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)

Sheep anterior-pituitary cells permeabilized with Staphylococcus aureus alpha-toxin were used to investigate the role of cyclic AMP (cAMP) in exocytosis of luteinizing hormone (lutropin, LH) under conditions where the intracellular free Ca2+ concentration ([Ca2+]free) is clamped by Ca2+ buffers. At resting [Ca2+]free (pCa 7), cAMP rapidly stimulated LH exocytosis (within 5 min) and continued to stimulate exocytosis for at least 30 min. When cAMP breakdown was inhibited by 3-isobutyl-1-methylxanthine (IBMX), the concentration giving half-maximal response (EC50) for cAMP-stimulated exocytosis was 10 microM. cAMP-stimulated exocytosis required millimolar concentrations of MgATP, as has been found with Ca2(+)- and phorbol-ester-stimulated LH exocytosis. cAMP caused a modest enhancement of Ca2(+)-stimulated LH exocytosis by decreasing in the EC50 for Ca2+ from pCa 5.6 to pCa 5.9, but had little effect on the maximal LH response to Ca2+. Activation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate (PMA) dramatically enhanced cAMP-stimulated LH exocytosis by both increasing the maximal effect 5-7-fold and decreasing the EC50 for cAMP to 3 microM. This synergism between cAMP and PMA was further augmented by increasing the [Ca2+]free. Gonadotropin-releasing hormone (gonadoliberin, GnRH) stimulated cAMP production in intact pituitary cells. Since GnRH stimulation is reported to activate PKC and increase the intracellular [Ca2+]free, our results suggest that a synergistic interaction of the cAMP, PKC and Ca2+ second-messenger systems is of importance in the mechanism of GnRH-stimulated LH exocytosis.
...
PMID:Cyclic AMP stimulates luteinizing-hormone (lutropin) exocytosis in permeabilized sheep anterior-pituitary cells. Synergism with protein kinase C and calcium. 170 Aug 98

Previous studies have demonstrated enhanced phosphorylation of phospholipase C-tau (PLC-tau), a key regulatory enzyme in phosphoinositide metabolism, in cells treated with platelet-derived growth factor (PDGF) and epidermal growth factor, both of which act via specific receptor tyrosine kinases. Our studies on BALB/c-3T3 cells show that agents that promote cellular cyclic AMP accumulation also increase the phosphorylation, specifically the serine phosphorylation, of this enzyme. Increased phosphorylation of PLC-t (2-3-fold) was evident within 5-10 min of addition of isobutylmethylxanthine (IBMX) and either cholera toxin or forskolin to cells, and persisted for at least 3 h. Treatment of cells with cyclic AMP agonists also enhanced, with similar kinetics, the phosphorylation of a 76 kDa protein co-precipitated by anti-PLC-tau monoclonal antibodies. Brief exposure of cells to cholera toxin/IBMX or forskolin/IBMX decreased inositol phosphate formation induced by the GTP-binding protein (G-protein) activator aluminium fluoride by approx. 50%, but was without effect on PDGF-stimulated inositol phosphate formation. These findings suggest that PLC-tau, and perhaps the 76 kDa co-precipitated protein, are substrates of cyclic AMP-dependent protein kinase in BALB/c-3T3 cells: however, the lack of effect of cyclic AMP elevation on PDGF-stimulated inositol phosphate formation indicates that the intrinsic activity of PLC-tau is unaltered by cyclic AMP-mediated phosphorylation.
...
PMID:Cyclic AMP agonists induce the phosphorylation of phospholipase C-tau and of a 76 kDa protein co-precipitated by anti-(phospholipase C-tau) monoclonal antibodies in BALB/c-3T3 cells. Relationship to inositol phosphate formation. 170 22

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.
...
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

1. Intracellular mechanisms and second messengers involved in chloride current activation by intracellular GTP gamma S (guanosine 5'-O-(3-thiotriphosphate] in bovine chromaffin cells were studied using the whole-cell patch-clamp technique combined with measurements of intracellular calcium [Ca2+]i. 2. No correlation between the time of current activation and the appearance of [Ca2+]i transients was observed; intracellular introduction of sufficient EGTA (10 mM) to suppress the [Ca2+]i transients did not affect the current activation by GTP gamma S. 3. The cyclic nucleotides, cyclic AMP or cyclic GMP, did not activate the current when introduced intracellularly (50-250 microM). The ability of GTP gamma S to activate the current decreased when cyclic GMP (250 microM), together with MgATP (2 mM), was added to the perfusate. 4. Neomycin (0.5-1 mM), a presumed inhibitor of phospholipase C effectively prevented the current activation by GTP gamma S but it did not prevent [Ca2+]i transients. 5. Modulation of protein kinase C activity using specific inhibitors (H-7, 300 microM; polymyxin B, 400 U/ml) or activators (phorbol ester PMA, 100 nM, 20-90 min at 37 degrees C) did not affect the current activation by GTP gamma S nor did it cause current activation in the absence of GTP gamma S. 6. Activation of the current by GTP gamma S could be prevented by incubating the cells for 10-15 min with 2.5 microM p-bromophenacyl bromide (p-BPB), an inhibitor of phospholipase A2 activity. Exogenous arachidonic acid (5-10 microM), applied extracellularly or intracellularly, neither activated the current itself nor did it interfere with its activation by GTP gamma S. 7. Activation of the current by GTP gamma S could also be prevented by incubating the cells with 1 microM-nordihydroguaiaretic acid (NDGA), an inhibitor of lipoxygenase, but not with indomethacin (2 microM), an inhibitor of cyclo-oxygenase pathway of arachidonic acid metabolism. 8. It is suggested that chloride current activation by GTP gamma S in bovine chromaffin cells involves G protein-mediated stimulation of phospholipase A2 activity and subsequent formation of lipoxygenase product(s) of arachidonic acid metabolism.
...
PMID:Second messengers mediating activation of chloride current by intracellular GTP gamma S in bovine chromaffin cells. 171 42

The effects of norepinephrine (NE), carbachol (CCh), NaF, 3-isobutyl-1-methylxanthine (IBMX), and high K+ concentration (80 mM) depolarization on inositol trisphosphate (IP3) accumulation, cyclic AMP (cAMP) formation, and contraction were investigated in the dilator and sphincter smooth muscles of the sympathetically denervated as well as the normal rabbit eye. (a) In the denervated dilator muscle, NE-stimulated IP3 production and contraction are enhanced. (b) In the sphincter muscle of rabbits that have undergone sympathetic denervation. CCh-stimulated IP3 production and contraction are attenuated. (c) The increase in tension by a maximal effective dose of NaF (209 mM) in the dilator was 12.5 and 18 mg of tension/mg wet weight in normal and denervated tissue, respectively, and in the sphincter was 33.8 and 15.2 mg of tension/mg wet weight in normal and denervated tissue, respectively. NaF had no effect on cAMP formation. (d) Addition of NE had no effect on cAMP formation in both the normal and denervated dilator, whereas basal and IBMX-induced cAMP formation increased. in the denervated sphincter over that of the normal tissue by 15 and 60%, respectively. (e) Isoproterenol (5 microM) increased cAMP formation in the normal and denervated sphincter by 47 and 91%, respectively. (f) Whereas CCh inhibits cAMP formation in the normal sphincter, it lost its inhibitory effect in the sphincter with denervation. (g) IBMX (0.1 mM) attenuated the CCh-stimulated IP3 production and contraction of the sphincter by approximately 30% of their respective controls. (h) High K+ concentration depolarization attenuated contraction in both dilator and sphincter muscles with denervation. These observations suggest that an increase in the level of cAMP in the iris sphincter due to sympathetic denervation could lead to inhibition of phospholipase C (or other target sites, such as phosphorylation of the muscarinic receptor, Gp protein itself, myosin light chain kinase, or the IP3 receptor), IP3 production, and contraction. In conclusion, we suggest that the supersensitivity and subsensitivity observed after surgical sympathetic denervation of the iris dilator and sphincter muscles, respectively, are caused by alterations in the efficiency of coupling, probably through the Gp proteins, between their respective receptors and the breakdown of polyphosphoinositides by phospholipase C. In addition, we propose that the sympathetic nervous system can regulate, through alterations in cAMP levels, the muscarinic stimulation of IP3 accumulation and contraction in the iris sphincter. These findings add further support to the hypothesis that there are reciprocal interactions between the cAMP and IP3-Ca2+ signaling systems and the contractile response in the iris smooth muscle.
...
PMID:Effects of surgical sympathetic denervation on myo-inositol trisphosphate production and contraction in the dilator and sphincter smooth muscles of the rabbit iris: evidence for interaction between the cyclic AMP and calcium signaling systems. 171 29

In GH(1)2C1 rat pituitary cells treated with 5-azacytidine, the stimulatory effects exerted by vasoactive intestinal peptide (VIP), the GTP analogue guanyl-5'-yl imidodiphosphate (Gpp(NH)p), 12-O-tetradecanoyl phorbol 13-acetate, cholera toxin and pertussis toxin on the membrane-bound adenylyl cyclase were almost completely abolished. The corresponding inhibitory effect of somatostatin was increased. Alterations in adenylyl cyclase responsiveness began at the end of the drug treatment, and were most pronounced on day 5 after removal of 5-azacytidine. The cells subsequently and completely recovered after 10 days in the absence of the drug. Measurements of cholera toxin- and VIP-enhanced cyclic AMP levels in intact cells confirmed these results, and VIP appeared to have no stimulatory effect on GH secretion after 5-azacytidine treatment. Down-regulation of G alpha s RNA also occurred on day 5 after cessation of drug treatment. ADP-ribosylation subsequent to stimulation with pertussis toxin was markedly increased, indicating an enhancement of G alpha i and/or G alpha o. Furthermore, both basal and Gpp(NH)p-stimulated phospholipase C activities were augmented by pre-exposure to 5-azacytidine. Treatment of GH(1)2C1 rat pituitary tumour cells with 5-azacytidine therefore causes a marked but temporary increase in the ratio of G alpha i/G alpha s protein levels.
...
PMID:Signal transduction alterations in GH(1)2C1 rat pituitary tumour cells following treatment with 5-azacytidine. 171 9

The mechanism of arachidonic acid (AA)-induced LH release was characterized using sheep pituitary cells in primary culture permeabilized with Staphylococcal alpha-toxin. In intact cells, exogenous AA evoked release of LH in a manner which was partially dependent on extracellular Ca2+. At similar concentrations, AA also caused cell permeabilization as monitored by efflux of [3H]2-deoxyglucose metabolites. In alpha-toxin-permeabilized cells where cytosolic Ca2+ was clamped at resting levels, AA retained its ability to cause LH release. Unlike the stimulation of exocytosis produced by Ca2+, phorbol ester or cyclic AMP, AA-evoked release was independent of ATP and was not inhibited by pretreatment with N-ethyl maleimide. These findings indicated that exogenous AA does not cause LH release by Ca2+ influx or mobilization or by activating protein kinase C. The results suggest that LH release induced by exogenous AA is probably due to its detergent-like properties, and does not represent true exocytosis.
...
PMID:Arachidonic acid-induced LH release is ATP-independent and insensitive to N-ethyl maleimide. 173 62

These experiments examined the mechanism by which phenylephrine enhances beta-adrenoceptor-stimulated cyclic AMP formation in rat hypothalamic and preoptic area slices. To this end we manipulated phospholipase C. phospholipase A2, and protein kinase C activity in slices and assessed the effects of these manipulations on phenylephrine augmentation of isoproterenol-stimulated cyclic AMP generation. Since previous work indicated that estrogen enhances the alpha 1-component of cyclic AMP formation, we examined slices from both gonadectomized and estrogen-treated animals. The alpha 1-antagonist prazosin eliminated phenylephrine augmentation of the beta-response, suggesting that alpha 1-adrenergic receptors mediate the potentiation of cyclic AMP formation. Inhibition of protein kinase C by H7 attenuated the alpha 1-augmentation of beta-stimulated cyclic AMP formation. Staurosporine, a more potent protein kinase C inhibitor, completely abolished the alpha 1-augmenting response. In addition, phenylephrine potentiation of the isoproterenol response was not observed if protein kinase C was first stimulated directly with a synthetic diacylglycerol (1-oleoyl-2-acetyl-sn-glycerol) or phorbol ester (phorbol 12,13-dibutyrate). Neomycin, an inhibitor of phospholipase C, decreased alpha 1-receptor enhancement of beta-stimulated cyclic AMP formation, whereas quinacrine, an inhibitor of phospholipase A2, did not. The data suggest that the postreceptor mechanism involved in alpha 1-adrenergic receptor potentiation of cyclic AMP generation in hypothalamic and preoptic area slices includes activation of phospholipase C and protein kinase C.
...
PMID:Protein kinase C and phospholipase C mediate alpha 1- and beta-adrenoceptor intercommunication in rat hypothalamic slices. 184 2

Agents which elevate cellular cAMP (prostaglandin E2, theophylline, and forskolin) or mimic cAMP action (dibutyryl cAMP) are known to inhibit human neutrophil activation (superoxide generation and secretion) by receptor-linked agonists such as formyl-methionyl-leucyl-phenylalanine (fMLP). Herein, we show that these agents also markedly inhibit fMLP-stimulated diradylglycerol generation (assayed by mass methods). The magnitude of inhibition correlated with the ability of a given agent or combination of agents to elevate cAMP. Both 1,2-diacylglycerol and 1-O-alkyl,2-acyl glycerol generation were affected. Effects on the latter species, as well as a lack of effect on fMLP-stimulated inositol phosphate release, implied that cAMP affected diradylglycerol generation from a source other than phospholipase C-dependent phosphoinositide hydrolysis, since phosphatidylinositols do not contain appreciable quantities of the 1-O-alkyl linkage. In cells in which the phosphatidylcholine pool was prelabeled using 1-O-[3H]octadecyl-2-lyso-sn-glycero-3-phosphocholine, prostaglandin E2 plus theophylline inhibited the fMLP-activated rapid generation of [3H]phosphatidic acid and its subsequent conversion to [3H]diradylglycerol, implying an effect at the level of phospholipase D. In the presence of ethanol, the fMLP-activated transphosphatidylation of [3H]phosphatidylcholine to generate [3H]phosphatidylethanol (a phospholipase D-dependent reaction) was also markedly inhibited. In contrast, when phorbol 12-myristate 13-acetate was used to activate cells, cAMP-related agents had no effect on phospholipase D activity, diradylglycerol generation, or superoxide generation. The data indicate an inhibitory effect of cyclic AMP on receptor-mediated phospholipase D activation at a site proximal to phospholipase D (e.g., the receptor or G protein). These studies provide a new example of "cross-talk" among signal transduction systems.
...
PMID:Cyclic AMP-elevating agents block chemoattractant activation of diradylglycerol generation by inhibiting phospholipase D activation. 184 76

Serotonin 5-HT1A receptors have been reported to be negatively coupled to muscarinic receptor-stimulated phosphoinositide turnover in the rat hippocampus. In the present study, we have investigated further the pharmacological specificity of this negative control and attempted to elucidate the mechanism whereby 5-HT1A receptor activation inhibits the carbachol-stimulated phosphoinositide response in immature or adult rat hippocampal slices. Various 5-HT1A receptor agonists were found to inhibit carbachol (10 microM)-stimulated formation of total inositol phosphates in immature rat hippocampal slices with the following rank order of potency (IC50 values in nM): 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (11) greater than ipsapirone (20) greater than gepirone (120) greater than RU 24969 (140) greater than buspirone (560) greater than 1-(m-trifluoromethylphenyl)piperazine (1,500) greater than methysergide (5,644); selective 5-HT1B, 5-HT2, and 5-HT3 receptor agonists were inactive. The potency of the 5-HT1A receptor agonists investigated as inhibitors of the carbachol response was well correlated (r = 0.92) with their potency as inhibitors of the forskolin-stimulated adenylate cyclase in guinea pig hippocampal membranes. 8-OH-DPAT (10 microM) fully inhibited the carbachol-stimulated formation of inositol di-, tris-, and tetrakisphosphate but only partially antagonized (-40%) inositol monophosphate production. The effect of 8-OH-DPAT on carbachol-stimulated phosphoinositide turnover was not prevented by addition of tetrodotoxin (1 microM), by prior destruction of serotonergic afferents, by experimental manipulations causing an increase in cyclic AMP levels (addition of 10 microM forskolin), or by changes in membrane potential (increase in K+ concentration or addition of tetraethylammonium). Prior intrahippocampal injection of pertussis toxin also failed to alter the ability of 8-OH-DPAT to inhibit the carbachol response. Carbachol-stimulated phosphoinositide turnover in immature rat hippocampal slices was inhibited by the protein kinase C activators phorbol 12-myristate 13-acetate (10 microM) and arachidonic acid (100 microM). Moreover, the inhibitory effect of 8-OH-DPAT on the carbachol response was blocked by 10 microM quinacrine (a phospholipase A2 inhibitor) but not by BW 755C (100 microM), a cyclooxygenase and lipoxygenase inhibitor. These results collectively suggest that 5-HT1A receptor activation inhibits carbachol-stimulated phosphoinositide turnover by stimulating a phospholipase A2 coupled to 5-HT1A receptors, leading to arachidonic acid release. Arachidonic acid could in turn activate a gamma-protein kinase C with as a consequence an inhibition of carbachol-stimulated phosphoinositide turnover. This inhibition may be the consequence of a phospholipase C phosphorylation and/or a direct effect on the muscarinic receptor.(ABSTRACT TRUNCATED AT 400 WORDS)
...
PMID:Potential mechanisms involved in the negative coupling between serotonin 5-HT1A receptors and carbachol-stimulated phosphoinositide turnover in the rat hippocampus. 184 78


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

---