Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanism of labour is not fully understood and further research into this important physiological process is needed. In some species, notably sheep, parturition is due to activation of the fetal hypothalamic-pituitary-adrenal axis. However, in primates, this axis appears to have a supportive, rather than essential role. Successful parturition requires an increase in coordinated uterine contractility together with changes in connective tissue that allow cervical ripening and dilatation. In most mammals, however, these changes are synchronised by a fall in maternal progesterone levels and a rise in oestrogens. This is not the case in women in whom the onset of labour occurs without apparent changes in circulating steroid levels. The basis of uterine contractility is the interaction between actin and myosin in myometrial smooth muscle cells. This is driven by calcium through Ca(2+)-calmodulin-dependent myosin light chain kinase (MLCK) activity. Moreover, calcium sensitisation occurs via activation of Rho kinase, a calcium-independent pathway that promotes contractility by inhibiting myosin phosphatase and probably by phosphorylating myosin on the same site as MLCK. Uterine activity can be modulated by many G-protein coupled receptors (GPCRs). For example, receptors coupled to Galpha(q) (oxytocin-, prostanoid FP and TP, endothelin-receptors) stimulate contractility by activating the phospholipase C/Ca(2+) pathway; receptors coupled to Galpha(s) (beta(2)-adrenoceptors, prostanoid EP2 and IP, some 5-hydroxytryptamine receptors e.g. 5-HT(7)) relax the uterus by increasing myometrial cyclic AMP levels; and receptors coupled to Galpha(i) (alpha(2)-adrenoceptors, muscarinic, 5-HT(1)) potentiate contractility, probably by inhibiting cAMP production. Because of its relative abundance in pregnant uterine tissue, the oxytocin receptor is an obvious target for tocolytic therapy. Oxytocin antagonists have been introduced into clinical practice for the management of preterm labour and offer the advantage of uterine selectivity and fewer side effects than conventional beta-agonist therapy.
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PMID:Mechanisms of labour--biochemical aspects. 1276 10

The sodium/proton exchanger type 1 (NHE-1) plays an important role in the proliferation of vascular smooth muscle cells (VSMC). We have examined the regulation of NHE-1 by two potent mitogens, serotonin (5-HT, 5-hydroxytryptamine) and angiotensin II (Ang II), in cultured VSMC derived from rat aorta. 5-HT and Ang II rapidly activated NHE-1 via their G protein-coupled receptors (5-HT(2A) and AT(1)) as assessed by proton microphysiometry of quiescent cells and by measurements of intracellular pH on a FLIPR (fluorometric imaging plate reader). Activation of NHE-1 was blocked by inhibitors of phospholipase C, CaM, and Jak2 but not by pertussis toxin or inhibitors of protein kinase C. Immunoprecipitation/immunoblot studies showed that 5-HT and Ang II induce phosphorylation of Jak2 and induce the formation of signal transduction complexes that included Jak2, CaM, and NHE-1. The cell-permeable Ca(2+) chelator BAPTA-AM blocked activation of Jak2, complex formation between Jak2 and CaM, and tyrosine phosphorylation of CaM, demonstrating that elevated intracellular Ca(2+) is essential for those events. Thus, mitogen-induced activation of NHE-1 in VSMC is dependent upon elevated intracellular Ca(2+) and is mediated by the Jak2-dependent tyrosine phosphorylation of CaM and subsequent increased binding of CaM to NHE-1, similar to the pathway previously described for the bradykinin B(2) receptor in inner medullary collecting duct cells of the kidney [Mukhin, Y. V., et al. (2001) J. Biol. Chem. 276, 17339-17346]. We propose that this pathway represents a fundamental mechanism for the rapid regulation of NHE-1 by G(q/11) protein-coupled receptors in multiple cell types.
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PMID:Mitogen-induced activation of Na+/H+ exchange in vascular smooth muscle cells involves janus kinase 2 and Ca2+/calmodulin. 1279 14

The 5-hydroxytryptamine 2A receptor (5-HT2AR) is a member of the class I family of rhodopsin-related G protein-coupled receptors. The receptor is known to activate phospholipase C via the heterotrimeric G proteins Gq/11, but we showed previously that it can also signal through the phospholipase D (PLD) pathway in an ADP-ribosylation factor (ARF)-dependent manner that seems to be independent of Gq/11 (Mitchell et al., 1998). Both coimmunoprecipitation experiments and the effects of negative mutant ARF constructs on 5-HT2AR-induced PLD activation here suggested that ARF1 may play a greater role than ARF6 in the function of this receptor. Furthermore, we demonstrated using glutathione S-transferase (GST)-fusion proteins of receptor domains that ARF1 and ARF6 bind to the third intracellular loop (i3) and the carboxy terminal tail (ct) of the 5-HT2AR. The association of ARF1 with the ct domain of the receptor was stronger than its interaction with i3, or the interactions of ARF6 with either construct. Experiments using ARF mutants that are deficient in GTP loading, and the in vitro addition of GTPgammaS suggested that GTP loading enhances ARF1 binding to the receptor. The N376PxxY motif in the transmembrane 7 domain of the receptor (rather than a N376DPxxY mutant form) was shown to be essential for ARF-dependent PLD signaling and ARF1 coimmunoprecipitation. In GST-fusion proteins of the 5-HT2AR ct domain, mutation of Asn376 to Asp also markedly reduced ARF1-HA binding, although additional motifs in the Asn376-Asn384 sequence and to a lesser extent elsewhere, seem also to contribute to the interaction.
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PMID:Selective interaction of ARF1 with the carboxy-terminal tail domain of the 5-HT2A receptor. 1457 74

This study examined the time course and possible mechanisms of agonist-induced desensitization of 5-hydroxytryptamine serotonin 2A receptors in the rat frontal cortex and hypothalamic paraventricular nucleus after 1, 4, and 7 days of treatment with (-)-1-(2,5-dimethoxy-4-iodophenyl)2-aminopropane HCl [(-)-DOI] (1 mg/kg i.p.), a selective 5-HT(2A/2C) receptor agonist. In the frontal cortex, 5-HT-mediated phospholipase C (PLC) enzyme activity decreased by 24 to 30% after 4 to 7 days of (-)-DOI treatment without any significant changes in the guanosine 5'-3-O-(thio)triphosphate-mediated PLC enzyme activity. Additionally, treatment with (-)-DOI did not significantly change the levels of G(alpha11), regulator of G protein signaling (RGS)4, or RGS7 proteins in the frontal cortex, whereas G(alphaq) protein levels in the frontal cortex decreased (47%) only after 7 daily (-)-DOI injections. The functional status of 5-HT(2A) receptors in the hypothalamic paraventricular nucleus was examined using 5-HT(2A) receptor-mediated increases in plasma hormone levels. Plasma adrenocorticotrophic hormone (ACTH) and oxytocin measurements showed that 5-HT(2A) receptor desensitization began after only 1 day of (-)-DOI treatment, and the desensitization continued to increase after 4 and 7 days of treatment (ACTH response decreased 64.2-67.7%; oxytocin response decreased 82.3-90.1%). There were no significant alterations in levels of G(alphaq) or G(alpha11) lamic paraventricular proteins in the hypothanucleus. In conclusion, these results suggest that chronically administered (-)-DOI induces desensitization of 5-HT(2A) receptors in vivo, via a reduction in the ability of 5-HT(2A) receptors to activate G proteins without consistently altering levels of G(alpha) proteins or RGS proteins.
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PMID:Agonist-induced serotonin 2A receptor desensitization in the rat frontal cortex and hypothalamus. 1497 28

Glucose-induced insulin secretion is inhibited by 5-hydroxytryptamine (5HT). In the present studies the specificity of 5HT inhibition of release and the potential biochemical mechanisms involved were investigated. Dose-dependent inhibition of 15 mM glucose-induced secretion was induced by a prior 3 h incubation with 5HT. At the highest 5HT concentration (500 microM) employed, both first and second phase responses to 15 mM glucose were reduced 50-60%. In addition, this level (500 microM) of 5HT virtually abolished 10 mM glucose-induced secretion. In contrast, secretion in response to the protein kinase C activator phorbol 12-myristate 13-acetate (500 nM) was immune to 500 microM 5HT pre-treatment. Glucose usage rates were comparable in both control and 500 microM 5HT-pretreated islets. However, the generation of inositol phosphates and the efflux of 3H-inositol from 3H-inositol-prelabeled islets in response to stimulatory glucose were impaired in parallel with insulin secretion. Based on these observations the following conclusions were reached: (1) 5HT impairs glucose-induced insulin release by altering glucose-induced activation of phospholipase C. (2) Biochemical events distal to phospholipase C remain intact despite this proximal biochemical lesion. (3) Amperometric analysis of 5HT release from 5HT-pretreated islets must take into consideration its profound adverse impact on glucose-induced insulin secretion.
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PMID:Effects of prior 5-hydroxytryptamine exposure on rat islet insulin secretory and phospholipase C responses. 1503 91

Serotonin (5-hydroxytryptamine; 5-HT) transporters (SERTs) are critical determinants of synaptic 5-HT inactivation and the targets for multiple drugs used to treat psychiatric disorders. In support of prior studies, we found that short-term (5-30 min) application of the adenosine receptor (AR) agonist 5'-N-ethylcarboxamidoadenosine (NECA) induces an increase in 5-HT uptake Vmax in rat basophilic leukemia 2H3 cells that is enhanced by pretreatment with the cGMP phosphodiesterase inhibitor sildenafil. NECA stimulation is blocked by the A3 AR antagonist 3-ethyl-5-benzyl-2-methyl-phenylethynyl-6-phenyl-1,4(+/-)dihydropyridine-3,5-dicarboxylate (MRS1191), by the phospholipase C inhibitor 1-(6-[[17beta-3-methoxyestra-1,3,5(10)-trien-17-yl] amino]hexyl)-1H-pyrrole-2,5-dione (U73122), by the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester, and by the guanyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. Hydroxylamine, a nitric-oxide donor, and 8-bromo-cGMP, a membrane-permeant analog of cGMP, mimic the effects of NECA on 5-HT uptake, whereas the protein kinase G (PKG) inhibitor N-[2-(methylamino)ethy]-5-isoquinoline-sulfonamide (H8) blocks NECA, hydroxylamine, and 8-bromo-cGMP effects. NECA stimulation activates p38 mitogen-activated protein kinase (MAPK), whereas p38 MAPK inhibitors block NECA stimulation of SERT activity, as does the protein phosphatase 2A (PP2A) inhibitor calyculin A. 5-HT-displaceable [125I]3beta-(4-iodophenyl)-tropane-2beta-carboxylic acid methylester tartrate (RTI-55) whole-cell binding is increased by NECA or sildenafil, and both surface binding and cell surface SERT protein are elevated after NECA or sildenafil stimulation of AR/SERT-cotransfected Chinese hamster ovary cells. Whereas p38 MAPK inhibition blocks NECA stimulation of 5-HT activity, it fails to blunt stimulation of SERT surface density. Moreover, inactivation of existing surface SERTs fails to eliminate NECA stimulation of SERT. Together, these results reveal two PKG-dependent pathways supporting rapid SERT regulation by A3 ARs, one leading to enhanced SERT surface trafficking, and a separate, p38 MAPK-dependent process augmenting SERT intrinsic activity.
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PMID:Adenosine receptor, protein kinase G, and p38 mitogen-activated protein kinase-dependent up-regulation of serotonin transporters involves both transporter trafficking and activation. 1515 39

Metabotropic G protein-coupled receptors have recently been recognized as targets for anesthetics and analgesics. In particular, G(q)-coupled receptors such as muscarinic M(1) receptors (M(1)R) and 5-hydroxytryptamine (5-HT) type 2A receptors have been reported to be targets for anesthetics. Much less is known, however, about the effects of anesthetics on G(i)-coupled receptors. Here we report a method to analyze functions of G(i)-coupled receptors in Xenopus oocytes expressing a chimeric G alpha protein. A chimeric G alpha(q) protein G alpha(qi5), which contains carboxy-terminus five amino acids of G alpha(i), enables G(i)-coupled receptors to couple to Gq-coupled receptor-mediated downstream pathways such as activation of phospholipase C. We determined acetylcholine (ACh)-induced Ca(2+)-activated Cl(-) currents in Xenopus oocytes coexpressing G(i)-coupled muscarinic M(2)receptors (M(2)R) with the chimeric G alpha(qi5). Although ACh did not induce any currents in oocytes expressing M(2)R alone, it caused robust Cl(-) currents in oocytes coexpressing M(2)R with G alpha(qi5). The EC(50) of the ACh-induced Cl(-) current mediated through G alpha(qi5) was 0.2 micromol/l, which was 2.2 times higher than that of the ACh-induced G protein-activated inwardly rectifying K(+) currents activated by G beta gamma subunits liberated from endogenously expressed G alpha(i) in Xenopus oocytes. Other G(i)-coupled somatostatin type 2, 5-HT(1A) and delta-opioid receptors, when coexpressed with G alpha(qi5) in oocytes, also caused robust Ca(2+)-activated Cl(-) currents. In oocytes coexpressing M(2)R and G alpha(qi5), a volatile anesthetic halothane inhibited M(2)R-induced Cl(-) currents in a concentration-dependent manner with the IC(50) of 1.1 mmol/l, suggesting that halothane inhibits M(2)R-induced cellular responses at clinically relevant concentrations. Treatment with the protein kinase C inhibitor GF109203X produced a 3.5-fold enhancement of the initial Cl(-) currents induced by 1 micromol/l ACh in oocytes expressing M(2)R and G(qi5). The rate of halothane-induced inhibition of Cl(-) currents elicited by ACh, however, was not changed in such oocytes pretreated with GF109203X. These findings suggest that halothane inhibits the M(2)R-induced signaling by acting at sites other than PKC activity. Collectively these findings suggest that the use of oocyte expressing G alpha(qi5) would be helpful to examine the effects of anesthetics or analgesics on the function of G(i)-coupled receptors in the Xenopus oocyte expression system.
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PMID:Analysis of the effects of halothane on Gi-coupled muscarinic M2 receptor signaling in Xenopus oocytes using a chimeric G alpha protein. 1545 70

There is a high degree of cross-talk between tyrosine phosphorylation and the serine/threonine phosphorylation signaling pathways. Here we show a physical and functional interaction between the classical protein kinase C isoform (cPKC), PKCalpha, and two major nonreceptor tyrosine kinases in platelets, Syk and Src. In the presence of the cPKC-selective inhibitor Go6976, platelet 5-hydroxytryptamine release was abolished in response to co-activation of glycoproteins VI and Ib-IX-V by the snake venom alboaggregin A, whereas platelet aggregation was substantially inhibited. Of the two platelet cPKCs, PKCalpha but not PKCbeta was activated, occurring in an Syk- and phospholipase C-dependent manner. Syk and PKCalpha associate in a stimulation-dependent manner, requiring Syk but not PKC activity. PKCalpha and Syk also co-translocate from the cytosol to the plasma membrane upon platelet activation, in a manner dependent upon the activities of both kinases. Although PKCalpha is phosphorylated on tyrosine downstream of Syk, we provide evidence against phosphorylation of Syk by PKCalpha, consistent with a lack of effect of PKCalpha inhibition on Syk activity. PKCalpha also associates with Src; although in contrast to interaction with Syk, PKCalpha activity is required for the association of these kinases but not the stimulation-induced translocation of Src to the cell membrane. Finally, the activity of Src is negatively regulated by PKC, as shown by potentiation of Src activity in the presence of the PKC inhibitors GF109203X or Go6976. Therefore, there is a complex interplay between PKCalpha, Syk, and Src involving physical interaction, phosphorylation, translocation within the cell, and functional activity regulation.
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PMID:Functional interaction of protein kinase Calpha with the tyrosine kinases Syk and Src in human platelets. 1558 6

Several receptors, including those for AVP (Arg8-vasopressin) and 5-HT (5-hydroxytryptamine), share an ability to stimulate PLC (phospholipase C) and so production of IP3 (inositol 1,4,5-trisphosphate) and DAG (diacylglycerol) in A7r5 vascular smooth muscle cells. Our previous analysis of the effects of AVP on Ca2+ entry [Moneer, Dyer and Taylor (2003) Biochem. J. 370, 439-448] showed that arachidonic acid released from DAG stimulated NO synthase. NO then stimulated an NCCE (non-capacitative Ca2+ entry) pathway, and, via cGMP and protein kinase G, it inhibited CCE (capacitative Ca2+ entry). This reciprocal regulation ensured that, in the presence of AVP, all Ca2+ entry occurred via NCCE to be followed by a transient activation of CCE only when AVP was removed [Moneer and Taylor (2002) Biochem. J. 362, 13-21]. We confirm that, in the presence of AVP, all Ca2+ entry occurs via NCCE, but 5-HT, despite activating PLC and evoking release of Ca2+ from intracellular stores, stimulates Ca2+ entry only via CCE. We conclude that two PLC-coupled receptors differentially regulate CCE and NCCE. We also address evidence that, in some A7r5 cells lines, AVP fails either to stimulate NCCE or inhibit CCE [Brueggemann, Markun, Barakat, Chen and Byron (2005) Biochem. J. 388, 237-244]. Quantitative PCR analysis suggests that these cells predominantly express TRPC1 (transient receptor potential canonical 1), whereas cells in which AVP reciprocally regulates CCE and NCCE express a greater variety of TRPC subtypes (TRPC1=6>2>3).
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PMID:Different phospholipase-C-coupled receptors differentially regulate capacitative and non-capacitative Ca2+ entry in A7r5 cells. 1591 94

Highly selective serotonin (5-hydroxytryptamine, 5-HT) receptor antagonists developed for mammals are ineffective in Aplysia due to the evolutionary divergence of neurotransmitter receptors and because the higher ionic strength of physiological saline for marine invertebrates reduces antagonist affinity. It has therefore been difficult to identify antagonists that specifically block individual signaling cascades initiated by 5-HT. We studied two broad-spectrum 5-HT receptor antagonists that have been characterized biochemically in Aplysia CNS: methiothepin and spiperone. Methiothepin is highly effective in inhibiting adenylyl cyclase (AC)-coupled 5-HT receptors in Aplysia. Spiperone, which blocks phospholipase C (PLC)-coupled 5-HT receptors in mammals, does not block AC-coupled 5-HT receptors in Aplysia. In electrophysiological studies, we explored whether methiothepin and spiperone can be used in parallel to distinguish between the AC-cAMP and PLC-protein kinase C (PKC) modulatory cascades that are initiated by 5-HT. 5-HT-induced broadening of the sensory neuron action potential in the presence of tetraethylammonium/nifedipine, which is mediated by modulation of the S-K+ currents, was used an assay for the AC-cAMP cascade. Spike broadening initiated by 5 microM 5-HT was unaffected by 100 microM spiperone, whereas it was effectively blocked by 100 microM methiothepin. Facilitation of highly depressed sensory neuron-to-motor neuron synapses by 5-HT was used as an assay for the PLC-PKC cascade. Spiperone completely blocked facilitation of highly depressed synapses by 5 microM 5-HT. In contrast, methiothepin produced a modest, nonsignificant, reduction in the facilitation of depressed synapses. Interestingly, these experiments revealed that the PLC-PKC cascade undergoes desensitization during exposure to 5-HT.
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PMID:Serotonin receptor antagonists discriminate between PKA- and PKC-mediated plasticity in aplysia sensory neurons. 1623 85


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