Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.4.3 (phospholipase C)
18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Major histocompatibility complex (MHC) class II are expressed on most activated human lymphocytes. They direct antigen presentation events in dendritic cells and B cells (collectively called antigen presenting cells), but the role for MHC class II in human T cells is not well understood. To understand the role of surface MHC class II and to identify the molecules involved in signaling, we have defined the early activation sequence in T cells when MHC class II are engaged by a specific antibody. Specifically, we have characterized the involvement of phosphotyrosine kinases, phospholipase C (PLC), and Ca2+ mobilization. With the engagement by either whole anti-class II antibody or its Fab fragments, the enzymatic activity of p56lck and ZAP-70 increased, but there was no increase in p59fyn activity. In addition, the intracellular free Ca2+ increased, which was due to enhanced influx and not to the mobilization of intracytoplasmic Ca2+. These events did not require cross-linking because they were not significantly augmented by the addition of antispecies antibody. The coimmunoprecipitation of tyrosine phosphorylated PLC-gamma1 with surface MHC class II suggested that PLC-gamma1 could be recruited to MHC class II after engagement. These results show the complexities of the early signals transduced by the engagement of surface MHC class II on T cells.
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PMID:Early human T cell activation events with engagement of surface MHC class II. 970 72

Tumor-associated lymphocytes (TALs) freshly isolated from patients with cancer usually manifest reduced proliferative and cytolytic functions. To determine whether alterations in signal transduction contribute to functional impairments seen in TALs, we purified populations of T and natural killer (NK) cells by negative selection from ascites of seven patients with ovarian carcinoma. The average purity was 84 +/- 5% for CD3(+) TALs and 77 +/- 10% for CD3(-)CD56(+)CD16(+) TALs. Expression of several signal transduction molecules, including the CD3-epsilon, CD3-zeta, and FcepsilonRI-gamma chains, p56(lck) protein tyrosine kinase, and phospholipase C-gamma1, was studied in these cells using Western blotting. A marked decrease in expression of zeta and FcepsilonRI-gamma associated with CD3 or FcgammaRIIIA was observed in T or NK cells obtained from TALs, as compared to T or NK cells purified from normal peripheral blood. Expression of CD3-epsilon, as assessed using flow cytometry, Western blotting, or ELISA was also reduced in purified TAL-T cells relative to that in normal peripheral blood T cells. Surface expression of CD3 on T cells and FcgammaRIIIA on NK cells obtained from TALs was significantly decreased in comparison to normal peripheral blood lymphocytes (PBLs): the mean fluorescence intensity of CD3 was 277 +/- 18 for TAL-T (n = 7) versus 349 +/- 13 for PBL-T (n = 9) and that of CD16 was 58 +/- 1 for TAL-NK (n = 7) versus 385 +/- 55 for PBL-NK (n = 23) cells. These observations suggest a defect in assembly of T cell receptor and FcgammaRIIIA multicomponent transmembrane receptors, which are zeta and gamma dependent. In addition to alterations in expression, the function of these receptors was also modified, since cross-linking of CD3 on TAL-T and CD16 on TAL-NK cells with the respective monoclonal antibodies resulted in a pattern of protein phosphorylation that was distinct from that observed in normal PBLs. Expression of tyrosine kinase p56(lck) and its kinase activity were also depressed, while expression of phospholipase C-gamma1 appeared to be normal in most preparations of the TALs tested. In vitro proliferation of TAL-T in response to anti-CD3 monoclonal antibody and TAL-NK cells to interleukin 2 were significantly depressed as was the ability to produce IFN-gamma. In contrast, TAL-T cells were able to produce interleukin 10 at levels similar to those secreted by normal PBLs. Thus, in TALs obtained from patients with advanced ovarian cancer, alterations in expression and activity of signaling molecules were associated with reduced cellular functions such as proliferation and production of certain cytokines.
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PMID:Alterations in expression and function of signal-transducing proteins in tumor-associated T and natural killer cells in patients with ovarian carcinoma. 981 3

Recent studies have demonstrated altered expression and function of signaling molecules in T and natural killer cells in patients with cancer. The impairment of immune cell functions in advanced cancer may result from defects in signal transduction. We studied purified T cells obtained from peripheral blood or tumor-involved lymph nodes (LNs) of 45 patients with advanced metastatic melanoma for the presence of abnormalities in expression or activity of various signaling molecules. Western blot analyses demonstrated reduced expression of CD3-zeta in 10 of 11 preparations of T cells obtained from tumor-involved LNs. Similar reduction in expression of CD3-zeta was demonstrated by immunostaining performed in situ on frozen sections of melanoma tissues. Expression of p56(lck) and Zap-70, but not phospholipase C-gamma1, was reduced in these patients' T cells relative to those obtained from normal individuals. In 50% of the patients, reduced expression of CD3-zeta and p56(lck) was observed in T lymphocytes obtained both from tumor-involved LNs and from peripheral blood. To determine whether deficient expression of these signaling molecules is reversible, T cells from melanoma-involved LNs were incubated in the presence of interleukin 2 (IL-2) for 48 h, and lysates from fresh or cultured lymphocytes were compared for changes in expression of signaling molecules. Cells cultured in the presence of IL-2 demonstrated increased expression of CD3-zeta and p56(lck), which approached the levels detected in normal T cells. However, the level of p56(lck) kinase activity did not normalize in any of the LN-derived lymphocytes cultured in the presence of IL-2. Decreased expression of CD3-zeta or p56(lck) observed in the patients' T cells was not reversed by immunotherapy with IL-2 at low or high dose in those patients with metastatic melanoma who failed to respond to therapy. However, in three patients who achieved clinical responses, the initially reduced expression of zeta in peripheral blood T cells normalized following IL-2 therapy.
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PMID:Expression and activity of signaling molecules in T lymphocytes obtained from patients with metastatic melanoma before and after interleukin 2 therapy. 981 96

In this report the molecular mechanism(s) involved in the rapid and selective endocytosis of cell surface glycoprotein CD4 induced by exogenous monosialoganglioside GM3 in human peripheral blood lymphocytes have been investigated. Inhibition of the GM3-induced CD4 down-modulation was observed in the presence of specific protein kinase C (PKC) inhibitors. Scanning confocal microscopy revealed the translocation and clustering on the cell surface of PKC isozymes delta and theta (more evidently than alpha and beta) after GM3 treatment, suggesting the involvement of these isozymes in the ganglioside-induced CD4 down-modulation. Exogenous GM3 induced phosphorylation of CD4 molecule, which then dissociated from p56(lck), as early as after 5 min. Moreover, addition of GM3 resulted in a rapid (1 min) cytosolic phospholipase A2 activation with consequent arachidonic acid release, whereas no phosphatidylinositol-phospholipase C activity was observed. Both PKC translocation and CD4 down-modulation were blocked by the trifluoromethylketone analog of arachidonic acid, a selective inhibitor of cytosolic phospholipase A2 and by mitogen-activated protein kinase inhibitor PD98059. Taken together, these findings strongly suggest that GM3 may trigger a novel mechanism of modulation of the CD4 surface expression through the activation of enzyme(s) involved in the regulation of cellular functions.
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PMID:A novel mechanism of CD4 down-modulation induced by monosialoganglioside GM3. Involvement of serine phosphorylation and protein kinase c delta translocation. 985 52

Bivalent lectins as bridging molecules between cells or cell surface lectins as docking points are involved in mediation of cell adhesion by specific recognition of suitable glycoconjugates on an opposing surface. The initial contact formation by a lectin can lead to intracellular post-binding events which effect stable cell association even in the presence of the haptenic sugar. To delineate the participation of intracellular signaling pathways in the cascade of reactions to establish firm association, reagents with proven inhibitory capacity on certain biochemical targets provide suitable tools. Using this approach with rat thymocytes and the galactoside-binding lectin from mistletoe (Viscum album L. agglutinin, VAA) as a model, a panel of 27 inhibitors with impact on e.g. several types of kinases, tyrosine phosphatases, NO synthases, G proteins, enzymes of arachidonate and cyclic nucleotide metabolism and calmodulin was systematically tested with respect to their capacity to impair the formation of lactose-resistant cell aggregates. In addition to the recently reported effectiveness of N-ethylmaleimide, nordihydroguaiaretic acid, and trifluoperazine the agents diacylglycerol kinase inhibitor II, emodin, D609, DPI, KT5720, KT5926, MK-886, bisindolylmaleimide I, and (+/-)methoxyverapamil were able to reduce aggregate stability in the presence of the haptenic sugar. Thus, various types of kinases including p561lck tyrosine kinase, lipoxygenases, phosphatidylcholine-specific phospholipase C as well as calmodulin and Ca(2+)-currents, but not modulators of the metabolism of cyclic nucleotides, NO synthases, MAP kinases, tyrosine phosphatases and phospholipase A (preferentially group II) and C can play a role in eliciting contact stability. More than one principal signaling pathway appears to be linked to the measurable parameter, since inhibitory substances show additive properties in co-incubation assays and differentially affect two lectin-elicited cellular activities, i.e. intracellular movement of Ca(2+)-ions and H2O2-generation, which can accompany cell adhesion and aggregation. Pronounced differences in the extent of modulation of H2O2-generation in human neutrophils by the same set of substances emphasizes that general conclusions on the post-binding effects for a certain lectin in different cell types are definitely precluded. In aggregate, the approach to employ inhibitors with target selectivity intimates an involvement of protein kinases A, C, Ca2+/calmodulin-dependent protein kinase II, p56lck tyrosine kinase, leukotrienes and/or hydroxyeicosatetraenoic acids, phosphatidylcholine-specific phospholipase C and Ca(2+)-fluxes in events following initial binding of a galactoside-specific plant lectin to rat thymocytes which establish firm cell contacts.
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PMID:Dissection of the impact of various intracellular signaling pathways on stable cell aggregate formation of rat thymocytes after initial lectin-dependent cell association of using a plant lectin as model and target-selective inhibitors. 1048 33

Activation of T cells requires co-stimulation of the TCR and accessory receptors like CD2, CD4, CD8, CD11a or CD28. Engagement of the TCR without co-stimulation results in anergy / apoptosis. Here we show that induction of the shift of the tyrosine kinase p56lck from 56 kDa to apparent 60 kDa in resting human peripheral blood T cells (PBT) is strictly dependent on co-stimulation through both TCR and accessory receptors. In contrast, triggering of the TCR alone is only sufficient to induce the lck shift in preactivated cells like T cell clones or the T lymphoma line Jurkat. Our studies predict an involvement of a phospholipase C isoform which surprisingly acts downstream of a phorbolester-sensitive, H7-insensitive protein kinase C. Inhibition of the lck shift in vivo by U73122, a specific inhibitor of phospholipase C, correlates with reduced activation of the MAP-kinases ERK1 / 2. Moreover, the MEK1-specific inhibitor PD98059 blocks the lck shift in vivo. These findings demonstrate that activation of the MEK1-ERK1 / 2 pathway is required for lck conversion in vivo. The lck shift is not inducible by co-stimulation through acidic sphingomyelinase or ceramides which even prevent ERK2 activation in PBT. Moreover, it is resistant to treatment with W7, KN62 and cyclosporin A.
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PMID:Conversion of p56(lck) to p60(lck) in human peripheral blood T lymphocytes is dependent on co- stimulation through accessory receptors: involvement of phospholipase C, protein kinase C and MAP-kinases in vivo. 1067 Dec 21

Peripheral T lymphocyte activation in response to TCR/CD3 stimulation is reduced in type 1 diabetic patients. To explore the basis of this deficiency, a comprehensive analysis of the signal transduction pathway downstream of the TCR/CD3 complex was performed for a cohort of patients (n = 38). The main result of the study shows that T cell hyporesponsiveness is positively correlated with a reduced amount of p56(lck) in resting T lymphocytes. Upon CD3-mediated activation, this defect leads to a hypophosphorylation of the CD3zeta-chain and few other polypeptides without affecting the recruitment of ZAP70. Other downstream effectors of the TCR/CD3 transduction machinery, such as phosphatidylinositol 3-kinase p85alpha, p59(fyn), linker for activation of T cells (LAT), and phospholipase C-gamma1, are not affected. In some patients, the severity of this phenotypic deficit could be linked to low levels of p56(lck) mRNA and resulted in the failure to efficiently induce the expression of the CD69 early activation marker. We propose that a primary deficiency in human type 1 diabetes is a defect in TCR/CD3-mediated T cell activation due to the abnormal expression of the p56(lck) tyrosine kinase.
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PMID:Specific deficiency of p56lck expression in T lymphocytes from type 1 diabetic patients. 1106 48

TCR- but not CD2-triggered IL-2 production is p56(lck) dependent. To test the hypothesis that p59(fyn), a second src-family protein tyrosine kinase (PTK) expressed in T lymphocytes, might be an essential upstream component of the CD2 signaling pathway, we generated human (h) CD2 transgenic (tg) fyn(+/+) and fyn(-/-) mice. Clustering of hCD2 molecules on resting peripheral T lymphocytes results in Ca(2+) mobilization, activation of MAPK and cellular proliferation. In contrast, in the absence of p59(fyn), these CD2-initiated activities are markedly reduced, while TCR-triggered proliferation is unaffected. Several CD2 pathway components regulated by p59(fyn) have been identified including phospholipase C-gamma1 (PLC-gamma1), Vav, protein kinase C-theta isoform (PKC-theta), docking protein (Dok), focal adhesion kinase (FAK) and Pyk2. Decreased inducible PKC-theta catalytic activity and Vav phosphorylation likely account for diminished p38 and JNK activation in hCD2tg fyn(-/-) mice. Moreover, deficiency in fyn-dependent PLC-gamma1 catalytic activity may contribute to reduced PKC-alpha-dependent ERK activation. Of note, CD2-dependent Dok but not linker from activated T cells (LAT) tyrosine phosphorylation requires p59(fyn). Furthermore, that FAK and Pyk2 are target substrates implies that p59(fyn) may be an important regulator of T cell adhesion as well. Collectively, these data identify p59(fyn) as a key PTK in CD2-mediated activation of mature T lymphocytes.
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PMID:A critical role for p59(fyn) in CD2-based signal transduction. 1109 70

Rheumatoid arthritis (RA) synovial fluid (SF)-T lymphocytes appear relatively inactive in situ and respond only weakly to diverse stimuli ex vivo. To characterize the molecular defects underlying this hyporesponsiveness we analyzed the expression level of several proteins involved in TCR-proximal signal transduction. As compared to peripheral blood (PB)-T lymphocytes, SF-T cells from some (but not all) of the patients analyzed expressed lower levels of TCRalphabeta, CD3epsilon, TCRzeta, p56(lck) and LAT, while p59(fyn), phospholipase C-gamma1 and ZAP-70 expression was unaltered. Semi-quantitative analysis of T cells from several patients revealed that the degree of TCRzeta chain and p56(lck) modulation correlated statistically significantly with the level of SF-T cell hyporesponsiveness. The differential reactivity of p56(lck) specific monoclonal and polyclonal antibodies in SF-T but not PB-T lymphocytes indicated that p56(lck) modulation consists of a conformational change rather than loss of expression. Our results indicate that multiple signaling molecules can be modulated in RA SF-T cells and show for the first time a direct quantitative correlation between T cell hyporesponsiveness and modulation of TCRzeta and of p56(lck), a critical protein tyrosine kinase required for T cell activation.
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PMID:A potential role for protein tyrosine kinase p56(lck) in rheumatoid arthritis synovial fluid T lymphocyte hyporesponsiveness. 1122 99

CD4 is a 56-kDa membrane glycoprotein expressed by a subset of T cells, by cells of the monocyte/macrophage lineage, and by eosinophils and dendritic cells. CD4 serves as a coreceptor for HIV and IL-16. T cell CD4 mediates signal transduction by associating with the protein tyrosine kinase p56(lck); this interaction does not exist in monocytes. We wished to elucidate the mechanism(s) by which monocyte CD4 transduces signals. Stimulation of CD4 on Thp-1 monocytic cells induced a Ca(2+) flux and the time-dependent activation of phosphotyrosine proteins ranging from 35 to 180 kDa. We identified the 140- and 85-kDa proteins as phospholipase C gamma (PLC-gamma) and the regulatory subunit of phosphatidylinositol 3-kinase (PI-3K), respectively. Using immunoprecipitation/Western immunoblotting however, we were unable to show any direct association between CD4 and PLC-gamma, PI-3K, or other known signaling proteins. To identify proteins capable of associating with the cytoplasmic tail of CD4, we fused it with gluthatione S-transferase and used the fusion protein in far Western and pull-down experiments. In both types of experiments, the fusion protein routinely associated with 45- and 55-kDa proteins. Mass spectrometry analysis of the tryptic peptides generated from these two proteins indicated novel sequences.
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PMID:CD4 is active as a signaling molecule on the human monocytic cell line Thp-1. 1221 22


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