Participation of IRS-4 and PI3-K in angiotensin II and insulin crosstalk in HEPG2 cells

VILLARREAL, RODRIGO; URANGA, ROMINA; SALVADOR, GABRIELA; CIUFFO, GLADYS

Villa Carlos Paz, Córdoba, Argentina

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2008

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB)

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 well as its potential physiological role.