Anthrax lethal toxin-induced inflammasome formation and caspase-1 activation are late events dependent on ion fluxes and the proteasome.
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.
Wickliffe
Katherine E
KE
Bacterial Toxins and Therapeutics Section, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Leppla
Stephen H
SH
Moayeri
Mahtab
M
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*
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