Anthrax lethal toxin triggers the formation of a membrane-associated inflammasome complex in murine macrophages.
Multiple microbial components trigger the formation of an inflammasome complex that contains pathogen-specific nucleotide oligomerization and binding domain (NOD)-like receptors (NLRs), caspase-1, and in some cases the scaffolding protein ASC. The NLR protein Nalp1b has been linked to anthrax lethal toxin (LT)-mediated cytolysis of murine macrophages. Here we demonstrate that in unstimulated J774A.1 macrophages, caspase-1 and Nalp1b are membrane associated and part of approximately 200- and approximately 800-kDa complexes, respectively. LT treatment of these cells resulted in caspase-1 recruitment to the Nalp1b-containing complex, concurrent with processing of cytosolic caspase-1 substrates. We further demonstrated that Nalp1b and caspase-1 are able to interact with each other. Intriguingly, both caspase-1 and Nalp1b were membrane associated, while the caspase-1 substrate interleukin-18 was cytosolic. Caspase-1-associated inflammasome components included, besides Nalp1b, proinflammatory caspase-11 and the caspase-1 substrate alpha-enolase. Asc was not part of the Nalp1b inflammasome in LT-treated macrophages. Taken together, our findings suggest that LT triggers the formation of a membrane-associated inflammasome complex in murine macrophages, resulting in cleavage of cytosolic caspase-1 substrates and cell death.
Nour
Adel M
AM
Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Yeung
Yee-Guide
YG
Santambrogio
Laura
L
Boyden
Eric D
ED
Stanley
E Richard
ER
Brojatsch
Jürgen
J
D000818:Animals; D000942:Antigens, Bacterial / Q000276:immunology / Q000378:metabolism*; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000276:immunology / Q000378:metabolism*; D001427:Bacterial Toxins / Q000276:immunology / Q000378:metabolism*; D015153:Blotting, Western; D020170:Caspase 1 / Q000276:immunology / Q000378:metabolism*; D020169:Caspases / Q000276:immunology / Q000378:metabolism; D053471:Caspases, Initiator; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D007249:Inflammation / Q000276:immunology / Q000378:metabolism; D008264:Macrophages / Q000276:immunology / Q000378:metabolism* / Q000382:microbiology; D051379:Mice; D008856:Microscopy, Fluorescence; D010751:Phosphopyruvate Hydratase / Q000276:immunology / Q000378:metabolism; D014162:Transfection
D000942:Antigens, Bacterial; D051017:Apoptosis Regulatory Proteins; D001427:Bacterial Toxins; C509168:Nalp1b protein, mouse; C030325:anthrax toxin; C101136:Casp4 protein, mouse; D020169:Caspases; D053471:Caspases, Initiator; D020170:Caspase 1; D010751:Phosphopyruvate Hydratase