title: Protein kinase C inhibits insulin-induced Akt activation in vascular smooth muscle cells.
abstract: Protein kinase C (PKC) activation, enhanced by hyperglycemia, is associated with many tissue abnormalities observed in diabetes. Akt is a serine/threonine kinase that mediates various biological responses induced by insulin. We hypothesized that the negative regulation of Akt in the vasculature by PKC could contribute to insulin resistant states and, may therefore play a role in the pathogenesis of cardiovascular disease. In this study, we specifically looked at the ability of PKC to inhibit Akt activation induced by insulin in cultured rat aortic vascular smooth muscle cells (VSMCs). Activation of Akt was determined by immunoblotting with a phospho-Akt antibody that selectively recognizes Ser473 phosphorylated Akt. A PKC activator, phorbol 12-myristate 13-acetate (PMA), inhibited insulin-dependent Akt phosphorylation. However, PMA did not inhibit platelet-derived growth factor (PDGF)-induced activation of Akt. We further showed that the PKC inhibitor, G06983, blocked the PMA-induced inhibition of Akt phosphorylation by insulin. In addition, we demonstrated that PMA inhibited the insulin-induced tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1). From these data, we conclude that PKC is a potent negative regulator of the insulin signal in the vasculature, which indicate an important role of PKC in the development of insulin resistance in cardiovascular disease.
authors.affiliation: Department of Anatomy & Physiology, Meharry Medical College, Nashville, TN 37208, USA. emotley@mmc.edu
authors.forename: E D
authors.initials: ED
authors.lastname: Motley
authors.forename: S M
authors.initials: SM
authors.lastname: Kabir
authors.forename: K
authors.initials: K
authors.lastname: Eguchi
authors.forename: A L
authors.initials: AL
authors.lastname: Hicks
authors.forename: C D
authors.initials: CD
authors.lastname: Gardner
authors.forename: C M
authors.initials: CM
authors.lastname: Reynolds
authors.forename: G D
authors.initials: GD
authors.lastname: Frank
authors.forename: S
authors.initials: S
authors.lastname: Eguchi
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000166:cytology; D002478:Cells, Cultured; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000037:antagonists & inhibitors*; D007328:Insulin / Q000494:pharmacology*; D007329:Insulin Antagonists / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D011972:Receptor, Insulin / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D007004:Hypoglycemic Agents; D007328:Insulin; D007329:Insulin Antagonists; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D010750:Phosphoproteins; D010982:Platelet-Derived Growth Factor; D011518:Proto-Oncogene Proteins; D011972:Receptor, Insulin; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate