Drosophila Parkin requires PINK1 for mitochondrial translocation and ubiquitinates Mitofusin

Abstract

Loss of the E3 ubiquitin ligase Parkin causes early onset Parkinson's disease, a neurodegenerative disorder of unknown etiology. Parkin has been linked to multiple cellular processes including protein degradation, mitochondrial homeostasis, and autophagy; however, its precise role in pathogenesis is unclear. Recent evidence suggests that Parkin is recruited to damaged mitochondria, possibly affecting mitochondrial fission and/or fusion, to mediate their autophagic turnover. The precise mechanism of recruitment and the ubiquitination target are unclear. Here we show in Drosophila cells that PINK1 is required to recruit Parkin to dysfunctional mitochondria and promote their degradation. Furthermore, PINK1 and Parkin mediate the ubiquitination of the profusion factor Mfn on the outer surface of mitochondria. Loss of Drosophila PINK1 or parkin causes an increase in Mfn abundance in vivo and concomitant elongation of mitochondria. These findings provide a molecular mechanism by which the PINK1/Parkin pathway affects mitochondrial fission/fusion as suggested by previous genetic interaction studies. We hypothesize that Mfn ubiquitination may provide a mechanism by which terminally damaged mitochondria are labeled and sequestered for degradation by autophagy.is a common neurodegenerative disorder principally affecting the degeneration of nigral dopaminergic neurons. The pathogenic mechanisms are unknown, but valuable insight has been gained from identifying gene mutations causative for familial forms of PD (1). Loss-of-function mutations in PINK1 and parkin are the major cause of autosomal recessive, early onset PD. PINK1 encodes a mitochondria-targeted kinase (2) whereas parkin encodes an E3 ubiquitin ligase (3), a class of enzymes that conjugate ubiquitin to target substrates. This modification is usually considered in the context of substrate degradation by the proteasome, but ubiquitination also serves many other cellular functions. Consequently, much emphasis has been put on elucidating a link between Parkin dysfunction and protein aggregation. Despite the identification of numerous putative Parkin substrates, an unequivocal causative link between substrate aggregation and pathogenesis remains debatable.There is strong evidence, however, that supports an important role for Parkin in regulating mitochondrial homeostasis (4). Studies have revealed a conserved function of Parkin acting downstream of PINK1 to protect mitochondrial integrity and prevent oxidative stress-induced apoptosis (5-8). Recently, we and others have reported that Drosophila parkin and PINK1 genetically interact with components of the mitochondrial fission and fusion machinery (9-12), suggesting that loss of PINK1/parkin function may lead to excess mitochondrial fusion. Consistent with this, mitochondrial elongation has been reported in cells derived from PD patients with parkin mutations (13). However, the effects of parkin or PINK1 deficiency in mammalian cells remain unresolved because additional reports describe inconsistent phenotypes in PINK...

E2F1-dependent miR-421 regulates mitochondrial fragmentation and myocardial infarction by targeting Pink1

“…Next, we explored how Pink1 altered mitochondrial morphology in our model. Previous reports showed that Parkin requires Pink1 for mitochondrial translocation and recruitment 21,22 . Thus, we tested whether Parkin was also recruited to the mitochondria or it was a separate pathway in our signalling axis.…”

Autophagy and ageing: Insights from invertebrate model organisms

“…Subsequently, mitofusin (Mfn; a profusion factor on the outer mitochondrial membrane) is ubiquitinated in a Parkin-dependent manner for degradation by the proteasome (Narendra et al, 2010;Ziviani et al, 2010). Decreasing the levels of Mfn via the PIKN1/Parkin pathway promotes mitochondrial fission, or alternatively inhibits mitochondrial fusion (Poole et al, 2008(Poole et al, , 2010Yang et al, 2008).…”

PINK1 as a Molecular Checkpoint in the Maintenance of Mitochondrial Function and Integrity

“…Moreover, PINK1 deficiency or point mutations induce mitochondrial fragmentation in immortal or primary human neuronal cells, indicating that PINK1 and Parkin inhibit mitochondrial fission in human neuronal cells (Exner et al, 2007;Kim et al, 2008a). Recently, several groups reported that the pro-mitochondrial fusion protein Marf and its human homolog, mitofusin (Mfn), are specifically ubiquitinated and degraded by Parkin in both human and Drosophila systems (Gegg et al, 2010;Tanaka et al, 2010;Ziviani et al, 2010). Therefore, the exact molecular mechanisms underlying these different mitochondrial remodeling patterns are expected to be elucidated soon.…”