Interleukin-5 and eosinophil cationic protein in nasal lavages of rhinitis patients

The production of interleukin-5 and eosinophil cationic protein (ECP) in the nasal cavity was examined in 24 patients with rhinitis who were allergic to the house dust mite. During a double-blind placebo-controlled cross-over study, fluticasone propionate aqueous nasal spray (200 μg) was administered twice daily for 2 weeks. After four basal nasal lavages provocation with house dust mite extract was performed and nasal lavages were collected every hour for 9.5 h. Interleukin-5 was present in detectable amounts in nasal lavages from patients allergic to house dust mite. Nasal challenge with house dust mite extract caused immediate nasal symptoms and increased levels of interleukin-5. Between 3.5 and 8.5 h after the challenge symptoms recurred and interleukin-5 levels increased, reflecting a late phase reaction. Eosinophil cationic protein, a marker of activated eosinophils, was released between 6.5 and 9.5 h after challenge. Treatment with fluticasone propionate (as an aqueous nasal spray) significantly decreased the evoked interleukin-5 and ECP levels in the late phase reaction. This response was correlated with an improved symptom score. This could indicate that the number and activity of eosinophils are increased during the late phase allergic reaction, a response that is inhibited by corticosteroids

A bacterial protein targets the BAHD1 chromatin complex to stimulate type III interferon response

International audienceIntracellular pathogens such as $Listeria\ monocytogenes$ subvert cellular functions through the interaction of bacterial effectors with host components. Here we found that a secreted listerial virulence factor, LntA, could target the chromatin repressor BAHD1 in the host cell nucleus to activate interferon IFN-stimulated genes (ISGs). IFN-$\lambda$ expression was induced in response to infection of epithelial cells with bacteria lacking LntA; however, the BAHD1-chromatin associated complex repressed downstream ISGs. In contrast, in cells infected with $lntA$-expressing bacteria, LntA prevented BAHD1 recruitment to ISGs and stimulated their expression. Murine listeriosis decreased in BAHD1$^{+/-}$ mice or when $lntA$ was constitutively expressed. Thus, the LntA-BAHD1 interplay may modulate IFN-$\lambda$-mediated immune response to control bacterial colonization of the host

An RNA-Binding Protein Secreted by a Bacterial Pathogen Modulates RIG-I Signaling.

RNA-binding proteins (RBPs) perform key cellular activities by controlling the function of bound RNAs. The widely held assumption that RBPs are strictly intracellular has been challenged by the discovery of secreted RBPs. However, extracellular RBPs have been described in eukaryotes, while secreted bacterial RBPs have not been reported. Here, we show that the bacterial pathogen Listeria monocytogenes secretes a small RBP that we named Zea. We show that Zea binds a subset of L. monocytogenes RNAs, causing their accumulation in the extracellular medium. Furthermore, during L. monocytogenes infection, Zea binds RIG-I, the non-self-RNA innate immunity sensor, potentiating interferon-β production. Mouse infection studies reveal that Zea affects L. monocytogenes virulence. Together, our results unveil that bacterial RNAs can be present extracellularly in association with RBPs, acting as "social RNAs" to trigger a host response during infection

Recruitment of the Major Vault Protein by InlK: A Listeria monocytogenes Strategy to Avoid Autophagy

L. monocytogenes is a facultative intracellular bacterium responsible for listeriosis. It is able to invade, survive and replicate in phagocytic and non-phagocytic cells. The infectious process at the cellular level has been extensively studied and many virulence factors have been identified. Yet, the role of InlK, a member of the internalin family specific to L. monocytogenes, remains unknown. Here, we first show using deletion analysis and in vivo infection, that InlK is a bona fide virulence factor, poorly expressed in vitro and well expressed in vivo, and that it is anchored to the bacterial surface by sortase A. We then demonstrate by a yeast two hybrid screen using InlK as a bait, validated by pulldown experiments and immunofluorescence analysis that intracytosolic bacteria via an interaction with the protein InlK interact with the Major Vault Protein (MVP), the main component of cytoplasmic ribonucleoproteic particules named vaults. Although vaults have been implicated in several cellular processes, their role has remained elusive. Our analysis demonstrates that MVP recruitment disguises intracytosolic bacteria from autophagic recognition, leading to an increased survival rate of InlK over-expressing bacteria compared to InlK− bacteria. Together these results reveal that MVP is hijacked by L. monocytogenes in order to counteract the autophagy process, a finding that could have major implications in deciphering the cellular role of vault particles

Lmo1656 is a secreted virulence factor of Listeria monocytogenes that interacts with the sorting nexin 6-BAR complex

Listeria monocytogenes (Lm) is a facultative intracellular bacterial pathogen and the causative agent of listeriosis, a rare but fatal disease. During infection, Lm can traverse several physiological barriers; it can cross the intestine and placenta barrier and, in immunocompromised individuals, the blood-brain barrier. With the recent plethora of sequenced genomes available for Lm, it is clear that the complete repertoire of genes used by Lm to interact with its host remains to be fully explored. Recently, we focused on secreted Lm proteins because they are likely to interact with host cell components. Here, we investigated a putatively secreted protein of Lm, Lmo1656, that is present in most sequenced strains of Lm but absent in the nonpathogenic species Listeria innocua. lmo1656 gene is predicted to encode a small, positively charged protein. We show that Lmo1656 is secreted by Lm. Furthermore, deletion of the lmo1656 gene (Δlmo1656) attenuates virulence in mice infected orally but not intravenously, suggesting that Lmo1656 plays a role during oral listeriosis. We identified sorting nexin 6 (SNX6), an endosomal sorting component and BAR domain-containing protein, as a host cell interactor of Lmol656. SNX6 colocalizes with WT Lm during the early steps of infection. This colocalization depends on Lmo1656, and RNAi of SNX6 impairs infection in infected tissue culture cells, suggesting that SNX6 is utilized by Lm during infection. Our results reveal that Lmo1656 is a novel secreted virulence factor of Lm that facilitates recruitment of a specific member of the sorting nexin family in the mammalian host

Control of Listeria superoxide dismutase by phosphorylation

International audienceSuperoxide dismutases (SODs) are enzymes that protect organisms against superoxides and reactive oxygen species (ROS) produced during their active metabolism. ROS are major mediators of phagocytes microbicidal activity. Here we show that the cytoplasmic Listeria monocytogenes MnSOD is phosphorylated on serine and threonine residues and less active when bacteria reach the stationary phase. We also provide evidence that the most active nonphosphorylated form of MnSOD can be secreted via the SecA2 pathway in culture supernatants and in infected cells, where it becomes phosphorylated. A Deltasod deletion mutant is impaired in survival within macrophages and is dramatically attenuated in mice. Together, our results demonstrate that the capacity to counteract ROS is an essential component of L. monocytogenes virulence. This is the first example of a bacterial SOD post-translationally controlled by phosphorylation, suggesting a possible new host innate mechanism to counteract a virulence factor

Lmo1656 is a secreted virulence factor of Listeria monocytogenes that interacts with the sorting nexin 6–BAR complex

International audienceListeria monocytogenes (Lm) is a facultative intracellular bacterial pathogen and the causative agent of listeriosis, a rare but fatal disease. During infection, Lm can traverse several physiological barriers; it can cross the intestine and placenta barrier and, in immunocompromised individuals, the blood– brain barrier. With the recent plethora of sequenced genomes available for Lm, it is clear that the complete repertoire of genes used by Lm to interact with its host remains to be fully explored. Recently, we focused on secreted Lm proteins because they are likely to interact with host cell components. Here, we investigated a putatively secreted protein of Lm, Lmo1656, that is present in most sequenced strains of Lm but absent in the nonpathogenic species Listeria innocua. lmo1656 gene is predicted to encode a small, positively charged protein. We show that Lmo1656 is secreted by Lm. Furthermore, deletion of the lmo1656 gene (lmo1656) attenuates virulence in mice infected orally but not intravenously, suggesting that Lmo1656 plays a role during oral listeriosis. We identified sorting nexin 6 (SNX6), an endosomal sorting component and BAR domain– containing protein, as a host cell interactor of Lmol656. SNX6 colocal-izes with WT Lm during the early steps of infection. This colocalization depends on Lmo1656, and RNAi of SNX6 impairs infection in infected tissue culture cells, suggesting that SNX6 is utilized by Lm during infection. Our results reveal that Lmo1656 is a novel secreted virulence factor of Lm that facilitates recruitment of a specific member of the sorting nexin family in the mam-malian host. The foodborne pathogen Listeria monocytogenes (Lm) 5 can cross several physiological barriers and infect multiple cell types. The pathogenic potential of Lm relies on the ability of this bacterium to cross multiple physiological barriers as well as its ability to enter and replicate within a wide variety of host cell types (for recent reviews, see Refs. 1 and 2). Upon binding to host cell surface receptors, Lm induces its internalization into both professional phagocytes and nonphagocytic cells (for a recent review, see Ref. 2). From there, Lm escapes into the cyto-sol by rupturing its vacuole. Lm is able to evade host cell immune responses (for a recent review, see Ref. 3) and subvert the host cell actin cytoskeleton to drive intra-and intercellular motility (for recent reviews, see Refs. 4 –6). Secreted and surface-exposed Lm proteins can encounter host components and serve as virulence factors. For example, the secreted pore-forming toxin listeriolysin O (LLO) is one of the most well-characterized and potent virulence factors of Lm (for a review, see Ref. 7). Secretion of LLO occurs prior to Lm entry into the host cell. It inserts into the host plasma membrane and makes large pores. The resulting ion flux drives a diverse array of responses within the cell from global deSUMOylation (8) to mitochondrial fragmentation (9). Upon entry, Lm can escape into the host cytosol by lysing the phagosomal membrane through the combined actions of secreted LLO and phospholipases A and B (PlcA and PlcB) (10 –12). Recent work has uncovered novel secreted Lm virulence factors and their binding partners in the host cell. The secreted protein Listeria nuclear targeted protein A (LntA) targets the host epigenetic regulator BAHD1, altering host cell transcription (13). The small secreted protein internalin C (InlC) sequesters Tuba, a Cdc42 guanine exchange factor, to induce relaxation of membrane cortical tension, thereby facilitating increased bacterial cell-to-cell spread (14, 15). InlC also directly binds to host IB kinase , interfering with host innate immunity (16). The recent plethora of genomics data and the rise of bioin-formatics pipelines have enabled the rapid comparison of mu

Riboswitches. Sequestration of a two-component response regulator by a riboswitch-regulated noncoding RNA.

International audienceRiboswitches are ligand-binding elements contained within the 5' untranslated regions of bacterial transcripts, which generally regulate expression of downstream open reading frames. Here, we show that in Listeria monocytogenes, a riboswitch that binds vitamin B12 controls expression of a noncoding regulatory RNA, Rli55. Rli55, in turn, controls expression of the eut genes, whose products enable ethanolamine utilization and require B12 as a cofactor. Defects in ethanolamine utilization, or in its regulation by Rli55, significantly attenuate Listeria virulence in mice. Rli55 functions by sequestering the two-component response regulator EutV by means of a EutV-binding site contained within the RNA. Thus, Rli55 is a riboswitch-regulated member of the small group of regulatory RNAs that function by sequestering a protein and reveals a distinctive mechanism of signal integration in bacterial gene regulation