title: Heat shock inhibits caspase-1 activity while also preventing its inflammasome-mediated activation by anthrax lethal toxin.
abstract: Anthrax lethal toxin (LT) rapidly kills macrophages from certain mouse strains in a mechanism dependent on the breakdown of unknown protein(s) by the proteasome, formation of the Nalp1b (NLRP1b) inflammasome and subsequent activation of caspase-1. We report that heat-shocking LT-sensitive macrophages rapidly protects them against cytolysis by inhibiting caspase-1 activation without upstream effects on LT endocytosis or cleavage of the toxin's known cytosolic substrates (mitogen-activated protein kinases). Heat shock protection against LT occurred through a mechanism independent of de novo protein synthesis, HSP90 activity, p38 activation or proteasome inhibition and was downstream of mitogen-activated protein kinase cleavage and degradation of an unknown substrate by the proteasome. The heat shock inhibition of LT-mediated caspase-1 activation was not specific to the Nalp1b (NLRP1b) inflammasome, as heat shock also inhibited Nalp3 (NLRP3) inflammasome-mediated caspase-1 activation in macrophages. We found that heat shock induced pro-caspase-1 association with a large cellular complex that could prevent its activation. Additionally, while heat-shocking recombinant caspase-1 did not affect its activity in vitro, lysates from heat-shocked cells completely inhibited recombinant active caspase-1 activity. Our results suggest that heat shock inhibition of active caspase-1 can occur independently of an inflammasome platform, through a titratable factor present within intact, functioning heat-shocked cells.
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: Tera C
authors.initials: TC
authors.lastname: Levin
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: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D000942:Antigens, Bacterial / Q000633:toxicity*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001427:Bacterial Toxins / Q000633:toxicity*; D002352:Carrier Proteins / Q000378:metabolism; D020170:Caspase 1 / Q000378:metabolism*; D061945:Caspase Inhibitors; D002460:Cell Line; D002470:Cell Survival; D006358:Hot Temperature; D008264:Macrophages / Q000201:enzymology* / Q000528:radiation effects*; D051379:Mice; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000942:Antigens, Bacterial; D051017:Apoptosis Regulatory Proteins; D001427:Bacterial Toxins; D002352:Carrier Proteins; D061945:Caspase Inhibitors; C529636:NALP1 protein, mouse; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C492716:Nlrp3 protein, mouse; C030325:anthrax toxin; D020170:Caspase 1