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Molecular and Cellular Biology, June 2004, p. 5447-5458, Vol. 24, No. 12
0270-7306/04/$08.00+0     DOI: 10.1128/MCB.24.12.5447-5458.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Unconventional Myosin Myo1c Promotes Membrane Fusion in a Regulated Exocytic Pathway{dagger}

Avirup Bose,1 Stacey Robida,1 Paul S. Furcinitti,1 Anil Chawla,1 Kevin Fogarty,2 Silvia Corvera,1 and Michael P. Czech1*

Program in Molecular Medicine,1 Biomedical Imaging Group, Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 016052

Received 17 October 2003/ Returned for modification 17 November 2003/ Accepted 19 March 2004

Glucose homeostasis is controlled in part by regulation of glucose uptake into muscle and adipose tissue. Intracellular membrane vesicles containing the GLUT4 glucose transporter move towards the cell cortex in response to insulin and then fuse with the plasma membrane. Here we show that the fusion step is retarded by the inhibition of phosphatidylinositol (PI) 3-kinase. Treatment of insulin-stimulated 3T3-L1 adipocytes with the PI 3-kinase inhibitor LY294002 causes the accumulation of GLUT4-containing vesicles just beneath the cell surface. This accumulation of GLUT4-containing vesicles near the plasma membrane prior to fusion requires an intact cytoskeletal network and the unconventional myosin motor Myo1c. Remarkably, enhanced Myo1c expression under these conditions causes extensive membrane ruffling and overrides the block in membrane fusion caused by LY294002, restoring the display of GLUT4 on the cell exterior. Ultrafast microscopic analysis revealed that insulin treatment leads to the mobilization of GLUT4-containing vesicles to these regions of Myo1c-induced membrane ruffles. Thus, localized membrane remodeling driven by the Myo1c motor appears to facilitate the fusion of exocytic GLUT4-containing vesicles with the adipocyte plasma membrane.

* Corresponding author. Mailing address: Program in Molecular Medicine, Department of Physiology, University of Massachusetts Medical School, 55 Lake Ave. North, Worcester, MA 01605. Phone: (508) 856-2254. Fax: (508) 856-1617. E-mail: michael.czech{at}umassmed.edu.

{dagger} Supplemental material for this article may be found at http://mcb.asm.org/.

Molecular and Cellular Biology, June 2004, p. 5447-5458, Vol. 24, No. 12
0022-538X/04/$08.00+0     DOI: 10.1128/MCB.24.12.5447-5458.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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