title: Endophilin B1/Bif-1 stimulates BAX activation independently from its capacity to produce large scale membrane morphological rearrangements.
abstract: Endophilin B1/BAX-interacting factor 1 (Bif-1) is a protein that cooperates with dynamin-like protein 1 (DLP1/Drp1) to maintain normal mitochondrial outer membrane (MOM) dynamics in healthy cells and also contributes to BAX-driven MOM permeabilization (MOMP), the irreversible commitment point to cell death for the majority of apoptotic stimuli. However, despite its importance, exactly how Bif-1 fulfils its proapoptotic role is unknown. Here, we demonstrate that the stimulatory effect of Bif-1 on BAX-driven MOMP and on BAX conformational activation observed in intact cells during apoptosis can be recapitulated in a simplified system consisting of purified proteins and MOM-like liposomes. In this reconstituted model system the N-BAR domain of Bif-1 reproduced the stimulatory effect of Bif-1 on functional BAX activation. This process was dependent on physical interaction between Bif-1 N-BAR and BAX as well as on the presence of the mitochondrion-specific lipid cardiolipin. Despite that Bif-1 N-BAR produced large scale morphological rearrangements in MOM-like liposomes, this phenomenon could be separated from functional BAX activation. Furthermore, DLP1 also caused global morphological changes in MOM-like liposomes, but DLP1 did not stimulate BAX-permeabilizing function in the absence or presence of Bif-1. Taken together, our findings not only provide direct evidence for a functional interplay between Bif-1, BAX, and cardiolipin during MOMP but also add significantly to the growing body of evidence indicating that components of the mitochondrial morphogenesis machinery possess proapoptotic functions that are independent from their recognized roles in normal mitochondrial dynamics.
authors.affiliation: Unidad de Biofísica, Centro Mixto Consejo Superior de Investigaciones Cientificas, Universidad del Pais Vasco/Euskal Herriko Unibertsitatea, 48080 Bilbao, Spain.
authors.forename: Aitor
authors.initials: A
authors.lastname: Etxebarria
authors.forename: Oihana
authors.initials: O
authors.lastname: Terrones
authors.forename: Hirohito
authors.initials: H
authors.lastname: Yamaguchi
authors.forename: Ane
authors.initials: A
authors.lastname: Landajuela
authors.forename: Olatz
authors.initials: O
authors.lastname: Landeta
authors.forename: Bruno
authors.initials: B
authors.lastname: Antonsson
authors.forename: Hong-Gang
authors.initials: HG
authors.lastname: Wang
authors.forename: Gorka
authors.initials: G
authors.lastname: Basañez
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002308:Cardiolipins / Q000737:chemistry / Q000378:metabolism; D034281:Dynamins; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006801:Humans; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008297:Male; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008930:Mitochondria, Liver / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000378:metabolism; D008954:Models, Biological; D017434:Protein Structure, Tertiary / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D051028:bcl-2-Associated X Protein / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C494826:BAX protein, human; C494828:Bax protein, rat; D002308:Cardiolipins; D008081:Liposomes; D008869:Microtubule-Associated Proteins; D024101:Mitochondrial Proteins; C429293:SH3GLB1 protein, human; D051028:bcl-2-Associated X Protein; D020558:GTP Phosphohydrolases; C110768:DNM1L protein, human; C519851:Dnm1l protein, rat; D034281:Dynamins