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Molecular and Cellular Biology, November 1999, p. 7771-7781, Vol. 19, No. 11
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

A Role for Protein Kinase Bbeta /Akt2 in Insulin-Stimulated GLUT4 Translocation in Adipocytes

Michelle M. Hill,1 Sharon F. Clark,1 David F. Tucker,2 Morris J. Birnbaum,3 David E. James,1,* and S. Lance Macaulay2

Centre for Molecular and Cellular Biology and Department of Physiology and Pharmacology, University of Queensland, Brisbane, Queensland 4072,1 and CSIRO Health Sciences and Nutrition, Parkville, Victoria 3052,2 Australia, and Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-61483

Received 21 June 1999/Returned for modification 23 July 1999/Accepted 19 August 1999

Insulin stimulates glucose uptake into muscle and fat cells by promoting the translocation of glucose transporter 4 (GLUT4) to the cell surface. Phosphatidylinositide 3-kinase (PI3K) has been implicated in this process. However, the involvement of protein kinase B (PKB)/Akt, a downstream target of PI3K in regulation of GLUT4 translocation, has been controversial. Here we report that microinjection of a PKB substrate peptide or an antibody to PKB inhibited insulin-stimulated GLUT4 translocation to the plasma membrane by 66 or 56%, respectively. We further examined the activation of PKB isoforms following treatment of cells with insulin or platelet-derived growth factor (PDGF) and found that PKBbeta is preferentially expressed in both rat and 3T3-L1 adipocytes, whereas PKBalpha expression is down-regulated in 3T3-L1 adipocytes. A switch in growth factor response was also observed when 3T3-L1 fibroblasts were differentiated into adipocytes. While PDGF was more efficacious than insulin in stimulating PKB phosphorylation in fibroblasts, PDGF did not stimulate PKBbeta phosphorylation to any significant extent in adipocytes, as assessed by several methods. Moreover, insulin, but not PDGF, stimulated the translocation of PKBbeta to the plasma membrane and high-density microsome fractions of 3T3-L1 adipocytes. These results support a role for PKBbeta in insulin-stimulated glucose transport in adipocytes.

* Corresponding author. Mailing address: Centre for Molecular and Cellular Biology and Department of Physiology and Pharmacology, University of Queensland, Brisbane, Queensland 4072, Australia. Phone: 61 7 3365 4986. Fax: 61 7 3365 4388. E-mail: D.James{at}cmcb.uq.edu.au.

Molecular and Cellular Biology, November 1999, p. 7771-7781, Vol. 19, No. 11
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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