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)

We have investigated the role of phorbol esters on different biological effects induced by insulin in muscle, such as activation of system A transport activity, glucose utilization and insulin receptor function. System A transport activity was measured by monitoring the uptake of the system A-specific analogue alpha-(methyl)aminoisobutyric acid (MeAIB), by intact rat extensor digitorum longus muscle. The addition of 12-O-tetradecanoylphorbol 13-acetate (TPA, 0.5 microM) for 60 or 180 min did not modify basal MeAIB uptake by muscle, suggesting that insulin signalling required to stimulate MeAIB transport does not involve protein kinase C activation. However, TPA added 30 min before insulin (100 nM) markedly inhibited insulin-stimulated MeAIB uptake. The addition of polymyxin B (0.1 mM) or H-7 (1 mM), protein kinase C inhibitors, alone or in combination with TPA leads to impairment of insulin-stimulated MeAIB uptake. This paradoxical pattern is incompatible with a unique action of Polymyxin B or H-7 on protein kinase C activity. Therefore these agents are not suitable tools with which to investigate whether a certain insulin effect is mediated by protein kinase C. TPA did not cause a generalized inhibition of insulin action. Thus both TPA and insulin increased 3-O-methylglucose uptake by muscle, and their effects were not additive. Furthermore, TPA did not modify insulin-stimulated lactate production by muscle. In keeping with this selective modification of insulin action, treatment of muscles with TPA did not modify insulin receptor binding or kinase activities. In conclusion, phorbol esters do not mimic insulin action on system A transport activity; however, they markedly inhibit insulin-stimulated amino acid transport, with no modification of insulin receptor function in rat skeletal muscle. It is suggested that protein kinase C activation causes a selective post-receptor modification on the biochemical pathway by which insulin activates system A amino acid transport in muscle.
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PMID:Protein kinase C activators selectively inhibit insulin-stimulated system A transport activity in skeletal muscle at a post-receptor level. 219 49

Several growth factors and mitogens have been shown to activate the proto-oncogene product Raf-1 protein kinase in murine fibroblasts, apparently through a direct agonist-stimulated tyrosine phosphorylation of the Raf-1 protein. We investigated the possibility that insulin could also activate the Raf-1 kinase, since its receptor also contains an intrinsic insulin-activated protein tyrosine kinase activity. In several cell lines expressing relatively large numbers of insulin receptors, insulin rapidly stimulated the phosphorylation of immunoreactive Raf-1 protein. In H35 cells, a line of well differentiated rat hepatoma cells, the effect of insulin was maximal by 6 min and at 7 nM insulin and occurred normally in cells virtually completely depleted of protein kinase C activity. The insulin-stimulated increase in Raf-1 protein phosphorylation occurred concurrently with a 3-fold increase in Raf-1 protein kinase activity. However, phosphoamino acid analysis showed that only phosphoserine and a trace of phosphothreonine were present in the Raf-1 protein after insulin stimulation of the cells. This was true even when investigated at shorter times (4 min) after insulin stimulation and despite the use of phosphotyrosine phosphatase inhibitors. We conclude that insulin can rapidly activate the Raf-1 kinase in some insulin-sensitive cell types but that this activation probably occurs through a mechanism distinct from direct phosphorylation of the Raf-1 protein by the insulin receptor protein tyrosine kinase.
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PMID:Insulin activates the Raf-1 protein kinase. 219 71

Insulin and phorbol esters rapidly induce the transcription and cytoplasmic accumulation of a specific mRNA (p33) in rat hepatoma cells. We have studied the effects of insulin desensitization on the regulation of p33 gene expression by insulin and phorbol esters. Insulin desensitization is associated with down-regulation of the insulin receptor and post-receptor defects. When cells were treated with insulin (5 x 10(-7) M) for 24 h, a greater than 50% reduction in insulin binding was observed and insulin's stimulation of p33 transcription and cytoplasmic mRNA levels was prevented. The induction of p33 gene transcription and mRNA levels by phorbol esters was also decreased. Beta-tubulin gene expression was unaffected by insulin or phorbol esters and the stimulatory effect of dexamethasone on p33 gene expression was not impaired. Since insulin desensitization impaired phorbol esters' induction of p33 gene expression, one intracellular defect in insulin-desensitized cells may include an alteration in protein kinase C-dependent events.
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PMID:Decreased induction of an hepatic mRNA by phorbol esters after insulin desensitization. 228 74

Phosphorylation of the insulin receptor beta-subunit on serine/threonine residues by protein kinase C reduces both receptor kinase activity and insulin action in cultured cells. Whether this mechanism regulates insulin action in intact animals was investigated in rats rendered insulin-resistant by 3 days of starvation. Insulin-stimulated autophosphorylation of the partially purified hepatic insulin receptor beta-subunit was decreased by 45% in starved animals compared to fed controls. This autophosphorylation defect was entirely reversed by removal of pre-existing phosphate from the receptor with alkaline phosphatase, suggesting that increased basal phosphorylation on serine/threonine residues may cause the decreased receptor tyrosine kinase activity. Tryptic removal of a C-terminal region of the receptor beta-subunit containing the Ser/Thr phosphorylation sites similarly normalized receptor autophosphorylation. To investigate which kinase(s) may be responsible for such increased Ser/Thr phosphorylation in vivo, protein kinase C and cAMP-dependent protein kinase A in liver were studied. A 2-fold increase in protein kinase C activity was found in both cytosol and membrane extracts from starved rats as compared to controls, while protein kinase A activity was diminished in the cytosol of starved rats. A parallel increase in protein kinase C was demonstrated by immunoblotting with a polyclonal antibody which recognizes several protein kinase C isoforms. These findings suggest that in starved, insulin-resistant animals, an increase in hepatic protein kinase C activity is associated with increased Ser/Thr phosphorylation which in turn decreases autophosphorylation and function of the insulin receptor kinase.
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PMID:Increased protein kinase C activity is linked to reduced insulin receptor autophosphorylation in liver of starved rats. 235 98

The mechanism of the inhibitory action of glucocorticoids on glucose uptake is incompletely understood. Treatment with corticosteroids of cells in which glucose uptake is stimulated at insulin postbinding and postreceptor sites may clarify the site of the steroid inhibitory action. Hydrogen peroxide, which has been shown to stimulate the insulin receptor tyrosine kinase, and phorbol myristate acetate (PMA) which stimulates protein kinase C were, therefore, used as stimulators of glucose transport in this study. These studies demonstrate that dexamethasone and the sphingoid bases, sphinganine and sphingosine, inhibit glucose uptake that has been stimulated at either the receptor kinase or protein kinase C level in both 3T3-L1 and 3T3-C2 cells. These data confirm glucocorticoid inhibitory action at a post binding level and support the suggestion that some corticosteroid inhibitory effects may be mediated by an action on sphingolipid metabolism.
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PMID:Inhibitory action of sphingosine, sphinganine and dexamethasone on glucose uptake: studies with hydrogen peroxide and phorbol ester. 236 44

It has been found that 1,2- but not 1,3-diacylglycerols stimulated phosphorylation of the insulin receptor of cultured human monocyte-like (U-937) and lymphoblastoid (IM-9) cells both in the intact- and broken-cell systems. The stimulation of the receptor's beta-subunit phosphorylation was dose-dependent, with optimal effect at 100 micrograms/ml of diacylglycerol. The effects of insulin and 1,2-diacylglycerols on the phosphorylation of partially purified insulin receptors were additive. Phosphoamino acid analysis showed a major effect of diacylglycerols on phosphorylation of tyrosine residues. The diacylglycerols also stimulated tyrosine kinase activity of the partially purified U-937 and IM-9 insulin receptors 2.5-3.5-fold when measured by phosphorylation of an exogenous substrate, poly(Glu80Tyr20) in the absence of any added insulin, calcium or phospholipid. Since this diacylglycerol effect could not be reproduced under conditions optimal for protein kinase C activation and the purified protein kinase C did not stimulate phosphorylation of the beta-subunit of the insulin receptor in this system, it is unlikely that the diacylglycerol effect was mediated by protein kinase C. Since these exogenous 1,2-diacylglycerols at the same high concentration also inhibited 125I-insulin binding to the insulin receptor of the intact U-937 and IM-9 cells, diacylglycerols could modulate the function of the insulin receptor and insulin action in human mononuclear cells.
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PMID:Diacylglycerols modulate phosphorylation of the insulin receptor from human mononuclear cells. 240 58

Two site-specific antibodies that immunoprecipitate the human insulin receptor have been prepared by immunizing rabbits with chemically synthesized peptides derived from the cDNA-predicted amino acid sequence of the beta subunit of the proreceptor. Antibodies to the carboxyl terminus (AbP5) and to a domain around tyrosine-960 (AbP4) specifically recognize the beta subunit of the receptor on immunoblots. Both antibodies immunoprecipitated 125I-labeled insulin-receptor complexes and the autophosphorylated receptor. Although neither antibody inhibited insulin binding to the receptor, both insulin-dependent autophosphorylation and exogenous substrate phosphorylation were inhibited by AbP4. Inhibition by AbP4 was dependent upon the phosphorylation state of the receptor; it was not detected when the receptor was autophosphorylated prior to addition of AbP4. AbP4 did not inhibit activity of the related epidermal growth factor (EGF)-receptor tyrosine protein kinase nor did it inhibit the activity of cAMP-dependent kinase or protein kinase C. The observation that an antibody directed to residues 952-967 of the proreceptor neutralizes the protein kinase activity of the beta subunit suggests that this region may play a critical role in the function of the hormone-dependent, protein tyrosine-specific kinase activity of the insulin receptor.
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PMID:An antipeptide antibody that specifically inhibits insulin receptor autophosphorylation and protein kinase activity. 241 75

We have studied the insulin-stimulated phosphorylation of proteins in NIH 3T3 cells expressing high numbers of human insulin receptors (HIR 3.5 cells) using the technique of giant two-dimensional gel electrophoresis. In serum-deprived cells, insulin stimulated the phosphorylation of more than 25 proteins; all but two of these were also phosphorylated in response to 15% (v/v) fetal bovine serum, which also stimulated the phosphorylation of additional proteins thought to be direct substrates for protein kinase C. In cells pretreated insulin specifically stimulated the phosphorylation insulin specifically stimulated the phosphorylation of at least 26 predominantly cytosolic proteins, only one of which was observed in insulin-treated cells not exposed to phenylarsine oxide. Serum was without effect in cells pretreated with phenylarsine oxide. In phenylarsine oxide-pretreated cells, phosphoamino acid analysis of 10 of the most highly labeled insulin-stimulated phosphoproteins showed that all 10 were labeled predominantly or exclusively on tyrosine residues. The phosphorylation of several of these could be stimulated in vitro by the addition of insulin to a detergent extract of cells in the presence of Mn2+ and ATP. In general, the insulin-stimulated phosphorylations observed in the presence of phenylarsine oxide were more rapid than those observed in its absence. Finally, a variety of other growth factors and mitogens did not stimulate any of the insulin-stimulated phosphorylations in the presence of phenylarsine oxide. Thus, the use of this inhibitor apparently unmasked a number of novel insulin-specific protein phosphorylations that were ordinarily undetectable. We suggest that at least some of these proteins may be direct substrates for the insulin receptor protein tyrosine kinase and may play significant roles in insulin action.
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PMID:Insulin-stimulated protein tyrosine phosphorylation in intact cells evaluated by giant two-dimensional gel electrophoresis. 247 42

In two-dimensional tryptic phosphopeptide mapping, the beta-subunit of the insulin receptor phosphorylated by 12-O-tetradecanoylphorbol-13-acetate in rat hepatoma cells (H-35) was separated into one phosphothreonine-containing peptide and several phosphoserine-containing peptides. The synthetic peptide coding residues 1327-1343 in the C-terminal region of the rat insulin receptor was phosphorylated at the threonine residue by protein kinase C in a phosphatidylserine and oleoylacetylglycerol dependent manner. Tryptic digest of this phosphopeptide migrated to the same position as the phosphothreonine containing peptide obtained from the beta-subunit in two-dimensional phosphopeptide mapping. These data suggested that Thr 1336 of the insulin receptor is the site of phosphorylation by protein kinase C in intact cells.
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PMID:Identification of a phosphorylation site of the rat insulin receptor catalyzed by protein kinase C in an intact cell. 250 75

We have characterized a plasma membrane phosphatidylinositol 4,5-bisphosphate (PIP2)-specific phospholipase C (PLC) and a cytosolic phosphatidylinositol (PI)-specific PLC in human liver. Epinephrine, 1 x 10(-5) M, and vasopressin, 1 x 10(-8) M, stimulated PIP2-PLC which was enhanced by guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S). PI-PLC stimulation was not observed by these agents. Insulin and insulin-like growth factors (IGF-I and IGF-II) in the presence and absence of GTP gamma S did not stimulate PIP2-PLC or PI-PLC in plasma membranes and cytosol preparations nor phosphoinositide breakdown in isolated human hepatocytes. Furthermore, serendipitly we found that PIP2-PLC activity was increased in liver membranes from obese patients with type II diabetes when compared to obese and lean controls. We conclude that in human liver, insulin and IGFs are not members of the family of hormones generating inositol trisphosphate (IP3) as a second messenger. Furthermore, the increased PIP2-PLC in diabetic liver may result in: (a) increased intracellular concentrations of IP3 and thus increased Ca2+, which has been postulated to induce insulin resistance; and (b) increased diacylglycerol and thus increased protein kinase C which phosphorylates the insulin receptor at serine residues inactivating the insulin receptor kinase. While the mechanism of increased PIP2-PLC activity in diabetes is unknown, it may initiate a cascade of events that result in insulin resistance.
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PMID:Effect of insulin and insulin-like growth factors I and II on phosphatidylinositol and phosphatidylinositol 4,5-bisphosphate breakdown in liver from humans with and without type II diabetes. 254 Jan 78


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