Mitochondrial processing peptidase regulates PINK1 processing, import and Parkin recruitment

Abstract

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.

PINK1 protects against cell death induced by mitochondrial depolarization, by phosphorylating Bcl-xL and impairing its pro-apoptotic cleavage

“…We could not detect any association between the two endogenous proteins in untreated cells, likely because of the very low levels of endogenous PINK1, which is rapidly processed by voltagedependent mitochondrial proteases. 24 Conversely, the interaction between endogenous PINK1 and Bcl-xL was evident in cells treated with the mitochondrial uncoupler CCCP (Figure 1d), which is known to inhibit mitochondrial proteases, resulting in the selective accumulation of PINK1 on the surface of depolarized mitochondria. 18 Accordingly, in CCCP-treated SH-SY5Y cells, Bcl-xL strongly colocalized with PINK1 wt at the outer mitochondrial membrane; on the other hand, a PINK1 mutant lacking the mitochondrial target sequence (PINK1-DN) failed to accumulate on depolarized mitochondria and displayed impaired colocalization with Bcl-xL.…”

“…24 Indeed, other groups also failed to demonstrate the interaction between endogenous PINK1 and other binding partners such as Parkin or Miro in basal conditions. 17,19 Conversely, the interaction between endogenous PINK1 and Bcl-xL was observed in cells treated with the mitochondrial uncoupler CCCP, that inhibits mitochondrial proteases and induces a robust accumulation of PINK1 at the outer membrane of depolarized mitochondria.…”

The mitochondrial dynamics in cancer and immune-surveillance

“…These receptors mediate the engulfment of targeted mitochondria by autophagosome for lysis [125][126][127]. Other Parkin/ PINK1-independent pathways can mediate mitophagy alternatively involving NIX/BNIP3, Ambra1, ULK1 or cardiolipin in neurons [128][129][130][131][132].…”

The pathways of mitophagy for quality control and clearance of mitochondria

“…48 In healthy mitochondria, PINK1 is constitutively imported, probably via the TIM/TOM complex, to the inner membrane where it is cleaved by several proteases including the mitochondrial-processing protease (MPP) and the inner membrane presenilin-associated rhomboid-like protease PARL, and ultimately proteolytically degraded ( Figure 4A). [70][71][72][73] Loss of mitochondrial membrane potential may be the event that acutely activates this pathway; loss of the potential gradient precludes import of PINK1 to the inner membrane, thereby stabilizing intact PINK1 on the mitochondrial outer membrane where it interacts with the TOM complex. 74 In this manner, PINK1 serves as a sensor for mitochondrial damage.…”