Detection of bacterial Type IV secretion by the unfolded protein response

描述（由申请人提供）：先天免疫系统通过保守微生物结构的模式识别来检测组织中微生物的存在，称为病原体相关分子模式（PAMPs）。然而，PAMPs可以存在于所有微生物中，无论其致病潜力如何。为了将病原体与其他具有较低致病潜力的微生物区分开来，先天免疫系统可以通过尚未完全解决的机制检测病原体诱导的过程，例如宿主细胞质中微生物产物的存在。由于病原体表达的PAMPs可以并行激活许多模式识别受体，因此识别涉及病原体诱导过程检测的信号通路通常是困难的。流产布鲁氏菌是一种隐形病原体，表达修饰的PAMPs，不再作为模式识别受体的激动剂。因此，在B. abortus感染期间产生的宿主反应完全依赖于检测一种毒力因子的部署，即IV型分泌系统（T4SS），作为病原体诱导的过程。在这里，我们建议使用这种模式生物来定义一种新的信号通路，该信号通路涉及感知t4ss依赖性蛋白注射到宿主细胞质中作为病原体诱导的过程。本应用程序的目的是研究T4SS底物VceC易位到宿主细胞中如何诱导促炎反应并改变疾病结果。我们的中心假设是，T4SS底物VceC的易位激活了未折叠蛋白反应（UPR），随后诱导NF-kB依赖性炎症反应，从而促进了B.流产诱导的体内炎症。我们将通过识别UPR下游激活炎症反应的先天免疫信号分子，并通过在体内测试这些途径的作用，来验证我们的假设。这项工作的成功完成将推动该领域向前发展，将普遍定期循环作为先天免疫系统的一个组成部分，作为病原体诱导的过程检测靶向内质网的微生物蛋白。这一新概念不仅对细菌发病机制，而且对病毒发病机制、先天免疫都有重要影响

DESCRIPTION (provided by applicant): The innate immune system detects the presence of microbes in tissue by pattern recognition of conserved microbial structures, known as pathogen-associated molecular patterns (PAMPs). However PAMPs can be present in all microbes regardless of their pathogenic potential. To distinguish pathogens from other microbes with lower disease-causing potential, the innate immune system can detect pathogen-induced processes, such as the presence of microbial products in the host cell cytosol, through mechanisms that are not fully resolved. Identification of signaling pathways involved in the detection of pathogen-induced processes is often difficult, because PAMPs expressed by a pathogen can activate many pattern recognition receptors in parallel. Brucella abortus is a stealthy pathogen expressing modified PAMPs that no longer serve as agonists for pattern recognition receptors. As a result, host responses generated during B. abortus infection are entirely dependent on detecting the deployment of a virulence factor, the type IV secretion system (T4SS), as a pathogen-induced process. Here we propose to use this model organism to define a new signaling pathway involved in sensing the T4SS-dependent injection of proteins into the host cell cytosol as a pathogen-induced process. The objective of this application is to study how translocation of the T4SS substrate VceC into host cells induces pro-inflammatory responses and alters the disease outcome. Our central hypothesis is that translocation of the T4SS substrate VceC activates the unfolded protein response (UPR) with consequent induction of NF-kB- dependent inflammatory responses, thereby contributing to B. abortus-induced inflammation in vivo. We will test our hypothesis by identifying the innate immune signaling molecules downstream of the UPR that activate inflammatory responses and by testing the role of these pathways in vivo. Successful completion of this work will move the field forward by establishing the UPR as a component of the innate immune system that detects microbial proteins targeting the ER as a pathogen-induced process. This new concept has important ramifications not only for bacterial pathogenesis, but also for viral pathogenesis, innate immunity and the pathogenesis of certain inflammatory disorders involving the UPR, such as type 1 diabetes and inflammatory bowel disease.