Bijlsma Jetta J E, Groisman Eduardo A
Department of Molecular Microbiology, Howard Hughes Medical Institute, Washington University School of Medicine, Campus Box 8230, 660 S. Euclid Avenue, St Louis, MO 63110, USA.
Mol Microbiol. 2005 Jul;57(1):85-96. doi: 10.1111/j.1365-2958.2005.04668.x.
Spi/Ssa is a unique type three secretion system that functions exclusively when Salmonella enterica is inside eukaryotic cells. Expression of the Spi/Ssa system and its secreted effectors is dependent on SsrB/SpiR, a two-component regulatory system encoded in the SPI-2 pathogenicity island that also harbours the spi/ssa genes. Here we determine that the PhoP/PhoQ two-component system controls the intramacrophage expression of spi/ssa genes by regulating the SsrB/SpiR system. We establish that PhoP regulates transcription of the response regulator SsrB and demonstrate binding of the PhoP protein to the ssrB promoter both in vivo using chromatin immunoprecipitation in Salmonella-infected macrophages, and in vitro using purified PhoP protein. We show that PhoP controls the SpiR sensor post-transcriptionally and identify a region in the 5' untranslated region of the spiR message that is required for this effect. The demonstration that the PhoP/PhoQ system is directly involved in the regulation of the SPI-2 pathogenicity island highlights PhoP/PhoQ's central role in Salmonella virulence. We suggest that different regulatory systems convey distinct signals over time to produce the SsrB/SpiR system, which then modulates expression of the Spi/Ssa apparatus and secreted effectors.
Spi/Ssa是一种独特的三型分泌系统，仅在肠炎沙门氏菌处于真核细胞内时发挥作用。Spi/Ssa系统及其分泌效应蛋白的表达依赖于SsrB/SpiR，这是一种双组分调节系统，由SPI-2致病岛编码，该致病岛也包含spi/ssa基因。在这里，我们确定PhoP/PhoQ双组分系统通过调节SsrB/SpiR系统来控制spi/ssa基因在巨噬细胞内的表达。我们证实PhoP调节反应调节因子SsrB的转录，并通过在感染沙门氏菌的巨噬细胞中使用染色质免疫沉淀法在体内以及使用纯化的PhoP蛋白在体外证明PhoP蛋白与ssrB启动子的结合。我们表明PhoP在转录后控制SpiR传感器，并确定spiR信息的5'非翻译区中的一个区域是产生这种效应所必需的。PhoP/PhoQ系统直接参与SPI-2致病岛调节的证明突出了PhoP/PhoQ在沙门氏菌毒力中的核心作用。我们认为不同的调节系统会随着时间传递不同的信号以产生SsrB/SpiR系统，然后该系统调节Spi/Ssa装置和分泌效应蛋白的表达。
