The GrlR-GrlA regulatory system coordinately controls the expression of flagellar and LEE-encoded type III protein secretion systems in enterohemorrhagic Escherichia coli
The GrlR-GrlA regulatory system coordinately controls the expression of flagellar and LEE-encoded type III protein secretion systems in enterohemorrhagic Escherichia coli
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DOI：
10.1128/jb.00352-06
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发表时间：
2006-08-01
影响因子：
3.2
通讯作者：
Watanabe, Haruo
中科院分区：
文献类型：
--
作者：
Iyoda, Sunao;Koizumi, Nobuo;Watanabe, Haruo
肠细胞消失位点 (LEE) 的基因功能对于肠出血性大肠杆菌 (EHEC) 的完全毒力至关重要。 LEE 基因表达的严格控制是由多个调控元件的协调活动介导的。我们之前报道过 ClpX/ClpP 蛋白酶通过下调细胞内 GrIR 水平（LEE 基因表达的负调节因子）来正控制 LEE 表达。我们进一步揭示，GrIR 对 LEE 表达的负面影响是通过 GrIA（LEE 表达的正调节因子）介导的。在这项研究中，我们发现 FliC 蛋白（鞭毛丝的主要成分）在 clpXP 突变型肠出血性大肠杆菌中过量产生，正如之前针对沙门氏菌报道的那样。我们进一步发现 clpXP grlR 双突变体中 FliC 表达减少。为了确定该表型的介体，比较了野生型、grlR、grL4 和 grlR grL4 菌株中的 FliC 蛋白水平。 FliC 蛋白的稳态水平仅在 grlR 突变体中降低，表明 GrIR 对 FliC 表达的正向调节是由 GrIA 介导的。相应地，在grlR突变体中细胞运动性也降低，但在grL4或grlR grL4突变体中则没有。由于多拷贝质粒中 grL4 的过度表达强烈抑制 FliC 水平以及细胞运动，因此我们得出结论，GrIA 充当鞭毛基因表达的负调节因子。事实上，组成型表达 FlhD/FlhC 的 EHEC 菌株不能粘附到 HeLa 细胞，这一事实使我们推测，GrIA 依赖性鞭毛调节子的抑制对于 EHEC 与宿主细胞的有效细胞粘附很重要。
The gene function of the locus of enterocyte effacement (LEE) is essential for full virulence of enterohemorrhagic Escherichia coli (EHEC). Strict control of LEE gene expression is mediated by the coordinated activities of several regulatory elements. We previously reported that the ClpX/ClpP protease positively controls LEE expression by down-regulating intracellular levels of GrIR, a negative regulator of LEE gene expression. We further revealed that the negative effect of GrIR on LEE expression was mediated through GrIA, a positive regulator of LEE expression. In this study, we found that the FliC protein, a major component of flagellar filament, was overproduced in clpXP mutant EHEC, as previously reported for Salmonella. We further found that FliC expression was reduced in a clpXP grlR double mutant. To determine the mediators of this phenotype, FliC protein levels in wild-type, grlR, grL4, and grlR grL4 strains were compared. Steady-state levels of FliC protein were reduced only in the grlR mutant, suggesting that positive regulation of FliC expression by GrIR is mediated by GrIA. Correspondingly, cell motility was also reduced in the grlR mutant, but not in the grL4 or grlR grL4 mutant. Because overexpression of grL4 from a multicopy plasmid strongly represses the FliC level, as well as cell motility, we conclude that GrIA acts as a negative regulator of flagellar-gene expression. The fact that an EHEC strain constitutively expressing FlhD/FlhC cannot adhere to HeLa cells leads us to hypothesize that GrIA-dependent repression of the flagellar regulon is important for efficient cell adhesion of EHEC to host cells.