title: Cellular adaptation to anthrax lethal toxin-induced mitochondrial cholesterol enrichment, hyperpolarization, and reactive oxygen species generation through downregulating MLN64 in macrophages.
abstract: Cellular adaptation to different stresses related to survival and function has been demonstrated in several cell types. Anthrax lethal toxin (LeTx) induces rapid cell death, termed "pyroptosis," by activating NLRP1b/caspase-1 in murine macrophages. We and others (S. D. Ha et al., J. Biol. Chem. 282:26275-26283, 2007; I. I. Salles et al., Proc. Natl. Acad. Sci. U. S. A. 100:12426 -12431, 2003) have shown  that RAW264.7 cells preexposed to sublethal doses of LeTx become resistant to subsequent high cytolytic doses of LeTx, termed toxin-induced resistance (TIR). To date, the cellular mechanisms of pyroptosis and TIR are largely unknown. We found that LeTx caused NLRP1b/caspase-1-dependent mitochondrial dysfunction, including hyperpolarization and generation of reactive oxygen species, which was distinct from that induced by stimuli such as NLRP3-activating ATP. In TIR cells, these mitochondrial events were not detected, although caspase-1 was activated, in response to LeTx. We identified that downregulation of the late endosomal cholesterol-transferring protein MLN64 in TIR cells was involved in TIR. The downregulation of MLN64 in TIR cells was at least in part due to DNA methyltransferase 1-mediated DNA methylation. In wild-type RAW264.7 cells and primary bone marrow-derived macrophages, LeTx caused NLRP1b/caspase-1-dependent mitochondrial translocation of MLN64, resulting in cholesterol enrichment, membrane hyperpolarization, reactive oxygen species (ROS) generation, and depletion of free glutathione (GSH). This study demonstrates for the first time that MLN64 plays a key role in LeTx/caspase-1-induced mitochondrial dysfunction.
authors.affiliation: Department of Microbiology and Immunology and Centre for Human Immunology, Siebens-Drake Research Institute, University of Western Ontario, London, Ontario, Canada.
authors.forename: Soon-Duck
authors.initials: SD
authors.lastname: Ha
authors.forename: Sangwook
authors.initials: S
authors.lastname: Park
authors.forename: Chae Young
authors.initials: CY
authors.lastname: Han
authors.forename: Marilyn L
authors.initials: ML
authors.lastname: Nguyen
authors.forename: Sung Ouk
authors.initials: SO
authors.lastname: Kim
mesh_terms: D000818:Animals; D000881:Anthrax / Q000235:genetics / Q000276:immunology* / Q000821:virology; D000942:Antigens, Bacterial / Q000276:immunology*; D001408:Bacillus anthracis / Q000276:immunology*; D001427:Bacterial Toxins / Q000276:immunology*; D020170:Caspase 1 / Q000276:immunology; D016923:Cell Death / Q000187:drug effects; D002460:Cell Line; D002478:Cells, Cultured; D002784:Cholesterol / Q000276:immunology*; D019175:DNA Methylation; D015536:Down-Regulation; D005978:Glutathione / Q000276:immunology; D008264:Macrophages / Q000187:drug effects / Q000276:immunology / Q000378:metabolism / Q000821:virology*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000276:immunology / Q000821:virology*; D010750:Phosphoproteins / Q000032:analysis / Q000235:genetics* / Q000276:immunology; D017382:Reactive Oxygen Species / Q000276:immunology; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: D000942:Antigens, Bacterial; D001427:Bacterial Toxins; C486529:MLN64 protein, mouse; D010750:Phosphoproteins; D017382:Reactive Oxygen Species; C030325:anthrax toxin; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D002784:Cholesterol; D020170:Caspase 1; D005978:Glutathione