Protrudin acts at ER-endosome contacts to promote KIF5-mediated endosomal fission and endosome-to-Golgi transport

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Abstract
Fission of transport tubules from early endosomes is required for endosomal sorting, but mechanisms of endosomal tubule fission (ETF) are incompletely understood. We show protrudin acts at ER-endosome contacts to promote ETF and endosome-to-Golgi traffic. Protrudin-mediated ETF required its ability to interact with ER-localised VAP proteins, endosomal phosphoinositides and KIF5. These properties also regulated the distance between protrudin and endosomal tubules. The defective ETF phenotype of increased endosomal tubulation in cells lacking protrudin was phenocopied by depletion of KIF5, but not FYCO1, a motor protein adaptor implicated in protrudin-dependent late endosome motility. It also required intact microtubules and dynein, consistent with a model where protrudin facilitates a tug-of-war between KIF5 and dynein to fission tubules. In addition to its direct role, protrudin links many other machineries involved in ETF, thus our findings elucidate how ETF is co-ordinated. These machineries are enriched for proteins implicated in hereditary motor neuron disorders, and protrudin or KIF5 depletion caused defective ETF in human neurons. Summary Protrudin binds ER-localised VAPs and endosomal phosphoinositides to form ER-endosome contacts that promote endosomal tubule fission and endosome-to-Golgi traffic. Protrudin recruits KIF5 to provide a FYCO1-independent force to fission endosomal tubules in neurons and non-polarised cells.

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