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)

CD59, the membrane regulator of autologous C5b-9 channel formation, exhibits variable sensitivity to cleavage by phosphatidylinositol-specific phospholipase C (PI-PLC), an enzyme that releases glyco-inositolphospholipid (GPI)-anchored proteins from cell surfaces. To determine whether the GPI-anchor phospholipid of CD59 is similar to that of decay-accelerating factor (DAF) and whether variation in its structure underlies its variable enzyme susceptibility, the GPI anchors of the two proteins expressed on erythrocytes, polymorphonuclear and mononuclear leucocytes were compared in situ and after purification. Flow cytometric analyses of PI-PLC-treated cells showed parallel cell type specific release of both proteins as a function of enzyme concentration. Non-denaturing PAGE analyses of alkaline/hydroxylamine-treated proteins (affinity-purified from [125I]-surface-labelled cells) provided evidence for (i) comparable proportions of GPI-anchor acylation, and (ii) alkali-resistant rather than alkali-sensitive lipid substituents in erythrocytes. These findings argue that the differential C5b-9 sensitivity that distinguishes paroxysmal nocturnal haemoglobinuria II and III erythrocytes does not derive from expression of CD59 molecules with alternative GPI-anchor phospholipid structures.
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PMID:Structural properties of the glycoplasmanylinositol anchor phospholipid of the complement membrane attack complex inhibitor CD59. 137 55

The triggering of T- or B-cell antigen-specific receptors is accompanied by rapid tyrosine phosphorylation of distinct cellular substrates, one of which is the gamma 1 isoform of inositol phospholipid-specific phospholipase C (PLC-gamma 1). This phosphorylation event, mediated by a putative protein tyrosine kinase coupled to the antigen receptor, probably stimulates the enzymatic activity of PLC-gamma 1, thereby promoting inositol phospholipid hydrolysis and other downstream signal transduction events. Recently, another ubiquitously expressed PLC isoform, PLC-gamma 2 (which shares 50.2% amino acid homology with PLC-gamma 1), has been identified. PLC-gamma 2-specific antibodies were used to evaluate the distribution and potential signaling role of this isoform in lymphocytes. Here, we report that, in contrast to T lymphocytes that express predominantly PLC-gamma 1, the major isoform expressed in murine and human resting B cells is PLC-gamma 2. Among B-cell tumor lines, all five murine B-lymphoma lines tested and one of six human B-lymphoblastoid cell lines also expressed predominantly PLC-gamma 2. However, three other human lines preferentially expressed PLC-gamma 1, and two others displayed similar levels of the two PLC-gamma isoforms. Furthermore, the triggering of B-cell surface immunoglobulin by anti-receptor antibodies was accompanied by a rapid tyrosine phosphorylation of PLC-gamma 2, which peaked after 5 min of stimulation. Conversely, and in agreement with recent reports, triggering of the T-cell antigen receptor complex led to the predominant phosphorylation of PLC-gamma 1 on tyrosine. These findings identify PLC-gamma 2 as a substrate for a B-cell putative protein tyrosine kinase coupled to the antigen receptor and suggest that its tyrosine phosphorylation constitutes a critical and early event in B-cell activation and, furthermore, that PLC-gamma 1 and PLC-gamma 2 may participate in similar but distinct signal transduction pathways in lymphocytes.
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PMID:Predominant expression and activation-induced tyrosine phosphorylation of phospholipase C-gamma 2 in B lymphocytes. 137 28

Rat oligodendrocytes, which activate the classical pathway of complement in the absence of antibody, are highly sensitive in a reactive lysis assay using human C5b6 and EDTA serum. Oligodendrocytes may be relatively deficient in glycolipid-linked complement regulatory protein(s), since digestion with phosphatidylinositol-specific phospholipase C (PI-PLC) failed to increase their sensitivity to serum, whereas complement-insensitive astrocytes, when treated with PI-PLC, became strikingly sensitive. To test the hypothesis that oligodendrocytes lack terminal complement regulatory molecule(s), human erythrocyte CD59, a recently described complement regulatory protein, was purified to homogeneity. The biological activity of the preparation was confirmed by reincorporating the protein into guinea-pig erythrocytes through its glycolipid anchor, which resulted in dose-dependent protection against human C5b6 and EDTA serum. Incorporation of 10(5) molecules of human CD59 into rat oligodendrocytes resulted in good protection against homologous human complement (76%), and significant protection against rat complement homologous to the cell (36%). Protection could be reversed using an antibody to CD59.
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PMID:Oligodendrocytes lack glycolipid anchored proteins which protect them against complement lysis. Restoration of resistance to lysis by incorporation of CD59. 137 23

Stimulation of certain receptor tyrosine kinases results in the tyrosine phosphorylation and activation of phospholipase C gamma (PLC gamma), an enzyme that catalyses the hydrolysis of phosphatidylinositol (PtdIns). This hydrolysis generates diacylglycerol and free inositol phosphate, which in turn activate protein kinase C and increase intracellular Ca2+, respectively. PLC gamma physically associates with activated receptor tyrosine kinases, suggesting that it is a substrate for direct phosphorylation by these kinases. Here we report that a fibroblast growth factor (FGF) receptor with a single point mutation at residue 766 replacing tyrosine with phenylalanine fails to associate with PLC gamma in response to FGF. This mutant receptor also failed to mediate PtdIns hydrolysis and Ca2+ mobilization after FGF stimulation. However, the mutant receptor phosphorylated itself and several other cellular proteins, and it mediated mitogenesis in response to FGF. These findings show that a point mutation in the FGF receptor selectively eliminates activation of PLC gamma and that neither Ca2+ mobilization nor PtdIns hydrolysis are required for FGF-induced mitogenesis.
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PMID:Point mutation of an FGF receptor abolishes phosphatidylinositol turnover and Ca2+ flux but not mitogenesis. 137 97

Stimulation of growth factor receptors with tyrosine kinase activity is followed by rapid receptor dimerization, tyrosine autophosphorylation and phosphorylation of signalling molecules such as phospholipase C gamma (PLC gamma) and the ras GTPase-activating protein. PLC gamma and GTPase-activating protein bind to specific tyrosine-phosphorylated regions in growth factor receptors through their src-homologous SH2 domains. Growth factor-induced tyrosine phosphorylation of PLC gamma is essential for stimulation of phosphatidylinositol hydrolysis in vitro and in vivo. We have shown that a short phosphorylated peptide containing tyrosine at position 766 from a conserved region of the fibroblast growth factor (FGF) receptor is a binding site for the SH2 domain of PLC gamma (ref. 8). Here we show that an FGF receptor point mutant in which Tyr 766 is replaced by a phenylalanine residue (Y766F) is unable to associate with and tyrosine-phosphorylate PLC gamma or to stimulate hydrolysis of phosphatidylinositol. Nevertheless, the Y766F FGF receptor mutant can be autophosphorylated, and can phosphorylate several cellular proteins and stimulate DNA synthesis. Our data show that phosphorylation of the conserved Tyr 766 of the FGF receptor is essential for phosphorylation of PLC gamma and for hydrolysis of phosphatidylinositol, but that elimination of this hydrolysis does not affect FGF-induced mitogenesis.
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PMID:Point mutation in FGF receptor eliminates phosphatidylinositol hydrolysis without affecting mitogenesis. 137 98

Steel factor (SF), the ligand for the proto-oncogene c-kit, acts synergistically with GM-CSF or IL-3 to support the growth of normal human hematopoietic progenitor cells. We examined the effects of SF on GM-CSF or IL-3 induced proliferation of a human factor-dependent cell line, MO7. SF supported MO7 cell proliferation as well as IL-3 or GM-CSF alone, and its addition dramatically enhanced (three- to sixfold) maximal GM-CSF or IL-3 stimulated proliferation. SF did not increase the number or affinity of cell surface GM-CSF receptors. We examined several early events of signal transduction in an effort to elucidate the biochemical mechanisms of synergy of these factors. Since each of these three cytokines is believed to function in part through activation of a tyrosine kinase, we examined their effects on cellular phosphotyrosine containing proteins. Each cytokine induced rapid, transient, and concentration dependent tyrosine phosphorylation of a number of substrates. For GM-CSF and IL-3, these phosphoproteins were indistinguishable (150, 125, 106, 93, 80, 79, 73, 44, 42, and 36 kDa), while SF induced major or minor tyrosine phosphorylation of 205, 140-150, 116, 106, 94, 90, 80, 79, 73, 44, 42, 39, 36, 32 kDa phosphoproteins. Two other signal transduction intermediates known to be phosphorylated and activated by GM-CSF and IL-3, the 70-75 kDa Raf-1 kinase, and p42 mitogen-activated protein kinase-2 (MAPK), were also phosphorylated by SF. Combinations of GM-CSF or IL-3 with SF did not further increase the phosphorylation of Raf-1 or p42 MAPK when compared to any of the factors alone. In contrast SF, but not GM-CSF or IL-3, induced tyrosine phosphorylation of phospholipase C-gamma (PLC-gamma). These results indicate that SF and GM-CSF/IL-3 have partially overlapping effects on early signal transducing events, as well as striking differences, such as tyrosine phosphorylation of PLC-gamma. This cell line should provide a useful model system to investigate the complicated process of hematopoietic growth factor synergy.
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PMID:Granulocyte-macrophage colony-stimulating factor and steel factor induce phosphorylation of both unique and overlapping signal transduction intermediates in a human factor-dependent hematopoietic cell line. 138 14

Calphobindins (CPBs) I, II and III which we isolated and characterized from placenta belong to a family of calcium and phospholipid binding proteins represented by lipocortins known to inhibit phospholipase A2(PLA2). The amino acid sequence of three CPBs shares much homology with lipocortins I and II, so we investigated the functions of CPBs in affecting the enzymatic activities of PLA2 and also phospholipase C(PLC). In our experiments CPBs I, II and III showed an apparent dose-dependent inhibition of PLA2 and PLC activities, and all three proteins had a more potent inhibitory effect than lipocortins. The inhibition was overcome by high phospholipid substrate concentrations, for example, in the presence of 2.9 x 10(-9)M PLA2 and 2.6 x 10(-7)M CPB I, the inhibition decreased from 85 to 9% as phosphatidylethanolamine was increased from 10 to 100 microM. A similar result was observed in the case of PLC also. The evidence strongly suggests that the inhibitory effect of CPBI results from binding of the proteins to the phospholipid substrate rather than from a direct action on the phospholipase itself.
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PMID:[Inhibitory effects of calphobindins on phospholipase A2 and phospholipase C]. 138 68

In order to study the structure-activity relationships of phenothiazine derivatives inhibiting phosphatidylinositol-specific phospholipase C (PI-PLC), the synthesis of some phenothiazine amide, amine and ester derivatives was performed mainly by reacting 10H-phenothiazine-10-propanoyl chloride with some amines and alcohols; the resulting amides were reduced with borane to yield the corresponding amines. Starting from 2-chloro and 2-trifluoromethyl-10H-phenothiazine-10-propanoyl chloride two amides were synthesized. The inhibiting activity on PI-PLC from human platelets is reported.
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PMID:Synthesis of phenothiazine derivatives as potential inhibitors of phospholipase C. 138 3

Two novel sites of autophosphorylation were localized to the C-terminal tail of the PDGF beta-receptor. To evaluate the importance of these phosphorylation sites, receptor mutants in which Tyr1009, Tyr1021 or both were replaced with phenylalanine residues, were expressed in porcine aortic endothelial (PAE) cells. These mutants were similar to the wild type receptor with regard to protein tyrosine kinase activity and ability to induce mitogenicity in response to PDGF-BB. However, both the Y1009F and Y1021F mutants showed a decreased ability to mediate association with and the tyrosine phosphorylation of phospholipase C-gamma (PLC-gamma) compared to the wild type PDGF beta-receptor; in the case of the Y1009F/Y1021F double mutant, no association or phosphorylation of PLC-gamma could be detected. These data show that tyrosine phosphorylation of PLC-gamma is dependent on autophosphorylation of the PDGF beta-receptor at Tyr1009 and Tyr1021.
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PMID:Identification of two C-terminal autophosphorylation sites in the PDGF beta-receptor: involvement in the interaction with phospholipase C-gamma. 139 85

We have purified to homogeneity the 33-kDa phosphatidylinositol-specific phospholipase C (PI-PLC) from the culture fluid of Listeria monocytogenes, a facultative intracellular pathogen. The protein was overexpressed, and secretion of PI-PLC was further enhanced by the addition of divalent cations to the culture medium. The basic protein (pI, approximately 9.4) was complexed with anionic proteins in the crude culture fluid. It bound to DEAE-Sepharose and was eluted from Sephacryl S-200 near the void volume in low-ionic-strength buffer, suggesting aggregates of greater than or equal to 150 kDa. Gel filtration chromatography on Sephacryl S-200 in the presence of 1 M ammonium sulfate resulted in disaggregation and complete separation of PI-PLC, which interacted with the column matrix. Amino-terminal sequencing of the pure protein gave results consistent with the previously deduced sequence and showed that the signal cleavage site was between alanine 29 and tyrosine 30. The enzyme was specific for PI and showed no activity with phosphatidylethanolamine, phosphatidylcholine, or phosphatidylserine. It did not cleave PI-4-phosphate or PI-4,5-bisphosphate, but it was active on the membrane form of the variable surface glycoprotein from Trypanosoma brucei, a PI-glycan-anchored protein. When assayed with deoxycholate-mixed micelles of PI, activity was highly dependent on added salt. Activation by salt was also observed with Triton X-100-mixed micelles. The optimal concentration of CaCl2 or MgCl2 was lower than that of KCl or (NH4)2SO4, but activity was not specifically dependent on divalent cations and was not inhibited by addition of EDTA. With deoxycholate, the optimum pH was 7.0. A broader pH optimum ranging from 5.5 to 6.5 was observed with Triton X-100-mixed micelles. These results are consistent with a postulated role for secreted PI-PLC in the acidified primary phagocytic vesicle of infected cells.
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PMID:Purification and characterization of Listeria monocytogenes phosphatidylinositol-specific phospholipase C. 139 18


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