Host Response--Salmonella Enterica Serovar Typhimurium

伤寒沙门氏菌是人类胃肠炎的常见原因，可引起小鼠的系统性伤寒样疾病。沙门氏菌致病岛SPI1和SPI2上编码的两个三型分泌系统(TTS)是致病所必需的，它们用于将细菌效应蛋白转运到宿主细胞中。SPI1和SPI2 TTSS在发病机制中有不同的表达，发挥着不同的作用。SPI1TTSS是在细胞外诱导的，它移位了许多协同介导非吞噬细胞侵袭的效应物。其中SopB/SigD是一种肌醇磷酸酶，参与摄取，但也诱导哺乳动物丝氨酸苏氨酸激酶Akt/PKB的激活。因此，野生型鼠伤寒沙门氏菌而不是sigD缺失突变株在感染的宿主细胞中诱导Akt磷酸化和激活。Akt激活在发病机制中的作用尚不清楚，然而，在培养的上皮细胞中，我们发现它可以阻止细胞凋亡的发生。野生型鼠伤寒沙门氏菌可阻断喜树碱诱导的细胞凋亡，这与caspase 3活性降低有关。这可能对胞内细菌的生存和复制具有重要意义。在巨噬细胞中，沙门氏菌对Akt的激活更为复杂，因为在缺乏SigD的情况下，内毒素会激活该激酶。然而，我们发现SopB/SigD，增加了巨噬细胞诱导型一氧化氮合酶的水平和一氧化氮的产生。 为了更好地了解SigD和其他SPI1效应分子的易位机制，我们还对SigD与其伴侣SiGe的结合进行了详细的分析。这项工作是与加拿大不列颠哥伦比亚大学的Natalie Strynadka博士合作进行的。

Salmonella enterica serovar Typhimurium is a common cause of gastroenteritis in humans and can cause a systemic typhoid-like disease in mice. Essential for pathogenesis are two Type Three Secretion Sytems (TTSS), encoded on Salmonella Pathogenicity Islands SPI1 and SPI2 that are used to translocate bacterial effector proteins into the host cell. The SPI1 and SPI2 TTSSs are differentially expressed and perform distinct roles in pathogenesis. The SPI1 TTSS, which is induced extracellularly, translocates a number of effectors that co-operatively mediate invasion of non-phagocytic cells. One of these effectors, SopB/SigD, is an inositol phosphatase that is involved in uptake but also induces the activation of mammalian serine threonine kinase Akt/PKB. Thus wild type S. Typhimurium but not the sigD deletion mutant strain induces Akt phosphorylation and activation in infected host cells. The role of Akt activation in pathogenesis remains unclear, however, in cultured epithelial cells we found that it can prevent the onset of apoptosis. Wild type serovar Typhimurium, but not the sigD deletion mutant strain, can block the induction of apoptosis by camptothecin and this is associated with decreased activation of caspase 3. This may be important for the survival and replication of intracellular bacteria. In macrophages activation of Akt by Salmonella is more complex since lipopolysaccharide will activate the kinase in the absence of SigD. However, we have found that SopB/SigD, increased inducible nitric oxide synthase levels and nitric oxide production in macrophages. To better understand the mechanism of translocation of SigD and other SPI1 effectors we have also carried out a detailed analysis of SigD binding to its chaperone SigE. This work is being carried out in collaboration with Dr. Natalie Strynadka at the University of British Columbia in Canada.