title: Inactivation of prosurvival Bcl-2 proteins activates Bax/Bak through the outer mitochondrial membrane.
abstract: The mechanism of Bax/Bak activation remains a central question in mitochondria-dependent apoptotic signaling. While it is established that all proapoptotic Bcl-2 homology 3 (BH3)-only proteins bind and neutralize the anti-apoptotic Bcl-2 family proteins, how this neutralization leads to Bax/Bak activation has been actively debated. Here, genome editing was used to generate cells deficient for all eight proapoptotic BH3-only proteins (OctaKO) and those that lack the entire Bcl-2 family (Bcl-2 allKO). Although the OctaKO cells were resistant to most apoptotic stimuli tested, they underwent Bax/Bak-dependent and p53/Rb-independent apoptosis efficiently when both Bcl-xL and Mcl-1, two anti-apoptotic Bcl-2 proteins, were inactivated or eliminated. Strikingly, when expressed in the Bcl-2 allKO cells, both Bax and Bak spontaneously associated with the outer mitochondrial membrane (OMM) through their respective helix 9, and this association triggered their homo-oligomerization/activation. Together, these results strongly suggest that the OMM, not BH3-only proteins or p53/Rb, is the long-sought-after direct activator of Bax/Bak following BH3-only-mediated neutralization of anti-apoptotic Bcl-2 proteins.
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, Fred and Pamela Buffett Cancer Center, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA;
authors.forename: Katelyn L
authors.initials: KL
authors.lastname: O'Neill
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, Fred and Pamela Buffett Cancer Center, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA;
authors.forename: Kai
authors.initials: K
authors.lastname: Huang
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, Fred and Pamela Buffett Cancer Center, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA; Xiangya Hospital, Central South University, Changsha 410008, China.
authors.forename: Jingjing
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, Fred and Pamela Buffett Cancer Center, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA;
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, Fred and Pamela Buffett Cancer Center, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA;
authors.forename: Xu
authors.initials: X
authors.lastname: Luo
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D002460:Cell Line; D005786:Gene Expression Regulation / Q000235:genetics; D020868:Gene Silencing; D045325:HCT116 Cells; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D051336:Mitochondrial Membranes / Q000378:metabolism*; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics*; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics* / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000235:genetics* / Q000378:metabolism*
chemical_list: C579095:MCL1 protein, human; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein
keywords: BH3-only; Bax/Bak activation; anti-apoptotic Bcl-2 proteins; outer mitochondrial membrane