Early response in macrophages by exposure to a low concentration of anthrax lethal toxin

Abstract

The central role in the pathogenesis of anthrax is played by the two classical anthrax toxins. Three factors that are secreted by the bacterium combine to form two bipartite toxins. Edema toxin, consisting of the protective antigen (PA) and the edema factor (EF), causes the edema associated with anthrax infection. Lethal toxin (LeTx), composed of PA and the lethal factor (LF), is believed to be responsible for causing death in systemic anthrax infections. LF is a zinc-dependent endoproteinase that cleaves the N-terminus of mitogen-activated protein kinase kinases (MAPKKs) and functionally impairs cells of both the innate and adaptive immune systems. To analyze the cellular mechanisms underlying the host-pathogen interaction in anthrax infection, we examined the murine macrophage cell line RAW 264.7 following treatment with a relatively low concentration of LeTx (0.1 mu s/mL of PA, 0.1 mu g/mL of LF). Analysis of the gene expression pattern of macrophages treated with low concentrations of LeTx indicated changes in the expression levels of many genes 90 min after toxin treatment. These genes represent the early response in intoxicated macrophages and may contribute to the identification of survival or death factors. Additionally, we demonstrate that the activation of the putative phosphatase and tensin homology on chromosome 10 (PTEN) signal transduction pathway regulates cell death by decreasing the levels of phosphorylated glycogen synthase kinase 3 beta (GSK-3 beta) through activation of protein phosphatase 1 catalytic subunit alpha (PP1c) in lethal toxin-intoxicated murine macrophages. Furthermore, genes regulating growth and proliferation, transcription factor genes, and immune responsive genes were differentially expressed as a consequence of lethal toxin-mediated macrophage cytotoxicity.