UNC-108/Rab2 Regulates Post-endocytic Trafficking in C. elegans

Monitoring Editor: Sandra LemmonFollowing endocytosis, membrane proteins are often sorted between two alternative pathways: a recycling pathway, and a degradation pathway. Relatively little is known about how trafficking through these alternative pathways are differentially regulated. Here we identify UNC-108/Rab2 as a regulator of post-endocytic trafficking in both neurons and coelomocytes. Mutations in the C. elegans Rab2 gene unc-108, caused the GFP-tagged glutamate receptor, GLR-1 (GLR-1::GFP), to accumulate in the ventral cord and in neuronal cell bodies. In neuronal cell bodies of unc-108/Rab2 mutants, GLR-1::GFP was found in tubulovesicular structures that colocalized with markers for early and recycling endosomes, including Syntaxin-13 and Rab8. GFP-tagged Syntaxin-13 also accumulated in the ventral cord of unc-108/Rab2 mutants. UNC-108/Rab2 was not required for ubiquitin-mediated sorting of GLR-1::GFP into the multivesicular body (MVB) degradation pathway. Mutations disrupting the MVB pathway and unc-108/Rab2 mutations had additive effects on GLR-1::GFP levels in the ventral cord. In coelomocytes, post-endocytic trafficking of the marker Texas Red-BSA was delayed. These results demonstrate that UNC-108/Rab2 regulates post-endocytic trafficking, most likely at the level of early or recycling endosomes, and that UNC-108/Rab2 and the MVB pathway define alternative post-endocytic trafficking mechanisms that operate in parallel. These results define a new function for Rab2 in protein trafficking. 10.1091/mbc.E07-11-1120