The Role of NF-κB and H3K27me3 Demethylase, Jmjd3, on the Anthrax Lethal Toxin Tolerance of RAW 264.7 Cells

BACKGROUND: In Bacillus anthracis, lethal toxin (LeTx) is a critical virulence factor that causes immune suppression and toxic shock in the infected host. NF-κB is a key mediator of the inflammatory response and is crucial for the plasticity of first level immune cells such as macrophages, monocytes and neutrophils. In macrophages, this inflammatory response, mediated by NF-κB, can regulate host defense against invading pathogens. A Jumonji C family histone 3 lysine-27 (H3K27) demethylase, Jmjd3, plays a crucial role in macrophage plasticity and inflammation. Here we report that NF-κB and Jmjd3 can modulate the LeTx intoxication resistance of RAW 264.7 cells. PRINCIPAL FINDINGS: This study showed that a 2 h exposure of macrophages to LeTx caused substantial cell death with a survival rate of around 40%. The expression of the Jmjd3 gene was induced 8-fold in intoxication-resistant cells generated by treatment with lipopolysaccharides of RAW 264.7 cells. These intoxication-resistant cell lines (PLx intox and PLxL intox) were maintained for 8 passages and had a survival rate of around 100% on secondary exposure to LeTx and lipopolysaccharides. Analysis of NF-κB gene expression showed that the expression of p100, p50 and p65 was induced around 20, 7 and 4 fold, respectively, in both of the intoxication-resistant cell lines following a 2 h treatment with PLxL (0.1+0.1+1 µg/ml). In contrast, these NF-κB genes were not induced following treatment with PLx treatment at the same concentrations. CONCLUSIONS: Although LeTx influences macrophage physiology and causes defects of some key signaling pathways such as GSK3β which contributes to cytotoxicity, these results indicate that modulation of NF-κB by p50, p100 and Jmjd3 could be vital for the recovery of murine macrophages from exposure to the anthrax lethal toxin.