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)

Much work on the signal transduction mechanisms underlying neurotransmission has been directed towards studying the roles of the cyclic AMP and phosphoinositide pathways. Upon ligand binding, the transmitter receptors interact with heterotrimeric G proteins, allowing G alpha and G beta gamma subunits to disengage. The free G alpha then modulates the activity of adenylyl cyclase and phospholipase C. It has been suggested that the G beta gamma complex which is activated through muscarinic or neuropeptide receptors can stimulate mitogen-activated protein kinase (MAPK) via activation of the small guanine-nucleotide-binding protein Ras. Sequential activation of the intermediates in the Ras/Raf serine-threonine protein kinase/MAPK kinase/MAPK/transcription factor pathway has emerged as a central mechanism for controlling cell proliferation and differentiation in yeast, worms, fruitflies and mammals. Here we show, by analysis of Drosophila mutants, that synaptic current and modulation of K+ current, triggered by a pituitary adenylyl cyclase-activating polypeptide-like neuropeptide, are mediated by coactivation of the Ras/Raf and Rutabaga-adenylyl cyclase pathways. Thus the Ras/Raf pathway also appears to be essential for G-protein-coupled neurotransmission.
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PMID:Mediation of PACAP-like neuropeptide transmission by coactivation of Ras/Raf and cAMP signal transduction pathways in Drosophila. 779 75

The P2U purinoceptor mediated effect on cellular cAMP was investigated in DDT1 MF-2 smooth muscle cells. Stimulation of these receptors by ATP or UTP caused a pronounced decrease of about 50% in cellular cAMP levels in forskolin or isoprenaline pretreated cells. This action of the nucleotides was concentration dependent with an IC50 of 9.4 +/- 0.2 microM and 29.0 +/- 0.5 microM for UTP and ATP, respectively and was inhibited by the P2-purinoceptor antagonist suramin. The cAMP level appeared to be modified by intracellular Ca2+, represented by an initial decline in cAMP. Neither inactivation of protein kinase C by staurosporine nor elevated cytoplasmic Ca2+ concentrations interfered with the sustained decrease in cAMP levels induced by ATP or UTP, showing that this effect is not mediated via the phospholipase C pathway known to be activated after P2U purinoceptor stimulation in DDT1 MF-2 cells. Pertussis toxin inhibited the action of these nucleotides on the cellular cAMP level. It can be concluded that the P2U purinoceptor in DDT1 MF-2 cells is coupled to different G-proteins, activating phospholipase C and inhibiting adenylyl cyclase activity.
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PMID:The phospholipase C activating P2U purinoceptor also inhibits cyclicAMP formation in DDT1 MF-2 smooth muscle cells. 780 68

The effect of lysophosphatidic acid (LPA) on the proliferation of normal and tumor mouse mammary epithelial cells in primary, serum-free, collagen gel cell culture was evaluated. LPA stimulated the growth of normal mammary epithelial cells from mature virgin mice. The growth of pregnancy-dependent tumors (PDT) was generally stimulated, although the response was attenuated in some of these tumors compared to normal cells. In contrast, the growth of 70% of ovarian-independent tumors (OIT) was inhibited by LPA; the remainder were unaffected. LPA stimulated cAMP accumulation and phosphoinositide (PI) hydrolysis in normal, PDT, and OIT. Thus, the regulation of adenylyl cyclase and PI-specific phospholipase C by LPA is similar in normal and tumor cells. Pertussis toxin (PT) partially inhibited LPA-stimulated growth in normal cells but did not affect LPA-stimulated PI hydrolysis or cAMP accumulation. Thus, PT-sensitive and -insensitive proliferative pathways are activated. PT also inhibited LPA-stimulated growth of PDT but generally had no effect on the growth of OIT. These results show that the mitogenic response to LPA is attenuated in the hormone-dependent phenotype and switches to growth inhibition in hormone-independent tumors. Furthermore, LPA stimulates multiple signal transduction pathways mediated by PT-sensitive and -insensitive G proteins. The PT-sensitive pathways are not tightly coupled to the proliferative response to LPA in tumor cells. These data suggest that alterations in G protein function may occur during tumor progression.
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PMID:Analysis of the proliferative response to lysophosphatidic acid in primary cultures of mammary epithelium: differences between normal and tumor cells. 781 18

The regulation of phospholipase A2 by G protein-coupled receptors is examined in CHO cells which normally express the purinergic receptor and have been transfected with bovine rhodopsin. The purinergic receptor has been reported to activate both phospholipase C and phospholipase A2 in this cell line. In contrast, bovine rhodopsin by itself is not able to activate phospholipase A2. However, the photoreceptor does potentiate purinergic receptor-mediated phospholipase A2 activation in a light-dependent manner. Both the purinergic receptor stimulation of phospholipase A2 and the enhanced activity mediated by rhodopsin are completely pertussis toxin-sensitive, suggesting the regulation of phospholipase A2 by a member of the Gi family of G proteins. Both of these receptors also inhibit adenylyl cyclase activity. Rhodopsin-mediated inhibition of adenylyl cyclase is pertussis toxin-sensitive, whereas inhibition by the purinergic receptor is calcium-sensitive but not pertussis toxin-sensitive. These results suggest (1) that rhodopsin is similar to other receptors that normally couple to Gi when expressed in cultured cells and (2) that regulation of adenylyl cyclase and PLA2 in CHO cells by rhodopsin and the purinergic receptor occur via distinct pathways.
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PMID:The coupling of pertussis toxin-sensitive G proteins to phospholipase A2 and adenylyl cyclase in CHO cells expressing bovine rhodopsin. 781 32

1. Stimulation of P2Y-purinoceptors on turkey erythrocytes and many other cell types results in activation of phospholipase C. In contrast, we have observed recently that P2Y-purinoceptors on C6 rat glioma cells are not coupled to phospholipase C, but rather, inhibit adenylyl cyclase. 2. In this study we investigated the pharmacological selectivity of the P2-purinoceptor antagonists, suramin, reactive blue 2, and pyridoxal phosphate 6-azophenyl 2',4'-disulphonic acid (PPADS) for phospholipase C- and adenylyl cyclase-coupled P2Y-purinoceptors. 3. In C6 glioma cells, suramin and reactive blue 2 competitively antagonized the inhibitory effect of 2MeSATP on adenylyl cyclase (pKB = 5.4 +/- 0.2 and 7.6 +/- 0.1, respectively), whereas PPADS at concentrations up to 100 microM had no effect. 4. In contrast, in the turkey erythrocyte preparation, PPADS at concentrations up to 30 microM was a competitive antagonist of P2Y-purinoceptor-stimulated phospholipase C activity (pKB = 5.9 +/- 0.1). Suramin and reactive blue 2 produced both a shift to the right of the concentration-effect of 2MeSATP for the activation of phospholipase C and a significant decrease in the maximal inositol phosphate response. 5. Turkey erythrocytes also express a phospholipase C-coupled beta-adrenoceptor. Concentrations of PPADS that competitively inhibited the P2Y-purinoceptor-mediated response had only minimal effects on the activation of phospholipase C by beta-adrenoceptors. In contrast, suramin and reactive blue 2 produced a non-competitive inhibition, characterized by decreases in the maximal response to isoprenaline with no change in the potency of this beta-adrenoceptor agonist. 6. The differential effect of PPADS on P2Y-purinoceptors of C6 glioma cells and turkey erythrocytes adds further support to the idea that different P2Y-purinoceptor subtypes mediate coupling to adenylylcyclic and phospholipase C.
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PMID:Differential effects of P2-purinoceptor antagonists on phospholipase C- and adenylyl cyclase-coupled P2Y-purinoceptors. 783 15

Cd2+ provokes an immediate production of inositol trisphosphate and the release of Ca2+ from internal stores in human fibroblasts and some other mammalian cells. Ni2+, Co2+, Fe2+, and Mn2+ evoke the release of stored Ca2+, but are less potent than Cd2+ (apparent K0.5 = 40 nM). Zn2+ and Cu2+ competitively inhibit Ca2+ release evoked by Cd2+ without affecting Ca2+ release by hormones such as bradykinin. Zn2+ has the same apparent Ki value (80-90 nM) towards the five agonist metals, which suggests that the metals interact with the same site. Many other divalent cations neither released stored Ca2+ nor affected Cd(2+)-evoked Ca2+ release. The agonist metals appear to activate phospholipase C via a G protein rather than a tyrosine kinase. The production of reactive oxygen species is probably not involved in Ca2+ release by the metals. Cd2+ and other stimuli that raise cytosolic-free Ca2+ induce cyclic (AMP) production, apparently by activating a calmodulin-dependent adenylyl cyclase. We suggest that an orphan receptor mediates the hormonelike responses to Cd2+ and the other agonist metals. The receptor is referred to as an orphan because its physiological stimulus is unknown. Growth of the fibroblasts in high Zn2+ desensitizes them to the five agonist metals without affecting Ca2+ release by bradykinin or histamine. A several hour incubation in culture medium with normal Zn2+ fully restores responsiveness to the five active metals. Growth in high Zn2+ appears to repress the synthesis of the putative orphan receptor because inhibitors of RNA or protein synthesis, or asparagine-linked glycosylation, prevented the restoration of metal responsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Transmembrane signals and protooncogene induction evoked by carcinogenic metals and prevented by zinc. 784 95

To examine their role in insulin secretion, actin filaments (AFs) were disrupted by Clostridium botulinum C2 toxin that ADP-ribosylates G-actin. Ribosylation also prevents polymerization of G-actin to F-actin and inhibits AF assembly by capping the fast-growing end of F-actin. Pretreatment of HIT-T15 cells with the toxin inhibited stimulated insulin secretion in a time- and dose-dependent manner. The toxin did not affect cellular insulin content or nonstimulated secretion. In static incubation, toxin treatment caused 45-50% inhibition of secretion induced by nutrients alone (10 mM glucose + 5 mM glutamine + 5 mM leucine) or combined with bombesin (phospholipase C-activator) and 20% reduction of that potentiated by forskolin (stimulator of adenylyl cyclase). In perifusion, the stimulated secretion during the first phase was marginally diminished, whereas the second phase was inhibited by approximately 80%. Pretreatment of HIT cells with wartmannin, a myosin light chain kinase inhibitor, caused a similar pattern of inhibition of the biphasic insulin release as C2 toxin. Nutrient metabolism and bombesin-evoked rise in cytosolic free Ca2+ were not affected by C2 toxin, indicating that nutrient recognition and the coupling between receptor activation and second messenger generation was not changed. In the toxin-treated cells, the AF web beneath the plasma membrane and the diffuse cytoplasmic F-actin fibers disappeared, as shown both by staining with an antibody against G- and F-actin and by staining F-actin with fluorescent phallacidin. C2 toxin dose-dependently reduced cellular F-actin content. Stimulation of insulin secretion was not associated with changes in F-actin content and organization. Treatment of cells with cytochalasin E and B, which shorten AFs, inhibited the stimulated insulin release by 30-50% although differing in their effects on F-actin content. In contrast to HIT-T15 cells, insulin secretion was potentiated in isolated rat islets after disruption of microfilaments with C2 toxin, most notably during the first phase. This effect was, however, diminished, and the second phase became slightly inhibited when the islets were degranulated. These results indicate an important role for AFs in insulin secretion. In the poorly granulated HIT-T15 cells actin-myosin interactions may participate in the recruitment of secretory granules to the releasable pool. In native islet beta-cells the predominant function of AFs appears to be the limitation of the access of granules to the plasma membrane.
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PMID:Effect of disruption of actin filaments by Clostridium botulinum C2 toxin on insulin secretion in HIT-T15 cells and pancreatic islets. 786 85

Agonist-dependent phosphorylation of G protein-coupled receptors (GPRs) by G protein-coupled receptor kinases (GRKs) is proposed to be a key event initiating homologous receptor desensitization. A technical limitation hindering identification of GPRs as GRK substrates has been the necessity to use purified and reconstituted receptors in GRK assays. Here, the human m2 and human m3 (hm3) muscarinic cholinergic receptors (mAChRs), which couple to attenuation of adenylyl cyclase and stimulation of phospholipase C, respectively, were expressed in Spodoptera frugiperda insect cells and an in vitro approach to studying GPR phosphorylation by GRKs in crude membranes was developed. The m2 mAChR, a known substrate of certain GRKs, was used to validate the approach. The GRK isoform beta-adrenergic receptor kinase (beta ARK)1 phosphorylated the membrane-bound human m2 mAChRs in an agonist-dependent manner. The results demonstrated that endogenous membrane-bound beta gamma subunits of G proteins stimulated the phosphorylation of the membrane-bound m2 mAChR. To reveal new GRK substrates, we tested the expressed hm3 mAChRs. The membrane-bound hm3 mAChRs were phosphorylated by beta ARK1 in an agonist-dependent, G beta gamma-enhanced manner. This is the first demonstration that hm3 mAChRs can serve as substrates for GRKs. The stoichiometry of receptor phosphorylation was approximately 2 mol of phosphate/mol of receptors in the absence of G beta gamma and approximately 4 mol of phosphate/mol of receptors upon addition of G beta gamma. When the specificity of various GRKs towards mAChRs was assessed, beta ARK2 phosphorylated the agonist-activated hm3 mAChRs as efficiently as did beta ARK1; however, neither GRK5 nor GRK6 significantly phosphorylated the hm3 mAChRs under similar conditions. The approach of studying GRK-mediated phosphorylation of GPRs in their membrane-bound state identified the hm3 mAChRs as new substrates for GRKs. This approach should be valuable in identifying other new substrates of GRKs and should aid in studies that elucidate GRK/GPR pairing.
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PMID:Agonist-dependent phosphorylation of human muscarinic receptors in Spodoptera frugiperda insect cell membranes by G protein-coupled receptor kinases. 787 29

The human C5a receptor is known to signal through Gi proteins. The ability of the cloned C5a receptor to inhibit adenylyl cyclase or to stimulate phospholipase C through Gi proteins was examined in transfected cells. Activation of recombinant C5a receptors resulted in the stimulation of phospholipase C in Ltk- cells and inhibition of adenylyl cyclase in 293 cells. Pertussis toxin potently abolished both responses indicating the involvement of Gi proteins. Previous studies have shown that Gi-mediated inhibition of adenylyl cyclase can be similarly regulated by the pertussis toxin-insensitive GZ. In 293 cells co-transfected with the alpha subunit of GZ, the C5a-mediated inhibition of cAMP accumulation became pertussis toxin-resistant, signifying functional coupling between the C5a receptor and GZ. However, GZ cannot substitute for Gi in the C5a-induced stimulation of phospholipase C or inhibition of adenylyl cyclase in Ltk- cells.
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PMID:The human chemoattractant complement C5a receptor inhibits cyclic AMP accumulation through Gi and Gz proteins. 788 33

5-Hydroxytryptamine (5-HT) receptors contain seven putative transmembrane domains and couple via different guanine nucleotide binding proteins to specific effector enzymes. Studies with other receptors identify the second and third intracellular loops or the C-terminus of the receptor as important for selective effector coupling. However, it is not known which regions of the 5-HT receptor determine effector coupling specificity. To address this question, we constructed a chimeric 5-HT receptor in which the third intracellular (i3) loop is derived from the 5-HT2A receptor, which is coupled to activation of phospholipase C, and the rest of the sequence is derived from the 5-HT1B receptor, which is coupled to inhibition of adenylyl cyclase. The chimeric receptor exhibited ligand binding properties similar to those of the 5-HT1B receptor and distinct from those of the 5-HT2A receptor. This suggests that the i3 loop is not critical for the unique pharmacology of the 5-HT1B receptor. In contrast, the chimeric receptor exhibited signaling properties similar to those of the 5-HT2A receptor and distinct from those of the 5-HT1B receptor. This indicates that the i3 loop determines the effector coupling specificity of the 5-HT2A receptor.
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PMID:The third intracellular loop of the 5-hydroxytryptamine2A receptor determines effector coupling specificity. 789 Oct 70


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