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MBC in Press, published online ahead of print February 15, 2006
Mol. Biol. Cell 10.1091/mbc.E06-01-0074

A more recent version of this article appeared on May 1, 2006
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Submitted on January 25, 2006
Revised on February 7, 2006
Accepted on February 8, 2006

A Second SNARE Role for Exocytic SNAP25 in Endosome Fusion

Yoshikatsu Aikawa,* Kara L. Lynch, Kristin L. Boswell, and Thomas F.J. Martin

Department of Biochemistry, University of Wisconsin, Madison, WI 53706

Monitoring Editor: Sandra Schmid

SNARE proteins play key roles in membrane fusion but their sorting to specific membranes is poorly understood. Moreover, individual SNARE proteins can function in multiple membrane fusion events dependent upon their trafficking itinerary. SNAP25 is a plasma membrane Q-SNARE essential for Ca2+-dependent secretory vesicle-plasma membrane fusion in neuroendocrine cells. However, a substantial intracellular pool of SNAP25 is maintained by endocytosis. To assess the role of endosomal SNAP25, we expressed botulinum neurotoxin E (BoNT E) light chain in PC12 cells, which specifically cleaves SNAP25. BoNT E expression altered the intracellular distribution of SNAP25 shifting it from a perinuclear recycling endosome to sorting endosomes, which indicates that SNAP25 is required for its own endocytic trafficking. The trafficking of syntaxin 13 and endocytosed cargo was similarly disrupted by BoNT E expression as was an endosomal SNARE complex comprised of SNAP25/syntaxin 13/VAMP 2. The siRNA-mediated down-regulation of SNAP25 exerted effects similar to those of BoNT E expression. Our results indicate that SNAP25 has a second function as an endosomal Q-SNARE in trafficking from the sorting endosome to the recycling endosome, and that BoNT E has effects linked to disruption of the endosome recycling pathway.

*Present address: Department of Pharmaceutical Technology, Tokushima-bunri University, Saniki-city, Kagawa 769-2193, Japan.

Address correspondence to: Thomas F.J. Martin (tfmartin{at}wisc.edu)






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