DIFFERENT REQUIREMENTS FOR NSF, SNAP, AND RAB PROTEINS IN APICAL AND BASOLATERAL TRANSPORT IN MDCK CELLS

We used an in vitro system based on streptolysin O-permeabilized MDCK cells to study the involvement of NSF, SNAP, SNAREs, and Rab proteins in polarized membrane transport of epithelial cells. In MDCK cells, tr ansport from the trans-Golgi network (TGN) to the basolateral plasma m embrane is inhibited by anti-NSF antibodies and stimulated by alpha-SN AP. In contrast, transport from the TGN to the apical cell surface is not affected by anti-NSF antibodies or alpha-SNAP. Furthermore, apical transport is insensitive to Rab-GDI and tetanus and botulinum neuroto xins, which inhibit basolateral transport, These results provide evide nce that the Rab-NSF-SNAP-SNARE mechanism operates in basolateral tran sport, while other molecules constitute the machinery for vesicular de livery in the apical pathway.