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Query: UMLS:C0011849 (diabetes)
 277,896 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The insulin receptor contains in its beta-subunit a tyrosine (-) specific protein kinase. It is believed that transmission of an insulin signal across the plasma membrane of target cells of insulin action occurs through activation of this kinase, autophosphorylation of the insulin receptor beta-subunit and subsequent phosphorylation of other cellular substrates. We studied the insulin receptor kinase in a number of insulin resistant cell systems in order to elucidate if defects of this kinase are a possible cause of cellular insulin resistance. Three different patterns of kinase abnormalities were found, in different insulin resistant cells: 1. In an insulin resistance melanoma cell line a reduced receptor kinase autophosphorylation was found apparently due to a defect of the tyrosine autophosphorylation sites of this receptor; 2. Catecholamine and phorbol ester induced insulin resistance of isolated rat fat cells as well as human fat cells was associated with a decreased activity of the insulin receptor tyrosine kinase which was apparently due to a modulation of the ATP binding site of the insulin receptor tyrosine kinase; 3. The receptor kinase isolated from the skeletal muscle of diabetic Zucker rats (fa/fa) was found to be insulin insensitive with no major alteration of maximal responsiveness. These results suggested that different forms of kinase defects exist which can contribute to the pathogenesis of cellular insulin resistance. Based on these data studies in skeletal muscle from type II diabetic patients were started. Results from five patients so far suggest that, here as well, an abnormality of the insulin receptor kinase exists which might be involved in the pathogenesis of insulin resistance in type II diabetes.
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PMID:Insulin receptor kinase defects as a possible cause of cellular insulin resistance. 282 Aug 11

The effect of sulfonylureas tolbutamide and glyburide on adenylate cyclase- and cAMP-dependent protein kinase (A-kinase) was examined in rat liver cytosol. Both tolbutamide and glyburide inhibited the A-kinase activity in a dose-dependent manner. Half-maximal inhibition was obtained at 10 mM with tolbutamide and at 0.2 mM with glyburide, indicating that glyburide was 50-fold as potent as tolbutamide. Neither tolbutamide nor glyburide affected [3H]cAMP binding to the protein kinase, but both inhibited the activity of catalytic units of the A-kinase. Lineweaver-Burk double-reciprocal plots revealed that the inhibitory effects of these drugs were noncompetitive with respect to the protein substrate histone, as well as to the phosphate-donor substrate ATP. Thus, tolbutamide and glyburide inhibited the A-kinase activity in rat liver cytosol, and it was suggested that, through the inhibition of A-kinase, the sulfonylureas would affect the carbohydrate metabolism in the liver. In fact, the relative potencies of these two drugs on A-kinase activity corresponded well with those of their reported antidiabetic effects.
Diabetes 1988 Jul
PMID:Effect of tolbutamide and glyburide on cAMP-dependent protein kinase activity in rat liver cytosol. 283 57

Insulin is thought to influence some metabolic events by decreasing the intracellular concentration of cyclic AMP (cAMP). To test whether this explains the repression of hepatic phosphoenolpyruvate carboxykinase (PEPCK) by insulin we measured intracellular cAMP, cAMP-dependent protein kinase, mRNAPEPCK, and PEPCK gene transcription in cultured Reuber H4IIE hepatoma cells treated with forskolin with and without insulin. In untreated cells, the concentration of cAMP was 2.9 pmol/mg of protein. Forskolin at 1, 10, and 50 microM increased the level of cAMP to 9.2, 35.8, and 115 pmol/mg of protein, respectively; 5 nM insulin had no significant effect on these cAMP concentrations. In untreated cells, the activity ratio of cAMP-dependent protein kinase was 0.43, and 50 microM forskolin increased this to 0.96; insulin had no effect on this ratio at times from 15-180 min. In untreated cells mRNAPEPCK bound 15 cpm of a 32P-labeled cDNA probe per microgram of total cellular RNA. Forskolin, at 1, 10, and 50 microM increased this to 48, 96, and 115 cpm/microgram RNA. Insulin (5 nM), in combination with 0, 1, 10, and 50 microM forskolin, decreased the concentration of mRNAPEPCK to 5, 8, 23, and 29 cpm/micrograms RNA, respectively. Finally, the rate of transcription of the PEPCK gene was 85, 168, 630, 823, and 884 parts per million (ppm) in H4IIE cells treated for 30 min with 0, 1, 5, 10, and 50 microM forskolin, respectively, while the corresponding rates in the presence of 5 nM insulin were 49, 45, 84, 85, and 136 ppm.(ABSTRACT TRUNCATED AT 250 WORDS)
Diabetes 1986 May
PMID:Insulin decreases H4IIE cell PEPCK mRNA by a mechanism that does not involve cAMP. 300 46

The distribution of the spontaneous and trypsin-stimulated phosphorylase phosphatase activities between glycogen particles and cytosol was examined in muscle extracts obtained from rats that had been fasted, made diabetic with streptozotocin or injected with adrenaline. In all conditions the particle-bound phosphatase activities decreased, glycogen was degraded and phosphorylase was released from the particles into the cytosol. However, in fasting and diabetes (but not after adrenaline) the combined glycogen particle + cytosolic phosphatase activities decreased, indicating that the activity lost from the particles was not simply shifted to the cytosol. Fasting and diabetes (but not adrenaline) also decreased the phosphatase-activating ability of the muscle extracts, which was, at least in part, attributable to the protein kinase FA. These data indicate the presence of at least two different mechanisms affecting the phosphatase system, one modified by fasting and diabetes, the other by adrenaline.
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PMID:Effects of streptozotocin-diabetes, fasting and adrenaline on phosphorylase phosphatase activities of rat skeletal muscle. 301 88

Alkali-dissociated, purified preparations of prototype coxsackievirus B4 release a protein kinase that catalyzes the incorporation of gamma-phosphate from 32P-labeled ATP into three virus capsid proteins (VP1, VP3, VP4), several additional proteins of the particle, and exogenous acceptor proteins. Using protamine sulfate as an acceptor protein, we detected nearly 20-fold more enzyme activity in membrane-bound virions (MBV) than in virions of the virus. The activity in the MBV is cyclic nucleotide-independent, divalent cation-dependent, and has a pH optimum of 8.0. Phosphoserine is labeled with 32P. The enzyme activity sediments at about 5S and is separated into at least two peaks of heterogeneous proteins by ion-exchange chromatography. The patterns of phosphorylation by these enzyme peaks are somewhat similar. Coxsackievirus-associated protein kinase appears to be located internally in the virus and may be host-cell-coded. The enzyme appears to be lacking in a variant of the virus that produced diabetes in mice.
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PMID:Protein kinase in nondiabetogenic coxsackievirus B4. 301 40

GTP, in physiologic concentration, enhances the binding of cAMP to a protein in the hepatic cytosol that may be the regulatory subunit of protein kinase II. Ingestion of carbohydrate suppresses hepatic gluconeogenesis and glycogenolysis, two processes that are stimulated by cAMP. In this study, we have examined the possibility that carbohydrate inhibits these processes partly by decreasing the sensitivity of the GTP-responsive cAMP-binding protein to the effect of GTP. We found that 100 muM GTP was much less effective in enhancing cAMP binding in the hepatic cytosol of rats given 15% glucose for 2 days than in the cytosol of fasted rats [21 +/- 3% (mean +/- SE) increase vs. 67 +/- 6%, P less than .01]. Corresponding results were noted in diethylaminoethyl (DEAE)-cellulose extracts of the hepatic cytosol of these rats. GTP stimulation of cAMP binding was also diminished in the hepatic cytosol of diabetic rats treated for 7 days with insulin compared with that of untreated diabetic rats (29 +/- 10 vs. 81 +/- 11% increase, P less than .01), but this could have been due to increased food intake in the treated rats. We conclude that GTP stimulation of hepatic cAMP binding is decreased in the carbohydrate-fed state and that this effect may be mediated by the increase in plasma insulin induced by carbohydrate. Our observations suggest that some of the cellular effects of cAMP may be regulated by modulation of the stimulatory effect of GTP on the GTP-responsive cAMP-binding protein.
Diabetes 1987 Jan
PMID:Effects of fasting, feeding, and insulin on enhancing effect of GTP on cAMP binding in rat hepatic cytosol. 302 42

Acute hormonal regulation of liver carbohydrate metabolism mainly involves changes in the cytosolic levels of cAMP and Ca2+. Epinephrine, acting through beta 2-adrenergic receptors, and glucagon activate adenylate cyclase in the liver plasma membrane through a mechanism involving a guanine nucleotide-binding protein that is stimulatory to the enzyme. The resulting accumulation of cAMP leads to activation of cAMP-dependent protein kinase, which, in turn, phosphorylates many intracellular enzymes involved in the regulation of glycogen metabolism, gluconeogenesis, and glycolysis. These are (1) phosphorylase b kinase, which is activated and, in turn, phosphorylates and activates phosphorylase, the rate-limiting enzyme for glycogen breakdown; (2) glycogen synthase, which is inactivated and is rate-controlling for glycogen synthesis; (3) pyruvate kinase, which is inactivated and is an important regulatory enzyme for glycolysis; and (4) the 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase bifunctional enzyme, phosphorylation of which leads to decreased formation of fructose 2,6-P2, which is an activator of 6-phosphofructo-1-kinase and an inhibitor of fructose 1,6-bisphosphatase, both of which are important regulatory enzymes for glycolysis and gluconeogenesis. In addition to rapid effects of glucagon and beta-adrenergic agonists to increase hepatic glucose output by stimulating glycogenolysis and gluconeogenesis and inhibiting glycogen synthesis and glycolysis, these agents produce longer-term stimulatory effects on gluconeogenesis through altered synthesis of certain enzymes of gluconeogenesis/glycolysis and amino acid metabolism. For example, P-enolpyruvate carboxykinase is induced through an effect at the level of transcription mediated by cAMP-dependent protein kinase. Tyrosine amino-transferase, serine dehydratase, tryptophan oxygenase, and glucokinase are also regulated by cAMP, in part at the level of specific messenger RNA synthesis. The sympathetic nervous system and its neurohumoral agonists epinephrine and norepinephrine also rapidly alter hepatic glycogen metabolism and gluconeogenesis acting through alpha 1-adrenergic receptors. The primary response to these agonists is the phosphodiesterase-mediated breakdown of the plasma membrane polyphosphoinositide phosphatidylinositol 4,5-P2 to inositol 1,4,5-P3 and 1,2-diacylglycerol. This involves a guanine nucleotide-binding protein that is different from those involved in the regulation of adenylate cyclase. Inositol 1,4,5-P3 acts as an intracellular messenger for Ca2+ mobilization by releasing Ca2+ from the endoplasmic reticulum.(ABSTRACT TRUNCATED AT 400 WORDS)
Diabetes Metab Rev 1987 Jan
PMID:Mechanisms of hormonal regulation of hepatic glucose metabolism. 303 41

We have determined glucose transport, insulin binding, and insulin-receptor kinase activity in adipose tissue from morbidly obese patients with and without non-insulin-dependent diabetes mellitus (NIDDM). The insulin sensitivity and responsiveness of glucose transport in freshly isolated adipocytes were significantly reduced in NIDDM subjects compared with nondiabetics. This was due in part to decreased insulin binding in adipocytes. Reduced specific 125I-labeled insulin binding was also observed in crude detergent extracts and partially purified insulin receptors from adipose tissue. In addition, the basal and insulin-stimulated tyrosine-specific protein kinase activity per milligram of protein was significantly decreased in NIDDM patients compared with nondiabetics. The differences between maximally insulin-stimulated and basal kinase activities expressed by insulin-binding activity were also significantly reduced in NIDDM subjects. We conclude that insulin resistance in morbidly obese patients with NIDDM is due to both insulin-binding and postbinding defects. One of the postbinding defects in NIDDM appears to be impaired insulin-receptor kinase activity of fat tissue.
Diabetes 1987 May
PMID:Insulin-receptor kinase activity of adipose tissue from morbidly obese humans with and without NIDDM. 303 15

The ontogeny of the structural and functional characteristics of insulin receptors is determined by examining insulin binding, subunit structure, autophosphorylation, and tyrosine-specific protein kinase activity in partially purified solubilized liver receptors from fetal (approximately 21 days postconception), neonatal (1- and 7-day-old), and adult rats. Specific 125I-labeled insulin binding to these receptor preparations in the presence of different insulin concentrations was higher in fetal and neonatal rats compared with that in the adult rats. The electrophoretic mobilities of the alpha- and beta-subunits on sodium dodecyl sulfate-polyacrylamide gel electrophoresis autoradiography were similar at different stages of development. Insulin-stimulated autophosphorylation of insulin receptors was similar in the different groups. With fixed amounts of protein, the tyrosine-specific protein kinase activity in the presence of different insulin concentrations (1 X 10(-8) to 1 X 10(-6) M) was significantly higher in the fetal and neonatal rats than in adult rats. However, when expressed as a function of insulin-binding activity, the insulin-stimulated tyrosine-specific protein kinase activity in fetal and neonatal rats appears to be similar to that in adult rats because of decreased insulin binding in the latter group. These results demonstrate the structural and functional similarities of hepatic insulin receptors in fetal, neonatal, and adult rats. The relative differences in insulin-mediated biological functions in fetal and adult rat livers as reported previously are due to alterations in a step(s) distal to activation of insulin-receptor kinase.
Diabetes 1987 Oct
PMID:Subunit structure, autophosphorylation, and tyrosine-specific protein kinase activity of hepatic insulin receptors in fetal, neonatal, and adult rats. 330 86

The development of insulin-dependent diabetes mellitus is thought to be dependent on either the autoimmunity or the interaction of environmental agents with the pancreatic beta cells, or both in a genetically susceptible host. As environmental factors affecting the induction of type I diabetes, diabetogenic chemicals and viruses are likely candidates as primary injurious agents for pancreatic beta cells in man and animal. A number of structurally diverse chemicals including alloxan, streptozotocin, chlorozotocin, vacor, and cyproheptadine are diabetogenic mainly in rodents and sometimes in man. The possible mechanisms for the beta cell destruction by these chemicals include (a) generation of oxygen free radicals and alteration of endogenous scavengers of these reactive species; (b) breakage of DNA and consequent increase in the activity of poly ADP ribose synthetase, and enzyme depleting NAD in beta cells; and (c) inhibition of active calcium transport and calmodulin-activated protein kinase activity. Regarding viruses, a number of different viruses including encephalomyocarditis virus, Mengovirus, Coxsackie B viruses, and Reoviruses can infect and destroy pancreatic beta cells mainly in rodents and sometimes in humans. In the murine model, the development of encephalomyocarditis and Coxsackie B virus-induced diabetes is dependent on the genetic background of the host and the genetic makeup of the virus. Mengo-2T virus has caused diabetes in strains of mice resistant to encephalomyocarditis virus-induced diabetes. In contrast to encephalomyocarditis virus, Coxsackie B viruses, and Mengovirus, reovirus type 1 seems to be somewhat associated with an autoimmune response in the induction of diabetes. In addition to the murine model, cotton rats become diabetic when inoculated with Mengovirus 2T. Furthermore, cumulative environmental insults with Coxsackie B viruses and chemicals result in diabetes in non-human primates. In man, there may be 2 possible roles for viruses in the pathogenesis of insulin-dependent diabetes mellitus. The one is acute cytolytic infection of beta cells (e.g., Coxsackie B viruses), which may sometimes induce diabetes in genetically predisposed individuals, and the other one is slow and persistent infection (e.g., congenital cytomegalovirus and Rubella), which may induce autoimmunity, leading to type I diabetes.
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PMID:Effects of environmental factors on the development of insulin-dependent diabetes mellitus. 331 67


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