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The FEBS Journal Feb 2018Bax and Bak are members of the Bcl-2 family and core regulators of the intrinsic pathway of apoptosis. Upon apoptotic stimuli, they are activated and oligomerize at the... (Review)
Review
Bax and Bak are members of the Bcl-2 family and core regulators of the intrinsic pathway of apoptosis. Upon apoptotic stimuli, they are activated and oligomerize at the mitochondrial outer membrane (MOM) to mediate its permeabilization, which is considered a key step in apoptosis. However, the molecular mechanism underlying Bax and Bak function has remained a key question in the field. Here, we review recent structural and biophysical evidence that has changed our understanding of how Bax and Bak promote MOM permeabilization. We also discuss how the spatial regulation of Bcl-2 family preference for binding partners contributes to regulate Bax and Bak activation. Finally, we consider the contribution of mitochondrial composition, dynamics and interaction with other organelles to apoptosis commitment. A new perspective is emerging, in which the control of apoptosis by Bax and Bak goes beyond them and is highly influenced by additional mitochondrial components.
Topics: Animals; Apoptosis; Apoptosis Regulatory Proteins; Dimerization; Humans; Lipid Bilayers; Lipid Mobilization; Mitochondria; Mitochondrial Dynamics; Mitochondrial Membrane Transport Proteins; Mitochondrial Membranes; Models, Biological; Porosity; Protein Conformation; Protein Interaction Domains and Motifs; Protein Multimerization; Proto-Oncogene Proteins c-bcl-2; bcl-2 Homologous Antagonist-Killer Protein; bcl-2-Associated X Protein
PubMed: 28755482
DOI: 10.1111/febs.14186 -
Science Advances May 2023Degradation of defective mitochondria is an essential process to maintain cellular homeostasis and it is strictly regulated by the ubiquitin-proteasome system (UPS) and...
Degradation of defective mitochondria is an essential process to maintain cellular homeostasis and it is strictly regulated by the ubiquitin-proteasome system (UPS) and lysosomal activities. Here, using genome-wide CRISPR and small interference RNA screens, we identified a critical contribution of the lysosomal system in controlling aberrant induction of apoptosis following mitochondrial damage. After treatment with mitochondrial toxins, activation of the PINK1-Parkin axis triggered a BAX- and BAK-independent process of cytochrome c release from mitochondria followed by APAF1 and caspase 9-dependent apoptosis. This phenomenon was mediated by UPS-dependent outer mitochondrial membrane (OMM) degradation and was reversed using proteasome inhibitors. We found that the subsequent recruitment of the autophagy machinery to the OMM protected cells from apoptosis, mediating the lysosomal degradation of dysfunctional mitochondria. Our results underscore a major role of the autophagy machinery in counteracting aberrant noncanonical apoptosis and identified autophagy receptors as key elements in the regulation of this process.
Topics: Mitophagy; bcl-2-Associated X Protein; Apoptosis; Autophagy; Mitochondria; Ubiquitin
PubMed: 37224250
DOI: 10.1126/sciadv.adg8156 -
The EMBO Journal Apr 2022The apoptotic executioner protein BAX and the dynamin-like protein DRP1 co-localize at mitochondria during apoptosis to mediate mitochondrial permeabilization and...
The apoptotic executioner protein BAX and the dynamin-like protein DRP1 co-localize at mitochondria during apoptosis to mediate mitochondrial permeabilization and fragmentation. However, the molecular basis and functional consequences of this interplay remain unknown. Here, we show that BAX and DRP1 physically interact, and that this interaction is enhanced during apoptosis. Complex formation between BAX and DRP1 occurs exclusively in the membrane environment and requires the BAX N-terminal region, but also involves several other BAX surfaces. Furthermore, the association between BAX and DRP1 enhances the membrane activity of both proteins. Forced dimerization of BAX and DRP1 triggers their activation and translocation to mitochondria, where they induce mitochondrial remodeling and permeabilization to cause apoptosis even in the absence of apoptotic triggers. Based on this, we propose that DRP1 can promote apoptosis by acting as noncanonical direct activator of BAX through physical contacts with its N-terminal region.
Topics: Apoptosis; Dynamins; Mitochondria; bcl-2-Associated X Protein
PubMed: 35023587
DOI: 10.15252/embj.2021108587 -
Molecular Cell Mar 2022BAX and BAK are key apoptosis regulators that mediate the decisive step of mitochondrial outer membrane permeabilization. However, the mechanism by which they assemble...
BAX and BAK are key apoptosis regulators that mediate the decisive step of mitochondrial outer membrane permeabilization. However, the mechanism by which they assemble the apoptotic pore remains obscure. Here, we report that BAX and BAK present distinct oligomerization properties, with BAK organizing into smaller structures with faster kinetics than BAX. BAK recruits and accelerates BAX assembly into oligomers that continue to grow during apoptosis. As a result, BAX and BAK regulate each other as they co-assemble into the same apoptotic pores, which we visualize. The relative availability of BAX and BAK molecules thereby determines the growth rate of the apoptotic pore and the relative kinetics by which mitochondrial contents, most notably mtDNA, are released. This feature of BAX and BAK results in distinct activation kinetics of the cGAS/STING pathway with implications for mtDNA-mediated paracrine inflammatory signaling.
Topics: Animals; Apoptosis; Cell Line, Tumor; DNA, Mitochondrial; Humans; Inflammation; Mitochondria; Protein Multimerization; bcl-2 Homologous Antagonist-Killer Protein; bcl-2-Associated X Protein
PubMed: 35120587
DOI: 10.1016/j.molcel.2022.01.008 -
Nature Communications Mar 2022Deregulation of the BCL-2 family interaction network ensures cancer resistance to apoptosis and is a major challenge to current treatments. Cancer cells commonly evade...
Deregulation of the BCL-2 family interaction network ensures cancer resistance to apoptosis and is a major challenge to current treatments. Cancer cells commonly evade apoptosis through upregulation of the BCL-2 anti-apoptotic proteins; however, more resistant cancers also downregulate or inactivate pro-apoptotic proteins to suppress apoptosis. Here, we find that apoptosis resistance in a diverse panel of solid and hematological malignancies is mediated by both overexpression of BCL-XL and an unprimed apoptotic state, limiting direct and indirect activation mechanisms of pro-apoptotic BAX. Both survival mechanisms can be overcome by the combination of an orally bioavailable BAX activator, BTSA1.2 with Navitoclax. The combination demonstrates synergistic efficacy in apoptosis-resistant cancer cells, xenografts, and patient-derived tumors while sparing healthy tissues. Additionally, functional assays and genomic markers are identified to predict sensitive tumors to the combination treatment. These findings advance the understanding of apoptosis resistance mechanisms and demonstrate a novel therapeutic strategy for cancer treatment.
Topics: Aniline Compounds; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Apoptosis Regulatory Proteins; Drug Synergism; Humans; Neoplasms; Sulfonamides; bcl-2-Associated X Protein; bcl-X Protein
PubMed: 35256598
DOI: 10.1038/s41467-022-28741-7 -
Thrombosis Research Nov 2023In a healthy individual, the lifespan of most platelets is tightly regulated by intrinsic, or mitochondrial, apoptosis. This is a special form of programmed cell death... (Review)
Review
In a healthy individual, the lifespan of most platelets is tightly regulated by intrinsic, or mitochondrial, apoptosis. This is a special form of programmed cell death governed by the BCL-2 family of proteins, where the prosurvival protein BCL-X maintains platelet viability by restraining the prodeath proteins BAK and BAX. Restriction of platelet lifespan by activation of BAK and BAX mediated intrinsic apoptosis is essential to maintain a functional, haemostatically reactive platelet population. This review focuses on the molecular regulation of intrinsic apoptosis in platelets, reviews conditions linked to enhanced platelet death, discusses ex vivo storage of platelets and describes caveats associated with the assessment of platelet apoptosis.
Topics: Humans; bcl-2-Associated X Protein; Blood Platelets; Apoptosis; bcl-X Protein
PubMed: 36739256
DOI: 10.1016/j.thromres.2022.11.024 -
Biochemical Society Transactions Jun 2022Apoptosis is a common cell death program that is important in human health and disease. Signaling in apoptosis is largely driven through protein-protein interactions.... (Review)
Review
Apoptosis is a common cell death program that is important in human health and disease. Signaling in apoptosis is largely driven through protein-protein interactions. The BCL-2 family proteins function in protein-protein interactions as key regulators of mitochondrial poration, the process that initiates apoptosis through the release of cytochrome c, which activates the apoptotic caspase cascade leading to cellular demolition. The BCL-2 pore-forming proteins BAK and BAX are the key executors of mitochondrial poration. We review the state of knowledge of protein-protein and protein-lipid interactions governing the apoptotic function of BAK and BAX, as determined through X-ray crystallography and NMR spectroscopy studies. BAK and BAX are dormant, globular α-helical proteins that participate in protein-protein interactions with other pro-death BCL-2 family proteins, transforming them into active, partially unfolded proteins that dimerize and associate with and permeabilize mitochondrial membranes. We compare the protein-protein interactions observed in high-resolution structures with those derived in silico by AlphaFold, making predictions based on combining experimental and in silico approaches to delineate the structural basis for novel protein-protein interaction complexes of BCL-2 family proteins.
Topics: Apoptosis; Humans; Lipids; Proto-Oncogene Proteins c-bcl-2; bcl-2 Homologous Antagonist-Killer Protein; bcl-2-Associated X Protein
PubMed: 35521828
DOI: 10.1042/BST20220323 -
Nature Communications Feb 2021The BCL-2 family protein BAX has essential activity in mitochondrial regulation of cell death. While BAX activity ensures tissue homeostasis, when dysregulated it...
The BCL-2 family protein BAX has essential activity in mitochondrial regulation of cell death. While BAX activity ensures tissue homeostasis, when dysregulated it contributes to aberrant cell death in several diseases. During cellular stress BAX is transformed from an inactive cytosolic conformation to a toxic mitochondrial oligomer. Although the BAX transformation process is not well understood, drugs that interfere with this process are useful research tools and potential therapeutics. Here, we show that Eltrombopag, an FDA-approved drug, is a direct inhibitor of BAX. Eltrombopag binds the BAX trigger site distinctly from BAX activators, preventing them from triggering BAX conformational transformation and simultaneously promoting stabilization of the inactive BAX structure. Accordingly, Eltrombopag is capable of inhibiting BAX-mediated apoptosis induced by cytotoxic stimuli. Our data demonstrate structure-function insights into a mechanism of BAX inhibition and reveal a mechanism for Eltrombopag that may expand its use in diseases of uncontrolled cell death.
Topics: 3T3 Cells; Animals; Apoptosis; Benzoates; Cell Death; Humans; Hydrazines; Magnetic Resonance Spectroscopy; Mice; Models, Biological; Models, Molecular; Protein Stability; Pyrazoles; bcl-2-Associated X Protein
PubMed: 33602934
DOI: 10.1038/s41467-021-21224-1 -
Philosophical Transactions of the Royal... Aug 2017The permeabilization of the mitochondrial outer membrane by Bax and Bak during apoptosis is considered a key step and a point of no return in the signalling pathway. It... (Review)
Review
The permeabilization of the mitochondrial outer membrane by Bax and Bak during apoptosis is considered a key step and a point of no return in the signalling pathway. It is always closely related to the reorganization of mitochondrial cristae that frees cytochrome to the intermembrane space and to massive mitochondrial fragmentation mediated by the dynamin-like protein Drp1. Despite multiple evidence in favour of a functional link between these processes, the molecular mechanisms that connect them and their relevance for efficient apoptosis signalling remain obscure. In this review, we discuss recent progress on our understanding of how Bax forms pores in the context of Drp1-stabilized signalling platforms at apoptotic foci in mitochondria.This article is part of the themed issue 'Membrane pores: from structure and assembly, to medicine and technology'.
Topics: Animals; Apoptosis; Mitochondria; Mitochondrial Membranes; Signal Transduction; bcl-2-Associated X Protein
PubMed: 28630156
DOI: 10.1098/rstb.2016.0217 -
Trends in Cell Biology Dec 2016Cellular commitment to the mitochondrial pathway of apoptosis is accomplished when proapoptotic B cell chronic lymphocytic leukemia/lymphoma (BCL)-2 proteins compromise... (Review)
Review
Cellular commitment to the mitochondrial pathway of apoptosis is accomplished when proapoptotic B cell chronic lymphocytic leukemia/lymphoma (BCL)-2 proteins compromise mitochondrial integrity through the process of mitochondrial outer membrane permeabilization (MOMP). For nearly three decades, intensive efforts focused on the identification and interactions of two key proapoptotic BCL-2 proteins: BCL-2 antagonist killer (BAK) and BCL-2-associated X (BAX). Indeed, we now have critical insights into which BCL-2 proteins interact with BAK/BAX to either preserve survival or initiate MOMP. In contrast, while mitochondria are targeted by BAK/BAX, a molecular understanding of how these organelles govern BAK/BAX function remains less clear. Here, we integrate recent mechanistic insights of proapoptotic BCL-2 protein function in the context of mitochondrial environment, and discuss current and potential pharmacological opportunities to control MOMP in disease.
Topics: Amino Acid Sequence; Animals; Apoptosis; Humans; Membrane Potential, Mitochondrial; Mitochondria; Models, Biological; bcl-2 Homologous Antagonist-Killer Protein; bcl-2-Associated X Protein
PubMed: 27498846
DOI: 10.1016/j.tcb.2016.07.002