Shigella protein complex-mediated repression of innate immunity early during infection

哺乳动物细胞利用多种机制来识别和响应入侵的细菌。这包括 炎性小体介导的促炎细胞因子的分泌促进免疫细胞向 感染部位和与LC3相关的吞噬作用进入细菌，促进病原体清除。 进入人体后不久，炎症体成分和LC3被招募到人类病原体福氏志贺氏菌中 进入宿主细胞，然而胞内细菌的一个亚群避免与这些标记相关联。这是怎么回事 亚群逃脱了这些先天免疫因素的识别，目前还不完全清楚。我们观察到 与Lc3无关的亚群普遍与宿主蛋白TOCA-1相关。我们 发现TOCA-1与一小部分蛋白质形成复合体，由福氏志贺氏菌通过 三型分泌系统。在福氏杆菌转位的~30个蛋白中，我观察到TOCA-1 专门与IPAB、IcsB、OspC3和IpgD相互作用。我们已经证明了IcsB抑制与Lc3相关的 吞噬作用，以及其他研究表明，OspC3抑制caspase激活，增加了 这种复合体的功能是抑制先天免疫反应。具体地说，我假设(1) TOCA-1、IcsB、IpgD、OspC3和IPAB复合体以定义的排列形式形成；(2)TOCA-1-S；Flexneri 分泌的蛋白质复合体通过 膜包埋转位蛋白IPAB；和(3)复合体形成本身坐标限制 Lc3相关的吞噬作用与OspC3介导的抑制caspase激活。以下是具体的 AIMS旨在测试这一假设的各个方面： 1.确定TOCA-1与第三型福氏志贺氏菌复合体形成的相关性 分泌与TOCA-1共同沉淀的蛋白质。 2.检测TOCA-1-S。福氏杆菌分泌蛋白复合体本身对先天免疫的限制 宿主细胞的反应。 这一提议将产生对福氏志贺氏菌如何逃避先天免疫反应的机械性见解 宿主细胞在感染早期。在这些研究中获得的结果可能具有重要的意义 对于我们对细胞内病原体的先天免疫反应的理解。

Mammalian cells utilize multiple mechanisms to recognize and respond to invading bacteria. This includes inflammasome-mediated secretion of pro-inflammatory cytokines to promote recruitment of immune cells to the site of infection and LC3-associated phagocytosis of entering bacteria to promote pathogen elimination. Inflammasome components and LC3 are recruited to the human pathogen Shigella flexneri soon after entry into host cells, yet a subpopulation of intracellular bacteria avoids association with these markers. How this subpopulation escapes recognition by these innate immune factors is incompletely understood. We observed the subpopulation that does not associate with LC3 universally associates with the host protein Toca-1. We discovered that Toca-1 forms a complex with a small subset of proteins translocated into cells by S. flexneri via a type three secretion system. Among the ~30 proteins translocated by S. flexneri, I observed that Toca-1 specifically interacts with IpaB, IcsB, OspC3, and IpgD. We have shown that IcsB represses LC3-associated phagocytosis, and others have demonstrated that OspC3 inhibits caspase activation, raising the possibility that this complex functions in aggregate to inhibit innate immune responses. Specifically, I hypothesize that (1) the Toca-1, IcsB, IpgD, OspC3, and IpaB complex forms in a defined arrangement; (2) that the Toca-1-S. flexneri secreted protein complex is assembled on the vacuolar membrane or on vacuolar membrane fragments via the membrane-embedded translocon protein IpaB; and (3) that complex formation per se coordinates restriction of LC3-associated phagocytosis with OspC3-mediated inhibition of caspase activation. The following specific aims are designed to test aspects of this hypothesis: 1. To define the dependency of complex formation between Toca-1 and S. flexneri type three secreted proteins that precipitate with Toca-1. 2. To test whether the Toca-1-S. flexneri secreted protein complex per se restricts innate immune responses in host cells. This proposal will generate mechanistic insights into how S. flexneri evades the innate immune response in host cells early during infection. The results obtained in these studies are likely to have important implications for our understanding of the innate immune response to intracellular pathogens in general.