as a key component of its tumor-suppressive activity; however its nuclear function remains poorly defined. Here we show that nuclear PTEN interacts with APC/C, promotes APC/C association with CDH1, and thereby enhances the tumor-suppressive activity of the APC-CDH1 complex. We find that nuclear exclusion but not phosphatase inactivation of PTEN impairs APC-CDH1. This nuclear function of PTEN provides a straightforward mechanistic explanation for the fail-safe cellular senescence response elicited by acute PTEN loss and the tumor-suppressive activity of catalytically inactive PTEN. Importantly, we demonstrate that PTEN mutant and PTEN null states are not synonymous as they are differentially sensitive to pharmacological inhibition of APC-CDH1 targets such as PLK1 and Aurora kinases. This finding identifies a strategy for cancer patient stratification and, thus, optimization of targeted therapies. PAPERCLIP:
Any process that decreases the rate, frequency, or extent of dendritic spine morphogenesis, the process in which the anatomical structures of a dendritic spine are generated and organized. A dendritic spine is a protrusion from a dendrite and a specialized subcellular compartment involved in synaptic transmission.
Any process that prevents the establishment or decreases the extent of the excitatory postsynaptic potential (EPSP) which is a temporary increase in postsynaptic potential due to the flow of positively charged ions into the postsynaptic cell. The flow of ions that causes an EPSP is an excitatory postsynaptic current (EPSC) and makes it easier for the neuron to fire an action potential.
Any process that stops, prevents, or reduces the frequency, rate or extent of focal adhesion assembly, the establishment and maturation of focal adhesions.
Evidence
1:
Inferred from Mutant PhenotypeUniProtKB
The tumor suppressor PTEN is a phosphatase with sequence similarity to the cytoskeletal protein tensin. Here the cellular roles of PTEN were investigated. Overexpression of PTEN inhibited cell migration, whereas antisense PTEN enhanced migration. Integrin-mediated cell spreading and the formation of focal adhesions were down-regulated by wild-type PTEN but not by PTEN with an inactive phosphatase domain. PTEN interacted with the focal adhesion kinase FAK and reduced its tyrosine phosphorylation. Overexpression of FAK partially antagonized the effects of PTEN. Thus, PTEN phosphatase may function as a tumor suppressor by negatively regulating cell interactions with the extracellular matrix.
PTEN is a frequently mutated tumor suppressor gene that opposes the PI3K/AKT pathway through dephosphorylation of phosphoinositide-3,4,5-triphosphate. Recently, nuclear compartmentalization of PTEN was found as a key component of its tumor-suppressive activity; however its nuclear function remains poorly defined. Here we show that nuclear PTEN interacts with APC/C, promotes APC/C association with CDH1, and thereby enhances the tumor-suppressive activity of the APC-CDH1 complex. We find that nuclear exclusion but not phosphatase inactivation of PTEN impairs APC-CDH1. This nuclear function of PTEN provides a straightforward mechanistic explanation for the fail-safe cellular senescence response elicited by acute PTEN loss and the tumor-suppressive activity of catalytically inactive PTEN. Importantly, we demonstrate that PTEN mutant and PTEN null states are not synonymous as they are differentially sensitive to pharmacological inhibition of APC-CDH1 targets such as PLK1 and Aurora kinases. This finding identifies a strategy for cancer patient stratification and, thus, optimization of targeted therapies. PAPERCLIP:
Any process that stops, prevents, or reduces the frequency, rate or extent of signal transduction mediated by the phosphatidylinositol 3-kinase cascade.
The phosphatidylinositol 3-kinase (PI3K) signaling pathway modulates growth, proliferation and cell survival in diverse tissue types and plays specialized roles in the nervous system including influences on neuronal polarity, dendritic branching and synaptic plasticity. The tumor-suppressor phosphatase with tensin homology (PTEN) is the central negative regulator of the PI3K pathway. Germline PTEN mutations result in cancer predisposition, macrocephaly and benign hamartomas in many tissues, including Lhermitte-Duclos disease, a cerebellar growth disorder. Neurological abnormalities including autism, seizures and ataxia have been observed in association with inherited PTEN mutation with variable penetrance. It remains unclear how loss of PTEN activity contributes to neurological dysfunction. To explore the effects of Pten deficiency on neuronal structure and function, we analyzed several ultra-structural features of Pten-deficient neurons in Pten conditional knockout mice. Using Golgi stain to visualize full neuronal morphology, we observed that increased size of nuclei and somata in Pten-deficient neurons was accompanied by enlarged caliber of neuronal projections and increased dendritic spine density. Electron microscopic evaluation revealed enlarged abnormal synaptic structures in the cerebral cortex and cerebellum. Severe myelination defects included thickening and unraveling of the myelin sheath surrounding hypertrophic axons in the corpus callosum. Defects in myelination of axons of normal caliber were observed in the cerebellum, suggesting intrinsic abnormalities in Pten-deficient oligodendrocytes. We did not observe these abnormalities in wild-type or conditional Pten heterozygous mice. Moreover, conditional deletion of Pten drastically weakened synaptic transmission and synaptic plasticity at excitatory synapses between CA3 and CA1 pyramidal neurons in the hippocampus. These data suggest that Pten is involved in mechanisms that control development of neuronal and synaptic structures and subsequently synaptic function.
Any process that stops, prevents, or reduces the frequency, rate or extent of the protein kinase B signaling cascade, a series of reactions mediated by the intracellular serine/threonine kinase protein kinase B.
Evidence
1:
Inferred from Mutant PhenotypeUniProtKB
Proc. Natl. Acad. Sci. U.S.A. 97, 4233-4238 (2000)[PubMed:10760291]
PTEN is a tumor suppressor gene mutated in human cancers. Although many mutations target the phosphatase domain, others create a truncated protein lacking the C-terminal PDZ-binding motif or a protein that extends beyond the PDZ-binding motif. Using the yeast two-hybrid system, we isolated a membrane-associated guanylate kinase family protein with multiple PDZ domains [AIP-1 (atrophin interacting protein 1), renamed MAGI-2 (membrane associated guanylate kinase inverted-2)]. MAGI-2 contains eight potential protein-protein interaction domains and is localized to tight junctions in the membrane of epithelial cells. PTEN binds to MAGI-2 through an interaction between the PDZ-binding motif of PTEN and the second PDZ domain of MAGI-2. MAGI-2 enhances the ability of PTEN to suppress Akt activation. Furthermore, certain PTEN mutants have reduced stability, which is restored by adding the minimal PDZ-binding motif back to the truncated protein. We propose that MAGI-2 improves the efficiency of PTEN signaling through assembly of a multiprotein complex at the cell membrane.
Endothelial cell (EC) migration, cell-cell adhesion, and the formation of branching point structures are considered hallmarks of angiogenesis; however, the underlying mechanisms of these processes are not well understood. Lipid phosphate phosphatase 3 (LPP3) is a recently described p120-catenin-associated integrin ligand localized in adherens junctions (AJs) of ECs. Here, we tested the hypothesis that LPP3 stimulates beta-catenin/lymphoid enhancer binding factor 1 (beta-catenin/LEF-1) to induce EC migration and formation of branching point structures. In subconfluent ECs, LPP3 induced expression of fibronectin via beta-catenin/LEF-1 signaling in a phosphatase and tensin homologue (PTEN)-dependent manner. In confluent ECs, depletion of p120-catenin restored LPP3-mediated beta-catenin/LEF-1 signaling. Depletion of LPP3 resulted in destabilization of beta-catenin, which in turn reduced fibronectin synthesis and deposition, which resulted in inhibition of EC migration. Accordingly, reexpression of beta-catenin but not p120-catenin in LPP3-depleted ECs restored de novo synthesis of fibronectin, which mediated EC migration and formation of branching point structures. In confluent ECs, however, a fraction of p120-catenin associated and colocalized with LPP3 at the plasma membrane, via the C-terminal cytoplasmic domain, thereby limiting the ability of LPP3 to stimulate beta-catenin/LEF-1 signaling. Thus, our study identified a key role for LPP3 in orchestrating PTEN-mediated beta-catenin/LEF-1 signaling in EC migration, cell-cell adhesion, and formation of branching point structures.
Any process that decreases the rate, frequency or extent of ribosome biogenesis. Ribosome biogenesis is the cellular process that results in the biosynthesis of constituent macromolecules, assembly, and arrangement of constituent parts of ribosome subunits.
Proc. Natl. Acad. Sci. U.S.A. 94, 9052-9057 (1997)[PubMed:9256433]
Protein tyrosine phosphatases (PTPs) have long been thought to play a role in tumor suppression due to their ability to antagonize the growth promoting protein tyrosine kinases. Recently, a candidate tumor suppressor from 10q23, termed P-TEN, was isolated, and sequence homology was demonstrated with members of the PTP family, as well as the cytoskeletal protein tensin. Here we show that recombinant P-TEN dephosphorylated protein and peptide substrates phosphorylated on serine, threonine, and tyrosine residues, indicating that P-TEN is a dual-specificity phosphatase. In addition, P-TEN exhibited a high degree of substrate specificity, showing selectivity for extremely acidic substrates in vitro. Furthermore, we demonstrate that mutations in P-TEN, identified from primary tumors, tumor cells lines, and a patient with Bannayan-Zonana syndrome, resulted in the ablation of phosphatase activity, demonstrating that enzymatic activity of P-TEN is necessary for its ability to function as a tumor suppressor.
J. Biol. Chem. 273, 13375-13378 (1998)[PubMed:9593664]
Phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) is a key molecule involved in cell growth signaling. We demonstrated that overexpression of PTEN, a putative tumor suppressor, reduced insulin-induced PtdIns(3,4,5)P3 production in human 293 cells without effecting insulin-induced phosphoinositide 3-kinase activation. Further, transfection of the catalytically inactive mutant of PTEN (C124S) caused PtdIns(3,4,5)P3 accumulation in the absence of insulin stimulation. Purified recombinant PTEN catalyzed dephosphorylation of PtdIns(3,4,5)P3, specifically at position 3 on the inositol ring. PTEN also exhibited 3-phosphatase activity toward inositol 1,3,4,5-tetrakisphosphate. Our results raise the possibility that PTEN acts in vivo as a phosphoinositide 3-phosphatase by regulating PtdIns(3,4,5)P3 levels. As expected, the C124S mutant of PTEN was incapable of catalyzing dephosphorylation of PtdIns(3,4,5)P3 consistent with the mechanism observed in protein-tyrosine phosphatase-catalyzed reactions.
The PTEN (phosphatase and tensin homolog) phosphatase is unique in mammals in terms of its tumor suppressor activity, exerted by dephosphorylation of the lipid second messenger PIP(3) (phosphatidylinositol 3,4,5-trisphosphate), which activates the phosphoinositide 3-kinase/Akt/mTOR (mammalian target of rapamycin) oncogenic pathway. Loss-of-function mutations in the PTEN gene are frequent in human cancer and in the germline of patients with PTEN hamartoma tumor-related syndromes (PHTSs). In addition, PTEN is mutated in patients with autism spectrum disorders (ASDs), although no functional information on these mutations is available. Here, we report a comprehensive in vivo functional analysis of human PTEN using a heterologous yeast reconstitution system. Ala-scanning mutagenesis at the catalytic loops of PTEN outlined the critical role of residues within the P-catalytic loop for PIP(3) phosphatase activity in vivo. PTEN mutations that mimic the P-catalytic loop of mammalian PTEN-like proteins (TPTE, TPIP, tensins and auxilins) affected PTEN function variably, whereas tumor- or PHTS-associated mutations targeting the PTEN P-loop produced complete loss of function. Conversely, Ala-substitutions, as well as tumor-related mutations at the WPD- and TI-catalytic loops, displayed partial activity in many cases. Interestingly, a tumor-related D92N mutation was partially active, supporting the notion that the PTEN Asp92 residue might not function as the catalytic general acid. The analysis of a panel of ASD-associated hereditary PTEN mutations revealed that most of them did not substantially abrogate PTEN activity in vivo, whereas most of PHTS-associated mutations did. Our findings reveal distinctive functional patterns among PTEN mutations found in tumors and in the germline of PHTS and ASD patients, which could be relevant for therapy.
Proc. Natl. Acad. Sci. U.S.A. 95, 13513-13518 (1998)[PubMed:9811831]
Since their discovery, protein tyrosine phosphatases have been speculated to play a role in tumor suppression because of their ability to antagonize the growth-promoting protein tyrosine kinases. Recently, a tumor suppressor from human chromosome 10q23, called PTEN or MMAC1, has been identified that shares homology with the protein tyrosine phosphatase family. Germ-line mutations in PTEN give rise to several related neoplastic disorders, including Cowden disease. A key step in understanding the function of PTEN as a tumor suppressor is to identify its physiological substrates. Here we report that a missense mutation in PTEN, PTEN-G129E, which is observed in two Cowden disease kindreds, specifically ablates the ability of PTEN to recognize inositol phospholipids as a substrate, suggesting that loss of the lipid phosphatase activity is responsible for the etiology of the disease. Furthermore, expression of wild-type or substrate-trapping forms of PTEN in HEK293 cells altered the levels of the phospholipid products of phosphatidylinositol 3-kinase and ectopic expression of the phosphatase in PTEN-deficient tumor cell lines resulted in the inhibition of protein kinase (PK) B/Akt and regulation of cell survival.
Any process that enhances the establishment or increases the extent of the excitatory postsynaptic potential (EPSP) which is a temporary increase in postsynaptic potential due to the flow of positively charged ions into the postsynaptic cell. The flow of ions that causes an EPSP is an excitatory postsynaptic current (EPSC) and makes it easier for the neuron to fire an action potential.
ISSOrtholog Curator
Positive regulation of protein ubiquitination involved in ubiquitin-dependent protein catabolic processdefinition[GO:2000060]
Any process that activates or increases the frequency, rate or extent of protein ubiquitination involved in ubiquitin-dependent protein catabolic process.
PTEN is a frequently mutated tumor suppressor gene that opposes the PI3K/AKT pathway through dephosphorylation of phosphoinositide-3,4,5-triphosphate. Recently, nuclear compartmentalization of PTEN was found as a key component of its tumor-suppressive activity; however its nuclear function remains poorly defined. Here we show that nuclear PTEN interacts with APC/C, promotes APC/C association with CDH1, and thereby enhances the tumor-suppressive activity of the APC-CDH1 complex. We find that nuclear exclusion but not phosphatase inactivation of PTEN impairs APC-CDH1. This nuclear function of PTEN provides a straightforward mechanistic explanation for the fail-safe cellular senescence response elicited by acute PTEN loss and the tumor-suppressive activity of catalytically inactive PTEN. Importantly, we demonstrate that PTEN mutant and PTEN null states are not synonymous as they are differentially sensitive to pharmacological inhibition of APC-CDH1 targets such as PLK1 and Aurora kinases. This finding identifies a strategy for cancer patient stratification and, thus, optimization of targeted therapies. PAPERCLIP:
Positive regulation of sequence-specific DNA binding transcription factor activitydefinition[GO:0051091]
Any process that activates or increases the frequency, rate or extent of activity of a transcription factor, any factor involved in the initiation or regulation of transcription.
Endothelial cell (EC) migration, cell-cell adhesion, and the formation of branching point structures are considered hallmarks of angiogenesis; however, the underlying mechanisms of these processes are not well understood. Lipid phosphate phosphatase 3 (LPP3) is a recently described p120-catenin-associated integrin ligand localized in adherens junctions (AJs) of ECs. Here, we tested the hypothesis that LPP3 stimulates beta-catenin/lymphoid enhancer binding factor 1 (beta-catenin/LEF-1) to induce EC migration and formation of branching point structures. In subconfluent ECs, LPP3 induced expression of fibronectin via beta-catenin/LEF-1 signaling in a phosphatase and tensin homologue (PTEN)-dependent manner. In confluent ECs, depletion of p120-catenin restored LPP3-mediated beta-catenin/LEF-1 signaling. Depletion of LPP3 resulted in destabilization of beta-catenin, which in turn reduced fibronectin synthesis and deposition, which resulted in inhibition of EC migration. Accordingly, reexpression of beta-catenin but not p120-catenin in LPP3-depleted ECs restored de novo synthesis of fibronectin, which mediated EC migration and formation of branching point structures. In confluent ECs, however, a fraction of p120-catenin associated and colocalized with LPP3 at the plasma membrane, via the C-terminal cytoplasmic domain, thereby limiting the ability of LPP3 to stimulate beta-catenin/LEF-1 signaling. Thus, our study identified a key role for LPP3 in orchestrating PTEN-mediated beta-catenin/LEF-1 signaling in EC migration, cell-cell adhesion, and formation of branching point structures.
The aggregation, arrangement and bonding together of a set of components to form a postsynaptic density, a region that lies adjacent to the cytoplasmic face of the postsynaptic membrane at excitatory synapse.
The aggregation, arrangement and bonding together of a set of components to form a presynaptic membrane, a specialized area of membrane of the axon terminal that faces the plasma membrane of the neuron or muscle fiber with which the axon terminal establishes a synaptic junction.
The increase in size or mass of the prostate gland where the increase in size or mass has the specific outcome of the progression of the gland, from its formation to its mature state.
J. Biol. Chem. 272, 29403-29406 (1997)[PubMed:9367992]
In Saccharomyces cerevisiae the CDC14 gene is essential for cell cycle progression. Strains carrying the cdc14-1(ts) allele enter the cell cycle and arrest at restrictive temperatures. We have identified two human cDNAs encoding proteins which share sequence identity to the yeast CDC14p. The cell cycle arrest in cdc14-1(ts) can be specifically complemented by the human cDNAs suggesting that they are functionally equivalent to the yeast CDC14 gene. Another clone identified in the search for human CDC14-like proteins corresponded to the putative tumor suppressor gene PTEN/MMAC1 (phosphatase and tensin homologue deleted on chromosome 10 or mutated in multiple advanced cancers 1). Analysis of the PTEN/MMAC1 showed that it did not complement the cdc14-1(ts) allele and that it is more closely related to the yeast open reading frame YNL128W. Human CDC14p and PTEN/MMAC1 were expressed as recombinant proteins, and both were shown to have kinetic properties characteristic of dual specific phosphatases. The human CDC14p was localized in the nucleus while PTEN/MMAC1 has been reported to be localized in the cytoplasm. Our results suggest that CDC14 and YNL128W/PTEN/MMAC1 represent two related, but distinct, families of human and yeast phosphatases.
Proc. Natl. Acad. Sci. U.S.A. 94, 9052-9057 (1997)[PubMed:9256433]
Protein tyrosine phosphatases (PTPs) have long been thought to play a role in tumor suppression due to their ability to antagonize the growth promoting protein tyrosine kinases. Recently, a candidate tumor suppressor from 10q23, termed P-TEN, was isolated, and sequence homology was demonstrated with members of the PTP family, as well as the cytoskeletal protein tensin. Here we show that recombinant P-TEN dephosphorylated protein and peptide substrates phosphorylated on serine, threonine, and tyrosine residues, indicating that P-TEN is a dual-specificity phosphatase. In addition, P-TEN exhibited a high degree of substrate specificity, showing selectivity for extremely acidic substrates in vitro. Furthermore, we demonstrate that mutations in P-TEN, identified from primary tumors, tumor cells lines, and a patient with Bannayan-Zonana syndrome, resulted in the ablation of phosphatase activity, demonstrating that enzymatic activity of P-TEN is necessary for its ability to function as a tumor suppressor.
A series of reactions, mediated by the intracellular serine/threonine kinase protein kinase B, which occurs as a result of a single trigger reaction or compound.
Endothelial cell (EC) migration, cell-cell adhesion, and the formation of branching point structures are considered hallmarks of angiogenesis; however, the underlying mechanisms of these processes are not well understood. Lipid phosphate phosphatase 3 (LPP3) is a recently described p120-catenin-associated integrin ligand localized in adherens junctions (AJs) of ECs. Here, we tested the hypothesis that LPP3 stimulates beta-catenin/lymphoid enhancer binding factor 1 (beta-catenin/LEF-1) to induce EC migration and formation of branching point structures. In subconfluent ECs, LPP3 induced expression of fibronectin via beta-catenin/LEF-1 signaling in a phosphatase and tensin homologue (PTEN)-dependent manner. In confluent ECs, depletion of p120-catenin restored LPP3-mediated beta-catenin/LEF-1 signaling. Depletion of LPP3 resulted in destabilization of beta-catenin, which in turn reduced fibronectin synthesis and deposition, which resulted in inhibition of EC migration. Accordingly, reexpression of beta-catenin but not p120-catenin in LPP3-depleted ECs restored de novo synthesis of fibronectin, which mediated EC migration and formation of branching point structures. In confluent ECs, however, a fraction of p120-catenin associated and colocalized with LPP3 at the plasma membrane, via the C-terminal cytoplasmic domain, thereby limiting the ability of LPP3 to stimulate beta-catenin/LEF-1 signaling. Thus, our study identified a key role for LPP3 in orchestrating PTEN-mediated beta-catenin/LEF-1 signaling in EC migration, cell-cell adhesion, and formation of branching point structures.
The dual-specificity phosphatase PTEN/MMAC1/TEP1 has recently been identified as the tumor suppressor gene most frequently mutated and/or deleted in human tumors. Germline mutations of PTEN give rise to Cowden Disease (CD), an autosomal dominantly-inherited cancer syndrome which predisposes to increased risk of developing breast and thyroid tumors. However, PTEN mutations have rarely been detected in sporadic thyroid carcinomas. In this study, we confirm that PTEN mutations in sporadic thyroid cancer are infrequent as we found one point mutation and one heterozygous deletion of PTEN gene in 26 tumors and eight cell lines screened. However, we report that PTEN expression is reduced both at the mRNA and at the protein level - in five out of eight tumor-derived cell lines and in 24 out of 61 primary tumors. In most cases, decreased PTEN expression is correlated with increased phosphorylation of the PTEN-regulated protein kinase Akt/PKB. Moreover, we demonstrate that PTEN may act as a suppressor of thyroid cancerogenesis as the constitutive re-expression of PTEN into two different thyroid tumor cell lines markedly inhibits cell growth. PTEN-dependent inhibition of BrdU incorporation is accompanied by enhanced expression of the cyclin-dependent kinase inhibitor p27kip1 and can be overcome by simultaneous co-transfection of an excess p27kip1 antisense plasmid. Accordingly, in a subset of thyroid primary carcinomas and tumor-derived cell lines, a striking correlation between PTEN expression and the level of p27kip1 protein was observed. In conclusion, our findings demonstrate that inactivation of PTEN may play a role in the development of sporadic thyroid carcinomas and that one key target of PTEN suppressor activity is represented by the cyclin-dependent kinase inhibitor p27kip1.
Any process that modulates the rate, frequency or extent of neuron projection development. Neuron projection development is the process whose specific outcome is the progression of a neuron projection over time, from its formation to the mature structure. A neuron projection is any process extending from a neural cell, such as axons or dendrites (collectively called neurites).
The PTEN gene is a tumor suppressor localized in the frequently altered chromosomal region 10q23. The tumor suppressor function of the PTEN protein (PTEN) has been linked to its ability to dephosphorylate the lipid second-messenger phosphatidylinositol 3,4, 5-trisphosphate and phosphatidylinositol 3,4-bisphosphate and, by doing so, to antagonize the phosphoinositide 3-kinase pathway. The PTEN protein consists of an amino-terminal phosphatase domain, a lipid binding C2 domain, and a 50-amino-acid C-terminal domain (the "tail") of unknown function. A number of studies have shown that the tail is dispensable for both phosphatase activity and blocking cell growth. Here, we show that the PTEN tail is necessary for maintaining protein stability and that it also acts to inhibit PTEN function. Thus, removing the tail results in a loss of stability but does not result in a loss of function because the resultant protein is more active. Furthermore, tail-dependent regulation of stability and activity is linked to the phosphorylation of three residues (S380, T382, and T383) within the tail. Therefore, the tail is likely to mediate the regulation of PTEN function through phosphorylation.
The process that organizes a synapse so that it attains its fully functional state. Synaptic maturation plays a critical role in the establishment of effective synaptic connections in early development.
ISSOrtholog Curator
Enzymatic activity
This protein acts as an enzyme. It is known to catalyze the following reactions
Proc. Natl. Acad. Sci. U.S.A. 94, 9052-9057 (1997)[PubMed:9256433]
Protein tyrosine phosphatases (PTPs) have long been thought to play a role in tumor suppression due to their ability to antagonize the growth promoting protein tyrosine kinases. Recently, a candidate tumor suppressor from 10q23, termed P-TEN, was isolated, and sequence homology was demonstrated with members of the PTP family, as well as the cytoskeletal protein tensin. Here we show that recombinant P-TEN dephosphorylated protein and peptide substrates phosphorylated on serine, threonine, and tyrosine residues, indicating that P-TEN is a dual-specificity phosphatase. In addition, P-TEN exhibited a high degree of substrate specificity, showing selectivity for extremely acidic substrates in vitro. Furthermore, we demonstrate that mutations in P-TEN, identified from primary tumors, tumor cells lines, and a patient with Bannayan-Zonana syndrome, resulted in the ablation of phosphatase activity, demonstrating that enzymatic activity of P-TEN is necessary for its ability to function as a tumor suppressor.
It has long been postulated that protein tyrosine phosphatases may act as tumor suppressors because of their ability to counteract the oncogenic actions of protein tyrosine kinases. Here we report the cloning and characterization of a novel human protein tyrosine phosphatase, TEP1. TEP1 contains the protein tyrosine phosphatase signature motif, and we show that it possesses an intrinsic protein tyrosine phosphatase activity. TEP1 also shares extensive homology with tensin, a cytoskeletal protein localized to focal adhesions, and with auxilin, a protein involved in synaptic vesicle transport. Immunofluorescence studies show that TEP1 is a cytoplasmic protein. The abundance of TEP1 transcription is altered in many transformed cells. In the transforming growth factor beta-sensitive cells, TEP1 expression is rapidly down-regulated by transforming growth factor beta, a cytokine shown to be involved in regulating cell adhesion and cell motility. We have also mapped the gene encoding TEP1 to chromosome 10q23, a locus that is frequently deleted in a variety of human cancers. TEP1 protein is identical to the protein encoded by the candidate tumor suppressor gene PTEN/MMAC1. Our functional studies of the TEP1 protein suggest that its tumor suppressor function may associate with its intrinsic protein tyrosine phosphatase activity and its cytoplasmic localization.
J. Biol. Chem. 273, 13375-13378 (1998)[PubMed:9593664]
Phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) is a key molecule involved in cell growth signaling. We demonstrated that overexpression of PTEN, a putative tumor suppressor, reduced insulin-induced PtdIns(3,4,5)P3 production in human 293 cells without effecting insulin-induced phosphoinositide 3-kinase activation. Further, transfection of the catalytically inactive mutant of PTEN (C124S) caused PtdIns(3,4,5)P3 accumulation in the absence of insulin stimulation. Purified recombinant PTEN catalyzed dephosphorylation of PtdIns(3,4,5)P3, specifically at position 3 on the inositol ring. PTEN also exhibited 3-phosphatase activity toward inositol 1,3,4,5-tetrakisphosphate. Our results raise the possibility that PTEN acts in vivo as a phosphoinositide 3-phosphatase by regulating PtdIns(3,4,5)P3 levels. As expected, the C124S mutant of PTEN was incapable of catalyzing dephosphorylation of PtdIns(3,4,5)P3 consistent with the mechanism observed in protein-tyrosine phosphatase-catalyzed reactions.
Proc. Natl. Acad. Sci. U.S.A. 95, 13513-13518 (1998)[PubMed:9811831]
Since their discovery, protein tyrosine phosphatases have been speculated to play a role in tumor suppression because of their ability to antagonize the growth-promoting protein tyrosine kinases. Recently, a tumor suppressor from human chromosome 10q23, called PTEN or MMAC1, has been identified that shares homology with the protein tyrosine phosphatase family. Germ-line mutations in PTEN give rise to several related neoplastic disorders, including Cowden disease. A key step in understanding the function of PTEN as a tumor suppressor is to identify its physiological substrates. Here we report that a missense mutation in PTEN, PTEN-G129E, which is observed in two Cowden disease kindreds, specifically ablates the ability of PTEN to recognize inositol phospholipids as a substrate, suggesting that loss of the lipid phosphatase activity is responsible for the etiology of the disease. Furthermore, expression of wild-type or substrate-trapping forms of PTEN in HEK293 cells altered the levels of the phospholipid products of phosphatidylinositol 3-kinase and ectopic expression of the phosphatase in PTEN-deficient tumor cell lines resulted in the inhibition of protein kinase (PK) B/Akt and regulation of cell survival.
J. Biol. Chem. 273, 13375-13378 (1998)[PubMed:9593664]
Phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) is a key molecule involved in cell growth signaling. We demonstrated that overexpression of PTEN, a putative tumor suppressor, reduced insulin-induced PtdIns(3,4,5)P3 production in human 293 cells without effecting insulin-induced phosphoinositide 3-kinase activation. Further, transfection of the catalytically inactive mutant of PTEN (C124S) caused PtdIns(3,4,5)P3 accumulation in the absence of insulin stimulation. Purified recombinant PTEN catalyzed dephosphorylation of PtdIns(3,4,5)P3, specifically at position 3 on the inositol ring. PTEN also exhibited 3-phosphatase activity toward inositol 1,3,4,5-tetrakisphosphate. Our results raise the possibility that PTEN acts in vivo as a phosphoinositide 3-phosphatase by regulating PtdIns(3,4,5)P3 levels. As expected, the C124S mutant of PTEN was incapable of catalyzing dephosphorylation of PtdIns(3,4,5)P3 consistent with the mechanism observed in protein-tyrosine phosphatase-catalyzed reactions.
Proc. Natl. Acad. Sci. U.S.A. 94, 9052-9057 (1997)[PubMed:9256433]
Protein tyrosine phosphatases (PTPs) have long been thought to play a role in tumor suppression due to their ability to antagonize the growth promoting protein tyrosine kinases. Recently, a candidate tumor suppressor from 10q23, termed P-TEN, was isolated, and sequence homology was demonstrated with members of the PTP family, as well as the cytoskeletal protein tensin. Here we show that recombinant P-TEN dephosphorylated protein and peptide substrates phosphorylated on serine, threonine, and tyrosine residues, indicating that P-TEN is a dual-specificity phosphatase. In addition, P-TEN exhibited a high degree of substrate specificity, showing selectivity for extremely acidic substrates in vitro. Furthermore, we demonstrate that mutations in P-TEN, identified from primary tumors, tumor cells lines, and a patient with Bannayan-Zonana syndrome, resulted in the ablation of phosphatase activity, demonstrating that enzymatic activity of P-TEN is necessary for its ability to function as a tumor suppressor.
It has long been postulated that protein tyrosine phosphatases may act as tumor suppressors because of their ability to counteract the oncogenic actions of protein tyrosine kinases. Here we report the cloning and characterization of a novel human protein tyrosine phosphatase, TEP1. TEP1 contains the protein tyrosine phosphatase signature motif, and we show that it possesses an intrinsic protein tyrosine phosphatase activity. TEP1 also shares extensive homology with tensin, a cytoskeletal protein localized to focal adhesions, and with auxilin, a protein involved in synaptic vesicle transport. Immunofluorescence studies show that TEP1 is a cytoplasmic protein. The abundance of TEP1 transcription is altered in many transformed cells. In the transforming growth factor beta-sensitive cells, TEP1 expression is rapidly down-regulated by transforming growth factor beta, a cytokine shown to be involved in regulating cell adhesion and cell motility. We have also mapped the gene encoding TEP1 to chromosome 10q23, a locus that is frequently deleted in a variety of human cancers. TEP1 protein is identical to the protein encoded by the candidate tumor suppressor gene PTEN/MMAC1. Our functional studies of the TEP1 protein suggest that its tumor suppressor function may associate with its intrinsic protein tyrosine phosphatase activity and its cytoplasmic localization.
Proc. Natl. Acad. Sci. U.S.A. 95, 13513-13518 (1998)[PubMed:9811831]
Since their discovery, protein tyrosine phosphatases have been speculated to play a role in tumor suppression because of their ability to antagonize the growth-promoting protein tyrosine kinases. Recently, a tumor suppressor from human chromosome 10q23, called PTEN or MMAC1, has been identified that shares homology with the protein tyrosine phosphatase family. Germ-line mutations in PTEN give rise to several related neoplastic disorders, including Cowden disease. A key step in understanding the function of PTEN as a tumor suppressor is to identify its physiological substrates. Here we report that a missense mutation in PTEN, PTEN-G129E, which is observed in two Cowden disease kindreds, specifically ablates the ability of PTEN to recognize inositol phospholipids as a substrate, suggesting that loss of the lipid phosphatase activity is responsible for the etiology of the disease. Furthermore, expression of wild-type or substrate-trapping forms of PTEN in HEK293 cells altered the levels of the phospholipid products of phosphatidylinositol 3-kinase and ectopic expression of the phosphatase in PTEN-deficient tumor cell lines resulted in the inhibition of protein kinase (PK) B/Akt and regulation of cell survival.
Proc. Natl. Acad. Sci. U.S.A. 94, 9052-9057 (1997)[PubMed:9256433]
Protein tyrosine phosphatases (PTPs) have long been thought to play a role in tumor suppression due to their ability to antagonize the growth promoting protein tyrosine kinases. Recently, a candidate tumor suppressor from 10q23, termed P-TEN, was isolated, and sequence homology was demonstrated with members of the PTP family, as well as the cytoskeletal protein tensin. Here we show that recombinant P-TEN dephosphorylated protein and peptide substrates phosphorylated on serine, threonine, and tyrosine residues, indicating that P-TEN is a dual-specificity phosphatase. In addition, P-TEN exhibited a high degree of substrate specificity, showing selectivity for extremely acidic substrates in vitro. Furthermore, we demonstrate that mutations in P-TEN, identified from primary tumors, tumor cells lines, and a patient with Bannayan-Zonana syndrome, resulted in the ablation of phosphatase activity, demonstrating that enzymatic activity of P-TEN is necessary for its ability to function as a tumor suppressor.
J. Biol. Chem. 273, 13375-13378 (1998)[PubMed:9593664]
Phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) is a key molecule involved in cell growth signaling. We demonstrated that overexpression of PTEN, a putative tumor suppressor, reduced insulin-induced PtdIns(3,4,5)P3 production in human 293 cells without effecting insulin-induced phosphoinositide 3-kinase activation. Further, transfection of the catalytically inactive mutant of PTEN (C124S) caused PtdIns(3,4,5)P3 accumulation in the absence of insulin stimulation. Purified recombinant PTEN catalyzed dephosphorylation of PtdIns(3,4,5)P3, specifically at position 3 on the inositol ring. PTEN also exhibited 3-phosphatase activity toward inositol 1,3,4,5-tetrakisphosphate. Our results raise the possibility that PTEN acts in vivo as a phosphoinositide 3-phosphatase by regulating PtdIns(3,4,5)P3 levels. As expected, the C124S mutant of PTEN was incapable of catalyzing dephosphorylation of PtdIns(3,4,5)P3 consistent with the mechanism observed in protein-tyrosine phosphatase-catalyzed reactions.
Proc. Natl. Acad. Sci. U.S.A. 95, 13513-13518 (1998)[PubMed:9811831]
Since their discovery, protein tyrosine phosphatases have been speculated to play a role in tumor suppression because of their ability to antagonize the growth-promoting protein tyrosine kinases. Recently, a tumor suppressor from human chromosome 10q23, called PTEN or MMAC1, has been identified that shares homology with the protein tyrosine phosphatase family. Germ-line mutations in PTEN give rise to several related neoplastic disorders, including Cowden disease. A key step in understanding the function of PTEN as a tumor suppressor is to identify its physiological substrates. Here we report that a missense mutation in PTEN, PTEN-G129E, which is observed in two Cowden disease kindreds, specifically ablates the ability of PTEN to recognize inositol phospholipids as a substrate, suggesting that loss of the lipid phosphatase activity is responsible for the etiology of the disease. Furthermore, expression of wild-type or substrate-trapping forms of PTEN in HEK293 cells altered the levels of the phospholipid products of phosphatidylinositol 3-kinase and ectopic expression of the phosphatase in PTEN-deficient tumor cell lines resulted in the inhibition of protein kinase (PK) B/Akt and regulation of cell survival.
It has long been postulated that protein tyrosine phosphatases may act as tumor suppressors because of their ability to counteract the oncogenic actions of protein tyrosine kinases. Here we report the cloning and characterization of a novel human protein tyrosine phosphatase, TEP1. TEP1 contains the protein tyrosine phosphatase signature motif, and we show that it possesses an intrinsic protein tyrosine phosphatase activity. TEP1 also shares extensive homology with tensin, a cytoskeletal protein localized to focal adhesions, and with auxilin, a protein involved in synaptic vesicle transport. Immunofluorescence studies show that TEP1 is a cytoplasmic protein. The abundance of TEP1 transcription is altered in many transformed cells. In the transforming growth factor beta-sensitive cells, TEP1 expression is rapidly down-regulated by transforming growth factor beta, a cytokine shown to be involved in regulating cell adhesion and cell motility. We have also mapped the gene encoding TEP1 to chromosome 10q23, a locus that is frequently deleted in a variety of human cancers. TEP1 protein is identical to the protein encoded by the candidate tumor suppressor gene PTEN/MMAC1. Our functional studies of the TEP1 protein suggest that its tumor suppressor function may associate with its intrinsic protein tyrosine phosphatase activity and its cytoplasmic localization.
Protein involved in apoptotic programmed cell death. Apoptosis is characterized by cell morphological changes, including blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation and chromosomal DNA fragmentation, and eventually death. Unlike necrosis, apoptosis produces cell fragments, called apoptotic bodies, that phagocytic cells are able to engulf and quickly remove before the contents of the cell can spill out onto surrounding cells and cause damage. In general, apoptosis confers advantages during an organism's life cycle.
Protein involved in the biochemical reactions of lipids. Lipids are a diverse class of compounds which are insoluble in water but soluble in organic solvents. They include fats, oils, triacylglycerols, fatty acids, glycolipids, phospholipids and steroids.
Enzyme which catalyzes hydrolysis reaction, i.e. the addition of the hydrogen and hydroxyl ions of water to a molecule with its consequent splitting into two or more simpler molecules.
Enzyme that catalyzes the hydrolysis of phosphate monoesters bonds of phosphoserines, phosphothreonines, phosphotyrosines or phosphoaspartic acids. While many protein phosphatases inhibit the activities of phosphorylation cascades, some activate them.
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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