RAB17 LOCALIZES TO RECYCLING ENDOSOMES AND REGULATES RECEPTOR-MEDIATED TRANSCYTOSIS IN EPITHELIAL-CELLS

The small GTPase Rab17 is restricted to epithelial cells and its expre ssion is induced during cell polarization. This observation has led to the suggestion that the protein may function in transcytosis, a pathw ay connecting the apical and basolateral endocytic systems. To analyze whether Rab17 plays a Pole in transcellular transport, we generated M adin-Darby canine kidney (MDCK) cell lines stably coexpressing wild-ty pe or mutant Rab17 and the transcytotic polymeric immunoglobulin recep tor (pIgR), Rab17 expressed in MDCK cells was found on small vesicles and tubules in the apical region of the cells. A significant fraction of the Rab17-positive structures was accessible to dimeric IgA interna lized from the apical or basolateral cell surface via the pIgR. Furthe rmore, basolateral to apical transcytosis of dimeric IgA was impaired in MDCK cells overexpressing Rab17. Our data provides morphological an d biochemical evidence for a role of Rab17 in the regulation of transc ellular traffic through apical recycling endosomes in epithelial cells .