Bacterial effectors targeting the IKK/NF-kB pathway

描述(申请人提供)：尽管减少水、肉类和蔬菜的细菌污染的成本很高，但产生志贺毒素的大肠杆菌(STEC)和相关的肠道病原体(如沙门氏菌、志贺氏菌、耶尔森氏菌)正导致越来越频繁的食源性腹泻疾病的爆发，从而构成巨大的健康负担。这些病原体使用III型分泌系统(T3SS)将毒力蛋白(效应物)注入宿主细胞。虽然T3SS效应器显然在细菌毒力中发挥了重要作用，但它们颠覆宿主细胞功能以促进病原体生存的机制尚不完全清楚。我们正在研究以STEC效应器为靶点的哺乳动物信号转导通路，最终目的是提高我们预防和治疗的能力 细菌感染。我们已经取得了重要而独特的发现，与人类严重腹泻疾病爆发相关的STEC菌株表达一对同源效应物，通过扰乱通常由核因子-kB途径协调的感染转录反应，从而差异地调节宿主的先天免疫。核糖体蛋白S3(RPS3)作为核因子-kB亚基具有辅助核功能，调节着天然免疫应答关键基因的核因子-kB活性。我们发现NleH1效应蛋白抑制RPS3核转位，降低特定启动子上的NF-kB活性。具体地说，NleH1抑制Ik�激酶复合体(IKK�)磷酸化RPS3，这是其核转位的关键要求。STEC菌株还编码一种名为NleH2的同源效应器。尽管NleH2与NleH1有84%的同源性，但NleH2刺激而不是抑制RPS3/NF-kB依赖的转录。我们假设NleH1和NleH2效应是通过颠覆通常由RPS3/NF-kB调控的对感染的促炎反应来促进细菌毒力的，并提出了以下具体目标：1)使用腹泻疾病的动物模型来量化NleH效应对细菌毒力的重要性。2)研究NleH1抑制IKK�磷酸化以阻止其核输入的分子机制。3)阐明NleH1和NleH2在调节RPS3/NF-kB依赖的信号转导中的机制差异及其病理生理意义。这项拟议中的研究的成功完成将1)揭示这些细菌效应物如何选择性地调节先天免疫；2)阐明病原体如何进化以选择核糖体蛋白的辅助核功能；以及3)表征细菌如何在特定的时空环境中将其毒力蛋白整合到宿主信号转导通路中。

DESCRIPTION (provided by applicant): Despite costly attempts to reduce bacterial contamination of water, meat, and vegetables, Shiga toxin- producing E. coli (STEC) and related enteric pathogens (e.g. Salmonella, Shigella, Yersinia) are causing increasingly frequent outbreaks of food-borne diarrheal disease, thus constituting enormous health burdens. These pathogens use a type III secretion system (T3SS) to inject virulence proteins (effectors) into host cells. While T3SS effectors clearly play essential roles in bacterial virulence, the mechanisms by which they subvert the functions of host cells to promote pathogen survival are incompletely characterized. We are studying the mammalian signal transduction pathways targeted by STEC effectors, with the ultimate goal of improving our ability to prevent and to treat bacterial infections. We have made the important and unique discovery that the STEC strains associated with severe diarrheal disease outbreaks in humans express a pair of homologous effectors that differentially regulate host innate immunity by disrupting the transcriptional responses to infection that are normally coordinated by the NF-kB pathway. NF-kB activity at key innate immune response genes is regulated by ribosomal protein S3 (RPS3), which possesses an accessory nuclear function as an NF-kB subunit. We discovered that the NleH1 effector protein inhibits RPS3 nuclear translocation, reducing NF-kB activity at specific promoters. Specifically, NleH1 inhibits the Ik� kinase complex (IKK�) from phosphorylating RPS3, a critical requirement for its nuclear translocation. STEC strains also encode a homologous effector named NleH2. Despite sharing 84 % identity with NleH1, NleH2 stimulates rather than inhibits RPS3/NF-kB-dependent transcription. We hypothesize that the NleH1 and NleH2 effectors promote bacterial virulence by subverting the pro- inflammatory responses to infection normally regulated by RPS3/NF-kB and propose the following specific aims: 1) Quantify the importance of NleH effectors to bacterial virulence using animal models of diarrheal disease. 2) Characterize the molecular mechanism by which NleH1 inhibits IKK� phosphorylation of RPS3 to prevent its nuclear import. 3) Elucidate mechanistic differences between NleH1 and NleH2 and their pathophysiological significance in regulating RPS3/NF-kB-dependent signaling. Successful completion of the proposed research will 1) reveal how these bacterial effectors selectively modulate innate immunity; 2) clarify how pathogens have evolved to co-opt the accessory nuclear functions of ribosomal proteins; and 3) characterize how bacteria have integrated their virulence proteins into host signal transduction pathways in specific spatiotemporal contexts.