1,721,229 research outputs found
Molecular determinants of insulin action
No full textInsulin rapidly stimulates tyrosine phosphorylation of a 185-kDa protein in most cell types. This protein, insulin receptor substrate 1 (IRS-1), has been implicated as the first postreceptor step in insulin signal transmission based on studies with insulin receptor mutants. In cell culture and in vitro, phosphory-lated IRS-1 associates with the lipid-metabolizing enzyme phosphatidylinosi-tol 3-kinase (PI 3-kinase), resulting in activation of this enzyme. Thus, the insulin receptor, IRS-1 and PI-3 kinase represent three of the earliest steps in insulin action at the cellular level. We have recently demonstrated that insulin is capable of stimulating PI 3-kinase activity in liver and muscle in vivo in animals and that IRS-1 phosphorylation may play a significant role in the association/activation with PI 3-kinase in vivo
Metabolic Aspects of Bariatric Surgery
No full textInsulin resistance is a nearly universal finding in morbid obesity. It may be compensated and latent or uncompensated with single or multiple clinical abnormalities. Although lifestyle interventions and medical measures alone may control most metabolic problems in the short term, the ultimate benefits of such an approach are usually limited by the complexity of available therapeutic regimens and the difficulty of maintaining full patient compliance. Many studies now document that bariatric surgery can effectively and safely control these complications in the short term and long term or even prevent their occurrence. Further investigations are needed to understand better the mechanisms involved and to define more clearly the appropriate indications and contraindications of the treatments proposed
Insulin and dexamethasone regulate insulin receptors, insulin receptor substrate-1, and phosphatidylinositol 3-kinase in Fao hepatoma cells
No full textInsulin rapidly stimulates tyrosine kinase activity of its receptor, resulting in phosphorylation of the cytosolic substrate, insulin receptor substrate-1 (IRS-1), which, in turn, associates with phosphatidylinositol 3-kinase (PI 3-kinase), thus activating the enzyme. In the present study we have examined these three early postreceptor components of the insulin action pathway in rat hepatoma (Fao) cells and have determined the effects of two hormones that can induce insulin resistance, dexamethasone and insulin. Dexamethasone (1 microM) induced a time- and dose-dependent increase in insulin receptor levels in Fao cells, reaching 135 +/- 3% of basal levels after 24 h (P < 0.05). There was a simultaneous increase in IRS-1 protein to 255 +/- 66% of the control value (P < 0.05) and a parallel increase in IRS-1 phosphorylation. Insulin stimulation of IRS-1-associated PI 3-kinase was also increased by 70% in cells treated with dexamethasone despite only a minimal increase in PI 3-kinase protein, as determined by immunoblotting. Prolonged insulin treatment induced a time- and dose-dependent decrease in insulin receptor and IRS-1 protein levels, reaching nadirs of 40 +/- 4% (P < 0.01) and 15 +/- 6% (P < 0.005) of control levels, respectively, after 24 h with 100 nM insulin. There was also a decrease in the phosphorylation of insulin receptors and IRS-1, a marked decrease in the association between IRS-1 and PI 3-kinase, and an 82% decrease in insulin-stimulated PI 3-kinase activity without a significant change in PI 3-kinase protein levels. When cells were exposed to both insulin and dexamethasone, the effect of insulin to reduce insulin receptor and IRS-1 levels and insulin-stimulated IRS-1 phosphorylation dominated. These data suggest that regulation of the insulin receptor, IRS-1, and PI 3-kinase contributes significantly to the insulin resistance induced by chronic hyperinsulinemia, but that glucocorticoid-induced insulin resistance is located beyond these early steps in insulin action
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