title: µ-Calpain conversion of antiapoptotic Bfl-1 (BCL2A1) into a prodeath factor reveals two distinct alpha-helices inducing mitochondria-mediated apoptosis.
abstract: Anti-apoptotic Bfl-1 and pro-apoptotic Bax, two members of the Bcl-2 family sharing a similar structural fold, are classically viewed as antagonist regulators of apoptosis. However, both proteins were reported to be death inducers following cleavage by the cysteine protease µ-calpain. Here we demonstrate that calpain-mediated cleavage of full-length Bfl-1 induces the release of C-terminal membrane active α-helices that are responsible for its conversion into a pro-apoptotic factor. A careful comparison of the different membrane-active regions present in the Bfl-1 truncated fragments with homologous domains of Bax show that helix α5, but not α6, of Bfl-1 induces cell death and cytochrome c release from purified mitochondria through a Bax/Bak-dependent mechanism. In contrast, both helices α5 and α6 of Bax permeabilize mitochondria regardless of the presence of Bax or Bak. Moreover, we provide evidence that the α9 helix of Bfl-1 promotes cytochrome c release and apoptosis through a unique membrane-destabilizing action whereas Bax-α9 does not display such activities. Hence, despite a common 3D-structure, C-terminal toxic domains present on Bfl-1 and Bax function in a dissimilar manner to permeabilize mitochondria and induce apoptosis. These findings provide insights for designing therapeutic approaches that could exploit the cleavage of endogenous Bcl-2 family proteins or the use of Bfl-1/Bax-derived peptides to promote tumor cell clearance.
authors: Institut de Biologie et Chimie des Protéines (IBCP), CNRS UMR 5086, Université Lyon 1, IFR 128, Lyon, France.
authors: Juan García
authors: JG
authors: Valero
authors: Aurélie
authors: A
authors: Cornut-Thibaut
authors: Romain
authors: R
authors: Jugé
authors: Anne-Laure
authors: AL
authors: Debaud
authors: Diana
authors: D
authors: Giménez
authors: Germain
authors: G
authors: Gillet
authors: Nathalie
authors: N
authors: Bonnefoy-Bérard
authors: Jesús
authors: J
authors: Salgado
authors: Gilles
authors: G
authors: Salles
authors: Abdel
authors: A
authors: Aouacheria
authors: Jérôme
authors: J
authors: Kucharczak
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D002154:Calpain / Q000378:metabolism*; D045744:Cell Line, Tumor; D045304:Cytochromes c / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D051379:Mice; D018613:Microscopy, Confocal; D015778:Minor Histocompatibility Antigens; D008928:Mitochondria / Q000378:metabolism*; D017433:Protein Structure, Secondary; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: C096816:BCL2-related protein A1; D015778:Minor Histocompatibility Antigens; D019253:Proto-Oncogene Proteins c-bcl-2; D045304:Cytochromes c; D002154:Calpain