Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In COS-7 cell membranes expressing cloned delta-opioid receptor, [D-Ser2, Leu5]enkephalin-Thr6, an opioid delta-agonist, showed no significant stimulation of high-affinity GTPase, while this agonist binding showed a guanine nucleotide sensitivity. Significant stimulation of GTPase activity by this agonist was observed only when the cells were pretreated with 0.1 microM calphostin C, a protein kinase C inhibitor, and when this inhibitor was further added to the reaction mixture at 1 microM. These findings suggest that protein kinase C is involved in the heterologous desensitization of delta-opioid receptor in the cells.
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PMID:Protein kinase C inhibitor potentiates the agonist-induced GTPase activity in COS cell membranes expressing delta-opioid receptor. 875 Aug 96

Synaptic vesicle recycling is a neuronal specialization of endocytosis that requires the GTPase activity of dynamin I and is triggered by membrane depolarization and Ca2+ entry. To establish the relationship between dynamin I GTPase activity and Ca2+, we used purified dynamin I and analyzed its interaction with Ca2+ in vitro. We report that Ca2+ bound to dynamin I and this was abolished by deletion of dynamin's C-terminal tail. Phosphorylation of dynamin I by protein kinase C promoted formation of a dynamin I tetramer and increased Ca2+ binding to the protein. Moreover, Ca2+ inhibited dynamin I GTPase activity after stimulation by phosphorylation or by phospholipids but not after stimulation with a GST-SH3 fusion protein containing the SH3 domain of phosphoinositide 3-kinase. These results suggest that in resting nerve terminals, phosphorylation of dynamin I by protein kinase C converts it to a tetramer that functions as a Ca(2+)-sensing protein. By binding to Ca2+, dynamin I GTPase activity is specifically decreased, possibly to regulate synaptic vesicle recycling.
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PMID:Calcium binds dynamin I and inhibits its GTPase activity. 878 38

Prolonged stimulation of gonadotropin receptors in granulosa cells leads to desensitization of the cellular response to gonadotropic hormones which is evident by decrease in cAMP formation. In order to explore the mechanism of desensitization and to examine whether protein phosphorylation may play a role in this phenomenon, we have studied the effect of various stimulators and inhibitors of protein phosphorylation on FSH-induced cAMP formation in the FSH-responsive cell line, GFSHR-17, recently established in our laboratory. Both ovine and human FSH activated the hormone sensitive adenylate cyclase in a dose-dependent manner with an ED50 of 0.5 nM. This stimulation was followed by a sharp decrease in cAMP formation after 30 min incubation of the cell with the hormone. When cells were preincubated for 60 min with staurosporine, cAMP accumulation during 20 min of FSH stimulation was elevated about 500%, compared to cells stimulated by FSH alone. Staurosporine alone showed a negligible effect on cAMP accumulation in these cells. In cells stimulated with forskolin, a non-specific activator of adenylate cyclase, or with cholera toxin (CT), an inhibitor of GTPase activity associated with Gs of adenylate cyclase, preincubation with staurosporine increased cAMP formation in these cells by only 50-70 or 80-120%, respectively. Preincubation of cells with the protein kinase C (PKC) inhibitors chelerythrine and GF109203X increased FSH-stimulated accumulation of cAMP by 50 and 30%, respectively. These drugs exhibit a similar effect on forskolin-stimulated cells. Preincubation of cells for 60 min with a PKC stimulator, TPA, suppressed FSH-mediated cAMP response in these cells by 40%. Tyrosine kinase inhibitors such as AG18, AG33 and genistein exhibit a modest inhibitory effect of up to 20% on FSH-stimulated cAMP accumulation. All the above results were obtained both in the presence and absence of IBMX, a potent inhibitor of the cellular phosphodiesterases. Upon prolonged incubation with FSH (3 h) cells pretreated with staurosporine exhibited a much slower rate of decline in intracellular cAMP levels. Moreover, in desensitized cells, following 1 or 2 h of continuous stimulation with FSH, staurosporine could markedly enhance cAMP formation in the presence of FSH. Our data suggest that staurosporine-sensitive phosphorylation of serine or threonine in the FSH receptor-cyclase system may be responsible for desensitization of the FSH coupled activation of cAMP formation, while reactivation of the system can be achieved by protein dephosphorylation at these specific sites. Because specific inhibition of PKC could not mimic the staurosporine effect on FSH-stimulated cAMP formation, nor could activation of kinase C antagonize it, it is suggested that a specific staurosporine-sensitive receptor kinase may be responsible for modulation of the coupling between the gonadotropin receptor and the adenylate cyclase system.
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PMID:Activation of FSH-responsive adenylate cyclase by staurosporine: role for protein phosphorylation in gonadotropin receptor desensitization. 882 63

PKN is a newly discovered protein kinase that has been shown to mediate GTPase Rho dependent intracellular signalling. We show in this report that the mouse PKN gene is situated at the mouse EP1 prostanoid receptor gene locus and that the two genes are overlapping in a tail-to-tail manner. An "exon trap" strategy was used to identify the overlap phenomenon. By using RT-PCR and 3' RACE we have identified two major PKN transcripts that are produced by alternative polyadenylation. The 3' end of the short PKN transcript overlaps the 3' untranslated region of the EP1 gene with approximately 280 bp, while the long PKN transcript overlaps the whole EP1 gene. Remarkably, none of the three transcripts originating from this locus display the consensus AAUAAA polyadenylation signal. The last seven exons of the PKN gene, corresponding to the last third of the PKN cDNA, have been recognised in 7.2 kb of continuous genomic sequence that we have collected from the EP1/PKN genetic locus. The 3' part of the PKN gene is highly fragmented and its intron/exon organisation is reminiscent of that of the Drosophila protein kinase C gene. The possibility of a natural antisense regulation of these genes is discussed.
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PMID:The mouse genes for the EP1 prostanoid receptor and the PKN protein kinase overlap. 885 5

The high affinity GTPase activity in the mouse spinal cord was increased in a concentration-dependent manner by a selective delta 2-opioid receptor agonist, [D-Ala2]deltorphin II (0.1-1 microM). This increase of GTPase activity induced by [D-Ala2]deltorphin II was completely blocked by co-incubation with a selective delta 2-opioid receptor antagonist, naltriben (0.1 microM). A protein kinase C activator, phorbol 12,13-dibutyrate (PDB; 0.1-10 microM), which given alone had no effect on basal GTPase activity, blocked dose-dependently the increase of GTPase activity induced by [D-Ala2]deltorphin II (1 microM). Our results indicate the possibility that activation of protein kinase C by phorbol ester uncouples the delta 2-opioid receptor from G-proteins in the spinal cord.
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PMID:Phorbol ester blocks the increase of a high affinity GTPase activity induced by delta 2-opioid receptor agonist in the mouse spinal cord. 888 28

The naturally occurring phospholipid, lysophosphatidylcholine (lyso-PC), regulates a broad range of cell processes, including gene transcription, mitogenesis, monocyte chemotaxis, smooth muscle relaxation, and platelet activation. Despite the growing list of cellular effects attributable to lyso-PC, the mechanism(s) by which it alters cell function have not been elucidated. In this report, we have examined the effects of exogenous lyso-PC on signal transduction processes within a variety of lyso-PC-responsive cells, including human platelets, monocyte-like THP-1 cells, and the megakaryoblastic cell line, MEG-01. Pretreatment of each of these cells with increasing concentrations of lyso-PC (25-150 microg/ml) was associated with a progressive increase in the cytosolic concentration of cAMP. The accumulation of cAMP in platelets correlated closely with the ability of lyso-PC to inhibit multiple platelet processes, including platelet aggregation, agonist-induced protein kinase C activation, thromboxane A2 generation, and the tyrosine phosphorylation of platelet proteins. In each of the cell types examined, the ability of lyso-PC to increase the cellular levels of cAMP was synergistically enhanced by pretreating the cells with the cAMP phosphodiesterase inhibitor, theophylline (5 mM), and was specifically inhibited by the P-site inhibitor of adenylyl cyclase, 2,5-dideoxyadenosine. A role for the stimulatory G-protein, Gs, in the lyso-PC-induced activation of adenylyl cyclase was suggested by the ability of the GTPase inhibitor, guanylyl 5'-thiophosphate (0.2 mM), to inhibit the lyso-PC-stimulated increase in cAMP, and also by the ability of cholera toxin to inhibit increases in membrane GTPase activity in response to lyso-PC. The functional significance of lyso-PC-induced activation of adenylyl cyclase was investigated in MEG-01 cells. Treatment of these cells with either lyso-PC or dibutyryl cAMP for 36-40 h resulted in a 3-5-fold increase in the surface expression of the natural anticoagulant protein, thrombomodulin (TM). The ability of lyso-PC to increase TM expression was abolished by pretreating these cells with the adenylyl cyclase inhibitor, 2,5-dideoxyadenosine, whereas the dibutyryl cAMP-induced increase in TM remained insensitive to adenylyl cyclase inhibition. These studies define an important role for the adenylyl cyclase signaling system in mediating cellular effects induced by lyso-PC.
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PMID:The bioactive phospholipid, lysophosphatidylcholine, induces cellular effects via G-protein-dependent activation of adenylyl cyclase. 890 Feb

Serotonin (5-HT) is a potent mitogen in many cells types, an action which is frequently mediated through pertussis toxin-sensitive G proteins. In the current study, we used pharmacological inhibitors and dominant negative signaling constructs to delineate elements which participate in the activation of MAPK, a growth-associated mitogen-activated protein kinase, by human G protein-coupled 5-HT1A receptor transfected into CHO-K1 cells in a stable manner. The activation pathway does not directly involve phorbol ester-sensitive protein kinase C types, but does require (i) pertussis toxin-sensitive G protein beta gamma-subunits, (ii) a staurosporine- and genistein-sensitive protein kinase, (iii) phosphoinositide-3'-kinase activity, (iv) activation of Sos in a multimolecular complex that contains p46Shc, and p52Shc, and Grb2, (v) the GTPase p21Ras, and (vi) the protein kinase p74Raf-1. These data demonstrate that the 5-HT1A receptor mediates MAPK activity by convergence upon a common activation pathway that is shared with receptor tyrosine kinases.
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PMID:Ras-dependent activation of fibroblast mitogen-activated protein kinase by 5-HT1A receptor via a G protein beta gamma-subunit-initiated pathway. 890 12

A previously uncharacterized 22-kDa Ca(2+)-binding protein that also binds guanosine nucleotides was characterized, cloned, and analyzed by electrophysiological techniques. The cloned protein, calexcitin, contains two EF-hands and also has homology with GTP-binding proteins in the ADP ribosylation factor family. In addition to binding two molecules of Ca2+, calexcitin bound GTP and possessed GTPase activity. Calexictin is also a high affinity substrate for protein kinase C. Application of calexcitin to the inner surface of inside-out patches of human fibroblast membranes, in the presence of Ca2+ and the absence of endogenous Ca2+/calmodulin kinase type II or protein kinase C activity, reduced the mean open time and mean open probability of 115 +/- 6 pS K+ channels. Calexcitin thus appears to directly regulate K+ channels. When microinjected into molluscan neurons or rabbit cerebellar Purkinje cell dendrites, calexcitin was highly effective in enhancing membrane excitability. Because calexcitin translocates to the cell membrane after phosphorylation, calexcitin could serve as a Ca(2+)-activated signaling molecule that increases cellular excitability, which would in turn increase Ca2+ influx through the membrane. This is also the first known instance of a GTP-binding protein that binds Ca2+.
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PMID:Calexcitin: a signaling protein that binds calcium and GTP, inhibits potassium channels, and enhances membrane excitability. 894 17

The Rho family belongs to the Ras-related small GTP-binding protein (G protein) superfamily and regulates various cell functions in which the actomyosin system is involved, including cell morphology, membrane ruffling, cell motility, cell aggregation, cytokinesis, smooth muscle contraction, and yeast budding. Three GDP/GTP exchange proteins (GEPs), named Smg GDS, Dbl, and Rho GDI, and two GTPase activating proteins (GAPs), named Rho GAP and p190 associated with Ras GAP, have been identified. The Rho activity is likely to be regulated by protein kinase C which is linked through phospholipase C to the tyrosine kinase-type membrane receptors and the heterotrimeric G protein-linked receptors. It is likely that both Ras and Rho receive signals from the membrane receptors through different pathways and transduce signals to genes and cytoskeleton, respectively. In carcinogenesis, mutational activation of any component in the Ras signaling pathway may cause abnormal cell proliferation, whereas mutational activation of any component in the Rho signaling pathway may cause invasiveness and metastasis of carcinoma cells.
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PMID:Rho small G protein and cytoskeletal control. 898 86

The expression of H-ras and N-ras was found to be increased in liver of rats fed with the carcinogen N-nitrosodiethylamine (NDEA). There were, however, variations in time at which these were expressed and in the extent of expression of the two genes. N-ras appeared to be more aggressive than H ras. This overexpression could be correlated with an inhibition in the functioning of GTPase activating protein (GAP). The activity of GAP in increasing the intrinsic GTPase activity of p21RAS was found to be much less in NDEA-treated rats as compared to that in control rats. It was observed that GAP isolated from NDEA-treated rats was extensively phosphorylated by protein kinase C, and this might be the reason for its decreased activity. It is speculated that phosphorylated GAP helps keep the p21RAS in the more active GTP-bound state.
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PMID:Activation of ras oncogenes during hepatocarcinogenesis induced by N-nitrosodiethylamine: possible involvement of PKC and GAP. 902 Sep 14


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