Activation of phospholipase C and protein kinase C is required for expression of anthrax lethal toxin cytotoxicity in J774A.1 cells

Anthrax lethal toxin (LT) comprises two proteins: the protective antigen (P A) and the lethal factor (LF). The LT is cytotoxic to macrophage-like cell line J774A.1. Pre-treatment oi these cells with neomycin, a phospholipase C inhibitor, protected them against anthrax LT cytotoxicity. Protection obta ined with neomycin indicated that LT stimulates phospholipase C in these ce lls. It was found that levels oi inositol 1,4,5-triphosphate (IP3) dramatic ally increased in toxin-treated cells. The rise in IP3 levels was proportio nal to the dose of LF that was allowed to bind to receptor-bound PA. By usi ng protein kinase C (PKC) inhibitors, we found that the activation oi PKC i s required for mediating anthrax LT cytoxicity. Activation of phospholipase C or PKC is not required for the binding of PA to the cell surface recepto rs or for the uptake or internalisation oi the toxin. In this study, we dem onstrate that the IP3 signalling cascade is initiated by anthrax lethal tox in in J774A.1 cells. The second messengers generated during the cascade aid LF in mediating lethality only after its translocation into the cytosol. C ELL SIGNAL 11;2:111-116, 1999. (C) 1998 Elsevier Science Inc.