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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 have previously shown that soluble fractions obtained from human HL-60 granulocytes contain a phospholipase C which is markedly stimulated by the stable GTP analogue guanosine 5'-[3-O-thio]triphosphate (Camps, M., Hou, C., Jakobs, K. H. and Gierschik, P. (1990) Biochem. J. 271, 743-748]. To investigate whether this stimulation was due to a soluble alpha subunit of a heterotrimeric guanine-nucleotide-binding protein or a soluble low-molecular-mass GTP-binding protein, we have examined the effect of purified guanine-nucleotide-binding protein beta gamma dimers on the phospholipase-C-mediated formation of inositol phosphates by HL-60 cytosol. We found that beta gamma subunits, purified from bovine retinal transducin (beta gamma t), markedly stimulated the hydrolysis of phosphatidylinositol 4,5-bisphosphate by this phospholipase C preparation. The stimulation of phospholipase C by beta gamma t was not secondary to a phospholipase-A2-mediated generation of arachidonic acid, was prevented by the GDP-liganded transducin alpha subunit and was additive to activation of phospholipase C by guanosine 5'-[3-O-thio]triphosphate. Beta gamma t also stimulated soluble phospholipase C from human and bovine peripheral neutrophils, as well as membrane-bound, detergent-solubilized phospholipase C from HL-60 cells. Stimulation of soluble HL-60 phospholipase C was not restricted to beta gamma t, but was also observed with highly purified beta gamma subunits from bovine brain. Fractionation of HL-60 cytosol by anion-exchange chromatography revealed the existence of at least two distinct forms of phospholipase C in HL-60 granulocytes. Only one of these forms was sensitive to stimulation by beta gamma t, demonstrating that stimulation of phospholipase C by beta gamma subunits is isozyme specific. Taken together, our results suggest that guanine-nucleotide-binding protein beta gamma subunits may play an important and active role in mediating the stimulation of phospholipase C by heterotrimeric guanine-nucleotide-binding proteins.
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PMID:Stimulation of phospholipase C by guanine-nucleotide-binding protein beta gamma subunits. 160 65

The fourth member of mammalian beta-type phospholipase C isozymes, PLC-beta 4, was recently purified from bovine retina, and the corresponding cDNA was cloned from rat brain and sequenced. PLC-beta 4 has now been shown to differ from the other three mammalian beta-type isozymes (PLC-beta 1, -beta 2, and -beta 3) in that it is selectively inhibited by ribonucleotides. The inhibition requires the 5'-phosphate and 2'-hydroxyl groups of ribose as well as the base moiety. Thus, deoxyribonucleotides and ribose 5-phosphate were not inhibitory. The monophosphate, diphosphate, and triphosphate nucleoside derivatives were all inhibitory, whereas cyclic nucleotides were ineffective. Purine nucleotides were more potent inhibitors than pyrimidine nucleotides; the 50% inhibitory concentrations were 20-30 microM for AMP and GMP, and 100-200 microM for UMP and CMP. Unlike the other beta-type isozymes, PLC-beta 4 contains the GX4GKS consensus sequence for the recognition of the phosphoryl group of nucleotides. In the absence of ribonucleotides, the specific activity of PLC-beta 4 toward phosphatidyl-inositol 4,5-bisphosphate was four to five times the average specific activity of PLC-beta 1 and PLC-beta 3. Thus, nucleotide-dependent inhibition may serve to reduce the activity of PLC-beta 4 in the absence of a hormonal signal. The regulation of PLC-beta 4 by G-proteins was also studied. Similar to the other three PLC-beta isozymes, PLC-beta 4 was activated by the alpha subunit of Gq but not by the transducin alpha subunit. However, unlike other PLC-beta isozymes, PLC-beta 4 was not responsive to activation by G beta gamma subunits.
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PMID:Regulation of phospholipase C-beta 4 by ribonucleotides and the alpha subunit of Gq. 792 27

Neuropeptide Y (NPY) significantly potentiates the constrictor actions of noradrenaline and ATP on blood vessels via a pertussis toxin (PTX)-sensitive mechanism involving Gi/o (alpha beta gamma) protein subunits (Gi/o, GTP-binding proteins sensitive to PTX). In Chinese hamster ovary K1 (CHO K1) cells expressing specific receptors for these neurotransmitters, stimulation of Gi/o protein-coupled receptors for NPY and other neurotransmitters can augment the Gq/11-coupled (Gq/11, GTP-binding proteins insensitive to PTX) alpha 1B adrenoceptor- or ATP receptor-induced arachidonic acid (AA) release and inositol phosphate (IP) production (early events which may precede vasoconstriction). In this study, we have assessed the role of G beta gamma subunits in the synergistic interaction between Gi/o- (NPY Y1, 5-hydroxytryptamine 5-HT1B, adenosine A1) and Gq/11- [ATP P2Y2 (P2U)]-coupled receptors on AA release by using the specific abilities of regions of the beta-adrenergic receptor kinase (beta ARK1 residues 495-689) and the transducin alpha subunit to associate with G-protein beta gamma subunit dimers and to act as G beta gamma subunit scavengers. Transient expression of beta ARK1(495-689) in CHO K1 cells heterologously expressing NPY Y1 receptors had no significant effect on the PTX-insensitive ability of ATP to stimulate AA release. Stimulation of NPY Y1 receptors (as well as the endogenous 5-hydroxytryptamine 5-HT1B receptor and the transiently expressed human adenosine A1 receptor) resulted in a PTX-sensitive augmentation of ATP-stimulated AA release, which was inhibited by expression of both G beta gamma subunit scavengers. Expression of beta ARK1(495-689) similarly inhibited NPY Y1 receptor augmentation of ATP-stimulated IP production (a measure of phospholipase C activity), a step thought to precede the NPY Y1 receptor-augmented protein kinase C-dependent AA release previously observed in these cells. These experiments demonstrate that G beta gamma subunits, as inhibited by two different G beta gamma scavengers, significantly contribute to the synergistic interaction between NPY Y1 Gi/o- and Gq/11-coupled receptor activity, and are required for the augmentation of IP production and AA release observed in this model cell system.
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PMID:Role of G-protein beta gamma subunits in the augmentation of P2Y2 (P2U)receptor-stimulated responses by neuropeptide Y Y1 Gi/o-coupled receptors. 935 46

We have shown previously that activation of endogenously expressed, Galphaq/11-coupled P2Y2 nucleotide receptors with UTP reveals an intracellular Ca2+ response to activation of recombinant, Galphai-coupled CXC chemokine receptor 2 (CXCR2) in human embryonic kidney cells. Here, we characterize further this cross talk and demonstrate that phospholipase C (PLC) and inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]-dependent Ca2+ release underlies this potentiation. The putative Ins(1,4,5)P3 receptor antagonist 2-aminoethoxydiphenyl borane reduced the response to CXCR2 activation by interleukin-8, as did sustained inhibition of phosphatidylinositol 4-kinase with wortmannin, suggesting the involvement of phosphoinositides in the potentiation. Against a Li+ block of inositol monophosphatase activity, costimulation of P2Y2 nucleotide receptors and CXCR2 caused phosphoinositide accumulation that was significantly greater than that after activation of P2Y2 nucleotide receptors or CXCR2 alone, and was more than additive. Thus, PLC activity, as well as Ca2+ release, was enhanced. In these cells, agonist-mediated Ca2+ release was incremental in nature, suggesting that a potentiation of Ins(1,4,5)P3 generation in the presence of coactivation of P2Y2 nucleotide receptors and CXCR2 would be sufficient for additional Ca2+ release. Potentiated Ca2+ signaling by CXCR2 was markedly attenuated by expression of either regulator of G protein signaling 2 or the Gbetagamma-scavenger Galphat1 (transducin alpha subunit), indicating the involvement of Galphaq and Gbetagamma subunits, respectively.
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PMID:Cross talk between P2Y2 nucleotide receptors and CXC chemokine receptor 2 resulting in enhanced Ca2+ signaling involves enhancement of phospholipase C activity and is enabled by incremental Ca2+ release in human embryonic kidney cells. 1297 84

We studied the functions of betagamma-subunits of G(i/o) protein using the Xenopus oocyte expression system. Isoproterenol (ISO) elicited cAMP production and slowly activating Cl(-) currents in oocytes expressing beta(2)-adrenoceptor and the protein kinase A-dependent Cl(-) channel encoded by the cystic fibrosis transmembrane conductance regulator (CFTR) gene. 5-Hydroxytryptamine (5-HT), [d-Ala(2), d-Leu(5)]-enkephalin (DADLE), and baclofen enhanced ISO-induced cAMP levels and CFTR currents in oocytes expressing beta(2)-adrenoceptor-CFTR and 5-HT(1A) receptor (5-HT(1A)R), delta-opioid receptor, or GABA(B) receptor, respectively. 5-HT also enhanced pituitary adenylate cyclase activating peptide (PACAP) 38-induced cAMP levels and CFTR currents in oocytes expressing PACAP receptor, CFTR and 5-HT(1A)R. The 5-HT-induced enhancement of G(s)-coupled receptor-mediated currents was abrogated by pretreatment with pertussis toxin (PTX) and coexpression of G transducin alpha (G(t)alpha). The 5-HT-induced enhancement was further augmented by coexpression of the Gbetagamma-activated form of adenylate cyclase (AC) type II but not AC type III. Thus betagamma-subunits of G(i/o) protein contribute to the enhancement of G(s)-coupled receptor-mediated responses. 5-HT and DADLE did not elicit any currents in oocytes expressing 5-HT(1A)R or delta-opioid receptor alone. They elicited Ca(2+)-activated Cl(-) currents in oocytes coexpressing these receptors with the Gbetagamma-activated form of phospholipase C (PLC)-beta2 but not with PLC-beta1. These currents were inhibited by pretreatment with PTX and coexpression of G(t)alpha, suggesting that betagamma-subunits of G(i/o) protein activate PLC-beta2 and then cause intracellular Ca(2+) mobilization. Our results indicate that betagamma-subunits of G(i/o) protein participate in diverse intracellular signals, enhancement of G(s)-coupled receptor-mediated responses, and intracellular Ca(2+) mobilization.
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PMID:Involvement of G protein betagamma-subunits in diverse signaling induced by G(i/o)-coupled receptors: study using the Xenopus oocyte expression system. 1515 2