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 effects of an exogenous Type I phospholipase C (PLC) from clostridium perfringens on arachidonic acid release and prostaglandin synthesis from gastric mucosa by determining PGE2 release from organ cultured rabbit mucosal biopsies as well as PGE2 synthesis and substrate-dependent inactivation of the prostaglandin cyclooxygenase from endogenously released arachidonic acid in mucosal homogenate. PLC dose dependently stimulated PGE2 secretion from organ cultured mucosa to 145% and 245% at 0.1 and 1.0 U/ml during a 60 minute culture period. This effect was not affected by the calmodulin antagonist N-(6-aminohexyl)-1-5-chloro-1-naphthalene-sulfonamide (W-7) or the intracellular calcium chelator 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N',-tetraacetic acid-acetoxymethyl ester (BAPTA-AM). PLC could not be substituted by phorbol-12-myristate 13-acetate (PMA), an analogue of the diacylglycerol second messenger functions. During a 15 minute preincubation of mucosal homogenate at 37 degrees C, 1mM CaCl2 stimulated PGE2 synthesis from endogenous arachidonic acid about 5-fold compared to an EDTA-control. In contrast, the residual prostaglandin synthesizing capacity, determined by incubation with excess 14C-labelled arachidonic acid, was reduced by CaCl2 to 37% of the EDTA-value. Quinacrine, an inhibitor of arachidonic acid release from phosphatidylethanolamine, reduced both the stimulation of PGE2 synthesis and the inactivation of prostaglandin cyclooxygenase. Therefore we conclude, that this Ca(2+)-effect reflects activation of the Ca-dependent phospholipase A2 (PLA2) and, as a consequence, substrate-induced inactivation of the prostaglandin cyclooxygenase.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Activation of PGE2-secretion from gastric mucosa by a type I phospholipase C is mediated by a direct release of arachidonic acid. 130 34

We previously reported that pertussis toxin (PTX)-sensitive GTP-binding protein is involved in the coupling of prostaglandin E2 (PGE2) receptor to phospholipase C in osteoblast-like MC3T3-E1 cells (1). In the present study, we analyzed the mechanism of PGE2-induced arachidonic acid (AA) release in MC3T3-E1 cells. PGE2 stimulated the release of AA and the formation of inositol trisphosphate (IP3) dose dependently in the range between 1 nM and 10 microM. The effect of PGE2 on AA release (ED50 was 80 nM) was more potent than that on IP3 formation (ED50 was 0.8 microM). Quinacrine, a phospholipase A2 inhibitor, suppressed the PGE2-induced AA release but had little effect on the IP3 formation. NaF, a GTP-binding protein activator, mimicked PGE2 by stimulating the AA release. The AA release stimulated by a combination of PGE2 and NaF was not additive. PTX had little effect on the PGE2-induced AA release. These results strongly suggest that the AA release and the phosphoinositide hydrolysis are separately stimulated by PGE2 in osteoblast-like cells, and the PGE2-induced AA release is mediated by PTX-insensitive GTP-binding protein.
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PMID:Mechanism of prostaglandin E2-induced arachidonic acid release in osteoblast-like cells: independence from phosphoinositide hydrolysis. 132 13

Synaptoneurosomes obtained from the cortex of rat brain prelabeled with [14C]arachidonic acid [( 14C]AA) were used as a source of substrate and enzyme in studies on the regulation of AA release. A significant amount of AA is liberated in the presence of 2 mM EGTA, independently of Ca2+, primarily from phosphatidic acid and polyphosphoinositides (poly-PI). Quinacrine, an inhibitor of phospholipase A2 (PLA2), suppressed AA release by about 60% and neomycin, a putative inhibitor of phospholipase C (PLC), reduced AA release by about 30%. An additive effect was exhibited when both inhibitors were given together. Ca2+ activated AA release. The level of Ca2+ present in the synaptoneurosomal preparation (endogenous level) and 5 microM CaCl2 enhance AA liberation by approximately 25%, whereas 2 mM CaCl2 resulted in a 50% increase in AA release relative to EGTA. The source for Ca(2+)-dependent AA release is predominantly phosphatidylinositol (PI); however, a small pool may also be liberated from neutral lipids. Carbachol, an agonist of the cholinergic receptor, stimulated Ca(2+)-dependent AA release by about 17%. Bradykinin enhanced the effect of carbachol by about 10-15%. This agonist-mediated AA release occurs specifically from phosphoinositides (PI + poly-PI). Quinacrine almost completely suppresses calcium-and carbachol-mediated AA release. Neomycin inhibits this process by about 30% and totally suppresses the effect of bradykinin. Our results indicate that both phospholipases PLA2 and PLC with subsequent action of DAG lipase are responsible for Ca(2+)-independent AA release. Ca(2+)-dependent and carbachol-mediated AA liberation occurs mainly as the result of PLA2 action. A small pool of AA is probably also released by PLC, which seems to be exclusively responsible for the effect of bradykinin.
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PMID:Ca(2+)-independent, Ca(2+)-dependent, and carbachol-mediated arachidonic acid release from rat brain cortex membrane. 191 75

Brain cortex membranes labeled with [14C]arachidonic acid were used as the source of substrate and enzyme for the assay of arachidonic acid (AA) liberation. A significant amount of AA was released Ca2(+)-independently, mainly from phosphatidic acid, polyphosphoinositides and phosphatidylserine. Quinacrine, inhibitor of phospholipase A2 (PLA2), suppressed AA release by 60% and neomycin, inhibitor of phospholipase C (PLC) by about 30%. Both inhibitors applied together have an additive effect. Physiological calcium level elevated AA liberation by 50%, whereas 2 mM calcium enhanced this process by a further 30%. Carbachol, exclusively in the presence of calcium, activated AA release selectively from phosphatidylinositol and diglycerides. We suggest that Ca2(+)-independent PLA2 and PLC play an important role in AA liberation, and that physiological increments of calcium may have serious implications.
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PMID:Regulation of arachidonic acid release by enzyme(s) of rat brain cortex. 212 31

Release of arachidonic acid (AA) from 1-stearoyl-2-[14C]arachidonyl-glycerophosphoinositol (PI) by plasma membrane-bound enzyme(s) is a calcium-dependent reaction and is markedly activated at 4 x 10(-4) M CaCl2. In the presence of Ca2+, the agonist of the cholinergic receptor (carbachol) enhances, in a dose-related manner, AA release. Moreover, GTP and its non-hydrolysable analogs GTP gamma S and GppNHp and also NaF additionally increase the carbachol-mediated liberation of AA from PI. On the contrary, in the absence of Ca2+ carbachol and GTP gamma S have no stimulatory effect on AA release. Guanosine-5'-O-2-thiodiphosphate GDP gamma S, which inhibits the function of GTP-binding proteins, also suppresses carbachol-mediated activation of AA release from PI. The stimulatory effect of carbachol and guanine nucleotides was observed exclusively in the brain plasma membrane (there was no effect on mitochondria, microsome and cytosolic enzymes). Quinacrine, the inhibitor of phospholipase A2, completely inhibits carbachol- and guanine nucleotide-activated AA release and greatly (by about 60-70%) decreases Ca(2+)-dependent AA liberation from phosphatidylinositol. These results indicate that GTP-binding protein(s) are involved in the regulation of carbachol-mediated AA release. The main pool of this acid is liberated from phosphatidylinositol by phospholipase A2 and only a small pool of AA may be released indirectly as the result of PI hydrolysis by sequential action of phospholipase C and diacylglycerol lipase.
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PMID:Guanine nucleotides and fluoride enhance carbachol-mediated arachidonic acid release from phosphatidylinositol. Evidence for involvement of GTP-binding protein in phospholipase A2 activation. 251 94

The possible role of the phospholipase enzymes in the prolactin stimulation of mitogenesis in Nb2 node lymphoma cells was investigated. Two phospholipase inhibitors including quinacrine and alpha-para-dibromoacetophenone (BPB) were employed. Quinacrine at concentrations of 1-5 microM attenuated the magnitude of the PRL stimulation of cell division; at concentrations of 10 microM and above quinacrine abolished the PRL response. BPB at concentrations of 1-10 microM also inhibited the mitogenic effect of PRL in a concentration response fashion. The polyunsaturated fatty acid arachidonic acid partially reversed the inhibitory effects of these drugs. In further studies, exogenously added phospholipase C at concentrations of 5-50 ng/ml was found to potentiate the mitogenic effect of prolactin when prolactin was employed at a concentration that evoked a half-maximal response. By itself, however, phospholipase C had no effect on the rate of cell division. Phospholipase A2 either by itself or in the presence of prolactin was without effect.
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PMID:Possible involvement of the phospholipases in the mitogenic actions of prolactin (PRL) on Nb2 node lymphoma cells. 310 86

Regulatory effects of phospholipase A2 (PLA2) on acetylcholine receptor (AChR) cluster formation were investigated in developing mouse myotubes co-cultured with spinal cord explant, using quinacrine, cortisone, tetracaine and related agents. AChR was visualized using the fluorescence-conjugated alpha-bungarotoxin. Peak fluorescence intensity and total fluorescence within the fluorescence stain were measured as indices of AChR cluster formation and AChR content, respectively. Both indices were gradually increased from day 9 to 13 in culture. PLA2 (0.2-1.0 micrograms/ml), melittin (10 micrograms/ml) and arachidonic acid (100 microM), added to the culture medium from the second day, clearly inhibited both indices at days 11 and 13, whereas the addition of phospholipase C (1 microgram/ml) inhibited peak fluorescence but did not affect total fluorescence. The co-existence of PLA2 with its inhibitors--quinacrine (3 microM), cortisone (0.01 microM) and tetracaine (30 microM)--significantly overcame the PLA2-induced inhibition of both indices. The elevation of calcium ion concentrations from 2.9 to 10 mM abolished the increase of both indices. Quinacrine (10 microM), cortisone (0.1 microM) and tetracaine (100 microM) alone similarly inhibited both fluorescence indices. The addition of EGTA (2 mM) from day 8 overcame tetracaine-induced inhibition but not quinacrine- or cortisone-induced inhibition. These results suggest that the formation of AChR clusters in developing myotubes is negatively controlled by endogenous PLA2 activity. This overcoming of PLA2-induced inhibition by tetracaine may be dependent on calcium ion mobilization, whereas that by quainacrine and cortisone may not.
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PMID:Calcium-dependent regulation of phospholipase A2 and its inhibitors, including tetracaine, for acetylcholine receptor cluster formation in mouse myotubes co-cultured with spinal cord explant. 350 94

In stimulated platelets phosphatidylinositol is degraded by a phosphatidylinositol-specific phospholipase C to 1,2-diacylglycerol which is then phosphorylated to phosphatidic acid. Thrombin stimulation of horse and human platelets prelabeled with [32P]orthophosphate induces the formation of [32P]lysophosphatidylinositol, suggesting that phosphatidylinositol is also degraded by a phospholipase of A type activity. Stimulation of platelets prelabeled with 32P or with 32P plus [3H]inositol produces a lysophosphatidylinositol which has a 32P-specific activity and a 3H/32P ratio which has a 32P-specific activity and a 3H/32P ratio identical with those of phosphatidylinositol. These results suggest that the lysophosphatidylinositol derives from phosphatidylinositol. Thrombin stimulation of platelets double label with 32P and [3H]arachidonate induces loss of [3H]arachidonate from phosphatidylinositol and formation of [32P]lysophosphatidylinositol, suggesting the involvement of a phospholipase A2 activity. Ionophore A23187 also induces the formation of lysophosphatidylinositol in horse and human platelets. With either stimulus, [32P]lysophosphatidylinositol appears within seconds after stimulation and parallels the loss of [3H]arachidonic acid from phosphatidylinositol. The lysophosphatidylinositol produced by thrombin or by ionophore A23187 represents 40% of the degraded phosphatidylinositol as assessed by lipid phosphorus. Quinacrine, which inhibits the liberation of arachidonic acid from phospholipids, also blocks the formation of lysophosphatidylinositol. The results presented here indicate that phosphatidylinositol is degraded by both phospholipases, C and A2, in stimulated platelets.
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PMID:Formation of lysophosphatidylinositol in platelets stimulated with thrombin or ionophore A23187. 680 48

1. Calcium (Ca2+, 0.1-100 microM) stimulated concentration-dependent contractions in small strips from the rabbit mesenteric artery in which the smooth muscle cells had been permeabilized with Staphylococcus aureus alpha-toxin. 2. 5-Hydroxytryptamine (5-HT) and phenylephrine, each in the presence of 10 microM guanosine 5'-triphosphate (GTP), concentration-dependently stimulated additional contractions in strips sub-maximally contracted by the presence of a buffered concentration of calcium (0.3 microM). All the additional contraction was abolished with the selective inhibitor of protein kinase C, Ro 31-8220 (10 microM). 3. Quinacrine (10-50 microM), an inhibitor of phospholipase A2, selectively inhibited the sensitization to 5-HT, but did not alter the sensitization to either phenylephrine or GTP. 4. Myofilament sensitization to calcium was mimicked by exogenous arachidonic acid (300 microM, in the presence of indomethacin, miconazole and BW755c) and the stable analogue of arachidonic acid, 5,8,11,14-eicosatetrayonic acid (ETYA, 100 microM), and in both cases did not require the additional presence of GTP. Ro 31-8220, but not quinacrine, reduced the sensitization to arachidonic acid by around 30%. 5. These results indicate that G protein-linked myofilament sensitization to calcium in the mesenteric artery that follows the activation of 5-HT receptors, but not alpha 1-receptors, involves phospholipase A2. The sensitization stimulated by each of these different receptors, and a component of the response to arachidonic acid, also appears to involve the activation of protein kinase C.
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PMID:Phospholipase A2 and protein kinase C contribute to myofilament sensitization to 5-HT in the rabbit mesenteric artery. 886 67

We provided evidence that calcium-calmodulin plays a major role in bradykinin-induced arachidonic acid release by bovine aortic endothelial cells. In cells labeled for 16 hr with 3H-arachidonic acid, ionomycin and Ca2(+)-mobilizing hormones such as bradykinin, thrombin and platelet activating factor induced arachidonic acid release. However, arachidonic acid release was not induced by agents known to increase cyclic AMP (forskolin, isoproterenol) or cyclic GMP (sodium nitroprusside). Bradykinin induced the release of arachidonic acid in a dose-dependent manner (EC50 = 1.6 +/- 0.7 nM). This increase was rapid, reaching a maximal value of fourfold above basal level in 15 min. In a Ca2(+)-free medium, bradykinin was still able to release arachidonic acid but with a lower efficiency. Quinacrine (300 microM), a blocker of PLA2, completely inhibited bradykinin-induced arachidonic acid release. The B2 bradykinin receptor antagonist HOE-140 completely inhibited bradykinin-induced arachidonic acid release. The B1-selective agonist DesArg9-bradykinin was inactive and the B1-selective antagonist [Leu8] DesArg9-bradykinin had no significant effect on bradykinin-induced arachidonic acid release. The phospholipase C inhibitor U-73122 (100 microM) decreased bradykinin-induced arachidonic acid release. The calmodulin inhibitor W-7 (50 microM) drastically reduced the bradykinin- and ionomycin-induced arachidonic acid release. Also, forskolin decreased bradykinin-induced arachidonic acid release. These results suggest that the activation of PLA2 by bradykinin in BAEC is a direct consequence of phospholipase C activation. Ca2(+)-calmodulin appears to be the prominent activator of PLA2 in this system.
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PMID:Calcium-calmodulin plays a major role in bradykinin-induced arachidonic acid release by bovine aortic endothelial cells. 891 80


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