Insulin-like growth factor receptor-1 stimulates phosphorylation of the beta2-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 beta2-adrenergic receptor (Karoor, V., Baltensperger, K., Paul, H., Czech, M. P., and Malbon, C. C. (1995) J. Biol. Chem. 270, 25305-25308). Insulin-like growth factor-1 (IGF-1), another member of the growth factor family operating via receptors with intrinsic tyrosine kinase, is shown in the present work to stimulate in vivo the phosphorylation of the beta2-adrenergic receptor. Analysis of tryptic digests prepared from phosphorylated beta2-adrenergic receptors of IGF-1-treated, metabolically labeled smooth muscle cells was performed using reversed-phase high performance liquid chromatography, two-dimensional peptide mapping, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The results of these separate analyses reveal that IGF-1 stimulates phosphorylation predominantly on tyrosyl residues Y132/141 of the second intracellular loop of the beta2-adrenergic receptor rather than the C-terminal region targeted by the activated insulin receptor (Y350/354, Y364), although both growth factors block beta-adrenergic agonist action. These data demonstrate selective phosphorylation of a G-protein-linked receptor by receptor tyrosine kinases for insulin and IGF-1 mapping to spatially distinct regions of this heptihelical membrane receptor.
Department of Molecular Pharmacology, Diabetes and Metabolic Diseases Research Center, School of Medicine, State University of New York, Stony Brook, New York 11794-8651, USA.
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D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D006224:Cricetinae; D007328:Insulin / Q000378:metabolism*; D008969:Molecular Sequence Data; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism; D010449:Peptide Mapping; D010766:Phosphorylation; D018343:Receptors, Adrenergic, beta-2 / Q000737:chemistry / Q000378:metabolism*; D017451:Receptors, Somatomedin / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014357:Trypsin
D007328:Insulin; D018343:Receptors, Adrenergic, beta-2; D017451:Receptors, Somatomedin; D014357:Trypsin