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

---

Query: EC:3.1.4.3 (phospholipase C)
18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

ATP promoted biphasic effects on both basal and fMLP-stimulated arachidonic acid (AA) release in neutrophil-like HL60 cells: stimulation in the micromolar range (EC50 = 3.2 +/- 0.9 microM) and inhibition at higher concentrations (EC50 = 90 +/- 11 microM). ATP also inhibited UTP- and platelet activating factor-stimulated AA release. Only stimulatory effects of ATP on basal or fMLP-stimulated phospholipase C were observed. The inhibitory effect of ATP on AA release was not due to reacylation of released AA, chelation of extracellular Ca2+, cell permeabilization, or changes in the rise of [Ca2+]i induced by agonist. The inhibition was rapid, being detected within 5-15 s. The inhibitory effect of ATP on fMLP-stimulated AA release could be desensitized by pretreatment of the cells with 2 mM ATP, but not 20 microM ATP, the concentration that resulted in maximal release of AA and inositol phosphates. The inhibition by ATP was neither dependent on generation of adenosine by ATP hydrolysis nor the result of direct interaction of ATP with P1 purinergic receptors. Among other nucleotides tested (CTP, GTP, ITP, TTP, XTP, adenosine 5'-(beta,gamma-methylene)triphosphate (AMP-PCP), adenyl-5'-yl imidodiphosphate (AMP-P(NH)P), ADP, adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), and UTP), only UTP and ATP gamma S displayed biphasic effects with potencies and efficacies almost identical to those of ATP. The other nucleotides only exhibited stimulatory effects (EC50 = 60-300 microM). The results are consistent with a model of dual regulation of AA release by two distinct subtypes of P2U receptors in HL60 cells.
...
PMID:Dual regulation of arachidonic acid release by P2U purinergic receptors in dibutyryl cyclic AMP-differentiated HL60 cells. 131 16

Membranes of cultured newborn rat cardiomyocytes contain enzymatic activities that regulate the formation and the breakdown of inositol 1,4,5-trisphosphate (1,4,5-IP3). GTP gamma S increased the rate of exogenous [3H]phosphatidyl 4,5-bisphosphate ([3H]PIP2) hydrolysis (EC50: 40 microM). This effect was dependent on the presence of deoxycholate and maximal at 2 mM deoxycholate. GTP gamma S increased the efficacy of phospholipase C (PLC) (by 2.3-fold), but did not alter the apparent affinity of the enzyme for PIP2. Other nucleotides, GDP beta S and ATP gamma S, and pyrophosphate also stimulated PIP2 hydrolysis, while AlF4- was ineffective. The effect of GTP gamma S was not inhibited by GDP beta S. The agonists norepinephrine and thrombin, which by themselves had no effect, did not potentiate the response to GTP gamma S. In contrast, 1,4,5-IP3 hydrolysis was decreased by GTP gamma S (EC50: 100 microM) as well as by other nucleotides and by pyrophosphate, but not by AlF4-. GDP beta S did not antagonize the GTP gamma S-induced inhibition of IP3 hydrolysis. These results suggest that GTP can stimulate the hydrolysis of exogenous PIP2 by an action on membrane-bound PLC at a site beyond the G protein activating PLC and inhibit the hydrolysis of 1,4,5-IP3 by a mechanism common to all nucleotides. Thus, GTP can regulate 1,4,5-IP3 metabolism by stimulating its formation and inhibiting its breakdown.
...
PMID:Regulation of inositol 1,4,5-trisphosphate metabolism by guanine nucleotides in membranes of cultured newborn rat cardiomyocytes. 131 33

The signal transduction of prostaglandin E2 (PGE2) and thromboxane A2 (TXA2), cyclooxygenase products of arachidonic acid, was investigated in smooth muscle preparations and 1321N1 human astrocytoma cells. While PGE2 has been known to stimulate (via EP2 receptor) or inhibit (via EP3 receptor) adenylate cyclase, PGE2 activated phosphatidylinositol 4,5-bisphosphate (PIP2)-specific phospholipase C (PLase C) in non-vascular smooth muscles (via EP1 receptor), resulting in accumulations of inositol trisphosphate (IP3) and diacylglycerol to elicit intracellular Ca2+ mobilization. On the other hand, STA2, a TXA2 receptor analogue, also accumulated IP3 in human astrocytoma cells. [3H]SQ 29548, a TXA2 receptor antagonist, specifically bound to astrocytoma membranes. TXA2-receptor antagonists (ONO NT-126, S-145, SQ29548 and ONO3708) concentration-dependently inhibited PIP2-specific PLase C activation by STA2, and they also inhibited [3H]SQ 29548 binding in human astrocytoma cells. The Ki value of each antagonist in PIP2-specific PLase C inhibition was similar to that in [3H]SQ29548 binding inhibition. In membrane preparations, STA2 activated PIP2-specific PLase C in the presence of GTP gamma S. Pertussis toxin (IAP) did not affect STA2-induced PLase C activation. The results suggest that stimulation of TXA2 receptors activates PIP2-specific PLase C via an IAP-insensitive G-protein.
...
PMID:[Signal transduction of prostaglandin E2 and thromboxane A2]. 131 76

[3H]Inositol ([3H]Ins) labeling of phosphoinositides was studied in rat brain cortical membranes. [3H]Ins was incorporated into a common lipid pool through both CMP-dependent and independent mechanisms. These are as follows: (1) a reverse reaction catalyzed by phosphatidyl-inositol (PtdIns) synthase, and (2) the reaction performed by the PtdIns headgroup exchange enzyme, respectively. Membrane phosphoinositides prelabeled in either CMP-dependent or independent fashions were hydrolyzed by guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S)- and carbachol-stimulated phospholipase C. Unlike CMP-dependent labeling, however, CMP-independent incorporation of [3H]Ins into lipids was inhibited by 1 mM (0.04%) sodium deoxycholate. Thus, when PtdIns labeling and phospholipase C stimulation were studied in a concerted fashion, [3H]Ins was incorporated into lipids primarily through the PtdIns synthase-catalyzed reaction because of the presence of deoxycholate required to observe carbachol-stimulation of phospholipase C. Little direct breakdown of [3H]PtdIns was detected because production of myo-[3H]inositol 1-monophosphate was minimal and myo-[3H]inositol 1,4-bisphosphate was the predominant product. Although PtdIns labeling and 3H-polyphosphoinositide formation were unaffected by GTP gamma S and carbachol and had no or little lag period, GTP gamma S- and carbachol-stimulated appearance of 3H-Ins phosphates exhibited an appreciable lag (10 min). Also, flux of label from [3H]Ins to 3H-Ins phosphates was restricted to a narrow range of free calcium concentrations (10-300 nM). These results show the concerted activities of PtdIns synthase, PtdIns 4-kinase, and phospholipase C, and constitute a simple assay for guanine nucleotide-dependent agonist stimulation of phospholipase C in a brain membrane system using [3H]Ins as labeled precursor.
...
PMID:Concerted CMP-dependent [3H]inositol labeling of phosphoinositides and agonist activation of phospholipase C in rat brain cortical membranes. 131 77

Platelet activity is increased in persons with insulin dependent diabetes mellitus (IDDM). Receptor-medicated phospholipase C (PLC) activation and hydrolysis of phosphatidylinositol bisphosphate (PIP2) accompanies platelet activation. Previous work from our laboratory has shown that PIP2 hydrolysis is decreased in platelets of persons with IDDM. PIP2 hydrolysis is mediated via a phosphoinositide(PI)-specific PLC. PI-PLC activity is regulated by guanine nucleotide(GTP)-binding proteins. We therefore examined the hypothesis that platelet aggregations and PI turnover in platelet from subjects with IDDM is linked to alterations in PI-specific PLC activity. We found thrombin induced platelet aggregation was increased in the IDDM group. Basal PI and PIP2-specific PLC activity was not statistically different for the two groups. Guanine-nucleotide stimulated PIP2-specific PLC activity was decreased in the IDDM platelets. The mechanism for the reduced PLC activity and its role in the platelet hyperaggregation requires further study.
...
PMID:Reduced guanine nucleotide-stimulated polyphosphoinositide specific phospholipase C in platelet hyperaggregation in IDDM. 131 91

A possible role for altered signal transduction mechanisms in impaired alpha 1-adrenergic-stimulated secretory function during aging was investigated in parotid cells prepared from adult (6 mo) and old (24 mo) rats. Compared with adults, epinephrine-stimulated 45Ca2+ efflux and inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] production were reduced 31 and 36% in cells of old rats, respectively. There was a highly significant correlation between 45Ca2+ efflux and Ins(1,4,5)P3 production. In saponin-permeabilized cells, no significant differences in Ins(1,4,5)P3-stimulated 45Ca2+ efflux in adult and old preparations were observed. When G proteins were stimulated by guanosine 5'-O-(3-thiotriphosphate) or NaF, no age differences in Ins(1,4,5)P3 production were detected. Stimulation of phosphoinositide-specific phospholipase C (PLC) by CaCl2 in adult and old cells was also comparable. Moreover, no differences in immunolabeled common alpha (GTP binding site), Gi alpha, PLC-gamma, or PLC-delta could be detected in either cytosol or membranes of adult and old preparations. In the absence of 5'-guanylylimidodiphosphate [Gpp(NH)p], no age-related changes in epinephrine competition for [3H]prazosin binding sites were observed. Approximately 30% of the agonist binding sites existed in a high-affinity form at both ages. Gpp(NH)p caused large rightward shifts of epinephrine displacement curves in adult membranes (converting all binding sites to the low-affinity form), but not old. Moreover, epinephrine was much more effective in stimulating G protein low-Km GTPase in parotid membranes from adult than old rats. These data suggest that age-related impairments in alpha 1-adrenergic responsiveness are mediated, at least in part, by the functional alterations in the coupling of G proteins with alpha 1-adrenergic receptors.
...
PMID:Altered coupling of alpha 1-adrenergic receptor-G protein in rat parotid during aging. 131 99

The effects of guanosine 5'-[beta-thio]triphosphate (GTP beta[S]) on G proteins have been examined in Chinese hamster lung fibroblasts (CCL39 line) permeabilized with alpha-toxin from Staphylococcus aureus. Although much less effective than guanosine 5'-[gamma-thio]triphosphate (GTP gamma[S]), both (Rp) and (Sp) diastereomers of GTP beta[S] were found to activate three G protein-mediated pathways: inhibition of forskolin-stimulated adenylate cyclase (mediated by Gi), potentiation of receptor-mediated activation of adenylate cyclase (mediated by Gs), and activation of phosphoinositide breakdown (mediated by Gp). Activation of Gi and Gs occurred above 3 microM-GTP beta[S], but activation of Gp only occurred above 100 microM-GTP beta[S]. Moreover, the order of effectiveness of the two diastereomers was not the same for the three G protein-mediated processes. Whereas both Gi and Gs were more effectively activated (about 5-fold) by (Sp)-GTP beta[S] than by (Rp)-GTP beta[S], Gp showed a marked preference for the (Rp) isomer. Indeed, (Rp)-GTP beta[S] induced the formation of inositol phosphates with a shorter latency and was a better competitor of GDP for binding to Gp than the (Sp) isomer. These results point to different guanine nucleotide-binding properties for Gi and Gs on the one hand and Gp on the other. At least two distinct Gp proteins, differing by their sensitivity to pertussis toxin, are present in CCL39 cells. Since pretreatment of cells with pertussis toxin completely suppressed the effects of (Rp)-GTP beta[S] on Gi, while only slightly attenuating its effects on Gp, we believe that it is the pertussis toxin-insensitive Gp which prefers the (Rp) isomer. Therefore (Rp)-GTP beta[S] may be a valuable tool for the selective activation and the biochemical characterization of this pertussis toxin-insensitive Gp.
...
PMID:Activation of G proteins by (Rp) and (Sp) diastereomers of guanosine 5'-[beta-thio]triphosphate in hamster fibroblasts. Differential stereospecificity of Gi, Gs and Gp. 131 29

Phosphoinositide phospholipase C (PLC) activity extracted from bovine liver plasma membranes with sodium cholate was stimulated by GTP gamma S-activated G alpha q/G alpha 11, whereas the enzyme from liver cytosol was not. The membrane-associated PLC was subjected to chromatography on heparin-Sepharose, Q Sepharose, and S300HR, enabling the isolation of the G-protein stimulated activity and its resolution from PLC-gamma and PLC-delta. Following gel filtration, two proteins of 150 and 140 kDa were found to correspond to the activatable enzyme. These proteins were identified immunologically as members of the PLC-beta family and were completely resolved by chromatography on TSK Phenyl 5PW. The 150-kDa enzyme was markedly responsive to GTP gamma S-activated alpha-subunits of G alpha q/G alpha 11 or to purified Gq/G11 in the presence of GTP gamma S. The response of this PLC was of much greater magnitude than that of the 140-kDa enzyme. The partially purified 150-kDa enzyme showed specificity for PtdIns(4,5)P2 and PtdIns4P as compared to PtdIns and had an absolute dependence upon Ca2+. These characteristics were similar to those of the brain PLC-beta 1. The immunological and biochemical properties of the 150-kDa membrane-associated enzyme are consistent with its being the PLC-beta isozyme that is involved in receptor-G-protein-mediated generation of inositol 1,4,5-triphosphate in liver.
...
PMID:Identification in bovine liver plasma membranes of a Gq-activatable phosphoinositide phospholipase C. 132 Sep 35

Apical membrane ion channels control the rate of transepithelial electrolyte transport in many epithelia. One way to study such channels in their native location, the apical membrane, is to eliminate the resistance of the basolateral membrane to ion flow. Then the opening and closing of apical channels can be measured as a transepithelial current, free from the influence of basolateral membrane transport processes. To develop a method that would permeabilize an epithelial basolateral membrane to ions and nucleotides, we examined the effect of Staphylococcus aureus alpha-toxin on the Cl(-)-secreting T84 epithelial cell line. alpha-Toxin permeabilized the basolateral, but not the apical membrane to Cl-, adenosine 3',5'-cyclic monophosphate (cAMP), and GTP. However, the integrity of signal-transduction pathways, the regulation of apical membrane Cl- channels, and the transepithelial resistance remained intact. In the course of examining the effect of ATP, we found that the basolateral membrane contained purinergic receptors that both stimulated Cl- secretion on their own and, at high concentrations, inhibited cAMP-induced Cl- secretion. These effects of extracellular ATP were eliminated after prolonged exposure to ATP, suggesting receptor downregulation. In addition, depletion of intracellular ATP following permeabilization prevented cAMP-dependent regulation of apical Cl- channels. We conclude that alpha-toxin may prove to be a useful tool for studying the regulation and properties of apical membrane ion channels.
...
PMID:Staphylococcus aureus alpha-toxin permeabilizes the basolateral membrane of a Cl(-)-secreting epithelium. 132 49

Purified M1 muscarinic cholinergic receptor and Gq/11 were coreconstituted in lipid vesicles. Addition of purified phospholipase C-beta 1 (PLC-beta 1) further stimulated the receptor-promoted steady-state GTPase activity of Gq/11 up to 20-fold. Stimulation depended upon receptor-mediated GTP-GDP exchange. Addition of PLC-beta 1 caused a rapid burst of hydrolysis of Gq/11-bound GTP that was at least 50-fold faster than in its absence. Thus, PLC-beta 1 stimulates hydrolysis of Gq/11-bound GTP and acts as a GTPase-activating protein (GAP) for its physiologic regulator, Gq/11. GTPase-stimulating activity was specific both for PLC-beta 1 and Gq/11. Such GAP activity by an effector coupled to a trimeric G protein can reconcile slow GTP hydrolysis by pure G proteins in vitro with fast physiologic deactivation of G protein-mediated signaling.
...
PMID:Phospholipase C-beta 1 is a GTPase-activating protein for Gq/11, its physiologic regulator. 132 96


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---