title: Constitutive proteasome-mediated turnover of Bfl-1/A1 and its processing in response to TNF receptor activation in FL5.12 pro-B cells convert it into a prodeath factor.
abstract: Bfl-1/A1 is generally recognized as a Bcl-2-related inhibitor of apoptosis. We show that Bfl-1 undergoes constitutive ubiquitin/proteasome-mediated turnover. Moreover, while Bfl-1 suppresses apoptosis induced by staurosporine or cytokine withdrawal, it is proapoptotic in response to tumor necrosis factor (TNF) receptor activation in FL5.12 pro-B cells. Its anti- versus proapoptotic effect is regulated by two proteolytic events: (1) its constitutive proteasome-mediated turnover and (2) its TNF/cycloheximide (CHX)-induced cleavage by mu-calpain, or a calpain-like activity, coincident with acquisition of a proapoptotic phenotype. In vitro studies suggest that calpain-mediated cleavage of Bfl-1 occurs between its Bcl-2 homology (BH)4 and BH3 domains. This would be consistent with the generation of a proapoptotic Bax-like BH1-3 molecule. Overall, our studies uncovered two new regulatory mechanisms that play a decisive role in determining Bfl-1's prosurvival versus prodeath activities. These findings might provide important clues to counteract chemoresistance in tumor cells that highly express Bfl-1.
authors.affiliation: Center for Advanced Biotechnology and Medicine, UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ 08854-5638, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Kucharczak
authors.forename: M J
authors.initials: MJ
authors.lastname: Simmons
authors.forename: C S
authors.initials: CS
authors.lastname: Duckett
authors.forename: C
authors.initials: C
authors.lastname: Gélinas
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D001402:B-Lymphocytes / Q000166:cytology*; D002154:Calpain / Q000378:metabolism; D016923:Cell Death; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D008239:Lysine / Q000737:chemistry; D051379:Mice; D015778:Minor Histocompatibility Antigens; D008954:Models, Biological; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D010641:Phenotype; D010957:Plasmids / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011485:Protein Binding; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry / Q000378:metabolism*; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D019311:Staurosporine / Q000494:pharmacology; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism
chemical_list: C096816:BCL2-related protein A1; D015778:Minor Histocompatibility Antigens; D019253:Proto-Oncogene Proteins c-bcl-2; D018124:Receptors, Tumor Necrosis Factor; D025801:Ubiquitin; D049452:Green Fluorescent Proteins; D003513:Cycloheximide; D002154:Calpain; C449002:mu-calpain; D046988:Proteasome Endopeptidase Complex; D019311:Staurosporine; D008239:Lysine