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)

1. Membrane currents were recorded by a patch-clamp pipette technique in cultured cells from rat portal vein using the whole-cell mode. 2. Noradrenaline (NA, 10(-5) M) and phorbol-12,13-dibutyrate (PDBu, 10(-7) M) produced an increase in voltage-dependent inward current carried by barium (5 mM), but their effects were not additive. Calcium-activated chloride current was evoked by NA but not by PDBu. 3. The NA-induced increase in peak voltage-dependent inward current was inhibited by intracellular application of GDP-beta-S (10(-3) M) while the effect of PDBu was unchanged. GDP-beta-S blocked the NA-induced chloride current but had no effect on the caffeine-induced chloride current. 4. Inclusion of GTP-gamma-S (10(-5)-10(-4) M) in the pipette solution increased the voltage-dependent inward current and inhibited the NA- or PDBu-induced increase in peak current. GTP-gamma-S potentiated the effect of NA on calcium-activated chloride current. At higher concentrations (10(-3) M), GTP-gamma-S activated the chloride current and prevented the effects of NA or caffeine on this current. 5. The combination of 10(-5) M-aluminium chloride and 10(-2) M-sodium fluoride had an effect similar to that of high concentrations of GTP-gamma-S on both inward current and calcium-activated chloride current. In contrast, arachidonic acid (10(-3) M) had no effect on calcium and chloride conductances activated by NA. 6. Cells responded normally to NA after pre-treatment for 4-30 h with 10 micrograms ml-1 pertussis toxin (PTx). 7. It is concluded that the stimulation of calcium and chloride conductances by NA is mediated through activation of a PTx-insensitive GTP-binding protein. This effect may involve activation of phospholipase C enzyme and production of both D-myo-inositol 1,4,5-trisphosphate which depletes calcium stores and diacylglycerol which activates protein kinase C.
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PMID:GTP-binding proteins mediate noradrenaline effects on calcium and chloride currents in rat portal vein myocytes. 170 Jan 11

The localization of several GTP-binding regulatory proteins in teh apical membrane of intestinal epithelial cells has prompted us to investigate a possible role for G-proteins as modulators of apical Cl- channels. In membrane vesicles isolated from rat small intestine or human HT29-cl.19A colon carcinoma cells, the entrapment of guanosine 5'-O-(3-thiophosphate (GTP gamma S) led to a large increase in Cl- conductance, as evidenced by an increased 125I- uptake and faster SPQ quenching. The enhancement was observed in the presence, but not in the absence of the K+ ionophore valinomycin, indicating that the increased Cl- permeability is not secondary to the opening of K+ channels. The effect of GTP gamma S was counteracted by guanosine 5'-O-(2-thiophosphate (GDP beta S) and appeared to be independent of cytosolic messengers, including ATP, cAMP, and Ca2+, suggesting that protein phosphorylation and/or phospholipase C activation is not involved. Patch clamp analysis of apical membrane patches of HT29-cl.19A colonocytes revealed a GTP gamma S-activated, inwardly rectifying, anion-selective channel with a unitary conductance of 20 +/- 4 pS. No spontaneous channel openings were observed in the absence of GTP gamma S, while the open time probability (Po) increases dramatically to 0.81 +/- 0.09 upon addition with GTP gamma S. Since the electrophysiological characteristics and regulatory properties of this channel are markedly different from those of the more widely studied cAMP/protein kinase A-operated channel, we propose the existence of a separate Cl(-)-selective ion channel in the apical border of intestinal epithelial cells. Our results suggest an alternative regulatory pathway in transepithelial salt transport and a possible site for anomalous channel regulation as observed in cystic fibrosis patients.
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PMID:G-proteins mediate intestinal chloride channel activation. 170 25

Dual inhibitory and stimulatory actions of guanine nucleotides on luteinizing-hormone (LH) exocytosis were observed in primary sheep gonadotropes permeabilized with staphylococcal alpha-toxin. At resting cytosolic [Ca2+]free (pCa 7), 5'-[gamma-thio]triphosphate (GTP[S]) and guanosine 5'-[beta gamma-imido]triphosphate (p[NH]ppG) stimulated rapid LH exocytosis, which was maximal between 5 and 10 min. GTP[S] and p[NH]ppG had similar potencies (50% of maximum effect at 20-50 microM), but the effect of p[NH]ppG was more prolonged. Experiments carried out in the presence of saturating concentrations of phorbol 12-myristate 13-acetate (PMA), or in PMA-desensitized cells, suggested that stimulation by p[NH]ppG is mediated by a mechanism additional to protein kinase C (PKC) activation. Furthermore, p[NH]ppG stimulated LH exocytosis in the presence of saturating cyclic AMP (cAMP) concentrations, although its effect was less than additive. However, when both PMA and cAMP were present, p[NH]ppG did not stimulate a further increase in the rate of LH exocytosis. In contrast, pretreatment of cells with GTP[S] at low [Ca2+]free markedly inhibited subsequent responses to Ca2+, cAMP, PMA, and cAMP plus PMA. This inhibitory effect required lower GTP[S] concentrations than the stimulatory effect (50% inhibition at 1-10 microM), and was not observed with p[NH]ppG. A similar inhibition was observed with adenosine 5'-[gamma-thio]triphosphate, probably by its conversion into GTP[S]. These results suggest that the stimulatory actions of guanine nucleotides can be accounted for by the combined activation of PKC and generation of cAMP, resulting from activation of conventional signal-transducing GTP-binding proteins. The inhibitory effect of GTP[S] can be clearly distinguished and indicates the involvement of a distinct GTP-binding protein in exocytosis at a site distal to second-messenger generation.
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PMID:Inhibition of luteinizing-hormone exocytosis by guanosine 5'-[gamma-thio]triphosphate reveals involvement of a GTP-binding protein distal to second-messenger generation. 170 5

Substance P (SP) stimulates polyphosphoinositide breakdown in the rat anterior pituitary through an NK-1 receptor. In the present study we present evidence that the coupling between the SP-NK1 receptor complex and polyphosphoinositide-specific phospholipase C (PI-PLC) in rat anterior pituitary membranes may involve a mechanism consistent with a GTP-binding protein. The formation of inositol phosphates from [3H]myo-inositol-labelled anterior pituitary membranes induced by SP was potentiated by GTP and non-hydrolysable guanine nucleotides. The stimulatory effects of SP alone and SP plus GTP could be blocked by addition of GDP-beta-S (guanosine 5-O-(thiodiphosphate] in excess. Basal and SP plus guanine nucleotide-induced inositol phosphate formation were stimulated by fluoride, whereas the effect of SP alone was inhibited. Pretreatment of anterior pituitary membranes with sodium deoxycholate attenuated the inositol phosphate response elicited by GTP and GTP-gamma-S, whereas basal and SP-stimulated inositol phosphate production showed a peak at 1 mg sodium deoxycholate/ml. SP, fluoride and guanine nucleotide stimulatory effects on hydrolysis of polyphosphoinositide (PPI) were unaffected by pretreatment of anterior pituitary cells with cholera or pertussis toxin for 12h. Treatment of anterior pituitary membranes with cholera and pertussis toxin yielded [32P]ADP-ribosylation of two proteins with molecular masses of 45 and 41 kDa respectively. We conclude that SP coupling to PI-PLC through the NK1 receptor in the rat anterior pituitary involves a GTP-binding mechanism distinct from the G-proteins associated with adenylate cyclase, Gs and Gi.
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PMID:Substance P stimulation of polyphosphoinositide hydrolysis in rat anterior pituitary membranes involves a GTP-dependent mechanism. 171 80

Endothelins (ETs) are a family of vasoactive peptides with profound biological actions in diverse cell systems. Among its varied actions, ET stimulates phospholipase C (PLC) in cultured mesangial cells. We investigated the presence of specific ET receptors in rat mesangial cells in culture, and studied the role of GTP-binding proteins (G proteins) in coupling PLC to the endothelin receptor. [125I]ET binding was time- and temperature-dependent, and Scatchard analysis of saturation data showed a single class of high-affinity binding sites. Heterologous displacement with two related peptides, ET-3 and sarafotoxin (SFTX), revealed the presence of two binding sites for these isopeptides. Preincubation of cells with ET-1 reduced the receptor number without affecting Kd, and this effect was not prevented by protein kinase C inhibition or downregulation. We confirmed the presence of a 41- to 43-kDa pertussis toxin substrate in rat mesangial cell membranes in an ADP ribosylation assay. ET-1 inhibits and GDP beta S enhances toxin-catalyzed transfer of ADP-ribose to this substrate. ET-1 potentiated GTP gamma S-induced phosphatidylinositol (PI) hydrolysis in a concentration-dependent manner. In addition, pertussis toxin partially inhibited ET-stimulated PI hydrolysis in intact mesangial cells. Pertussis toxin also reduced the magnitude of ET-stimulated intracellular free calcium [( Ca2+ )i]. Thus, ET-1 binds to specific receptors on rat mesangial cells and activates PLC, in part, through a pertussis toxin-sensitive G-protein.
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PMID:Endothelin receptors and coupled GTP-binding proteins in glomerular mesangial cells. 172 39

Endothelin-1 (ET-1)- and lysophosphatidic acid (LPA)-stimulated PtdIns(4,5)P2 hydrolysis has been studied in Rat-1 fibroblasts. Although both agonists caused the dose-dependent accumulation of inositol phosphates, a number of differences were observed. LPA induced a transient increase in Ins(1,4,5)P3 mass which returned to basal levels within 90 s, whereas the response to ET-1 did not desensitize, with levels remaining at 3-4 times basal values for up to 15 min. Stimulated decreases in mass levels of PtdIns(4,5)P2 mirrored Ins(1,4,5)P3 formation for both agonists. Experiments with electropermeabilized cells demonstrated that the effects of both agonists are stimulated by a phospholipase C controlled by a guanine-nucleotide-binding regulatory protein; however, there are differences in the nature of these interactions. The inositol phosphate response to ET-1 is poorly potentiated by guanosine 5'-[gamma-thio]triphosphate (GTP[S]) and markedly inhibited by guanosine 5'-[beta-thio]diphosphate (GDP[S]), whereas that to LPA is potentiated by GTP[S] but is relatively insensitive to GDP[S]. In addition, LPA decreased the lag time for the onset of GTP[S]-stimulated [3H]InsP3 accumulation, whereas ET-1 was without effect. Phorbol 12-myristate 13-acetate treatment of the cells inhibited LPA-stimulated, but not ET-1-stimulated, inositol phosphate formation in both intact and permeabilized cells, suggesting that the site of protein kinase C-mediated phosphorylation may be blocked in ET-1-stimulated Rat-1 cells. The results indicate that the receptor-G-protein-phospholipase C interaction for the two agonists may not conform to the same model.
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PMID:Differences in the regulation of endothelin-1- and lysophosphatidic-acid-stimulated Ins(1,4,5)P3 formation in rat-1 fibroblasts. 176 24

Antibody-dependent cellular cytotoxicity is initiated when low affinity Fc receptors (Fc gamma R type III/CD16) on NK cells bind to sensitized (i.e., antibody coated) target cells. Fc gamma R cross-linkage induces the activation of phospholipase C (PLC), which hydrolyses membrane phosphoinositides, generating inositol-1,4,5-trisphosphate and sn-1,2-diacylglycerol as second messengers. However, the mechanism that couples Fc gamma R stimulation to PLC activation remains unknown. In this study, we investigated whether the Fc gamma R is coupled to PLC via a guanine nucleotide-binding (G) protein or an alternative pathway. Stimulation of electropermeabilized human NK cells with GTP gamma S induced inositol phosphate (IP) release, indicating the presence of a G protein-linked PLC activity in these cells. However, stimulation with both anti-Fc gamma R mAb and GTP gamma S provoked additive rather than synergistic increases in IP formation. Furthermore, exogenous GDP strongly inhibited GTP gamma S-stimulated IP release, but failed to inhibit the response to anti-Fc gamma R mAb stimulation. These results suggested GTP gamma S and anti-Fc gamma R mAb activated PLC through distinct regulatory mechanisms, and that Fc gamma R was not linked to PLC via a G protein. Hence, an alternative transduction mechanism for Fc gamma R-PLC coupling was considered. Antibody-mediated Fc gamma R cross-linkage was shown to rapidly stimulate tyrosine phosphorylation of multiple proteins in NK cells. Pretreatment with the tyrosine kinase inhibitor, herbimycin A, inhibited these phosphorylation events and disrupted the coupling between Fc gamma R ligation and PLC activation. These observations suggest that Fc gamma R in NK cell is coupled to PLC via a G protein-independent, but tyrosine kinase-dependent pathway.
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PMID:Fc gamma receptor signal transduction in natural killer cells. Coupling to phospholipase C via a G protein-independent, but tyrosine kinase-dependent pathway. 183 64

In permeabilized human T lymphocytes, phospholipase C (PLC)-mediated metabolism of polyphosphatidylinositols can be stimulated by triggering the T cell antigen receptor/CD3 antigen complex (Ti/CD3) with the CD3 antibody UCHT1 or by activation of G proteins with the non-hydrolyzable guanine nucleotide analogue, guanosine 5'-O-(3-thiotrisphosphate) (GTP[S]). Ti/CD3 induction of inositol phosphate production demonstrated no dependence on exogenous guanine nucleotides. Furthermore, Ti/CD3 stimulation did not influence the kinetics or dose-response of GTP[S]-induced inositol phosphate production, suggesting that the Ti/CD3 complex does not regulate guanine nucleotide exchange on the G protein pool stimulated by GTP[S]. These data indicate that the Ti/CD3 complex is not G protein-linked to PLC in a manner analogous to the G protein linkage of receptors to adenylate cyclase. However, the inhibitory guanine nucleotide, GDP, antagonizes not only GTP[S]-induced polyphosphatidylinositol hydrolysis but also UCHT1-induced inositol phosphate production. These data infer that a G protein can modulate the coupling of the Ti/CD3 complex to PLC and that there may be some "cross-talk" between Ti/CD3 and G protein PLC coupling mechanisms.
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PMID:An analysis of the role of guanine nucleotide binding proteins in antigen receptor/CD3 antigen coupling to phospholipase C. 184 78

We examined the possibility that, in addition to stimulation of guanylate cyclase (GC), atrial natriuretic peptide (ANP) also activates phospholipase C (PLC) in cultured rat inner medullary collecting tubule (RIMCT) cells. ANP (10(-12)M) causes marked release of inositol trisphosphate (IP3) at a concentration that does not stimulate GC. Concentrations of ANP that stimulate GC (greater than or equal to 10(-10) M) result in attenuated IP3 release. Similarly, exogenous dibutyryl guanosine 3',5'-cyclic monophosphate (10(-6) M) markedly inhibits the response to 10(-10) M ANP. Inhibition of cyclic nucleotide-dependent protein kinase by H 8, but not inhibition of protein kinase C by H 7, restores the response to 10(-8) and 10(-6) M ANP. Therefore, activation of cyclic nucleotide-dependent protein kinase inhibits ANP-stimulated PLC activity. Activation of protein kinase C by phorbol 12-myristate-13-acetate (PMA) decreases ANP-stimulated IP3 production. Pretreatment with H 7, but not H 8, prevents inhibition by PMA. To explore a potential role for G proteins, we examined the effect of guanine nucleotide analogues on ANP-stimulated IP3 production in saponin-permeabilized cells. ANP-stimulated IP3 production is enhanced by GTP gamma S and is inhibited by GDP beta S. Similarly, preincubation with pertussis toxin prevents ANP-stimulated IP3 release. We conclude that ANP stimulates PLC in RIMCT cells via a pertussis toxin-sensitive G protein. Stimulation of PLC is inhibited on activation of either cyclic nucleotide or Ca2+-phospholipid dependent protein kinases.
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PMID:ANP stimulates phospholipase C in cultured RIMCT cells: roles of protein kinases and G protein. 184 66

Heterotrimeric GTP-binding proteins from bovine brain were resolved by fast protein liquid chromatography chromatography using Mono Q columns. Two distinct forms of the protein Go were identified. Both forms had stochiometric amounts of alpha- and beta gamma-subunits. The a-subunits of both forms were recognized by an alpha o-specific antiserum, but not by any of the alpha i-specific antisera. The two forms showed distinct migration patterns on 9% sodium dodecyl sulfate-polyacrylamide gels containing 4-8 M urea gradients. Neither form comigrated with the recombinant alpha o1. Both the recombinant alpha o1 and the most abundant form of Go were recognized by an antiserum, H-660, against a peptide encoding amino acids 3-17 of alpha i2. H-660 has been shown previously to recognize alpha o and alpha i (Mumby, S. M., Pang, I. K., Gilman, A. G., and Sternweis, P. C. (1988) J. Biol. Chem. 263, 2020-2026). This more abundant form is called Go A most likely corresponds to the cloned alpha o1. The less abundant form, Go B, was not recognized by H-660. However, both forms of bovine brain Go were recognized by GC/2, an antiserum against the N-terminal region of alpha o1. Hence alpha oA and alpha oB may be different in their N terminus regions. Neither form of bovine brain Go was recognized by an antisera made to a peptide encoding the unique regions of the cloned alpha o2 from HIT cells (Hsu W. H., Rudolph, U., Sanford, J., Bertrand, P., Olate, J., Nelson, C., Moss, L.E., Boyd, A. E., III, Codina, J., and Birnbaumer, L. (1990) J. Biol. Chem. 265, 11220-11226). Go A and Go B have similar guanine nucleotide binding and release properties. Both release GDP within 1 min in the absence of added Mg2+. Both bind guanosine (GTP gamma S) rapidly as well. However Go A binds GTP gamma S about 2.5-fold faster than Go B, in the absence of added Mg2+ ion. Both forms of Go as well as the recombinant alpha o (alpha o1) can increase muscarinic stimulation of inositol trisphosphate-mediated Cl- current in Xenopus oocytes. These data indicate that we have identified two structurally distinct forms of Go that have different guanine nucleotide binding properties and are capable of functioning in the receptor-regulated phospholipase C pathway in Xenopus oocytes.
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PMID:Two forms of the bovine brain Go that stimulate the inositol trisphosphate-mediated Cl- currents in Xenopus oocytes. Distinct guanine nucleotide binding properties. 185 56


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