Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Phosphorylation of membrane glycoproteins has often been invoked as a determinant of receptor internalization and receptor trafficking in a more general sense. Here we have studied the trafficking of major histocompatibility complex (MHC) Class I molecules and transferrin receptor (Tfr) related to their phosphorylation status in the human lymphoblastoid cell line JY. High resolution isoelectric focusing (IEF) allows the visualization of phosphorylated and non-phosphorylated protein species simultaneously, using protein backbone-labeling. Analysis on IEF was combined with a neuraminidase protection assay, in which sialic acid modification of the N-linked glycans present on Tfr and Class I molecules is used as a reporter group for cell surface expression. Phosphorylation of Class I heavy chains and Tfr was induced by exposure of cells to the phorbol ester tetradecanoyl phorbol acetate. We show that 1) phosphorylation of MHC Class I molecules is restricted to the cell surface fraction, 2) phosphorylation of MHC Class I molecules by protein kinase C (PKC) is not correlated with their internalization, as no internalization of Class I molecules, phosphorylated or non-phosphorylated, could be detected, 3) the initial rate, but not the final extent of the internalization of Tfr is affected by activation of PKC, and 4) phosphorylated Tfr behaves in a manner identical to non-phosphorylated Tfr in terms of internalization. The effect of activation of PKC on internalization of Tfr therefore most likely takes place at the level of the internalization machinery. Our data concerning the internalization of MHC Class I molecules contrast with earlier studies describing constitutive internalization in the B lymphoblastoid cell line A 46 and in HPB-ALL cells.
 ...
PMID:Activation of protein kinase C accelerates internalization of transferrin receptor but not of major histocompatibility complex class I, independent of their phosphorylation status. 142 99

The role of the CD45 phosphotyrosine phosphatase in coupling the T cell antigen receptor complex (TCR) to intracellular signals was investigated. CD45- HPB-ALL T cells were transfected with cDNA encoding the CD45RA+B+C- isoform. The tyrosine kinase activity of p59fyn was found to be 65% less in CD45- cells than in CD45+ cells, whereas p56lck kinase activity was comparable in both sub-clones. In CD45- cells the TCR was uncoupled from protein tyrosine phosphorylation, phospholipase C gamma 1 regulation, inositol phosphate production, calcium signals, diacylglycerol production and protein kinase C activation. Restoration of TCR coupling to all these pathways correlated with the increased p59fyn activity observed in CD45-transfected cells. Co-aggregation of CD4- or CD8-p56lck kinase with the TCR in CD45- cells restored TCR-induced protein tyrosine phosphorylation, phospholipase C gamma 1 regulation and calcium signals. Receptor-mediated calcium signals were largely due (60-90%) to Ca2+ influx, and only a minor component (10-40%) was caused by Ca2+ release from intracellular stores. Maximal CD3-mediated Ca2+ influx occurred at CD3 mAb concentrations at which inositol phosphate production was non-detectable. These results indicate that CD45-regulated p59fyn plays a critical role in coupling the TCR to specific intracellular signalling pathways and that CD4- or CD8-p56lck can only restore signal transduction coupling in CD45- cells when brought into close association with the TCR.
 ...
PMID:CD45 tyrosine phosphatase-activated p59fyn couples the T cell antigen receptor to pathways of diacylglycerol production, protein kinase C activation and calcium influx. 146 15

Ligation of the CD3 receptor induces multiple signal transduction events that modify the activation state of the T cell. We have compared two lines that express biologically active CD3 receptors but differ in their biochemical activation pathways during ligation of this receptor. Jurkat cells respond to anti-CD3 with Ca2+ mobilization, PKC activation, induction of protein tyrosine phosphorylation, and activation of newly characterized lymphoid microtubule associated protein-2 kinase (MAP-2K). MAP-2K itself is a 43-kDa phosphoprotein that requires tyrosine phosphorylation for activation. Although ligation of the CD3 receptor in HPB-ALL could stimulate tyrosine phosphorylation of a 59- kDa substrate, there was no associated induction of [Ca2+]i flux, PKC, or MAP-2K activation. A specific PKC agonist, PMA, which bypasses the CD3 receptor, could, however, activate MAP-2K in HPB-ALL cells. This implies that defective stimulation of PKC by the CD3 receptor is responsible for its failure to activate MAP-2K in HPB-ALL. The defect in PKC activation is likely distal to the CD3 receptor as A1F14- failed to activate MAP-2K in HPB-ALL but was effective in Jurkat cells. The stimulatory effect of PMA on MAP-2K activity in HPB-ALL was accompanied by tyrosine phosphorylation of this kinase which implies that PKC may, in some way, regulate tyrosine phosphorylation of MAP-2K. A candidate for this role is pp56lck which underwent posttranslational modification (seen as mobility change on SDS-PAGE) during anti-CD3 and PMA stimulation in Jurkat or PMA treatment in HPB-ALL. There was, in fact, exact coincidence between induction of PKC activity, posttranslational modification of lck and tyrosine phosphorylation/activation of MAP-2K. Lck kinase activity in an immune complex kinase assay was unchanged during PMA treatment. An alternative explanation is that modification of lck may alter its substrate profile. We therefore looked at the previously documented ability of PKC to dissociate lck from the CD4 receptor and found that PMA could reduce the stoichiometry of the lck interaction with CD4 in HPB-ALL and to a lesser extent in Jurkat cells. These results imply the existence of a kinase cascade that is initiated by PKC and, in the course of which, lck and MAP-2K may interact.
 ...
PMID:Protein kinase C plays a role in the induction of tyrosine phosphorylation of lymphoid microtubule-associated protein-2 kinase. Evidence for a CD3-associated cascade that includes pp56lck and that is defective in HPB-ALL. 171 87

T cell receptor-CD3 complex (TCR-CD3)-mediated signal transduction was analyzed in HPB-ALL and Jurkat T cell lines. Both cell lines express high levels of TCR-CD3 complex on the cell surface, but provide different model systems for TCR-CD3 signaling in T cells. Jurkat responds with both inositol phosphate generation and intracellular Ca2+ mobilization after triggering of TCR-CD3, whereas TCR-CD3 triggering of HPB-ALL induces Ca2+ mobilization without detectable inositol phosphate generation. By employing a permeabilized cell system, we show that the HPB-ALL line expressed normal levels of Ca2(+)-induced phospholipase C activity. However, the TCR-CD3 on this cell line seems to be uncoupled from phospholipase C activation. In agreement with this result we also show, by analysis of protein kinase C-dependent phosphorylation of three distinct substrates, that TCR-CD3 in HPB-ALL is apparently uncoupled from protein kinase C activation. These findings may have implications for understanding signal-transducing pathways in T cells at various stages of differentiation.
 ...
PMID:Signal transduction through the T cell receptor-CD3 complex. Evidence for heterogeneity in receptor coupling. 197 May 88

CD43 (sialophorin, gpL115) is a sialoglycoprotein expressed on a wide variety of blood cells including lymphocytes, monocytes, neutrophils, and platelets. L10, an anti-CD43 mAb, has been shown to induce monocyte-dependent activation and proliferation of human T lymphocytes. We have studied the signaling mechanism involved in this activation process. Treatment of PBMC and purified populations of T cells and monocytes with L10 induced the hydrolysis of phosphoinositides with the resultant generation of the phosphoinositide-derived second messengers diacylglycerol and inositol phosphates. This was associated with the translocation of protein kinase C from cytosol to membrane fractions and an increase in free intracellular Ca2+ in treated cells. In human leukemic T cell lines, the magnitude of signaling via CD43 did not correlate with the density of the TCR/CD3 surface expression nor with the intensity of signaling via the TCR/CD3. Moreover, a mutant derived from the leukemic T cell line HPB-ALL that was severely defective in TCR/CD3 surface expression and signaling nevertheless had normal CD43 surface expression and signaling compared with the parent cell line. It is concluded that CD43 is functionally coupled to the phospholipase C/phosphoinositides signaling pathway. In human T cells, signaling via CD43 proceeds independently of TCR/CD3. The widespread expression of CD43 suggests a potentially important role for this molecule in orchestrating the activation of multiple cell types.
 ...
PMID:Mechanism of mononuclear cell activation by an anti-CD43 (sialophorin) agonistic antibody. 254 4

Signals from many receptor-ligand interactions are mediated by enhancement of phospholipid hydrolysis which generates metabolic intermediates stimulating protein kinase C (PKC) and elevating cellular calcium. Pharmacologic agents such as phorbol 12, 13-dibutyrate (PDBu) and ionomycin selectively stimulate PKC and elevate intracellular calcium to directly stimulate downstream mechanisms critical to cell growth and function. This study examines the effects of PDBu, ionomycin, and rIL-2 on childhood ALL blasts of early B lineage with respect to various aspects of cell activation, including DNA synthesis, induction of non-MHC restricted tumoricidal activity, and changes in morphology and phenotype. Five childhood ALL samples were tested. A marked heterogeneity was seen among the ALL samples with respect to in vitro growth following manipulation with PDBu, ionomycin, and/or rIL-2, whereas normal peripheral blood lymphocytes (PBL) were consistently stimulated to grow with the combination of PDBu and ionomycin. Growth responsiveness did not appear to correlate with morphologic or phenotypic classification of the leukemia samples. Four of the five leukemia samples developed substantial non-MHC restricted cytotoxicity to K562 (natural killer cell (NK) sensitive) and Daudi (NK resistant) targets in response to rIL-2. This functional cytotoxic response correlated with morphologic changes in the cells and the appearance of granules. Phenotypic analyses of the ALL samples at the time of their peak cytotoxic function were consistent with the fresh ALL phenotype and showed no major change in cell populations. Three of the five ALL samples also retained rIL-2 induced cytotoxic capabilities when exposed simultaneously to the combination of PDBu and ionomycin, whereas rIL-2 induced tumoricidal activity in normal PBL and bone marrow cultures was inhibited by these reagents. These data show that morphologically and phenotypically similar ALL blasts have heterogeneous proliferative responses to the PKC and calcium modulators PDBu and ionomycin, as well as to rIL-2. Cytotoxic responses are also different from those of normal PBL and bone marrow cells with respect to kinetics and responsiveness to inducing agents. Thus current morphologic and phenotypic classifications of ALL may not adequately reflect the heterogeneity of this disorder as described here.
 ...
PMID:Induction of tumoricidal activity and alterations of growth by interleukin-2 and manipulation of protein kinase C and cytosolic calcium in childhood acute lymphocytic leukemia cells. 278 55

An early consequence of stimulation of T cells via their Ag receptor is the activation of protein kinase C (PKC). It has recently been shown that PKC activity resides in a family of homologous proteins. Inasmuch as T cells are phenotypically and functionally heterogeneous, we examined the possibility that this heterogeneity may be reflected in differential expression of message for PKC isoenzyme genes. RNA from six leukemic T cell lines was probed for PKC-alpha, -beta, and -gamma message before and after activation. These studies revealed significant differences among these lines. None expressed mRNA for PKC-gamma. Whereas all cells possessed message for PKC-alpha, there was consistent variability in the level expressed. The greatest heterogeneity was seen with PKC-beta. Two cell lines, HUT 78 and HPB-ALL, did not hybridize with the beta probe under any conditions tested. We subsequently used these PKC-beta negative cells to study the role of this isoenzyme in mediating some of the effects seen with phorbol esters that directly bind to and activate PKC. Our results indicate that PKC-beta, which is expressed in some T cells, is not necessary for PMA-induced CD3 or CD4 internalization, IL-2 production, or acquisition of the p55 chain of the IL-2 receptor.
 ...
PMID:Heterogeneity of protein kinase C isoenzyme gene expression in human T cell lines. Protein kinase C-beta is not required for several T cell functions. 278 92

Three monoclonal antibodies reactive with different structural domains of the T3-T cell receptor complex of the human T cell leukemia line, HPB-ALL, were previously shown to activate a membrane potential-sensitive, La3+-inhibitable Ca2+ influx (Oettgen, H. C., Terhorst, C., Cantley, L. C., and Rosoff, P. M. (1985) Cell 40, 583-590). OKT3 (anti-T3), WT-31 (anti-receptor constant region), and T40/25 (anti-receptor variable region) also enhance the activity of the Na+/H+ exchanger in these cells. The associated rise in pHi was dependent on the presence of external Ca2+ and Na+, was inhibited by dimethylamiloride and La3+, and was maintained for at least 20 min. Phorbol esters, which are co-mitogenic in T cells and activate protein kinase C, also stimulated the exchanger, but by a mechanism not requiring an elevation in cytoplasmic Ca2+; the rise in pHi rapidly peaked and returned to baseline levels within 20 min. Pretreatment with phorbols prevented an increase in pHi by OKT3 although a transient additive effect was observed when the two were added simultaneously. Receptor function was maintained in the presence of phorbol esters as OKT3 still stimulated a Ca2+ influx. These data demonstrate the existence of two interdependent pathways to activate Na+/H+ exchange in T lymphocytes and suggest a pathway of internal regulation of antigen-activated signal transduction.
 ...
PMID:Stimulation of the T3-T cell receptor-associated Ca2+ influx enhances the activity of the Na+/H+ exchanger in a leukemic human T cell line. 299 91

Activators of protein kinase C induced a rapid decrease (within 15 min) in the surface expression of the T3 antigen and T-lymphocyte antigen receptor (Ti) on HPB-ALL cells, and a concomitant phosphorylation of the T3 gamma and delta polypeptides; the gamma chain was more extensively phosphorylated than the delta chain. No phosphorylation of the T3 epsilon chain and the Ti alpha and beta polypeptides was detected. Evidence was obtained that the T3 gamma chain is phosphorylated only on serine residues.
 ...
PMID:Activation of protein kinase C modulates the expression of the T3/T cell antigen receptor complex on human T lymphocytes. 387 56

As judged by indirect immunofluorescence, phorbol 12,13-dibutyrate and 1-oleoyl-2-acetylglycerol induced a rapid, concentration-dependent decrease of about 50% in the surface expression of the T3 antigen on human T lymphoblasts, and of T3 and the T-cell antigen receptor on HPB-ALL cells. Direct binding experiments using 125I-labeled antibody indicated that the reduction in T3 expression corresponded to a decrease in the number of antigen molecules rather than a change in their affinity. Biochemical analyses revealed that phorbol dibutyrate induced a rapid, prominent phosphorylation of the T3 Mr 26,000 gamma chain and to a lesser extent of the Mr 21,000 delta chain. No phosphorylation of the T3 epsilon chain or of the alpha and beta subunits of the T-cell antigen receptor was detected. The data suggest that protein kinase C induces a phosphorylation of the T3 gamma and delta chains that may lead to the down-regulation of the T3/T-cell antigen receptor complex.
 ...
PMID:Activators of protein kinase C down-regulate and phosphorylate the T3/T-cell antigen receptor complex of human T lymphocytes. 393 68


1 2 3 Next >>