Functional cross-talk between angiotensin II and epidermal growth factor receptors in NIH3T3 fibroblasts

Background: The main angiotensin (Ang) II subtype receptors (AT1R and AT2R) are involved in cellular growth processes and exert functionally antagonistic effects. Objective: To characterize the mechanisms by which Ang II receptors influence growth, by investigating the interactions between Ang II subtype receptors and epidermal growth factor (EGF) receptors on mitogen-activated protein kinase (MAPK) pathway activation. Design and methods: The experiments were performed using a mouse fibroblast cell line, NIH3T3, by transient co-transfection with rat AT1R or AT2R expression vectors, or both. Extracellular-signal-regulated kinase (ERK)1/2 phosphorylation was analysed by western blot and the ERK activity was evaluated using PathDetect, an in-vivo signal transduction pathway frans-reporting system. Selective Ang II receptor antagonists (losartan for AT1R and PD123319 for AT2R) were used to investigate the contributions of each receptor to the response observed. Results: Our data show that, in this cellular model, both Ang II receptors phosphorylate ERK1/2. However, in the cells expressing AT1R, the EGF-induced MAPK pathway was enhanced in the presence of Ang II in a synergistic fashion. In contrast, a reduction of EGF-induced MAPK activation was observed in the cells expressing AT2R. In cells expressing both Ang II subtype receptors, Ang II promoted an enhancement of EGF-induced MAPK activation. However, in the presence of the AT1R antagonist, losartan, the effect of EGF was reduced. Conclusion: These data indicate the existence of an opposite cross-talk of AT1R and AT2R with EGF receptors, and suggest a complex functional interaction between these pathways in the regulation of cellular growth processes.