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IFN? inhibits the cytosolic replication of Shigella flexneri via the cytoplasmic RNA sensor RIG-I.

ABSTRACT: The activation of host cells by interferon gamma (IFN?) is essential for inhibiting the intracellular replication of most microbial pathogens. Although significant advances have been made in identifying IFN?-dependent host factors that suppress intracellular bacteria, little is known about how IFN? enables cells to recognize, or restrict, the growth of pathogens that replicate in the host cytoplasm. The replication of the cytosolic bacterial pathogen Shigella flexneri is significantly inhibited in IFN?-stimulated cells, however the specific mechanisms that mediate this inhibition have remained elusive. We found that S. flexneri efficiently invades IFN?-activated mouse embryonic fibroblasts (MEFs) and escapes from the vacuole, suggesting that IFN? acts by blocking S. flexneri replication in the cytosol. This restriction on cytosolic growth was dependent on interferon regulatory factor 1 (IRF1), an IFN?-inducible transcription factor capable of inducing IFN?-mediated cell-autonomous immunity. To identify host factors that restrict S. flexneri growth, we used whole genome microarrays to identify mammalian genes whose expression in S. flexneri-infected cells is controlled by IFN? and IRF1. Among the genes we identified was the pattern recognition receptor (PRR) retanoic acid-inducible gene I (RIG-I), a cytoplasmic sensor of foreign RNA that had not been previously known to play a role in S. flexneri infection. We found that RIG-I and its downstream signaling adaptor mitochondrial antiviral signaling protein (MAVS)--but not cytosolic Nod-like receptors (NLRs)--are critically important for IFN?-mediated S. flexneri growth restriction. The recently described RNA polymerase III pathway, which transcribes foreign cytosolic DNA into the RIG-I ligand 5'-triphosphate RNA, appeared to be involved in this restriction. The finding that RIG-I responds to S. flexneri infection during the IFN? response extends the range of PRRs that are capable of recognizing this bacterium. Additionally, these findings expand our understanding of how IFN? recognizes, and ultimately restricts, bacterial pathogens within host cells.

SUBMITTER: Jehl SP

PROVIDER: S-EPMC3415441 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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IFNγ inhibits the cytosolic replication of Shigella flexneri via the cytoplasmic RNA sensor RIG-I.

Jehl Stephanie P SP Nogueira Catarina V CV Zhang Xuqing X Starnbach Michael N MN

PLoS pathogens 20120809 8

The activation of host cells by interferon gamma (IFNγ) is essential for inhibiting the intracellular replication of most microbial pathogens. Although significant advances have been made in identifying IFNγ-dependent host factors that suppress intracellular bacteria, little is known about how IFNγ enables cells to recognize, or restrict, the growth of pathogens that replicate in the host cytoplasm. The replication of the cytosolic bacterial pathogen Shigella flexneri is significantly inhibited ...[more]

PMID: 22912573

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Project description:Shigella flexneri is an intracellular human pathogen that invades colonic cells and causes bloody diarrhea. S. flexneri evolved from commensal Escherichia coli, and genome comparisons reveal that S. flexneri has lost approximately 20% of its genes through the process of pathoadaptation, including a disproportionate number of genes associated with the turnover of the nucleotide-based second messenger cyclic di-GMP (c-di-GMP); however, the remaining c-di-GMP turnover enzymes are highly conserved. c-di-GMP regulates many behavioral changes in other bacteria in response to changing environmental conditions, including biofilm formation, but this signaling system has not been examined in S. flexneri. In this study, we expressed VCA0956, a constitutively active c-di-GMP synthesizing diguanylate cyclase (DGC) from Vibrio cholerae, in S. flexneri to determine if virulence phenotypes were regulated by c-di-GMP. We found that expressing VCA0956 in S. flexneri increased c-di-GMP levels, and this corresponds with increased biofilm formation and reduced acid resistance, host cell invasion, and plaque size. We examined the impact of VCA0956 expression on the S. flexneri transcriptome and found that genes related to acid resistance were repressed, and this corresponded with decreased survival to acid shock. We also found that individual S. flexneri DGC mutants exhibit reduced biofilm formation and reduced host cell invasion and plaque size, as well as increased resistance to acid shock. This study highlights the importance of c-di-GMP signaling in regulating S. flexneri virulence phenotypes. IMPORTANCE The intracellular human pathogen Shigella causes dysentery, resulting in as many as one million deaths per year. Currently, there is no approved vaccine for the prevention of shigellosis, and the incidence of antimicrobial resistance among Shigella species is on the rise. Here, we explored how the widely conserved c-di-GMP bacterial signaling system alters Shigella behaviors associated with pathogenesis. We found that expressing or removing enzymes associated with c-di-GMP synthesis results in changes in Shigella's ability to form biofilms, invade host cells, form lesions in host cell monolayers, and resist acid stress.

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IFN? inhibits the cytosolic replication of Shigella flexneri via the cytoplasmic RNA sensor RIG-I.

Publications

IFNγ inhibits the cytosolic replication of Shigella flexneri via the cytoplasmic RNA sensor RIG-I.

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