DRP1 and BIF-1 regulations in mitochondrial dynamics during apoptosi

Abstract

Recent studies have revealed that mttochondrial fragmentation is a critical event in apoptosts. Mitochondria become fragmented and notably, the fragmentation causes the permeabiliLation of the mitochondrial outet membrane and consequently contributes to mitochondrial dysfunction and apoptotic cell death. In apoptosts, mitochondrial fragmentation in\'olvcs the activations of Drp I. a ke} fission protein. and Bif-1, a protein onginally identified to interact .... ith Ra\.. flo, .. ever, the molecular mechanisms b) '' hich Drp I and Bif-1 regulate mit0chondrial d}nam ic during apoptosts remain unclear. In the first study of tn) thesis \\Ork. I investigated Drp I regulation and its role tn apoptosis of rat proximal tubular cell (RP I C) follm.,.ing. AlP depletion. During ATP depletton. Drp I .... as sho\\tn to he dephosphory Ia ted at scnne-637 The dephosphorylation could be suppressed by cyclosporine A and FK506, t\\0 calcineurin inhibitors, which also prevented mitochondrial fragmentation. Bax accumulation. cytochrome c release and apoptosis 111 RP fC. The results suggest that Drp 1 is activated by calcineurin-mediated dephosphor} lation at serin-637 Upon acti\ation. Drp I stunulates mitochondrial fragtllentation and the permeabiltzation 0f outer membrane. resulting in the release of apoptogenic factor and apoptosis. In the second stud). I detected Bif-1 translocatton to mitochondria during apoptosis of RPl C. Notably, apoptotic events including mitochondrial fragmentation. Ba\. insertion and oligomerization. and C)tochrome c release ''ere all suppressed in Bif-1 deficient cells. Mechanisticall}. we shO\\Cd that during apoptosis. Bif-1 bound to prohibitin-2 (PHB2), a mitochondrial protein implicated in mitochondrial inner membrane regulation. Furthermore. PIIB2 wa~ c,ho\\11 to form hetero-oligomeric complex with prohibitin-1 (PH B I) in control celb and the complex broke dov .. n upon apoptosis, which was accompanied by the proteolysiS of optic atroph) I (OPA I), the mitochondrial inner membrane fusion protein. In Btf-1 deficient cells, the breakdown of PliB complexes and OPA I proteolysis \\Crc both inhibited supporting a ~ritical role of Bif-1 in mitochondrialmner membrane fragmentation b) regulating PHB2 and OPAl. Our studies ha\e shed ne\\ light on the critical molecular mechanisms responsible for the alteratton of mitochondrial d) namtcs upon cell c,tre ·o,. resulting in mitochondrial fragmentatiOn. injury and apoptosis.