title: NsrR, GadE, and GadX interplay in repressing expression of the Escherichia coli O157:H7 LEE pathogenicity island in response to nitric oxide.
abstract: Expression of genes of the locus of enterocyte effacement (LEE) is essential for adherence of enterohemorrhagic Escherichia coli (EHEC) to intestinal epithelial cells. Gut factors that may modulate LEE gene expression may therefore influence the outcome of the infection. Because nitric oxide (NO) is a critical effector of the intestinal immune response that may induce transcriptional regulation in enterobacteria, we investigated its influence on LEE expression in EHEC O157:H7. We demonstrate that NO inhibits the expression of genes belonging to LEE1, LEE4, and LEE5 operons, and that the NO sensor nitrite-sensitive repressor (NsrR) is a positive regulator of these operons by interacting directly with the RNA polymerase complex. In the presence of NO, NsrR detaches from the LEE1/4/5 promoter regions and does not activate transcription. In parallel, two regulators of the acid resistance pathway, GadE and GadX, are induced by NO through an indirect NsrR-dependent mechanism. In this context, we show that the NO-dependent LEE1 down-regulation is due to absence of NsrR-mediated activation and to the repressor effect of GadX. Moreover, the inhibition of expression of LEE4 and LEE5 by NO is due to loss of NsrR-mediated activation, to LEE1 down-regulation and to GadE up-regulation. Lastly, we establish that chemical or cellular sources of NO inhibit the adherence of EHEC to human intestinal epithelial cells. These results highlight the critical effect of NsrR in the regulation of the LEE pathogenicity island and the potential role of NO in the limitation of colonization by EHEC.
authors.affiliation: INRA, UR454 Microbiologie, Centre de Clermont-Ferrand-Theix, Saint-Genès-Champanelle, France.
authors.forename: Priscilla
authors.initials: P
authors.lastname: Branchu
authors.affiliation: INRA, UR454 Microbiologie, Centre de Clermont-Ferrand-Theix, Saint-Genès-Champanelle, France.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Matrat
authors.affiliation: INRA, UR454 Microbiologie, Centre de Clermont-Ferrand-Theix, Saint-Genès-Champanelle, France.
authors.forename: Marjolaine
authors.initials: M
authors.lastname: Vareille
authors.affiliation: INRA, UR454 Microbiologie, Centre de Clermont-Ferrand-Theix, Saint-Genès-Champanelle, France.
authors.forename: Annie
authors.initials: A
authors.lastname: Garrivier
authors.affiliation: INRA, UR454 Microbiologie, Centre de Clermont-Ferrand-Theix, Saint-Genès-Champanelle, France.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Durand
authors.affiliation: Groupe de Recherche sur les Maladies Infectieuses du Porc and Centre de Recherche en Infectiologie Porcine, Université de Montréal, Saint-Hyacinthe, Québec, Canada.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Crépin
authors.affiliation: Groupe de Recherche sur les Maladies Infectieuses du Porc and Centre de Recherche en Infectiologie Porcine, Université de Montréal, Saint-Hyacinthe, Québec, Canada.
authors.forename: Josée
authors.initials: J
authors.lastname: Harel
authors.affiliation: INRA, UR454 Microbiologie, Centre de Clermont-Ferrand-Theix, Saint-Genès-Champanelle, France.
authors.forename: Grégory
authors.initials: G
authors.lastname: Jubelin
authors.affiliation: INRA, UR454 Microbiologie, Centre de Clermont-Ferrand-Theix, Saint-Genès-Champanelle, France.
authors.forename: Alain P
authors.initials: AP
authors.lastname: Gobert
mesh_terms: D051777:AraC Transcription Factor / Q000096:biosynthesis* / Q000235:genetics; D001422:Bacterial Adhesion / Q000502:physiology; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D004847:Epithelial Cells / Q000378:metabolism / Q000382:microbiology; D019453:Escherichia coli O157 / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000096:biosynthesis* / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D044404:Genomic Islands / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism / Q000382:microbiology; D009569:Nitric Oxide / Q000378:metabolism*; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D051777:AraC Transcription Factor; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C479562:GadE protein, E coli; C446316:GadX protein, E coli; C529899:NsrR protein, E coli; D014157:Transcription Factors; D009569:Nitric Oxide