Article

Francisella tularensis LVS folate metabolism and pseudouridine synthase gene mutants modulate macrophage caspase-1 activation.

Inflammation Program.
Infection and immunity (Impact Factor: 4.16). 10/2012; DOI: 10.1128/IAI.00991-12
Source: PubMed

ABSTRACT Francisella tularensis is a Gram-negative bacterium and the causative agent of the disease tularemia. Escape of F. tularensis from the phagosome into the cytosol of the macrophage triggers the activation of the AIM2 inflammasome through a mechanism that is not well understood. Activation of the AIM2 inflammasome results in autocatalytic cleavage of caspase-1, resulting in the processing and secretion of IL-1β and IL-18, which play a crucial role in innate immune responses against F. tularensis. We have identified the 5-formyltetrahydrofolate cycloligase gene (FTL_0724) as being important for F. tularensis live vaccine strain (LVS) virulence. Infection of mice in vivo with a F. tularensis LVS FTL_0724 mutant resulted in diminished mortality compared to mice infected with wild-type LVS. The FTL_0724 mutant also induced increased inflammasome-dependent IL-1β and IL-18 secretion and cytotoxicity in macrophages in vitro. In contrast, infection of macrophages with a F. tularensis LVS rluD pseudouridine synthase (FTL_0699) mutant resulted in diminished IL-1β and IL-18 secretion from macrophages in vitro compared to macrophages infected with wild-type LVS. In addition the FTL_0699 mutant was not attenuated in vivo. These findings further illustrate that F. tularensis LVS possesses numerous genes that influence its ability to activate the inflammasome, which is a key host strategy to control infection with this pathogen in vivo.

Download full-text

Full-text

Available from: Ann M Janowski, Jul 08, 2014
0 Followers
 · 
103 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Escherichia coli K12 is a commensal bacteria and one of the best-studied model organisms. Salmonella enterica serovar Typhimurium, on the other hand, is a facultative intracellular pathogen. These two prokaryotic species can be considered related phylogenetically and they share a large amount of their genetic material, which is commonly termed the 'core genome'. Despite their shared core genome, both species display very different life styles and it is unclear to what extent the core genome, apart from the species-specific genes, plays a role in this lifestyle divergence. In this study, we focus on the differences in expression domains for the orthologous genes in E. coli and S. Typhimurium. The iterative comparison of coexpression methodology was used on large expression compendia of both species to uncover the conservation and divergence of gene expression. We found that gene expression conservation occurs mostly independent from amino acid similarity. According to our estimates, at least more than one quarter of the orthologous genes has a different expression domain in E. coli than in S. Typhimurium. Genes involved with key cellular processes are most likely to have conserved their expression domains whereas genes showing diverged expression are associated with metabolic processes that, although present in both species, are regulated differently. The expression domains of the shared 'core' genome of E. coli and S. Typhimurium, consisting of highly conserved orthologs, have been tuned to help accommodate the differences in lifestyle and the pathogenic potential of Salmonella.
    Molecular Biology and Evolution 02/2013; DOI:10.1093/molbev/mst029 · 14.31 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In the aftermath of the 2001 anthrax attacks in the U.S., numerous efforts were made to increase the level of preparedness against a biological attack both in the US and worldwide. As a result, there has been an increase in research interest in the development of vaccines and other countermeasures against a number of agents with the potential to be used as biological weapons. One such agent, Francisella tularensis, has been the subject of a surge in the level of research being performed, leading to a substantial increase in knowledge of the pathogenic mechanisms of the organism and the induced immune responses. This information has facilitated the development of multiple new Francisella vaccine candidates. Herein we review the latest live attenuated F. tularensis vaccine efforts. Historically, live attenuated vaccines have demonstrated the greatest degree of success in protection against tularemia and the greatest promise in recent efforts to develop of a fully protective vaccine. This review summarizes recent live attenuated Francisella vaccine candidates and the lessons learned from those studies, with the goal of collating known characteristics associated with successful attenuation, immunogenicity, and protection.
    Vaccine 06/2013; 31(35). DOI:10.1016/j.vaccine.2013.05.096 · 3.49 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Francisella tularensis is an important human pathogen responsible for causing tularemia. F. tularensis has long been developed as a biological weapon and is now classified as a category A agent by the CDC on account of its possible use as a bioterror agent. F. tularensis represses inflammasome; a cytosolic multi-protein complex that activates caspase-1 to produce pro-inflammatory cytokines IL-1β and IL-18. However, the Francisella factors and the mechanisms through which F. tularensis mediates these suppressive effects remain relatively unknown. Utilizing a mutant of F. tularensis in FTL_0325 gene, this study investigated the mechanisms of inflammasome repression by F. tularensis. We demonstrate that muted IL-1β and IL-18 responses generated in macrophages infected with F. tularensis LVS or the virulent SchuS4 strain are due to a predominant suppressive effect on TLR2-dependent signal 1. Our results also demonstrate that FTL_0325 of F. tularensis impacts proIL-1β expression as early as two hrs post-infection and delays activation of AIM2 and NLRP3-inflammasomes in a TLR2-dependent fashion. An enhanced activation of caspase-1 and IL-1β observed in FTL_0325 mutant infected macrophages at 24 hrs post-infection was independent of both AIM2 and NLRP3. Further, F. tularensis LVS delayed pyroptotic cell death of the infected macrophages in a FTL_0325 dependent manner during the early stages of infection. In vivo studies in mice revealed that suppression of IL-1β by FTL_0325 early during infection facilitates the establishment of a fulminate infection by F. tularensis. Collectively, this study provides evidence that F. tularensis LVS represses inflammasome activation and that F. tularensis encoded FTL_0325 mediates this effect.
    Journal of Biological Chemistry 07/2013; DOI:10.1074/jbc.M113.490086 · 4.60 Impact Factor