Published 19 June 2006. doi:10.1083/jcb.200603132
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 173, Number 6, 937-948
Apical targeting of syntaxin 3 is essential for epithelial cell polarity
Nikunj Sharma1,3,
Seng Hui Low1,2,
Saurav Misra4,
Bhattaram Pallavi1, and
Thomas Weimbs1,2
1 Department of Molecular, Cellular, and Developmental Biology, 2 Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, CA 93106
3 Department of Biological, Geological, and Environmental Sciences, Cleveland State University, Cleveland, OH 44115
4 Department of Molecular Cardiology, Lerner Research Institute, The Cleveland Clinic, Cleveland, OH 44195
Correspondence to Thomas Weimbs: weimbs{at}lifesci.ucsb.edu
In polarized epithelial cells, syntaxin 3 localizes to the apical plasma membrane and is involved in membrane fusion of apical trafficking pathways. We show that syntaxin 3 contains a necessary and sufficient apical targeting signal centered around a conserved FMDE motif. Mutation of any of three critical residues within this motif leads to loss of specific apical targeting. Modeling based on the known structure of syntaxin 1 revealed that these residues are exposed on the surface of a three-helix bundle. Syntaxin 3 targeting does not require binding to Munc18b. Instead, syntaxin 3 recruits Munc18b to the plasma membrane. Expression of mislocalized mutant syntaxin 3 in Madin-Darby canine kidney cells leads to basolateral mistargeting of apical membrane proteins, disturbance of tight junction formation, and loss of ability to form an organized polarized epithelium. These results indicate that SNARE proteins contribute to the overall specificity of membrane trafficking in vivo, and that the polarity of syntaxin 3 is essential for epithelial cell polarization.
Abbreviations used in this paper: DOX, doxycycline; TEER, transepithelial electrical resistance.

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