Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The [32P]PIP2/[32P]PA and the [32P]PIP/[32P]PA relationships were demonstrated to be remarkably similar after stimulation of [32P]Pi-prelabelled platelets for 90 s with various combinations and concentrations of agonists and inhibitors. Thus the activity of the PI and PIP kinases with the corresponding phosphomonoesterases may be tightly controlled during receptor-mediated platelet stimulation involving phospholipase C activation.
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PMID:Evidence for tight metabolic control of the receptor-activated polyphosphoinositide cycle in human platelets. 255 3

1-Oleoyl-2-acetyl-sn-glycerol (OAG), the membrane-permeable analogue of 1,2-diacylglycerol (DAG), which stimulates ascites tumor cell proliferation, was used to study its effect on phosphoinositide metabolism. Culturing of ascites cells labeled with [3H]inositol at low serum concentration in the presence of OAG suppressed the radioactivity level of the inositol phosphates, particularly IP3. Membrane-bound, Ca(2+)- and GTP gamma S-sensitive PI- and PIP2-specific phosphodiesterase (phospholipase C) showed much lower activities in OAG-stimulated cells, which could be enhanced by GTP gamma S in these but not in the unstimulated cells. A high susceptibility to Ca2+ of the PI- and PIP2-specific phospholipase C of non-stimulated cells was observed. The PIP-kinase activity was similarly reduced by about 85% in OAG-stimulated cells. These data indicate a negative feedback regulation of the phosphoinositide metabolism mediated by OAG. Reduction in synthesis and degradation of PIP2, which furnishes the two second messengers, DAG and IP3, provides a means of controlling the intracellular level of these molecules, which is important for a balanced proliferation rate.
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PMID:Effect of 1-oleoyl-2-acetyl-sn-glycerol on inositol lipid metabolism of ascites tumor cells in culture. 256 33

Rabbit platelets were labelled with [3H]inositol and a membrane fraction was isolated in the presence of ATP, MgCl2 and EGTA. Incubation of samples for 10 min with 0.1 microM-Ca2+free released [3H]inositol phosphates equivalent to about 2.0% of the membrane [3H]phosphoinositides. Addition of 10 microM-guanosine 5'-[gamma-thio]triphosphate (GTP[S]) caused an additional formation of [3H]inositol phosphates equivalent to 6.6% of the [3H]phosphoinositides. A half-maximal effect was observed with 0.4 microM-GTP[S]. The [3H]inositol phosphates that accumulated consisted of 10% [3H]inositol monophosphate, 88% [3H]inositol bisphosphate ([3H]IP2) and 2% [3H]inositol trisphosphate ([3H]IP3). Omission of ATP and MgCl2 led to depletion of membrane [3H]polyphosphoinositides and marked decreases in the formation of [3H]inositol phosphates. Thrombin (2 units/ml) or GTP (4-100 microM) alone weakly stimulated [3H]IP2 formation, but together they acted synergistically to exert an effect comparable with that of 10 microM-GTP[S]. The action of thrombin was also potentiated by 0.1 microM-GTP[S]. Guanosine 5'-[beta-thio]diphosphate not only inhibited the effects of GTP[S], GTP and GTP with thrombin, but also blocked the action of thrombin alone, suggesting that this depended on residual GTP. Incubation with either GTP[S] or thrombin and GTP decreased membrane [3H]phosphatidylinositol 4-phosphate ([H]PIP) and prevented an increase in [3H]phosphatidylinositol 4,5-bisphosphate ([3H]PIP2) observed in controls. Addition of unlabelled IP3 to trap [3H]IP3 before it was degraded to [3H]IP2 showed that only about 20% of the additional [3H]inositol phosphates that accumulated with GTP[S] or thrombin and GTP were derived from the action of phospholipase C on [3H]PIP2. The results provide further evidence that guanine-nucleotide-binding protein mediates signal transduction between the thrombin receptor and phospholipase C, and suggest that PIP may be a major substrate of this enzyme in the platelet.
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PMID:Activation of phospholipase C associated with isolated rabbit platelet membranes by guanosine 5'-[gamma-thio]triphosphate and by thrombin in the presence of GTP. 282 Mar 81

In this study we have used a density perturbation method to isolate anti-Thy-1 antibody-induced Thy-1 caps from mouse T-lymphoma cells in the absence of detergents, and then compared the phospholipid composition of these capped membranes with that of uncapped membranes. Initial phospholipid analysis by two-dimensional thin layer chromatography (2-D TLC) reveals a significant increase in the amount of 32P-labeled phosphatidylcholine in the Thy-1 capped membrane. In contrast, no significant changes are observed in the labeling of phosphatidylserine, phosphatidylethanolamine, or the sphingomyelins. Therefore, it is suggested that phosphatidylcholine may be involved in the organization and/or regulation of Thy-1 antigen redistribution. The composition of phosphoinositide in uncapped and capped membranes was analysed separately using one-dimensional thin layer chromatography (1-D TLC) to resolve phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PlP), and phosphatidylinositol 4, 5-bisphosphate (PIP2) from all other phospholipids. This analysis reveals a significant reduction in levels of PIP and PIP2, but not PI, in Thy-1 caps. Through the use of ion exchange column chromatography, we have found an increased production of all three species of inositol phosphates during anti-Thy-1 antibody-induced capping. Inositol 1, 4, 5-triphosphate (IP3) shows the most significant increase, compared to the much smaller increases in inositol 4, 5-bisphosphate (IP2) and inositol monophosphate (IP). These results suggest that the binding of anti-Thy-1 antibody to Thy-1 antigen activates phospholipase C which, in turn, initiates polyphosphoinositide turnover and IP3 production. It is proposed that these observed effects are the result of early signal transducing events which are prerequisite steps in Thy-1 receptor cap formation.
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PMID:Isolation of Thy-1 caps and analysis of their phospholipid composition in mouse T-lymphoma cells. 282 3

Studies on the phosphorylation of inositol phospholipids of rat liver membranes have shown that [gamma S]pppG stimulates 32P incorporation from [gamma-32P]ATP into PI and PIP. This effect appeared specific for stable GTP analogues and could not be reproduced by other compounds. ADP-ribosylation of the membranes with cholera toxin resulted in a large decrease of PIP2 without changes in the level of PIP. Since an activation of phospholipase C can be ruled out, the lowering of PIP2 is explained on the basis of an inhibition of PIP kinase (EC 2.7.1.68). From these results it appears that a novel cholera-toxin-sensitive G-protein is involved in the regulation of PIP kinase.
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PMID:Evidence for a cholera-toxin-sensitive G-protein involved in the regulation of phosphatidylinositol 4-phosphate kinase of rat liver membranes. 284 7

Two different methods were used to study directly alpha-thrombin modulation of polyphosphoinositide breakdown in membranes prepared from Chinese hamster lung (CHL) fibroblasts. In the first one we labelled the lipid pool by incubating the intact cells with myo-[3H]inositol prior to membrane isolation; in the other we used exogenous [3H]PIP2 with phosphatidylethanolamine (1:10) added as liposomes to freshly isolated membranes. A Ca2+-dependent PIP2 and PIP phospholipase C activity was characterized by measuring the rate of formation of inositol tris- and bisphosphate. Basal phospholipase C activity was stimulated up to 3-fold by GTP or GTP-gamma-S. Of the two mitogens, alpha-thrombin and EGF, known to stimulate DNA synthesis in Chinese hamster fibroblasts, only alpha-thrombin is a potent activator of PIP2 breakdown in intact cells. Consistent with this observation, alpha-thrombin but not EGF potentiated GTP-gamma-S-dependent phospholipase C activity in membrane preparations. These results strongly support the hypothesis that a GTP-binding protein couples alpha-thrombin receptor to PIP2 hydrolysis. Because both methods used to assay phospholipase C gave identical results, we conclude that the coupling is at the level of PIP2-phosphodiesterase activity.
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PMID:Evidence for a GTP-binding protein coupling thrombin receptor to PIP2-phospholipase C in membranes of hamster fibroblasts. 302 38

The tumor-promoting phorbol ester PMA increased the incorporation of 32P-phosphate into PIP (150%) and PIP2 (50%) in human platelets over the same range of concentrations that stimulate protein kinase C activity (i.e. 1-10 ng/ml). PMA also increased the total content of PIP (2.5-fold) and PIP2 (1.5-fold). The increase in 32P-PIP and 32P-PIP2 was 50% completed at 2 min after 10 ng/ml PMA, and was maximal by 20 min. The increase in PIP and PIP2 was accompanied by a fall of 32P-PI and PI mass over the same time period and concentration range of PMA, but no 32P-PA was formed, indicating that phosphoinositide hydrolysis by phospholipase C was not stimulated. Inhibition of phospholipase C activity by increasing platelet cyclic AMP did not duplicate the effects of PMA. We conclude that PMA may directly affect inositol lipid kinases and/or phosphatases, or that PMA stimulation of protein kinase C provides feedback regulation of the enzymes that determine the levels of polyphosphoinositides involved in transmembrane stimulus-response coupling.
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PMID:Phorbol myristate acetate stimulates formation of phosphatidyl inositol 4-phosphate and phosphatidyl inositol 4,5-bisphosphate in human platelets. 609 4

Investigations were carried out on the influence of rat liver plasma membranes phospholipid composition on phospholipase C activity using PIP, PIP2, PC and PE as substrates. The membrane phospholipids were modified by incorporation of definite phospholipids with the aid of lipid transfer proteins or after partial delipidation with exogenous phospholipases A2 and C. The results indicated that sphingomyelin inhibited all phospholipase C activities. The incorporation of two different molecular species of phosphatidylcholine did not alter significantly the investigated phospholipase C activities, indicating that membrane fluidity was not essential in this case. Phosphatidylglycerol, phosphatidylserine, phosphatidylinositol and phosphatidylethanolamine served as specific activators of plasma membrane-bound phospholipase C when PIP, PIP2 and PC were used as substrates. However, these four phospholipids inhibited phospholipase C activity towards PE. The role of phosphoinositide-specific phospholipase C in the production of second messengers as well as the eventual biological significance of PC and PE as substrates for phospholipase C is discussed.
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PMID:Phospholipase C activities in rat liver plasma membranes depend on the phospholipid composition. 792 83

We studied thrombin-induced metabolism of phosphoinositide, protein phosphorylation and platelet aggregation in platelets from 32 NIDDM patients and 12 control subjects. To clarify the effect of diet, sulphonylureas, or insulin treatment, the subjects were divided into three groups based on the type of treatment. Thrombin-induced platelet aggregation was measured with an aggregometer. Low-dose thrombin (0.25 U/ml)-stimulated platelet aggregation in diabetic patients was significantly increased compared with the control subjects. Platelet aggregation in the sulphonylurea and insulin groups was significantly lower than in the diet group. On the other hand, in platelets incubated with [32P]orthophosphate, thrombin-induced incorporation of 32P radioactivity into phosphatidic acid (PA) was significantly lower in the sulphonylurea and insulin groups than in the diet group. Thrombin-induced incorporation of [32P] radioactivity into phosphatidylinositol (PIP) for 10 s was significantly higher in the sulphonylurea group than in the diet group. There were no differences in thrombin-induced 47 kDa protein phosphorylation between platelets from the diet, sulphonylurea, or insulin groups. These results suggest that sulphonylureas and insulin induce suppression of thrombin-induced activation of phospholipase C, which mediates hydrolysis of PIP and PIP2 and production of PA, which leads to inhibition of platelet aggregation.
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PMID:Thrombin-induced platelet aggregation, phosphoinositide metabolism and protein phosphorylation in NIDDM patients treated by diet, sulphonylurea or insulin. 792 50

Membrane-depleted rat liver nuclei contain diacylglycerol (DAG) kinase showing a specific activity which doubles that of the whole homogenate. In contrast, cytoplasmic and plasma membrane marker enzymes attain a specific activity of 0.4% at the most, when nuclear DAG kinase approaches 4.5% of the total tissue activity. The enzyme shows a Km of 161 and 200 microM for ATP in both nuclei and microsomes whereas the Km for DAG is 75 microM in nuclei and 658 microM in microsomes. Octylglucoside, CHAPS and Triton X-100 behave mainly as inhibitors, while deoxycholate stimulates the enzyme activity in both cellular fractions, increasing specific activity (3.2-fold in nuclei and 29.1-fold in microsomes) and decreasing Km for DAG (39 microM in nuclei and 237 microM in microsomes). Phospholipids and ceramide stimulate the enzyme activity in isolated nuclei, while no effect occurs in the microsomal fraction. At variance, sphingosine behaves as an inhibitor in both cellular fractions. DAG kinase also utilizes endogenous substrates mobilized by Bacillus cereus phospholipase C, which hydrolyses nuclear phosphatidylcholine and phosphatidylethanolamine and by phosphatidylinositol-specific phospholipase C, which hydrolyses nuclear PI and PIP. These data indicate that nuclear DAG can be controlled by converting it into phosphatidic acid by the action of a nuclear enzyme and support the contention that protein kinase C activity can be modulated at the nuclear level by a discrete system involving phospholipase C and DAG kinase that could operate independently from the cytoplasm.
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PMID:Diacylglycerol kinase activity in rat liver nuclei. 794 64


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