CA-074Me protection against anthrax lethal toxin

Anthrax lethal toxin (LT) activates the NLRP1b (NALP1b) inflammasome and Caspase-1 in macrophages from certain inbred mouse strains, but the mechanism by which this occurs is poorly understood. We report here that similar to several NLRP3 (NALP3, cryopyrin)-activating stimuli, LT activation of the NLRP1b inflammasome involves lysosomal membrane permeabilization (LMP) and subsequent cytoplasmic Cathepsin B activity. CA-074Me, a potent Cathepsin B Inhibitor, protects LT-sensitive macrophages from cell death and prevents the activation of Caspase-1. RNA interference knockdown of Cathepsin B expression, however, cannot prevent LT-mediated cell death, suggesting that CA-074Me may also act on other cellular proteases released during LMP. CA-074Me appears to function downstream of LT translocation to the cytosol (as assessed by mitogen-activated protein kinase kinase cleavage), K(+) effluxes, and Proteasome activity. The initial increase in cytoplasmic activity of Cathepsin B occurs at the same time or shortly before Caspase-1 activation but precedes a larger-scale lysosomal destabilization correlated closely with cytolysis. We present results suggesting that LMP may be involved in the activation of the NLRP1b inflammasome.