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)

Epidermal growth factor (EGF) rapidly stimulates the formation of inositol 1,4,5-trisphosphate in a variety of cell types. Previously we have found that in intact cells stimulation of phospholipase C (PLC) activity by EGF is correlated with the retention of increased amounts of PLC activity by a phosphotyrosine immunoaffinity matrix, suggesting that the EGF-receptor tyrosine kinase phosphorylates PLC. We now define parameters of the mechanism by which EGF addition to A-431 cells stimulates phosphotyrosine immunoisolation of PLC activity and demonstrate that EGF addition to A-431 cells increases tyrosine phosphorylation of PLC. EGF rapidly and reversibly stimulated the anti-phosphotyrosine recovery of increased PLC activity when cells were treated with growth factor at 3 degrees C, indicating that receptor internalization is not required and that the phosphorylation event occurs prior to formation of inositol 1,4,5-trisphosphate. Also, the EGF stimulation of anti-phosphotyrosine recovery of PLC activity occurred in the absence of extracellular Ca2+. Stimulation of PLC activity in intact cells by other agonists, such as bradykinin or ATP, did not result in increased anti-phosphotyrosine recovery of PLC activity, suggesting two separate mechanisms exist in A-431 cells for hormone-stimulated formation of inositol phosphates. Finally, using monoclonal antibodies that specifically recognize three distinct PLC isozymes, we show that an approximately 145-kDa PLC isozyme (PLC-II) is present in A-431 cells and that EGF treatment of A-431 cells stimulates phosphorylation of PLC-II on both tyrosine and serine residues.
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PMID:Epidermal growth factor stimulates tyrosine phosphorylation of phospholipase C-II independently of receptor internalization and extracellular calcium. 246 93

Porcine or bovine endothelial cells cultured on microcarrier beads, packed into adapted chromatographic columns, perfused with Krebs' buffer and activated with appropriate stimuli (e.g. bradykinin, ADP or phospholipase C) release EDRF and prostacyclin into the perfusing fluid. In the effluent EDRF and prostacyclin might be bio-assayed using the Vane's superfusion cascade (rabbit aortic strips and bovine coronary artery strips, respectively) against nitroglycerine (GTN) and synthetic prostacyclin standards. Prostacyclin might be also quantified as 6-keto-PGF1 alpha by RIA. A spatial separation of the generator (endothelial cells) from the effector (vascular smooth muscle) has allowed to prove that EDRF is nitric oxide, that its activity is inhibited by superoxide anions and by chemicals which act via free radicals, finally, that the release of EDRF and prostacyclin is coupled by a receptor-mediated activation of phospholipase C. Although so successful, the above technique suffers from its essentials, i.e. from using cultured cells instead of fresh intact endothelial cells. Cultured endothelial cells are not responsive to many receptor agonists including acetylcholine, substance P and 5-hydroxytryptamine. Unlike fresh intact endothelial preparations the cultured cells which are perfused with Krebs' buffer generate superoxide anions at such concentrations that it might be obligatory infusing superoxide dismutase in order to detect EDRF. Nonetheless, a couple of data obtained with the cultured endothelial cells have been reproduced in the fresh cell preparations, e.g. release of EDRF by ADP and ATP, a coupled release of EDRF and prostacyclin by phospholipase C or a paradoxical augmentation of the sodium-nitroprusside-induced vasorelaxation by methylene blue.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Endothelium-derived relaxing factor (EDRF) from cultured and fresh endothelial cells. 247 Mar 61

The biochemical events encompassing the dephosphorylation of protein kinase C substrates by protein kinase A activators have been investigated in a neurotumor cell line, NCB-20. Treatment of [32P]orthophosphate-labeled cells with protein kinase A activators (e.g. forskolin, dibutyryl cAMP, prostaglandin E1) resulted in an inhibition of protein kinase C activity due to a failure of the protein kinase C complex to translocate into the membrane. Phospholipase C activity, as measured by the synchronous release of diacylglycerol and inositol phosphates (inositol 1,4,5-trisphosphate, inositol 1,4-bisphosphate, and inositol 1-phosphate) in response to bradykinin, was inhibited up to 50% following exposure to protein kinase A activators. At the same time, phospholipase C-specific inositol phospholipid substrates (phosphatidylinositol, phosphatidylinositol 4-phosphate, and phosphatidylinositol 4,5-bisphosphate) were found to accumulate in NCB-20 cells following treatment with protein kinase A activators. This suggests that phospholipase C may be altered through protein kinase A-mediated protein phosphorylation. Second messenger generation (inositol phosphates, diacylglycerol, and Ca2+) is therefore inhibited through cyclic AMP-mediated shutdown of the inositol lipid cycle at the level of phospholipase C.
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PMID:Rapid dephosphorylation of protein kinase C substrates by protein kinase A activators results from inhibition of diacylglycerol release. 247 91

The ability of a variety of agonists to induce formation of inositol phosphates and 1,2-diacylglycerol in cultured adult human keratinocytes has been investigated. Histamine, bradykinin, and thrombin significantly stimulated formation of inositol mono-, bis-, and trisphosphate and 1,2-diacylglycerol within 5 min after addition. Aluminum fluoride also caused a dose-dependent accumulation of inositol phosphates suggesting the participation of a GTP binding protein in the regulation of phospholipase C-catalyzed phosphoinositide hydrolysis. These data demonstrate that human keratinocytes possess the capacity for phospholipase C-mediated signal transduction and suggest that this pathway may participate in the regulation of keratinocyte function.
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PMID:Agonist-induced hydrolysis of phosphoinositides and formation of 1,2-diacylglycerol in adult human keratinocytes. 247 31

Carbachol, histamine and bradykinin activate phospholipase C in pertussis toxin-insensitive manner in human astrocytoma cells. Pretreatments of the cells with these agonists resulted in the reduction of GTP gamma S-induced accumulation of inositol phosphates in membrane preparations. Treatment of cells with carbachol mobilized GTP gamma S binding activities as well as muscarinic receptors from heavy membrane fraction to light fraction, reflecting from an agonist-induced desensitization. The treatment of the cells with agonists reduced a 32 kDa GTP binding protein in heavy membrane fraction, determined by a photoaffinity labeling with [35S]GTP gamma S. The data suggest that the 32 kDa GTP binding protein is involved in desensitization by agonists which activate phospholipase C in human astrocytoma cells.
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PMID:GTP gamma S binding activities were reduced in heavy membrane fraction during desensitization by Ca-mobilizing agonists in human astrocytoma cells. 250 Jun 83

The hormonal stimulation of phospholipase C and the consequent activation of the Ca2+-phosphatidylinositol cascade in eukaryotic cells is associated with modifications of the [Ca2+]i (intracellular Ca2+ concentration) which modulates cellular functions. In this study, these modifications were investigated in primary cultures of human thyroid cells. The mean apparent basal [Ca2+]i of human thyrocytes measured using the intracellularly trapped fluorescent indicator Quin-2 was found to be 89 +/- 16 nM (n = 49). ATP and, to a lesser extent, ADP, but not AMP or adenosine, elicited a concentration-dependent biphasic rise in human thyrocytes [Ca2+]i and increased their 45Ca2+ efflux. The first transient phase of the [Ca2+]i rise induced by ATP was resistant to extracellular Ca2+ depletion, whereas the second sustained phase was abolished in these conditions. This suggests that although the first phase of this response involves a release of Ca2+ from intracellular stores, the second phase requires extracellular Ca2+ influx. The response of human thyrocytes to analogs of ATP is compatible with a P2-purinergic effect of ATP on these cells. Bradykinin and TRH affected the human thyrocyte [Ca2+]i and 45Ca2+ efflux similarly to ATP. The human thyrocyte [Ca2+]i and the 45Ca2+ efflux were not modified by carbachol, a nonhydrolyzable analog of acetylcholine. The present results suggest the presence of P2-purinergic receptors to ATP and of receptors to TRH and bradykinin on human follicular thyroid cells. They also confirm that the Ca2+-phosphatidylinositol cascade is present in these cells and suggest that this cascade is modulated by ATP, TRH, and bradykinin. As this cascade is involved in the regulation of protein iodination, and therefore of thyroid hormones synthesis, these agents might have an important role in the regulation of the thyroid function.
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PMID:Adenosine triphosphate, bradykinin, and thyrotropin-releasing hormone regulate the intracellular Ca2+ concentration and the 45Ca2+ efflux of human thyrocytes in primary culture. 250 91

Infection of cultured endothelial cells with Trypanosoma cruzi alters intracellular Ca2+ homeostasis. To help understand the biochemical basis for this phenomenon, we determined the influence of infection on inositol phosphate formation in a broken cell preparation. Inositol phosphates participate in the regulation of cytosolic Ca2+. In uninfected endothelial cells, bradykinin guanosine 5'-O-thiophosphate (GTP tau S), and calcium all stimulated inositol phosphate (IP1), inositol bisphosphate (IP2), and inositol trisphosphate (IP3) formation within 5 sec of incubation. At longer periods of incubation with GTP tau S and bradykinin, formation of IP1 was linear for 30 sec, whereas the rate of IP2 and IP3 generation was maximal at 20 and 5 sec, respectively. Second, infection markedly changed these aspects of inositol phosphate generation. First, unstimulated (basal) levels of IP1 and IP3 were markedly increased over those levels in membranes of uninfected cells. Infection decreased the rate of formation for the three inositol phosphates in response to GTP tau S and bradykinin. Finally, infection diminished the magnitude of inositol phosphate synthesis in response to Ca2+ for IP1, IP2, and IP3, respectively. Studies on G proteins using cholera and pertussis toxin were carried out to determine if the infection-associated changes in inositol phosphate generation could be attributed to functional changes in these regulatory proteins known to participate in the activation of phospholipase C. Infection markedly decreased the magnitude of cholera and pertussis toxin-dependent ADP ribosylation, as compared to control uninfected cells. Incubation of uninfected endothelial cells with cholera and pertussis toxin also decreased the magnitude of cholera and pertussis toxin ADP ribosylation. Despite the similar effects of infection and toxin treatment on subsequent toxin-catalyzed ADP ribosylation, toxin treatment did not influence inositol phosphate generation. Collectively, these results demonstrate an influence of infection on receptor-dependent and -independent synthesis of inositol phosphates, possibly by an action on phospholipase C. The results help to explain the apparent infection-associated increase in basal Ca2+ previously observed and suggest that interference with signal transduction may be a consequence of the presence of the parasite.
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PMID:Trypanosoma cruzi: infection of cultured human endothelial cells alters inositol phosphate synthesis. 250 35

In order to define the molecular mechanisms involved in the hypertrophy of the arterial walls observed in essential hypertension, vascular smooth muscle cells were isolated from aortas of spontaneously hypertensive (SHR) and control (WKY) rats, and cultured (until the 4th sub-culture) in the presence of growth factors (foetal calf serum: FCS) and various vasoactive drugs. Growth rate was determined by cell counting and measurement of nuclear thymidine incorporation, and activation of phospholipase C by measurement of the inositol phosphates formed from preincorporated tritiated myo-inositol; the expression of the cellular oncogenes, c-fos and c-myc was visualized by hybridization of Northern blots performed from total RNA. In the presence of low concentrations of FCS (2 p. 100, 5 p. 100) angiotensin II (10(-7)M) and bradykinin (3 X 10(-6)M) increase the growth of both kind of cells. The inositol phosphate formation and the expression of c-fos and c-myc are also dose-dependently stimulated by these vasoactive drugs, and the cultures from SHR are more responsive than those from WKY rats. Phospholipase C hyperreactivity therefore appears to be involved in the increased proliferative ability of vascular smooth muscle cells from SHR. However other molecular processes may be involved, as suggested by the growth inhibition exerted by heparin without any action on PLC activity.
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PMID:[Molecular mechanisms controlling the proliferation of aortic smooth muscle cells in spontaneously hypertensive rats]. 251 Jun 66

The endothelium plays an important role in the control of vascular tone and platelet activity. This is mainly achieved by the release of autacoids, particularly EDRF (identical with nitric oxide, NO) and PGI2. The release of both autacoids is evoked by physical factors like hypoxia and shear stress and by various chemical compounds like acetylcholine, ATP and bradykinin. These agonists bind to membrane receptors coupled to phospholipase C, thereby increasing production of inositol-1,4,5-trisphosphate (IP3). IP3 mobilizes Ca2+ from intracellular stores, thus elevating the intracellular free calcium concentration ([Ca2+]i), in synergy with a simultaneously induced transmembrane Ca2+ influx. The level of [Ca2+]i closely correlates with endothelial production of PGI2 whereas Ca2+ influx is apparently a decisive signal for the sustained release of EDRF. This influx may be facilitated by an agonist-induced membrane hyperpolarization probably being mediated by activation of Ca2+-dependent K+ channels. Depolarization of the endothelial cell membrane on the other hand (evoked by raising the extracellular K+ concentration) attenuates the Ca2+ influx as well as EDRF release. The agonist-induced endothelial hyperpolarization may also be electrotonically transmitted to adjacent smooth muscle cells via myoendothelial gap junctions and may act synergistically with the EDRF-mediated relaxation. Alternatively, spread of this electrical signal along the endothelial lining may enhance the release of autacoids.
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PMID:Mechanisms controlling the production of endothelial autacoids. 251 73

In neuroblastoma x glioma hybrid cells (NG 108-15) labelled with [32P]-trisodium phosphate, [3H]-inositol and [14C]-arachidonic acid, bradykinin stimulated the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) while it had no effect on the release of [14C]-arachidonic acid (AA). The effect on PIP2 was time- and dose-dependent with a maximal effect on [3H]-inositol- and [32P]-labelled cells after 10-30 s of stimulation with 10(-6) M bradykinin. However, the hydrolysis of [14C]-AA labelled PIP2 was delayed compared to the effect on [3H]- and [14C]-PIP2 and was not detectable until after 60 s of stimulation. Bradykinin stimulation resulted in an increased formation of [3H]-inositol phosphates (IP) and [32P]- and [14C]-phosphatidic acid (PA) but the time course for PA formation did not follow the time-course for PIP2 hydrolysis. A reduced labelling of [32P]- and [14C]-phosphatidylcholine was also found in stimulated cells suggesting that PA may derive from other sources than PIP2. In conclusion, our results indicate that bradykinin activates phospholipase C, but not phospholipase A2, in NG 108-15 cells.
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PMID:Bradykinin effects on phospholipid metabolism and its relation to arachidonic acid turnover in neuroblastoma x glioma hybrid cells (NG 108-15). 251 58


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