Human angiotensin II type-2 receptor inhibition of insulin-mediated ERK-2 activity via a G-protein coupled signaling pathway

While it has been shown that the angiotensin type-2 (AT₂) receptor plays an important role in the development and differentiation of many tissues, the second messengers involved in its signaling pathways are just beginning to be understood. To further determine the signaling pathways for the AT₂ receptor, we have investigated whether human angiotensin type-2 receptor transfected into Chinese hamster ovary (CHO) cells can modulate insulin-induced extracellular signal-related protein kinase (ERK-2) phosphorylation via a G-protein coupled mechanism. Our results indicate that the human AT₂ receptor decreases insulin-induced ERK-2 phosphorylation through a G-protein mediated pathway since inhibition was attenuated by pertussis toxin (a G_i/G₀ inhibitor). Our findings further indicate that the inhibitory response was insensitive to sodium orthovanadate (a PTPase inhibitor), but sensitive (attenuated) to okadaic acid, suggesting an important role for protein phosphatase 2A (PP2A). We have also shown that alanine substitution of the putative G-protein coupling DRY^141-143 motif of the second intracellular loop significantly decreases the human AT ₂ receptor's ability to inhibit insulin-induced ERK-2 phosphorylation. Our results support the hypothesis that the AT₂ receptor inhibits insulin-induced ERK-2 activity via a G-protein coupled pathway involving the up-regulation of PP2A.