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Molecular and Cellular Biology, November 2001, p. 7852-7861, Vol. 21, No. 22
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.22.7852-7861.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Activation of Protein Kinase Czeta Induces Serine Phosphorylation of VAMP2 in the GLUT4 Compartment and Increases Glucose Transport in Skeletal Muscle

Liora Braiman,1 Addy Alt,1 Toshio Kuroki,2 Motoi Ohba,3 Asia Bak,1 Tamar Tennenbaum,1 and Sanford R. Sampson1,*

Faculty of Life Sciences, Gonda-Goldschmied Center, Bar-Ilan University, Ramat-Gan 52900, Israel,1 and Institute of Molecular Oncology2 and Department of Microbiology,3 Showa University, Shinagawa-ku, Tokyo 142-8555, Japan

Received 14 February 2001/Returned for modification 30 March 2001/Accepted 20 August 2001

Insulin stimulates glucose uptake into skeletal muscle tissue mainly through the translocation of glucose transporter 4 (GLUT4) to the plasma membrane. The precise mechanism involved in this process is presently unknown. In the cascade of events leading to insulin-induced glucose transport, insulin activates specific protein kinase C (PKC) isoforms. In this study we investigated the roles of PKCzeta in insulin-stimulated glucose uptake and GLUT4 translocation in primary cultures of rat skeletal muscle. We found that insulin initially caused PKCzeta to associate specifically with the GLUT4 compartments and that PKCzeta together with the GLUT4 compartments were then translocated to the plasma membrane as a complex. PKCzeta and GLUT4 recycled independently of one another. To further establish the importance of PKCzeta in glucose transport, we used adenovirus constructs containing wild-type or kinase-inactive, dominant-negative PKCzeta (DNPKCzeta ) cDNA to overexpress this isoform in skeletal muscle myotube cultures. We found that overexpression of PKCzeta was associated with a marked increase in the activity of this isoform. The overexpressed, active PKCzeta coprecipitated with the GLUT4 compartments. Moreover, overexpression of PKCzeta caused GLUT4 translocation to the plasma membrane and increased glucose uptake in the absence of insulin. Finally, either insulin or overexpression of PKCzeta induced serine phosphorylation of the GLUT4-compartment-associated vesicle-associated membrane protein 2. Furthermore, DNPKCzeta disrupted the GLUT4 compartment integrity and abrogated insulin-induced GLUT4 translocation and glucose uptake. These results demonstrate that PKCzeta regulates insulin-stimulated GLUT4 translocation and glucose transport through the unique colocalization of this isoform with the GLUT4 compartments.


* Corresponding author. Mailing address: Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel. Phone: 972 3 531 8203. Fax: 972 3 736 9929. E-mail: sampsos{at}mail.biu.ac.il.


Molecular and Cellular Biology, November 2001, p. 7852-7861, Vol. 21, No. 22
0270-7306/01/$04.00+0   DOI: 10.1128/MCB.21.22.7852-7861.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.



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