J. Neurochem. (2011) 117, 856–867. Abstract Intramembrane proteolysis is a conserved mechanism that regulates a variety of cellular processes ranging from transcription control to signaling. In mitochondria, the inner membrane rhomboid protease PARL has been implicated in the control of life span and apoptosis by a so far uncharacterized mechanism. Here, we show that PARL cleaves human Pink1, which is implicated in Parkinson’s disease, within its conserved membrane anchor. Mature Pink1 is then free to be released into the cytosol or the mitochondrial intermembrane space. Upon depolarization of the mitochondrial membrane potential, the canonical import of Pink1 and PARL‐catalyzed processing is blocked, leading to accumulation of the Pink1 precursor. As targeting of this precursor to the outer mitochondrial membrane has been shown to trigger mitophagy, we suggest that the PARL‐catalyzed removal of the Pink1 signal sequence in the canonical import pathway acts as a cellular checkpoint for mitochondrial integrity. Furthermore, we show that two Parkinson’s disease‐causing mutations decrease the processing of Pink1 by PARL, with attendant implications for pathogenesis.

Mutations in PINK1 and PARK2/Parkin are a main risk factor for familial Parkinson disease. While the physiological mechanism of their activation is unclear, these proteins have been shown in tissue culture cells to serve as a key trigger for autophagy of depolarized mitochondria. Here we show that ablation of the mitochondrial rhomboid protease PARL leads to retrograde translocation of an intermembrane space-bridging PINK1 import intermediate. Subsequently, it is rerouted to the outer membrane in order to recruit PARK2, which phenocopies mitophagy induction by uncoupling agents. Consistent with a role of this retrograde translocation mechanism in neurodegenerative disease, we show that pathogenic PINK1 mutants which are not cleaved by PARL affect PINK1 kinase activity and the ability to induce PARK2-mediated mitophagy. Altogether we suggest that PARL is an important intrinsic player in mitochondrial quality control, a system substantially impaired in Parkinson disease as indicated by reduced removal of damaged mitochondria in affected patients.