Bodero Maria D, Harden Elizabeth A, Munson George P
Department of Microbiology and Immunology, University of Miami Miller School of Medicine, Miami, FL 33101, USA.
BMC Microbiol. 2008 Oct 14;8:180. doi: 10.1186/1471-2180-8-180.
Enterotoxigenic Escherichia coli (ETEC) is a major cause of infant and child mortality in developing countries. This enteric pathogen causes profuse watery diarrhea by elaborating one or more enterotoxins that intoxicate eukaryotic cells and ultimately leads to a loss of water to the intestinal lumen. Virulence is also dependent upon fimbrial adhesins that facilitate colonization of the small intestine.
The expression of CS1 fimbriae is positively regulated by Rns, a member of the AraC/XylS superfamily of transcriptional regulators. Based on fimbrial protein homology, CS1 fimbriae have been categorized as subclass 5b along with CS17, CS19, and PCFO71 fimbriae. In this study we show that Rns positively regulates the expression of these other subclass 5b members. DNase I footprinting revealed a Rns binding site adjacent to the -35 hexamer of each fimbrial promoter. The CS17 and PCFO71 fimbrial promoters carry a second Rns binding site centered at -109.5, relative to the Rns-dependent transcription start site. This second binding site is centered at -108.5 for the CS19 promoter. Mutagenesis of either site reduced Rns-dependent transcription from each promoter indicating that the molecules bound to these sites apparently function independently of one another, with each having an additive effect upon fimbrial promoter activation.
This study demonstrates that the ETEC virulence regulator Rns is required for the expression of all known 5b fimbriae. Since Rns is also known to control the expression of additional ETEC fimbriae, including those within subclasses 5a and 5c, the inactivation or inhibition of Rns could be an effective strategy to prevent ETEC infections.
产肠毒素大肠杆菌（ETEC）是发展中国家婴幼儿死亡的主要原因。这种肠道病原体通过产生一种或多种肠毒素来引起大量水样腹泻，这些肠毒素会使真核细胞中毒，最终导致水分流失到肠腔。毒力还取决于有助于在小肠定植的菌毛黏附素。
CS1菌毛的表达受Rns正向调控，Rns是转录调节因子AraC/XylS超家族的成员。基于菌毛蛋白同源性，CS1菌毛与CS17、CS19和PCFO71菌毛一起被归类为5b亚类。在本研究中，我们表明Rns正向调控这些其他5b亚类成员的表达。DNase I足迹分析揭示了一个与每个菌毛启动子的-35六聚体相邻的Rns结合位点。相对于Rns依赖的转录起始位点，CS17和PCFO71菌毛启动子带有第二个以-109.5为中心的Rns结合位点。对于CS19启动子，这个第二个结合位点以-108.5为中心。任一位点的诱变都会降低每个启动子的Rns依赖转录，这表明与这些位点结合的分子显然彼此独立发挥作用，每个位点对菌毛启动子激活都有累加效应。
本研究表明，ETEC毒力调节因子Rns是所有已知5b菌毛表达所必需的。由于已知Rns还控制其他ETEC菌毛的表达，包括5a和5c亚类中的菌毛，因此使Rns失活或抑制Rns可能是预防ETEC感染的有效策略。
