THE BETA-ADRENERGIC-RECEPTOR IS A SUBSTRATE FOR THE INSULIN-RECEPTOR TYROSINE KINASE

G-protein-linked receptors and intrinsic tyrosine kinase growth recept ors represent two prominent modalities in cell signaling, Cross-regula tion among members of both receptor superfamilies has been reported, i ncluding the counter-regulatory effects of insulin on beta-adrenergic catecholamine action, Cells stimulated by insulin show loss of functio n and increased phosphotyrosine content of beta(2)-adrenergic receptor s. Phosphorylation of tyrosyl residues 350/354 of beta(2)-adrenergic r eceptors is obligatory for counter-regulation by insulin (Karoor, V., Baltensperger, K., Paul, H., Czech, M., and Malbon, C. C. (1995) J. Bi ol. Chem. 270, 25305-25308), suggesting the hypothesis that G-protein- linked receptors themselves may act as substrates for the insulin rece ptor and other growth factor receptors. This hypothesis was evaluated directly using recombinant human insulin receptor, hamster beta(2)-adr energic receptor, and an in vitro reconstitution and phosphorylation a ssay. Insulin is shown to stimulate insulin receptor-catalyzed phospho rylation of the beta(2)-adrenergic receptor. Phosphoamino acid analysi s establishes that insulin receptor-catalyzed phosphorylation of the b eta(2)-adrenergic receptor in vitro is confined to phosphotyrosine. Hi gh pressure liquid chromatography and two-dimensional mapping reveal i nsulin receptor-catalyzed phosphorylation of the beta(2)-adrenergic re ceptor at residues Tyr(132)/Tyr(141), Tyr(350)/Tyr(354), and Tyr(364), known sites of phosphorylation in response to insulin in vivo. Insuli n-like growth factor-I receptor as well as the insulin receptor displa ys the capacity to phosphorylate the beta 2-adrenergic receptor in vit ro, establishing a new paradigm, i.e. G-protein-linked receptors actin g as substrates for intrinsic tyrosine kinase growth factor receptors.