INSULIN-LIKE GROWTH-FACTOR RECEPTOR-1 STIMULATES PHOSPHORYLATION OF THE BETA(2)-ADRENERGIC RECEPTOR IN-VIVO ON SITES DISTINCT FROM THOSE PHOSPHORYLATED IN RESPONSE TO INSULIN

G-protein-linked receptors have been shown to be substrates for growth factor receptors with intrinsic tyrosine kinase activity typified by the ability of insulin to both phosphorylate tyrosyl residues in the C terminus of and to counter-regulate the action of the beta(2)-adrener gic receptor (Karoor, V., Baltensperger, K., Paul, H., Czech, M. P., a nd Malbon, C, C, (1995) J. Biol. Chem, 270, 25305-25308). Insulin-like growth factor-1 (IGF-1), another member of the growth factor family o perating via receptors with intrinsic tyrosine kinase, is shown in the present work to stimulate in vivo the phosphorylation of the beta(2)- adrenergic receptor. Analysis of tryptic digests prepared from phospho rylated beta(2)-adrenergic receptors of IGF-1-treated, metabolically l abeled smooth muscle cells was performed using reversed-phase high per formance liquid chromatography, two-dimensional peptide mapping, and m atrix-assisted laser desorption/ionization time-of-flight mass spectro metry. The results of these separate analyses reveal that IGF-1 stimul ates phosphorylation predominantly on tyrosyl residues Y132/141 of the second intracellular loop of the beta(2)-adrenergic receptor rather t han the C-terminal region targeted by the activated insulin receptor ( Y350/354, Y364), although both growth factors block beta-adrenergic ag onist action. These data demonstrate selective phosphorylation of a G- protein-linked receptor by receptor tyrosine kinases for insulin and I GF-1 mapping to spatially distinct regions of this heptihelical membra ne receptor.