Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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

Insulin stimulates tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1), which in turn binds to and activates phosphatidylinositol 3-kinase (PI 3-kinase). In the present study, we have examined these processes in animal models of insulin-resistant and insulin-deficient diabetes mellitus. After in vivo insulin stimulation, there was a 60-80% decrease in IRS-1 phosphorylation in liver and muscle of the ob/ob mouse. There was no insulin stimulation of PI 3-kinase (85 kD subunit) association with IRS-1, and IRS-1-associated PI 3-kinase activity was reduced 90%. Insulin-stimulated total PI 3-kinase activity was also absent in both tissues of the ob/ob mouse. By contrast, in the streptozotocin diabetic rat, IRS-1 phosphorylation increased 50% in muscle, IRS-1-associated PI 3-kinase activity was increased two- to threefold in liver and muscle, and there was a 50% increase in the p85 associated with IRS-1 after insulin stimulation in muscle. In conclusion, (a) IRS-1-associated PI 3-kinase activity is differentially regulated in hyperinsulinemic and hypoinsulinemic diabetic states; (b) PI 3-kinase activation closely correlates with IRS-1 phosphorylation; and (c) reduced PI 3-kinase activity may play a role in the pathophysiology of insulin resistant diabetic states, such as that seen in the ob/ob mouse.
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PMID:Regulation of phosphatidylinositol 3-kinase activity in liver and muscle of animal models of insulin-resistant and insulin-deficient diabetes mellitus. 769 86

Insulin receptor substrates-1 (IRS-1) is the major cytoplasmic substrate of the insulin and IGF-1 receptors. Recent studies have identified multiple sequence variants of IRS-1, especially in patients with non-insulin-dependent diabetes mellitus. In the present study, we have examined insulin-stimulated processes in 32D(IR) cells, a myeloid progenitor cell stably overexpressing the insulin receptor, transfected with wild-type human-IRS-1 or the most common human variant of IRS-1 in which glycine 972 is replaced by arginine. As compared to wild-type IRS-1, insulin stimulation of cells transfected with mutant IRS-1 exhibited a 32% decrease in incorporation of [3H]thymidine into DNA (P = 0.002), a 36% decrease in IRS-1 associated phosphatidylinositol (PI) 3-kinase activity (P = 0.004) and a 25% decrease in binding of the p85 regulatory subunit of PI 3-kinase to IRS-1 (P = 0.002). There was also a tendency for a decrease in Grb2 binding to IRS-1 and insulin-stimulated mitogen-activated protein kinase activity, however, these were not statistically significant. The changes occurred with no change in insulin receptor or IRS-1 tyrosine phosphorylation. These data indicate that the mutation in codon 972 in IRS-1 impairs insulin-stimulated signaling, especially along the PI 3-kinase pathway, and may contribute to insulin resistance in normal and diabetic populations.
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PMID:A common amino acid polymorphism in insulin receptor substrate-1 causes impaired insulin signaling. Evidence from transfection studies. 864 50

Protein kinase C consists of a family of at least 12 isoforms which exhibit clear differences in their cofactor dependence and responsiveness to phospholipids. Insulin effects on PKC translocation/activation are now clearly established but responsiveness to this hormone was observed so far only for the classical PKC-isoforms alpha and beta. While activation of the classical PKC's requires Ca2+ and occurs mainly through Diacylglycerol (DAG), stimulation of the atypical isoform PKC-zeta appears to function through a different mechanism involving PI-3-kinase activation. In the present study we used rat-1 fibroblasts stably over-expressing human insulin receptor to investigate whether insulin can activate PKC-zeta and whether such an effect might be related to insulin's effect on PI-3-kinase. After stimulation of the cells with insulin (10(-7) mol/l) for one to ten minutes, a rapid translocation of PKC-zeta to the plasma membrane was detectable, as determined by immunoblotting of plasma membrane proteins with antibodies against PKC-zeta. In parallel immunoblots applying antibodies against the regulatory subunit of PI-3-kinase (p85), an insulin-induced translocation of p85 was detectable within one minute after stimulation. The translocation of p85 was associated with an increase in PI-3-kinase activity at the plasma membrane. The data show that insulin stimulates translocation of PKC-zeta in rat-1 fibroblasts. The parallel kinetics of PI-3-kinase translocation/activation and PKC-zeta translocation are compatible with the idea that the insulin effect on PKC-zeta is transduced through PI-3-kinase activation.
Exp Clin Endocrinol Diabetes 1996
PMID:Insulin leads to a parallel translocation of PI-3-kinase and protein kinase C zeta. 875 May 65

Glucose transport in skeletal muscle can be mediated by two separate pathways, one stimulated by insulin and the other by muscle contraction. High-fat feeding impairs glucose transport in muscle, but the mechanism remains unclear. FVB mice (3 weeks old) were fed a high-fat diet (55% fat, 24% carbohydrate, 21% protein) or standard chow for 3-4 weeks or 8 weeks. Insulin-stimulated glucose transport, assessed with either 2-deoxyglucose or 3-O-methylglucose was decreased 35-45% (P < 0.001) in isolated soleus muscle, regardless of diet duration. Similarly, glucose transport stimulated by okadaic acid, a serine/threonine phosphatase inhibitor, was also 45% lower with high-fat feeding, but the glucose transport response to hypoxia or N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) (which are stimulators of the "contraction pathway") was intact. Hexokinase I, II, and total activity were normal in soleus muscle from high-fat-fed mice. GLUT4 expression in soleus muscle from the high-fat-fed mice was also normal, but the insulin-stimulated cell surface recruitment of GLUT4 assessed by exofacial photolabeling with [3H]-ATB bis-mannose was reduced by 50% (P < 0.001). Insulin-receptor substrate 1 (IRS-1) associated phosphatidylinositol (PI) 3-kinase activity stimulated by insulin was also reduced by 36% (P < 0.001), and expression of p85 and p110b subunits of PI 3-kinase was normal. In conclusion, high-fat feeding selectively impairs insulin-stimulated, but not contraction-pathway-mediated, glucose transport by reducing GLUT4 translocation to the plasma membrane. This appears to result from an acquired defect in insulin activation of PI 3-kinase. Since effects of okadaic acid on glucose transport are independent of PI 3-kinase, a second signaling defect may also be induced.
Diabetes 1997 Feb
PMID:High-fat feeding impairs insulin-stimulated GLUT4 recruitment via an early insulin-signaling defect. 900 Jun 97

Malnutrition is related to diabetes in tropical countries. In experimental animals, protein deficiency may affect insulin secretion. However, the effect of malnutrition on insulin receptor phosphorylation and further intracellular signaling events is not known. Therefore, we decided to evaluate the rate of insulin secretion and the early molecular steps of insulin action in insulin-sensitive tissues of an animal model of protein deficiency. Pancreatic islets isolated from rats fed a standard (17%) or a low (6%) protein diet were studied for their secretory response to increasing concentrations of glucose in the culture medium. Basal as well as maximal rates of insulin secretion were significantly lower in the islets isolated from rats fed a low protein diet. Moreover, the dose-response curve to glucose was significantly shifted to the right in the islets from malnourished rats compared with islets from control rats. During an oral glucose tolerance test, there were significantly lower circulating concentrations of insulin in the serum of rats fed a low protein diet in spite of no difference in serum glucose concentration between the groups, suggesting an increased peripheral insulin sensitivity. Immunoblotting and immunoprecipitation were used to study the phosphorylation of the insulin receptor and the insulin receptor substrate-1 as well as the insulin receptor substrate-1-p85 subunit of phosphatidylinositol 3-kinase association in response to insulin. Values were greater in hind-limb muscle from rats fed a low protein diet compared with controls. No differences were detected in the total amount of protein corresponding to the insulin receptor or insulin receptor substrate-1 between muscle from rats fed the two diets. Therefore, we conclude that a decreased glucose-induced insulin secretion in pancreatic islets from protein-malnourished rats is responsible, at least in part, for an increased phosphorylation of the insulin receptor, insulin receptor substrate-1 and its association with phosphatidylinositol 3-kinase. These might represent some of the factors influencing the equilibrium in glucose concentrations observed in animal models of malnutrition and undernourished subjects.
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PMID:Glucose-induced insulin secretion is impaired and insulin-induced phosphorylation of the insulin receptor and insulin receptor substrate-1 are increased in protein-deficient rats. 908 23

Insulin receptor substrate-1 (IRS-1) is one of the major substrates of insulin receptor tyrosine kinase and mediates various insulin signals downstream. In this study, we have examined the impact of three natural IRS-1 mutations identified in NIDDM patients (G971R, P170R, and M209T) on insulin signaling. G971R is located near src homology 2 protein binding sites, and P170R and M209T are located in the phosphotyrosine binding domain of IRS-1. 32D-IR cells, stably overexpressing human insulin receptor, were transfected with wild-type human IRS-1 cDNA (WT) or three mutant IRS-1 cDNAs and analyzed. All the cell lines expressing mutant IRS-1 showed a significant reduction in [3H]thymidine incorporation compared with WT. Upon insulin stimulation, cells expressing G971R showed a 39% decrease (P < 0.005) in phosphatidylinositol 3-kinase (PI 3-kinase) activity, a 43% decrease (P < 0.01) in binding of the 85-kDa regulatory subunit of PI 3-kinase, and a 22% decrease (P < 0.05) in mitogen-activated protein kinase activity compared with those expressing WT. Cells expressing P170R and M209T showed slight but significant decreases in PI 3-kinase activity (17 and 14%, respectively; both P < 0.05) and in binding of p85 (22 and 16%, respectively; both P < 0.05) and a greater decrease in mitogen-activated protein kinase activity (41 and 43%, respectively; both P < 0.005) compared with WT. After insulin stimulation, cells expressing P170R and M209T showed significant decreases in IRS-1 phosphorylation (37 and 42%, respectively; both P < 0.05) and in IRS-1 binding to the insulin receptor (48 and 53%, respectively; P < 0.01) compared with WT. G971R showed no changes in IRS-1 phosphorylation and in IRS-1 binding to the insulin receptor compared with WT. These data suggest that the impaired mitogenic response of P170R and M209T was mainly due to reduced binding to the insulin receptor, whereas the impaired response of G971R was mainly due to reduced association with PI 3-kinase p85.
Diabetes 1997 Jun
PMID:Impact of natural IRS-1 mutations on insulin signals: mutations of IRS-1 in the PTB domain and near SH2 protein binding sites result in impaired function at different steps of IRS-1 signaling. 916 61

Several polymorphisms have been identified in the amino acid sequence of human insulin receptor substrate-1 (IRS-1). Some of the variant sequences have been reported to be increased in prevalence among patients with noninsulin-dependent diabetes mellitus (NIDDM). This observation led to the hypothesis that these amino acid substitutions may impair the function of IRS-1, thereby causing the insulin resistance seen in patients with NIDDM. To address this question, we have designed studies to evaluate the effects of three variant sequences identified in our laboratory: Gly819-->Arg, Gly972-->Arg, and Arg1221-->Cys. We constructed four IRS-1 expression vectors for transfection in COS-7 cells: wild-type, single mutant (Gly819-->Arg), double mutant (Gly819-->Arg; Gly972-->Arg), and triple mutant (Gly819-->Arg; Gly972-->Arg; Arg1221-->Cys) IRS-1. The mutations did not alter the level of expression or the extent of insulin receptor-mediated tyrosine phosphorylation of recombinant IRS-1. Moreover, the mutations did not lead to a detectable impairment in the association of recombinant IRS-1 with important downstream effectors, including the p85 subunit of phosphatidylinositol 3-kinase and growth factor receptor-binding protein-2. We conclude that these amino acid substitutions do not appear to cause a major defect in the function of IRS-1, as judged by our assays. However, this type of assay probably lacks the sensitivity to detect subtle functional defects. In light of the suggestive associations observed in epidemiological studies, it is premature to totally discard the hypothesis that variant sequences of IRS-1 may contribute to the pathogenesis of NIDDM. Nevertheless, our studies cannot be interpreted as lending support to that hypothesis.
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PMID:Expression of variant forms of insulin receptor substrate-1 identified in patients with noninsulin-dependent diabetes mellitus. 939 40

Prolonged exposure of 3T3-L1 adipocytes to micromolar concentrations of H2O2 results in an impaired response to the acute metabolic effects of insulin. In this study, we further characterized the mechanisms by which oxidative stress impairs insulin stimulation of glucose transport activity. Although insulin induced a 2.5-fold increase in plasma membrane GLUT4 content and a 50% reduction in its abundance in the low-density microsomal (LDM) fraction in control cells, oxidation completely prevented these responses. The net effect of insulin on 2-deoxyglucose uptake activity was reduced in oxidized cells and could be attributed to GLUT1 translocation. Insulin stimulation of insulin receptor substrate (IRS) 1 tyrosine phosphorylation and the association of IRS-1 with phosphatidylinositol (PI) 3-kinase were not impaired by oxidative stress. However, a 1.9-fold increase in the LDM content of the p85 subunit of PI 3-kinase after insulin stimulation was observed in control, but not in oxidized, cells. Moreover, although insulin induced an increase in IRS-1-associated PI 3-kinase activity in the LDM in control cells, this effect was prevented by oxidation. These findings suggest that prolonged low-grade oxidative stress impairs insulin-stimulated GLUT4 translocation, potentially by interfering with compartment-specific activation of PI 3-kinase.
Diabetes 1998 Oct
PMID:Prolonged oxidative stress impairs insulin-induced GLUT4 translocation in 3T3-L1 adipocytes. 975 93

In a recent study we have demonstrated that 3T3-L1 adipocytes exposed to low micromolar H2O2 concentrations display impaired insulin stimulated GLUT4 translocation from internal membrane pools to the plasma membrane (Rudich, A., Tirosh, A., Potashnik, R., Hemi, R., Kannety, H., and Bashan, N. (1998) Diabetes 47, 1562-1569). In this study we further characterize the cellular mechanisms responsible for this observation. Two-hour exposure to approximately 25 microM H2O2 (generated by adding glucose oxidase to the medium) resulted in disruption of the normal insulin stimulated insulin receptor substrate (IRS)-1 and phosphatidylinositol (PI) 3-kinase cellular redistribution between the cytosol and an internal membrane pool (low density microsomal fraction (LDM)). This was associated with reduced insulin-stimulated IRS-1 and p85-associated PI 3-kinase activities in the LDM (84 and 96% inhibition, respectively). The effect of this finding on the downstream insulin signal was demonstrated by a 90% reduction in insulin stimulated protein kinase B (PKB) serine 473 phosphorylation and impaired activation of PKBalpha and PKBgamma. Both control and oxidized cells exposed to heat shock displayed a wortmannin insensitive PKB serine phosphorylation and activity. These data suggest that activation of PKB and GLUT4 translocation are insulin signaling events dependent upon a normal insulin induced cellular compartmentalization of PI 3-kinase and IRS-1, which is oxidative stress-sensitive. These findings represent a novel cellular mechanism for the induction of insulin resistance in response to changes in the extracellular environment.
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PMID:Oxidative stress disrupts insulin-induced cellular redistribution of insulin receptor substrate-1 and phosphatidylinositol 3-kinase in 3T3-L1 adipocytes. A putative cellular mechanism for impaired protein kinase B activation and GLUT4 translocation. 1018 55

Even among young, healthy individuals, there is more than a 10-fold variation in insulin sensitivity; however, taken in combination, all the known modifiers of insulin sensitivity - including obesity and a variety of environmental factors - explain less than one third of this variation. It is possible that genetic factors could account for the bulk of the variance observed, and hence play a major role in the development of impaired insulin sensitivity, ie insulin resistance. From the genetic point of view, insulin resistance is thought to be due to the inheritance of a number of mutations in a variety of genes. Three complementary approaches have been applied in the search for mutations: mutational analysis of candidate genes; linkage analysis of candidate genes or chromosomal regions for insulin resistance in familial type 2 diabetes; and random genome mapping with quantitative trait loci (QTL) analysis. Mutational analysis of the insulin signalling cascade has identified a glycine-arginine (Gly-Arg) substitution at codon 972 of the insulin receptor substrate-1 (IRS-1) gene with a carrier prevalence of 9% among Caucasians. Expression of this variant in 32-D cells is associated with a significant (20-30%) impairment of insulin-stimulated PI3-kinase activity, as well as reduced binding of IRS-1 to the p85 regulatory subunit of PI3-kinase. Genotype/phenotype studies stratified according to body mass index (BMI) indicate that obese subjects who are heterozygous for the mutant allele have a 50% decrease in insulin sensitivity, compared with wild-type obese subjects. This suggests that there may be an interaction between the mutant allele and obesity, such that, in the presence of obesity, the mutant variant may aggravate the obesity-associated insulin resistance. Mutational analysis has also shown that homozygous carriers of a codon Met 326 Ile mutation in the p85 subunit of phosphatidylinositol-3 (PI3)-kinase (about 2% of the Caucasian population) have lower glucose tolerance, glucose effectiveness. A further Asp to Tyr polymorphism has been identified at codon 905 of the gene encoding the regulatory subunit of glycogen-associated protein phosphatase-1 (PP1G). Individuals who are heterozygous for this polymorphism constitute 18% of the Caucasian population and appear to exhibit both tissue-specific and pathway-specific insulin resistance. It is likely that inherited insulin resistance will eventually prove to be related to subtle mutations in many such genes of the insulin signalling network and the numerous genetic components controlling energy metabolism.
Exp Clin Endocrinol Diabetes 1999
PMID:Genetics of insulin resistance. 1032 50


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