Broad activation of the ubiquitin–proteasome system by Parkin is critical for mitophagy

TLDR

Parkin, an E3 ubiquitin ligase implicated in Parkinson's disease, promotes degradation of dysfunctional mitochondria by autophagy. The study demonstrates that Parkin, upon translocation to mitochondria, activates the ubiquitin–proteasome system to broadly degrade outer membrane proteins. Parkin translocates to mitochondria, where it activates the ubiquitin–proteasome system to ubiquitinate and degrade outer membrane proteins, including mitofusins, in a manner essential for mitophagy. The study shows that Parkin-mediated UPS activation leads to K48‑linked polyubiquitination, 26S proteasome recruitment, and rapid degradation of outer membrane proteins, and that blocking the proteasome abolishes mitophagy, establishing a causal link between UPS remodeling of the outer membrane proteome and autophagy.

Abstract

Parkin, an E3 ubiquitin ligase implicated in Parkinson's disease, promotes degradation of dysfunctional mitochondria by autophagy. Using proteomic and cellular approaches, we show that upon translocation to mitochondria, Parkin activates the ubiquitin–proteasome system (UPS) for widespread degradation of outer membrane proteins. This is evidenced by an increase in K48-linked polyubiquitin on mitochondria, recruitment of the 26S proteasome and rapid degradation of multiple outer membrane proteins. The degradation of proteins by the UPS occurs independently of the autophagy pathway, and inhibition of the 26S proteasome completely abrogates Parkin-mediated mitophagy in HeLa, SH-SY5Y and mouse cells. Although the mitofusins Mfn1 and Mfn2 are rapid degradation targets of Parkin, we find that degradation of additional targets is essential for mitophagy. These results indicate that remodeling of the mitochondrial outer membrane proteome is important for mitophagy, and reveal a causal link between the UPS and autophagy, the major pathways for degradation of intracellular substrates.