Microbial Pattern Recognition and Signaling by the Adhesion GPCR BAI1

通过粘附 GPCR BAI1 进行微生物模式识别和信号传导

• 批准号: 8691698
• 负责人: James E. Casanova
• 金额: $ 38.2万
• 依托单位: UNIVERSITY OF VIRGINIA
• 依托单位国家: 美国
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2016-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8691698
• 关键词: Adhesions; Adopted; Amino Acids; Antibiotics; Apoptotic; BAI1 gene; Bacteria; Bacterial Infections; Binding; Binding Sites; Biochemical; Biological Assay; C Type Lectin Receptors; C-terminal; Calorimetry; Cells; Charge; Communicable Diseases; Complex; Cytoplasmic Tail; Data; Development; Ectopic Expression; Elements; Exhibits; Extracellular Domain; Family; Fibroblasts; G Protein-Coupled Receptor Genes; Goals; Gram-Negative Bacteria; Gram-Positive Bacteria; Health; Host Defense; Immune response; Immune system; In Vitro; Infection; Infectious Agent; Inflammation; Inflammatory; Inflammatory Response; Interferons; Invaded; Ligand Binding; Ligands; Ligation; Lipopolysaccharides; Liver; MAP Kinase Modules; Mediating; Microbe; Monomeric GTP-Binding Proteins; Mus; Nature; Organism; Orphan; Pathway interactions; Pattern Recognition; Pattern recognition receptor; Phagocytes; Phagocytosis; Physiological; Predisposition; Proteins; Reactive Oxygen Species; Receptor Activation; Receptor Signaling; Research; Role; Salmonella; Salmonella infections; Salmonella typhimurium; Sentinel; Series; Side; Signal Pathway; Signal Transduction; Specificity; Spleen; Structure; Surface; TLR4 gene; Tissues; Toll-like receptors; Work; base; chemokine; cytokine; in vivo; insight; intraperitoneal; macrophage; member; microbial; microorganism; mouse model; next generation; novel; pathogen; pathogenic bacteria; receptor; response; scavenger receptor; uptake

DESCRIPTION (provided by applicant): 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) that 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, including scavenger receptors and C-type lectin receptors 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 is expressed on macrophages and recognizes the surface lipopolysaccharide (LPS) of Gram-negative bacteria using an array of thrombospondin repeats (TSRs) in its extracellular domain. TSRs in several secreted proteins have been shown to bind microbial products, but this is the first evidence of a transmembrane receptor that uses TSRs to mediate the phagocytic clearance of specific pathogens. Binding of bacteria to BAI1 triggers phagocytosis through a mechanism involving activation of the small GTPase Rac by the Elmo/Dock180 GEF complex, which interacts directly with BAI1. An emerging theme is that pattern recognition receptors often cooperate with each other to enhance downstream signaling responses. Our preliminary data suggest that BAI1 acts synergistically with the Toll-like receptor TLR4 to promote the synthesis of inflammatory cytokines/chemokines. BAI1 is an orphan GPCR-like receptor and apart from its ability to activate Rac, almost nothing is known about how it transmits signals to the cell interior or which signaling pathways are activated in response to BAI1 ligation. The overall goal of the proposed research is to define the role of BAI1 in host defense against bacterial infection. In Aim 1, we will define the mode of interaction of LPS with the BAI1 TSRs, using a combination of biochemical, biophysical and structural approaches. In Aim 2, we will identify components of the signaling machinery that interact with BAI1, define the signaling pathways activated in response to LPS or bacterial activation of the receptor, and elucidate the mechanisms of crosstalk between BAI1 and TLR4. In Aim 3, we will characterize the role of BAI1 in host defense in vivo, using a mouse model of Salmonella infection. Together these studies will provide unique structural, biochemical and physiological insights into a new class of pattern recognition receptor that may have important functions in the innate immune response to bacterial pathogens.

描述（由申请人提供）：先天免疫系统形成了针对入侵微生物病原体的特定宿主防御的第一道防线。先天免疫反应不可或缺的是模式识别受体 (PRR)，它可以识别多种病原微生物表达的保守决定簇。其中包括 Toll 样受体（其响应病原体识别而促进炎症信号传导和吞噬细胞募集），以及几个吞噬性 PRR 家族，包括清道夫受体和 C 型凝集素受体（介导吞噬细胞从感染组织中清除微生物）。每个受体家族都包含多个成员，可以识别独特的微生物成分谱，并且它们共同提供针对多种传染性生物体的保护。我们发现了一种新型模式识别受体 BAI1，它在巨噬细胞上表达，并利用其胞外域中的一系列血小板反应蛋白重复序列​​ (TSR) 来识别革兰氏阴性细菌的表面脂多糖 (LPS)。几种分泌蛋白中的 TSR 已被证明可以结合微生物产物，但这是跨膜受体利用 TSR 介导特定病原体吞噬清除的第一个证据。细菌与 BAI1 的结合通过 Elmo/Dock180 GEF 复合物激活小 GTPase Rac 的机制触发吞噬作用，该复合物直接与 BAI1 相互作用。一个新兴的主题是模式识别受体经常相互合作以增强下游信号反应。我们的初步数据表明，BAI1 与 Toll 样受体 TLR4 协同作用，促进炎症细胞因子/趋化因子的合成。 BAI1 是一种孤儿 GPCR 样受体，除了其激活 Rac 的能力之外，我们对它如何将信号传递到细胞内部或响应 BAI1 连接而激活哪些信号通路几乎一无所知。本研究的总体目标是确定 BAI1 在宿主防御细菌感染中的作用。在目标 1 中，我们将结合生物化学、生物物理和结构方法来定义 LPS 与 BAI1 TSR 的相互作用模式。在目标 2 中，我们将鉴定与 BAI1 相互作用的信号传导机制的组成部分，定义响应 LPS 或细菌激活受体而激活的信号传导途径，并阐明 BAI1 和 TLR4 之间的串扰机制。在目标 3 中，我们将使用沙门氏菌感染的小鼠模型来表征 BAI1 在宿主体内防御中的作用。这些研究将为一类新型模式识别受体提供独特的结构、生化和生理学见解，这种受体可能在针对细菌病原体的先天免疫反应中发挥重要作用。