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.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Animals
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Apoptosis
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B-Lymphocytes / cytology*
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Calpain / metabolism
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Cell Death
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Cell Line
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Cycloheximide / pharmacology
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Flow Cytometry
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Green Fluorescent Proteins / metabolism
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Humans
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Immunoprecipitation
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Lysine / chemistry
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Mice
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Minor Histocompatibility Antigens
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Models, Biological
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Molecular Sequence Data
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Mutagenesis
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Mutation
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Phenotype
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Plasmids / metabolism
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Proteasome Endopeptidase Complex / metabolism*
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Protein Binding
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Protein Biosynthesis
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Protein Structure, Tertiary
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Proto-Oncogene Proteins c-bcl-2 / chemistry
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Proto-Oncogene Proteins c-bcl-2 / metabolism*
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Receptors, Tumor Necrosis Factor / metabolism*
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Sequence Homology, Amino Acid
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Staurosporine / pharmacology
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Transfection
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Ubiquitin / metabolism
Substances
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BCL2-related protein A1
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Minor Histocompatibility Antigens
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Proto-Oncogene Proteins c-bcl-2
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Receptors, Tumor Necrosis Factor
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Ubiquitin
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Green Fluorescent Proteins
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Cycloheximide
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Calpain
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mu-calpain
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Proteasome Endopeptidase Complex
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Staurosporine
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Lysine