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)

Previous studies have demonstrated that although both mammalian and avian erythrocytes express an inducible inositol bisphosphate-specific phospholipase C, only the latter possess the guanine nucleotide-binding protein (Gp) that regulates this activity. In confirmation of previous reports, turkey erythrocyte plasma membranes responded to guanosine 5'-0-(3-thio)triphosphate (GTP-gamma-S) and fluoroaluminates with hydrolysis of phosphoinositides, release of inositol phosphates, and generation of diacylglycerol, whereas human erythrocyte plasma membranes exhibited no such changes when incubated with known activators of guanine nucleotide regulatory proteins. We next contrasted responses of intact turkey and human erythrocytes to fluoroaluminates to develop a model to investigate the cellular effects of Gp activation. When turkey erythrocytes were exposed to fluoroaluminates, cellular levels of diacylglycerol and phosphatidic acid rapidly increased as phosphoinositides were hydrolyzed. The alterations in the lipid composition of turkey erythrocytes effected by fluoroaluminates were remarkable; phosphatidic acid levels increased over 30-fold, whereas levels of polyphosphoinositides were decreased to less than 10% of those present before stimulation. In contrast, fluoroaluminates caused only minor alterations in the diacylglycerol and phospholipid content of intact human erythrocytes. To define the role of inositol-specific phospholipase C activation in the transmembrane conveyance of extracellular Ca++, we compared the influx of extracellular Ca++ in human and turkey erythrocytes exposed to fluoroaluminates. Fluoroaluminates initiated a sustained influx of extracellular 45Ca++ into turkey, but not human, erythrocytes. These results provide strong support for the hypothesis that Gp activation results in an influx of calcium into stimulated cells. Moreover, the data demonstrate that comparison of responses of human and turkey erythrocytes to fluoroaluminates provides a well-defined method for investigating the mechanisms and consequences of Gp activation in intact cells.
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PMID:Gp-regulated phosphoinositide hydrolysis in turkey and human erythrocytes exposed to fluoride ion: relationship to calcium influx. 130 78

Previous work from this laboratory has shown that the electrically evoked release of enkephalin from the guinea pig myenteric plexus is regulated by an opiate receptor-mediated, concentration-dependent mechanism. Low concentrations (nanomolar) of opioids enhance release, whereas higher concentrations (10-100 nM) inhibit release. Each opioid effect is mediated by a different guanine nucleotide-binding protein. We now demonstrate that activation of cholinergic receptors in the myenteric plexus is a prerequisite for opioid excitatory effects, but not inhibitory effects, on enkephalin release. Pretreatment with the muscarinic cholinergic receptor antagonist atropine abolishes the opioid facilitation of stimulated enkephalin release but does not alter the inhibition of release that is observed with higher concentrations of opioid agonist. Exposure to the calcium ionophore A23187 overcomes the abolishment of opioid enhancement of enkephalin release produced by cholinergic receptor blockade. In tissue treated with both atropine and A23187, the magnitude of the opioid enhancement of release is indistinguishable from that observed in untreated preparations. This suggests that the lack of stimulation-induced generation of elevated cytosolic calcium is responsible for the abolishment of facilitory opioid effects when cholinergic receptors are blocked. The known coupling of muscarinic receptors to phospholipase C activation and the generation of inositol trisphosphate (which elevates cytosolic calcium) could suggest that this second messenger is critical for the manifestation of opioid facilitation of enkephalin release.
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PMID:Opioid enhancement of evoked [Met5]enkephalin release requires activation of cholinergic receptors: possible involvement of intracellular calcium. 131 58

The effects of aluminium on inositol phosphate formation were examined in murine neuroblastoma cells labelled with [3H]-myo-inositol. In aluminium-pretreated cells, the bradykinin-triggered inositol triphosphate, IP3, release and the change in intracellular [Ca2+] were appreciably less compared with the control group. Stimulating digitonin-permeabilized cells with non-hydrolyzable guanosine 5'-[gamma-thio]-triphosphate, GTP[S], inositol phosphate formation decreased in the presence of aluminium. A primary target of aluminium toxicity may reside on the guanine nucleotide-binding protein(Gp)/phospholipase C system, at a site different from that of the GTP[S] binding site.
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PMID:Aluminium interferes with signal transduction in neuroblastoma cells. 133 97

The receptor that interacts with the mammalian bombesin-related peptide neuromedin B (NMB) is ubiquitous in the gastrointestinal tract and central nervous system. However, little is known regarding its cellular mechanisms of action. This receptor has been recently cloned, sequenced, and stably transfected into BALB 3T3 fibroblasts, permitting detailed study of the pharmacology and coupled biological activities of this receptor. In the present study, we compare the ability of transfected receptors to alter cell function with that of receptors natively expressed in small numbers by the rat glioblastoma cell line C6. NMB inhibited binding of 125I-[D-Tyro]NMB with high affinity in transfected cells (Ki = 3.08 +/- 0.14 nM) and in C6 cells (Ki = 1.90 +/- 1.10 nM), whereas the bombesin-related agonists gastrin-releasing peptide (GRP) and [D-Phe6, D-Ala11, Leu14]bombesin(6-16) (GRP analogue) had 100- and 300-fold lower affinities, respectively, for NMB receptors in either cell type. For both cell systems, maximal binding was observed between 5 and 15 min at 22 degrees. Both cell types internalized NMB at similar rates, with > 70% of bound ligand being internalized by 60 min at 22 degrees. The nonhydrolyzable guanosine analogue guanosine 5'-(beta,gamma-imido)triphosphate was equipotent in causing a decrease in binding of 125I-[D-Tyro]NMB due to decreased receptor affinity in both cell types, without a change in receptor number, demonstrating that the NMB receptor remained coupled to a guanine nucleotide-binding protein in both native and transfected cells. In both cell systems, NMB increased inositol monophosphate, inositol bisphosphate, and inositol trisphosphate in a time-dependent fashion. Inositol phosphates were increased in a dose-dependent fashion, with similar half-maximal values being obtained for NMB in both cell types (transfected, 1.01 +/- 0.09 nM; C6, 2.09 +/- 0.15 nM) and for the GRP analogue (transfected, 1855 +/- 140 nM; C6, 2129 +/- 250 nM). NMB mobilized intracellular Ca2+ in both cell systems, and the dose-response curves were superimposible (EC50 for transfected, 0.10 +/- 0.08 nM; C6, 0.11 +/- 0.02 nM). These data demonstrate that activation of the receptor for NMB stimulates phospholipase C and increases intracellular Ca2+. These results also demonstrate that transfected and native NMB receptors behave similarly, suggesting that the transfected cell line will be useful in future studies investigating ligand-receptor interactions, as well as in molecular biological studies of the structure-function relationship of the receptor.
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PMID:Neuromedin B receptors retain functional expression when transfected into BALB 3T3 fibroblasts: analysis of binding, kinetics, stoichiometry, modulation by guanine nucleotide-binding proteins, and signal transduction and comparison with natively expressed receptors. 133 12

We have characterized a G-protein-coupled glutamate receptor in primary cultures of striatal neurons. Glutamate, quisqualate, or trans-1-aminocyclopentane-1,3-dicarboxylate inhibited by 30-40% either forskolin-stimulated cAMP production in intact cells or forskolin plus vasoactive intestinal peptide-activated adenylyl cyclase assayed in neuronal membrane preparations. These inhibitory effects were suppressed after treatment of striatal neurons with Bordetella pertussis toxin, suggesting the involvement of a heterotrimeric guanine nucleotide-binding protein (G protein) of the G(i)/G(o) subtype. The pharmacological profile of this glutamate receptor negatively coupled to adenylyl cyclase was different from that of the metabotropic Qp glutamate receptor coupled to phospholipase C in striatal neurons and from that of the recently cloned "mGluR2" glutamate receptor, which is negatively coupled to adenylyl cyclase when expressed in non-neuronal cells.
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PMID:Characterization of a metabotropic glutamate receptor: direct negative coupling to adenylyl cyclase and involvement of a pertussis toxin-sensitive G protein. 135 3

Recently, we demonstrated that aggregation of the high affinity IgE receptor in rat basophilic leukemia (RBL-2H3) cells results in rapid tyrosine phosphorylation of a 72-kDa protein (pp72). Here we investigated the relationship of pp72 phosphorylation to guanine nucleotide-binding protein (G protein) activation and phosphatidylinositol hydrolysis. The activation of G proteins by NaF in intact cells or by guanosine 5'-O-(3-thiotriphosphate) in streptolysin O-permeabilized cells induced both phosphatidylinositol hydrolysis and histamine release without tyrosine phosphorylation of pp72. Similarly, in RBL-2H3 cells expressing the G protein-coupled muscarinic acetylcholine receptor, carbachol activated phospholipase C and induced secretion without concomitant pp72 phosphorylation. Therefore, pp72 phosphorylation was not induced by G protein activation or as a consequence of phosphatidylinositol hydrolysis. To investigate whether pp72 tyrosine phosphorylation precedes the activation of phospholipase C, we studied the effect of the tyrosine kinase inhibitor genistein. Preincubation of cells with genistein decreased, in parallel, antigen-induced tyrosine phosphorylation of pp72 (IC50 = 34 micrograms/ml) and histamine release (IC50 = 31 micrograms/ml). However, genistein at concentrations of up to 60 micrograms/ml did not inhibit phosphatidylinositol hydrolysis nor did it change the amount of the secondary messenger inositol (1,4,5)-triphosphate. Previous observations showed that there was no pp72 tyrosine phosphorylation after activation of protein kinase C or after an increase in intracellular calcium. Taken together, these results suggest that pp72 tyrosine phosphorylation represents a distinct, independent signaling pathway induced specifically by aggregation of the Fc epsilon RI.
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PMID:Fc epsilon RI-induced protein tyrosine phosphorylation of pp72 in rat basophilic leukemia cells (RBL-2H3). Evidence for a novel signal transduction pathway unrelated to G protein activation and phosphatidylinositol hydrolysis. 137 2

In the guinea pig myometrium, carbachol, oxytocin, and fluoroaluminates stimulated the breakdown of phosphatidylinositol 4,5-bisphosphate, which was insensitive to pertussis toxin [Biochem. J. 255:705-713 (1988)]. We now demonstrate that an increased accumulation of inositol phosphates, with an early production of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], could also be obtained with K+ (30 mM) and the Ca2+ ionophore ionomycin. Removal of extracellular Ca2+ or addition of the Ca2+ channel antagonists nifedipine and verapamil almost totally abolished stimulations elicited by high K+ and partially attenuated receptor- and fluoroaluminate-mediated increases in inositol phosphates. Isoproterenol similarly attenuated the accumulation of inositol phosphates elicited by carbachol, oxytocin, and fluoroaluminates (maximal inhibition, 35%; EC50, 0.5 nM), with no change in the rate of Ins(1,4,5)P3, inositol bisphosphate, and inositol monophosphate generation. The beta-adrenergic receptor-induced inhibition was prevented by pertussis toxin and could not be reproduced by forskolin, indicating that cAMP was not involved. Experimental findings were, rather, consistent with a predominant role for Ca2+. Thus, inhibition due to isoproterenol was lost in a Ca(2+)-depleted medium and was not additive with that caused by nifedipine. Accumulation of inositol phosphates triggered by high K+ was insensitive to the beta-adrenergic receptor inhibition. The inhibitory effect of isoproterenol, similar to that of nifedipine, was counteracted by ionomycin and also by the Ca2+ channel agonist Bay K 8644. These data indicate that in the myometrium 1) phospholipase C can be activated through a voltage-gated Ca2+ entry-dependent process that contributes at least partially to the stimulations triggered by receptor- and/or guanine nucleotide-binding protein-mediated activation and 2) beta-adrenergic receptor activation is linked via a cAMP-independent, pertussis toxin-sensitive pathway to an inhibition of voltage-gated Ca2+ channels, resulting in an attenuation of the Ca(2+)-associated generation of inositol phosphates.
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PMID:Activation of beta-adrenergic receptors inhibits Ca2+ entry-mediated generation of inositol phosphates in the guinea pig myometrium, a cyclic AMP-independent event. 137 85

The neuropeptide galanin potently inhibits insulin release, hippocampal acetylcholine release and firing of locus coeruleus cells, and stimulates feeding and release of growth hormone. Galanin regulates K+ channels, adenylyl cyclase and phospholipase C by acting at Gi/Go protein-coupled high-affinity receptors. Galanin receptor agonists such as the N-terminal fragment galanin1-16 act synergistically with morphine in the somatosensory system and have potential analgetic application. Galanin antagonists may be useful therapeutic agents in endocrinology, neurology and psychiatry. The enhancing effect of such agents on hippocampal cholinergic function would be useful in treatment of Alzheimer's disease. Recent synthesis of a series of high-affinity galanin antagonists, reviewed, along with galanin's actions, by Tamas Bartfai and colleagues, opens the possibility of examining the functions of endogenous galanin and test the pharmacological usefulness of antagonism of galanin function in the endocrine, somatosensory and central nervous systems.
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PMID:Galanin and galanin antagonists: molecular and biochemical perspectives. 138 14

The peptide angiotensin II (AngII) has been reported to stimulate phosphoinositide-specific phospholipase C (PLC) activity in the murine neuroblastoma cell line N1E-115. In the present study, polyclonal antibodies raised against a PLC isoenzyme, PLC-alpha, reacted with a 60-kDa protein present in both membrane and cytosolic fractions of differentiated N1E-115 cells. In order to examine the possible association of PLC-alpha with cell surface AngII receptors (AngII-Rs), membranes from differentiated N1E-115 cells were solubilized, using the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS). CHAPS (1%) solubilized AngII-Rs, from N1E-115 cells, that maintained their high affinity for agonists. Gel filtration analysis of the solubilized membranes revealed that the majority of the specific binding of 125I-AngII eluted as a large protein complex with a molecular mass of 380 kDa and that agonist binding was partially reduced by guanosine-5'-O-(3-thio)triphosphate (GTP gamma S), within this complex. CHAPS also effectively solubilized immunoreactive PLC-alpha, from N1E-115 cell membranes, that was similarly present within the 380-kDa AngII-binding complex. Anti-PLC-alpha antisera immunoprecipitated approximately 16% of the total phosphatidylinositol-4,5-bisphosphate-specific PLC activity in the 1% CHAPS extract and 40% of cytosolic PLC activity. Moreover, a 60-kDa 35S-Trans S-labeled protein, comigrating with immunoreactive PLC-alpha, was immunoprecipitated from the 1% CHAPS extract by the antisera. In addition, anti-PLC-alpha antisera immunoprecipitated approximately 20% of solubilized AngII-Rs prebound with 125I-AngII but failed to precipitate receptors prebound with the antagonist 125I-Sarc1,Ile8-AngII. The anti-PLC-alpha antisera also immunoprecipitated AngII-Rs when intact membranes were labeled with 125I-AngII before solubilization in 1% CHAPS, suggesting that the AngII-R interaction with PLC-alpha was not the result of detergent-promoted protein-protein interaction. On the other hand, monoclonal antibodies against another PLC isozyme, PLC-gamma, did not precipitate AngII-Rs in solubilized N1E-115 membranes. Finally, the formation of the immunoprecipitated AngII-R-PLC-alpha complex was disrupted by the nonhydrolyzable guanine nucleotide analog GTP gamma S, suggesting that the interaction between AngII-Rs and PLC-alpha is likely to involve a heterotrimeric guanine nucleotide-binding protein in neuron-like cells.
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PMID:Association of solubilized angiotensin II receptors with phospholipase C-alpha in murine neuroblastoma NIE-115 cells. 151 21

Angiotensin II (AII) is an important regulator of aldosterone secretion by adrenal glomerulosa cells. All interacts with a specific receptor coupled to a guanine nucleotide-binding protein that controls the activity of phospholipase C. Recently, novel All nonpeptide antagonists (DuP-753 and PD-123319) have been shown to discriminate between two subclasses of All receptors in many different tissues. Our studies confirmed that 125I-All specifically labeled two classes of binding sites for All in a membrane preparation of bovine adrenal glomerulosa cells. The first class (DuP-753 sensitive) represented approximately 85% of the total binding sites for All and possessed a high affinity (IC50 of 92.9 +/- 19.5 nM) for DuP-753. PD-123319 did not have any effect on 125I-All binding to this site. The second class of binding sites was more sensitive to PD-123319, with an IC50 of 6.9 +/- 3.7 nM, and had a much lower affinity for DuP-753 (IC50 around 10 microM). The two classes of receptors had different affinities for All. All showed an affinity around 2 nM for All type 1 receptor (AT1)(DuP-753 sensitive) and a higher affinity, around 0.3 nM, for All type 2 receptor (AT2) (PD-123319 sensitive). All-induced steroidogenesis was completely abolished in the presence of 3 microM DuP-753, indicating that this activity was mediated through a DuP-753-sensitive receptor. We also found that polyvinyl sulfate (PVS), a polyanion, could partly inhibit the binding of 125I-All to bovine adrenal glomerulosa cell membranes, with half-maximal efficiency at 17.3 +/- 8.2 nM. The inhibitory effect of PVS was selective for AT1. The inhibitory effect of PVS was due to a change in the affinity state of the receptor. Unexpectedly, PVS had no effect on All-induced steroidogenesis or on All binding to intact bovine adrenal glomerulosa cells. However, the inhibitory effect of PVS on All binding was recovered after permeabilization of cells. Direct interaction of polyanions with AT1 was suggested by the capacity of solubilized photoaffinity-labeled 125I-AT1 to adsorb to heparin-agarose gels. The adsorption of 125I-AT1 to heparin-agarose was inhibited by prior incubation of solubilized receptor with heparin or PVS. These results suggest that All-induced steroidogenesis is mediated by a DuP-753-sensitive receptor and that PVS decreases the affinity of this receptor by interacting with an intracellular domain (possibly the positively charged domain responsible for coupling with guanine nucleotide-binding proteins).
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PMID:Modulation of angiotensin II binding affinity by allosteric interaction of polyvinyl sulfate with an intracellular domain of the DuP-753-sensitive angiotensin II receptor of bovine adrenal glomerulosa. 156 28


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