Mitochondrial processing peptidase regulates PINK1 processing, import and Parkin recruitment

Mutations in phosphatase and tensin homologue‐induced kinase 1 (PINK1) cause recessively inherited Parkinson's disease (PD), a neurodegenerative disorder linked to mitochondrial dysfunction. In healthy mitochondria, PINK1 is rapidly degraded in a process involving both mitochondrial proteases and the proteasome. However, when mitochondrial import is compromised by depolarization, PINK1 accumulates on the mitochondrial surface where it recruits the PD‐linked E3 ubiquitin ligase Parkin from the cytosol, which in turn mediates the autophagic destruction of the dysfunctional organelles. Using an unbiased RNA‐mediated interference (RNAi)‐based screen, we identified four mitochondrial proteases, mitochondrial processing peptidase (MPP), presenilin‐associated rhomboid‐like protease (PARL), m‐AAA and ClpXP, involved in PINK1 degradation. We find that PINK1 turnover is particularly sensitive to even modest reductions in MPP levels. Moreover, PINK1 cleavage by MPP is coupled to import such that reducing MPP activity induces PINK1 accumulation at the mitochondrial surface, leading to Parkin recruitment and mitophagy. These results highlight a new role for MPP in PINK1 import and mitochondrial quality control via the PINK1–Parkin pathway. Dysfunctional mitochondria express high surface levels of the Parkinson's disease‐linked protein PINK1, which in turn recruits Parkin for mitophagy. Fon and colleagues now show that levels of PINK1 are kept low in normal mitochondria through degradation by the mitochondrial processing peptidase (MPP).