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ArgR-regulated genes are derepressed in the Legionella-containing vacuole.

ABSTRACT: Legionella pneumophila is an intracellular pathogen that infects protozoa in aquatic environments and when inhaled by susceptible human hosts replicates in alveolar macrophages and can result in the often fatal pneumonia called Legionnaires' disease. The ability of L. pneumophila to replicate within host cells requires the establishment of a specialized compartment that evades normal phagolysosome fusion called the Legionella-containing vacuole (LCV). Elucidation of the biochemical composition of the LCV and the identification of the regulatory signals sensed during intracellular replication are inherently challenging. L-Arginine is a critical nutrient in the metabolism of both prokaryotic and eukaryotic organisms. We showed that the L. pneumophila arginine repressor homolog, ArgR, is required for maximal intracellular growth in the unicellular host Acanthamoeba castellanii. In this study, we present evidence that the concentration of L-arginine in the LCV is sensed by ArgR to produce an intracellular transcriptional response. We characterized the L. pneumophila ArgR regulon by global gene expression analysis, identified genes highly affected by ArgR, showed that ArgR repression is dependent upon the presence of L-arginine, and demonstrated that ArgR-regulated genes are derepressed during intracellular growth. Additional targets of ArgR that may account for the argR mutant's intracellular multiplication defect are discussed. These results suggest that L-arginine availability functions as a regulatory signal during Legionella intracellular growth.

SUBMITTER: Hovel-Miner G

PROVIDER: S-EPMC2937375 | biostudies-literature | 2010 Sep

REPOSITORIES: biostudies-literature

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ArgR-regulated genes are derepressed in the Legionella-containing vacuole.

Hovel-Miner Galadriel G Faucher Sebastien P SP Charpentier Xavier X Shuman Howard A HA

Journal of bacteriology 20100709 17

Legionella pneumophila is an intracellular pathogen that infects protozoa in aquatic environments and when inhaled by susceptible human hosts replicates in alveolar macrophages and can result in the often fatal pneumonia called Legionnaires' disease. The ability of L. pneumophila to replicate within host cells requires the establishment of a specialized compartment that evades normal phagolysosome fusion called the Legionella-containing vacuole (LCV). Elucidation of the biochemical composition o ...[more]

PMID: 20622069

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Project description:The inflammasome is essential for host defense against intracellular bacterial pathogens, including Legionella pneumophila, the causative agent of the severe pneumonia Legionnaires' disease. Inflammasomes recruit and activate caspases, which promote IL-1 family cytokine release and pyroptosis to restrict infection. In mice, interferon (IFN) signaling promotes inflammasome responses against L. pneumophila and other bacteria, in part, through inducing a family of IFN-inducible GTPases known as guanylate-binding proteins (GBPs). Within murine macrophages, IFN promotes the rupture of the L. pneumophila-containing vacuole (LCV), while GBPs are dispensable for vacuole rupture. Instead, GBPs facilitate the lysis of cytosol-exposed L. pneumophila. In contrast, the functions of IFN-γ and GBPs in human inflammasome responses to L. pneumophila are poorly understood. Here, we show that IFN-γ enhances caspase-1- and caspase-4-dependent inflammasome responses to L. pneumophila in human macrophages. We find that human GBP1 is required for these IFN-γ-driven inflammasome responses. Furthermore, we find that GBP1 co-localizes with L. pneumophila and/or LCVs in a type IV secretion system (T4SS)-dependent manner and facilitates damage to the LCV, resulting in increased bacterial access to the host cell cytosol. Our findings reveal species- and pathogen-specific differences in how GBPs function during infection. IMPORTANCE Inflammasomes are essential for host defense against intracellular bacterial pathogens like Legionella, as they activate caspases, which promote cytokine release and cell death to control infection. In mice, interferon (IFN) signaling promotes inflammasome responses against bacteria by inducing a family of IFN-inducible GTPases known as guanylate-binding proteins (GBPs). Within murine macrophages, IFN promotes the rupture of the Legionella-containing vacuole (LCV), while GBPs are dispensable for this process. Instead, GBPs facilitate the lysis of cytosol-exposed Legionella. In contrast, the functions of IFN and GBPs in human inflammasome responses to Legionella are poorly understood. We show that IFN-γ enhances inflammasome responses to Legionella in human macrophages. Human GBP1 is required for these IFN-γ-driven inflammasome responses. Furthermore, GBP1 co-localizes with Legionella and/or LCVs in a type IV secretion system (T4SS)-dependent manner and promotes damage to the LCV, which leads to increased exposure of the bacteria to the host cell cytosol. Thus, our findings reveal species- and pathogen-specific differences in how GBPs function to promote inflammasome responses.

Dataset Information

ArgR-regulated genes are derepressed in the Legionella-containing vacuole.

Publications

ArgR-regulated genes are derepressed in the Legionella-containing vacuole.

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