BAX insertion, oligomerization, and outer membrane permeabilization in brain mitochondria: Role of permeability transition and SH-redox regulation |
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Authors: | Tatiana Brustovetsky Youyun Yang Jiang-Ting Zhang Bruno Antonsson |
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Institution: | a Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, IN 46202, USAb Stark Neuroscience Research Institute, Indiana University School of Medicine, Indianapolis, IN 46202, USAc Simon Cancer Center, Indiana University School of Medicine, Indianapolis, IN 46202, USAd Merck Serono, Geneva Research Center, Geneva, Switzerland |
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Abstract: | BAX cooperates with truncated BID (tBID) and Ca2+ in permeabilizing the outer mitochondrial membrane (OMM) and releasing mitochondrial apoptogenic proteins. The mechanisms of this cooperation are still unclear. Here we show that in isolated brain mitochondria, recombinant BAX readily self-integrates/oligomerizes in the OMM but produces only a minuscule release of cytochrome c, indicating that BAX insertion/oligomerization in the OMM does not always lead to massive OMM permeabilization. Ca2+ in a mitochondrial permeability transition (mPT)-dependent and recombinant tBID in an mPT-independent manner promoted BAX insertion/ oligomerization in the OMM and augmented cytochrome c release. Neither tBID nor Ca2+ induced BAX oligomerization in the solution without mitochondria, suggesting that BAX oligomerization required interaction with the organelles and followed rather than preceded BAX insertion in the OMM. Recombinant Bcl-xL failed to prevent BAX insertion/oligomerization in the OMM but strongly attenuated cytochrome c release. On the other hand, a reducing agent, dithiothreitol (DTT), inhibited BAX insertion/oligomerization augmented by tBID or Ca2+ and suppressed the BAX-mediated release of cytochrome c and Smac/DIABLO but failed to inhibit Ca2+-induced swelling. Altogether, these data suggest that in brain mitochondria, BAX insertion/oligomerization can be dissociated from OMM permeabilization and that tBID and Ca2+ stimulate BAX insertion/oligomerization and BAX-mediated OMM permeabilization by different mechanisms involving mPT induction and modulation of the SH-redox state. |
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Keywords: | tBID truncated BID mPT mitochondrial permeability transition OMM outer mitochondrial membrane ER endoplasmic reticulum CsA cyclosporin A COX IV cytochrome oxidase subunit IV CHAPS 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate NP-40 Nonidet P-40 [octylphenoxy] polyethoxyethanol OG octyl glucoside Tr X-100 Triton X-100 SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis EGS ethylene glycol bis(succinimidyl succinate) DSS disuccinimidyl suberate BMH bismaleimidohexane |
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