title: Mitochondrial permeabilization relies on BH3 ligands engaging multiple prosurvival Bcl-2 relatives, not Bak.
abstract: The Bcl-2 family regulates apoptosis by controlling mitochondrial integrity. To clarify whether its prosurvival members function by sequestering their Bcl-2 homology 3 (BH3)-only ligands or their multidomain relatives Bak and Bax, we analyzed whether four prosurvival proteins differing in their ability to bind specific BH3 peptides or Bak could protect isolated mitochondria. Most BH3 peptides could induce temperature-dependent cytochrome c release, but permeabilization was prevented by Bcl-x(L), Bcl-w, Mcl-1, or BHRF1. However, their protection correlated with the ability to bind Bak rather than the added BH3 peptide and could be overcome only by BH3 peptides that bind directly to the appropriate prosurvival member. Mitochondria protected by both Bcl-x(L)-like and Mcl-1 proteins were disrupted only by BH3 peptides that engage both. BH3-only reagents freed Bak from Bcl-x(L) and Mcl-1 in mitochondrial and cell lysates. The findings support a model for the control of apoptosis in which certain prosurvival proteins sequester Bak/Bax, and BH3-only proteins must neutralize all protective prosurvival proteins to allow Bak/Bax to induce mitochondrial disruption.
authors: The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria 3050, Australia.
authors: Rachel T
authors: RT
authors: Uren
authors: Grant
authors: G
authors: Dewson
authors: Lin
authors: L
authors: Chen
authors: Stephanie C
authors: SC
authors: Coyne
authors: David C S
authors: DC
authors: Huang
authors: Jerry M
authors: JM
authors: Adams
authors: Ruth M
authors: RM
authors: Kluck
mesh_terms: D000818:Animals; D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008024:Ligands; D008099:Liver / Q000166:cytology; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000378:metabolism; D010063:Ovum / Q000166:cytology; D010446:Peptide Fragments / Q000378:metabolism*; D010539:Permeability; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D013696:Temperature; D014982:Xenopus laevis; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism*
chemical_list: D051023:BH3 Interacting Domain Death Agonist Protein; C474007:Bax protein (53-86); D008024:Ligands; C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D050998:bcl-2 Homologous Antagonist-Killer Protein