title: Role of IRS-4 in PI3-K activation by insulin in HepG2 cells, modulation by Angiotensin II.
abstract: Insulin receptor substrate-4 (IRS-4) has a limited tissue expression and its modulation by tyr-phosphorylation is still controversial. We evaluated the participation of IRS-4 in the cross-talk between Angiotensin II (Ang II) and Insulin (Ins) receptors in HepG2 cells. Ins (10(-7)M) induced tyr-phosphorylation of IRS-4 (maximal at 5 min), an effect potentiated by Ang II AT(1) receptors. Phosphatydilinositol-3 kinase (PI3-K) inhibitors Wortmanin or LY294002 reduced Ang II effect on tyr-phosphorylation of IRS-4 to a level comparable to that of Ins alone. Physical association between IRS-4 substrate and PI3-K was demonstrated by co-immunoprecipitation. Recruitment of PI3-K by IRS-4 was induced by Ins (10(-7)M, 5 min) not by Ang II (10(-7)M) and this was inhibited by Wortmanin and LY294002. Ang II did not modify either the association or activation of PI3-K in immunocomplexes. The present data provide novel evidence of IRS-4 phosphorylation mediated by Ins, an effect modulated by Ang II. We report also Ins-induced PI3-K activation mediated by IRS-4. Our findings suggest a role for IRS-4 as a docking protein in the Ins signaling pathway that involves PI3-K association and activation. The present data suggest a possible participation of IRS-4 in cell proliferation Ins-induced.
authors.affiliation: Instituto Multidisciplinario de Investigaciones Biológicas (IMIBIO-SL, CONICET), Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis, Ejército de los Andes 950, 5700 San Luis, Argentina.
authors.forename: Rodrigo Sebastián
authors.initials: RS
authors.lastname: Villarreal
authors.forename: Myriam Liliana
authors.initials: ML
authors.lastname: Forneris
authors.forename: Romina María
authors.initials: RM
authors.lastname: Uranga
authors.forename: Gabriela Alejandra
authors.initials: GA
authors.lastname: Salvador
authors.forename: Gladys María
authors.initials: GM
authors.lastname: Ciuffo
mesh_terms: D000804:Angiotensin II / Q000378:metabolism / Q000494:pharmacology*; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects*; D056945:Hep G2 Cells; D006801:Humans; D047468:Immunoprecipitation; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding
chemical_list: D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D000804:Angiotensin II; D019869:Phosphatidylinositol 3-Kinases