The first characterization of the WASH complex in C. elegans endocytic recycling

The quantity and distribution of proteins in the plasma membrane play an essential role in regulating a cell’s response to its environment and resulting physiology. This cell surface protein mosaic is largely influenced by the endocytic recycling pathway, misregulation of which has been implicated in a variety of human conditions, including neurodegenerative diseases and cancer. Endocytosis and subsequent intracellular movement of cargo requires both membrane fission and vesicle movement, with the force for these processes provided by a spatially and temporally regulated dynamic branched actin network, generated by Arp2/3-mediated actin polymerization. While it has been determined that endocytosis requires the nucleation promoting factors WASP and WAVE at the plasma membrane, a role for the structurally-related WASH complex for this process in C. elegans remains more elusive. In mammalian systems, the WASH complex seems to act at early endosomes, facilitating retrograde trafficking via its FAM21 subunit interacting with retromer. However, a homologous protein to FAM21 in the Caenorhabditis elegans WASH complex has yet to be identified. This work provides the first characterization of the C. elegans WASH complex, detailing its function on RAB-5-, PI(3)P-positive early endosomes to ensure proper sorting during endocytic recycling, likely through retrograde trafficking to the Golgi apparatus. Through RNAis and genetic crosses, these experiments reveal a functionally important role for the WASH complex in this pathway that is distinct from other nucleation promoting factors, including the WAVE complex, despite similarities between the two. Furthermore, proper recycling may be mediated in part by the protein C05G5.2, as these data suggest this could be the previously unidentified C. elegans FAM21 homolog.M.S.Includes bibliographical reference