Mitofusin 1 and mitofusin 2 are ubiquitinated in a PINK1/parkin-dependent manner upon induction of mitophagy

Abstract

Mitochondrial dysfunction and perturbed degradation of proteins have been implicated in Parkinson's disease (PD) pathogenesis. Mutations in the Parkin and PINK1 genes are a cause of familial PD. PINK1 is a putative kinase associated with mitochondria, and loss of PINK1 expression leads to mitochondrial dysfunction, which increases with time. Parkin is suggested to be downstream of PINK1 and also mediates the removal of damaged mitochondria by macroautophagy (mitophagy). We investigated whether mitochondrial dysfunction in dopaminergic SH-SY5Y cells following decreased PINK1 expression by RNAi may in part be due to the inhibition of mitophagy. Reduced flux through the macroautophagy pathway was found to be coincident with the inhibition of ATP synthesis following 12 days of PINK1 silencing. Overexpression of parkin in these cells restored both autophagic flux and ATP synthesis. Overexpression and RNAi studies also indicated that PINK1 and parkin were required for mitophagy following CCCP-induced mitochondrial damage. The ubiquitination of several mitochondrial proteins, including mitofusin 1 and mitofusin 2, were detected within 3 h of CCCP treatment. These post-translational modifications were reduced following the silencing of parkin or PINK1. The ubiquitination of mitochondrial proteins appears to identify mitochondria for degradation and facilitate mitophagy. PINK1 and parkin are thus required for the removal of damaged mitochondria in dopaminergic cells, and inhibition of this pathway may lead to the accumulation of defective mitochondria which may contribute to PD pathogenesis.

Parkin Mediates Proteasome-dependent Protein Degradation and Rupture of the Outer Mitochondrial Membrane

“…Ubiquitination of VDAC1 may recruit the autophagy adaptor p62, which interacts with microtubule-associated protein light chain 3 (LC3) on the autophagosomal membrane (8); however, the requirement of p62 remains controversial (18 -21). Ubiquitination of mitofusin may affect mitochondrial fission or fusion, which would facilitate mitophagy (11,14,15).Mitochondrial degradation by autophagy has been extensively studied, whereas the involvement of the proteasome in Parkin-mediated mitochondrial degradation is less clear. As the proteasome has been found on mitochondria (22), it is possible that it has a more direct role in mitochondrial protein degradation together with Parkin.…”

“…Targeting of Parkin to mitochondria requires PTEN-induced putative kinase 1 (Pink1), 3 another Parkinson disease-associated gene product (7)(8)(9)(10)(11)(12)(13)(14). Pink1 is an extremely unstable mitochondrial protein, but it is stabilized upon mitochondrial depolarization and subsequently recruits Parkin.…”

“…However, the precise role of Parkin in the induction of mitophagy has not been fully elucidated. To date, several mitochondrial proteins, voltage-dependent anion channel 1 (VDAC1) (8), mitofusin (a mitochondrial pro-fusion factor) (11,14,15), Bcl-2 (16), and Drp1 (17), have been shown to be ubiquitinated by Parkin. Ubiquitination of VDAC1 may recruit the autophagy adaptor p62, which interacts with microtubule-associated protein light chain 3 (LC3) on the autophagosomal membrane (8); however, the requirement of p62 remains controversial (18 -21).…”

“…Ubiquitination of VDAC1 may recruit the autophagy adaptor p62, which interacts with microtubule-associated protein light chain 3 (LC3) on the autophagosomal membrane (8); however, the requirement of p62 remains controversial (18 -21). Ubiquitination of mitofusin may affect mitochondrial fission or fusion, which would facilitate mitophagy (11,14,15).…”

Mitophagy in hematopoietic stem cells

“…[105][106][107][108] The degradation of mitofusins, and likely other proteins as well, relies on PARK2-mediated recruitment of VCP (valosin containing protein), a type II AAA ubiquitin-selective chaperone ATPase. 109 PARK2's translocation to mitochondria also leads to the recruitment of SQSTM1/p62 and HDAC6 (histone deacetylase 6), both of which promote aggregation of the mitochondria and have been implicated in mitophagy, 108,110 although the necessity of SQSTM1/p62 for mitophagy has been debated.…”