UBXD8 mediates mitochondria‐associated degradation to restrain apoptosis and mitophagy

Abstract

The hexameric AAA‐ATPase valosin‐containing protein (VCP) is essential for mitochondrial protein quality control. How VCP is recruited to mammalian mitochondria remains obscure. Here we report that UBXD8, an ER‐ and lipid droplet‐localized VCP adaptor, also localizes to mitochondria and locally recruits VCP. UBXD8 associates with mitochondrial and ER ubiquitin E3 ligases and targets their substrates for degradation. Remarkably, both mitochondria‐ and ER‐localized UBXD8 can degrade mitochondrial and ER substrates in cis and in trans . UBXD8 also associates with the TOM complex but is dispensable for translocation‐associated degradation. UBXD8 knockout impairs the degradation of the pro‐survival protein Mcl1 but surprisingly sensitizes cells to apoptosis and mitochondrial stresses. UBXD8 knockout also hyperactivates mitophagy. We identify pro‐apoptotic BH3‐only proteins Noxa, Bik, and Bnip3 as novel UBXD8 substrates and determine that UBXD8 inhibits apoptosis via degrading Noxa and restrains mitophagy via degrading Bnip3. Collectively, our characterizations reveal UBXD8 as the major mitochondrial adaptor of VCP and unveil its role in apoptosis and mitophagy regulation. image UBXD8 is a mammalian VCP adaptor that dually localizes to mitochondria and the ER to mediate mitochondria‐ and ER‐associated protein degradation. UBXD8 facilitates the degradation of mitochondrial substrates to restrain apoptosis and mitophagy. UBXD8 is a VCP adaptor that dually localizes to mitochondria and the ER. UBXD8 associates with mitochondrial and ER ubiquitin E3 ligases and facilitates the degradation of their substrates. UBXD8 and UBXD2 (ER‐specific VCP adaptor) mediate substrate degradation in cis and in trans . UBXD8 inhibits apoptosis via degrading Noxa and restrains mitophagy via degrading Bnip3.