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J. Biol. Chem., Vol. 283, Issue 1, 324-331, January 4, 2008

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Snapin Interacts with the Exo70 Subunit of the Exocyst and Modulates GLUT4 Trafficking^*

Yiqun Bao¹, Jamie A. Lopez¹, David E. James, An NHMRC Senior Principal Research Fellow², and Walter Hunziker³

From the Epithelial Cell Biology Laboratory, Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore 138673, Singapore and the Diabetes and Obesity Research Program, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst New South Wales, Sydney 2010, Australia

The exocyst is a multisubunit complex that has been implicated in the transport of vesicles from the Golgi complex to the plasma membrane, possibly acting as a vesicle tether and contributing to the specificity of membrane fusion. Here we characterize a novel interaction between the Exo70 subunit of the exocyst and Snapin, a ubiquitous protein known to associate with at least two t-SNAREs, SNAP23 and SNAP25. The interaction between Exo70 and Snapin is mediated via an N-terminal coil-coil domain in Exo70 and a C-terminal helical region in Snapin. Exo70 competes with SNAP23 for Snapin binding, suggesting that Snapin does not provide a direct link between the exocyst and the SNARE complex but, rather, mediates cross-talk between the two complexes by sequential interactions. The insulin-regulated trafficking of GLUT4 to the plasma membrane serves to facilitate glucose uptake in adipocytes, and both SNAP23 and the exocyst have been implicated in this process. In this study, depletion of Snapin in adipocytes using RNA interference inhibits insulin-stimulated glucose uptake. Thus, Snapin interacts with the exocyst and plays a modulatory role in GLUT4 vesicle trafficking.

Received for publication, August 17, 2007 , and in revised form, October 2, 2006.

^* This work was supported in part by the Agency for Science and Technology (A^*STAR), Singapore and by grants from the National Health and Medical Research Council and Diabetes Australia (to D. E. J.) and a National Health and Medical Research Council (NHMRC) Dora Lush postgraduate scholarship (to J. A. L.). 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.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Fig. S1.

¹ Both authors contributed equally to this work.

² To whom correspondence may be addressed. Tel.: 02-9295-8210; Fax: 02-9295-8201; E-mail: d.james{at}garvan.org.au. ³ To whom correspondence may be addressed. Tel.: 65-6586-9599; Fax: 65-6779-1117; E-mail: hunziker{at}imcb.a-star.edu.sg.

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