An unexpected journey for BNIP3

Mitophagy is a cellular process that enables the selective degradation of damaged, dysfunctional, or superfluous mitochondria. During mitophagy, specific proteins recognize and tag mitochondria for degradation. These tagged mitochondria are engulfed by specialized structures called phagophores that then mature into autophagosomes/mitophagosomes. Mitophagosomes subsequently transport their mitochondrial cargo to lysosomes, where the mitochondria are broken down and recycled. While the PINK1-PRKN-dependent mitophagy pathway is well understood, mitophagy can also occur independently of this pathway. BNIP3 and BNIP3L/NIX, paralogous membrane proteins on the outer mitochondrial membrane (OMM), serve as ubiquitin-independent mitophagy receptors. Historically, BNIP3 regulation was thought to be primarily transcriptional through HIF1A (hypoxia inducible factor 1 subunit alpha). However, recent work has revealed a significant post-translational dimension, highlighting the strong role of the ubiquitin-proteasome system (UPS) in BNIP3 regulation. With these emerging concepts in mind, we aimed to develop a unified understanding of how steady-state levels of BNIP3 are established and maintained and how this regulation governs underlying cell physiology.