PARTICIPATION OF IRS-4 AND PI3-K IN ANGIOTENSIN II AND INSULIN CROSSTALK IN HepG2 CELLS

VILLARREAL RODRIGO S., URANGA ROMINA M., SALVADOR GABRIELA AND CIUFFO GLADYS M

Carlos Paz, Códoba

Congreso; 44th Reunión Annual de SAIB-; 2008

Soc. Arg. de Investigac. BVioqca. y Biol. Mol

  The aim of the present study was to characterize the “cross-talk” between the signalling pathways of Insulin (Ins) and Angiotensin II (Ang II). Until now, the proteins involved in “cross-talk” between Ins and Ang II involved IRS-1 and IRS-2 substrates. In a previous study we observed the participation of IRS-4 in this cross-talk. By means of western blot and immunoprecipitation we demonstrated the association between IRS-4 and PI3K following stimulation with Ins and Ang II in HepG2 cells. PI3-K activity was measured in IRS-4 immunocomplexes. Ins induces Tyr-.phosphorylation of IRS-4 in HepG2 cells, a response blocked by pre-incubation with the Ins antagonist AG1024. Ang II AT1 receptors potentiates Ins effect on Tyr-phosphorylation of IRS-4. PI3-K inhibitors prevented the modulation by Ang II of Ins-induced Tyr-phosphorylation of IRS-4. In IRS-4 immunocomplexes we observed PI3-K association and activation after Ins stimulation, increased by Ang II. In the long term, Ins induces an increase of IRS-4 protein and mRNA level, supporting a functional role of this substrate in cellular growth. The present results would indicate for the first time a physiological role of IRS-4 substrate in response to Ins stimulation in the short and long term, an effect modulated by Ang II. Participation of IRS-4 in this signalling pathway is totally novel as it is a potential physiological role.