title: Vascular smooth muscle insulin resistance, but not hypertrophic signaling, is independent of angiotensin II-induced IRS-1 phosphorylation by JNK.
abstract: Angiotensin II (ANG II) has been implicated in the pathogenesis of diabetic micro- and macrovascular disease. In vascular smooth muscle cells (VSMCs), ANG II phosphorylates and degrades insulin receptor substrate-1 (IRS-1). While the pathway responsible for IRS-1 degradation in this system is unknown, c-Jun NH(2)-terminal kinase (JNK) has been linked with serine phosphorylation of IRS-1 and insulin resistance. We investigated the role of JNK in ANG II-induced IRS-1 phosphorylation, degradation, Akt activation, glucose uptake, and hypertrophic signaling, focusing on three IRS-1 phosphorylation sites: Ser302, Ser307, and Ser632. Maximal IRS-1 phosphorylation on Ser632 occurred at 5 min, on Ser307 at 30 min, and on Ser302 at 60 min. The JNK inhibitor SP600125 reduced ANG II-induced IRS-1 Ser307 phosphorylation (by 80%), IRS-1 Ser302 phosphorylation (by 70%), and IRS-1 Ser632 phosphorylation (by 50%). However, JNK inhibition had no effect on ANG II-mediated IRS-1 degradation, nor did it reverse the ANG II-induced decrease in Akt phosphorylation or glucose uptake. Transfection of VSMCs with mutants S307A, S302A, or S632A of IRS-1 did not block ANG II-mediated IRS-1 degradation. In contrast, JNK inhibition attenuated insulin-induced upregulation of collagen and smooth muscle α-actin in ANG II-pretreated cells. We conclude that phosphorylation of Ser307, Ser302, and Ser632 of IRS-1 is not involved in ANG II-mediated IRS-1 degradation, and that JNK alone does not mediate ANG II-stimulated IRS-1 degradation, but rather is responsible for the hypertrophic effects of insulin on smooth muscle.
authors: Department of Medicine, Division of Cardiology, Emory University, 1639 Pierce Dr., Atlanta, GA 30322, USA.
authors: Hirofumi
authors: H
authors: Hitomi
authors: Puja K
authors: PK
authors: Mehta
authors: Yoshihiro
authors: Y
authors: Taniyama
authors: Bernard
authors: B
authors: Lassègue
authors: Bonnie
authors: B
authors: Seidel-Rogol
authors: Alejandra
authors: A
authors: San Martin
authors: Kathy K
authors: KK
authors: Griendling
mesh_terms: D000199:Actins; D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006984:Hypertrophy / Q000378:metabolism; D047468:Immunoprecipitation; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism*; D007333:Insulin Resistance / Q000502:physiology*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D051381:Rats; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014162:Transfection
chemical_list: D000199:Actins; D000804:Angiotensin II; D004791:Enzyme Inhibitors; D055504:Insulin Receptor Substrate Proteins; D048031:JNK Mitogen-Activated Protein Kinases; C526296:Irs1 protein, rat; C498862:Acta2 protein, rat