Branchu Priscilla, Matrat Stéphanie, Vareille Marjolaine, Garrivier Annie, Durand Alexandra, Crépin Sébastien, Harel Josée, Jubelin Grégory, Gobert Alain P
INRA, UR454 Microbiologie, Centre de Clermont-Ferrand-Theix, Saint-Genès-Champanelle, France.
Groupe de Recherche sur les Maladies Infectieuses du Porc and Centre de Recherche en Infectiologie Porcine, Université de Montréal, Saint-Hyacinthe, Québec, Canada.
PLoS Pathog. 2014 Jan;10(1):e1003874. doi: 10.1371/journal.ppat.1003874. Epub 2014 Jan 9.
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.
肠细胞脱落位点（LEE）基因的表达对于肠出血性大肠杆菌（EHEC）黏附于肠道上皮细胞至关重要。因此，可能调节LEE基因表达的肠道因子可能会影响感染的结果。由于一氧化氮（NO）是肠道免疫反应的关键效应因子，可能诱导肠杆菌中的转录调控，我们研究了其对EHEC O157:H7中LEE表达的影响。我们证明，NO抑制属于LEE1、LEE4和LEE5操纵子的基因表达，并且NO传感器亚硝酸盐敏感阻遏物（NsrR）通过直接与RNA聚合酶复合物相互作用，是这些操纵子的正调控因子。在有NO的情况下，NsrR从LEE1/4/5启动子区域脱离，不激活转录。同时，耐酸途径的两个调节因子GadE和GadX通过间接的NsrR依赖性机制被NO诱导。在这种情况下，我们表明，NO依赖的LEE1下调是由于缺乏NsrR介导的激活以及GadX的阻遏作用。此外，NO对LEE4和LEE5表达的抑制是由于NsrR介导的激活丧失、LEE1下调以及GadE上调。最后，我们确定化学或细胞来源的NO抑制EHEC对人肠道上皮细胞的黏附。这些结果突出了NsrR在调节LEE致病岛中的关键作用以及NO在限制EHEC定植中的潜在作用。
