Mechanisms of a novel Salmonella virulence gene that involves in intramacrophage survival

鼠伤寒沙门菌血清型鼠伤寒沙门菌致病性岛2 （SPI-2）上的spiC基因是小鼠巨噬细胞存活和全身感染的必需基因。根据国家科研资助项目计划，对spiC基因的表达调控和功能进行了研究。spiC基因表达的调控：(1)spiC基因表达受到PhoP/PhoQ系统以及SPI-2中ssrA (spiR)/ssrB双组分调控基因的正调控。(2) spiC基因在细菌生长稳定期特异表达，并受sigma因子RpoS正调控。(3)低Mg^<2+> (10 μM)和低pH（5.0）条件下，spiC基因表达增加。(4)吞噬后巨噬细胞内鼠伤寒沙门氏菌spiC基因的表达随着时间的延长而增加，说明巨噬细胞的吞噬体环境诱导了spiC基因的表达。SpiC蛋白的功能：(1)SpiC是一种利用SPI-2型分泌系统转运到感染巨噬细胞胞浆中的效应物。(2) SpiC通过干扰吞噬体和溶酶体间室的融合在巨噬细胞存活中起重要作用。此外，当使用Sindbis病毒系统在巨噬细胞内表达SpiC时，正常的运输被阻断。(3) SpiC还参与了被沙门氏菌感染的巨噬细胞中白细胞介素-10表达的增加，白细胞介素-10是巨噬细胞的一种失活剂。我计划研究IL-10表达与巨噬细胞存活之间的关系。

The spiC gene in the Salmonella Pathogenicity Island 2 (SPI-2) on the Salmonella enterica serovar Typhimurium chromosome is required for intramacrophage survival and systemic infection in mice. I have investigated the regulation of expression and the function of spiC gene according to the project plan of Grant-in-Aid for Scientific Research.1. The regulation of spiC gene expression : (1) The spiC gene expression was positively regulated by the PhoP/PhoQ system, as well as the ssrA (spiR)/ssrB two-component regulatory genes in the SPI-2. (2) The spiC gene was specifically expressed when the bacteria are in stationary phase of growth, and was positively regulated by the sigma factor RpoS.(3) The spiC gene expression increased with the condition of low Mg^<2+> (10 μM) and low pH (5.0). (4) The expression of spiC gene in S.Typhimurium inside macrophages increased with time after phagocytosis, indicating that the phagosomal environment of macrophages induces the spiC gene expression.2. The function of SpiC protein : (1) SpiC is a effector translocated into the cytosol of infected macrophages using the type III secretion system of SPI-2. (2) SpiC play an important in intramacrophage survival by interfering with the fusion between the phagosome and lysosomal compartments. Furthermore, when SpiC was expressed inside macrophages using a Sindbis virus system, the normal trafficking was blocked. (3) SpiC also participates in the increase of expression of Interleukin-10, which is known to be a deactivator of macrophages, in macrophages infected with Salmonella. I am planning to examine the relationship between the IL-10 expression and intramacrophage survial.