Snazarus and its human ortholog SNX25 regulate autophagic flux by affecting VAMP8 endocytosis

Autophagy, the degradation and recycling of cytosolic components in the lysosome, is an essential cellular mechanism. It is a membrane-mediated process that is linked to vesicular trafficking events. The sorting nexin (SNX) protein family controls the sorting of a large array of cargoes, and various SNXs can impact autophagy. To gain a better understanding of their functions in vivo under nutrient starvation, we screened all Drosophila SNXs by RNAi in the fat body. Significantly, depletion of snazarus (snz) strongly impacted autolysosome formation and led to decreased autophagic flux. Interestingly, we observed altered distribution of Vamp7-positive vesicles with snz depletion and snz roles were conserved in human cells. SNX25 is the closest ortholog to snz, and we demonstrate a role for it in VAMP8 trafficking. We found that this activity was dependent on the SNX25 PX domain, and independent of SNX25 anchoring at the ER. We also demonstrate that differentially spliced forms of SNX14 and SNX25 are present in cancer cells. This work identifies a conserved role for snz/SNX25 as regulators of autophagic flux, and show differential isoform expression between orthologs.