Bacillus anthracis, the causative agent of anthrax, produces three toxin polypeptides: protective antigen (PA), lethal factor (LF) and edema factor (EF). PA binds to receptors expressed on the surface of host cells and allows cellular entry of LF and EF. The function of LF in anthrax pathogenesis has been extensively studied by investigating its action in both cultured macrophages and animal models. By contrast, very little is known about the regulatory targets and pathogenic mechanism of EF. We found that EF, with its adenylate cyclase activity, promotes motility and survival of macrophages in vitro. Our preliminary data also suggest that EF suppresses production of certain proinflammatory cytokines while activating a number of novel target genes that include the cytokine vascular endothelial growth factor (VEGF). VEGF is known to increase vascular permeability, thereby causing edema, and also promote the growth of lymphatic and blood vessels. Based on these findings, we propose that EF may play a role in accelerating the migration of B. anthracis-infected macrophages to lymph nodes and spreading of the bacterium to the blood circulation. To test this idea, we plan to pursue the following specific aims: 1) Identify the transcription factors that link cAMP signaling to the expression of EF target genes in macrophages;2) Determine the mechanisms by which EF promotes macrophage motility and survival;and 3) Determine the mechanisms by which EF activates VEGF expression in macrophages and lymphangiogenesis in mice. In addition to providing better insight into the mechanism of anthrax pathogenesis, we aim at devising an efficient method to prevent the spreading of B. anthracis toward fatal systemic infection by modulating the function of EF-targeted host proteins.
We are investigating the mechanisms by which anthrax bacteria manipulate macrophages, major cell participants in the first-strike arm of the immune system, disturbing the signaling system and commandeering the cells as transport, thus allowing the bacteria to spread in the body. Using cultured macrophage cells and mice, we will study exactly how edema factor, one of the toxin proteins produced by anthrax bacteria, activates host genes and thereby directs the spreading of this deadly bacterium. Our hope is that these efforts will lead to the discovery of new targets for the treatment of anthrax and other infectious diseases.
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