title: Novel role of the nitrite transporter NirC in Salmonella pathogenesis: SPI2-dependent suppression of inducible nitric oxide synthase in activated macrophages.
abstract: Activation of macrophages by interferon gamma (IFN-gamma) and the subsequent production of nitric oxide (NO) are critical for the host defence against Salmonella enterica serovar Typhimurium infection. We report here the inhibition of IFN-gamma-induced NO production in RAW264.7 macrophages infected with wild-type Salmonella. This phenomenon was shown to be dependent on the nirC gene, which encodes a potential nitrite transporter. We observed a higher NO output from IFN-gamma-treated macrophages infected with a nirC mutant of Salmonella. The nirC mutant also showed significantly decreased intracellular proliferation in a NO-dependent manner in activated RAW264.7 macrophages and in liver, spleen and secondary lymph nodes of mice, which was restored by complementing the gene in trans. Under acidified nitrite stress, a twofold more pronounced NO-mediated repression of SPI2 was observed in the nirC knockout strain compared to the wild-type. This enhanced SPI2 repression in the nirC knockout led to a higher level of STAT-1 phosphorylation and inducible nitric oxide synthase (iNOS) expression than seen with the wild-type strain. In iNOS knockout mice, the organ load of the nirC knockout strain was similar to that of the wild-type strain, indicating that the mutant is exclusively sensitive to the host nitrosative stress. Taken together, these results reveal that intracellular Salmonella evade killing in activated macrophages by downregulating IFN-gamma-induced NO production, and they highlight the critical role of nirC as a virulence gene.
authors.affiliation: Center for Infectious Disease Research and Biosafety Laboratories, Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Priyanka
authors.initials: P
authors.lastname: Das
authors.affiliation: Center for Infectious Disease Research and Biosafety Laboratories, Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Amit
authors.initials: A
authors.lastname: Lahiri
authors.affiliation: Center for Infectious Disease Research and Biosafety Laboratories, Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Ayan
authors.initials: A
authors.lastname: Lahiri
authors.affiliation: Center for Infectious Disease Research and Biosafety Laboratories, Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Dipshikha
authors.initials: D
authors.lastname: Chakravortty
mesh_terms: D000818:Animals; D027321:Anion Transport Proteins / Q000502:physiology*; D001426:Bacterial Proteins / Q000378:metabolism* / Q000502:physiology*; D018929:Cell Culture Techniques; D015964:Gene Expression Regulation, Bacterial; D054884:Host-Pathogen Interactions; D007371:Interferon-gamma / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism / Q000382:microbiology*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D009569:Nitric Oxide / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism*; D010766:Phosphorylation; D050794:STAT1 Transcription Factor / Q000378:metabolism; D012475:Salmonella / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology*; D012481:Salmonella Infections, Animal / Q000378:metabolism / Q000382:microbiology*; D014774:Virulence
chemical_list: D027321:Anion Transport Proteins; D001426:Bacterial Proteins; D008565:Membrane Proteins; C088104:NirC protein, Bacteria; C440638:SPI-2 protein, Salmonella; D050794:STAT1 Transcription Factor; D009569:Nitric Oxide; D007371:Interferon-gamma; D052247:Nitric Oxide Synthase Type II