title: Codependent and independent effects of nitric oxide-mediated suppression of PhoPQ and Salmonella pathogenicity island 2 on intracellular Salmonella enterica serovar typhimurium survival.
abstract: Here we show that the Salmonella enterica serovar Typhimurium PhoQ sensor kinase lessens the cytotoxicity of reactive nitrogen species (RNS) generated by inducible nitric oxide synthase (iNOS) in the innate response of mononuclear phagocytic cells. This observation is consistent with the expression patterns of PhoP-activated genes during moderate nitrosative stress in the innate host response. In contrast, RNS synthesized during high-NO fluxes of gamma interferon (IFN-gamma)-activated macrophages repress PhoP-activated lpxO, pagP, and phoP gene transcription. Because PhoP-regulated Salmonella pathogenicity island 2 (SPI2) genes are also repressed by high-order RNS (39), we investigated whether the NO-mediated inhibition of PhoPQ underlies the repression of SPI2. Our studies indicate that a third of the expression of the SPI2 spiC gene recorded in nonactivated macrophages depends on PhoQ. Transcription of spiC is repressed in IFN-gamma-primed macrophages in an iNOS-dependent manner, irrespective of the phoQ status of the bacteria. Transcription of spiC is restored in IFN-gamma-treated, iNOS-deficient macrophages to levels sustained by a phoQ mutant in nonactivated phagocytes, suggesting that most NO-dependent repression of spiC is due to the inhibition of PhoPQ-independent targets. Comparison of the intracellular fitness of spiC, phoQ, and spiC phoQ mutants revealed that PhoPQ and SPI2 have codependent and independent effects on S. Typhimurium survival during innate nitrosative stress. However, the intracellular survival of most S. Typhimurium bacteria is conferred by the PhoPQ two-component regulator, and the SPI2 type III secretion system is repressed by high-order RNS of IFN-gamma-activated macrophages.
authors.affiliation: Department of Microbiology, University of Colorado at Denver School of Medicine, Mail Stop 8333, P.O. Box 6511, Aurora, CO 80045, USA.
authors.forename: Travis J
authors.initials: TJ
authors.lastname: Bourret
authors.forename: Miryoung
authors.initials: M
authors.lastname: Song
authors.forename: Andrés
authors.initials: A
authors.lastname: Vázquez-Torres
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D006790:Host-Parasite Interactions; D007371:Interferon-gamma / Q000276:immunology / Q000378:metabolism; D008262:Macrophage Activation / Q000276:immunology; D008264:Macrophages / Q000276:immunology / Q000382:microbiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009569:Nitric Oxide / Q000378:metabolism* / Q000494:pharmacology; D052247:Nitric Oxide Synthase Type II / Q000172:deficiency / Q000235:genetics; D026361:Reactive Nitrogen Species / Q000276:immunology / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012480:Salmonella Infections / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D012486:Salmonella typhimurium / Q000235:genetics / Q000276:immunology; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; C079792:PhoQ protein, Bacteria; D026361:Reactive Nitrogen Species; C440638:SPI-2 protein, Salmonella; C120280:SpiC protein, Salmonella; D009569:Nitric Oxide; D007371:Interferon-gamma; D052247:Nitric Oxide Synthase Type II