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Science (New York, N.Y.) Apr 2006Accumulation of misfolded protein in the endoplasmic reticulum (ER) triggers an adaptive stress response-termed the unfolded protein response (UPR)-mediated by the ER...
Accumulation of misfolded protein in the endoplasmic reticulum (ER) triggers an adaptive stress response-termed the unfolded protein response (UPR)-mediated by the ER transmembrane protein kinase and endoribonuclease inositol-requiring enzyme-1alpha (IRE1alpha). We investigated UPR signaling events in mice in the absence of the proapoptotic BCL-2 family members BAX and BAK [double knockout (DKO)]. DKO mice responded abnormally to tunicamycin-induced ER stress in the liver, with extensive tissue damage and decreased expression of the IRE1 substrate X-box-binding protein 1 and its target genes. ER-stressed DKO cells showed deficient IRE1alpha signaling. BAX and BAK formed a protein complex with the cytosolic domain of IRE1alpha that was essential for IRE1alpha activation. Thus, BAX and BAK function at the ER membrane to activate IRE1alpha signaling and to provide a physical link between members of the core apoptotic pathway and the UPR.
Topics: Animals; Apoptosis; DNA-Binding Proteins; Endoplasmic Reticulum; Endoplasmic Reticulum Chaperone BiP; Endoribonucleases; Gene Expression Regulation; Heat-Shock Proteins; Humans; Kidney; Liver; Mice; Mice, Knockout; Mitochondria; Molecular Chaperones; Nuclear Proteins; Phosphorylation; Protein Folding; Protein Serine-Threonine Kinases; Protein Structure, Tertiary; Proto-Oncogene Proteins c-bcl-2; Recombinant Proteins; Regulatory Factor X Transcription Factors; Signal Transduction; Transcription Factor CHOP; Transcription Factors; Tunicamycin; bcl-2 Homologous Antagonist-Killer Protein; bcl-2-Associated X Protein; eIF-2 Kinase
PubMed: 16645094
DOI: 10.1126/science.1123480 -
Cell Death and Differentiation Jun 2022BAX and BAK are generally considered as fully interchangeable for mitochondrial permeabilization and consequent apoptotic cell death. Garcia-Saez and colleagues have...
BAX and BAK are generally considered as fully interchangeable for mitochondrial permeabilization and consequent apoptotic cell death. Garcia-Saez and colleagues have recently documented striking kinetic differences that influence BAX and BAK oligomerization at the mitochondrial surface. These data have important implications for inflammatory responses driven by mitochondrial DNA.
Topics: Apoptosis; DNA, Mitochondrial; Mitochondria; bcl-2 Homologous Antagonist-Killer Protein; bcl-2-Associated X Protein
PubMed: 35347233
DOI: 10.1038/s41418-022-00985-2 -
Nature Structural & Molecular Biology Nov 2020BAK and BAX are essential mediators of apoptosis that oligomerize in response to death cues, thereby causing permeabilization of the mitochondrial outer membrane. Their...
BAK and BAX are essential mediators of apoptosis that oligomerize in response to death cues, thereby causing permeabilization of the mitochondrial outer membrane. Their transition from quiescent monomers to pore-forming oligomers involves a well-characterized symmetric dimer intermediate. However, no essential secondary interface that can be disrupted by mutagenesis has been identified. Here we describe crystal structures of human BAK core domain (α2-α5) dimers that reveal preferred binding sites for membrane lipids and detergents. The phospholipid headgroup and one acyl chain (sn2) associate with one core dimer while the other acyl chain (sn1) associates with a neighboring core dimer, suggesting a mechanism by which lipids contribute to the oligomerization of BAK. Our data support a model in which, unlike for other pore-forming proteins whose monomers assemble into oligomers primarily through protein-protein interfaces, the membrane itself plays a role in BAK and BAX oligomerization.
Topics: Binding Sites; Crystallography, X-Ray; Humans; Membrane Lipids; Molecular Docking Simulation; Protein Binding; Protein Multimerization; bcl-2 Homologous Antagonist-Killer Protein
PubMed: 32929280
DOI: 10.1038/s41594-020-0494-5 -
EMBO Reports Dec 2009
Review
Topics: Animals; Apoptosis; Humans; Mitochondrial Membranes; Models, Biological; Permeability; Voltage-Dependent Anion Channels; bcl-2 Homologous Antagonist-Killer Protein; bcl-2-Associated X Protein
PubMed: 19949413
DOI: 10.1038/embor.2009.249 -
Oncotarget Oct 2016
Topics: Cell Death; Proto-Oncogene Proteins c-bcl-2; bcl-2 Homologous Antagonist-Killer Protein; bcl-2-Associated X Protein
PubMed: 27626173
DOI: 10.18632/oncotarget.11948 -
Cell Death and Differentiation Jan 2017Necroptosis is a form of programmed cell death that critically depends on RIP3 and MLKL. However, the contribution of mitochondria to necroptosis is still poorly...
Necroptosis is a form of programmed cell death that critically depends on RIP3 and MLKL. However, the contribution of mitochondria to necroptosis is still poorly understood. In the present study, we discovered that mitochondrial perturbations play a critical role in Smac mimetic/Dexamethasone (Dexa)-induced necroptosis independently of death receptor ligands. We demonstrate that the Smac mimetic BV6 and Dexa cooperate to trigger necroptotic cell death in acute lymphoblastic leukemia (ALL) cells that are deficient in caspase activation due to absent caspase-8 expression or pharmacological inhibition by the caspase inhibitor zVAD.fmk, since genetic silencing or pharmacological inhibition of RIP3 or MLKL significantly rescue BV6/Dexa-induced necroptosis. In addition, RIP3 or MLKL knockout mouse embryonic fibroblasts (MEFs) are protected from BV6/Dexa/zVAD.fmk-induced cell death. In contrast, antagonistic antibodies against the death receptor ligands TNFα, TRAIL or CD95 ligand fail to rescue BV6/Dexa-triggered cell death. Kinetic studies revealed that prior to cell death BV6/Dexa treatment causes hyperpolarization of the mitochondrial membrane potential (MMP) followed by loss of MMP, reactive oxygen species (ROS) production, Bak activation and disruption of mitochondrial respiration. Importantly, knockdown of Bak significantly reduces BV6/Dexa-induced loss of MMP and delays cell death, but not ROS production, whereas ROS scavengers attenuate Bak activation, indicating that ROS production occurs upstream of BV6/Dexa-mediated Bak activation. Consistently, BV6/Dexa treatment causes oxidative thiol modifications of Bak protein. Intriguingly, knockdown or knockout of RIP3 or MLKL protect ALL cells or MEFs from BV6/Dexa-induced ROS production, Bak activation, drop of MMP and disruption of mitochondrial respiration, demonstrating that these mitochondrial events depend on RIP3 and MLKL. Thus, mitochondria might serve as an amplification step in BV6/Dexa-induced necroptosis. These findings provide new insights into the role of mitochondrial dysfunctions during necroptosis and have important implications for the development of novel treatment approaches to overcome apoptosis resistance in ALL.
Topics: Amino Acid Chloromethyl Ketones; Animals; Antibodies; Apoptosis; Caspase Inhibitors; Cell Death; Cell Line; Dexamethasone; Free Radical Scavengers; Glucocorticoids; Humans; Jurkat Cells; Membrane Potential, Mitochondrial; Mice; Mice, Knockout; Mitochondria; Necrosis; Protein Kinases; Reactive Oxygen Species; Receptor-Interacting Protein Serine-Threonine Kinases; bcl-2 Homologous Antagonist-Killer Protein
PubMed: 27834956
DOI: 10.1038/cdd.2016.102 -
Nature Communications Jul 2020Many cellular stresses are transduced into apoptotic signals through modification or up-regulation of the BH3-only subfamily of BCL2 proteins. Through direct or indirect...
Many cellular stresses are transduced into apoptotic signals through modification or up-regulation of the BH3-only subfamily of BCL2 proteins. Through direct or indirect mechanisms, these proteins activate BAK and BAX to permeabilize the mitochondrial outer membrane. While the BH3-only proteins BIM, PUMA, and tBID have been confirmed to directly activate BAK through its canonical BH3 binding groove, whether the BH3-only proteins BMF, HRK or BIK can directly activate BAK is less clear. Here we show that BMF and HRK bind and directly activate BAK. Through NMR studies, site-directed mutagenesis, and advanced molecular dynamics simulations, we also find that BAK activation by BMF and possibly HRK involves a previously unrecognized binding groove formed by BAK α4, α6, and α7 helices. Alterations in this groove decrease the ability of BMF and HRK to bind BAK, permeabilize membranes and induce apoptosis, suggesting a potential role for this BH3-binding site in BAK activation.
Topics: Adaptor Proteins, Signal Transducing; Amino Acid Sequence; Animals; Apoptosis Regulatory Proteins; Binding Sites; Cells, Cultured; Humans; Jurkat Cells; Magnetic Resonance Spectroscopy; Mice, Knockout; Mitochondrial Membranes; Molecular Dynamics Simulation; Mutation; Protein Binding; Protein Domains; Proto-Oncogene Proteins c-bcl-2; Sequence Homology, Amino Acid; bcl-2 Homologous Antagonist-Killer Protein
PubMed: 32620849
DOI: 10.1038/s41467-020-17074-y -
Biochimica Et Biophysica Acta Apr 2011Bax and Bak are two nuclear-encoded proteins present in higher eukaryotes that are able to pierce the mitochondrial outer membrane to mediate cell death by apoptosis.... (Review)
Review
Bax and Bak are two nuclear-encoded proteins present in higher eukaryotes that are able to pierce the mitochondrial outer membrane to mediate cell death by apoptosis. Thus, organelles recruited by nucleated cells to supply energy can be recruited by Bax and Bak to kill cells. The two proteins lie in wait in healthy cells where they adopt a globular α-helical structure, seemingly as monomers. Following a variety of stress signals, they convert into pore-forming proteins by changing conformation and assembling into oligomeric complexes in the mitochondrial outer membrane. Proteins from the mitochondrial intermembrane space then empty into the cytosol to activate proteases that dismantle the cell. The arrangement of Bax and Bak in membrane-bound complexes, and how the complexes porate the membrane, is far from being understood. However, recent data indicate that they first form symmetric BH3:groove dimers which can be linked via an interface between the α6-helices to form high order oligomers. Here, we review how Bax and Bak change conformation and oligomerize, as well as how oligomers might form a pore. This article is part of a Special Issue entitled Mitochondria: the deadly organelle.
Topics: Animals; Apoptosis; Humans; Mitochondria; Molecular Biology; bcl-2 Homologous Antagonist-Killer Protein; bcl-2-Associated X Protein
PubMed: 21195116
DOI: 10.1016/j.bbamcr.2010.12.019 -
The EMBO Journal Oct 2021Permeabilization of the outer mitochondrial membrane initiates apoptotic cell death. B-cell lymphoma 2 (BCL-2) antagonist killer (BAK) and BCL-2-associated X (BAX)...
Permeabilization of the outer mitochondrial membrane initiates apoptotic cell death. B-cell lymphoma 2 (BCL-2) antagonist killer (BAK) and BCL-2-associated X (BAX) mediate mitochondrial poration, but how this process unfolds remains poorly defined. Two studies in this issue investigate the transition of dormant, inactive BAK monomer to a highly dynamic membrane-associated, pore-forming oligomer.
Topics: Apoptosis; Mitochondria; Mitochondrial Membranes; bcl-2 Homologous Antagonist-Killer Protein; bcl-2-Associated X Protein
PubMed: 34542920
DOI: 10.15252/embj.2021109529 -
Proceedings of the National Academy of... Jul 2017BAK and BAX are the essential effectors of apoptosis because without them a cell is resistant to most apoptotic stimuli. BAK and BAX undergo conformation changes to...
BAK and BAX are the essential effectors of apoptosis because without them a cell is resistant to most apoptotic stimuli. BAK and BAX undergo conformation changes to homooligomerize then permeabilize the mitochondrial outer membrane during apoptosis. How BCL-2 homology 3 (BH3)-only proteins bind to activate BAK and BAX is unclear. We report that BH3-only proteins bind inactive full-length BAK at mitochondria and then dissociate following exposure of the BAK BH3 and BH4 domains before BAK homodimerization. Using a functional obstructive labeling approach, we show that activation of BAK involves important interactions of BH3-only proteins with both the canonical hydrophobic binding groove (α2-5) and α6 at the rear of BAK, with interaction at α6 promoting an open groove to receive a BH3-only protein. Once activated, how BAK homodimers multimerize to form the putative apoptotic pore is unknown. Obstructive labeling of BAK beyond the BH3 domain and hydrophobic groove did not inhibit multimerization and mitochondrial damage, indicating that critical protein-protein interfaces in BAK self-association are limited to the α2-5 homodimerization domain.
Topics: Animals; Apoptosis; BH3 Interacting Domain Death Agonist Protein; Binding Sites; Cell Line; Cytochromes c; Disulfides; Epitopes; Fibroblasts; Hydrophobic and Hydrophilic Interactions; Mice; Mice, Inbred C57BL; Mitochondria; Mitochondrial Membranes; Protein Binding; Protein Domains; Protein Interaction Mapping; Protein Multimerization; bcl-2 Homologous Antagonist-Killer Protein; bcl-2-Associated X Protein
PubMed: 28673969
DOI: 10.1073/pnas.1702453114