title: Killing of macrophages by anthrax lethal toxin: involvement of the N-end rule pathway.
abstract: Macrophages from certain inbred mouse strains are rapidly killed (< 90 min) by anthrax lethal toxin (LT). LT cleaves cytoplasmic MEK proteins at 20 min and induces caspase-1 activation in sensitive macrophages at 50-60 min, but the mechanism of LT-induced death is unknown. Proteasome inhibitors block LT-mediated caspase-1 activation and can protect against cell death, indicating that the degradation of at least one cellular protein is required for LT-mediated cell death. Proteins can be degraded by the proteasome via the N-end rule, in which a protein's stability is determined by its N-terminal residue. Using amino acid derivatives that act as inhibitors of this pathway, we show that the N-end rule is required for LT-mediated caspase-1 activation and cell death. We also found that bestatin methyl ester, an aminopeptidase inhibitor protects against LT in vitro and in vivo and that the different inhibitors of the protein degradation pathway act synergistically in protecting against LT. We identify c-IAP1, a mammalian member of the inhibitor of apoptosis protein (IAP) family, as a novel N-end rule substrate degraded in macrophages treated with LT. We also show that LT-induced c-IAP1 degradation is independent of the IAP-antagonizing proteins Smac/DIABLO and Omi/HtrA2, but dependent on caspases.
authors.affiliation: Bacterial Toxins and Therapeutics Section, Laboratory of Bacterial Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Katherine E
authors.initials: KE
authors.lastname: Wickliffe
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Leppla
authors.forename: Mahtab
authors.initials: M
authors.lastname: Moayeri
mesh_terms: D000626:Aminopeptidases / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000818:Animals; D000881:Anthrax / Q000382:microbiology; D000942:Antigens, Bacterial / Q000378:metabolism*; D001408:Bacillus anthracis / Q000201:enzymology* / Q000472:pathogenicity; D001427:Bacterial Toxins / Q000378:metabolism*; D020170:Caspase 1 / Q000378:metabolism; D016923:Cell Death; D002478:Cells, Cultured; D051034:Inhibitor of Apoptosis Proteins / Q000302:isolation & purification / Q000378:metabolism*; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D008264:Macrophages / Q000378:metabolism* / Q000473:pathology; D053858:Metabolic Networks and Pathways; D008666:Metalloendopeptidases / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D013379:Substrate Specificity; D014774:Virulence
chemical_list: C529046:(-)-N-((2S,3R)-3-amino-2-hydroxy-4-phenyl-butyryl)-L-leucine methyl ester; D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D051034:Inhibitor of Apoptosis Proteins; C030325:anthrax toxin; D000626:Aminopeptidases; D020170:Caspase 1; D008666:Metalloendopeptidases; D007930:Leucine