The deubiquitinating enzyme USP20 stabilizes ULK1 and promotes autophagy initiation

Autophagy begins with the formation of autophagosomes, a process that depends on the activity of the serine/threonine kinase ULK1 (hATG1). Although earlier studies indicated that ULK1 activity is regulated by dynamic polyubiquitination, the deubiquitinase involved in the regulation of ULK1 remained unknown. In this study, we demonstrate that ubiquitin‐specific protease 20 (USP20) acts as a positive regulator of autophagy initiation through stabilizing ULK1. At basal state, USP20 binds to and stabilizes ULK1 by removing the ubiquitin moiety, thereby interfering with the lysosomal degradation of ULK1. The stabilization of basal ULK1 protein levels is required for the initiation of starvation‐induced autophagy, since the depletion of USP20 by RNA interference inhibits LC3 puncta formation, a marker of autophagic flux. At later stages of autophagy, USP20 dissociates from ULK1, resulting in enhanced ULK1 degradation and apoptosis. Taken together, our findings provide the first evidence that USP20 plays a crucial role in autophagy initiation by maintaining the basal expression level of ULK1. Synopsis The deubiquitinating enzyme USP20 acts as a positive regulator of autophagy initiation through the deubiquitination of ULK1. USP20 interferes with the lysosome‐dependent degradation of ULK1 and thereby maintains ULK1 stability at basal state. USP20 deubiquitinates and stabilizes ULK1 at basal state. USP20 depletion inhibits LC3 puncta formation after autophagy induction. The USP20‐ULK1 complex dissociates after autophagy induction, resulting in enhanced ubiquitination of ULK1 and its degradation through a lysosome‐dependent pathway. Graphical Abstract The deubiquitinating enzyme USP20 acts as a positive regulator of autophagy initiation through the deubiquitination of ULK1. USP20 interferes with the lysosome‐dependent degradation of ULK1 and thereby maintains ULK1 stability at basal state.