Cell-surface molecules can be recycled directly through a rapid sorting endosomal pathway or indirectly by accessing the endosomal recycling compartment (ERC) in the pericentrosomal region of the cell. Members of the Rab11 GTPase protein family, which are key regulators of membrane trafficking through the ERC, are enriched at the cytosolic face of this compartment; in addition, a Rab11 effector protein known as FIP3 is important for the structural integrity and subcellular localisation of the ERC. On page , Mary McCaffrey and colleagues provide new findings that clarify the role of FIP3 in endosomal trafficking. They report that FIP3 forms a ternary complex with Rab11a and a subunit of cytoplasmic dynein 1, dynein light intermediate chain 1 (DLIC-1). The FIP3—DLIC-1 interaction occurs in peripheral regions of the cell and precedes minus-end-directed microtubule-mediated transport of endosomal cargo (in which cytoplasmic dynein participates as a motor protein). If a truncation mutant encompassing the DLIC-1-binding region of FIP3 is expressed, proteins that are normally recycled through the ERC cannot access this compartment. Finally, microscopy experiments show that the Rab11a—FIP3—DLIC-1 complex moves from the periphery of the cell towards the centrally located ERC. The authors conclude that this ternary complex mediates transport from peripheral sorting endosomes to the pericentrosomal ERC.
