The overall objective of this application is to elucidate mechanisms by which anthrax lethal toxin contributes to the disease process. Lethal toxin is an essential virulence factor that allows Bacillus anthracis to colonize and kill the host. Furthermore, damage caused by lethal toxin is likely a contributing factor to the long-term pathologies displayed by surviving patients. It is critical, therefore, to gain a better understanding of how the toxin interacts with the host. Lethal factor is the enzymatic component of the toxin that cleaves mitogen activated protein kinase kinases after being delivered to the mammalian cell cytosol by the second toxin component, protective antigen. How lethal factor's enzymatic activity causes the cellular effects associated with the toxin is poorly understood.
The first aim of this proposal is to determine how lethal toxin interferes with cvtokine expression. We have discovered that lethal toxin destabilizes interleukin-8 mRNA in primary human endothelial cells. It has been shown that many transcripts are post-transcriptionally regulated by specific elements in their 3' untranslated regions and by the proteins that bind these regions. We will identify regulatory proteins and mRNA elements that are targeted by lethal toxin action; and identify other transcripts that are destabilized by the toxin.
Our second aim i s to determine how and why lethal toxin induces caspase-independent programmed cell death in human macrophages, but not in the immature monocvtes from which they were derived. We will use a combination of cellular fractionation and immunofluorescence techniques to identify proteins that mediate cell death; and compare toxin-sensitive and resistant cells to determine cellular properties that confer susceptibility to lethal toxin.
Our final aim i s to isolate lethal factor mutants that can cleave some of its substrates, but not others, so that the contributions of individual substrates to pathogenic processes can be assessed. To accomplish this, we will screen random lethal factor mutants for ones that are able to kill some cell types, but not others. This work will potentially identify new substrate binding determinants that could be targeted by therapeutics. ? ? Relevance: The goal of our research is to understand how anthrax lethal toxin damages human cells. A better understanding of how the toxin works will help doctors treat patients with anthrax and help researchers discover new drug treatments. ? ?

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Study Section
Host Interactions with Bacterial Pathogens Study Section (HIBP)
Program Officer
Breen, Joseph J
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University of Toronto
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M5 1-S8
Dennis, Melissa K; Mogridge, Jeremy (2014) A protective antigen mutation increases the pH threshold of anthrax toxin receptor 2-mediated pore formation. Biochemistry 53:2166-71
Neiman-Zenevich, Jana; Liao, Kuo-Chieh; Mogridge, Jeremy (2014) Distinct regions of NLRP1B are required to respond to anthrax lethal toxin and metabolic inhibition. Infect Immun 82:3697-703
Liao, Kuo-Chieh; Mogridge, Jeremy (2013) Activation of the Nlrp1b inflammasome by reduction of cytosolic ATP. Infect Immun 81:570-9
Garlick, Kristopher M; Batty, Sarah; Mogridge, Jeremy (2012) Binding of filamentous actin to anthrax toxin receptor 1 decreases its association with protective antigen. Biochemistry 51:1249-56
Frew, Bradley C; Joag, Vineet R; Mogridge, Jeremy (2012) Proteolytic processing of Nlrp1b is required for inflammasome activity. PLoS Pathog 8:e1002659
Chow, Edith M C; Batty, Sarah; Mogridge, Jeremy (2010) Anthrax lethal toxin promotes dephosphorylation of TTP and formation of processing bodies. Cell Microbiol 12:557-68
Ngai, Stephanie; Batty, Sarah; Liao, Kuo-Chieh et al. (2010) An anthrax lethal factor mutant that is defective at causing pyroptosis retains proapoptotic activity. FEBS J 277:119-27
Garlick, Kristopher M; Mogridge, Jeremy (2009) Direct interaction between anthrax toxin receptor 1 and the actin cytoskeleton. Biochemistry 48:10577-81
Go, Mandy Y; Chow, Edith M C; Mogridge, Jeremy (2009) The cytoplasmic domain of anthrax toxin receptor 1 affects binding of the protective antigen. Infect Immun 77:52-9
Liao, Kuo-Chieh; Mogridge, Jeremy (2009) Expression of Nlrp1b inflammasome components in human fibroblasts confers susceptibility to anthrax lethal toxin. Infect Immun 77:4455-62

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