TORC1, BORC, and ARL-8 cycling drive vesiculation of cell corpse phagolysosomes

Abstract

The dynamics of phagolysosomes leading to cargo clearance are important to provide cells with metabolites and avoid auto-immune responses, but little is known about how phagolysosomes finally resolve cell corpses and cell debris. We previously discovered that polar body phagolysosomes tubulate into small vesicles to facilitate corpse clearance within 1.5 hours in C. elegans. Here, we show that vesiculation depends on activating TORC1 through amino acid release by the solute transporter SLC-36.1. Downstream of TORC1, BLOC-1-related complex (BORC) recruits the Arf-like GTPase ARL-8 to the phagolysosome for tubulation by kinesin-1. We find that disrupting the regulated GTP-GDP cycle of ARL-8 reduces tubulation, delays corpse clearance, and mislocalizes ARL-8 away from lysosomes. We also demonstrate that mammalian phagocytes use BORC to promote phagolysosomal degradation, confirming the conserved importance of this pathway. Finally, we show that HOPS is required for rapid degradation of the small phagolysosomal vesicles. Thus, by observing single phagolysosomes over time, we identified the molecular pathway regulating phagolysosome vesiculation that promotes efficient resolution.