title: Anthrax lethal toxin-induced inflammasome formation and caspase-1 activation are late events dependent on ion fluxes and the proteasome.
abstract: Anthrax lethal toxin (LT) is cytotoxic to macrophages from certain inbred mouse strains. The gene controlling macrophage susceptibility to LT is Nalp1b. Nalp1b forms part of the inflammasome, a multiprotein complex involved in caspase-1 activation and release of interleukin (IL)-1beta and IL-18. We confirm the role of caspase-1 in LT-mediated death by showing that caspase inhibitors differentially protected cells against LT, with the degree of protection corresponding to each compound's ability to inhibit caspase-1. Caspase-1 activation and cytokine processing and release were late events inhibited by elevated levels of KCl and sucrose, by potassium channel blockers, and by proteasome inhibitors, suggesting that inflammasome formation requires a protein-degradation event and occurs downstream of LT-mediated potassium efflux. In addition, IL-18 and IL-1beta release was dependent on cell death, indicating that caspase-1-mediated cytotoxicity is independent of these cytokines. Finally, inducing NALP3-inflammasome formation in LT-resistant macrophages did not sensitize cells to LT, suggesting that general caspase-1 activation cannot account for sensitivity to LT and that a Nalp1b-mediated event is specifically required for death. Our data indicate that inflammasome formation is a contributing, but not initiating, event in LT-mediated cytotoxicity and that earlier LT-mediated events leading to ion fluxes are required for death.
authors.affiliation: Bacterial Toxins and Therapeutics Section, 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: D000818:Animals; D000942:Antigens, Bacterial / Q000502:physiology*; D017209:Apoptosis / Q000235:genetics; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000502:physiology; D001427:Bacterial Toxins; D020170:Caspase 1 / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020022:Genetic Predisposition to Disease; D020382:Interleukin-18 / Q000502:physiology; D053583:Interleukin-1beta / Q000502:physiology; D017136:Ion Transport; D008264:Macrophages / Q000187:drug effects / Q000276:immunology* / Q000382:microbiology; D051379:Mice; D008815:Mice, Inbred Strains; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism / Q000502:physiology; D046988:Proteasome Endopeptidase Complex / Q000502:physiology*
chemical_list: D000942:Antigens, Bacterial; D051017:Apoptosis Regulatory Proteins; D001427:Bacterial Toxins; D004791:Enzyme Inhibitors; D020382:Interleukin-18; D053583:Interleukin-1beta; C509168:Nalp1b protein, mouse; C030325:anthrax toxin; D020929:Mitogen-Activated Protein Kinase Kinases; D020170:Caspase 1; D046988:Proteasome Endopeptidase Complex