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Singh G, Moldoveanu T. Methods to Probe Conformational Activation and Mitochondrial Activity of Proapoptotic BAK. Methods Mol Biol 2019; 1877:185-200. [PMID: 30536007 DOI: 10.1007/978-1-4939-8861-7_13] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Mitochondrial outer membrane permeabilization (MOMP) is a crucial initiating event in apoptosis that activates the caspase cascade to execute cell demise. The effector B-cell lymphoma 2 (BCL-2) antagonist killer (BAK) forms mitochondrial apoptotic pores to mediate MOMP. In healthy cells, BAK resides at the outer mitochondrial membrane as a dormant monomer. Upon direct interactions with the BCL-2 homology 3 (BH3)-only proapoptotic proteins during apoptosis, BAK undergoes conformational changes to form the active species associated with apoptotic pores. We describe methods to purify mitochondria for MOMP assays and to detect conformational changes in native BAK associated with MOMP by using limited proteolysis and cross-linking analyses.
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Affiliation(s)
- Geetika Singh
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN, USA.,Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Tudor Moldoveanu
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN, USA. .,Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, TN, USA.
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2
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Zhang JY, Guo Y, Si JP, Sun XB, Sun GB, Liu JJ. A polysaccharide of Dendrobium officinale ameliorates H2O2-induced apoptosis in H9c2 cardiomyocytes via PI3K/AKT and MAPK pathways. Int J Biol Macromol 2017; 104:1-10. [DOI: 10.1016/j.ijbiomac.2017.05.169] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 05/05/2017] [Accepted: 05/30/2017] [Indexed: 10/19/2022]
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3
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Palchaudhuri R, Lambrecht MJ, Botham RC, Partlow KC, van Ham TJ, Putt KS, Nguyen LT, Kim SH, Peterson RT, Fan TM, Hergenrother PJ. A Small Molecule that Induces Intrinsic Pathway Apoptosis with Unparalleled Speed. Cell Rep 2015; 13:2027-36. [PMID: 26655912 DOI: 10.1016/j.celrep.2015.10.042] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Revised: 09/08/2015] [Accepted: 10/14/2015] [Indexed: 10/22/2022] Open
Abstract
Apoptosis is generally believed to be a process that requires several hours, in contrast to non-programmed forms of cell death that can occur in minutes. Our findings challenge the time-consuming nature of apoptosis as we describe the discovery and characterization of a small molecule, named Raptinal, which initiates intrinsic pathway caspase-dependent apoptosis within minutes in multiple cell lines. Comparison to a mechanistically diverse panel of apoptotic stimuli reveals that Raptinal-induced apoptosis proceeds with unparalleled speed. The rapid phenotype enabled identification of the critical roles of mitochondrial voltage-dependent anion channel function, mitochondrial membrane potential/coupled respiration, and mitochondrial complex I, III, and IV function for apoptosis induction. Use of Raptinal in whole organisms demonstrates its utility for studying apoptosis in vivo for a variety of applications. Overall, rapid inducers of apoptosis are powerful tools that will be used in a variety of settings to generate further insight into the apoptotic machinery.
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Affiliation(s)
- Rahul Palchaudhuri
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Michael J Lambrecht
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Rachel C Botham
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Kathryn C Partlow
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Tjakko J van Ham
- Cardiovascular Research Center and Division of Cardiology, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA; Broad Institute, Cambridge, MA 02142, USA
| | - Karson S Putt
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Laurie T Nguyen
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Seok-Ho Kim
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Randall T Peterson
- Cardiovascular Research Center and Division of Cardiology, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA; Broad Institute, Cambridge, MA 02142, USA
| | - Timothy M Fan
- Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61802, USA
| | - Paul J Hergenrother
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
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4
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Enhancing the peroxidase activity of cytochrome c by mutation of residue 41: implications for the peroxidase mechanism and cytochrome c release. Biochem J 2014; 458:259-65. [DOI: 10.1042/bj20131386] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Enzymatic and mitochondrial release analyses of residue 41 variants of native and cardiolipin-bound mammalian cytochromes c implicate mobility of the 40–57 Ω loop in induction of peroxidase activity, but show that loss of axial Fe co-ordination is not essential.
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5
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Tait SWG, Green DR. Mitochondrial regulation of cell death. Cold Spring Harb Perspect Biol 2013; 5:5/9/a008706. [PMID: 24003207 DOI: 10.1101/cshperspect.a008706] [Citation(s) in RCA: 340] [Impact Index Per Article: 30.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Although required for life, paradoxically, mitochondria are often essential for initiating apoptotic cell death. Mitochondria regulate caspase activation and cell death through an event termed mitochondrial outer membrane permeabilization (MOMP); this leads to the release of various mitochondrial intermembrane space proteins that activate caspases, resulting in apoptosis. MOMP is often considered a point of no return because it typically leads to cell death, even in the absence of caspase activity. Because of this pivotal role in deciding cell fate, deregulation of MOMP impacts on many diseases and represents a fruitful site for therapeutic intervention. Here we discuss the mechanisms underlying mitochondrial permeabilization and how this key event leads to cell death through caspase-dependent and -independent means. We then proceed to explore how the release of mitochondrial proteins may be regulated following MOMP. Finally, we discuss mechanisms that enable cells sometimes to survive MOMP, allowing them, in essence, to return from the point of no return.
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Affiliation(s)
- Stephen W G Tait
- Beatson Institute, Institute of Cancer Sciences, University of Glasgow, Glasgow G61 1BD, United Kingdom.
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6
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Zhang L, Wei S, Tang JM, Guo LY, Zheng F, Yang JY, Kong X, Huang YZ, Chen SY, Wang JN. PEP-1-CAT protects hypoxia/reoxygenation-induced cardiomyocyte apoptosis through multiple sigaling pathways. J Transl Med 2013; 11:113. [PMID: 23642335 PMCID: PMC3660214 DOI: 10.1186/1479-5876-11-113] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2012] [Accepted: 05/01/2013] [Indexed: 12/22/2022] Open
Abstract
Background Catalase (CAT) breaks down H2O2 into H2O and O2 to protects cells from oxidative damage. However, its translational potential is limited because exogenous CAT cannot enter living cells automatically. This study is aimed to investigate if PEP-1-CAT fusion protein can effectively protect cardiomyocytes from oxidative stress due to hypoxia/reoxygenation (H/R)-induced injury. Methods H9c2 cardomyocytes were pretreated with catalase (CAT) or PEP-1-CAT fusion protein followed by culturing in a hypoxia and re-oxygenation condition. Cell apoptosis were measured by Annexin V and PI double staining and Flow cytometry. Intracellular superoxide anion level was determined, and mitochondrial membrane potential was measured. Expression of apoptosis-related proteins including Bcl-2, Bax, Caspase-3, PARP, p38 and phospho-p38 was analyzed by western blotting. Results PEP-1-CAT protected H9c2 from H/R-induced morphological alteration and reduced the release of lactate dehydrogenase (LDH) and malondialdehyde content. Superoxide anion production was also decreased. In addition, PEP-1-CAT inhibited H9c2 apoptosis and blocked the expression of apoptosis stimulator Bax while increased the expression of Bcl-2, leading to an increased mitochondrial membrane potential. Mechanistically, PEP-1-CAT inhibited p38 MAPK while activating PI3K/Akt and Erk1/2 signaling pathways, resulting in blockade of Bcl2/Bax/mitochondrial apoptotic pathway. Conclusion Our study has revealed a novel mechanism by which PEP-1-CAT protects cardiomyocyte from H/R-induced injury. PEP-1-CAT blocks Bcl2/Bax/mitochondrial apoptotic pathway by inhibiting p38 MAPK while activating PI3K/Akt and Erk1/2 signaling pathways.
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Affiliation(s)
- Lei Zhang
- Institute of Clinical Medicine, Renmin Hospital, Hubei University of Medicine, Shiyan, Hubei 442000, China
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7
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Affiliation(s)
- Marco Colombini
- Department of Biology,
University of Maryland, College
Park, Maryland 20742, United States
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8
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Lofrumento DD, La Piana G, Abbrescia DI, Palmitessa V, La Pesa V, Marzulli D, Lofrumento NE. Valinomycin induced energy-dependent mitochondrial swelling, cytochrome c release, cytosolic NADH/cytochrome c oxidation and apoptosis. Apoptosis 2012; 16:1004-13. [PMID: 21739274 DOI: 10.1007/s10495-011-0628-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In valinomycin induced stimulation of mitochondrial energy dependent reversible swelling, supported by succinate oxidation, cytochrome c (cyto-c) and sulfite oxidase (Sox) [both present in the mitochondrial intermembrane space (MIS)] are released outside. This effect can be observed at a valinomycin concentration as low as 1 nM. The rate of cytosolic NADH/cyto-c electron transport pathway is also greatly stimulated. The test on the permeability of mitochondrial outer membrane to exogenous cyto-c rules out the possibility that the increased rate of exogenous NADH oxidation could be ascribed either to extensively damaged or broken mitochondria. Accumulation of potassium inside the mitochondria, mediated by the highly specific ionophore valinomycin, promotes an increase in the volume of matrix (evidenced by swelling) and the interaction points between the two mitochondrial membranes are expected to increase. The data reported and those previously published are consistent with the view that "respiratory contact sites" are involved in the transfer of reducing equivalents from cytosol to inside the mitochondria both in the absence and the presence of valinomycin. Magnesium ions prevent at least in part the valinomycin effects. Rather than to the dissipation of membrane potential, the pro-apoptotic property of valinomycin can be ascribed to both the release of cyto-c from mitochondria to cytosol and the increased rate of cytosolic NADH coupled with an increased availability of energy in the form of glycolytic ATP, useful for the correct execution of apoptotic program.
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Affiliation(s)
- Dario Domenico Lofrumento
- Department of Biological and Environmental Sciences and Technologies, Section of Human Anatomy, University of Salento, Lecce, Italy
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Landeta O, Landajuela A, Gil D, Taneva S, DiPrimo C, Sot B, Valle M, Frolov VA, Basañez G. Reconstitution of proapoptotic BAK function in liposomes reveals a dual role for mitochondrial lipids in the BAK-driven membrane permeabilization process. J Biol Chem 2011; 286:8213-8230. [PMID: 21196599 PMCID: PMC3048708 DOI: 10.1074/jbc.m110.165852] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Revised: 12/18/2010] [Indexed: 12/11/2022] Open
Abstract
BAK is a key effector of mitochondrial outer membrane permeabilization (MOMP) whose molecular mechanism of action remains to be fully dissected in intact cells, mainly due to the inherent complexity of the intracellular apoptotic machinery. Here we show that the core features of the BAK-driven MOMP pathway can be reproduced in a highly simplified in vitro system consisting of recombinant human BAK lacking the carboxyl-terminal 21 residues (BAKΔC) and tBID in combination with liposomes bearing an appropriate lipid environment. Using this minimalist reconstituted system we established that tBID suffices to trigger BAKΔC membrane insertion, oligomerization, and pore formation. Furthermore, we demonstrate that tBID-activated BAKΔC permeabilizes the membrane by forming structurally dynamic pores rather than a large proteinaceous channel of fixed size. We also identified two distinct roles played by mitochondrial lipids along the molecular pathway of BAKΔC-induced membrane permeabilization. First, using several independent approaches, we showed that cardiolipin directly interacts with BAKΔC, leading to a localized structural rearrangement in the protein that "primes" BAKΔC for interaction with tBID. Second, we provide evidence that selected curvature-inducing lipids present in mitochondrial membranes specifically modulate the energetic expenditure required to create the BAKΔC pore. Collectively, our results support the notion that BAK functions as a direct effector of MOMP akin to BAX and also adds significantly to the growing evidence indicating that mitochondrial membrane lipids are actively implicated in BCL-2 protein family function.
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Affiliation(s)
- Olatz Landeta
- From the Unidad de Biofísica (Centro Mixto Consejo Superior de Investigaciones Cientificas-Universidad del Pais Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), P.O. Box 644, 48080 Bilbao, Spain
| | - Ane Landajuela
- From the Unidad de Biofísica (Centro Mixto Consejo Superior de Investigaciones Cientificas-Universidad del Pais Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), P.O. Box 644, 48080 Bilbao, Spain
| | - David Gil
- CIC-BIOGUNE Structural Biology Unit, Parque Tecnologico Zamudio, Bizkaia, 48160 Derio, Spain
| | - Stefka Taneva
- From the Unidad de Biofísica (Centro Mixto Consejo Superior de Investigaciones Cientificas-Universidad del Pais Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), P.O. Box 644, 48080 Bilbao, Spain
| | - Carmelo DiPrimo
- Université de Bordeaux, INSERM U869, Institut Européen de Chimie et de Biologie, Pessac F-33607, France, and
| | - Begoña Sot
- the MRC Centre for Protein Engineering and MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, United Kingdom
| | - Mikel Valle
- CIC-BIOGUNE Structural Biology Unit, Parque Tecnologico Zamudio, Bizkaia, 48160 Derio, Spain
| | - Vadim A Frolov
- From the Unidad de Biofísica (Centro Mixto Consejo Superior de Investigaciones Cientificas-Universidad del Pais Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), P.O. Box 644, 48080 Bilbao, Spain,; the Departamento de Bioquímica y Biología Molecular, UPV/EHU, Leioa 48940, Spain,; Ikerbasque, Basque Foundation for Science, 48011 Bilbao, Spain
| | - Gorka Basañez
- From the Unidad de Biofísica (Centro Mixto Consejo Superior de Investigaciones Cientificas-Universidad del Pais Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), P.O. Box 644, 48080 Bilbao, Spain,.
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10
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Tam ZY, Cai YH, Gunawan R. Elucidating cytochrome C release from mitochondria: insights from an in silico three-dimensional model. Biophys J 2011; 99:3155-63. [PMID: 21081062 DOI: 10.1016/j.bpj.2010.09.041] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2010] [Revised: 09/06/2010] [Accepted: 09/13/2010] [Indexed: 11/28/2022] Open
Abstract
Mitochondrial regulation of apoptosis depends on the programmed release of proapoptotic proteins such as cytochrome c (Cyt c) through the outer mitochondrial membrane (OMM). Although a few key processes involved in this release have been identified, including the liberation of inner membrane-bound Cyt c and formation of diffusible pores on the OMM, other details like the transport of Cyt c within complex mitochondrial compartments, e.g., the cristae and crista junctions, are not yet fully understood (to our knowledge). In particular, a remodeling of the inner mitochondrial membrane accompanying apoptosis seen in a few studies, in which crista junctions widen, has been hypothesized to be a necessary step in the Cyt c release. Using a three-dimensional spatial modeling of mitochondrial crista and the crista junction, model simulations and analysis illustrated how the interplay among solubilization of Cyt c, fast diffusion of Cyt c, and OMM permeabilization gives rise to the observed experimental release profile. Importantly, the widening of the crista junction was found to have a negligible effect on the transport of free Cyt c from cristae. Finally, model simulations showed that increasing the fraction of free/loosely-bound Cyt c can sensitize the cell to apoptotic stimuli in a threshold manner, which may explain increased sensitivity to cell death associated with aging.
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Affiliation(s)
- Zhi Yang Tam
- Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore
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Abstract
Mitochondrial outer membrane permeabilization (MOMP) is often required for activation of the caspase proteases that cause apoptotic cell death. Various intermembrane space (IMS) proteins, such as cytochrome c, promote caspase activation following their mitochondrial release. As a consequence, mitochondrial outer membrane integrity is highly controlled, primarily through interactions between pro- and anti-apoptotic members of the B cell lymphoma 2 (BCL-2) protein family. Following MOMP by pro-apoptotic BCL-2-associated X protein (BAX) or BCL-2 antagonist or killer (BAK), additional regulatory mechanisms govern the mitochondrial release of IMS proteins and caspase activity. MOMP typically leads to cell death irrespective of caspase activity by causing a progressive decline in mitochondrial function, although cells can survive this under certain circumstances, which may have pathophysiological consequences.
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12
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Malouitre S, Dube H, Selwood D, Crompton M. Mitochondrial targeting of cyclosporin A enables selective inhibition of cyclophilin-D and enhanced cytoprotection after glucose and oxygen deprivation. Biochem J 2009; 425:137-48. [PMID: 19832699 PMCID: PMC2860807 DOI: 10.1042/bj20090332] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2009] [Revised: 10/02/2009] [Accepted: 10/15/2009] [Indexed: 12/24/2022]
Abstract
CsA (cyclosporin A) is a hydrophobic undecapeptide that inhibits CyPs (cyclophilins), a family of PPIases (peptidylprolyl cis-trans isomerases). In some experimental models, CsA offers partial protection against lethal cell injury brought about by transient ischaemia; this is believed to reflect inhibition of CyP-D, a mitochondrial isoform that facilitates formation of the permeability transition pore in the mitochondrial inner membrane. To evaluate this further, we have targeted CsA to mitochondria so that it becomes selective for CyP-D in cells. This was achieved by conjugating the inhibitor to the lipophilic triphenylphosphonium cation, enabling its accumulation in mitochondria due to the inner membrane potential. In a cell-free system and in B50 neuroblastoma cells the novel reagent (but not CsA itself) preferentially inhibited CyP-D over extramitochondrial CyP-A. In hippocampal neurons, mitochondrial targeting markedly enhanced the capacity of CsA to prevent cell necrosis brought about by oxygen and glucose deprivation, but largely abolished its capacity to inhibit glutamate-induced cell death. It is concluded that CyP-D has a major pathogenic role in 'energy failure', but not in glutamate excitotoxicity, where cytoprotection primarily reflects CsA interaction with extramitochondrial CyPs and calcineurin. Moreover, the therapeutic potential of CsA against ischaemia/reperfusion injuries not involving glutamate may be improved by mitochondrial targeting.
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Key Words
- cyclophilin (cyp)
- cyclosporin a (csa)
- glutamate toxicity
- hippocampal neuron
- ischaemia
- necrosis
- csa, cyclosporin a
- cyp, cyclophilin
- cyp-d+, cell line overexpressing cyp-d
- dcm, dichloromethane
- dmem, dulbecco's minimal essential medium
- dmf, dimethylformamide
- esi–ms, electrospray ionization ms
- fbs, fetal bovine serum
- fmoc, fluoren-9-ylmethoxycarbonyl
- hbss, hanks balanced salt solution
- i/r, ischaemia/reperfusion
- lda, lithium diisopropylamide
- l-name, ng-nitro-l-arginine-methyl ester
- mtcsa, mitochondrially targeted csa
- nba, neurobasal a
- nbqx, 2,3-dihydro-6-nitro-7-sulfamoylbenzoquinoxaline
- nmda, n-methyl-d-aspartate
- ogd, oxygen and glucose deprivation
- ppiase, peptidylprolyl cis–trans isomerase
- pt, permeability transition
- pybop, benzotriazol-1-yl-tris-pyrrolidinophosphonium hexafluorophosphate
- smbz-csa, [sarcosine-3(4-methylbenzoate)]-csa
- thf, tetrahydrofuran
- tmre, tetramethylrhodamine ethyl ester
- tpp+, triphenylphosphonium
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Affiliation(s)
- Sylvanie Malouitre
- *Research Department of Structural and Molecular Biology, University College London, Gower Street, London WC1E 6BT, U.K
| | - Henry Dube
- †Wolfson Institute for Biomedical Research, University College London, Gower Street, London WC1E 6BT, U.K
| | - David Selwood
- †Wolfson Institute for Biomedical Research, University College London, Gower Street, London WC1E 6BT, U.K
| | - Martin Crompton
- *Research Department of Structural and Molecular Biology, University College London, Gower Street, London WC1E 6BT, U.K
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Dissimilar mechanisms of cytochrome c release induced by octyl glucoside-activated BAX and by BAX activated with truncated BID. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1797:52-62. [PMID: 19664589 DOI: 10.1016/j.bbabio.2009.07.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2009] [Revised: 07/20/2009] [Accepted: 07/27/2009] [Indexed: 11/21/2022]
Abstract
In the present study, we compared alkali-resistant BAX insertion into the outer mitochondrial membrane, mitochondrial remodeling, mitochondrial membrane potential changes, and cytochrome c (Cyt c) release from isolated brain mitochondria triggered by recombinant BAX oligomerized with 1% octyl glucoside (BAX(oligo)) and by a combination of monomeric BAX (BAX(mono)) and caspase 8-cleaved C-terminal fragment of recombinant BID (truncated BID, t(c)BID). We also examined whether the effects induced by BAX(oligo) or by BAX(mono) activated with t(c)BID depended on induction of the mitochondrial permeability transition. The results obtained in this study revealed that t(c)BID plus BAX(mono) produced BAX insertion and Cyt c release without overt changes in mitochondrial morphology. On the contrary, treatment of mitochondria with BAX(oligo) resulted in BAX insertion and Cyt c release, which were accompanied by gross distortion of mitochondrial morphology. The effects of BAX(oligo) could be at least partially suppressed by mitochondrial depolarization. The effects of t(c)BID plus BAX(mono) were insensitive to depolarization. BAX(oligo) produced similar BAX insertion, mitochondrial remodeling, and Cyt c release in KCl- and in N-methyl-D-glucamine-based incubation media indicating a non-essential role for K+ influx into mitochondria in these processes. A combination of cyclosporin A and ADP, inhibitors of the mitochondrial permeability transition, attenuated Cyt c release, mitochondrial remodeling, and depolarization induced by BAX(oligo), but failed to influence the effects produced by t(c)BID plus BAX(mono). Thus, our results suggest a significant difference in the mechanisms of the outer mitochondrial membrane permeabilization and Cyt c release induced by detergent-oligomerized BAX(oligo) and by BAX activated with t(c)BID.
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