PHB2 (prohibitin 2) promotes PINK1-PRKN/Parkin-dependent mitophagy by the PARL-PGAM5-PINK1 axis.

ABSTRACT

Mitophagy, which is a conserved cellular process for selectively removing damaged or unwanted mitochondria, is critical for mitochondrial quality control and the maintenance of normal cellular physiology. However, the precise mechanisms underlying mitophagy remain largely unknown. Prior studies on mitophagy focused on the events in the mitochondrial outer membrane. PHB2 (prohibitin 2), which is a highly conserved membrane scaffold protein, was recently identified as a novel inner membrane mitophagy receptor that mediates mitophagy. Here, we report a new signaling pathway for PHB2-mediated mitophagy. Upon mitochondrial membrane depolarization or misfolded protein aggregation, PHB2 depletion destabilizes PINK1 in the mitochondria, which blocks the mitochondrial recruitment of PRKN/Parkin, ubiquitin and OPTN (optineurin), leading to an inhibition of mitophagy. In addition, PHB2 overexpression directly induces PRKN recruitment to the mitochondria. Moreover, PHB2-mediated mitophagy is dependent on the mitochondrial inner membrane protease PARL, which interacts with PHB2 and is activated upon PHB2 depletion. Furthermore, PGAM5, which is processed by PARL, participates in PHB2-mediated PINK1 stabilization. Finally, a ligand of PHB proteins that we synthesized, called FL3, was found to strongly inhibit PHB2-mediated mitophagy and to effectively block cancer cell growth and energy production at nanomolar concentrations. Thus, our findings reveal that the PHB2-PARL-PGAM5-PINK1 axis is a novel pathway of PHB2-mediated mitophagy and that targeting PHB2 with the chemical compound FL3 is a promising strategy for cancer therapy.Abbreviations AIFM1 apoptosis inducing factor mitochondria associated 1; ATP5F1A/ATP5A1 ATP synthase F1 subunit alpha; BAF bafilomycin A1; CALCOCO2/NDP52 calcium binding and coiled-coil domain 2; CCCP chemical reagent carbonyl cyanide m-chlorophenyl hydrazine; FL3 flavaglines compound 3; HSPD1/HSP60 heat shock protein family D (Hsp60) member 1; LC3B/MAP1LC3B microtubule associated protein 1 light chain 3 beta; MEF mouse embryo fibroblasts; MPP mitochondrial-processing peptidase; MT-CO2/COX2 mitochondrially encoded cytochrome c oxidase II; MTS mitochondrial targeting sequence; OA oligomycin and antimycin A; OPTN optineurin; OTC ornithine carbamoyltransferase; PARL presenilin associated rhomboid like; PBS phosphate-buffered saline; PGAM5 PGAM family member 5, mitochondrial serine/threonine protein phosphatase; PHB prohibitin; PHB2 prohibitin 2; PINK1 PTEN induced kinase 1; PRKN/Parkin parkin RBR E3 ubiquitin protein ligase; Roc-A rocaglamide A; TOMM20 translocase of outer mitochondrial membrane 20; TUBB tubulin beta class I.