RAB17 REGULATES MEMBRANE TRAFFICKING THROUGH APICAL RECYCLING ENDOSOMES IN POLARIZED EPITHELIAL-CELLS

A key feature of polarized epithelial cells is the ability to maintain the specific biochemical composition of the apical and basolateral pl asma membrane domains while selectively allowing transport of proteins and lipids from one pole to the opposite by transcytosis. The small G TPase, rab17, a member of the rab family of regulators of intracellula r transport, is specifically induced during cell polarization in the d eveloping kidney. We here examined its intracellular distribution and function in both nonpolarized and polarized cells. By confocal immunof luorescence microscopy, rab17 colocalized with internalized transferri n in the perinuclear recycling endosome of BHK-21 cells. In polarized Eph4 cells, rab17 associated with the apical recycling endosome that h as been implicated in recycling and transcytosis, The localization of rab17, therefore, strengthens the proposed homology between this compa rtment and the recycling endosome of nonpolarized cells. Basolateral t o apical transport of two membrane-bound markers, the transferrin rece ptor and the FcLR 5-27 chimeric receptor, was specifically increased i n Eph4 cells expressing rab17 mutants defective in either GTP binding or hydrolysis. Furthermore, the mutant proteins stimulated apical recy cling of FcLR 5-27, These results support a role for rab17 in regulati ng traffic through the apical recycling endosome, suggesting a functio n in polarized sorting in epithelial cells.