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)

We investigated the interaction of phospholipase C-gamma (PLC-gamma) with wild-type and mutant forms of the platelet-derived growth factor (PDGF) beta-receptor both in vivo and in vitro. After PDGF treatment of CHO cell lines expressing wild-type or either of two mutant (delta Ki and Y825F) PDGF receptors, PLC-gamma became tyrosine phosphorylated and associated with the receptor proteins. The receptor association and tyrosine phosphorylation of PLC-gamma correlated with the ability of these receptors to mediate ligand-induced phosphatidylinositol turnover. However, both the delta Ki and Y825F mutant receptors were deficient in transmitting mitogenic signals, suggesting that the PDGF-induced tyrosine phosphorylation and receptor association of PLC-gamma are not sufficient to account for the growth-stimulatory activity of PDGF. Wild-type and delta Ki mutant PDGF receptor proteins expressed with recombinant baculovirus vectors also associated in vitro with mammalian PLC-gamma. However, baculovirus-expressed c-fms, v-fms, c-src, and Raf-1 proteins failed to associate with PLC-gamma under similar conditions. Phosphatase treatment of the baculovirus-expressed PDGF receptor greatly decreased its association with PLC-gamma. This requirement for receptor phosphorylation was also observed in vivo, where PLC-gamma could not associate with a mutant PDGF receptor (K602A) defective in autophosphorylation. PLC-gamma also coimmunoprecipitated with two other putative receptor substrates, the serine-threonine kinase Raf-1 and the 85-kilodalton phosphatidylinositol-3' kinase, presumably through its association with the ligand-activated receptor. Furthermore, baculovirus-expressed Raf-1 phosphorylated purified PLC-gamma in vitro at sites which showed increased serine phosphorylation in vivo in response to PDGF. These results suggest that PDGF directly influences PLC activity by inducing the association of PLC-gamma with a receptor signaling complex, resulting in increased tyrosine and serine phosphorylation of PLC-gamma.
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PMID:Platelet-derived growth factor (PDGF)-dependent association of phospholipase C-gamma with the PDGF receptor signaling complex. 169 40

Phospholipase C-gamma 1 (PLC-gamma 1), an isozyme of the phosphoinositide-specific phospholipase C family, which occupies a central role in hormonal signal transduction pathways, is an excellent substrate for the epidermal growth factor (EGF) receptor tyrosine kinase. Epidermal growth factor elicits tyrosine phosphorylation of PLC-gamma 1 and phosphatidylinositol 4,5-bisphosphate hydrolysis in various cell lines. The ability of tyrosine phosphorylation to activate the catalytic activity of PLC-gamma 1 was tested. Tyrosine phosphorylation in intact cells or in vitro increased the catalytic activity of PLC-gamma 1. Also, treatment of EGF-activated PLC-gamma 1 with a tyrosine-specific phosphatase substantially decreased the catalytic activity of PLC-gamma 1. These results suggest that the EGF-stimulated formation of inositol 1,4,5-trisphosphate and diacylglycerol in intact cells results, at least in part, from catalytic activation of PLC-gamma 1 through tyrosine phosphorylation.
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PMID:Increase of the catalytic activity of phospholipase C-gamma 1 by tyrosine phosphorylation. 170 Aug 66

We have shown that platelets stimulated with thrombin or guanosine 5'-[gamma-thio]triphosphate (GTP[S]), both of which activate phospholipase C and protein kinase C (PKC), show enhancement of 3-phosphorylated phosphoinositide accumulation (3-PPI). We now report the following. (1) Inhibition of thrombin- or GTP[S]-stimulated PKC by pseudo-substrate peptide (RFARK) added to permeabilized platelets markedly inhibits 3-PPI, whereas the serine/threonine phosphatase inhibitor, okadaic acid, promotes 3-PPI. PKC activity, insufficient in itself for fully activating 3-PPI, appears crucial to receptor and post-receptor stimulation of 3-PPI, even when tyrosine phosphorylation is unimpaired. (2) Alteration of Gi by ADP-ribosylation only slightly affects the stimulation of 3-PPI by thrombin, and activation of the G-protein Gi by adrenaline has no effect on 3-PPI. (3) Inhibition of PKC blocks activated secretion of platelet-derived growth factor (PDGF). However, PDGF cannot promote platelet 3-PPI, and thus cannot account for the inhibitory effects of RFARK on 3-PPI.
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PMID:Protein kinase C regulates the stimulated accumulation of 3-phosphorylated phosphoinositides in platelets. 171 81

The RL cell line is an EBV-negative, surface IgM, IgD-positive B lymphoma line, which is significantly growth arrested in the presence of acrylamide-linked antibodies to the surface IgM receptor. We demonstrate here that activation of protein kinase C (PKC) with PMA abrogates anti-IgM-induced phosphoinositide turnover and Ca2+ mobilization; however, growth inhibition is not affected. In addition, inhibitors of PKC are unable to reverse the anti-IgM-mediated growth inhibition. Two-dimensional gel electrophoresis reveals a different pattern of protein phosphorylation after treatment of RL with PMA or anti-IgM. These data strongly suggest that anti-IgM-induced growth inhibition does not rely on phospholipase C-mediated phosphoinositide turnover, Ca2+ mobilization, or PKC activation. On the other hand, the phosphatase inhibitor orthovanadate results in an augmentation of proteins phosphorylated on tyrosine and the growth inhibition which follows anti-IgM treatment. Furthermore, protein tyrosine kinase inhibitors, genistein and herbimycin A, are able to reverse the anti-IgM-induced inhibition of growth. These data demonstrate that multiple signaling pathways are activated by the interaction of anti-IgM with its ligand, and suggest that tyrosine kinase activation is a critical component of the inhibitory response.
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PMID:Anti-IgM-mediated growth inhibition of a human B lymphoma cell line is independent of phosphatidylinositol turnover and protein kinase C activation and involves tyrosine phosphorylation. 191 71

MCH (melanin concentrating hormone) is a heptadecapeptide, Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val, which stimulates melanosome (melanin granule) aggregation to a perinuclear position within teleost fish integumental melanocytes, resulting in lightening of the skin. The mechanisms of action of MCH are unknown. Drugs that affect the diacylglycerol/inositol triphosphate pathway were used to investigate the possible roles of this pathway in the mechanisms of action of MCH on Synbranchus marmoratus (teleost) melanocytes. The shift of the dose-response curve to MCH in the presence of various concentrations of 4-bromophenacyl bromide and neomycin sulphate, phospholipase C inhibitors, suggests that phospholipase C is stimulated after MCH receptor activation. Low concentrations (10(-9) to 10(-8) M) of the phorbol ester TPA exhibited MCH-like activity, eliciting a dose-dependent melanosome aggregation. Higher doses, however, displaced to the right the dose-response curve to MCH, as did the protein kinase C inhibitors, dibucaine and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7). These results support the assumption that protein kinase C mediates the pigment aggregating activity of MCH. Both MCH and norepinephrine lightening actions were abolished by beta-glycerophosphate, a phosphatase inhibitor, suggesting that a protein dephosphorylation occurs during melanosome aggregation, and is, therefore, a common event triggered by MCH and norepinephrine, although both agonists act through separate receptors and exhibit different transduction mechanisms.
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PMID:Protein-kinase C mediates MCH signal transduction in teleost, synbranchus marmoratus, melanocytes. 194 11

The effects of sodium fluoride upon basal and agonist-stimulated inositol phospholipid breakdown have been investigated in rat brain miniprisms. NaF concentration dependently increased basal inositol phospholipid breakdown, with a maximum effect being seen at 20 mM. NaF reduced the inositol phospholipid breakdown responses to stimulation by carbachol, noradrenaline, serotonin and quisqualate, but not to the stimulation produced by raising the assay [K+] from 6 to 18 mM. More detailed study demonstrated NaF to have a 'levelling' effect, reducing all InsP/(Lipid + InsP) values greater than 0.15 (i.e. produced by carbachol at raised [K+], noradrenaline and by 50 mM K+) to about this value. Time-course experiments indicated that NaF treatment reduced the rate of carbachol-stimulated inositol phospholipid breakdown up to this InsP/(Lipid + InsP) level and thereafter blocked further breakdown. Inhibitory effects upon carbachol-stimulated inositol phospholipid breakdown were not seen with forskolin, sodium nitroprusside or 8BrcGMP. Under conditions where there is no de novo synthesis of phosphoinositides from [3H]myo-inositol, NaF reduced the total Lipid + InsP labelling by about 20%. NaF in addition inhibits the activity of Ins(1,4)P2-phosphatase in cerebral cortical homogenates. It is concluded that fluoride ions inhibit agonist-stimulated inositol phospholipid breakdown via actions not only on G-proteins but also on phosphoinositide-specific phospholipase C substrate availability.
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PMID:Multiple actions of fluoride ions upon the phosphoinositide cycle in the rat brain. 196 44

Choline, betaine and N,N-dimethylglycine as the sole carbon and nitrogen source induced a periplasmic acid phosphatase activity in Pseudomonas aeruginosa. This enzyme produced the highest rates of hydrolysis in phosphorylcholine and phosphorylethanolamine among the various phosphoric esters tested. At saturating concentrations of Mg2+, the Km values were 0.2 and 0.7 mM for phosphorylcholine and phosphorylethanolamine respectively. At high concentrations both compounds were inhibitors of the enzyme activity. The Ksi values for phosphorylcholine and phosphorylethanolamine were 1.0 and 3.0 mM respectively. The higher catalytic efficiency was that of phosphorylcholine. Considering these results it is possible to suggest that the Pseudomonas aeruginosa acid phosphatase is a phosphorylcholine phosphatase. The existence of this activity which is induced jointly with phospholipase C by different choline metabolites, in a high phosphate medium, suggests that the attack of Pseudomonas aeruginosa on the cell host may also be produced under conditions of high phosphate concentrations, when the alkaline phosphatase is absent.
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PMID:Identification of the Pseudomonas aeruginosa acid phosphatase as a phosphorylcholine phosphatase activity. 211 92

Inositol 1,4,5-trisphosphate (InsP3) is an important second messenger generated from the hydrolysis of phosphatidylinositol 4,5-bisphosphate by phospholipase C in response to Ca2(+)-mobilizing stimuli. InsP3 interacts with specific intracellular receptors and triggers the release of sequestered Ca2+ from an intracellular store. We have looked at the influence of 2,3-diphosphoglycerate on the action and metabolism of InsP3 in the bovine adrenal cortex. 2,3-Diphosphoglycerate blocked InsP3 binding to adrenal cortex microsomes with a half-maximal efficiency of 0.5 mM. Scatchard analyses revealed that 2,3-diphosphoglycerate did not change the maximal capacity of the microsomes, but decreased their binding affinity for InsP3. The Ca2(+)-releasing activity of InsP3 on the same microsomal preparation was monitored with the fluorescent indicator, Fura-2. 2,3-Diphosphoglycerate blocked this activity with a half-maximal efficiency of 2 mM. The effect of 2,3-diphosphoglycerate could be overcome by supramaximal doses of InsP3, indicating a competitive inhibitory effect. The activity of InsP3 phosphatase from bovine adrenal cortex microsomes was also studied. 2,3-Diphosphoglycerate inhibited the activity of the phosphatase with a half-maximal efficiency of 0.3 mM. Lineweaver-Burke plots revealed that this effect was competitive. Finally, 2,3-diphosphoglycerate was also able to inhibit the activity of a partially purified preparation of InsP3 kinase from bovine adrenal cortex cytosol. The half-maximal dose was around 10 mM and the Lineweaver-Burke plot showed that the inhibition was competitive. These results show that 2,3-diphosphoglycerate can be considered as a structural analog of InsP3. Its inhibitory effects, however, are not selective enough to use it as an InsP3 protective agent in Ca2(+)-mobilization studies.
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PMID:2,3-Diphosphoglycerate is a nonselective inhibitor of inositol 1,4,5-trisphosphate action and metabolism. 216 77

We explored the biochemical basis for the disorder pseudohypophosphatasia (PsHYPT) in one patient by examining the substrate specificity and localization of alkaline phosphatase (ALP) in cultured dermal fibroblasts. Despite substantial ALP activity, in cell homogenates, toward the artificial substrate 4-methyl-umbelliferyl phosphate (4-MUP), there was a marked deficiency in ALP activity toward the natural substrates pyridoxal 5'-phosphate (PLP) and phosphoethanolamine (PEA), indicating altered substrate specificity. Furthermore, although 4-MUP phosphatase (4-MUP-P'tase) activity was predominantly localized as an ecto-enzyme, the small amount of PLP phosphatase (PLP-P'tase) activity was intracellular. This differential localization was apparent in intact cells, since (1) brief acidification of the medium at 4 degrees C inactivated a majority of the 4-MUP-P'tase activity but only 15% of the PLP-P'tase activity (in contrast to greater than 85% inactivation of both in homogenates), (2) greater than 70% of the 4-MUP-P'tase activity but only 30% of the PLP-P'tase activity was released by phosphatidylinositol-specific phospholipase C (PI-PLC) digestion, and (3) degradation of extracellular PLP was less than 35% of that of disrupted cells. Both 4-MUP- and PLP-P'tase activities were predominantly in a lipid-anchored form that could be converted to a soluble, lipid-free form by PI-PLC digestion. Our findings suggest that the clinical and biochemical presentation of this PSHPT patient results from the production of two aberrant ALP species. One form of ALP has appropriate ectoorientation but is preferentially deficient in activity toward natural substrates; the other ALP species has appropriate substrate specificity but is sequestered from substrates by its intracellular location.
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PMID:Pseudohypophosphatasia: aberrant localization and substrate specificity of alkaline phosphatase in cultured skin fibroblasts. 217 30

Proteinkinase-C (PKC) stimulating phorbolesters induce in vitro insulin resistance of isolated adipocytes. This effect might be explained by an inhibition of insulin signal transduction at the level of the insulin receptor kinase. There is now some evidence that a phospholipase C is a potential candidate as a signal transducer at the postreceptor level. In order to determine whether phorbol esters might inhibit insulin signalling also at the level of a phospholipase C, we studied the insulin dependent [3H] phosphatidylinositol 4-monophosphate (PIP) hydrolysis of fat cell membranes. PIP hydrolysis was measured after in vitro stimulation with and without insulin. Insulin stimulated PIP hydrolysis in a dose dependent way. When plasma membranes from phorbolester (TPA) treated fat cells were used, this insulin stimulated phospholipase C activity was suppressed, provided, membranes have been prepared in a buffer containing serine phosphatase inhibitors. These data suggest that fat cell membranes contain an insulin dependent phospholipase C which is inhibited by TPA most likely via serine phosphorylation through proteinkinase C.
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PMID:TPA inhibits insulin stimulated PIP hydrolysis in fat cell membranes: evidence for modulation of insulin dependent phospholipase C by proteinkinase C. 217 67


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