Lethal factor of Bacillus anthracis cleaves the N-terminus of MAPKKs: analysis of the intracellular consequences in macrophages

The lethal toxin of Bacillus anthracis consists of two proteins, PA and LF, which together induce lethal effects in some animal species and cause macr ophage lysis. LF is a zinc-binding protein with metalloprotease activity. W ith a two-hybrid system approach we identified MAP kinase kinases (MAPKKs) Mek1 and Mek2 as proteins interacting with LF. LF was shown to cleave Mek1 and Mek2 and an additional MAPKK family member MKK3, within their N-termina l region. We examined macrophage cell lines and primary peritoneal cells wi th different sensitivities to LF bur did not find a direct correlation betw een MAPKKs cleavage and cell death. On the other hand, sublytic doses of LF cleave MAPKKs and cause a reduction in the LPS/IFN gamma -induced producti on of proinflammatory mediators. These findings are discussed with respect to the possible role of LF in the initial phase of infection.