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J. Cell Biol.,
Volume 141, Number 7, June 29, 1998 1503-1513

* Department of Anatomy, Department of Biochemistry and Biophysics, Cardiovascular Research Institute, We have investigated the controversial involvement of components of the SNARE (soluble N-ethyl
maleimide-sensitive factor [NSF] attachment protein
[SNAP] receptor) machinery in membrane traffic to
the apical plasma membrane of polarized epithelial (MDCK) cells. Overexpression of syntaxin 3, but not of
syntaxins 2 or 4, caused an inhibition of TGN to apical
transport and apical recycling, and leads to an accumulation of small vesicles underneath the apical plasma
membrane. All other tested transport steps were unaffected by syntaxin 3 overexpression. Botulinum neurotoxin E, which cleaves SNAP-23, and antibodies against
Department of
Dermatology and Veteran Administration Medical Center, University of California, San Francisco, California 94143-0452; § Department of Cellular Biochemistry and Biophysics, Memorial Sloan-Kettering Cancer Center, New York 10021;
Department of Biochemistry, University of Kentucky College of Medicine, Lexington, Kentucky 40536
-SNAP inhibit both TGN to apical and basolateral
transport in a reconstituted in vitro system. In contrast,
we find no evidence for an involvement of N-ethyl maleimide-sensitive factor in TGN to apical transport, whereas basolateral transport is NSF-dependent. We
conclude that syntaxin 3, SNAP-23, and
-SNAP are
involved in apical membrane fusion. These results demonstrate that vesicle fusion with the apical plasma
membrane does not use a mechanism that is entirely unrelated to other cellular membrane fusion events, but
uses isoforms of components of the SNARE machinery, which suggests that they play a role in providing
specificity to polarized membrane traffic.
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