SNARE protein trafficking in polarized MDCK cells

A key feature of polarized epithelial cells is the ability to maintain the specific biochemical composition of the apical and basolateral plasma membr ane domains. This polarity is generated and maintained by the continuous so rting of apical and basolateral components in the secretory and endocytic p athways. Soluble N-ethyl maleimide-sensitive factor attachment protein rece ptors (SNARE) proteins of vesicle-associated membrane protein (VAMP) and sy ntaxin families have been suggested to play a role in the biosynthetic tran sport to the apical and basolateral plasma membranes of polarized cells, wh ere they likely mediate membrane fusion. To investigate the involvement of SNARE proteins in membrane trafficking to the apical and basolateral plasma membrane in the endocytic pathway we have monitored the recycling of vario us VAMP and syntaxin molecules between intracellular compartments and the t wo plasma membrane domains in Madin-Darby canine kidney (MDCK) cells. Here we show that VAMP8/endobrevin cycles through the apical but not through the basolateral plasma membrane. Furthermore, we found that VAMP8 localizes to apical endosomal membranes in nephric tubule epithelium and in MDCK cells. This asymmetry in localization and cycling behavior suggests that VAMP8/ e ndobrevin may play a role in apical endosomal trafficking in polarized epit helium cells.