title: Akt mediates sequestration of the beta(2)-adrenergic receptor in response to insulin.
abstract: The counterregulation of catecholamine action by insulin includes insulin-stimulated sequestration of the beta(2)-adrenergic receptor. Herein we examined the signaling downstream of insulin receptor activation, focusing upon the role of 1-phosphatidylinositol 3-kinase and the serine-threonine protein kinase Akt (also known as protein kinase B) in the internalization of beta(2)-adrenergic receptors. Inhibition of 1-phosphatidylinositol 3-kinase by LY294002 blocks insulin-induced sequestration of the beta(2)-adrenergic receptor, implicating Akt in downstream signaling to the beta(2)-adrenergic receptor. Phosphorylation studies of the C-terminal cytoplasmic domain of the beta(2)-adrenergic receptor by Akt in vitro identified Ser(345) and Ser(346) within a consensus motif for Akt phosphorylation. Double mutation (i.e. S345A/S346A) within this motif abolishes insulin counterregulation of beta-adrenergic stimulation of cyclic AMP accumulation as well as insulin-stimulated sequestration. Furthermore, expression of constitutively activated Akt (T308D/S473D) mimics insulin action on cyclic AMP responses and beta(2)-adrenergic receptor internalization. Expression of the dominant-negative version of Akt (K179A/T308A/S473A), in contrast, abolishes both insulin counterregulation of the cyclic AMP response as well as insulin-stimulated sequestration of the beta(2)-adrenergic receptor. The action of the serine-threonine protein kinase Akt in insulin counterregulation mirrors the central role of protein kinase A in beta-agonist-induced desensitization.
authors.affiliation: Department of Molecular Pharmacology, University Medical Center, State University of New York/Stony Brook, Stony Brook, New York 11794-8651, USA.
authors.forename: Sergey
authors.initials: S
authors.lastname: Doronin
authors.forename: Elena
authors.initials: E
authors.lastname: Shumay
authors.forename: Hsien-yu
authors.initials: HY
authors.lastname: Wang
authors.forename: Craig C
authors.initials: CC
authors.lastname: Malbon
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004789:Enzyme Activation; D006801:Humans; D007328:Insulin / Q000502:physiology*; D008856:Microscopy, Fluorescence; D019869:Phosphatidylinositol 3-Kinases; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D018343:Receptors, Adrenergic, beta-2 / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014407:Tumor Cells, Cultured
chemical_list: D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D018343:Receptors, Adrenergic, beta-2; C494918:AKT1 protein, human