MARCH5-FUNDC1 axis fine-tunes hypoxia-induced mitophagy

Mitophagy is responsible for removal of damaged mitochondria and is therefore a fundamental process in mitochondrial quality control. Both ubiquitin-dependent and receptor-dependent pathways are considered to mediate mitophagy. These distinct mechanisms may be activated in response to distinct mitochondrial stresses. An intriguing question is whether and how crosstalk occurs between the distinct pathways to coordinate mitophagy. We have uncovered a striking piece of evidence to demonstrate that the mitophagy receptor FUNDC1 is a substrate of MARCH5, a mitochondrially localized E3 ubiquitin ligase. In response to hypoxia, MARCH5 degrades redundant FUNDC1 to fine-tune hypoxia-induced mitophagy, whereas ablation of MARCH5 leads to accumulation of FUNDC1 and an exaggerated mitophagic phenotype. Mechanistic studies demonstrate that hypoxic insult enhances the interaction of FUNDC1 with MARCH5, which ubiquitinates FUNDC1 at lysine 119 for subsequent degradation. MARCH5-based ubiquitination and degradation of FUNDC1 circumvents injudicious removal of cellular mitochondria. However, severe hypoxic stress leads to dephosphorylation of FUNDC1, increasing mitophagic flux.