Functional trans-inactivation of insulin receptor kinase by growth-inhibitory angiotensin II AT2 receptor

The present study demonstrates negative intracellular cross-talk between angiotensin II type 2 (AT(2)) and insulin receptors. AT(2) receptor stimulation leads to inhibition of insulin-induced extracellular signal-regulated protein kinase (ERK2) activity and cell proliferation in transfected Chinese hamster ovary (CHO-hAT(2)) cells. We show that AT(2) receptor interferes at the initial step of insulin signaling cascade, by impairing tyrosine phosphorylation of the insulin receptor (IR) beta-chain. AT(2)-mediated inhibition of IR phosphorylation is insensitive to pertussis toxin and is also detected in neuroblastoma N1E-115 and pancreatic acinar AR42J cells that express endogenous receptors. We present evidence that AT(2) receptor inhibits the autophosphorylating tyrosine kinase activity of IR, with no significant effect on insulin binding properties. AT(2)-mediated inactivation of IR does not mainly involve tyrosine dephosphorylation by vanadate-sensitive tyrosine phosphatases nor serine/threonine phosphorylation by protein kinase C. As a consequence of IR inactivation, AT(2) receptor inhibits tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) and signal-regulatory protein (SIRP alpha 1) and prevents subsequent association of both IRS-1 and SIRP alpha 1 with Src homology 2 (SH2)-containing tyrosine phosphatase SHP-2. Our results thus demonstrate functional trans-inactivation of IR kinase by G protein-coupled AT(2) receptor, illustrating a novel mode of negative communication between two families of membrane receptors.