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)

Gastrin-releasing peptide (GRP) and its amphibian homolog, bombesin, are potent secretogogues in mammals. We determined the roles of intracellular free Ca(2+) ([Ca(2+)](i)), protein kinase C (PKC), and mitogen-activated protein kinases (MAPK) in GRP receptor (GRP-R)-regulated secretion. Bombesin induced either [Ca(2+)](i) oscillations or a biphasic elevation in [Ca(2+)](i). The biphasic response was associated with peptide secretion. Receptor-activated secretion was blocked by removal of extracellular Ca(2+), by chelation of [Ca(2+)](i), and by treatment with inhibitors of phospholipase C, conventional PKC isozymes, and MAPK kinase (MEK). Agonist-induced increases in [Ca(2+)](i) were also inhibited by dominant negative MEK-1 and the MEK inhibitor, PD89059, but not by an inhibitor of PKC. Direct activation of PKC by a phorbol ester activated MAPK and stimulated peptide secretion without a concomitant increase in [Ca(2+)](i). Inhibition of MEK blocked both bombesin- and phorbol 12-myristate 13-acetate-induced secretion. GRP-R-regulated secretion is initiated by an increase in [Ca(2+)](i); however, elevated [Ca(2+)](i) is insufficient to stimulate secretion in the absence of activation of PKC and the downstream MEK/MAPK pathways. We demonstrated that the activity of MEK is important for maintaining elevated [Ca(2+)](i) levels induced by GRP-R activation, suggesting that MEK may affect receptor-regulated secretion by modulating the activity of Ca(2+)-sensitive PKC.
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PMID:Multiple protein kinase pathways are involved in gastrin-releasing peptide receptor-regulated secretion. 1044 56

We have established a rapid, sensitive, high-throughput assay that requires one assay condition to detect agonist effects from Gi-, Gs-, and Gq-coupled receptors. We utilized a vector containing a promoter with three multiple response elements, the vasoactive intestinal peptide promoter and a cAMP response element controlling the transcription of the luciferase gene. An adrenergic agonist, para-aminoclonidine, inhibited forskolin-stimulated luciferase expression when cells were cotransfected with the Gi-coupled alpha(2)-C adrenergic receptor and the MRE/CRE reporter vector. Further, we demonstrate that gastrin-releasing peptide, which activates a Gq-coupled GRP receptor, isoproterenol, which activates a Gs-coupled beta-adrenergic receptor, calcium ionophores, and phorbol 12-myristate 13-acetate, a stimulator of protein kinase C, can mediate increases in luciferase expression in the presence of forskolin but not in its absence. The effect at Gi-coupled receptor activation correlates with the phosphorylation of the CRE binding protein (CREB); however, the mechanisms mediating the responses to Gq- and Gs-coupled receptors are more complex. We demonstrate that this assay is useful for pharmacological analysis of both agonists and antagonists and has the potential to associate orphan G-protein-coupled receptors with their corresponding ligands.
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PMID:Measurement of responses from Gi-, Gs-, or Gq-coupled receptors by a multiple response element/cAMP response element-directed reporter assay. 1054 9

Gastrin-releasing peptide (GRP) receptors are present in pancreatic islets, though their regulation is unknown except for homologous desensitization. The modulation of binding of GRP to mouse pancreatic islets and INS-1 cells was studied. At 60 min (steady-state), total binding of [(125)I-Tyr(15)] GRP was 1.62 per cent of total radioactivity per 50 islets; non-specific binding (presence of 1 mM unlabelled GRP(1-27)) was 0.05 to 0.61 per cent of total radioactivity. A preincubation with 1000 nM cholecystokinin (CCK(8)) or with 1000 nM glucose-dependent insulinotropic peptide (GIP) augmented the number of GRP binding sites but not their affinity. [(125)I-Tyr(15)]GRP binding to INS-1 cells was saturable (90 min) and specific with respect to compounds that are not chemically related to GRP (e.g. calcitonin gene-regulated peptide-CGRP and atrial natriuretic peptide-ANP). Displacement studies showed one binding site with a K(d) of 0.39 nM and a B(max) of 13.2 fmoles mg(-1) protein. When the cells were pretreated for 24 h with 10 nM GIP or CCK(8), only GIP but not CCK(8) increased the B(max) of the GRP binding site. The affinity (K(d)) was not changed by either compound. This effect of GIP pretreatment was not affected by downregulating PKC by TPA (phorbol ester; long-term pretreatment). These data indicate that: (1) specific binding sites for GRP are present in mouse pancreatic islets and INS-1 cells; (2) the GRP binding is upregulated by GIP in both islets and INS-1 cells and additionally by CCK(8 ), albeit only in islets; and (3) PKC does not seem to be involved in the up-regulation process. Thus a positive interplay between both the incretins GIP and CCK(8) and the neurotransmitter GRP is obvious.
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PMID:Modulation of gastrin-releasing peptide (GRP) receptors in insulin secreting cells. 1058 10

The hormone bombesin (BBS) and its mammalian equivalent gastrin-releasing peptide (GRP) act through specific GRP receptors (GRP-R) to affect multiple cellular functions in the gastrointestinal tract; the intracellular signaling pathways leading to these effects are not clearly defined. Previously, we demonstrated that the human gastric cancer SIIA possesses GRP-R and that BBS stimulates activator protein-1 (AP-1) gene expression. The purpose of our present study was to determine the signaling pathways leading to AP-1 induction in SIIA cells. A rapid induction of c-jun and jun-B gene expression was noted after BBS treatment; this effect was blocked by specific GRP-R antagonists, indicating that BBS is acting through the GRP-R. The signaling pathways leading to increased AP-1 gene expression were delineated using phorbol 12-myristate 13-acetate (PMA), which stimulates protein kinase C (PKC)-dependent pathways, by forskolin (FSK), which stimulates protein kinase A (PKA)-dependent pathways, and by the use of various protein kinase inhibitors. Treatment with PMA stimulated AP-1 gene expression and DNA binding activity similar to the effects noted with BBS; FSK stimulated jun-B expression but produced only minimal increases of c-jun mRNA and AP-1 binding activity. Pretreatment of SIIA cells with either H-7 or H-8 (primarily PKC inhibitors) inhibited the induction of c-jun and jun-B mRNAs in response to BBS, whereas H-89 (PKA inhibitor) exhibited only minimal effects. Pretreatment with tyrphostin-25, a protein tyrosine kinase (PTK) inhibitor, attenuated the BBS-mediated induction of c-jun and jun-B, but the effect was not as pronounced as with H-7. Collectively, our results demonstrate that BBS acts through its receptor to produce a rapid induction of both c-jun and jun-B mRNA and AP-1 DNA binding activity in the SIIA human gastric cancer. Moreover, this induction of AP-1, in response to BBS, is mediated through both PKC- and PTK-dependent signal transduction pathways with only minimal involvement of PKA.
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PMID:Signaling mechanisms regulating bombesin-mediated AP-1 gene induction in the human gastric cancer SIIA. 1091 98

Somatostatin-14 (S-14) and somatostatin-28 (S-28) bind to five distinct membrane receptors (SSTRs), but S-28 has higher affinity for SSTR-5. Whether S-28 acting through SSTR-5 regulates inhibition of peptide YY (PYY) secretion was tested in fetal rat intestinal cell cultures. S-28 and S-14 caused dose-dependent inhibition of PYY secretion stimulated by gastrin-releasing peptide, but S-28 was more potent than S-14 (EC(50) 0.04 vs. 13.2 nM). PYY was inhibited by two analogs with affinity for SSTR-5, BIM-23268 and BIM-23052, more potently than S-14 and as effectively as S-28. The SSTR-5 analog L-362855 suppressed PYY equivalent only to S-14, but the structurally related peptide L-372588 (Phe to Tyr at position 2) was equipotent to S-28, whereas L-372587 (Phe to Tyr at position 7) caused no inhibition. An SSTR-2 analog decreased PYY secretion similar to S-14, and an SSTR-3 analog was ineffective. PYY secretion stimulated by phorbol 12-myristate 13-acetate and by forskolin was also more potently suppressed by S-28 and the octapeptide SSTR-5 analogs. The results indicate that S-28 mediates inhibition of gastrin-releasing peptide-stimulated PYY secretion through activation of SSTR-5 and includes suppression of cAMP- and protein kinase C-dependent pathways. Substitution of a single hydroxyl group confers differences in SSTR-5 agonist properties, suggesting region specificity for the intrinsic activity of this receptor subtype.
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PMID:Somatostatin receptor subtype-5 mediates inhibition of peptide YY secretion from rat intestinal cultures. 1105 95

Autocrine and paracrine signaling leading to stimulation of tumor cell growth is a common theme in human cancers. In addition to polypeptide growth factors such as EGF family members which signal through receptor tyrosine kinases, accumulating evidence supports the autocrine and paracrine involvement of specific neuropeptides with defined physiologic actions as neurotransmitters and gut hormones in lung, gastric, colorectal, pancreatic and prostatic cancers. These neuropeptides, including gastrin-releasing peptide, neuromedin B, neurotensin, gastrin, cholecystokinin and arginine vasopressin bind seven transmembrane-spanning receptors that couple to heterotrimeric G proteins. Studies with human small cell lung cancer (SCLC) cells support a requirement for balanced signaling through G(q) and G(12/13) proteins leading to intracellular Ca2+ mobilization, PKC activation and regulation of the ERK and JNK MAP kinase pathways. While specific neuropeptide antagonists offer promise for interrupting the single neuropeptide autocrine systems operating in pancreatic and prostatic cancers, SCLC is exemplified by multiple, redundant neuropeptide autocrine systems such that tumor growth cannot be inhibited with a single specific antagonist. However, a novel class of neuropeptide derivatives based on the substance P sequence have been defined that exhibit broad specificity for neuropeptide receptors and induce apoptosis in SCLC by functioning as biased agonists that stimulate discordant signal transduction. Thus, interruption of autocrine and paracrine neuropeptide signaling with specific antagonists or broad-spectrum biased agonists offer promising new therapeutic approaches to the treatment of human cancers.
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PMID:Autocrine and paracrine signaling through neuropeptide receptors in human cancer. 1131 3

The role of the different isoforms of protein kinase C (PKC) in modulating insulin secretion is still widely unknown. The aim of our studies was to investigate which isoforms are influenced by gastrin-releasing peptide (GRP), a neuropeptide which has been shown to modulate insulin secretion by activating PKC. Presence of PKC isoforms alpha, beta, gamma, delta, epsilon and zeta was tested by immunoblot analysis in whole pancreatic islets of mouse and rat and in the insulinoma cell line RINm5F. Effects of GRP, the truncated peptide GRP1-16 and KCl were also measured on translocation of PKC isoforms. In pancreatic islets of mouse and rat, the PKC isoforms alpha, beta, gamma, delta, epsilon and zeta could be detected. No PKCgamma activity was present in the pancreatic tumor cell line RINm5F. Incubation of mouse or rat islets or of RINm5F cells with GRP induced translocation of the PKC isoforms alpha, beta and zeta. The N-terminal portion of the peptide GRP1-16 induced partial translocation only of the PKC isoforms alpha, beta and zeta in mouse and rat islets in 4 out of 10 cases, but failed to show any effect on PKC isoforms in RINm5F cells. Depolarization of the islets by KCl did not translocate any tested PKC isoform. However, incubation with GRP followed by depolarization with KCl led to translocation of the PKC isoforms alpha, beta and zeta. It is suggested that PKC alpha, beta and/or zeta may play a role in the modulation of insulin secretion by GRP.
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PMID:Distribution and stimulation by gastrin-releasing peptide of protein kinase C subfamilies in insulin-secreting cells. 1139 8

GLP-1 (glucagon-like peptide-1) is a potent insulin secretagogue released from L cells in the intestine. The regulation of GLP-1 secretion has been described both in vivo and in vitro in several animal species, but data from human cellular models are lacking. For this purpose, factors and cell-signaling pathways regulating GLP-1 secretion were investigated in the NCI-H716 human intestinal cell line. After differentiation, these cells homogeneously produced 16.8 pmol GLP-1/mg protein with a basal release of 4.2% during a 2-h incubation period. Nutrients, such as palmitic acid, oleic acid, and meat hydrolysate, stimulated GLP-1 secretion in a dose-dependent manner, as did the cholinergic agonist carbachol and the neuromediator gastrin-releasing peptide. Along with stimulating GLP-1 release, gastrin-releasing peptide, like ionomycin, increased intracellular calcium levels. Activators of PKA and PKC were able to increase GLP-1 secretion in NCI-H716 cells. However, neither PKA activators nor meat hydrolysate increased proglucagon mRNA levels. These findings indicate that the NCI-H716 cell line constitutes a unique model to study the cellular mechanism of GLP-1 secretion in humans and suggest potential interspecies divergence in the regulation of proglucagon gene expression in enteroendocrine cells.
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PMID:A human cellular model for studying the regulation of glucagon-like peptide-1 secretion. 1156 18

Bombesin (BN) and structurally related peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB), injected into the lateral ventricle produce multiple effects such as hypothermia, anorexia and hormone release. In this study, the pharmacological characteristics of BN receptors mediating hypothermia in the central nervous system (CNS) were investigated using free-moving male Wistar rats. Intracerebroventricular injections of BN, GRP and NMB produced hypothermia in a dose-dependent manner. The BN (0.3 microg)-induced effect showed a short latency and a 4-h duration with a potency increased by more than 100 times compared to the NMB-induced effect. Pretreatment with [D-Tyr(6)]BN(6-13)methylester, a GRP receptor antagonist, inhibited the BN (0.3 microg)- and NMB (7 microg)-induced hypothermia. On the other hand, BIM23127, an NMB receptor antagonist, did not influence the hypothermia. Of the protein kinase C (PKC) inhibitors, chelerythrine, Go6983, staurosporine and GF109203X, the first two partially blocked the BN-induced hypothermia. A PKC activator, phorbol-12,13-dibutyrate, decreased the rectal temperature. Genistein (a tyrosine kinase inhibitor), Y-27632 (a Rho kinase inhibitor) and PD98059 (a MAPK inhibitor) tended to suppress the BN-induced hypothermia, however, these were not significant. The inhibitory effect of a mixture of the three inhibitors, chelerythrine, genistein and Y-27632, on the BN-induced hypothermia was of a similar degree to that of chelerythrine alone. The BN receptor mediating the hypothermia seem to be the GRP subtype, and the effect involves activation of PKC.
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PMID:Pharmacological characteristics of bombesin receptor mediating hypothermia in the central nervous system of rats. 1267 68

We investigated the effects of antagonists of growth hormone-releasing hormone (GHRH) alone and in combination with bombesin/gastrin-releasing peptide (BN/GRP) antagonist RC-3940-II on the growth of H-69 human small cell lung carcinoma (SCLC) xenografted into nude mice. Since the activation of the signaling pathways involving protein kinase C (PKC) and the subsequent steps involving mitogen-activated protein kinase (MAPK) and c-fos and c-jun oncogenes are known to be important mechanisms implicated in cellular growth, we investigated how the blockade of tumoral GHRH receptor splice variants and BN/GRP receptors by these antagonists could interfere with these intracellular signaling pathways. Treatment with GHRH antagonists JV-1-65 or MZ-J-7-110 for 4 weeks significantly (p<0.05) decreased the tumor volume by 22.7+/-3.0% and 36.7 +/- 3.6%, respectively, as compared to controls. A larger decrease in tumor volume of 73.0 +/- 9.5% (p<0.01) was produced by BN/GRP antagonist RC-3940-II and its combination with JV-I-65 caused the greatest tumor reduction of 91.0 +/- 9.8% (p<0.01) vs. controls. H-69 SCLC tumors expressed alpha-, betaII-, delta- and eta-PKC isoforms. Antagonists of GHRH and BN/GRP decreased significantly (p<0.05) the expression of betaII- and delta-, but not of alpha- and eta-PKC isoforms. They also inhibited MAPK levels, the effects being significant (p<0.05) in the groups that received BN/GRP antagonist. In addition, expression of c-fos and c-jun mRNA was reduced after combined treatment with JV-1-65 and RC-3940-II. The proliferation of H-69 SCLC cells "in vitro" was also significantly inhibited after incubation of cells with GHRH antagonist, PKC inhibitors or MAPK inhibitor. These findings suggest that the anti-proliferative effects of antagonists of GHRH and BN/GRP on H69-SCLC involve an inhibition of the signaling pathways of specific PKC isoforms, MAPK and c-fos and c-jun oncogenes.
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PMID:Suppression of growth of H-69 small cell lung carcinoma by antagonists of growth hormone releasing hormone and bombesin is associated with an inhibition of protein kinase C signaling. 1538 37


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