Interaction of Rab31 and OCRL-1 in oligodendrocytes: Its role in transport of mannose 6-phosphate receptors

Rab31, a protein that we cloned from an oligodendrocyte cDNA library, is required for transport of mannose 6-phosphate receptors (MPRs) from the TGN to endosomes and for the Golgi/TGN organization. Here we extend the knowledge of the mechanism of action of Rab31 by demonstrating its interaction with OCRL-1, a phosphatidylinositol 4, 5 diphosphate 5-phosphatase (PI(4,5)P2 5-phosphatase) that regulates the levels of PI(4,5)P2 and PI(4)P, molecules involved in transport and Golgi/TGN organization. We show that Rab31 interacts with OCRL-1 by yeast two hybrid system, GST-Rab31 pull-down experiments and coimmunoprecipitation of OCRL-1 using oligodendrocyte culture lysates. Rab31 and OCRL-1 colocalize in the TGN, post TGN carriers and endosomes. Cation-dependent-MPR (CD-MPR) is sorted to OCRL-1-containing carriers, but CD63 and vesicular stomatitis virus G (VSVG) are not. siRNA-mediated depletion of endogenous Rab31 causes collapse of the TGN apparatus and markedly decreases the levels of OCRL-1 in the TGN and endosomes. Our observations indicate that the role of Rab31 in the Golgi/TGN structure and transport of MPRs depends on its capability to recruit OCRL-1 to domains of the TGN where the formation of carriers occurs. The importance of our observations is highlighted by the fact that mutation of OCRL-1 causes demyelination in humans