Bcl-2 family member Bfl-1/A1 sequesters truncated bid to inhibit is collaboration with pro-apoptotic Bak or Bax.
Following caspase-8 mediated cleavage, a carboxyl-terminal fragment of the BH3 domain-only Bcl-2 family member Bid transmits the apoptotic signal from death receptors to mitochondria. In a screen for possible regulators of Bid, we defined Bfl-1/A1 as a potent Bid interacting protein. Bfl-1 is an anti-apoptotic Bcl-2 family member, whose preferential expression in hematopoietic cells and endothelium is controlled by inflammatory stimuli. Its mechanism of action is unknown. We find that Bfl-1 associates with both full-length Bid and truncated (t)Bid, via the Bid BH3 domain. Cellular expression of Bfl-1 confers protection against CD95- and Trail receptor-induced cytochrome c release. In vitro assays, using purified mitochondria and recombinant proteins, demonstrate that Bfl-1 binds full-length Bid, but does not interfere with its processing by caspase-8, or with its mitochondrial association. Confocal microscopy supports that Bfl-1, which at least in part constitutively localizes to mitochondria, does not impede tBid translocation. However, Bfl-1 remains tightly and selectively bound to tBid and blocks collaboration between tBid and Bax or Bak in the plane of the mitochondrial membrane, thereby preventing mitochondrial apoptotic activation. Lack of demonstrable interaction between Bfl-1 and Bak or Bax in the mitochondrial membrane suggests that Bfl-1 generally prevents the formation of a pro-apoptotic complex by sequestering BH3 domain-only proteins.
Pubmed ID: 11929871 RIS Download
Animals | Antigens, CD95 | Apoptosis | BH3 Interacting Domain Death Agonist Protein | COS Cells | Carrier Proteins | Caspase 8 | Caspase 9 | Caspases | Cytochrome c Group | DNA, Complementary | HeLa Cells | Humans | Immunoblotting | Jurkat Cells | Membrane Proteins | Mice | Microscopy, Confocal | Microscopy, Fluorescence | Mitochondria | Mitochondria, Liver | Plasmids | Precipitin Tests | Protein Binding | Protein Structure, Tertiary | Proto-Oncogene Proteins | Proto-Oncogene Proteins c-bcl-2 | Receptors, TNF-Related Apoptosis-Inducing Ligand | Receptors, Tumor Necrosis Factor | Recombinant Proteins | Time Factors | Two-Hybrid System Techniques | bcl-2 Homologous Antagonist-Killer Protein | bcl-2-Associated X Protein