Insulin-Stimulated Phosphorylation of the Akt Substrate AS160 Is Impaired in Skeletal Muscle of Type 2 Diabetic Subjects

  1. Håkan K.R. Karlsson1,
  2. Juleen R. Zierath1,
  3. Susan Kane2,
  4. Anna Krook3,
  5. Gustav E. Lienhard2 and
  6. Harriet Wallberg-Henriksson3
  1. 1Department of Surgical Sciences, Integrative Physiology Section, Karolinska Institutet, Stockholm, Sweden
  2. 2Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire
  3. 3Department of Physiology and Pharmacology, Integrative Physiology Section, Karolinska Institutet, Stockholm, Sweden
  1. Address correspondencereprint requests to Juleen R. Zierath, PhD, Karolinska Institutet, Department of Surgical Sciences, Integrative Physiology Section, S-171 77, Stockholm, Sweden. E-mail: juleen.zierath{at}fyfa.ki.se

Abstract

AS160 is a newly described substrate for the protein kinase Akt that links insulin signaling and GLUT4 trafficking. In this study, we determined the expression of and in vivo insulin action on AS160 in human skeletal muscle. In addition, we compared the effect of physiological hyperinsulinemia on AS160 phosphorylation in 10 lean−to−moderately obese type 2 diabetic and 9 healthy subjects. Insulin infusion increased the phosphorylation of several proteins reacting with a phospho-Akt substrate antibody. We focused on AS160, as this Akt substrate has been linked to glucose transport. A 160-kDa phosphorylated protein was identified as AS160 by immunoblot analysis with an AS160-specific antibody. Physiological hyperinsulinemia increased AS160 phosphorylation 2.9-fold in skeletal muscle of control subjects (P < 0.001). Insulin-stimulated AS160 phosphorylation was reduced 39% (P < 0.05) in type 2 diabetic patients. AS160 protein expression was similar in type 2 diabetic and control subjects. Impaired AS160 phosphorylation was related to aberrant Akt signaling; insulin action on Akt Ser473 phosphorylation was not significantly reduced in type 2 diabetic compared with control subjects, whereas Thr308 phosphorylation was impaired 51% (P < 0.05). In conclusion, physiological hyperinsulinemia increases AS160 phosphorylation in human skeletal muscle. Moreover, defects in insulin action on AS160 may impair GLUT4 trafficking in type 2 diabetes.

Footnotes

  • The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

    • Accepted March 10, 2005.
    • Received November 8, 2004.
| Table of Contents