1
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Subas Satish HP, Iyer S, Shi MX, Wong AW, Fischer KC, Wardak AZ, Lio D, Brouwer JM, Uren RT, Czabotar PE, Miller MS, Kluck RM. A novel inhibitory BAK antibody enables assessment of non-activated BAK in cancer cells. Cell Death Differ 2024:10.1038/s41418-024-01289-3. [PMID: 38582955 DOI: 10.1038/s41418-024-01289-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Revised: 03/21/2024] [Accepted: 03/22/2024] [Indexed: 04/08/2024] Open
Abstract
BAX and BAK are pro-apoptotic members of the BCL2 family that are required to permeabilize the mitochondrial outer membrane. The proteins can adopt a non-activated monomeric conformation, or an activated conformation in which the exposed BH3 domain facilitates binding either to a prosurvival protein or to another activated BAK or BAX protein to promote pore formation. Certain cancer cells are proposed to have high levels of activated BAK sequestered by MCL1 or BCLXL, thus priming these cells to undergo apoptosis in response to BH3 mimetic compounds that target MCL1 or BCLXL. Here we report the first antibody, 14G6, that is specific for the non-activated BAK conformer. A crystal structure of 14G6 Fab bound to BAK revealed a binding site encompassing both the α1 helix and α5-α6 hinge regions of BAK, two sites involved in the unfolding of BAK during its activation. In mitochondrial experiments, 14G6 inhibited BAK unfolding triggered by three diverse BAK activators, supporting crucial roles for both α1 dissociation and separation of the core (α2-α5) and latch (α6-α9) regions in BAK activation. 14G6 bound the majority of BAK in several leukaemia cell lines, and binding decreased following treatment with BH3 mimetics, indicating only minor levels of constitutively activated BAK in those cells. In summary, 14G6 provides a new means of assessing BAK status in response to anti-cancer treatments.
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Affiliation(s)
- Hema Preethi Subas Satish
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
- Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Sweta Iyer
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Melissa X Shi
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Agnes W Wong
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Karla C Fischer
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Ahmad Z Wardak
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Daisy Lio
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Jason M Brouwer
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Rachel T Uren
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Peter E Czabotar
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Michelle S Miller
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia.
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia.
| | - Ruth M Kluck
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia.
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia.
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2
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Diepstraten ST, Young S, La Marca JE, Wang Z, Kluck RM, Strasser A, Kelly GL. Lymphoma cells lacking pro-apoptotic BAX are highly resistant to BH3-mimetics targeting pro-survival MCL-1 but retain sensitivity to conventional DNA-damaging drugs. Cell Death Differ 2023; 30:1005-1017. [PMID: 36755070 PMCID: PMC10070326 DOI: 10.1038/s41418-023-01117-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Revised: 01/08/2023] [Accepted: 01/11/2023] [Indexed: 02/10/2023] Open
Abstract
BH3-mimetic drugs are an anti-cancer therapy that can induce apoptosis in malignant cells by directly binding and inhibiting pro-survival proteins of the BCL-2 family. The BH3-mimetic drug venetoclax, which targets BCL-2, has been approved for the treatment of chronic lymphocytic leukaemia and acute myeloid leukaemia by regulatory authorities worldwide. However, while most patients initially respond well, resistance and relapse while on this drug is an emerging and critical issue in the clinic. Though some studies have begun uncovering the factors involved in resistance to BCL-2-targeting BH3-mimetic drugs, little focus has been applied to pre-emptively tackle resistance for the next generation of BH3-mimetic drugs targeting MCL-1, which are now in clinical trials for diverse blood cancers. Therefore, using pre-clinical mouse and human models of aggressive lymphoma, we sought to predict factors likely to contribute to the development of resistance in patients receiving MCL-1-targeting BH3-mimetic drugs. First, we performed multiple whole genome CRISPR/Cas9 KO screens and identified that loss of the pro-apoptotic effector protein BAX, but not its close relative BAK, could confer resistance to MCL-1-targeting BH3-mimetic drugs in both short-term and long-term treatment regimens, even in lymphoma cells lacking the tumour suppressor TRP53. Furthermore, we found that mouse Eµ-Myc lymphoma cells selected for loss of BAX, as well as upregulation of the untargeted pro-survival BCL-2 family proteins BCL-XL and A1, when made naturally resistant to MCL-1 inhibitors by culturing them in increasing doses of drug over time, a situation mimicking the clinical application of these drugs. Finally, we identified therapeutic approaches which could overcome these two methods of resistance: the use of chemotherapeutic drugs or combined BH3-mimetic treatment, respectively. Collectively, these results uncover some key factors likely to cause resistance to MCL-1 inhibition in the clinic and suggest rational therapeutic strategies to overcome resistance that should be investigated further.
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Affiliation(s)
- Sarah T Diepstraten
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC, Australia.,Department of Medical Biology, University of Melbourne, Melbourne, VIC, Australia
| | - Savannah Young
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC, Australia
| | - John E La Marca
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC, Australia.,Department of Medical Biology, University of Melbourne, Melbourne, VIC, Australia
| | - Zilu Wang
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC, Australia.,Department of Medical Biology, University of Melbourne, Melbourne, VIC, Australia
| | - Ruth M Kluck
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC, Australia.,Department of Medical Biology, University of Melbourne, Melbourne, VIC, Australia
| | - Andreas Strasser
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC, Australia.,Department of Medical Biology, University of Melbourne, Melbourne, VIC, Australia
| | - Gemma L Kelly
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC, Australia. .,Department of Medical Biology, University of Melbourne, Melbourne, VIC, Australia.
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3
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Subas Satish HP, Zeglinski K, Uren RT, Nutt SL, Ritchie ME, Gouil Q, Kluck RM. NAb-seq: an accurate, rapid, and cost-effective method for antibody long-read sequencing in hybridoma cell lines and single B cells. MAbs 2022; 14:2106621. [PMID: 35965451 PMCID: PMC9377246 DOI: 10.1080/19420862.2022.2106621] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Affiliation(s)
- Hema Preethi Subas Satish
- Blood Cells and Blood Cancer Division, The Walter and Eliza Hall Institute of Medical Research , Melbourne, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Australia
| | - Kathleen Zeglinski
- Department of Medical Biology, University of Melbourne, Melbourne, Australia
- Epigenetics and Development Division, The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
| | - Rachel T. Uren
- Blood Cells and Blood Cancer Division, The Walter and Eliza Hall Institute of Medical Research , Melbourne, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Australia
| | - Stephen L. Nutt
- Department of Medical Biology, University of Melbourne, Melbourne, Australia
- Immunology Division, The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
| | - Matthew E. Ritchie
- Department of Medical Biology, University of Melbourne, Melbourne, Australia
- Epigenetics and Development Division, The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
| | - Quentin Gouil
- Department of Medical Biology, University of Melbourne, Melbourne, Australia
- Epigenetics and Development Division, The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
| | - Ruth M. Kluck
- Blood Cells and Blood Cancer Division, The Walter and Eliza Hall Institute of Medical Research , Melbourne, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Australia
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4
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Robin AY, Miller MS, Iyer S, Shi MX, Wardak AZ, Lio D, Smith NA, Smith BJ, Birkinshaw RW, Czabotar PE, Kluck RM, Colman PM. Structure of the BAK-activating antibody 7D10 bound to BAK reveals an unexpected role for the α1-α2 loop in BAK activation. Cell Death Differ 2022; 29:1757-1768. [PMID: 35279694 PMCID: PMC9433411 DOI: 10.1038/s41418-022-00961-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Revised: 02/13/2022] [Accepted: 02/17/2022] [Indexed: 11/08/2022] Open
Abstract
Pro-apoptotic BAK and BAX are activated by BH3-only proteins to permeabilise the outer mitochondrial membrane. The antibody 7D10 also activates BAK on mitochondria and its epitope has previously been mapped to BAK residues in the loop connecting helices α1 and α2 of BAK. A crystal structure of the complex between the Fv fragment of 7D10 and the BAK mutant L100A suggests a possible mechanism of activation involving the α1-α2 loop residue M60. M60 mutants of BAK have reduced stability and elevated sensitivity to activation by BID, illustrating that M60, through its contacts with residues in helices α1, α5 and α6, is a linchpin stabilising the inert, monomeric structure of BAK. Our data demonstrate that BAK's α1-α2 loop is not a passive covalent connector between secondary structure elements, but a direct restraint on BAK's activation.
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Affiliation(s)
- Adeline Y Robin
- Structural Biology Division, The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC, 3052, Australia
| | - Michelle S Miller
- Structural Biology Division, The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC, 3052, Australia
| | - Sweta Iyer
- Blood Cells and Blood Cancer Division, The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC, 3052, Australia
| | - Melissa X Shi
- Blood Cells and Blood Cancer Division, The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC, 3052, Australia
| | - Ahmad Z Wardak
- Structural Biology Division, The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC, 3052, Australia
| | - Daisy Lio
- Structural Biology Division, The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC, 3052, Australia
| | - Nicholas A Smith
- Department of Chemistry and Physics, La Trobe Institute for Molecular Sciences, La Trobe University, Melbourne, VIC, 3086, Australia
| | - Brian J Smith
- Department of Chemistry and Physics, La Trobe Institute for Molecular Sciences, La Trobe University, Melbourne, VIC, 3086, Australia
| | - Richard W Birkinshaw
- Structural Biology Division, The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC, 3052, Australia
| | - Peter E Czabotar
- Structural Biology Division, The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC, 3052, Australia
| | - Ruth M Kluck
- Blood Cells and Blood Cancer Division, The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC, 3052, Australia.
| | - Peter M Colman
- Structural Biology Division, The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC, 3052, Australia.
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5
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Ke FS, Holloway S, Uren RT, Wong AW, Little MH, Kluck RM, Voss AK, Strasser A. The BCL-2 family member BID plays a role during embryonic development in addition to its BH3-only protein function by acting in parallel to BAX, BAK and BOK. EMBO J 2022; 41:e110300. [PMID: 35758142 PMCID: PMC9340487 DOI: 10.15252/embj.2021110300] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Revised: 05/27/2022] [Accepted: 05/30/2022] [Indexed: 12/31/2022] Open
Abstract
The intrinsic apoptosis pathway, regulated by the BCL-2 protein family, is essential for embryonic development. Using mice lacking all known apoptosis effectors, BAX, BAK and BOK, we have previously defined the processes during development that require apoptosis. Rare Bok-/- Bax-/- Bak-/- triple knockout (TKO) mice developed to adulthood and several tissues that were thought to require apoptosis during development appeared normal. This raises the question if all apoptosis had been abolished in the TKO mice or if other BCL-2 family members could act as effectors of apoptosis. Here, we investigated the role of BID, generally considered to link the extrinsic and intrinsic apoptosis pathways, acting as a BH3-only protein initiating apoptosis upstream of BAX and BAK. We found that Bok-/- Bax-/- Bak-/- Bid-/- quadruple knockout (QKO) mice have additional developmental anomalies compared to TKO mice, consistent with a role of BID, not only upstream but also in parallel to BAX, BAK and BOK. Mitochondrial experiments identified a small cytochrome c-releasing activity of full-length BID. Collectively, these findings suggest a new effector role for BID in the intrinsic apoptosis pathway.
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Affiliation(s)
- Francine S Ke
- The Walter and Eliza Hall Institute of Medical Research (WEHI)MelbourneVicAustralia,Department of Medical BiologyUniversity of MelbourneMelbourneVicAustralia
| | - Steven Holloway
- The Walter and Eliza Hall Institute of Medical Research (WEHI)MelbourneVicAustralia
| | - Rachel T Uren
- The Walter and Eliza Hall Institute of Medical Research (WEHI)MelbourneVicAustralia,Department of Medical BiologyUniversity of MelbourneMelbourneVicAustralia
| | - Agnes W Wong
- The Walter and Eliza Hall Institute of Medical Research (WEHI)MelbourneVicAustralia
| | - Melissa H Little
- Department of PaediatricsUniversity of MelbourneMelbourneVicAustralia,Murdoch Children's Medical Research InstituteMelbourneVicAustralia
| | - Ruth M Kluck
- The Walter and Eliza Hall Institute of Medical Research (WEHI)MelbourneVicAustralia,Department of Medical BiologyUniversity of MelbourneMelbourneVicAustralia
| | - Anne K Voss
- The Walter and Eliza Hall Institute of Medical Research (WEHI)MelbourneVicAustralia,Department of Medical BiologyUniversity of MelbourneMelbourneVicAustralia
| | - Andreas Strasser
- The Walter and Eliza Hall Institute of Medical Research (WEHI)MelbourneVicAustralia,Department of Medical BiologyUniversity of MelbourneMelbourneVicAustralia
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6
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Birkinshaw RW, Iyer S, Lio D, Luo CS, Brouwer JM, Miller MS, Robin AY, Uren RT, Dewson G, Kluck RM, Colman PM, Czabotar PE. Structure of detergent-activated BAK dimers derived from the inert monomer. Mol Cell 2021; 81:2123-2134.e5. [PMID: 33794146 DOI: 10.1016/j.molcel.2021.03.014] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Revised: 01/11/2021] [Accepted: 03/09/2021] [Indexed: 01/27/2023]
Abstract
A body of data supports the existence of core (α2-α5) dimers of BAK and BAX in the oligomeric, membrane-perturbing conformation of these essential apoptotic effector molecules. Molecular structures for these dimers have only been captured for truncated constructs encompassing the core domain alone. Here, we report a crystal structure of BAK α2-α8 dimers (i.e., minus its flexible N-terminal helix and membrane-anchoring C-terminal segment) that has been obtained through the activation of monomeric BAK with the detergent C12E8. Core dimers are evident, linked through the crystal by contacts via latch (α6-α8) domains. This crystal structure shows activated BAK dimers with the extended latch domain present. Our data provide direct evidence for the conformational change converting BAK from inert monomer to the functional dimer that destroys mitochondrial integrity. This dimer is the smallest functional unit for recombinant BAK or BAX described so far.
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Affiliation(s)
- Richard W Birkinshaw
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia.
| | - Sweta Iyer
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Daisy Lio
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Cindy S Luo
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Jason M Brouwer
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Michelle S Miller
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Adeline Y Robin
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Rachel T Uren
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Grant Dewson
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Ruth M Kluck
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Peter M Colman
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Peter E Czabotar
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia.
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7
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Iyer S, Uren RT, Kluck RM. Probing BAK and BAX Activation and Pore Assembly with Cytochrome c Release, Limited Proteolysis, and Oxidant-Induced Linkage. Methods Mol Biol 2019; 1877:201-216. [PMID: 30536008 DOI: 10.1007/978-1-4939-8861-7_14] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Mitochondrial permeabilization is a key event in the intrinsic pathway of apoptosis, and is mediated by either of the BCL-2 family members BAK or BAX. These two proteins generate pores in the mitochondrial outer membrane that release factors such as cytochrome c into the cytosol to trigger caspase activation and apoptotic cell death. To generate pores, BAK and BAX undergo major changes including BAX translocation to the outer membrane, and partial unfolding, dimerization, and oligomerization. Here we describe biochemical protocols that can be used on most cell types to gain a population overview of BAK and BAX status.
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Affiliation(s)
- Sweta Iyer
- Molecular Genetics of Cancer Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, Australia
| | - Rachel T Uren
- Molecular Genetics of Cancer Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, Australia
| | - Ruth M Kluck
- Molecular Genetics of Cancer Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia.
- Department of Medical Biology, The University of Melbourne, Parkville, VIC, Australia.
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8
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Abstract
Apoptotic cell death via the mitochondrial pathway occurs in all vertebrate cells and requires the formation of pores in the mitochondrial outer membrane. Two Bcl-2 protein family members, Bak and Bax, form these pores during apoptosis, and how they do so has been investigated for the last two decades. Many of the conformation changes that occur during their transition to pore-forming proteins have now been delineated. Notably, biochemical, biophysical and structural studies indicate that symmetric homodimers are the basic unit of pore formation. Each dimer contains an extended hydrophobic surface that lies on the outer membrane, and is anchored at either end by a transmembrane domain. Membrane-remodelling events such as positive membrane curvature have been reported to accompany apoptotic pore formation, suggesting Bak and Bax form lipidic pores rather than proteinaceous pores. However, it remains unclear how symmetric dimers assemble to porate the membrane. Here, we review how clusters of dimers and their lipid-mediated interactions provide a molecular explanation for the heterogeneous assemblies of Bak and Bax observed during apoptosis.This article is part of the themed issue 'Membrane pores: from structure and assembly, to medicine and technology'.
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Affiliation(s)
- Rachel T Uren
- Molecular Genetics of Cancer Division, The Walter and Eliza Hall Institute of Medical Research, The University of Melbourne, 1G Royal Parade, Parkville, Victoria 3052, Australia.,Department of Medical Biology, The University of Melbourne, 1G Royal Parade, Parkville, Victoria 3052, Australia
| | - Sweta Iyer
- Molecular Genetics of Cancer Division, The Walter and Eliza Hall Institute of Medical Research, The University of Melbourne, 1G Royal Parade, Parkville, Victoria 3052, Australia.,Department of Medical Biology, The University of Melbourne, 1G Royal Parade, Parkville, Victoria 3052, Australia
| | - Ruth M Kluck
- Molecular Genetics of Cancer Division, The Walter and Eliza Hall Institute of Medical Research, The University of Melbourne, 1G Royal Parade, Parkville, Victoria 3052, Australia .,Department of Medical Biology, The University of Melbourne, 1G Royal Parade, Parkville, Victoria 3052, Australia
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9
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Hockings C, Alsop AE, Fennell SC, Lee EF, Fairlie WD, Dewson G, Kluck RM. Mcl-1 and Bcl-x L sequestration of Bak confers differential resistance to BH3-only proteins. Cell Death Differ 2018; 25:721-734. [PMID: 29459767 DOI: 10.1038/s41418-017-0010-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2017] [Revised: 09/22/2017] [Accepted: 10/09/2017] [Indexed: 12/22/2022] Open
Abstract
The prosurvival Bcl-2 family proteins Mcl-1 and Bcl-xL inhibit apoptosis by sequestering BH3-only proteins such as Bid and Bim (MODE 1) or the effector proteins Bak and Bax (MODE 2). To better understand the contributions of MODE 1 and MODE 2 in blocking cell death, and thus how to bypass resistance to cell death, we examined prescribed mixtures of Bcl-2 family proteins. In a Bim and Bak mixture, Bcl-xL and Mcl-1 each sequestered not only Bim but also Bak as it became activated by Bim. In contrast, in a Bid and Bak mixture, Bcl-xL preferentially sequestered Bid while Mcl-1 preferentially sequestered Bak. Notably, Bcl-xL could sequester Bak in response to the BH3 mimetic ABT-737, despite this molecule targeting Bcl-xL. These findings highlight the importance of Bak sequestration in resistance to anti-cancer treatments, including BH3 mimetics.
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Affiliation(s)
- Colin Hockings
- The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, 3052, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia.,Department of Chemical Engineering and Biotechnology, Cambridge, CB3 0AS, UK
| | - Amber E Alsop
- The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, 3052, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Stephanie C Fennell
- The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, 3052, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Erinna F Lee
- Olivia Newton-John Cancer Research Institute, Heidelberg, VIC, 3084, Australia.,School of Cancer Medicine, La Trobe University, Melbourne, VIC, 3086, Australia.,Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, Melbourne, VIC, 3086, Australia
| | - W Douglas Fairlie
- Olivia Newton-John Cancer Research Institute, Heidelberg, VIC, 3084, Australia.,School of Cancer Medicine, La Trobe University, Melbourne, VIC, 3086, Australia.,Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, Melbourne, VIC, 3086, Australia
| | - Grant Dewson
- The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, 3052, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Ruth M Kluck
- The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, 3052, Australia. .,Department of Medical Biology, The University of Melbourne, Parkville, VIC, 3010, Australia.
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10
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Uren RT, O'Hely M, Iyer S, Bartolo R, Shi MX, Brouwer JM, Alsop AE, Dewson G, Kluck RM. Disordered clusters of Bak dimers rupture mitochondria during apoptosis. eLife 2017; 6. [PMID: 28182867 PMCID: PMC5302884 DOI: 10.7554/elife.19944] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Accepted: 01/08/2017] [Indexed: 11/13/2022] Open
Abstract
During apoptosis, Bak and Bax undergo major conformational change and form symmetric dimers that coalesce to perforate the mitochondrial outer membrane via an unknown mechanism. We have employed cysteine labelling and linkage analysis to the full length of Bak in mitochondria. This comprehensive survey showed that in each Bak dimer the N-termini are fully solvent-exposed and mobile, the core is highly structured, and the C-termini are flexible but restrained by their contact with the membrane. Dimer-dimer interactions were more labile than the BH3:groove interaction within dimers, suggesting there is no extensive protein interface between dimers. In addition, linkage in the mobile Bak N-terminus (V61C) specifically quantified association between dimers, allowing mathematical simulations of dimer arrangement. Together, our data show that Bak dimers form disordered clusters to generate lipidic pores. These findings provide a molecular explanation for the observed structural heterogeneity of the apoptotic pore. DOI:http://dx.doi.org/10.7554/eLife.19944.001 A healthy organism must carefully remove unwanted, diseased or damaged cells. These unwanted cells can bring about their own death in a controlled process known as apoptosis. Maintaining an appropriate level of apoptosis is crucial to good health: excessive cell death can contribute to neurodegenerative disorders, whereas too little can result in cancer. All cells contain powerhouses called mitochondria, which produce energy. Mitochondria are the scene of a critical ‘point of no return’ in apoptosis. When a cell receives a death signal, a ‘killer’ protein known as Bak punches holes (or pores) in the membrane of the mitochondria. These pores allow toxic molecules to leak out from the mitochondria into the interior of the cell, where they trigger a series of events that dismantles the cell from the inside out. To create the pores, Bak undergoes extensive shape changes that allow the proteins to form dimers that then cluster and perforate the membrane. To investigate how Bak clusters assemble on the mitochondrial membrane, Uren et al. used cultured cells and biochemical techniques to show where the Bak dimers contacted each other before and after the pore formed; these findings were complemented with mathematical modelling. The results show that during apoptosis, Bak dimers contact each other at several different places (rather than at one or two places) to assemble into disorderly, ever-changing clusters. Based on these observations, Uren et al. suggest that the enlarging clusters stress the membrane and cause pores to form. The next step is to investigate whether physical forces that act within the mitochondrial membrane could drive the clustering of Bak proteins. This knowledge could ultimately enable us to learn how to manipulate apoptosis in cells, potentially as part of treatments for the diseases in which this cell death process occurs inappropriately. DOI:http://dx.doi.org/10.7554/eLife.19944.002
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Affiliation(s)
- Rachel T Uren
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Martin O'Hely
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Sweta Iyer
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Ray Bartolo
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
| | - Melissa X Shi
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Jason M Brouwer
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Amber E Alsop
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Grant Dewson
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Ruth M Kluck
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
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11
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Iyer S, Anwari K, Alsop AE, Yuen WS, Huang DCS, Carroll J, Smith NA, Smith BJ, Dewson G, Kluck RM. Identification of an activation site in Bak and mitochondrial Bax triggered by antibodies. Nat Commun 2016; 7:11734. [PMID: 27217060 PMCID: PMC4890306 DOI: 10.1038/ncomms11734] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Accepted: 04/25/2016] [Indexed: 12/31/2022] Open
Abstract
During apoptosis, Bak and Bax are activated by BH3-only proteins binding to the α2–α5 hydrophobic groove; Bax is also activated via a rear pocket. Here we report that antibodies can directly activate Bak and mitochondrial Bax by binding to the α1–α2 loop. A monoclonal antibody (clone 7D10) binds close to α1 in non-activated Bak to induce conformational change, oligomerization, and cytochrome c release. Anti-FLAG antibodies also activate Bak containing a FLAG epitope close to α1. An antibody (clone 3C10) to the Bax α1–α2 loop activates mitochondrial Bax, but blocks translocation of cytosolic Bax. Tethers within Bak show that 7D10 binding directly extricates α1; a structural model of the 7D10 Fab bound to Bak reveals the formation of a cavity under α1. Our identification of the α1–α2 loop as an activation site in Bak paves the way to develop intrabodies or small molecules that directly and selectively regulate these proteins. During apoptosis, Bak and Bax are activated by BH3-only proteins binding to a specific hydrophobic groove. Here, the authors show that antibodies can also activate Bak and mitochondrial Bax by binding to the α1-α2 loop, thus identifying a potential clinical target.
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Affiliation(s)
- Sweta Iyer
- Molecular Genetics of Cancer Division, The Walter and Eliza Hall Institute of Medical Research, Victoria 3052, Australia
| | - Khatira Anwari
- Molecular Genetics of Cancer Division, The Walter and Eliza Hall Institute of Medical Research, Victoria 3052, Australia
| | - Amber E Alsop
- Molecular Genetics of Cancer Division, The Walter and Eliza Hall Institute of Medical Research, Victoria 3052, Australia
| | - Wai Shan Yuen
- Development and Stem Cells Program, Monash Biomedicine Discovery Institute and Department of Anatomy and Developmental Biology, Monash University, Melbourne, Victoria 3800, Australia
| | - David C S Huang
- Cancer and Haematology Division, The Walter and Eliza Hall Institute of Medical Research, Victoria 3052, Australia
| | - John Carroll
- Development and Stem Cells Program, Monash Biomedicine Discovery Institute and Department of Anatomy and Developmental Biology, Monash University, Melbourne, Victoria 3800, Australia
| | - Nicholas A Smith
- Department of Chemistry and Physics, La Trobe Institute for Molecular Sciences, La Trobe University, Victoria 3086, Australia
| | - Brian J Smith
- Department of Chemistry and Physics, La Trobe Institute for Molecular Sciences, La Trobe University, Victoria 3086, Australia
| | - Grant Dewson
- Cell Signalling and Cell Death Division, The Walter and Eliza Hall Institute of Medical Research, Victoria 3052, Australia
| | - Ruth M Kluck
- Molecular Genetics of Cancer Division, The Walter and Eliza Hall Institute of Medical Research, Victoria 3052, Australia
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12
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Lee EF, Grabow S, Chappaz S, Dewson G, Hockings C, Kluck RM, Debrincat MA, Gray DH, Witkowski MT, Evangelista M, Pettikiriarachchi A, Bouillet P, Lane RM, Czabotar PE, Colman PM, Smith BJ, Kile BT, Fairlie WD. Physiological restraint of Bak by Bcl-xL is essential for cell survival. Genes Dev 2016; 30:1240-50. [PMID: 27198225 PMCID: PMC4888843 DOI: 10.1101/gad.279414.116] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Accepted: 04/18/2016] [Indexed: 12/21/2022]
Abstract
Lee et al. describe a mutation in mouse and human Bak that specifically disrupts its interaction with the prosurvival protein Bcl-xL. In vivo, loss of Bcl-xL binding to Bak led to significant defects in T-cell and blood platelet survival. Due to the myriad interactions between prosurvival and proapoptotic members of the Bcl-2 family of proteins, establishing the mechanisms that regulate the intrinsic apoptotic pathway has proven challenging. Mechanistic insights have primarily been gleaned from in vitro studies because genetic approaches in mammals that produce unambiguous data are difficult to design. Here we describe a mutation in mouse and human Bak that specifically disrupts its interaction with the prosurvival protein Bcl-xL. Substitution of Glu75 in mBak (hBAK Q77) for leucine does not affect the three-dimensional structure of Bak or killing activity but reduces its affinity for Bcl-xL via loss of a single hydrogen bond. Using this mutant, we investigated the requirement for physical restraint of Bak by Bcl-xL in apoptotic regulation. In vitro, BakQ75L cells were significantly more sensitive to various apoptotic stimuli. In vivo, loss of Bcl-xL binding to Bak led to significant defects in T-cell and blood platelet survival. Thus, we provide the first definitive in vivo evidence that prosurvival proteins maintain cellular viability by interacting with and inhibiting Bak.
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Affiliation(s)
- Erinna F Lee
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia; Department of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe University, Bundoora, Victoria 3086, Australia; Olivia Newton-John Cancer Research Institute, Heidelberg, Victoria 3084, Australia; School of Cancer Medicine, La Trobe University, Melbourne, Victoria 3084, Australia
| | - Stephanie Grabow
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Stephane Chappaz
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Grant Dewson
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Colin Hockings
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Ruth M Kluck
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Marlyse A Debrincat
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Daniel H Gray
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Matthew T Witkowski
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Marco Evangelista
- Olivia Newton-John Cancer Research Institute, Heidelberg, Victoria 3084, Australia; School of Cancer Medicine, La Trobe University, Melbourne, Victoria 3084, Australia
| | - Anne Pettikiriarachchi
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Philippe Bouillet
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Rachael M Lane
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Peter E Czabotar
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Peter M Colman
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Brian J Smith
- Department of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe University, Bundoora, Victoria 3086, Australia
| | - Benjamin T Kile
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - W Douglas Fairlie
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia; Department of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe University, Bundoora, Victoria 3086, Australia; Olivia Newton-John Cancer Research Institute, Heidelberg, Victoria 3084, Australia; School of Cancer Medicine, La Trobe University, Melbourne, Victoria 3084, Australia
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13
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Yeo JHC, Skinner JPJ, Bird MJ, Formosa LE, Zhang JG, Kluck RM, Belz GT, Chong MMW. A Role for the Mitochondrial Protein Mrpl44 in Maintaining OXPHOS Capacity. PLoS One 2015. [PMID: 26221731 PMCID: PMC4519308 DOI: 10.1371/journal.pone.0134326] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We identified Mrpl44 in a search for mammalian proteins that contain RNase III domains. This protein was previously found in association with the mitochondrial ribosome of bovine liver extracts. However, the precise Mrpl44 localization had been unclear. Here, we show by immunofluorescence microscopy and subcellular fractionation that Mrpl44 is localized to the matrix of the mitochondria. We found that it can form multimers, and confirm that it is part of the large subunit of the mitochondrial ribosome. By manipulating its expression, we show that Mrpl44 may be important for regulating the expression of mtDNA-encoded genes. This was at the level of RNA expression and protein translation. This ultimately impacted ATP synthesis capability and respiratory capacity of cells. These findings indicate that Mrpl44 plays an important role in the regulation of the mitochondrial OXPHOS capacity.
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Affiliation(s)
- Janet H C Yeo
- Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia; Department of Medical Biology, University of Melbourne, Parkville, VIC, Australia; St. Vincent's Institute of Medical Research, Fitzroy, VIC, Australia
| | | | - Matthew J Bird
- Murdoch Childrens Research Institute, Parkville, VIC, Australia; Department of Paediatrics, University of Melbourne, Parkville VIC, Australia
| | - Luke E Formosa
- Department of Biochemistry, La Trobe University, Bundoora, VIC, Australia
| | - Jian-Guo Zhang
- Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia; Department of Medical Biology, University of Melbourne, Parkville, VIC, Australia
| | - Ruth M Kluck
- Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia; Department of Medical Biology, University of Melbourne, Parkville, VIC, Australia
| | - Gabrielle T Belz
- Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia; Department of Medical Biology, University of Melbourne, Parkville, VIC, Australia
| | - Mark M W Chong
- St. Vincent's Institute of Medical Research, Fitzroy, VIC, Australia; Department of Medicine (St Vincent's), University of Melbourne, Parkville VIC, Australia
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14
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Hockings C, Anwari K, Ninnis RL, Brouwer J, O'Hely M, Evangelista M, Hinds MG, Czabotar PE, Lee EF, Fairlie WD, Dewson G, Kluck RM. Bid chimeras indicate that most BH3-only proteins can directly activate Bak and Bax, and show no preference for Bak versus Bax. Cell Death Dis 2015; 6:e1735. [PMID: 25906158 PMCID: PMC4650538 DOI: 10.1038/cddis.2015.105] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 03/17/2015] [Accepted: 03/17/2015] [Indexed: 01/01/2023]
Abstract
The mitochondrial pathway of apoptosis is initiated by Bcl-2 homology region 3 (BH3)-only members of the Bcl-2 protein family. On upregulation or activation, certain BH3-only proteins can directly bind and activate Bak and Bax to induce conformation change, oligomerization and pore formation in mitochondria. BH3-only proteins, with the exception of Bid, are intrinsically disordered and therefore, functional studies often utilize peptides based on just their BH3 domains. However, these reagents do not possess the hydrophobic membrane targeting domains found on the native BH3-only molecule. To generate each BH3-only protein as a recombinant protein that could efficiently target mitochondria, we developed recombinant Bid chimeras in which the BH3 domain was replaced with that of other BH3-only proteins (Bim, Puma, Noxa, Bad, Bmf, Bik and Hrk). The chimeras were stable following purification, and each immunoprecipitated with full-length Bcl-xL according to the specificity reported for the related BH3 peptide. When tested for activation of Bak and Bax in mitochondrial permeabilization assays, Bid chimeras were ~1000-fold more effective than the related BH3 peptides. BH3 sequences from Bid and Bim were the strongest activators, followed by Puma, Hrk, Bmf and Bik, while Bad and Noxa were not activators. Notably, chimeras and peptides showed no apparent preference for activating Bak or Bax. In addition, within the BH3 domain, the h0 position recently found to be important for Bax activation, was important also for Bak activation. Together, our data with full-length proteins indicate that most BH3-only proteins can directly activate both Bak and Bax.
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Affiliation(s)
- C Hockings
- 1] The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - K Anwari
- 1] The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - R L Ninnis
- 1] The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - J Brouwer
- 1] The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - M O'Hely
- 1] The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - M Evangelista
- 1] The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - M G Hinds
- School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - P E Czabotar
- 1] The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - E F Lee
- 1] The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - W D Fairlie
- 1] The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - G Dewson
- 1] The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - R M Kluck
- 1] The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
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15
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Alsop AE, Fennell SC, Bartolo RC, Tan IKL, Dewson G, Kluck RM. Dissociation of Bak α1 helix from the core and latch domains is required for apoptosis. Nat Commun 2015; 6:6841. [PMID: 25880232 DOI: 10.1038/ncomms7841] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2014] [Accepted: 03/03/2015] [Indexed: 02/06/2023] Open
Abstract
During apoptosis, Bak permeabilizes mitochondria after undergoing major conformational changes, including poorly defined N-terminal changes. Here, we characterize those changes using 11 antibodies that were epitope mapped using peptide arrays and mutagenesis. After Bak activation by Bid, epitopes throughout the α1 helix are exposed indicating complete dissociation of α1 from α2 in the core and from α6-α8 in the latch. Moreover, disulfide tethering of α1 to α2 or α6 blocks cytochrome c release, suggesting that α1 dissociation is required for further conformational changes during apoptosis. Assaying epitope exposure when α1 is tethered shows that Bid triggers α2 movement, followed by α1 dissociation. However, α2 reaches its final position only after α1 dissociates from the latch. Thus, α1 dissociation is a key step in unfolding Bak into three major components, the N terminus, the core (α2-α5) and the latch (α6-α8).
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Affiliation(s)
- Amber E Alsop
- 1] The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, University of Melbourne, Parkville, Victoria 3052, Australia
| | - Stephanie C Fennell
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Ray C Bartolo
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Iris K L Tan
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Grant Dewson
- 1] The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, University of Melbourne, Parkville, Victoria 3052, Australia
| | - Ruth M Kluck
- 1] The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia [2] Department of Medical Biology, University of Melbourne, Parkville, Victoria 3052, Australia
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16
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Iyer S, Bell F, Westphal D, Anwari K, Gulbis J, Smith BJ, Dewson G, Kluck RM. Bak apoptotic pores involve a flexible C-terminal region and juxtaposition of the C-terminal transmembrane domains. Cell Death Differ 2015; 22:1665-75. [PMID: 25744027 DOI: 10.1038/cdd.2015.15] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2014] [Revised: 01/07/2015] [Accepted: 01/21/2015] [Indexed: 12/22/2022] Open
Abstract
Bak and Bax mediate apoptotic cell death by oligomerizing and forming a pore in the mitochondrial outer membrane. Both proteins anchor to the outer membrane via a C-terminal transmembrane domain, although its topology within the apoptotic pore is not known. Cysteine-scanning mutagenesis and hydrophilic labeling confirmed that in healthy mitochondria the Bak α9 segment traverses the outer membrane, with 11 central residues shielded from labeling. After pore formation those residues remained shielded, indicating that α9 does not line a pore. Bak (and Bax) activation allowed linkage of α9 to neighboring α9 segments, identifying an α9:α9 interface in Bak (and Bax) oligomers. Although the linkage pattern along α9 indicated a preferred packing surface, there was no evidence of a dimerization motif. Rather, the interface was invoked in part by Bak conformation change and in part by BH3:groove dimerization. The α9:α9 interaction may constitute a secondary interface in Bak oligomers, as it could link BH3:groove dimers to high-order oligomers. Moreover, as high-order oligomers were generated when α9:α9 linkage in the membrane was combined with α6:α6 linkage on the membrane surface, the α6-α9 region in oligomerized Bak is flexible. These findings provide the first view of Bak carboxy terminus (C terminus) membrane topology within the apoptotic pore.
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Affiliation(s)
- S Iyer
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3050, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - F Bell
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3050, Australia
| | - D Westphal
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3050, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - K Anwari
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3050, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - J Gulbis
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3050, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - B J Smith
- Department of Chemistry and Physics, La Trobe Institute for Molecular Sciences, La Trobe University, Melbourne, Victoria 3086, Australia
| | - G Dewson
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3050, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - R M Kluck
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3050, Australia.,Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
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17
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Brouwer JM, Westphal D, Dewson G, Robin AY, Uren RT, Bartolo R, Thompson GV, Colman PM, Kluck RM, Czabotar PE. Bak core and latch domains separate during activation, and freed core domains form symmetric homodimers. Mol Cell 2014; 55:938-946. [PMID: 25175025 DOI: 10.1016/j.molcel.2014.07.016] [Citation(s) in RCA: 118] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2014] [Revised: 07/08/2014] [Accepted: 07/24/2014] [Indexed: 01/11/2023]
Abstract
Apoptotic stimuli activate and oligomerize the proapoptotic proteins Bak and Bax, resulting in mitochondrial outer-membrane permeabilization and subsequent cell death. This activation can occur when certain BH3-only proteins interact directly with Bak and Bax. Recently published crystal structures reveal that Bax separates into core and latch domains in response to BH3 peptides. The distinguishing characteristics of BH3 peptides capable of directly activating Bax were also elucidated. Here we identify specific BH3 peptides capable of "unlatching" Bak and describe structural insights into Bak activation and oligomerization. Crystal structures and crosslinking experiments demonstrate that Bak undergoes a conformational change similar to that of Bax upon activation. A structure of the Bak core domain dimer provides a high-resolution image of this key intermediate in the pore-forming oligomer. Our results confirm an analogous mechanism for activation and dimerization of Bak and Bax in response to certain BH3 peptides.
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Affiliation(s)
- Jason M Brouwer
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, Victoria 3052, Australia
| | - Dana Westphal
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, Victoria 3052, Australia
| | - Grant Dewson
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, Victoria 3052, Australia
| | - Adeline Y Robin
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, Victoria 3052, Australia
| | - Rachel T Uren
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, Victoria 3052, Australia
| | - Ray Bartolo
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia
| | - Geoff V Thompson
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia
| | - Peter M Colman
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, Victoria 3052, Australia
| | - Ruth M Kluck
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, Victoria 3052, Australia.
| | - Peter E Czabotar
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, Victoria 3052, Australia.
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18
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Ma S, Hockings C, Anwari K, Kratina T, Fennell S, Lazarou M, Ryan MT, Kluck RM, Dewson G. Assembly of the Bak apoptotic pore: a critical role for the Bak protein α6 helix in the multimerization of homodimers during apoptosis. J Biol Chem 2013; 288:26027-26038. [PMID: 23893415 DOI: 10.1074/jbc.m113.490094] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Bak and Bax are the essential effectors of the intrinsic pathway of apoptosis. Following an apoptotic stimulus, both undergo significant changes in conformation that facilitates their self-association to form pores in the mitochondrial outer membrane. However, the molecular structures of Bak and Bax oligomeric pores remain elusive. To characterize how Bak forms pores during apoptosis, we investigated its oligomerization under native conditions using blue native PAGE. We report that, in a healthy cell, inactive Bak is either monomeric or in a large complex involving VDAC2. Following an apoptotic stimulus, activated Bak forms BH3:groove homodimers that represent the basic stable oligomeric unit. These dimers multimerize to higher-order oligomers via a labile interface independent of both the BH3 domain and groove. Linkage of the α6:α6 interface is sufficient to stabilize higher-order Bak oligomers on native PAGE, suggesting an important role in the Bak oligomeric pore. Mutagenesis of the α6 helix disrupted apoptotic function because a chimera of Bak with the α6 derived from Bcl-2 could be activated by truncated Bid (tBid) and could form BH3:groove homodimers but could not form high molecular weight oligomers or mediate cell death. An α6 peptide could block Bak function but did so upstream of dimerization, potentially implicating α6 as a site for activation by BH3-only proteins. Our examination of native Bak oligomers indicates that the Bak apoptotic pore forms by the multimerization of BH3:groove homodimers and reveals that Bak α6 is not only important for Bak oligomerization and function but may also be involved in how Bak is activated by BH3-only proteins.
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Affiliation(s)
- Stephen Ma
- From the Walter and Eliza Hall Institute of Medical Research, Melbourne 3052, Australia,; the Department of Medical Biology, University of Melbourne, Melbourne 3010, Australia
| | - Colin Hockings
- From the Walter and Eliza Hall Institute of Medical Research, Melbourne 3052, Australia,; the Department of Medical Biology, University of Melbourne, Melbourne 3010, Australia
| | - Khatira Anwari
- From the Walter and Eliza Hall Institute of Medical Research, Melbourne 3052, Australia
| | - Tobias Kratina
- From the Walter and Eliza Hall Institute of Medical Research, Melbourne 3052, Australia,; the Department of Medical Biology, University of Melbourne, Melbourne 3010, Australia
| | - Stephanie Fennell
- From the Walter and Eliza Hall Institute of Medical Research, Melbourne 3052, Australia,; the Department of Medical Biology, University of Melbourne, Melbourne 3010, Australia
| | - Michael Lazarou
- the Biochemistry Section, Surgical Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, and
| | - Michael T Ryan
- the Department of Biochemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne 3086, Australia
| | - Ruth M Kluck
- From the Walter and Eliza Hall Institute of Medical Research, Melbourne 3052, Australia,; the Department of Medical Biology, University of Melbourne, Melbourne 3010, Australia
| | - Grant Dewson
- From the Walter and Eliza Hall Institute of Medical Research, Melbourne 3052, Australia,; the Department of Medical Biology, University of Melbourne, Melbourne 3010, Australia,.
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Czabotar PE, Westphal D, Dewson G, Ma S, Hockings C, Fairlie WD, Lee EF, Yao S, Robin AY, Smith BJ, Huang DCS, Kluck RM, Adams JM, Colman PM. Bax crystal structures reveal how BH3 domains activate Bax and nucleate its oligomerization to induce apoptosis. Cell 2013; 152:519-31. [PMID: 23374347 DOI: 10.1016/j.cell.2012.12.031] [Citation(s) in RCA: 422] [Impact Index Per Article: 38.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Revised: 10/11/2012] [Accepted: 12/10/2012] [Indexed: 02/06/2023]
Abstract
In stressed cells, apoptosis ensues when Bcl-2 family members Bax or Bak oligomerize and permeabilize the mitochondrial outer membrane. Certain BH3-only relatives can directly activate them to mediate this pivotal, poorly understood step. To clarify the conformational changes that induce Bax oligomerization, we determined crystal structures of BaxΔC21 treated with detergents and BH3 peptides. The peptides bound the Bax canonical surface groove but, unlike their complexes with prosurvival relatives, dissociated Bax into two domains. The structures define the sequence signature of activator BH3 domains and reveal how they can activate Bax via its groove by favoring release of its BH3 domain. Furthermore, Bax helices α2-α5 alone adopted a symmetric homodimer structure, supporting the proposal that two Bax molecules insert their BH3 domain into each other's surface groove to nucleate oligomerization. A planar lipophilic surface on this homodimer may engage the membrane. Our results thus define critical Bax transitions toward apoptosis.
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Affiliation(s)
- Peter E Czabotar
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria 3052, Australia.
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20
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Fleming P, Kvansakul M, Voigt V, Kile BT, Kluck RM, Huang DCS, Degli-Esposti MA, Andoniou CE. MCMV-mediated inhibition of the pro-apoptotic Bak protein is required for optimal in vivo replication. PLoS Pathog 2013; 9:e1003192. [PMID: 23468630 PMCID: PMC3585157 DOI: 10.1371/journal.ppat.1003192] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Accepted: 12/28/2012] [Indexed: 01/29/2023] Open
Abstract
Successful replication and transmission of large DNA viruses such as the cytomegaloviruses (CMV) family of viruses depends on the ability to interfere with multiple aspects of the host immune response. Apoptosis functions as a host innate defence mechanism against viral infection, and the capacity to interfere with this process is essential for the replication of many viruses. The Bcl-2 family of proteins are the principle regulators of apoptosis, with two pro-apoptotic members, Bax and Bak, essential for apoptosis to proceed. The m38.5 protein encoded by murine CMV (MCMV) has been identified as Bax-specific inhibitor of apoptosis. Recently, m41.1, a protein product encoded by the m41 open reading frame (ORF) of MCMV, has been shown to inhibit Bak activity in vitro. Here we show that m41.1 is critical for optimal MCMV replication in vivo. Growth of a m41.1 mutant was attenuated in multiple organs, a defect that was not apparent in Bak−/− mice. Thus, m41.1 promotes MCMV replication by inhibiting Bak-dependent apoptosis during in vivo infection. The results show that Bax and Bak mediate non-redundant functions during MCMV infection and that the virus produces distinct inhibitors for each protein to counter the activity of these proteins. The cytomegaloviruses (CMV) are a family of viruses that establish a latent infection that lasts for the life of the host, with the virus able to reactivate when the host is immunosuppressed. We have used murine CMV (MCMV) as a model to understand how CMV interferes with the anti-viral immune response. Apoptosis, or programmed cell death, is one of the defence mechanisms used by multicellular organisms to impair viral infection. In order for viral replication to proceed, many viruses have evolved mechanisms to prevent the apoptosis of infected host cells. Under most circumstances the activation of Bax, or the closely related protein Bak, is required for apoptosis to proceed. The m41.1 protein was recently identified as a candidate Bak inhibitor during in vitro infection. We have generated a mutant virus which is unable to produce the m41.1 protein and found that growth of this virus was attenuated in wild-type mice. Importantly, growth of the mutant virus was equivalent to that of the wild-type virus in mice lacking the Bak protein. These studies establish that m41.1 is an inhibitor of Bak and that the capacity to prevent apoptosis triggered by Bak is required for efficient replication of MCMV in vivo.
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Affiliation(s)
- Peter Fleming
- Immunology and Virology Program, Centre for Ophthalmology and Visual Science, The University of Western Australia, Nedlands, Western Australia, Australia
- Centre for Experimental Immunology, Lions Eye Institute, Nedlands, Western Australia, Australia
| | - Marc Kvansakul
- Department of Biochemistry, La Trobe University, Melbourne, Victoria, Australia
| | - Valentina Voigt
- Immunology and Virology Program, Centre for Ophthalmology and Visual Science, The University of Western Australia, Nedlands, Western Australia, Australia
- Centre for Experimental Immunology, Lions Eye Institute, Nedlands, Western Australia, Australia
| | - Benjamin T. Kile
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Victoria, Australia
| | - Ruth M. Kluck
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Victoria, Australia
| | - David C. S. Huang
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Victoria, Australia
| | - Mariapia A. Degli-Esposti
- Immunology and Virology Program, Centre for Ophthalmology and Visual Science, The University of Western Australia, Nedlands, Western Australia, Australia
- Centre for Experimental Immunology, Lions Eye Institute, Nedlands, Western Australia, Australia
| | - Christopher E. Andoniou
- Immunology and Virology Program, Centre for Ophthalmology and Visual Science, The University of Western Australia, Nedlands, Western Australia, Australia
- Centre for Experimental Immunology, Lions Eye Institute, Nedlands, Western Australia, Australia
- * E-mail:
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Ferrer PE, Frederick P, Gulbis JM, Dewson G, Kluck RM. Translocation of a Bak C-terminus mutant from cytosol to mitochondria to mediate cytochrome C release: implications for Bak and Bax apoptotic function. PLoS One 2012; 7:e31510. [PMID: 22442658 PMCID: PMC3307716 DOI: 10.1371/journal.pone.0031510] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2011] [Accepted: 01/11/2012] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND One of two proapoptotic Bcl-2 proteins, Bak or Bax, is required to permeabilize the mitochondrial outer membrane during apoptosis. While Bax is mostly cytosolic and translocates to mitochondria following an apoptotic stimulus, Bak is constitutively integrated within the outer membrane. Membrane anchorage occurs via a C-terminal transmembrane domain that has been studied in Bax but not in Bak, therefore what governs their distinct subcellular distribution is uncertain. In addition, whether the distinct subcellular distributions of Bak and Bax contributes to their differential regulation during apoptosis remains unclear. METHODOLOGY/PRINCIPAL FINDINGS To gain insight into Bak and Bax targeting to mitochondria, elements of the Bak C-terminus were mutated, or swapped with those of Bax. Truncation of the C-terminal six residues (C-segment) or substitution of three basic residues within the C-segment destabilized Bak. Replacing the Bak C-segment with that from Bax rescued stability and function, but unexpectedly resulted in a semi-cytosolic protein, termed Bak/BaxCS. When in the cytosol, both Bax and Bak/BaxCS sequestered their hydrophobic transmembrane domains in their hydrophobic surface groove. Upon apoptotic signalling, Bak/BaxCS translocated to the mitochondrial outer membrane, inserted its transmembrane domain, oligomerized, and released cytochrome c. Despite this Bax-like subcellular distribution, Bak/BaxCS retained Bak-like regulation following targeting of Mcl-1. CONCLUSIONS/SIGNIFICANCE Residues in the C-segment of Bak and of Bax contribute to their distinct subcellular localizations. That a semi-cytosolic form of Bak, Bak/BaxCS, could translocate to mitochondria and release cytochrome c indicates that Bak and Bax share a conserved mode of activation. In addition, the differential regulation of Bak and Bax by Mcl-1 is predominantly independent of the initial subcellular localizations of Bak and Bax.
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Affiliation(s)
- Pedro Eitz Ferrer
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
| | - Paul Frederick
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
| | - Jacqueline M. Gulbis
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Grant Dewson
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Ruth M. Kluck
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, Victoria, Australia
- * E-mail:
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22
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Dewson G, Ma S, Frederick P, Hockings C, Tan I, Kratina T, Kluck RM. Bax dimerizes via a symmetric BH3:groove interface during apoptosis. Cell Death Differ 2011; 19:661-70. [PMID: 22015607 DOI: 10.1038/cdd.2011.138] [Citation(s) in RCA: 145] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
During apoptotic cell death, Bax and Bak change conformation and homo-oligomerize to permeabilize mitochondria. We recently reported that Bak homodimerizes via an interaction between the BH3 domain and hydrophobic surface groove, that this BH3:groove interaction is symmetric, and that symmetric dimers can be linked via the α6-helices to form the high order oligomers thought responsible for pore formation. We now show that Bax also dimerizes via a BH3:groove interaction after apoptotic signaling in cells and in mitochondrial fractions. BH3:groove dimers of Bax were symmetric as dimers but not higher order oligomers could be linked by cysteine residues placed in both the BH3 and groove. The BH3:groove interaction was evident in the majority of mitochondrial Bax after apoptotic signaling, and correlated strongly with cytochrome c release, supporting its central role in Bax function. A second interface between the Bax α6-helices was implicated by cysteine linkage studies, and could link dimers to higher order oligomers. We also found that a population of Bax:Bak heterodimers generated during apoptosis formed via a BH3:groove interaction, further demonstrating that Bax and Bak oligomerize via similar mechanisms. These findings highlight the importance of BH3:groove interactions in apoptosis regulation by the Bcl-2 protein family.
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Affiliation(s)
- G Dewson
- The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
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23
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Westphal D, Dewson G, Czabotar PE, Kluck RM. Molecular biology of Bax and Bak activation and action. Biochim Biophys Acta 2010; 1813:521-31. [PMID: 21195116 DOI: 10.1016/j.bbamcr.2010.12.019] [Citation(s) in RCA: 378] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Received: 08/10/2010] [Revised: 12/17/2010] [Accepted: 12/19/2010] [Indexed: 12/26/2022]
Abstract
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.
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Lazarou M, Stojanovski D, Frazier AE, Kotevski A, Dewson G, Craigen WJ, Kluck RM, Vaux DL, Ryan MT. Inhibition of Bak activation by VDAC2 is dependent on the Bak transmembrane anchor. J Biol Chem 2010; 285:36876-83. [PMID: 20851889 DOI: 10.1074/jbc.m110.159301] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Bax and Bak are pro-apoptotic factors that are required for cell death by the mitochondrial or intrinsic pathway. Bax is found in an inactive state in the cytosol and upon activation is targeted to the mitochondrial outer membrane where it releases cytochrome c and other factors that cause caspase activation. Although Bak functions in the same way as Bax, it is constitutively localized to the mitochondrial outer membrane. In the membrane, Bak activation is inhibited by the voltage-dependent anion channel isoform 2 (VDAC2) by an unknown mechanism. Using blue native gel electrophoresis, we show that in healthy cells endogenous inactive Bak exists in a 400-kDa complex that is dependent on the presence of VDAC2. Activation of Bak is concomitant with its release from the 400-kDa complex and the formation of lower molecular weight species. Furthermore, substitution of the Bak transmembrane anchor with that of the mitochondrial outer membrane tail-anchored protein hFis1 prevents association of Bak with the VDAC2 complex and increases the sensitivity of cells to an apoptotic stimulus. Our results suggest that VDAC2 interacts with the hydrophobic tail of Bak to sequester it in an inactive state in the mitochondrial outer membrane, thereby raising the stimulation threshold necessary for permeabilization of the mitochondrial outer membrane and cell death.
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Affiliation(s)
- Michael Lazarou
- La Trobe Institute for Molecular Science, La Trobe University, Melbourne 3086, Australia
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25
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Dewson G, Kratina T, Czabotar P, Day CL, Adams JM, Kluck RM. Bak activation for apoptosis involves oligomerization of dimers via their alpha6 helices. Mol Cell 2009; 36:696-703. [PMID: 19941828 DOI: 10.1016/j.molcel.2009.11.008] [Citation(s) in RCA: 172] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2009] [Revised: 06/20/2009] [Accepted: 11/02/2009] [Indexed: 11/16/2022]
Abstract
A pivotal step toward apoptosis is oligomerization of the Bcl-2 relative Bak. We recently reported that its oligomerization initiates by insertion of an exposed BH3 domain into the groove of another Bak monomer. We now report that the resulting BH3:groove dimers can be converted to the larger oligomers that permeabilize mitochondria by an interface between alpha6 helices. Cysteine residues placed in alpha6 could be crosslinked only after apoptotic signaling. Cysteines placed at both interfaces established that the BH3:groove dimer is symmetric and that the alpha6:alpha6 interface can link these dimers into homo-oligomers containing at least 18 Bak molecules. A putative zinc-binding site in alpha6 was not required to form the alpha6:alpha6 interface, and its mutation in full-length Bak did not affect Bak conformation, oligomerization, or function. We conclude that alpha6:alpha6 interaction occurs during Bak oligomerization and proapoptotic function, but we find no evidence that zinc binding to that interface regulates apoptosis.
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Affiliation(s)
- Grant Dewson
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Parkville Victoria, Australia
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26
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Abstract
Mitochondrial outer membrane permeabilisation (MOMP) is the point of no return in many forms of apoptotic cell death. The killing effect of MOMP is twofold; it both initiates a proteolytic cascade of pro-apoptotic enzymes and damages mitochondrial function. Accordingly, prevention of MOMP can rescue cells from death. It is clear that either Bak or Bax, which are Bcl-2 family members, are required for MOMP to occur; however, the pore complexes that are formed by Bak and Bax remain poorly defined in terms of their composition, size, number and structure, as well as the mechanism by which they are regulated by other Bcl-2 family members. We recently reported that a key step leading to Bak homo-oligomerisation following an apoptotic stimulus involves transient exposure of the Bak BH3 domain before it binds to the hydrophobic groove of another activated Bak molecule to form a novel symmetric dimer. To form the higher-order oligomers that probably constitute the apoptotic pore complex, Bak dimers then interact via regions away from the BH3 domain and groove. The BH3:groove interaction within Bak homodimers supports a general model to explain the associations between Bcl-2 family members. In this Commentary, we discuss the implications of these findings for the regulation of apoptosis by Bcl-2 family proteins.
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Affiliation(s)
- Grant Dewson
- Walter and Eliza Hall Institute of Medical Research, Parkville, Melbourne, Victoria, Australia
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27
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Dewson G, Kratina T, Sim HW, Puthalakath H, Adams JM, Colman PM, Kluck RM. To trigger apoptosis, Bak exposes its BH3 domain and homodimerizes via BH3:groove interactions. Mol Cell 2008; 30:369-80. [PMID: 18471982 DOI: 10.1016/j.molcel.2008.04.005] [Citation(s) in RCA: 257] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2007] [Revised: 02/24/2008] [Accepted: 04/11/2008] [Indexed: 10/22/2022]
Abstract
The Bcl-2 relative Bak is thought to drive apoptosis by forming homo-oligomers that permeabilize mitochondria, but how it is activated and oligomerizes is unclear. To clarify these pivotal steps toward apoptosis, we have characterized multiple random loss-of-function Bak mutants and explored the mechanism of Bak conformation change during apoptosis. Single missense mutations located to the alpha helix 2-5 region of Bak, with most altering the BH3 domain or hydrophobic groove (BH1 domain). Loss of function invariably corresponded to impaired ability to oligomerize. An essential early step in Bak activation was shown to be exposure of the BH3 domain, which became reburied in dimers. We demonstrate that oligomerization involves insertion of the BH3 domain of one Bak molecule into the groove of another and may produce symmetric Bak dimers. We conclude that this BH3:groove interaction is essential to nucleate Bak oligomerization, which in turn is required for its proapoptotic function.
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Affiliation(s)
- Grant Dewson
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, Victoria 3050, Australia
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Uren RT, Dewson G, Chen L, Coyne SC, Huang DCS, Adams JM, Kluck RM. Mitochondrial permeabilization relies on BH3 ligands engaging multiple prosurvival Bcl-2 relatives, not Bak. ACTA ACUST UNITED AC 2007; 177:277-87. [PMID: 17452531 PMCID: PMC2064136 DOI: 10.1083/jcb.200606065] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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-xl, 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-xl–like and Mcl-1 proteins were disrupted only by BH3 peptides that engage both. BH3-only reagents freed Bak from Bcl-xl 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.
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Affiliation(s)
- Rachel T Uren
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria 3050, Australia
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30
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Willis SN, Fletcher JI, Kaufmann T, van Delft MF, Chen L, Czabotar PE, Ierino H, Lee EF, Fairlie WD, Bouillet P, Strasser A, Kluck RM, Adams JM, Huang DCS. Apoptosis initiated when BH3 ligands engage multiple Bcl-2 homologs, not Bax or Bak. Science 2007; 315:856-9. [PMID: 17289999 DOI: 10.1126/science.1133289] [Citation(s) in RCA: 858] [Impact Index Per Article: 50.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
A central issue in the regulation of apoptosis by the Bcl-2 family is whether its BH3-only members initiate apoptosis by directly binding to the essential cell-death mediators Bax and Bak, or whether they can act indirectly, by engaging their pro-survival Bcl-2-like relatives. Contrary to the direct-activation model, we show that Bax and Bak can mediate apoptosis without discernable association with the putative BH3-only activators (Bim, Bid, and Puma), even in cells with no Bim or Bid and reduced Puma. Our results indicate that BH3-only proteins induce apoptosis at least primarily by engaging the multiple pro-survival relatives guarding Bax and Bak.
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Affiliation(s)
- Simon N Willis
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3050, Australia
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Abstract
A key step in the initiation of apoptosis is the release from the mitochondrial intermembrane space of cytochrome c and other pro-apoptotic proteins such as Smac/DIABLO, Omi/HtrA2, apoptosis-inducing factor (AIF), and endonuclease G (EndoG). Discrepancies have arisen, however, as to whether all these proteins are released in different systems. Our results suggest that failure to observe cytochrome c release may be due to the use of different buffers because after permeabilization by caspase-8 cleaved human Bid (tBid), cytochrome c dissociation from mitochondria was highly dependent on ionic strength and required 50-80 mm KCl, NaCl, or LiCl. In addition, mitochondria isolated from apoptotic cells using low ionic strength buffer bound a greater proportion of endogenous cytochrome c. In contrast to cytochrome c, Smac/DIABLO and Omi/HtrA2 were released independent of ionic strength, and AIF and EndoG behaved as if they are exposed to the intermembrane space but tethered to or within the inner membrane. AIF and EndoG were also not released by active caspases, which suggests their involvement in apoptosis may be limited. In summary, whereas tBid permeabilizes the outer membrane to cytochrome c, Smac/DIABLO, and Omi/HtrA2, the release of cytochrome c during apoptosis will be underestimated unless sufficient ionic strength is maintained to overcome the electrostatic association of cytochrome c with membranes.
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Affiliation(s)
- Rachel T Uren
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria 3050, Australia
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32
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Affiliation(s)
- R M Kluck
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, CA 92121, USA
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33
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Abdullaev ZK, Bodrova ME, Chernyak BV, Dolgikh DA, Kluck RM, Pereverzev MO, Arseniev AS, Efremov RG, Kirpichnikov MP, Mokhova EN, Newmeyer DD, Roder H, Skulachev VP. A cytochrome c mutant with high electron transfer and antioxidant activities but devoid of apoptogenic effect. Biochem J 2002; 362:749-54. [PMID: 11879204 PMCID: PMC1222441 DOI: 10.1042/0264-6021:3620749] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
A cytochrome c mutant lacking apoptogenic function but competent in electron transfer and antioxidant activities has been constructed. To this end, mutant species of horse and yeast cytochromes c with substitutions in the N-terminal alpha-helix or position 72 were obtained. It was found that yeast cytochrome c was much less effective than the horse protein in activating respiration of rat liver mitoplasts deficient in endogenous cytochrome c as well as in inhibition of H(2)O(2) production by the initial segment of the respiratory chain of intact rat heart mitochondria. The major role in the difference between the horse and yeast proteins was shown to be played by the amino acid residue in position 4 (glutamate in horse, and lysine in yeast; horse protein numbering). A mutant of the yeast cytochrome c containing K4E and some other "horse" modifications in the N-terminal alpha-helix, proved to be (i) much more active in electron transfer and antioxidant activity than the wild-type yeast cytochrome c and (ii), like the yeast cytochrome c, inactive in caspase stimulation, even if added in 400-fold excess compared with the horse protein. Thus this mutant seems to be a good candidate for knock-in studies of the role of cytochrome c-mediated apoptosis, in contrast with the horse K72R, K72G, K72L and K72A mutant cytochromes that at low concentrations were less active in apoptosis than the wild-type, but were quite active when the concentrations were increased by a factor of 2-12.
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Affiliation(s)
- Ziedulla Kh Abdullaev
- Laboratory of Spectral Analysis, M.M. Shemyakin and Y.A. Ovchinnikov Institute of Bioorganic Chemistry, Moscow 177871, Russia
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34
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Affiliation(s)
- N J Waterhouse
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, La Jolla, California 92121, USA
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35
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Kaspar AA, Okada S, Kumar J, Poulain FR, Drouvalakis KA, Kelekar A, Hanson DA, Kluck RM, Hitoshi Y, Johnson DE, Froelich CJ, Thompson CB, Newmeyer DD, Anel A, Clayberger C, Krensky AM. A distinct pathway of cell-mediated apoptosis initiated by granulysin. J Immunol 2001; 167:350-6. [PMID: 11418670 DOI: 10.4049/jimmunol.167.1.350] [Citation(s) in RCA: 112] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Granulysin is an antimicrobial and tumoricidal molecule expressed in granules of CTL and NK cells. In this study, we show that granulysin damages cell membranes based upon negative charge, disrupts the transmembrane potential (Deltapsi) in mitochondria, and causes release of cytochrome c. Granulysin-induced apoptosis is blocked in cells overexpressing Bcl-2. Despite the release of cytochrome c, procaspase 9 is not processed. Nevertheless, activation of caspase 3 is observed in granulysin-treated cells, suggesting that granulysin activates a novel pathway of CTL- and NK cell-mediated death distinct from granzyme- and death receptor-induced apoptosis.
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Affiliation(s)
- A A Kaspar
- Division of Immunology and Transplantation Biology, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA 94305, USA
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36
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Abstract
Microcinematography was applied to the analysis of the kinetics of apoptotic cell death. Apoptosis was found to be a process that proceeds in different cells at different times after an initial stress, and therefore kinetic studies of apoptotic events in bulk cultures can be problematic. Using single cell analysis we found that stronger apoptotic stimuli induce an earlier onset of apoptosis, but that there is no relationship between time of onset and duration of the apoptotic process. That is, cells that initiate apoptosis shortly after induction do not proceed more rapidly through the process. This suggests an all-or-non-mechanism that is supported by some models of the biochemical pathways of apoptosis.
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Affiliation(s)
- J C Goldstein
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121, USA
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37
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von Ahsen O, Renken C, Perkins G, Kluck RM, Bossy-Wetzel E, Newmeyer DD. Preservation of mitochondrial structure and function after Bid- or Bax-mediated cytochrome c release. J Cell Biol 2000; 150:1027-36. [PMID: 10973993 PMCID: PMC2175243 DOI: 10.1083/jcb.150.5.1027] [Citation(s) in RCA: 196] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2000] [Accepted: 07/13/2000] [Indexed: 11/22/2022] Open
Abstract
Proapoptotic members of the Bcl-2 protein family, including Bid and Bax, can activate apoptosis by directly interacting with mitochondria to cause cytochrome c translocation from the intermembrane space into the cytoplasm, thereby triggering Apaf-1-mediated caspase activation. Under some circumstances, when caspase activation is blocked, cells can recover from cytochrome c translocation; this suggests that apoptotic mitochondria may not always suffer catastrophic damage arising from the process of cytochrome c release. We now show that recombinant Bid and Bax cause complete cytochrome c loss from isolated mitochondria in vitro, but preserve the ultrastructure and protein import function of mitochondria, which depend on inner membrane polarization. We also demonstrate that, if caspases are inhibited, mitochondrial protein import function is retained in UV-irradiated or staurosporine-treated cells, despite the complete translocation of cytochrome c. Thus, Bid and Bax act only on the outer membrane, and lesions in the inner membrane occurring during apoptosis are shown to be secondary caspase-dependent events.
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Affiliation(s)
- Oliver von Ahsen
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121
| | - Christian Renken
- Biology Department, San Diego State University, San Diego, California 92182
| | - Guy Perkins
- Department of Neurosciences, University of California San Diego, San Diego, California 92093
| | - Ruth M. Kluck
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121
| | - Ella Bossy-Wetzel
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121
| | - Donald D. Newmeyer
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121
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38
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Kluck RM, Ellerby LM, Ellerby HM, Naiem S, Yaffe MP, Margoliash E, Bredesen D, Mauk AG, Sherman F, Newmeyer DD. Determinants of cytochrome c pro-apoptotic activity. The role of lysine 72 trimethylation. J Biol Chem 2000; 275:16127-33. [PMID: 10821864 DOI: 10.1074/jbc.275.21.16127] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cytochrome c released from vertebrate mitochondria engages apoptosis by triggering caspase activation. We previously reported that, whereas cytochromes c from higher eukaryotes can activate caspases in Xenopus egg and mammalian cytosols, iso-1 and iso-2 cytochromes c from the yeast Saccharomyces cerevisiae cannot. Here we examine whether the inactivity of the yeast isoforms is related to a post-translational modification of lysine 72, N-epsilon-trimethylation. This modification was found to abrogate pro-apoptotic activity of metazoan cytochrome c expressed in yeast. However, iso-1 cytochrome c lacking the trimethylation modification also was devoid of pro-apoptotic activity. Thus, both lysine 72 trimethylation and other features of the iso-1 sequence preclude pro-apoptotic activity. Competition studies suggest that the lack of pro-apoptotic activity was associated with a low affinity for Apaf-1. As cytochromes c that lack apoptotic function still support respiration, different mechanisms appear to be involved in the two activities.
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Affiliation(s)
- R M Kluck
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121, USA
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39
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Abstract
Bcl-2 and its relative, Bcl-xL, inhibit apoptotic cell death primarily by controlling the activation of caspase proteases. Previous reports have suggested at least two distinct mechanisms: Bcl-2 and Bcl-xL may inhibit either the formation of the cytochrome c/Apaf-1/caspase-9 apoptosome complex (by preventing cytochrome c release from mitochondria) or the function of this apoptosome (through a direct interaction of Bcl-2 or Bcl-xL with Apaf-1). To evaluate this latter possibility, we added recombinant Bcl-xL protein to cell-free apoptotic systems derived from Jurkat cells and Xenopus eggs. At low concentrations (50 nM), Bcl-xL was able to block the release of cytochrome c from mitochondria. However, although Bcl-xL did associate with Apaf-1, it was unable to inhibit caspase activation induced by the addition of cytochrome c, even at much higher concentrations (1-5 microM). These observations, together with previous results obtained with Bcl-2, argue that Bcl-xL and Bcl-2 cannot block the apoptosome-mediated activation of caspase-9.
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Affiliation(s)
- D D Newmeyer
- La Jolla Institute for Allergy and Immunology, 10355 Science Center Road, San Diego, CA 92121, USA
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40
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Kluck RM, Esposti MD, Perkins G, Renken C, Kuwana T, Bossy-Wetzel E, Goldberg M, Allen T, Barber MJ, Green DR, Newmeyer DD. The pro-apoptotic proteins, Bid and Bax, cause a limited permeabilization of the mitochondrial outer membrane that is enhanced by cytosol. J Cell Biol 1999; 147:809-22. [PMID: 10562282 PMCID: PMC2156156 DOI: 10.1083/jcb.147.4.809] [Citation(s) in RCA: 256] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/1999] [Accepted: 10/12/1999] [Indexed: 01/01/2023] Open
Abstract
During apoptosis, an important pathway leading to caspase activation involves the release of cytochrome c from the intermembrane space of mitochondria. Using a cell-free system based on Xenopus egg extracts, we examined changes in the outer mitochondrial membrane accompanying cytochrome c efflux. The pro-apoptotic proteins, Bid and Bax, as well as factors present in Xenopus egg cytosol, each induced cytochrome c release when incubated with isolated mitochondria. These factors caused a permeabilization of the outer membrane that allowed the corelease of multiple intermembrane space proteins: cytochrome c, adenylate kinase and sulfite oxidase. The efflux process is thus nonspecific. None of the cytochrome c-releasing factors caused detectable mitochondrial swelling, arguing that matrix swelling is not required for outer membrane permeability in this system. Bid and Bax caused complete release of cytochrome c but only a limited permeabilization of the outer membrane, as measured by the accessibility of inner membrane-associated respiratory complexes III and IV to exogenously added cytochrome c. However, outer membrane permeability was strikingly increased by a macromolecular cytosolic factor, termed PEF (permeability enhancing factor). We hypothesize that PEF activity could help determine whether cells can recover from mitochondrial cytochrome c release.
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Affiliation(s)
- Ruth M. Kluck
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121
| | - Mauro Degli Esposti
- Department of Biochemistry and Molecular Biology, University of South Florida, College of Medicine, Tampa, Florida 33612
| | - Guy Perkins
- Department of Neurosciences, University of California San Diego, San Diego, California 92093
| | - Christian Renken
- Biology Department, San Diego State University, San Diego, California 92182
| | - Tomomi Kuwana
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121
| | - Ella Bossy-Wetzel
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121
| | - Martin Goldberg
- Paterson Institute, Christie Hospital NHS Trust, Manchester M20 9BX, United Kingdom
| | - Terry Allen
- Paterson Institute, Christie Hospital NHS Trust, Manchester M20 9BX, United Kingdom
| | - Michael J. Barber
- Department of Biochemistry and Molecular Biology, University of South Florida, College of Medicine, Tampa, Florida 33612
| | - Douglas R. Green
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121
| | - Donald D. Newmeyer
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121
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41
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Slee EA, Harte MT, Kluck RM, Wolf BB, Casiano CA, Newmeyer DD, Wang HG, Reed JC, Nicholson DW, Alnemri ES, Green DR, Martin SJ. Ordering the cytochrome c-initiated caspase cascade: hierarchical activation of caspases-2, -3, -6, -7, -8, and -10 in a caspase-9-dependent manner. J Cell Biol 1999; 144:281-92. [PMID: 9922454 PMCID: PMC2132895 DOI: 10.1083/jcb.144.2.281] [Citation(s) in RCA: 1480] [Impact Index Per Article: 59.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/1998] [Revised: 12/21/1998] [Indexed: 12/31/2022] Open
Abstract
Exit of cytochrome c from mitochondria into the cytosol has been implicated as an important step in apoptosis. In the cytosol, cytochrome c binds to the CED-4 homologue, Apaf-1, thereby triggering Apaf-1-mediated activation of caspase-9. Caspase-9 is thought to propagate the death signal by triggering other caspase activation events, the details of which remain obscure. Here, we report that six additional caspases (caspases-2, -3, -6, -7, -8, and -10) are processed in cell-free extracts in response to cytochrome c, and that three others (caspases-1, -4, and -5) failed to be activated under the same conditions. In vitro association assays confirmed that caspase-9 selectively bound to Apaf-1, whereas caspases-1, -2, -3, -6, -7, -8, and -10 did not. Depletion of caspase-9 from cell extracts abrogated cytochrome c-inducible activation of caspases-2, -3, -6, -7, -8, and -10, suggesting that caspase-9 is required for all of these downstream caspase activation events. Immunodepletion of caspases-3, -6, and -7 from cell extracts enabled us to order the sequence of caspase activation events downstream of caspase-9 and reveal the presence of a branched caspase cascade. Caspase-3 is required for the activation of four other caspases (-2, -6, -8, and -10) in this pathway and also participates in a feedback amplification loop involving caspase-9.
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Affiliation(s)
- E A Slee
- Molecular Cell Biology Laboratory, Department of Biology, National University of Ireland, Maynooth, Co. Kildare, Ireland
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42
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Kluck RM, Martin SJ, Hoffman BM, Zhou JS, Green DR, Newmeyer DD. Cytochrome c activation of CPP32-like proteolysis plays a critical role in a Xenopus cell-free apoptosis system. EMBO J 1997; 16:4639-49. [PMID: 9303308 PMCID: PMC1170090 DOI: 10.1093/emboj/16.15.4639] [Citation(s) in RCA: 313] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
In a cell-free system based on Xenopus egg extracts, Bcl-2 blocks apoptotic activity by preventing cytochrome c release from mitochondria. We now describe in detail the crucial role of cytochrome c in this system. The mitochondrial fraction, when incubated with cytosol, releases cytochrome c. Cytochrome c in turn induces the activation of protease(s) resembling caspase-3 (CPP32), leading to downstream apoptotic events, including the cleavage of fodrin and lamin B1. CPP32-like protease activity plays an essential role in this system, as the caspase inhibitor, Ac-DEVD-CHO, strongly inhibited fodrin and lamin B1 cleavage, as well as nuclear morphology changes. Cytochrome c preparations from various vertebrate species, but not from Saccharomyces cerevisiae, were able to initiate all signs of apoptosis. Cytochrome c by itself was unable to process the precursor form of CPP32; the presence of cytosol was required. The electron transport activity of cytochrome c is not required for its pro-apoptotic function, as Cu- and Zn-substituted cytochrome c had strong pro-apoptotic activity, despite being redox-inactive. However, certain structural features of the molecule were required for this activity. Thus, in the Xenopus cell-free system, cytosol-dependent mitochondrial release of cytochrome c induces apoptosis by activating CPP32-like caspases, via unknown cytosolic factors.
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Affiliation(s)
- R M Kluck
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, CA 92121, USA
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43
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Kluck RM, Bossy-Wetzel E, Green DR, Newmeyer DD. The release of cytochrome c from mitochondria: a primary site for Bcl-2 regulation of apoptosis. Science 1997. [PMID: 9027315 DOI: 10.1126/science.275.5303.1132275.5303.1132] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
In a cell-free apoptosis system, mitochondria spontaneously released cytochrome c, which activated DEVD-specific caspases, leading to fodrin cleavage and apoptotic nuclear morphology. Bcl-2 acted in situ on mitochondria to prevent the release of cytochrome c and thus caspase activation. During apoptosis in intact cells, cytochrome c translocation was similarly blocked by Bcl-2 but not by a caspase inhibitor, zVAD-fmk. In vitro, exogenous cytochrome c bypassed the inhibitory effect of Bcl-2. Cytochrome c release was unaccompanied by changes in mitochondrial membrane potential. Thus, Bcl-2 acts to inhibit cytochrome c translocation, thereby blocking caspase activation and the apoptotic process.
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Affiliation(s)
- R M Kluck
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, CA 92121, USA
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44
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Abstract
In a cell-free apoptosis system, mitochondria spontaneously released cytochrome c, which activated DEVD-specific caspases, leading to fodrin cleavage and apoptotic nuclear morphology. Bcl-2 acted in situ on mitochondria to prevent the release of cytochrome c and thus caspase activation. During apoptosis in intact cells, cytochrome c translocation was similarly blocked by Bcl-2 but not by a caspase inhibitor, zVAD-fmk. In vitro, exogenous cytochrome c bypassed the inhibitory effect of Bcl-2. Cytochrome c release was unaccompanied by changes in mitochondrial membrane potential. Thus, Bcl-2 acts to inhibit cytochrome c translocation, thereby blocking caspase activation and the apoptotic process.
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Affiliation(s)
- R M Kluck
- Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, CA 92121, USA
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45
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Abstract
Previous studies have established that a relationship exists between apoptosis and cell surface (ecto-) peptidase activity. Thus dose-dependent increases were found both in ectopeptidase activities and in the proportion of cells undergoing apoptosis in HeLa cell monolayers after exposure to UV and other perturbants causing arrest of DNA synthesis (indirectly or directly as a result of DNA damage). The nature of the correlation made no distinction as to whether an increase in peptidase activity was causal of, or consequential to apoptosis, nor whether the increase was a general response by all cells. As a wider approach to understanding the possible role played by ectopeptidases in apoptosis, we report the effect on expression of a known ectopeptidase, aminopeptidase N (CD13), by a myelomonocytic cell line induced to undergo apoptosis. Using THP-1 cultures exposed to low concentrations of ethanol, we used FACS technology to sort for early apoptotic cells that have an increased ability to sequester the vital dye Hoechst 33342 while excluding nonvital dyes. Apoptosis was verified by light, fluorescence, and transmission electron microscopy, and the presence of DNA fragmentation. These early apoptotic cells showed a significant loss in CD13 labeling. Another surface marker, CD33, behaved similarly, whereas CD14 was lost globally, and not just by the apoptotic cells. Peptidase assays confirmed that an aminopeptidase was shed into the bathing media and that this activity was inhibitable both by bestatin and by a CD13 neutralizing monoclonal antibody. In treated cells, there was no evidence for an increase in cell surface protease activity directed toward a highly aliphatic nonapeptide substrate used as a model for TGF-alpha scission from its precursor form. However, other cell surface proteases of different specificity are presumably responsible for the observed shedding of CD13.
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Affiliation(s)
- S B Brown
- Queensland Cancer Fund Research Unit, Bancroft Centre, P.O. Royal Brisbane Hospital, Australia
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46
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Kluck RM, McDougall CA, Harmon BV, Halliday JW. Calcium chelators induce apoptosis--evidence that raised intracellular ionised calcium is not essential for apoptosis. Biochim Biophys Acta 1994; 1223:247-54. [PMID: 8086495 DOI: 10.1016/0167-4889(94)90233-x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
A moderate sustained rise in intracellular ionised calcium has been observed to be associated with apoptosis occurring in many experimental systems. The application of extracellular and intracellular chelators of calcium has been reported to produce a decrease in apoptosis, while the addition of calcium ionophores often increases apoptosis. These findings, together with the observation of calcium-induced internucleosomal DNA cleavage in isolated nuclei, have suggested that DNA cleavage (and apoptosis) is a calcium-dependent process. However, a number of studies have shown that apoptosis is not always associated with a rise in the level of intracellular ionised calcium. In the present study, calcium chelators were found to induce apoptosis in cultured cells, concomitant with a decrease in both intracellular ionised calcium and total cell calcium content. Decreased intracellular ionised magnesium was also induced by extracellular chelators. These findings provide further evidence that a raised intracellular ionised calcium is not universally present during the induction of apoptosis. It is proposed that loss of calcium homeostasis, rather than a sustained rise in cytosolic calcium, is a determining factor in cell death by apoptosis.
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Affiliation(s)
- R M Kluck
- Liver Unit, Queensland Institute of Medical Research, Herston, Brisbane, Australia
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47
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Abstract
We have previously characterized the stimulation of HeLa cell surface peptidase activity directed toward a nonapeptide substrate in response to low fluences of ultraviolet irradiation [Brown et al. (1993): J Cell Biochem 51:102-115]. To explore the hypothesis that this comprised a global response to cell stress featuring the interruption of DNA synthesis, a variety of agents affecting macromolecular synthesis were applied to HeLa cell cultures. Actinomycin D, 5,6-dichloro-1 beta-ribofuranosyl benzimadazole, mitomycin C, ultraviolet light, and cycloheximide at doses which inhibited cell growth, but fell short of increasing the proportion of cells which had lost cell membrane impermeability to trypan blue, resulted in the concentration dependent increase in both amino- and endo-peptidase activities of intact HeLa cell cultures. gamma-Irradiation, despite inhibiting an increase in cell number over a 20-h observation period, had no effect on the expressed level of cell surface peptidase activity nor did the accumulation of cells in S or G2 phase by thymidine parasynchronization. Some of these agents were found to increase the proportion of cells in the culture undergoing apoptosis (programmed cell death), and a strong correlation was found between the extent of apoptosis and the degree of elevation in cell surface peptidase activity. Higher concentrations of perturbants in some instances increased the percentage of cells that were nonviable and an associated release of intracellular proteases overwhelmed the linear correlation with apoptotic cells. The present data do not distinguish between a homogeneous elevation of surface peptidase activity in all cells of treated cultures or the heterogeneous increase in only preapoptotic or apoptotic cells. Since sunburn of the skin increases both the occurrence of apoptotic keratinocytes (sunburn cells) in the affected epidermis and the release of membrane bound cell activators such as transforming growth factor alpha, it is suggested by way of extrapolation of these in vitro results, that the increase in cell surface proteolytic activity plays an integral part in the reparative responses of the epidermal cells in vivo.
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Affiliation(s)
- S B Brown
- Queensland Cancer Fund Research Unit, Queensland Institute of Medical Research, Bancroft Centre, Brisbane, Australia
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48
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Kluck RM, Chapman DE, Egan M, McDougall CA, Harmon BV, Moss DJ, Kerr JF, Halliday JW. Spontaneous apoptosis in NS-1 myeloma cultures: effects of cell density, conditioned medium and acid pH. Immunobiology 1993; 188:124-33. [PMID: 8406554 DOI: 10.1016/s0171-2985(11)80492-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Apoptosis is a form of cell death which plays an important role in many biological processes including the regulation of B and T lymphocyte functions. We report here the spontaneous development of extensive apoptosis in cultures of the NS-1 mouse myeloma cell line following overgrowth. The apoptosis was identified by both its ultrastructural features and its DNA fragmentation pattern. High cell density and conditioned medium, but not acid pH, were found to be major inducers of apoptosis in this experimental system.
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Affiliation(s)
- R M Kluck
- Queensland Institute for Medical Research, Australia
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49
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Dickinson RG, Fowler DW, Kluck RM. Maternofetal transfer of phenytoin, p-hydroxy-phenytoin and p-hydroxy-phenytoin-glucuronide in the perfused human placenta. Clin Exp Pharmacol Physiol 1989; 16:789-97. [PMID: 2612061 DOI: 10.1111/j.1440-1681.1989.tb01517.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
1. Transplacental transfer of the anti-epileptic agent phenytoin (PHT), its phase I metabolite, p-hydroxy-phenytoin (p-OH-PHT), and its phase II conjugate p-OH-PHT-glucuronide, was studied in term placental lobules perfused single pass in both maternal and fetal circuits. 2. Ratios of clearance of PHT, p-OH-PHT and p-OH-PHT-glucuronide to clearance of antipyrine were 1.08 +/- 0.03, 0.52 +/- 0.02 and 0.12 +/- 0.01 (mean and s.e.m.), respectively. 3. Transfer was positively correlated with lipophilicity as measured by the apparent partition coefficient determined between octanol and pH 7.4 buffer.
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Affiliation(s)
- R G Dickinson
- Department of Medicine, University of Queensland, Royal Brisbane Hospital, Herston, Australia
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50
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Abstract
1. The disposition of the anti-epileptic agents phenytoin (PHT) and phenobarbitone (PB) was investigated in lobules of term human placentae perfused using separate maternal and fetal circulations for 6 h periods. 2. No evidence for metabolism of PHT or PB to their p-hydroxylated or other derivatives was found either in perfused lobules or by incubation with placental microsomes. 3. Both PHT and PB were readily transferred across the placenta after administration to either the maternal or fetal perfusates. 4. PHT, unlike PB, showed considerable accumulation in placental tissue.
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Affiliation(s)
- R M Kluck
- Department of Medicine, University of Queensland, Royal Brisbane Hospital, Australia
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