Calcium-independent, phospholipid- and diacylglycerol (DAG)-dependent serine/threonine-protein kinase that mediates non-redundant functions in T-cell receptor (TCR) signaling, including T-cells activation, proliferation, differentiation and survival, by mediating activation of multiple transcription factors such as NF-kappa-B, JUN, NFATC1 and NFATC2. In TCR-CD3/CD28-co-stimulated T-cells, is required for the activation of NF-kappa-B and JUN, which in turn are essential for IL2 production, and participates to the calcium-dependent NFATC1 and NFATC2 transactivation. Mediates the activation of the canonical NF-kappa-B pathway (NFKB1) by direct phosphorylation of CARD11 on several serine residues, inducing CARD11 association with lipid rafts and recruitment of the BCL10-MALT1 complex, which then activates IKK complex, resulting in nuclear translocation and activation of NFKB1. May also play an indirect role in activation of the non-canonical NF-kappa-B (NFKB2) pathway. In the signaling pathway leading to JUN activation, acts by phosphorylating the mediator STK39/SPAK and may not act through MAP kinases signaling. Plays a critical role in TCR/CD28-induced NFATC1 and NFATC2 transactivation by participating in the regulation of reduced inositol 1,4,5-trisphosphate generation and intracellular calcium mobilization. After costimulation of T-cells through CD28 can phosphorylate CBLB and is required for the ubiquitination and subsequent degradation of CBLB, which is a prerequisite for the activation of TCR. During T-cells differentiation, plays an important role in the development of T-helper 2 (Th2) cells following immune and inflammatory responses, and, in the development of inflammatory autoimmune diseases, is necessary for the activation of IL17-producing Th17 cells. May play a minor role in Th1 response. Upon TCR stimulation, mediates T-cell protective survival signal by phosphorylating BAD, thus protecting T-cells from BAD-induced apoptosis, and by up-regulating BCL-X(L)/BCL2L1 levels through NF-kappa-B and JUN pathways. In platelets, regulates signal transduction downstream of the ITGA2B, CD36/GP4, F2R/PAR1 and F2RL3/PAR4 receptors, playing a positive role in 'outside-in' signaling and granule secretion signal transduction. May relay signals from the activated ITGA2B receptor by regulating the uncoupling of WASP and WIPF1, thereby permitting the regulation of actin filament nucleation and branching activity of the Arp2/3 complex. May mediate inhibitory effects of free fatty acids on insulin signaling by phosphorylating IRS1, which in turn blocks IRS1 tyrosine phosphorylation and downstream activation of the PI3K/AKT pathway. Phosphorylates MSN (moesin) in the presence of phosphatidylglycerol or phosphatidylinositol. Phosphorylates PDPK1 at 'Ser-504' and 'Ser-532' and negatively regulates its ability to phosphorylate PKB/AKT1.
T-lymphocyte stimulation requires activation of several protein kinases, including the major phorbol ester receptor protein kinase C (PKC), ultimately leading to induction of lymphokines, such as interleukin-2 (IL-2). The revelant PKC isoforms which are involved in the activation cascades of nuclear transcription factors involved in IL-2 production have not yet been clearly defined. We have examined the potential role of two representative PKC isoforms in the induction of the IL-2 gene, i.e., PKC-alpha and PKC-theta, the latter being expressed predominantly in hematopoietic cell lines, particularly T cells. Similar to that of PKC-alpha, PKC-theta overexpression in murine EL4 thymoma cells caused a significant increase in phorbol 12-myristate 13-acetate (PMA)-induced transcriptional activation of full-length IL-2-chloramphenicol acetyltransferase (CAT) and NF-AT-CAT but not of NF-IL2A-CAT or NF-kappaB promoter-CAT reporter gene constructs. Importantly, the critical AP-1 enhancer element was differentially modulated by these two distinct PKC isoenzymes, since only PKC-theta but not PKC-alpha overexpression resulted in an approximately 2.8-fold increase in AP-1-collagenase promoter CAT expression in comparison with the vector control. Deletion of the AP-1 enhancer site in the collagenase promoter rendered it unresponsive to PKC-theta. Expression of a constitutively active mutant PKC-theta A148E (but not PKC-alpha A25E) was sufficient to induce activation of AP-1 transcription factor complex in the absence of PMA stimulation. Conversely, a catalytically inactive PKC-theta K409R (but not PKC-alpha K368R) mutant abrogated endogenous PMA-mediated activation of AP-1 transcriptional complex. Dominant negative mutant Ha-RasS17N completely inhibited the PKC-O A148E-induced signal, PKC-O. Expression of a constitutively active mutant PKC-O A148E (but not PKC-alpha A25E) was sufficient to induce activation of AP-1 transcription factor complex in the absence of PMA stimulation. Conversely, a catalytically inactive PKC-O K409R (but not PKC-alpha K368R) mutant abrogated endogenous PMA-mediated activation of AP-1 transcriptional complex. Dominant negative mutant Ha-enRasS17N completely inhibited in the PKC-O A148E-induced signal, identifying PKC-theta as a specific constituent upstream of or parallel to Ras in the signaling cascade leading to AP transcriptional activation.
Protein kinase C-theta (PKCtheta) plays an important role in T-cell activation via stimulation of AP-1 and NF-kappaB. Here we report the isolation of SPAK, a Ste20-related upstream mitogen-activated protein kinase (MAPK), as a PKCtheta-interacting kinase. SPAK interacted with PKCtheta (but not with PKCalpha) via its 99 COOH-terminal residues. TCR/CD28 costimulation enhanced this association and stimulated the catalytic activity of SPAK. Recombinant SPAK was phosphorylated on Ser-311 in its kinase domain by PKCtheta, but not by PKCalpha. The magnitude and duration of TCR/CD28-induced endogenous SPAK activation were markedly impaired in PKCtheta-deficient T cells. Transfected SPAK synergized with constitutively active PKCtheta to activate AP-1, but not NF-kappaB. This synergistic activity, as well as the receptor-induced SPAK activation, required the PKCtheta-interacting region of SPAK, and Ser-311 mutation greatly reduced these activities of SPAK. Conversely, a SPAK-specific RNAi or a dominant-negative SPAK mutant inhibited PKCtheta- and TCR/CD28-induced AP-1, but not NF-kappaB, activation. These results define SPAK as a substrate and target of PKCtheta in a TCR/CD28-induced signaling pathway leading selectively to AP-1 (but not NF-kappaB) activation.
J. Immunol. 166, 5955-5963 (2001)[PubMed:11342610]
Protein kinase C (PKC)-activating phorbol esters protect T cells from Fas-induced apoptosis. However, the mechanism of this protective effect and the identity of the relevant PKC isoform(s) are poorly understood. Here, we show that PKCtheta plays a selective and important role in this protection. Fas triggering led to a selective caspase-3-dependent cleavage of the enzyme and proteasome-mediated degradation and inactivation of its catalytic fragment. These events preceded the onset of apoptosis. Pharmacological inhibition of PKCtheta promoted Fas-mediated apoptosis in three different types of T cells. Conversely, constitutively active PKCtheta (and, to a lesser degree, PKCepsilon) selectively protected T cells from Fas-induced apoptosis. We provide evidence that the distant Bcl-2 family member, BAD, is a PKCtheta substrate, is phosphorylated by TCR stimulation, and can mediate at least in part the anti-apoptotic effect of PKCtheta.
J. Immunol. 176, 6709-6716 (2006)[PubMed:16709830]
Productive engagement of TCR results in delivering signals required for T cell proliferation as well as T cell survival. Blocking TCR-mediated survival signals, T cells undergo apoptosis instead of proliferation upon TCR stimulation. During the activation process, T cells produce IL-2, which acts as an extrinsic survival factor. In addition, TCR stimulation results in up-regulation of Bcl-xL to enhance T cell survival intrinsically. We show in this study that protein kinase C (PKC)-theta is required for enhancing the survival of activated CD4+ T cells by up-regulating Bcl-xL. In response to TCR stimulation, CD4+ PKC-theta-/- T cells failed to up-regulate Bcl-xL, and underwent accelerated apoptosis via a caspase- and mitochondria-dependent pathway. Similar to PKC-theta-deficient primary CD4+ T cells, small interfering RNA-mediated knockdown of PKC-theta in Jurkat cells also resulted in apoptosis upon TCR stimulation. Forced expression of Bcl-xL was sufficient to inhibit apoptosis observed in PKC-theta knockdown cells. Furthermore, ectopic expression of PKC-theta stimulated a reporter gene driven by a mouse Bcl-xL promoter. Whereas an inactive form of PKC-theta or knockdown of endogenous PKC-theta led to inhibition of Bcl-xL reporter. PKC-theta-mediated activation of Bcl-xL reporter was inhibited by dominant-negative IkappaB kinase beta or dominant-negative AP-1. Thus, the PKC-theta-mediated signals may function not only in the initial activation of naive CD4+ T cells, but also in their survival during T cell activation by regulating Bcl-xL levels through NF-kappaB and AP-1 pathways.
PKC isoforms and CARMA1 play crucial roles in immunoreceptor-dependent NF-kappaB activation. We tested whether PKC-dependent phosphorylation of CARMA1 directly regulates this signaling cascade. B cell antigen receptor (BCR) engagement led to the progressive recruitment of CARMA1 into lipid rafts and to the association of CARMA1 with, and phosphorylation by, PKCbeta. Furthermore, PKCbeta interacted with the serine-rich CARMA1 linker, and both PKCbeta and PKCtheta phosphorylated identical serine residues (S564, S649, and S657) within this linker. Mutation of two of these sites ablated the functional activity of CARMA1. In contrast, deletion of the linker resulted in constitutive, receptor- and PKC-independent NF-kappaB activation. Together, our data support a model whereby CARMA1 phosphorylation controls NF-kappaB activation by triggering a shift from an inactive to an active CARMA1 conformer. This PKC-dependent switch regulates accessibility of the CARD and CC domains and controls assembly and full activation of the membrane-associated IkappaB kinase (IKK) signalosome.
Obesity and stress inhibit insulin action by activating protein kinases that enhance serine phosphorylation of IRS1 and have been thus associated to insulin resistance and the development of type II diabetes. The protein kinase C (PKC) is activated by free-fatty acids, and its activity is higher in muscle from obese diabetic patients. However, a molecular link between PKC and insulin resistance has not been defined yet. Here we show that PKC phosphorylates IRS1 at serine 1101 blocking IRS1 tyrosine phosphorylation and downstream activation of the Akt pathway. Mutation of Ser(1101) to alanine makes IRS1 insensitive to the effect of PKC and restores insulin signaling in culture cells. These results provide a novel mechanism linking the activation of PKC to the inhibition of insulin signaling.
Phosphopeptide mapping identified a major autophosphorylation site, phospho (p)Thr-219, between the tandem C1 domains of the regulatory fragment in protein kinase C (PKC)theta. Confirmation of this identification was derived using (p)Thr-219 antisera that reacted with endogenous PKCtheta in primary CD3+ T cells after stimulation with phorbol ester, anti-CD3 or vanadate. The T219A mutation abrogated the capacity of PKCtheta to mediate NF-kappaB, NF-AT and interleukin-2 promoter transactivation, and reduced PKCtheta's ability in Jurkat T cells to phosphorylate endogenous cellular substrates. In particular, the T219A mutation impaired crosstalk of PKCtheta with Akt/PKBalpha in NF-kappaB activation. Yet, this novel (p)Thr-219 site did not affect catalytic activity or second-messenger lipid-binding activity in vitro. Instead, the T219A mutation prevented proper recruitment of PKCtheta in activated T cells. The PKCthetaT219A mutant defects were largely rescued by addition of a myristoylation signal to force its proper membrane localization. We conclude that autophosphorylation of PKCtheta at Thr-219 plays an important role in the correct targeting and cellular function of PKCtheta upon antigen receptor ligation.
The E3 ubiquitin ligase Casitas B-lineage lymphoma (Cbl-b) is central to antigen-induced immune tolerance and regulates the CD28 dependence of T cell activation. Cbl-b undergoes ubiquitination and proteasomal degradation after adequate costimulation of T cells; however, the mechanism involved is unknown. Here, we identified protein kinase C-theta (PKC-theta) as the critical intermediary for the inactivation of Cbl-b in response to costimulation of T cells through CD28. PKC-theta associated with Cbl-b on stimulation of the T cell receptor. After costimulation of T cells through CD28, Cbl-b was ubiquitinated and degraded through a mechanism that depended on the kinase activity of PKC-theta. Consistent with this mechanism, the impaired responses of PKCtheta-deficient T cells were at least partially restored by the concomitant genetic loss of cblb. Thus, our data establish a nonredundant antagonism between PKC-theta and Cbl-b that regulates T cell activation responses.
J. Biol. Chem. 274, 19003-19010 (1999)[PubMed:10383400]
The protein kinase C (PKC) family has been clearly implicated in T-cell activation as have several nonreceptor protein-tyrosine kinases associated with the T-cell receptor, including p59fyn. This report demonstrates that thetaPKC and p59fyn specifically interact in vitro, in the yeast two-hybrid system, and in T-cells. Further indications of direct interaction are that p59fyn potentiates thetaPKC catalytic activity and that thetaPKC is a substrate for tyrosine phosphorylation by p59fyn. This interaction may account for the localization of thetaPKC following T-cell activation, pharmacological disruption of which results in specific cell-signaling defects. The demonstration of a physical interaction between a PKC and a protein-tyrosine kinase expands the class of PKC-anchoring proteins (receptors for activated C kinases (RACKs)) and demonstrates a direct connection between these two major T-cell-signaling pathways.
Evidence
2:
Inferred from Physical InteractionIntAct
The nonreceptor Bruton's tyrosine kinase (Btk) has been previously shown to associate physically and functionally with members of the protein kinase C (PKC) family of serine/threonine kinases in a variety of cell types. Here we show evidence for a novel interaction between Btk and PKCtheta; in platelets activated through the adhesion receptors GP Ib-V-IX and GP VI. Alboaggregin A, a snake venom component capable of activating both receptors in combination, leads to tyrosine phosphorylation of Btk downstream of Src family kinases. Inhibition of Btk by the selective antagonist LFM-A13 causes a reduction in calcium entry, although secretion of 5-hydroxytryptamine is potentiated. Btk is also phosphorylated on threonine residues in a PKC-dependent manner and associates with PKCtheta; upon platelet activation by either alboaggregin A or activation of GP Ib-V-IX alone by von Willebrand factor/ristocetin. PKCtheta; in turn becomes tyrosine-phosphorylated in a manner dependent upon Src family and Btk kinase activity. Inhibition of Btk activity by LFM-A13 leads to enhancement of PKCtheta; activity, whereas nonselective inhibition of PKC activity by bisindolylmaleimide I leads to reduction in Btk activity. We propose a reciprocal feedback interaction between Btk and PKCtheta; in platelets, in which PKCtheta; positively modulates activity of Btk, which in turn feeds back negatively upon PKCtheta;.
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
J. Biol. Chem. 275, 1902-1909 (2000)[PubMed:10636891]
Protein kinase C-theta (PKCtheta) is a Ca(2+)-independent PKC isoform that is selectively expressed in T lymphocytes (and muscle), and is thought to play an important role in T cell receptor-induced activation. To gain a better understanding of the function and regulation of PKCtheta, we have employed the yeast two-hybrid system to identify PKCtheta-interacting proteins. We report the isolation and characterization of a cDNA encoding a novel 335-amino acid (37. 5-kDa) PKCtheta-interacting protein termed PICOT (for PKC-interacting cousin of thioredoxin). PICOT is expressed in various tissues, including in T cells, where it colocalizes with PKCtheta. PICOT displays an N-terminal thioredoxin homology domain, which is required for the interaction with PKC. Comparison of the unique C-terminal region of PICOT with expressed sequence tag data bases revealed two tandem repeats of a novel domain that is highly conserved from plants to mammals. Transient overexpression of full-length PICOT (but not its N- or C-terminal fragments) in T cells inhibited the activation of c-Jun N-terminal kinase (but not extracellular signal-regulated kinase), and the transcription factors AP-1 or NF-kappaB. These findings suggest that PICOT and its evolutionary conserved homologues may interact with PKC-related kinases in multiple organisms and, second, that it plays a role in regulating the function of the thioredoxin system.
Evidence
2:
Inferred from Physical InteractionIntAct
The nonreceptor Bruton's tyrosine kinase (Btk) has been previously shown to associate physically and functionally with members of the protein kinase C (PKC) family of serine/threonine kinases in a variety of cell types. Here we show evidence for a novel interaction between Btk and PKCtheta; in platelets activated through the adhesion receptors GP Ib-V-IX and GP VI. Alboaggregin A, a snake venom component capable of activating both receptors in combination, leads to tyrosine phosphorylation of Btk downstream of Src family kinases. Inhibition of Btk by the selective antagonist LFM-A13 causes a reduction in calcium entry, although secretion of 5-hydroxytryptamine is potentiated. Btk is also phosphorylated on threonine residues in a PKC-dependent manner and associates with PKCtheta; upon platelet activation by either alboaggregin A or activation of GP Ib-V-IX alone by von Willebrand factor/ristocetin. PKCtheta; in turn becomes tyrosine-phosphorylated in a manner dependent upon Src family and Btk kinase activity. Inhibition of Btk activity by LFM-A13 leads to enhancement of PKCtheta; activity, whereas nonselective inhibition of PKC activity by bisindolylmaleimide I leads to reduction in Btk activity. We propose a reciprocal feedback interaction between Btk and PKCtheta; in platelets, in which PKCtheta; positively modulates activity of Btk, which in turn feeds back negatively upon PKCtheta;.
Evidence
3:
Inferred from Physical InteractionIntAct
Protein kinase C-θ (PKC-θ) is required for activation of the transcription factor NF-κB induced by signaling via the T cell antigen receptor (TCR); however, the direct activator of PKC-θ is unknown. We report that the kinase GLK (MAP4K3) directly activated PKC-θ during TCR signaling. TCR signaling activated GLK by inducing its direct interaction with the upstream adaptor SLP-76. GLK-deficient mice had impaired immune responses and were resistant to experimental autoimmune encephalomyelitis. Consistent with that, people with systemic lupus erythematosus had considerable enhanced GLK expression and activation of PKC-θ and the kinase IKK in T cells, and the frequency of GLK-overexpressing T cells was directly correlated with disease severity. Thus, GLK is a direct activator of PKC-θ, and activation of GLK-PKC-θ-IKK could be used as new diagnostic biomarkers and therapeutic targets for systemic lupus erythematosus.
Evidence
4:
Inferred from Physical InteractionUniProtKB
Regulation of cell polarity is an important biological event that governs diverse cell functions such as localization of embryonic determinants and establishment of tissue and organ architecture. The Rho family GTPases and the polarity complex Par6/Par3/atypical protein kinase C (PKC) play a key role in the signaling pathway, but the molecules that regulate upstream signaling are still not known. Here we identified the guanine nucleotide exchange factor ECT2 as an activator of the polarity complex. ECT2 interacted with Par6 as well as Par3 and PKCzeta. Coexpression of Par6 and ECT2 efficiently activated Cdc42 in vivo. Overexpression of ECT2 also stimulated the PKCzeta activity, whereas dominant-negative ECT2 inhibited the increase in PKCzeta activity stimulated by Par6. ECT2 localization was detected at sites of cell-cell contact as well as in the nucleus of MDCK cells. The expression and localization of ECT2 were regulated by calcium, which is a critical regulator of cell-cell adhesion. Together, these results suggest that ECT2 regulates the polarity complex Par6/Par3/PKCzeta and possibly plays a role in epithelial cell polarity.
Evidence
5:
Inferred from Physical InteractionIntAct
Protein kinase C-θ (PKC-θ) translocates to the center of the immunological synapse, but the underlying mechanism and its importance in T cell activation are unknown. Here we found that the V3 domain of PKC-θ was necessary and sufficient for localization to the immunological synapse mediated by association with the coreceptor CD28 and dependent on the kinase Lck. We identified a conserved proline-rich motif in V3 required for association with CD28 and immunological synapse localization. We found association with CD28 to be essential for PKC-θ-mediated downstream signaling and the differentiation of T helper type 2 cells (T(H)2 cells) and interleukin 17-producing helper T cells (T(H)17 cells) but not of T helper type 1 cells (T(H)1 cells). Ectopic expression of V3 sequestered PKC-θ from the immunological synapse and interfered with its functions. Our results identify a unique mode of CD28 signaling, establish a molecular basis for the immunological synapse localization of PKC-θ and indicate V3-based 'decoys' may be therapeutic modalities for T cell-mediated inflammatory diseases.
Evidence
6:
Inferred from Physical InteractionIntAct
Using yeast two-hybrid, we isolated atypical PKCzeta as a PKCtheta-interacting kinase and demonstrated that it selectively interacted with, and was phosphorylated by, PKCtheta. Importantly, however, both atypical PKCzeta and PKCiota were functionally required in TCR/CD28-mediated activation of NF-kappaB downstream of PKCtheta in Jurkat T cells albeit, activation responses of PKCzeta-deficient CD3+ T cells were comparable with wildtype controls. This normal activation thresholds of PKCzeta-/- T cells suggested that PKCiota, the closest structural relative, might play a compensatory role in TCR/CD28-induced signalling. Consistently, both PKCzeta and PKCiota resided in the plasma membrane lipid raft microdomains of Jurkat as well as primary mouse CD3+ T cells. Thus, PKCtheta, the established constituent of the immunological synapse, physically and functionally interacted with PKCzeta and PKCiota. Together, these data demonstrate that atypical PKCzeta/iota isotypes serve as direct downstream targets of PKCtheta in the signalling pathway leading to NF-kappaB activation in T lymphocytes.
Evidence
7:
Inferred from Physical InteractionIntAct
J. Biol. Chem. 274, 19003-19010 (1999)[PubMed:10383400]
The protein kinase C (PKC) family has been clearly implicated in T-cell activation as have several nonreceptor protein-tyrosine kinases associated with the T-cell receptor, including p59fyn. This report demonstrates that thetaPKC and p59fyn specifically interact in vitro, in the yeast two-hybrid system, and in T-cells. Further indications of direct interaction are that p59fyn potentiates thetaPKC catalytic activity and that thetaPKC is a substrate for tyrosine phosphorylation by p59fyn. This interaction may account for the localization of thetaPKC following T-cell activation, pharmacological disruption of which results in specific cell-signaling defects. The demonstration of a physical interaction between a PKC and a protein-tyrosine kinase expands the class of PKC-anchoring proteins (receptors for activated C kinases (RACKs)) and demonstrates a direct connection between these two major T-cell-signaling pathways.
J. Biol. Chem. 268, 4997-5004 (1993)[PubMed:8444877]
Members of the protein kinase C (PKC) family of serine/threonine kinases play a key role in regulating the differentiation and growth of diverse cell types and, to date, the cloning of seven mammalian PKC genes encoding eight distinct isoforms has been reported. Here we describe the molecular cloning and deduced primary structure of a cDNA encoding a novel PKC isoform, termed PKC theta, which was isolated in the course of attempts to identify PKC genes that are expressed selectively in hematopoietic cells. Degenerate oligonucleotide primers corresponding to conserved sequence motifs, which distinguish the PKC family from other protein kinases, were employed in polymerase chain reactions (PCR) to amplify partial core sequences of putative PKC genes from a human peripheral blood lymphocyte-derived cDNA library. DNA sequencing of selected clones revealed several PKC-related sequences, including one that, on the basis of sequence comparison with known PKC isoforms, represented a novel PKC isoform. The complete cDNA sequence was determined by anchored PCR cloning and sequencing the entire coding sequence, using cDNA derived from a human leukemic T cell line (Jurkat). Included within this approximately 2.7-kilobase pair cDNA is an open reading frame of 2,118 nucleotides encoding a putative 82-kDa protein. The deduced primary structure contains consensus sequences characteristic of protein kinase catalytic domains and, based on its amino acid sequence and domain structure, is a member of the PKC family. PKC theta displays the highest homology to PKC delta, lacks the Ca(2+)-binding C2 domain and, thus, belongs to the subfamily of Ca(2+)-independent PKC enzymes which also includes the delta, epsilon, zeta, and eta isoforms. RNase protection assays and semiquantitative PCR analysis indicated that, although PKC theta transcripts are expressed ubiquitously, the highest levels are found in hematopoietic tissues and cell lines, including T cells and thymocytes. In contrast, the expression levels in the brain and testes are considerably lower, and no transcripts were detected in several human carcinoma cell lines. A rabbit antiserum raised against a unique (V3 domain) bacterially expressed PKC theta fragment immunoprecipitated specifically an 82-kDa protein from Jurkat cell lysates. Thus, PKC theta represents an additional member of the PKC family, and its predominant expression in hematopoietic cells suggests that it may play a role in signal transduction and growth regulatory pathways unique to these cells.
The immediate defensive reaction (by vertebrate tissue) to infection or injury caused by chemical or physical agents. The process is characterized by local vasodilation, extravasation of plasma into intercellular spaces and accumulation of white blood cells and macrophages.
The process in which a signal is passed on to downstream components within the cell, which become activated themselves to further propagate the signal and finally trigger a change in the function or state of the cell.
J. Biol. Chem. 268, 14208-14214 (1993)[PubMed:7686153]
At least seven bacteriophage lambda clones encoding structurally related but unique polypeptides with PKC activity have been isolated from mammalian brain, epidermis, and lung cDNA libraries. The possibility that additional isoenzymes are expressed in human blood platelets or megakaryoblastoid human erythroleukemia cells was examined by polymerase chain reaction amplification of reverse transcribed RNA employing oligonucleotide primers corresponding to conserved peptide sequences. cDNAs encoding a novel PKC-related sequence, designated PKC-theta, and four (alpha, beta, delta, and eta) previously identified isoenzymes were isolated from reverse transcribed total RNA of human erythroleukemia cells and platelets. PKC-theta lacks a conserved region (C2) that is present in the calcium-dependent isoenzymes and therefore belongs to the group of novel, or nPKC, isoenzymes. Significantly increased [3H] phorbol 12,13-dibutyrate binding and cytoskeleton-associated calcium-independent PKC activity were found in COS cells expressing the transfected cDNA. Northern transfer analysis of mRNA from various human tissues revealed high level expression of PKC-theta in skeletal muscle, lung, and brain, and minimal expression in cardiac muscle, placenta, and liver. These findings extend the PKC family and suggest a novel approach to the study of diversity within this pathway of intracellular signal transduction.
Obesity and stress inhibit insulin action by activating protein kinases that enhance serine phosphorylation of IRS1 and have been thus associated to insulin resistance and the development of type II diabetes. The protein kinase C (PKC) is activated by free-fatty acids, and its activity is higher in muscle from obese diabetic patients. However, a molecular link between PKC and insulin resistance has not been defined yet. Here we show that PKC phosphorylates IRS1 at serine 1101 blocking IRS1 tyrosine phosphorylation and downstream activation of the Akt pathway. Mutation of Ser(1101) to alanine makes IRS1 insensitive to the effect of PKC and restores insulin signaling in culture cells. These results provide a novel mechanism linking the activation of PKC to the inhibition of insulin signaling.
J. Immunol. 176, 6709-6716 (2006)[PubMed:16709830]
Productive engagement of TCR results in delivering signals required for T cell proliferation as well as T cell survival. Blocking TCR-mediated survival signals, T cells undergo apoptosis instead of proliferation upon TCR stimulation. During the activation process, T cells produce IL-2, which acts as an extrinsic survival factor. In addition, TCR stimulation results in up-regulation of Bcl-xL to enhance T cell survival intrinsically. We show in this study that protein kinase C (PKC)-theta is required for enhancing the survival of activated CD4+ T cells by up-regulating Bcl-xL. In response to TCR stimulation, CD4+ PKC-theta-/- T cells failed to up-regulate Bcl-xL, and underwent accelerated apoptosis via a caspase- and mitochondria-dependent pathway. Similar to PKC-theta-deficient primary CD4+ T cells, small interfering RNA-mediated knockdown of PKC-theta in Jurkat cells also resulted in apoptosis upon TCR stimulation. Forced expression of Bcl-xL was sufficient to inhibit apoptosis observed in PKC-theta knockdown cells. Furthermore, ectopic expression of PKC-theta stimulated a reporter gene driven by a mouse Bcl-xL promoter. Whereas an inactive form of PKC-theta or knockdown of endogenous PKC-theta led to inhibition of Bcl-xL reporter. PKC-theta-mediated activation of Bcl-xL reporter was inhibited by dominant-negative IkappaB kinase beta or dominant-negative AP-1. Thus, the PKC-theta-mediated signals may function not only in the initial activation of naive CD4+ T cells, but also in their survival during T cell activation by regulating Bcl-xL levels through NF-kappaB and AP-1 pathways.
Evidence
2:
Inferred from Mutant PhenotypeUniProtKB
J. Immunol. 166, 5955-5963 (2001)[PubMed:11342610]
Protein kinase C (PKC)-activating phorbol esters protect T cells from Fas-induced apoptosis. However, the mechanism of this protective effect and the identity of the relevant PKC isoform(s) are poorly understood. Here, we show that PKCtheta plays a selective and important role in this protection. Fas triggering led to a selective caspase-3-dependent cleavage of the enzyme and proteasome-mediated degradation and inactivation of its catalytic fragment. These events preceded the onset of apoptosis. Pharmacological inhibition of PKCtheta promoted Fas-mediated apoptosis in three different types of T cells. Conversely, constitutively active PKCtheta (and, to a lesser degree, PKCepsilon) selectively protected T cells from Fas-induced apoptosis. We provide evidence that the distant Bcl-2 family member, BAD, is a PKCtheta substrate, is phosphorylated by TCR stimulation, and can mediate at least in part the anti-apoptotic effect of PKCtheta.
Any process that activates or increases the frequency, rate or extent of the chemical reactions and pathways resulting in the formation of interleukin-2.
PKC isoforms and CARMA1 play crucial roles in immunoreceptor-dependent NF-kappaB activation. We tested whether PKC-dependent phosphorylation of CARMA1 directly regulates this signaling cascade. B cell antigen receptor (BCR) engagement led to the progressive recruitment of CARMA1 into lipid rafts and to the association of CARMA1 with, and phosphorylation by, PKCbeta. Furthermore, PKCbeta interacted with the serine-rich CARMA1 linker, and both PKCbeta and PKCtheta phosphorylated identical serine residues (S564, S649, and S657) within this linker. Mutation of two of these sites ablated the functional activity of CARMA1. In contrast, deletion of the linker resulted in constitutive, receptor- and PKC-independent NF-kappaB activation. Together, our data support a model whereby CARMA1 phosphorylation controls NF-kappaB activation by triggering a shift from an inactive to an active CARMA1 conformer. This PKC-dependent switch regulates accessibility of the CARD and CC domains and controls assembly and full activation of the membrane-associated IkappaB kinase (IKK) signalosome.
J. Biol. Chem. 268, 4997-5004 (1993)[PubMed:8444877]
Members of the protein kinase C (PKC) family of serine/threonine kinases play a key role in regulating the differentiation and growth of diverse cell types and, to date, the cloning of seven mammalian PKC genes encoding eight distinct isoforms has been reported. Here we describe the molecular cloning and deduced primary structure of a cDNA encoding a novel PKC isoform, termed PKC theta, which was isolated in the course of attempts to identify PKC genes that are expressed selectively in hematopoietic cells. Degenerate oligonucleotide primers corresponding to conserved sequence motifs, which distinguish the PKC family from other protein kinases, were employed in polymerase chain reactions (PCR) to amplify partial core sequences of putative PKC genes from a human peripheral blood lymphocyte-derived cDNA library. DNA sequencing of selected clones revealed several PKC-related sequences, including one that, on the basis of sequence comparison with known PKC isoforms, represented a novel PKC isoform. The complete cDNA sequence was determined by anchored PCR cloning and sequencing the entire coding sequence, using cDNA derived from a human leukemic T cell line (Jurkat). Included within this approximately 2.7-kilobase pair cDNA is an open reading frame of 2,118 nucleotides encoding a putative 82-kDa protein. The deduced primary structure contains consensus sequences characteristic of protein kinase catalytic domains and, based on its amino acid sequence and domain structure, is a member of the PKC family. PKC theta displays the highest homology to PKC delta, lacks the Ca(2+)-binding C2 domain and, thus, belongs to the subfamily of Ca(2+)-independent PKC enzymes which also includes the delta, epsilon, zeta, and eta isoforms. RNase protection assays and semiquantitative PCR analysis indicated that, although PKC theta transcripts are expressed ubiquitously, the highest levels are found in hematopoietic tissues and cell lines, including T cells and thymocytes. In contrast, the expression levels in the brain and testes are considerably lower, and no transcripts were detected in several human carcinoma cell lines. A rabbit antiserum raised against a unique (V3 domain) bacterially expressed PKC theta fragment immunoprecipitated specifically an 82-kDa protein from Jurkat cell lysates. Thus, PKC theta represents an additional member of the PKC family, and its predominant expression in hematopoietic cells suggests that it may play a role in signal transduction and growth regulatory pathways unique to these cells.
Any process that modulates the rate, frequency or extent of platelet aggregation. Platelet aggregation is the adhesion of one platelet to one or more other platelets via adhesion molecules.
Novel PKCs (PRKCD, PRKCE, PRKCH and PRKCQ) are calcium-insensitive, but activated by diacylglycerol (DAG) and phosphatidylserine. Three specific sites; Thr-538 (activation loop of the kinase domain), Ser-676 (turn motif) and Ser-695 (hydrophobic region), need to be phosphorylated for its full activation.
Protein involved in immunity, any immune system process that functions in the response of an organism to a potential internal or invasive threat. The vertebrate immune system is formed by the innate immune system (composed of phagocytes, complement, antimicrobial peptides, etc) and by the adaptive immune system which consists of T- and B- lymphocytes.
Protein involved in the localized protective response to tissue damage, microbial infection, or the presence of foreign matter. It is characterized by swelling, redness, heat and pain and involves a complex series of events including vascular changes and accumulation of blood cells, such as neutrophil leucocytes and mononuclear phagocytes, at the site of injury.
Protein which catalyzes the phosphorylation of serine or threonine residues on target proteins by using ATP as phosphate donor. Such phosphorylation may cause changes in the function of the target protein. Protein kinases share a conserved catalytic core common to both serine/ threonine and tyrosine protein kinases.
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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