Loss of MIEF1/MiD51 confers susceptibility to BAX-mediated cell death and PINK1-PRKN-dependent mitophagy.

ABSTRACT

Mitochondrial dynamics is highly implicated in a plethora of cellular processes including apoptosis and mitophagy. However, little is known about the scope and precise functions of mitochondrial dynamics proteins for mitochondrial quality control and cellular homeostasis. Whether mitochondrial dynamics proteins serve in cellular processes reliant on mitochondrial fission-fusion is still not fully explored. MIEF1/MiD51 (mitochondrial elongation factor 1) is known to promote mitochondrial fission via the recruitment of GTPase protein DNM1L/DRP1 (dynamin 1 like), but the fundamental understandings of MIEF1 for mitochondrial-dependent cellular processes are largely elusive. Here, we report novel roles of MIEF1 in responding to apoptotic stimuli and mitochondrial damage. Given our result that staurosporine (STS) treatment induced the degradation of MIEF1 via the ubiquitin-proteasome system (UPS), we are motivated to explore the role of MIEF1 in apoptosis. MIEF1 loss triggered the imbalance of BCL2 family members on the mitochondria, consequently initiating the translocation of BAX onto the mitochondria, catalyzing the decrease of mitochondrial membrane potential and promoting the release of DIABLO/SMAC (diablo IAP-binding mitochondrial protein) and CYCS (cytochrome c, somatic). We further demonstrate that MIEF1 deficiency impaired mitochondrial respiration and induced mitochondrial oxidative stress, sensitizing cells to PINK1-PRKN-mediated mitophagy. The recruitment of PRKN to depolarized mitochondria modulated the UPS-dependent degradation of MFN2 (mitofusin 2) and FIS1 (fission, mitochondrial 1) specifically, to further promote mitophagy. Our findings uncover a bridging role of MIEF1 integrating cell death and mitophagy, unlikely dependent on mitochondrial dynamics, implying new insights to mechanisms determining cellular fate.Abbreviations ActD actinomycin D; BAX BCL2 associated X, apoptosis regulator; BAK1 BCL2 antagonist/killer 1; BCL2L1 BCL2 like 1; BMH 1,6-bismaleimidohexane; CCCP carbonyl cyanide 3-chlorophenylhydrazone; CHX cycloheximide; CQ chloroquine; CYCS cytochrome c, somatic; DIABLO diablo IAP-binding mitochondrial protein; DKO double knockout; DNM1L/DRP1 dynamin 1 like; FIS1 fission, mitochondrial 1; GFP green fluorescent protein; IP immunoprecipitation; MFN1 mitofusin 1; MFN2 mitofusin 2; MG132 carbobenzoxy-Leu-Leu-leucinal; MIEF1/MiD51 mitochondrial elongation factor 1; MIEF2/MiD49 mitochondrial elongation factor 2; MOMP mitochondrial outer membrane permeabilization; MTR MitoTracker Red; OA oligomycin plus antimycin A; OCR oxygen consumption rate; OMM outer mitochondrial membrane; PARP poly(ADP-ribose) polymerase; PI propidium iodide; PINK1 PTEN induced kinase 1; PRKN parkin RBR E3 ubiquitin protein ligase; ROS reactive oxygen species; SD standard deviation; STS staurosporine; TNF tumor necrosis factor; UPS ubiquitin-proteasome system; VDAC1 voltage dependent anion channel 1.