Abstract
Multidomain pro-apoptotic BAX and BAK, once activated, permeabilize mitochondria to trigger apoptosis, whereas anti-apoptotic BCL-2 members preserve mitochondrial integrity. The BH3-only molecules (BH3s) promote apoptosis by either activating BAX-BAK or inactivating anti-apoptotic members. Here, we present biochemical and genetic evidence that NOXA is a bona fide activator BH3. Using combinatorial gain-of-function and loss-of-function approaches in Bid(-/-)Bim(-/-)Puma(-/-)Noxa(-/-) and Bax(-/-)Bak(-/-) cells, we have constructed an interconnected hierarchical model that accommodates and explains how the intricate interplays between the BCL-2 members dictate cellular survival versus death. BID, BIM, PUMA and NOXA directly induce stepwise, bimodal activation of BAX-BAK. BCL-2, BCL-XL and MCL-1 inhibit both modes of BAX-BAK activation by sequestering activator BH3s and 'BH3-exposed' monomers of BAX-BAK, respectively. Furthermore, autoactivation of BAX and BAK can occur independently of activator BH3s through downregulation of BCL-2, BCL-XL and MCL-1. Our studies lay a foundation for targeting the BCL-2 family for treating diseases with dysregulated apoptosis.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Apoptosis Regulatory Proteins / genetics
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Apoptosis Regulatory Proteins / metabolism
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Apoptosis*
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BH3 Interacting Domain Death Agonist Protein / genetics
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BH3 Interacting Domain Death Agonist Protein / metabolism
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Bcl-2-Like Protein 11
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Cells, Cultured
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Cytochromes c / genetics
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Cytochromes c / metabolism
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Embryo, Mammalian / cytology
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Embryo, Mammalian / metabolism
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Fibroblasts / cytology
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Fibroblasts / metabolism*
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Immunoblotting
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Intestine, Small / cytology
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Intestine, Small / metabolism
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Membrane Proteins / genetics
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Membrane Proteins / metabolism
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Mice, Inbred C57BL
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Mice, Knockout
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Mitochondria / genetics
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Mitochondria / metabolism
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Models, Biological*
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Proto-Oncogene Proteins / genetics
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins c-bcl-2 / genetics
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Proto-Oncogene Proteins c-bcl-2 / metabolism*
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RNA Interference
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Reverse Transcriptase Polymerase Chain Reaction
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Tumor Suppressor Proteins / genetics
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Tumor Suppressor Proteins / metabolism
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bcl-2 Homologous Antagonist-Killer Protein / genetics
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bcl-2 Homologous Antagonist-Killer Protein / metabolism
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bcl-2-Associated X Protein / genetics
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bcl-2-Associated X Protein / metabolism
Substances
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Apoptosis Regulatory Proteins
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BCL2L11 protein, human
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BH3 Interacting Domain Death Agonist Protein
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Bcl-2-Like Protein 11
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Bcl2l11 protein, mouse
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Membrane Proteins
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PUMA protein, mouse
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Pmaip1 protein, mouse
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Proto-Oncogene Proteins
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Proto-Oncogene Proteins c-bcl-2
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Tumor Suppressor Proteins
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bcl-2 Homologous Antagonist-Killer Protein
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bcl-2-Associated X Protein
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Cytochromes c