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)

7B2 is a 23-kDa protein encoded by a single gene that is expressed in a variety of neuroendocrine tissues. Although its physiological role has not yet been elucidated, its presence in secretory granules suggests a function in the secretory machinery of certain neuronal and endocrine cells in various species. The present study characterizes the expression of 7B2 in endocrine pancreatic cells. We demonstrate that: (i) 7B2 is highly expressed in human insulinomas; (ii) its ultrastructural localization, associated with secretory granules of A and B cells of the islets, suggests a participation of 7B2 in the secretion of insulin and glucagon; (iii) sequences located in the first intron of the 7B2 gene are required for its transcription in either insulinoma or glucagonoma cell lines; and (iv) in a B cell-like insulinoma cell line, the transcription of 7B2 is regulated by protein kinase A and protein kinase C activators, while in an A-like insulinoma cell line, 7B2 gene transcription seems to be constitutively activated.
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PMID:Expression, intracellular localization, and gene transcription regulation of the secretory protein 7B2 in endocrine pancreatic cell lines and human insulinomas. 751 67

We have reported previously that the rat insulinoma cell lines, RINm5F and RINr1046-38, express the preprotachykinin(PPT)-A gene, which encodes the tachykinin peptides, substance P and neurokinin A. Because endocrine cells of the adult rat pancreas do not appear to express PPT-A, we investigated whether the gene is expressed by rat pancreatic endocrine cells during development. We used immunohistochemistry, employing different substance P and neurokinin A antibodies, to show that many endocrine cells of the fetal and neonatal rat pancreas synthesise these products of PPT-A gene expression. Colabeling experiments revealed that a significant number of both insulin-containing and non-insulin-containing cells express tachykinins. After postnatal day 20, the number of tachykinin-immunoreactive pancreatic islet cells declines and, as already reported, none were detected in the adult rat pancreas. The transient expression of PPT-A by the developing endocrine pancreas is a novel finding. Substance P and neurokinin A are known to have trophic actions and may serve as growth factors during pancreatic islet development. PPT-A gene expression by RINm5F and RINr1046-38 cells is further evidence that these cells resemble developing pancreatic endocrine cells. They are potentially valuable as unique models for studying the regulation of tachykinin biosynthesis. We provide evidence in this study, using quantitative PPT-A messenger RNA analysis, that PPT-A expression in RINm5F cells may be up-regulated by activation of protein kinase C, down-regulated by activation of glucocorticoid receptors, and is not significantly affected by changes in intracellular cAMP levels.
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PMID:Preprotachykinin-A gene expression occurs transiently in the developing rat endocrine pancreas and can be regulated in RINm5F cells. 753 64

In this report we demonstrate that approximately 1.1 kb of the rat glucagon gene promoter upstream of the transcriptional start site specifically directs the transcription of the reporter gene chloramphenicol acetyl transferase (CAT) (p[-1.1]GLU-CAT) in insulinoma beta-TC1 cells. On the contrary, the 350 bp closest to the transcription start site (p[-0.35]GLU-CAT) are ineffective in beta-TC1 cells. Both constructs are transcriptionally active in InR1-G9 glucagonoma cells. While protein kinase A and protein kinase C activators, acting through independent pathways, strongly increase both the transcription of p[-1.1]GLU-CAT and the accumulation of glucagon transcript in beta-TC1 cells, they are weaker activators in InR1-G9 cells. Our experiments suggest that some positive transcription control elements, necessary for the glucagon gene transcription in insulinoma beta-TC1 cells, are localized in the -350/-1100 region of the glucagon gene. Furthermore, our data indicate that glucagon gene transcription can be strongly activated through the protein kinase A pathway in some specific cellular contexts.
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PMID:The glucagon gene is transcribed in beta-like pancreatic cells. 779 81

To extend previous observations on the role of polyamines in insulin production, metabolism, and replication of insulin-secreting pancreatic beta cells, we have studied the role of polyamines in the regulation of the stimulus-secretion coupling of clonal rat insulinoma cells (RINm5F). For this purpose, RINm5F cells were partially depleted in their polyamine contents by use of the specific ornithine decarboxylase inhibitor difluoromethylornithine (DFMO), which led to an increase in cellular insulin and ATP contents. Analysis of different parts of the signal transduction pathway revealed that insulin secretion and the increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) after K(+)-induced depolarization were markedly enhanced in DFMO-treated cells. These effects were paralleled by increased voltage-activated Ca2+ currents, as judged by whole-cell patch-clamp analysis, probably reflecting increased channel activity rather than elevated number of channels per cell. DFMO treatment also rendered phospholipase C in these cells more sensitive to the muscarinic receptor agonist carbamylcholine, as evidenced by enhanced generation of inositol phosphates, increase in [Ca2+]i and insulin secretion, despite an unaltered ligand binding to muscarinic receptors and lack of effect on protein kinase C activity. In addition, the tumor promoter 12-O-tetradecanoylphorbol 13-acetate, at concentrations suggested to be specific for protein kinase C activation, evoked an increased insulin output in polyamine-deprived cells compared to control cells. The stimulatory effects of glucose or the cyclic AMP raising agent theophylline on insulin release were not increased by DFMO treatment. In spite of increased binding of sulfonylurea in DFMO-treated cells, there was no secretory response or altered increase in [Ca2+]i in response to the drug in these cells. It is concluded that partial polyamine depletion sensitizes the stimulus-secretion coupling at multiple levels in the insulinoma cells, including increased voltage-dependent Ca2+ influx and enhanced responsiveness to activators of phospholipase C and protein kinase C. In their entirety, our present results indicate that the behavior of the stimulus-secretion coupling of polyamine-depleted RINm5F insulinoma cells changes towards that of native beta cells, thus improving the usefulness of this cell line for studies of beta cell insulin secretion.
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PMID:Enhanced stimulus-secretion coupling in polyamine-depleted rat insulinoma cells. An effect involving increased cytoplasmic Ca2+, inositol phosphate generation, and phorbol ester sensitivity. 840 43

We studied the effect of protein kinase C (PKC) inhibition and activation on voltage-dependent Ca2+ channels in rat insulinoma RINm5F cells. PKC down-regulation by chronic (24 h) treatment with the PKC activator phorbol 12-myristate 13-acetate (PMA) reduced by about 60% the Ba2+ currents through L- and non-L, non-N-type high-voltage-activated Ca2+ channels, indicating that PKC tonically up-regulates the two main Ca2+ channel subtypes of RINm5F cells under basal conditions. Consistently, PKC activation by acute PMA application caused only a modest increase (average 23%) of Ba2+ currents in a minority of cells (24%). L- and non-L, non-N-type channels were differentially up-regulated by either basal or stimulated PKC activation. Acute up-regulation was predominant on L-type channels and caused an I/V shift of the Ba2+ currents in the hyperpolarizing direction. Non-L, non-N-type channels were less affected by acute PMA application, possibly reflecting a more effective tonic PKC up-regulatory action. Unexpectedly, the increase of Ba2+ currents during acute PMA application was followed by a progressive current decrease, which was also observed in isolation in another 24% of the cells and could be ascribed to PKC-induced ATP depletion, rather than to a direct effect of PKC on Ca2+ channels. We also provide evidence that PKC-mediated phosphorylation is not involved in the G-protein-mediated noradrenergic modulation of Ca2+ channels in RINm5F cells.
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PMID:Up-regulation of L- and non-L, non-N-type Ca2+ channels by basal and stimulated protein kinase C activation in insulin-secreting RINm5F cells. 870 14

The regulation of clonal rat insulinoma (RINm5F) cell proliferation and hormone accumulation was investigated with the aim of identifying putative compounds capable of inducing differentiation, i.e. decreased growth and increased insulin accumulation, by the tumor cells. In particular, interest was focused on the role of a number of peptides as well as pharmacological probes modulating various signal transduction systems and which have been shown to regulate normal beta-cell proliferation and insulin accumulation. Growth hormone stimulated insulin accumulation and inhibited DNA synthesis, whereas galanin and insulin-like growth factor I caused a moderate suppression of insulin accumulation but did not affect proliferation, while epidermal growth factor, transforming growth factor beta, platelet-derived growth factor, acidic and basic fibroblast growth factor, bradykinin and somatostatin were virtually inactive on all parameters tested. Exogenous prostaglandins E2 and F1 alpha were inactive, while the cycloxygenase inhibitor indomethacin slightly suppressed insulin accumulation. The cytokine IL-1 beta caused a significant decrease in both beta-cell mitogenesis and insulin accumulation, effects that were mediated through nitric oxide generation. The vitamin A derivative retinyl acetate slightly inhibited serum-stimulated DNA synthesis, but did not affect insulin accumulation. The vitamin E alpha-tocopherol significantly enhanced insulin release but did not affect mitogenesis. By contrast, gamma-tocopherol was inactive on both these parameters. The alpha-adrenergic agonist clonidine evoked a slight inhibition of serum-stimulated DNA synthesis, without influencing insulin accumulation, whereas phenylephrine did not affect any of these parameters. Carbamylcholine increased insulin accumulation, but not cell proliferation, whereas the adenylyl cyclase activator forskolin suppressed mitogenesis but did not affect insulin accumulation. Inhibition of protein kinase C with staurosporine or prolonged treatment with phorbol ester suppressed DNA synthesis, as did the tyrosine kinase inhibitor genistein. Stimulating Ca2+ influx by closing ATP-dependent K+ channels with glibenclamide enhanced DNA synthesis, while opening of these channels with diazoxide suppressed cell growth. Conversely, preventing Ca2+ influx by the Ca2+ channel antagonist D-600, chelating intracellular Ca2+ by fura-2 AM or inhibiting the Ca2+/calmodulin-dependent protein kinase by calmidazol resulted in a decreased DNA synthesis. On the other hand, uncontrolled influx or mobilization of Ca2+ by ionomycin or thapsigargin resulted in an arrested DNA synthesis. The present paper shows that RINm5F insulinoma cell proliferation and insulin accumulation can be modulated by various peptidergic and pharmacological agents regulating certain signal transduction pathways. However, mitogenesis in the insulinoma cells seemingly is controlled in a vastly different manner in comparison to that in normal beta-cells. The most spectacular finding in this screening study, i.e. that growth hormone, contrarily to its effect on normal beta-cells, suppresses insulinoma cell growth, merits further elucidation of the underlying mechanisms. Possibly the hormone might become of utility in a clinical setting in the treatment of patients with insulin-producing tumors.
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PMID:Regulation of insulinoma cell proliferation and insulin accumulation by peptides and second messengers. 880 83

Previous studies from our laboratory have demonstrated the presence of several isoforms of protein kinase C (PKC), Ca(2+)-independent and Ca(2+)-dependent, in both whole islets and tumor-derived beta cells. In the basal state, a major proportion of the isoform was found in the crude membrane fraction with smaller amounts found in both the cytosolic and cytoskeletal fractions. Whole islets showed a similar distribution of the isoform. These studies were done to analyze the effects of insulin secretagogues on the distribution of PKC delta to different cellular pools in isolated insulinoma beta cells. The phorbol ester, phorbol 12-myristate 13-acetate (PMA), produced a transient association of PKC delta with the beta cell cytoskeleton along with sustained decreases in cytosolic enzyme and transient increases in membrane enzyme. Neither glucose nor carbachol could acutely affect the subcellular distribution of PKC delta. Oleic acid decreased the amount of the enzyme associated with the cytoskeleton and led to a sustained decrease of cytosolic enzyme and a transient increase in membrane enzyme. Oleic acid was also able to prevent the increase in cytoskeletal enzyme induced by PMA. Both oleic acid and PMA potentiated glucose-induced insulin release but oleic acid, in contrast to PMA, was unable to initiate insulin release in the presence of substimulatory concentrations of glucose. These data demonstrate that different activators of PKC may have different effects on localization of the enzyme within the cells and suggest that there are at least three apparently distinct pools of PKC delta within the beta cell which may be important in insulin secretion or other aspects of beta cell function.
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PMID:Regulation of distinct pools of protein kinase C delta in beta cells. 882 22

Glucagon-like peptide-1 (GLP-1) stimulates glucose-induced insulin secretion by binding to a specific G protein-coupled receptor linked to activation of the adenylyl cyclase pathway. Here, using insulinoma cell lines, we studied homologous and heterologous desensitization of GLP-1-induced cAMP production. Preexposure of the cells to GLP-1 induced a decrease in GLP-1-mediated cAMP production, as assessed by a 3- to 5-fold rightward shift of the dose-response curve and an approximately 20 percent decrease in the maximal production of cAMP. Activation of protein kinase C by the phorbol ester phorbol 12-myristate 13-acetate (PMA) also induced desensitization of the GLP-1-mediated response, leading to a 6- to 9-fold shift in the EC50 and a 30% decrease in the maximal production of cAMP. Both forms of desensitization were additive, and the protein kinase C inhibitor RO-318220 inhibited PMA-induced desensitization, but not agonist-induced desensitization. GLP-1- and PMA-dependent desensitization correlated with receptor phosphorylation, and the levels of phosphorylation induced by the two agents were additive. Furthermore, PMA-induced, but not GLP-1-induced, phosphorylation was totally inhibited by RO-318220. Internalization of the GLP-1 receptor did not participate in the desensitization induced by PMA, as a mutant GLP-1 receptor lacking the last 20 amino acids of the cytoplasmic tail was found to be totally resistant to the internalization process, but was still desensitized after PMA preexposure. PMA and GLP-1 were not able to induce the phosphorylation of a receptor deletion mutant lacking the last 33 amino acids of the cytoplasmic tail, indicating that the phosphorylation sites were located within the deleted region. The cAMP production mediated by this deletion mutant was not desensitized by PMA and was only poorly desensitized by GLP-1. Together, our results indicate that the production of cAMP and, hence, the stimulation of insulin secretion induced by GLP-1 can be negatively modulated by homologous and heterologous desensitization, mechanisms that involve receptor phosphorylation.
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PMID:Desensitization and phosphorylation of the glucagon-like peptide-1 (GLP-1) receptor by GLP-1 and 4-phorbol 12-myristate 13-acetate. 883 46

We have previously identified expression of multiple protein kinase C (PKC) isoforms in insulinoma-derived beta-cells and whole islets. Both PKC delta and PKC alpha appear to be the more abundantly expressed isoforms. In this report we studied the effects of arachidonic acid (AA) on the subcellular distribution of PKC alpha and PKC delta. AA has been reported to activate both PKC alpha and PKC delta and it is thought to be an important second messenger in beta-cells. Here we report that AA interacted with and altered beta-cell pools of PKC delta preferentially over PKC alpha. AA (100 microM) over the course of 45 min reduced cytosolic levels of PKC delta (to 40 +/- 15%, compared to time zero control) leaving membrane- and cytoskeleton-associated levels near control levels. Analysis of whole cell homogenates showed a slight down-regulation of PKC delta indicating proteolysis. The down-regulation of cytosolic PKC delta appeared to be isoform specific since cytosolic PKC alpha remained at control levels over the time course. The response was dose-dependent and negligible at concentrations below 30 microM and occurred, at least partially, in the cytosolic compartment of the cell. Indomethacin also down-regulated cytosolic PKC delta preferentially over PKC alpha possibly through accumulation of AA. These findings suggest that cytosolic PKC delta may be a downstream target of this beta-cell second messenger.
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PMID:Arachidonic acid-induced down-regulation of protein kinase C delta in beta-cells. 889 99

Glucagon-like peptide-I (GLP-I) is an important insulinotropic incretin hormone. The GLP-I receptor belongs to the family of seven transmembrane domain receptors. We studied the regulation of its expression by the protein kinase C (PKC)-dependent pathway in rat insulinoma RINm5F cells. Cells were incubated for 3, 6 and 24 h with an optimal concentration of tissue plasminogen activator (TPA), an activator of PKC. TPA induced significantly lower GLP-I receptor mRNA levels under steady-state conditions after 6 and 24 h. The stability of the GLP-I receptor mRNA was unchanged. The number of GLP-I receptors present on RINm5F cells was reduced after 6 and 24 h. TPA did not influence the affinity of remaining receptors to its specific ligand. These data indicate that PKC activation downregulates the expression of the GLP-I receptor gene, mainly at the transcriptional level.
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PMID:Regulation of glucagon-like peptide-I receptor expression and transcription by the protein kinase C pathway. 890 97


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