title: Regulation of insulin receptor substrate-2 tyrosine phosphorylation in animal models of insulin resistance.
abstract: Insulin induces a wide variety of growth and metabolic responses in many cell types. These actions are initiated by insulin binding to its receptor and involve a series of alternative and complementary pathways created by the multiple substrates of the insulin receptor (insulin receptor substrates [IRSs]). We investigated IRS-1 and IRS-2 tyrosine phosphorylation; their association with phosphatidylinositol-3-OH kinase (PI3-K); and the phosphorylation of Akt, a serine-threonine kinase situated downstream of PI3-K, in liver and muscle of two animal models of insulin resistance: epinephrine- or dexamethasone-treated rats. We used in vivo insulin infusion followed by tissue extraction, immunoprecipitation, and immunoblotting. IRS-1 and IRS-2 protein expression did not change in liver and muscle of the epinephrine- treated rats, but in dexamethasone-treated rats IRS-1 presented an increase in liver and a decrease in muscle tissue. PI3-K and Akt protein expression did not change in liver or muscle of the two animal models of insulin resistance. There was a downregulation in insulin- induced IRS-1 and IRS-2 tyrosine phosphorylation and association with PI3-K in both models of insulin resistance. In parallel, insulin-induced Akt phosphorylation was reduced in both tissues of epinephrine-treated rats, and in liver but not in muscle of dexamethasonetreated rats. The reduction in insulin-induced Akt phosphorylation may help to explain the insulin resistance in liver and muscle of epinephrine-treated rats and in the liver of dexamethasone-treated rats.
authors.affiliation: Departamento de Clínica Médica, FCM, UNICAMP, Campinas, SP, Brasil.
authors.forename: Fernanda Alvarez
authors.initials: FA
authors.lastname: Rojas
authors.forename: Aparecida Emiko
authors.initials: AE
authors.lastname: Hirata
authors.forename: Mario J A
authors.initials: MJ
authors.lastname: Saad
mesh_terms: D000818:Animals; D003907:Dexamethasone / Q000494:pharmacology; D004195:Disease Models, Animal; D015536:Down-Regulation; D004837:Epinephrine / Q000502:physiology; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D008099:Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects / Q000378:metabolism*; D010750:Phosphoproteins / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000187:drug effects / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017208:Rats, Wistar; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D003907:Dexamethasone; D004837:Epinephrine; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D014443:Tyrosine; C526296:Irs1 protein, rat; C526299:Irs2 protein, rat; C494920:Akt1 protein, rat