Microbial Pattern Recognition and Signaling by the Adhesion GPCR BAI1

摘要 先天免疫系统是特定宿主抵御入侵微生物的第一道防线。 病原体。模式识别受体(PRRs)是先天免疫反应的组成部分，它 识别由多种病原微生物表达的保守决定因素。其中包括 是Toll样受体，它促进炎症信号和吞噬细胞募集 病原体识别和几个介导微生物吞噬清除的吞噬PRR家族 从受感染的组织中。每个受体家族都包含多个成员，这些成员识别独特的光谱 微生物成分，它们共同提供保护，免受各种传染病的侵袭。 我们已经确定了一种新的模式识别受体BAI1，它能特异性地识别表面 革兰氏阴性杆菌的脂多糖(LPS)。BAI1是一个鲜为人知的G-家族成员。 蛋白质偶联受体(GPCRs)，即所谓的粘附性GPCRs。细菌与BAI1的结合触发其 宿主吞噬细胞的快速内化和杀伤，通过激活小分子 GTPase RAC由Elmo/Dock全环基金复合体组成，与BAI1直接相互作用。是否以及如何发送信号 通过异源三聚体的G蛋白是否整合到这一过程中尚不清楚，并将成为目标1的重点。 先天免疫的一个新主题是，模式识别受体经常与 其他以增强下行信令响应。我们公布的和初步的数据表明，BAI1起作用 与Toll样受体TLR4结合，通过以下途径促进活性氧的产生 吞噬细胞，以及炎性细胞因子/趋化因子/干扰素亚群的合成 表达是由转录因子IRF3介导的。在目标2中，我们将确定信号如何从 BAI1影响TLR4介导的信号通路以驱动ROS的产生和促炎因子的转录 基因。 这项拟议研究的最终目标是确定BAI1在宿主防御中的作用 细菌感染。在目标3中，我们将表征缺乏BAI1的巨噬细胞和中性粒细胞 革兰氏阴性腹膜炎小鼠模型中的明确感染。BAI1驱动ROS产生的能力和 感染期间特定髓系细胞亚群中细胞因子/干扰素的合成也将被确定。同舟共济 这些研究将为新一类模式识别提供独特的生化和生理学见解 在对细菌病原体的先天免疫反应中具有重要功能的受体。此外，BAI1就是其中之一 在为数不多的具有已知生理配体的粘附性GPCRs中，对其信号特性的剖析将 揭示了对这类知之甚少的受体的新见解。

Abstract The innate immune system forms the first line of specific host defense against invading microbial pathogens. Integral to the innate immune response are Pattern Recognition Receptors (PRRs), which recognize conserved determinants expressed by a broad range of pathogenic microorganisms. Among these are the Toll-like receptors, which promote inflammatory signaling and phagocyte recruitment in response to pathogen recognition, and several families of phagocytic PRRs that mediate phagocytic clearance of microbes from infected tissues. Each receptor family contains multiple members that recognize a unique spectrum of microbial components, and collectively they provide protection against a wide range of infectious organisms. We have identified a novel pattern recognition receptor, BAI1, that specifically recognizes the surface lipopolysaccharide (LPS) of Gram-negative bacteria. BAI1 is a member of a poorly understood family of G- protein coupled receptors (GPCRs), the so-called Adhesion GPCRs. Binding of bacteria to BAI1 triggers their rapid internalization and killing by host phagocytes, through a mechanism involving activation of the small GTPase Rac by the Elmo/Dock GEF complex, which interacts directly with BAI1. Whether and how signaling through heterotrimeric G proteins is integrated into this process is not known, and will be the focus of Aim 1. An emerging theme in innate immunity is that pattern recognition receptors often cooperate with each other to enhance downstream signaling responses. Our published and preliminary data indicate that BAI1 acts in tandem with the Toll-like receptor TLR4 to promote the production of reactive oxygen species (ROS) by phagocytic cells, and the synthesis of a subset of inflammatory cytokines/chemokines/interferons whose expression is mediated by the transcription factor IRF3. In Aim 2 we will determine how signals derived from BAI1 influence TLR4-mediated signaling to drive ROS production and the transcription of pro-inflammatory genes. The ultimate goal of the proposed research is to define the role of BAI1 in host defense against bacterial infection. In Aim 3, we will characterize the ability of BAI1-deficient macrophages and neutrophils to clear infection in a mouse model of Gram-negative peritonitis. The ability of BAI1 to drive ROS production and cytokine/interferon synthesis in specific myeloid cell subsets during infection will also be determined. Together these studies will provide unique biochemical and physiological insights into a new class of pattern recognition receptor with important functions in the innate immune response to bacterial pathogens. Moreover, BAI1 is one of the few Adhesion GPCRs with known physiological ligands, and dissection of its signaling properties will reveal new insights into this poorly understood class of receptors.