Apical targeting of syntaxin 3 is essential for epithelial cell polarity.
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.
Sharma
Nikunj
N
Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, CA 93106, USA.
Low
Seng Hui
SH
Misra
Saurav
S
Pallavi
Bhattaram
B
Weimbs
Thomas
T
D020816:Amino Acid Motifs; D000818:Animals; D021961:Cell Membrane Structures / Q000378:metabolism; D016764:Cell Polarity / Q000502:physiology*; D002478:Cells, Cultured; D004285:Dogs; D004847:Epithelial Cells / Q000166:cytology* / Q000378:metabolism; D051938:Munc18 Proteins / Q000378:metabolism; D009154:Mutation; D021381:Protein Transport; D050765:Qa-SNARE Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D050600:SNARE Proteins / Q000378:metabolism; D050827:Syntaxin 1 / Q000737:chemistry
D051938:Munc18 Proteins; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; D050827:Syntaxin 1