USP20 deubiquitinates and stabilizes the ER-phagy receptor FAM134B to drive ER-phagy

The endoplasmic reticulum (ER) serves as a hub for various essential cellular processes, and maintaining ER homeostasis is essential for cell function. ER-phagy is a selective process that removes impaired ER subdomains through autophagosomes and lysosomal degradation. While the involvement of ubiquitination in autophagy regulation is well-established, its role in ER-phagy remains unclear. In our study, we screened deubiquitinating enzymes involved in ER-phagy and identified USP20 (ubiquitin specific peptidase 20) as a key regulator of ER-phagy under stress conditions. USP20 specifically cleaves K63- and K48-linked ubiquitin chains on the ER-phagy receptor FAM134B/RETREG1 (reticulophagy regulator 1), thereby stabilizing the substrate and promoting ER-phagy. Remarkably, despite lacking a transmembrane domain, USP20 is recruited to the ER through its interaction with VAPs (vesicle-associated membrane proteins). VAPs facilitate the recruitment of early autophagy proteins, including WIPI2, to specific ER subdomains, where USP20 and FAM134B are enriched. This recruitment of WIPI2 and other proteins plays a crucial role in facilitating FAM134B-mediated ER-phagy in response to cellular stress. Our findings highlight the critical role of USP20 in maintaining ER homeostasis by deubiquitinating and stabilizing FAM134B at distinct ER subdomains, where USP20 further recruits VAPs and promotes efficient ER-phagy.