A novel role for the TLR signaling adaptor TRAM

描述（由申请人提供）：Toll样受体（TLR）是膜受体，其细胞外结构域可以识别从入侵微生物释放的保守分子（例如LPS、CpG等）。TLR结合提醒宿主潜在病原体的存在并激活先天免疫。TLR信号通路中的遗传突变可导致免疫缺陷和免疫病理学。TLR通过与细胞质衔接子相互作用向细胞发出信号，所述细胞质衔接子募集下游信号传导分子并导致促炎细胞因子和I型干扰素的诱导。目前的TLR范式认为，除了TLR 3之外，所有13种哺乳动物TLR都通过衔接子MyD 88向宿主细胞发出信号，而TLR 3通过替代衔接子TRIF通过“MyD 88-非依赖性”途径发出信号。TLR 4还可以通过MyD 88非依赖性途径进行信号传导，因此通过交替使用两种不同的桥接衔接子之一来独特地通过MyD 88和TRIF进行信号传导：TIRAP/Mal以募集MyD 88或TRAM以募集TRIF。在最近对革兰氏阴性菌土拉弗朗西斯菌的免疫应答的研究中，我们发现了一种新的体内信号传导途径，该途径需要TRAM，但似乎不涉及“MyD 88-独立”TRIF信号传导途径。我们在单核细胞增生李斯特菌感染的小鼠模型中观察到了类似的途径。这些结果是令人惊讶的，因为TRAM的唯一已知功能是在经典的MyD 88非依赖性途径中将TLR 4桥连到TRIF。重要的是，TLR 2而不是TLR 4是识别和控制F所必需的。tularensis和L.单核细胞增多症感染的小鼠。因此，基于我们的初步研究，我们提出TRAM可以将TLR 4以外的TLR（例如TLR 2）与免疫激活联系起来，从而在TLR信号传导中发挥比以前已知的更广泛的作用。为了验证这一假设，我们将1）阐明肺土拉菌病小鼠模型中TRAM依赖性、TLR 4非依赖性信号传导调节宿主保护性反应的机制，2）定义新型TRAM依赖性信号传导途径的分子组分、细胞内位置和下游靶点。总之，这些研究将定义一个重要的TLR信号分子的新作用，揭示TLR特异性是如何控制的新的光，并扩大目前的TLR范式。拟议的研究是创新的，因为它们将定义一个关键TLR信号分子的新作用，并修改当前的TLR范式。它们是重要的，因为该途径是体内关键的免疫激活途径，并且其阐明可能为TLR信号传导和促炎性的治疗操作提供新的靶点。 公共卫生相关性：需要完全了解控制对微生物感染的免疫反应以及调节在慢性疾病如类风湿性关节炎和狼疮中观察到的有害炎症反应的信号通路。拟议的研究将表征TRAM信号分子的新作用，该分子以其在感染免疫反应中的作用而闻名。这些结果将为开发更好的治疗方法以增强疫苗和治疗慢性炎症性疾病提供有价值的信息。

DESCRIPTION (provided by applicant): The Toll-like receptors (TLRs) are membrane receptors whose extracellular domains can recognize conserved molecules released from invading microbes (e.g. LPS, CpG, etc). TLR binding alerts the host to the presence of potential pathogens and activates innate immunity. Inherited mutations in TLR signaling pathways can lead to immunodeficiency and immunopathology. TLRs signal cells by interacting with cytoplasmic adaptors that recruit downstream signaling molecules and lead to induction of proinflammatory cytokines and type I interferons. The current TLR paradigm asserts that all 13 mammalian TLRs, except TLR3, signal host cells via the adaptor MyD88, whereas TLR3 signals through a "MyD88-independent" pathway via the alternate adaptor TRIF. TLR4 can also signal via the MyD88-independent pathway and thus uniquely signals through both MyD88 and TRIF by alternate use of one of two different bridging adaptors: TIRAP/Mal to recruit MyD88 or TRAM to recruit TRIF. In recent studies of the immune response to the Gram-negative bacterium Francisella tularensis, we have uncovered a novel signaling pathway in vivo that requires TRAM but does not appear to involve the "MyD88-independent" TRIF signaling pathway. We have observed a similar pathway in a mouse model of Listeria monocytogenes infection. These results were surprising since TRAM's only known function has been to bridge TLR4 to TRIF in the classic MyD88-independent pathway. Importantly, TLR2, and not TLR4, is required for recognition and control of F. tularensis and L. monocytogenes infections in mice. Based on our preliminary studies, therefore, we propose that TRAM can link TLRs other than TLR4 (e.g. TLR2) to immune activation, and thus plays a broader role in TLR signaling than previously known. To test this hypothesis, we will 1) elucidate the mechanism(s) by which TRAM-dependent, TLR4- independent signaling regulates the host protective response in a mouse model of pulmonary tularemia, and 2) define the molecular components, intracellular location and downstream targets of the novel TRAM-dependent signaling pathway. Together, these studies will define a new role for an important TLR signaling molecule, shed new light on how TLR specificity is controlled, and expand the current TLR paradigm. The proposed studies are innovative because they will define a new role for a key TLR signaling molecule and modify the current TLR paradigm. They are significant because this pathway is a critical immune activation pathway in vivo, and its elucidation may provide new targets for therapeutic manipulation of TLR signaling and the pro-inflammatory. PUBLIC HEALTH RELEVANCE: A complete understanding is needed of the signaling pathways that control immune responses to microbial infections and that regulate the harmful inflammatory responses observed in chronic diseases such as rheumatoid arthritis and Lupus. The proposed studies will characterize a novel role for the TRAM signaling molecule, known for its role in immune responses to infections. The results will provide valuable information for the development of better therapeutics to enhance vaccines and to treat chronic inflammatory diseases.