Role of IRS-4 in PI3-K activation by insulin in HepG2 cells, modulation by Angiotensin II.
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.
Villarreal
Rodrigo Sebastián
RS
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.
Forneris
Myriam Liliana
ML
Uranga
Romina María
RM
Salvador
Gabriela Alejandra
GA
Ciuffo
Gladys María
GM
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
D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D000804:Angiotensin II; D019869:Phosphatidylinositol 3-Kinases