title: Bak but not Bax is essential for Bcl-xS-induced apoptosis.
abstract: Bcl-x(S), a proapoptotic member of the Bcl-2 protein family, is localized in the mitochondria and induces apoptosis in a caspase- and BH3-dependent manner by a mechanism involving cytochrome c release. The way in which Bcl-x(S) induces caspase activation and cytochrome c release, as well as the relationship between Bcl-x(S) and other proapoptotic members of the Bcl-2 family, is not known. Here we used embryonic fibroblasts derived from mice deficient in the multidomain proapoptotic members of the Bcl-2 family (Bax and Bak) and the apoptotic components of the apoptosome (Apaf-1 and caspase-9) to unravel the cascade of events by which Bcl-x(S) promotes apoptosis. Our results show that Bak but not Bax is essential for Bcl-x(S)-induced apoptosis. Bcl-x(S) induced activation of Bak, which in turn promoted apoptosis by apoptosome-dependent and -independent pathways. These findings provide the first evidence that a proapoptotic Bcl-2 family protein induces apoptosis exclusively via Bak.
authors.affiliation: Department of Neurobiochemistry, George S Wise Faculty of Life Sciences, Tel Aviv University, 69978 Ramat Aviv, Tel Aviv, Israel.
authors.forename: L
authors.initials: L
authors.lastname: Lindenboim
authors.forename: S
authors.initials: S
authors.lastname: Kringel
authors.forename: T
authors.initials: T
authors.lastname: Braun
authors.forename: C
authors.initials: C
authors.lastname: Borner
authors.forename: R
authors.initials: R
authors.lastname: Stein
mesh_terms: D000818:Animals; D017209:Apoptosis; D053477:Apoptotic Protease-Activating Factor 1; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D005347:Fibroblasts; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D011506:Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: C506593:Apaf1 protein, mouse; D053477:Apoptotic Protease-Activating Factor 1; C494773:Bak1 protein, mouse; C494827:Bax protein, mouse; C494812:Bcl2l1 protein, mouse; D008565:Membrane Proteins; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D045304:Cytochromes c; C506434:Casp9 protein, mouse; D053453:Caspase 9; D020169:Caspases