Molecular Mechanisms of Insulin Resistance in IRS-2-Deficient Hepatocytes

Molecular Mechanisms of Insulin Resistance in IRS-2-Deficient Hepatocytes Angela M. Valverde , 1 , Deborah J. Burks 2 , Isabel Fabregat 1 , Tracey L. Fisher 3 , José Carretero 2 , Morris F. White 3 and Manuel Benito 1 1 Instituto de Bioquímica/Departamento de Bioquímica y Biología Molecular II, Centro Mixto CSIC/UCM, Facultad de Farmacia, Universidad Complutense, Madrid, Spain 2 Departamento de Anatomia, Facultad de Medicina, Campus Charro, Salamanca, Spain 3 Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts Address correspondence and reprint requests to Angela M. Valverde, Instituto de Bioquímica/Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Ciudad Universitaria, 28040 Madrid, Spain. E-mail: valverde{at}farm.ucm.es Abstract To assess the role of insulin receptor (IR) substrate (IRS)-2 in insulin action and resistance in the liver, immortalized neonatal hepatocyte cell lines have been generated from IRS-2 −/− , IRS-2 +/− , and wild-type mice. These cells maintained the expression of the differentiated liver markers albumin and carbamoyl phosphate synthetase, as well as bear a high number of IRs. The lack of IRS-2 did not result in enhanced IRS-1 tyrosine phosphorylation or IRS-1-associated phosphatidylinositol (PI) 3-kinase activity on insulin stimulation. Total insulin-induced PI 3-kinase activity was decreased by 50% in IRS-2 −/− hepatocytes, but the translocation of PI-3,4,5-trisphosphate to the plasma membrane in these cells was almost completely abolished. Downstream PI 3-kinase, activation of Akt, glycogen synthase kinase (GSK)-3 (α and β isoforms), Foxo1, and atypical protein kinase C were blunted in insulin-stimulated IRS-2 −/− cells. Reconstitution of IRS-2 −/− hepatocytes with adenoviral IRS-2 restored activation of these pathways, demonstrating that IRS-2 is essential for functional insulin signaling in hepatocytes. Insulin induced a marked glycogen synthase activity in wild-type and heterozygous primary hepatocytes; interestingly, this response was absent in IRS-2 −/− cells but was rescued by infection with adenoviral IRS-2. Regarding gluconeogenesis, the induction of phosphoenolpyruvate carboxykinase and glucose 6-phosphatase by dibutyryl cAMP and dexamethasone was observed in primary hepatocytes of all genotypes. However, insulin was not able to suppress gluconeogenic gene expression in primary hepatocytes lacking IRS-2, but when IRS-2 signaling was reconstituted, these cells recovered this respons