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)

RGS (regulators of G protein signaling) proteins are GTPase activating proteins that inhibit signaling by heterotrimeric G proteins. All RGS proteins studied to date act on members of the Gialpha family, but not Gsalpha or G12alpha. RGS4 regulates Gialpha family members and Gqalpha. RGS2 (G0S8) is exceptional because the G proteins it regulates have not been identified. We report that RGS2 is a selective and potent inhibitor of Gqalpha function. RGS2 selectively binds Gqalpha, but not other Galpha proteins (Gi, Go, Gs, G12/13) in brain membranes; RGS4 binds Gqalpha and Gialpha family members. RGS2 binds purified recombinant Gqalpha, but not Goalpha, whereas RGS4 binds either. RGS2 does not stimulate the GTPase activities of Gsalpha or Gialpha family members, even at a protein concentration 3000-fold higher than is sufficient to observe effects of RGS4 on Gialpha family members. In contrast, RGS2 and RGS4 completely inhibit Gq-directed activation of phospholipase C in cell membranes. When reconstituted with phospholipid vesicles, RGS2 is 10-fold more potent than RGS4 in blocking Gqalpha-directed activation of phospholipase Cbeta1. These results identify a clear physiological role for RGS2, and describe the first example of an RGS protein that is a selective inhibitor of Gqalpha function.
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PMID:RGS2/G0S8 is a selective inhibitor of Gqalpha function. 940 22

Regulators of G protein signaling (RGS) proteins accelerate GTP hydrolysis by Galpha subunits, thereby attenuating signaling. RGS4 is a GTPase-activating protein for Gi and Gq class alpha subunits. In the present study, we used knockouts of Gq class genes in mice to evaluate the potency and selectivity of RGS4 in modulating Ca2+ signaling transduced by different Gq-coupled receptors. RGS4 inhibited phospholipase C activity and Ca2+ signaling in a receptor-selective manner in both permeabilized cells and cells dialyzed with RGS4 through a patch pipette. Receptor-dependent inhibition of Ca2+ signaling by RGS4 was observed in acini prepared from the rat and mouse pancreas. The response of mouse pancreatic acini to carbachol was about 4- and 33-fold more sensitive to RGS4 than that of bombesin and cholecystokinin (CCK), respectively. RGS1 and RGS16 were also potent inhibitors of Gq-dependent Ca2+ signaling and acted in a receptor-selective manner. RGS1 showed approximately 1000-fold higher potency in inhibiting carbachol than CCK-dependent signaling. RGS16 was as effective as RGS1 in inhibiting carbachol-dependent signaling but only partially inhibited the response to CCK. By contrast, RGS2 inhibited the response to carbachol and CCK with equal potency. The same pattern of receptor-selective inhibition by RGS4 was observed in acinar cells from wild type and several single and double Gq class knockout mice. Thus, these receptors appear to couple Gq class alpha subunit isotypes equally. Difference in receptor selectivity of RGS proteins action indicates that regulatory specificity is conferred by interaction of RGS proteins with receptor complexes.
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PMID:RGS proteins determine signaling specificity of Gq-coupled receptors. 992 Sep 1

Activation of protein kinase C (PKC) has been implicated as playing a key role in the pathogenesis of cardiac hypertrophy. This study investigates the response of several signal transduction proteins responsible for PKC activation during the transition from compensated pressure-overload hypertrophy (POH) to congestive heart failure (CHF). Pressure overload was produced on male, adult, Hartley strain guinea pigs using a ligature around the descending thoracic aorta. Sham-operated controls, POH, and CHF groups were identified based on left ventricular hypertrophy, pulmonary congestion, and isolated heart Langendorff mechanics. Quantitative immunoblotting revealed phospholipase C (PLC)-betaI and Galphaq were unchanged during POH and CHF, as were RGS2, RGS3, and RGS4 (regulators of G protein signaling, which are activators of intrinsic GTPase activity). Translocation of PKC-alpha, -epsilon, and -gamma from cytosolic to membranous fractions were significantly increased during POH and CHF. Cytosolic PKC activity was also elevated during POH. We conclude that differential PKC activation may be mediated by increases in Galphaq and PLC-betaI activity rather than upregulation of expression.
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PMID:PKC translocation without changes in Galphaq and PLC-beta protein abundance in cardiac hypertrophy and failure. 1060 Aug 49

The initial steps involved in mediating the transduction of PTH signal via its G protein-coupled receptors are well understood and occur through the activation of cAMP and phospholipase C pathways. However, the cellular and molecular mechanisms for subsequent receptor desensitization are less well understood. Recently, a new family of GTPase activating proteins known as regulators of G protein signaling (RGS), has been implicated in desensitization of several G protein-coupled ligand-induced processes. At present, it is not known whether any of the RGS proteins play a role in PTH signaling. Using the differential display method, we screened for genes that are selectively expressed after a single s.c. injection of human PTH (1-38) (8 microg/100 g) in osteoblast-enriched femoral metaphyseal spongiosa of young male rats (3-4 weeks old). We found and cloned one full-length complementary DNA that encodes a 211-amino acid RGS protein and shares 97% sequence identity with mouse and human RGS2. Based on sequence similarity, we have designated this clone as rat RGS2. Northern blot analysis confirmed that the expression of RGS2 messenger RNA (mRNA) is rapidly and transiently increased by human PTH (1-38) in both metaphyseal (4-to 5-fold) and diaphyseal (2- to 3-fold) bone, as well as in cultured osteoblast cultures (2- to 37-fold). In vitro, forskolin and dibutyryl cAMP similarly elevated RGS2 mRNA. In vivo, PTH analog (1-31) [which stimulates intracellular cAMP accumulation, PTHrP (1-34), and prostaglandin E2] induced RGS2 mRNA expression; whereas PTH analogs (3-34) and (7-34), which do not stimulate cAMP production, had no effect on expression. In tissue distribution analysis, RGS2 is widely expressed and was detected in all tissues examined (heart, spleen, liver, skeletal muscle, kidney, and testis), with significant expression in two nonclassical PTH-sensitive tissues: the brain, and the heart. After PTH injection, RGS2 mRNA expression was induced in rat bone but not in any of the other tissues examined. These findings demonstrate that RGS2 is regulated by PTH, prostaglandin E2, and PTHrP and that regulation by PTH in bone occurs via the cAMP pathway. Additionally, these results suggest the exciting possibility that increased RGS2 expression in osteoblasts may be one of the early events influencing PTH signaling.
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PMID:Dynamic regulation of RGS2 in bone: potential new insights into parathyroid hormone signaling mechanisms. 1061 20

G protein regulated inward rectifying potassium channels (GIRKs) are activated by G protein coupled receptors (GPCRs) via the G protein betagamma subunits. However, little is known about the effects of different GPCRs on the deactivation kinetics of transmitter-mediated GIRK currents. In the present study we investigated the influence of different GPCRs in the presence and absence of RGS proteins on the deactivation kinetics of GIRK channels by coexpressing the recombinant protein subunits in Xenopus oocytes. The stimulation of both G(i/o)- and G(q)-coupled pathways accelerated GIRK deactivation. GIRK currents deactivated faster upon stimulation of G(i/o)- and G(q)-coupled pathways by P(2)Y(2) receptors (P(2)Y(2)Rs) than upon activation of the G(i/o)-coupled pathway alone via muscarinic acetylcholine receptor M2 (M(2) mAChRs). This acceleration was found to be dependent on phospholipase C (PLC) and protein kinase C (PKC) activities and intracellular calcium. With the assumption that RGS2 has a higher affinity for Galpha(q) than Galpha(i/o), we demonstrated that the deactivation kinetics of GIRK channels can be differentially regulated by the relative amount of RGS proteins. These data indicate that transmitter-mediated deactivation of GIRK currents is modulated by crosstalk between G(i/o)- and G(q)-coupled pathways.
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PMID:Regulation of GIRK channel deactivation by Galpha(q) and Galpha(i/o) pathways. 1097 20

Many Regulators of G protein Signaling (RGS) proteins accelerate the intrinsic GTPase activity of G(ialpha) and G(qalpha)-subunits [i.e., behave as GTPase-activating proteins (GAPs)] and several act as G(qalpha)-effector antagonists. RGS3, a structurally distinct RGS member with a unique N-terminal domain and a C-terminal RGS domain, and an N-terminally truncated version of RGS3 (RGS3CT) both stimulated the GTPase activity of G(ialpha) (except G(zalpha)) and G(qalpha) but not that of G(salpha) or G(12alpha). RGS3 and RGS3CT had G(qalpha) GAP activity similar to that of RGS4. RGS3 impaired signaling through G(q)-linked receptors, although RGS3CT invariably inhibited better than did full-length RGS3. RGS3 potently inhibited G(qalpha)Q209L- and G(11alpha)Q209L-mediated activation of a cAMP-response element-binding protein reporter gene and G(qalpha)Q209L induced inositol phosphate production, suggesting that RGS3 efficiently blocks G(qalpha) from activating its downstream effector phospholipase C-beta. Whereas RGS2 and to a lesser extent RGS10 also inhibited signaling by these GTPase-deficient G proteins, other RGS proteins including RGS4 did not. Mutation of residues in RGS3 similar to those required for RGS4 G(ialpha) GAP activity, as well as several residues N terminal to its RGS domain impaired RGS3 function. A greater percentage of RGS3CT localized at the cell membrane than the full-length version, potentially explaining why RGS3CT blocked signaling better than did full-length RGS3. Thus, RGS3 can impair Gi- (but not Gz-) and Gq-mediated signaling in hematopoietic and other cell types by acting as a GAP for G(ialpha) and G(qalpha) subfamily members and as a potent G(qalpha) subfamily effector antagonist.
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PMID:RGS3 is a GTPase-activating protein for g(ialpha) and g(qalpha) and a potent inhibitor of signaling by GTPase-deficient forms of g(qalpha) and g(11alpha). 1099 41

RGS proteins (regulators of G protein signalling) negatively regulate G protein function as GTPase-activating proteins (GAP) for G protein alpha-subunits. The existence of mRNAs of different size for some of the RGS proteins, e.g. RGS3, suggests that these proteins may exist in isoforms due to alternative splicing. We therefore investigated RGS3 mRNA and protein expression in different human tissues. Ribonuclease protection assays and Northern blot analysis showed two specific mRNAs for RGS3 (RGS3L, RGS3S) in human myocardium, suggesting an additional, N-terminally truncated form of approximately 168 aa. When expressed as a recombinant protein RGS3S was recognized at approximately 23 kDa by an antipeptide antiserum originally raised against an RGS2 sequence. In membranes of human tissues this antiserum detected specific signals for RGS3L (approximately 70 kDa), RGS2 (approximately 30 kDa) and a 25-kDa protein, most likely RGS3S. Both RGS3S mRNA and the 25 kDa protein were abundant in human heart, whereas expression in liver, brain and myometrium was much weaker. To characterize RGS3S functionally, single turnover GTPase, adenylyl cyclase (AC) and phospholipase C (PLC) activities were determined. Both recombinant RGS3S and RGS16 increased Pi release from Galphai1 by about 150% and increased GTP- and GTP plus isoprenaline-stimulated AC activity by 20-30% in human left ventricular myocardial membranes. Additionally, both RGS proteins reduced basal and endothelin-stimulated PLC activity in these membranes by about 40%. We conclude that an additional truncated form of RGS3 is expressed in the human heart. As described for the full-length protein, RGS3S negatively regulates the activity of Gi/o- and Gq-, but not Gs-subfamily members.
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PMID:Evidence for a short form of RGS3 preferentially expressed in the human heart. 1133 Mar 40

Recently we demonstrated that ginsenosides, the active ingredients of Panax ginseng, enhanced Ca(2+)-activated Cl(-) current in the Xenopus oocyte through a signal transduction mechanism involving the activation of pertussis toxin-insensitive G protein and phospholipase C (PLC). However, it has not yet been determined precisely which G protein subunit(s) and which PLC isoform(s) participate in the ginsenoside signaling. To provide answers to these questions, we investigated the changes in ginsenoside effect on the Cl(-) current after intraoocyte injections of the cRNAs coding various G protein subunits, a regulator of G protein signaling (RGS2), and G beta gamma-binding proteins. In addition, we examined which of mammalian PLC beta 1-3 antibodies injected into the oocyte inhibited the action of ginsenosides on the Cl(-) current. Injection of G alpha(q) or G alpha(11) cRNA increased the basal Cl(-) current recorded 48 h after, and it further prevented ginsenosides from enhancing the Cl(-) current, whereas G alpha(i2) and G alpha(oA) cRNA injection had no significant effect. The changes following G alpha(q) cRNA injection were prevented when G beta(1)gamma(2) and G alpha(q) subunits were co-expressed by simultaneous injection of the cRNAs coding these subunits. Injection of cRNA coding G alpha(q)Q209L, a constitutively active mutant that does not bind to G beta gamma, produced effects similar to those of G alpha(q) cRNA injection. The effects of G alpha(q)Q209L cRNA injection, however, were not prevented by co-injection of G beta(1)gamma(2) cRNA. Injection of the cRNA coding RGS2, which interacts most selectively with G alpha(q/11) among various identified RGS isoforms and stimulates the hydrolysis of GTP to GDP in active GTP-bound G alpha subunit, resulted in a severe attenuation of ginsenoside effect on the Cl(-) current. Finally, antibodies against PLC beta 3, but not -beta 1 and -beta 2, markedly attenuated the ginsenoside effect examined at 3-h postinjection. These results suggest that G alpha(q/11) coupled to mammalian PLC beta 3-like enzyme mediates ginsenoside effect on Ca(2+)-activated Cl(-) current in the Xenopus oocyte.
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PMID:G alpha(q/11) coupled to mammalian phospholipase C beta 3-like enzyme mediates the ginsenoside effect on Ca(2+)-activated Cl(-) current in the Xenopus oocyte. 1167 55

Receptor-mediated modulation of KCNQ channels regulates neuronal excitability. This study concerns the kinetics and mechanism of M1 muscarinic receptor-mediated regulation of the cloned neuronal M channel, KCNQ2/KCNQ3 (Kv7.2/Kv7.3). Receptors, channels, various mutated G-protein subunits, and an optical probe for phosphatidylinositol 4,5-bisphosphate (PIP2) were coexpressed by transfection in tsA-201 cells, and the cells were studied by whole-cell patch clamp and by confocal microscopy. Constitutively active forms of Galphaq and Galpha11, but not Galpha13, caused a loss of the plasma membrane PIP2 and a total tonic inhibition of the KCNQ current. There were no further changes upon addition of the muscarinic agonist oxotremorine-M (oxo-M). Expression of the regulator of G-protein signaling, RGS2, blocked PIP2 hydrolysis and current suppression by muscarinic stimulation, confirming that the Gq family of G-proteins is necessary. Dialysis with the competitive inhibitor GDPbetaS (1 mM) lengthened the time constant of inhibition sixfold, decreased the suppression of current, and decreased agonist sensitivity. Removal of intracellular Mg2+ slowed both the development and the recovery from muscarinic suppression. When combined with GDPbetaS, low intracellular Mg2+ nearly eliminated muscarinic inhibition. With nonhydrolyzable GTP analogs, current suppression developed spontaneously and muscarinic inhibition was enhanced. Such spontaneous suppression was antagonized by GDPbetaS or GTP or by expression of RGS2. These observations were successfully described by a kinetic model representing biochemical steps of the signaling cascade using published rate constants where available. The model supports the following sequence of events for this Gq-coupled signaling: A classical G-protein cycle, including competition for nucleotide-free G-protein by all nucleotide forms and an activation step requiring Mg2+, followed by G-protein-stimulated phospholipase C and hydrolysis of PIP2, and finally PIP2 dissociation from binding sites for inositol lipid on the channels so that KCNQ current was suppressed. Further experiments will be needed to refine some untested assumptions.
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PMID:Regulation of KCNQ2/KCNQ3 current by G protein cycling: the kinetics of receptor-mediated signaling by Gq. 1517 19

We studied modulation of current in human embryonic kidney tsA-201 cells coexpressing rat erg1 channels with M(1) muscarinic receptors. Maximal current was inhibited 30% during muscarinic receptor stimulation, with a small positive shift of the midpoint of activation. Inhibition was attenuated by coexpression of the regulator of G-protein signalling RGS2 or of a dominant-negative protein, G(q), but not by N-ethylmaleimide or C3 toxin. Overexpression of a constitutively active form of G(q) (but not of G(13) or of G(s)) abolished the erg current. Hence it is likely that G(q/11), and not G(i/o) or G(13), mediates muscarinic inhibition. Muscarinic suppression of erg was attenuated by chelating intracellular Ca(2+) to < 1 nm free Ca(2+) with 20 mm BAPTA in the pipette, but suppression was normal if internal Ca(2+) was strongly clamped to a 129 nm free Ca(2+) level with a BAPTA buffer and this was combined with numerous other measures to prevent intracellular Ca(2+) transients (pentosan polysulphate, preincubation with thapsigargin, and removal of extracellular Ca(2+)). Hence a minimum amount of Ca(2+) was necessary for the inhibition, but a Ca(2+) elevation was not. The ATP analogue AMP-PCP did not prevent inhibition. The protein kinase C (PKC) blockers staurosporine and bisindolylmaleimide I did not prevent inhibition, and the PKC-activating phorbol ester PMA did not mimic it. Neither the tyrosine kinase inhibitor genistein nor the tyrosine phosphatase inhibitor dephostatin prevented inhibition by oxotremorine-M. Hence protein kinases are not needed. Experiments with a high concentration of wortmannin were consistent with recovery being partially dependent on PIP(2) resynthesis. Wortmannin did not prevent muscarinic inhibition. Our studies of muscarinic inhibition of erg current suggest a role for phospholipase C, but not the classical downstream messengers, such as PKC or a calcium transient.
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PMID:Muscarinic modulation of erg potassium current. 1523 86


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