Rab11 regulates the compartmentalization of early endosomes required for efficient transport from early endosomes to the trans-golgi network

Several GTPases of the Rab family, known to be regulators of membrane traff ic between organelles, have been described and localized to various intrace llular compartments. Rab11 has previously been reported to be associated wi th the pericentriolar recycling compartment, post-Golgi vesicles, and the t rans-Golgi network (TGN). We compared the effect of overexpression of wild- type and mutant forms of Rab11 on the different intracellular transport ste ps in the endocytic/degradative and the biosynthetic/exocytic pathways in H eLa cells. We also studied transport from endosomes to the Golgi apparatus using the Shiga toxin B subunit (STxB) and TGN38 as reporter molecules. Ove rexpression of both Rab11 wild-type (Rab11wt) and mutants altered the local ization of the transferrrin receptor (TfR), internalized Tf, the STxB, and TGN38. In cells overexpressing Rab11wt and in a GTPase-deficient Rab11 muta nt (Rab11Q70L), these proteins were found in vesicles showing characteristi cs of sorting endosomes lacking cellubrevin (Cb). In contrast, they were re distributed into an extended tubular network, together with Cb, in cells ov erexpressing a dominant negative mutant of Rab11 (Rab11S25N). This tubulari zed compartment was not accessible to Tf internalized at temperatures <20<d egrees>C, suggesting that it is of recycling endosomal origin. Overexpressi on of Rab11wt, Rab11Q70L, and Rab11S25N also inhibited STxB and TGN38 trans port from endosomes to the TGN. These results suggest that Rab11 influences endosome to TGN trafficking primarily by regulating membrane distribution inside the early endosomal pathway.