Rab17 localizes to recycling endosomes and regulates receptor-mediated transcytosis in epithelial cells.

The small GTPase Rab17 is restricted to epithelial cells and its expression is induced during cell polarization. This observation has led to the suggestion that the protein may function in transcytosis, a pathway connecting the apical and basolateral endocytic systems. To analyze whether Rab17 plays a role in transcellular transport, we generated Madin-Darby canine kidney (MDCK) cell lines stably coexpressing wild-type or mutant Rab17 and the transcytotic polymeric immunoglobulin receptor (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 internalized from the apical or basolateral cell surface via the pIgR. Furthermore, basolateral to apical transcytosis of dimeric IgA was impaired in MDCK cells overexpressing Rab17. Our data provides morphological and biochemical evidence for a role of Rab17 in the regulation of transcellular traffic through apical recycling endosomes in epithelial cells.