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)

The effects of serotonin on migration of cultured rat aortic smooth muscle cells (SMC) were studied to clarify the role of this substance in the pathogenesis of atherosclerosis. Serotonin alone did not stimulate SMC migration but stimulated it at physiological concentrations in the presence of other migration factors such as SMC-derived migration factor, platelet-derived migration factor and fibronectin. Checker-board analysis revealed that the serotonin effect was chemotactic. Moreover, serotonin effects were completely abolished by a selective inhibitor of the 5-HT2 receptor (MCI-9042), indicating that serotonin effects were mediated through the 5-HT2 receptor pathway. Finally, serotonin effects were also abolished by a phospholipase C inhibitor, U73122, suggesting that the 5-HT2 receptor mediated signal of serotonin was transduced by PLC. The results suggest that platelet-derived serotonin plays some role in the SMC dominant neointima formation.
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PMID:Serotonin (5-hydroxytryptamine, 5-HT) enhances migration of rat aortic smooth muscle cells through 5-HT2 receptors. 924 58

Smooth muscle cell-like mesangial cells play an important role in the regulation of glomerular blood flow and are involved in renal inflammatory reactions, thereby interacting with circulating cells. The platelet products serotonin (5-HT) and ATP induce similar, e.g. mitogenic, effects in mesangial cells, but differentially activate and induce inflammation-related genes. To get an insight into intracellular signaling steps, a very early step in the signaling cascade, the biphasic Ca2+ signal elicited by 5-HT and ATP in rat mesangial cells was investigated. Both phases of the Ca2+ signal, release from internal stores as well as influx of extracellular Ca2+, were dependent on phospholipase C activation as shown by the specific inhibitor U73122 (complete inhibition at 10 microM U73122). There was no evidence for voltage-gated L-type channels in these cells, suggesting that Ca2+ influx was mediated by Ca2+ release-activated channels. The L-type channel blocker verapamil, however, dose-dependently (0.1-10 microM) and specifically inhibited 5-HT-elicited Ca2+ signals by interference with binding of 5-HT to 5-HT2A receptors. 5-HT-mediated Ca2+ release was reduced by 80% when protein kinase C was activated by the phorbolester TPA (0.1 microM). Interaction of 5-HT2A receptors with phospholipase C was also inhibited by genistein (30% at 5 microM; 100% at 50 microM), an inhibitor of tyrosine kinases. Binding of 5-HT to its receptor reduced subsequent ATP-mediated Ca2+ signaling. The cross talk between the receptors was sensitive to genistein. ATP-mediated Ca2+ signaling was attributed to different types of P2y receptors and/or multiple G-proteins coupled, because the signal was partially inhibited by pertussis toxin (50%). In accordance, modulation of the ATP-mediated signaling by phosphorylation was less tightly controlled than 5-HT-mediated Ca2+ release. These data indicate that although the Ca2+ responses elicited by the two stimuli are comparable, interactions between receptors, G-proteins and target enzymes are regulated differentially.
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PMID:Mechanisms of serotonin-induced Ca2+ responses in mesangial cells. 927 31

Serotonin (5-hydroxytryptamine; 5-HT) 5-HT2A and 5-HT2C receptors belong to the class of phosphoinositide-specific phospholipase C (PLC)-linked receptors. Conditions were established for measuring 5-HT2A-linked and 5-HT2C-linked PLC activity in membranes prepared from previously frozen rat frontal cortex and caudate. In the presence of Ca2+ (300 nM) and GTPgammaS (1 microM), 5-HT increased PLC activity in caudate membranes. Pharmacological analysis using the selective 5-HT2A antagonist, spiperone, and the nonselective 5-HT(2A/2C) antagonist, mianserin, demonstrated that over half of the 5-HT-stimulated PLC activity was due to stimulation of 5-HT2C receptors as opposed to 5-HT2A receptors. Radioligand binding assays with [3H]RP 62203 and [3H]mesulergine were used to quantify 5-HT2A and 5-HT2C sites, respectively, in caudate. From these data, the Bmax for caudate 5-HT2A sites and 5-HT2C sites was 165.4 +/- 9.7 fmol/mg of protein and 49.7 +/- 3.3 fmol/mg of protein, respectively. In contrast to that in caudate, PLC activity in frontal cortex was stimulated by 5-HT in a manner that was inhibited by the 5-HT2A-selective antagonists, spiperone and ketanserin. Taken together, the results indicate that 5-HT2A- and 5-HT2C-linked PLC activity can be discerned in brain regions possessing both receptor subtypes using membranes prepared from previously frozen tissue. More importantly, significant 5-HT2C-mediated phosphoinositide hydrolysis was observed in caudate, despite the relatively low density of 5-HT2C sites. The significance of these observations with respect to the physiological function of 5-HT2C receptors is discussed.
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PMID:The serotonin 5-HT2C receptor is a prominent serotonin receptor in basal ganglia: evidence from functional studies on serotonin-mediated phosphoinositide hydrolysis. 932 73

In this study, we demonstrate that astroglial 5-HT2A receptors are linked to the mobilization of polyunsaturated fatty acids (PUFA). Stimulation of C6 glioma cells, prelabeled with [3H]arachidonate (AA, 20:4n6) and [14C]docosahexaenoate (DHA, 22:6n3), with serotonin and the 5-HT(2A/2C) receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) resulted in the mobilization of both [3H] and [14C] into the supernatant of the cell monolayers. The increased radioactivity in the supernatant was mainly associated with free fatty acids. Experiments using inhibitors of phosphoinositide-specific phospholipase C and PLA2, inhibited the DOI-stimulated mobilization of AA and DHA, suggesting the involvement of both phospholipases. Ketanserin (1 microM), a 5-HT(2A/2C) receptor antagonist, and MDL 100,907 (R(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-pi peridine-methanol) (1 microM), a highly selective antagonist for 5-HT2A receptors, significantly decreased the DOI-stimulated release of AA and DHA. These results indicate that the 5-HT2A receptor is coupled to the mobilization of PUFA. The release of AA and DHA in response to serotonin may represent a mechanism through which astroglia provide these polyunsaturated fatty acids to neurons.
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PMID:Mobilization of arachidonate and docosahexaenoate by stimulation of the 5-HT2A receptor in rat C6 glioma cells. 936 99

Vascular 5-Hydroxytryptamine2A (5-HT2A) receptor signaling and contraction has been associated with the activation of L-type calcium channels, phospholipase C (PLC) and, as we previously demonstrated, tyrosine kinase activation. We hypothesize the 5-HT2A receptor activates all three pathways independently to elicit contraction and that one of the tyrosine kinases activated by 5-HT is mitogen-activated protein kinase kinase (MEK). Endothelium-denuded rat thoracic aorta was mounted into isolated tissue baths for measurement of isometric contractile force. 5-HT, alpha-methyl-5-HT and 2,5-dimethoxy-4-iodoamphetamine all contracted the rat aorta, whereas the 5-HT2A receptor antagonist ketanserin (30 nM) blocked contraction to 5-HT. The tyrosine kinase inhibitor genistein (5 microM) shifted contraction to 5-HT, alpha-methyl-5-HT and DOI approximately 10-fold to the right, whereas daidzein (5 microM), the inactive isomer of genistein, was unable to shift 5-HT-induced contraction. PD098059 (10 microM), an inhibitor of MEK, shifted contraction to 5-HT approximately 7-fold to the right. We next examined the integration of tyrosine kinase activation in 5-HT2A receptor signaling. 5-HT-induced contraction was reduced individually by the PLC inhibitor 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (NCDC; 100 microM) or the Ca++ channel inhibitor nifedipine (50 nM); the remaining response to 5-HT was reduced by further addition of either genistein or PD098059. When nifedipine and NCDC were used in combination, a part of the contraction to 5-HT remained: this contraction was further reduced by genistein or PD098059. In cultured aortic smooth muscle cells, 5-HT (0.01-100 microM) stimulated tyrosyl-phosphorylation of 42- and 44-kDa proteins identified as Erk MAPKs; this phosphorylation was reduced by PD098059 (10 microM). Neither nifedipine nor NCDC reduced 5-HT (1 microM)-stimulated Erk MAPK tyrosyl-phosphorylation, but the combination of nifedipine, NCDC and PD098059 abolished 5-HT (1 microM)-stimulated Erk MAPK tyrosyl-phosphorylation. Taken together, these studies indicate that stimulation of a vascular 5-HT2A receptor activates Ca++ channels and PLC as well as MEK to cause rat aortic contraction and that MEK activation is at least partially independent of the two pathways classically associated with 5-HT2A receptors.
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PMID:Integration of mitogen-activated protein kinase kinase activation in vascular 5-hydroxytryptamine2A receptor signal transduction. 943 97

Mechanisms underlying the 5-HT2A receptor induction of intracellular Ca2+ mobilization and Ca2+ influx in type I astroglial cells in primary culture from newborn rat cerebral cortex were evaluated. The 5-HT-evoked Ca(2+)-transients, inhibited by the 5-HT2A antagonists ketanserin or 4-(4-fluorobenzoyl)-1-(4-phenylbutyl) piperidine oxalate, consisted of an initial peak caused by inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ release from internal stores, and a second sustained part which was due to Ca2+ transport over the plasma membrane. The responses were pertussis toxin-insensitive, suppressed by the phospholipase C inhibitor neomycin and were inhibited by the Ca(2+)-ATPase inhibitor thapsigargin. Furthermore, the responses were inhibited by the IP3 receptor antagonist heparin. When the second sustained part of the 5-HT-evoked response was studied, it was concluded that Ca2+ influx was not a result of opening of voltage operated calcium channels of either L, N or T-type. Instead it appeared that Ca2+ entered the cells through specialized voltage independent Ca2+ channels which were dependent of the IP3 production and subsequent Ca2+ release from internal stores. From this, we conclude that 5-HT opens Ca2+ channels in astrocytes which closely resemble depletion-operated Ca2+ channels (DOCCs).
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PMID:Stimulation of 5-HT2A receptors on astrocytes in primary culture opens voltage-independent Ca2+ channels. 954 27

Signaling pathways responsible for serotonin (5-HT)-mediated induction of early response genes prostaglandin G/H synthase-2 (PGHS-2, cyclooxygenase-2) and egr-1 were investigated in rat mesangial cells. Gene induction by 5-HT was dependent on 5-HT2A receptors that were pertussis toxin insensitive indicating coupling to a G-protein of the Gq family. Binding of 5-HT to this receptor activates phosphatidylinositol-specific phospholipase C (PLC) and release of Ca2+ from internal stores, but this activation was not related to PGHS-2 mRNA expression. Similarly, PI-3 kinase was not involved in 5-HT signaling. Instead, inhibition of phosphatidylcholine-specific PLC interfered with PGHS-2 and egr-1 mRNA induction, suggesting this enzyme as a link between 5-HT2A receptors and protein kinase C, an essential part of 5-HT-mediated signaling. The MAP kinase pathway was identified as common signaling pathway of 5-HT or phorbol ester-induced gene expression. Increase of intracellular cAMP by forskolin or dibutyryl cAMP did not induce PGHS-2 or egr-1 mRNA expression by itself, but strongly inhibited 5-HT-mediated mRNA induction. PGHS-2 mRNA and protein induction by 5-HT was also abolished by chelation of Ca2+ ions by EGTA, suggesting involvement of Ca2+-dependent enzymes. In contrast, egr-1 mRNA expression was superinduced in the presence of EGTA. Induction of Egr-1 protein was not changed by EGTA hinting to Ca2+-sensitive posttranscriptional steps. Activation of the Gq-coupled 5-HT2A receptor thus leads to the expression of the early response genes PGHS-2 and egr-1, using common as well as differing signaling elements that allow differential regulation of the expression of these genes that are functionally related to renal hemodynamics and proliferation of mesangial cells, respectively.
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PMID:Signaling pathways mediating induction of the early response genes prostaglandin G/H synthase-2 and egr-1 by serotonin via 5-HT2A receptors. 957 79

There are many examples of a single receptor coupling directly to more than one cellular signal transduction pathway. Although traditional receptor theory allows for activation of multiple cellular effectors by agonists, it predicts that the relative degree of activation of each effector pathway by an agonist (relative efficacy) must be the same. In the current experiments, we demonstrate that agonists at the human serotonin2A (5-HT2A) and 5-HT2C receptors activate differentially two signal transduction pathways independently coupled to the receptors [phospholipase C (PLC)-mediated inositol phosphate (IP) accumulation and phospholipase A2 (PLA2)-mediated arachidonic acid (AA) release]. The relative efficacies of agonists differed depending on which signal transduction pathway was measured. Moreover, relative to 5-HT, some 5-HT2C agonists (e.g., 3-trifluoromethylphenyl-piperazine) preferentially activated the PLC-IP pathway, whereas others (e.g., lysergic acid diethylamide) favored the PLA2-AA pathway. In contrast, when two dependent responses were measured (IP accumulation and calcium mobilization), agonist relative efficacies were not different. These data strongly support the hypothesis termed "agonist-directed trafficking of receptor stimulus" recently proposed by Kenakin [Trends Pharmacol Sci 16:232-238 (1995)]. Concentration-response curves to 5-HT2C agonists were fit well by a three-state model of receptor activation, suggesting that two active receptor states may be sufficient to explain pathway-dependent agonist efficacy. Rational drug design that optimizes preferential effector activity within a group of receptor-selective drugs holds the promise of increased selectivity in clinically useful agents.
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PMID:Effector pathway-dependent relative efficacy at serotonin type 2A and 2C receptors: evidence for agonist-directed trafficking of receptor stimulus. 965 94

Phosphorylation of the inactivation gate of a K+ channel (Kv3.4) by protein kinase C (PKC) slows rapid N-type inactivation. To demonstrate that such an effect could occur under more physiological conditions, Kv3.4 and a metabotropic serotonin (5-HT) receptor were coexpressed in Xenopus oocytes. Application of 5-HT 10 microM to these oocytes produced two main effects: 1) Enhanced activity of endogenous Ca(++)-dependent Cl- channels; and 2) Kv3.4 currents exhibited significantly slower inactivation than the control currents (time constants at +50 mV: 7.1 +/- 0.6 ms and 14.7 +/- 3 ms, before and after 5-HT, respectively). These results are consistent with the presence of receptor-coupled activation of phospholipase C. 5-HT had little or no effect on Kv3.4 current kinetics when four N-terminal serines were mutated to alanine. Peak currents exhibited, however, a slow run-down. This study demonstrates that physiological activation of PKC may regulate K+ channel inactivation by a direct action.
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PMID:Receptor-coupled regulation of K+ channel N-type inactivation. 971 29

We have investigated the possibility that the synthesis/accumulation of neurosteroids, i.e., brain-produced steroids putatively endowed with modulatory actions in the CNS, is regulated by monoaminergic receptor-mediated mechanisms. In minces of rat brain cortex, L-ascorbic acid concentration-dependently (0.07-1.0 mM) increases the levels of pregnenolone, allotetrahydrodeoxycorticosterone, and dehydroepiandrosterone. This effect of L-ascorbic acid is region-dependent: in hippocampus, progesterone and allopregnanolone are also increased, whereas dehydroepiandrosterone is unchanged, and in corpus striatum only progesterone is increased significantly. 5-Hydroxytryptamine (10 microM), 1-(3-chlorophenyl)piperazine (1.0 microM), and 5-methoxytryptamine (0.4 microM) mimic the effect of L-ascorbic acid, whereas a pretreatment with p-chlorophenylalanine (400 mg/kg i.p., 2 days) reduces the amplitude of the L-ascorbic acid effect on brain cortical neurosteroids. The effect of L-ascorbic acid is blocked by the nonselective serotonin antagonists methiothepin, clozapine, methysergide, and pizotifen, but not mesulergine, spiperone, MDL 72222, and DL-propranolol, nor by the catecholaminergic receptor antagonists prazosin and S(-)-sulpiride. L-Ascorbic acid is not additive with dibutyryl-cyclic AMP and, furthermore, the inhibition of adenylate cyclase by MDL 12330A, but not of phospholipase C by U-73122, markedly attenuates the L-ascorbic acid-induced increase of pregnenolone in rat brain cortical minces. Together these data suggest that L-ascorbic acid plays a role in the modulation of neurosteroidogenesis, presumably by favoring the activation of the purported serotonin type 6 receptor by endogenous serotonin.
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PMID:Modulation of neurosteroid synthesis/accumulation by L-ascorbic acid in rat brain tissue: inhibition by selected serotonin antagonists. 972 35


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