The SUMO Conjugating Enzyme Ubc9 is a Regulator of GLUT4 Turnover and Targeting to the Insulin-Responsive Storage Compartment in 3T3-L1 Adipocytes

  1. Li-Bin Liu,
  2. Waka Omata,
  3. Itaru Kojima and
  4. Hiroshi Shibata
  1. From the Department of Cell Biology, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan
  1. Address correspondence and reprint requests to Hiroshi Shibata, MD, PhD, Department of Cell Biology, Institute for Molecular and Cellular Regulation, Gunma University, 3-39-15 Showa-machi, Maebashi 371-8512, Japan. E-mail: hshibata{at}showa.gunma-u.ac.jp

Abstract

The small ubiquitin-related modifier (SUMO) conjugating enzyme Ubc9 has been shown to upregulate GLUT4 in L6 myoblast cells, although the mechanism of action has remained undefined. Here we investigated the physiological significance of Ubc9 in GLUT4 turnover and subcellular targeting by adenovirus vector–mediated overexpression and by small interfering RNA (siRNA)-mediated gene silencing of Ubc9 in 3T3-L1 adipocytes. Overexpression of Ubc9 resulted in an inhibition of GLUT4 degradation and promoted its targeting to the unique insulin-responsive GLUT4 storage compartment (GSC), leading to an increase in GLUT4 amount and insulin-responsive glucose transport in 3T3-L1 adipocytes. Overexpression of Ubc9 also antagonized GLUT4 downregulation and its selective loss in GSC induced by long-term insulin stimulation. By contrast, siRNA-mediated depletion of Ubc9 accelerated GLUT4 degradation and decreased the amount of the transporter, concurrent with its selective loss in GSC, which resulted in attenuated insulin-responsive glucose transport. Intriguingly, overexpression of the catalytically inactive mutant Ubc9-C93A produced effects indistinguishable from those with wild-type Ubc9, suggesting that Ubc9 regulates GLUT4 turnover and targeting to GSC by a mechanism independent of its catalytic activity. Thus, Ubc9 is a pivotal regulator of the insulin sensitivity of glucose transport in adipocytes.

Footnotes

  • Published ahead of print at http://diabetes.diabetesjournals.org on 29 May 2007. DOI: 10.2337/db06-1100.

  • L.-B.L. and W.O. contributed equally to this work.

  • 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 May 19, 2007.
    • Received August 8, 2006.
| Table of Contents

This Article

  1. Diabetes vol. 56 no. 8 1977-1985
  1. All Versions of this Article:
    1. db06-1100v1
    2. 56/8/1977 most recent