Mitochondrial proteins Bnip3 and Bnip3L are involved in anthrax lethal toxin-induced macrophage cell death.
Anthrax lethal toxin (LeTx) induces rapid cell death of RAW246.7 macrophages. We recently found that a small population of these macrophages is spontaneously and temporally refractory to LeTx-induced cytotoxicity. Analysis of genome-wide transcripts of a resistant clone before and after regaining LeTx sensitivity revealed that a reduction of two closely related mitochondrial proteins, Bcl-2/adenovirus E1B 19-kDa interacting protein 3 (Bnip3) and Bnip3-like (Bnip3L), correlates with LeTx resistance. Down-regulation of Bnip3 and Bnip3L was also found in "toxin-induced resistance" whereby sublethal doses of LeTx induce resistance to subsequent exposure to cytolytic toxin doses. The role of Bnip3 and Bnip3L in LeTx-induced cell death was confirmed by showing that overexpression of either Bnip3 or Bnip3L rendered the resistant cells susceptible to LeTx, whereas down-regulation of Bnip3 and Bnip3L in wild-type macrophages conferred resistance. The down-regulation of Bnip3 and Bnip3L mRNAs by LeTx occurred at both transcriptional and mRNA stability levels. Inhibition of the p38 pathway by lethal factor was responsible for the destabilization of Bnip3/Bnip3L mRNAs as confirmed by showing that p38 inhibitors stabilized Bnip3 and Bnip3L mRNAs and conferred resistance to LeTx cytotoxicity. Therefore, Bnip3/Bnip3L play a crucial role in LeTx-induced cytotoxicity, and down-regulation of Bnip3/Bnip3L is a mechanism of spontaneous or toxin-induced resistance of macrophages.
Ha
Soon-Duck
SD
Department of Microbiology and Immunology, Infectious Diseases Research Group, Siebens-Drake Research Institute, University of Western Ontario, London, Ontario N6G 2V4, Canada.
Ng
Dennis
D
Lamothe
Julie
J
Valvano
Miguel A
MA
Han
Jiahuai
J
Kim
Sung Ouk
SO
D000818:Animals; D000942:Antigens, Bacterial / Q000494:pharmacology*; D001427:Bacterial Toxins / Q000494:pharmacology*; D016923:Cell Death / Q000187:drug effects / Q000276:immunology; D002460:Cell Line; D015536:Down-Regulation / Q000187:drug effects / Q000276:immunology; D006801:Humans; D007113:Immunity, Innate / Q000187:drug effects*; D020935:MAP Kinase Signaling System / Q000187:drug effects* / Q000276:immunology; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D024101:Mitochondrial Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*
D000942:Antigens, Bacterial; C508686:BNip3 protein, mouse; D001427:Bacterial Toxins; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; C501741:Nix protein, mouse; D012333:RNA, Messenger; C030325:anthrax toxin; D048051:p38 Mitogen-Activated Protein Kinases