Initiation and regulation of antibacterial innate immunity

描述（由申请人提供）：本提案的目的是解释单一微生物产物细菌脂多糖（LPS）如何激活多种先天免疫应答途径。虽然TLR 4被广泛认为控制对LPS的转录应答，但存在TLR 4非依赖性应答。这种反应的实例包括内吞作用、转录因子NFAT的活化和半胱天冬酶-11对非典型炎性体的活化。这些不同的LPS反应之间的关系在很大程度上是未知的，但正如我们将描述的，至少有一些TLR 4非依赖性反应控制经典定义的TLR 4依赖性反应的LPS。了解微生物产品如何激活不同的信号转导途径可能允许设计药物或疫苗，可以靶向治疗途径的子集。我们的建议是建立在我们最近的发现，LPS诱导TLR 4的内吞作用的过程中，不需要一个功能性TLR 4信号（TIR）结构域，或任何其相关的衔接蛋白。相反，TLR 4是内吞途径的货物，其被LPS结合蛋白CD 14激活。虽然TLR 4不指导其自身的内吞作用，但该过程对于TLR 4诱导来自内体的TRIF依赖性信号转导是必需的。这一发现提供了一个例子，如何TLR 4依赖性和非依赖性的反应，LPS可以是相互依赖的。在这项授权申请中，我们提出1）确定共同的信号传导途径是否被CD 14激活以引发不同细胞类型特异性先天免疫应答，2）确定是否存在共同或不同的蛋白质复合物来调节不同的LPS诱导的信号传导途径，以及3）鉴定在感染的动物模型中直接响应于由病原性细菌感染产生的LPS的细胞群。总的来说，这项工作将提供重要的洞察力的手段， 对LPS的不同细胞反应是相互关联的。

DESCRIPTION (provided by applicant): The goal of this proposal is to explain how diverse innate immune response pathways can be activated by a single microbial product: bacterial lipopolysaccharide (LPS). While TLR4 is widely recognized to control transcriptional responses to LPS, TLR4-independent responses exist. Examples of such responses include endocytosis, activation of the transcription factor NFAT, and activation of non-canonical inflammasomes by caspase-11. The relationship between these diverse LPS responses is largely unknown, but as we will describe, at least some TLR4-independent responses control the classically-defined TLR4-dependent responses to LPS. Understanding how microbial products activate distinct signal transduction pathways may permit the design of drugs or vaccines that can target a subset of pathways therapeutically. Our proposal is founded on our recent discovery that LPS-induces the endocytosis of TLR4 by a process that does not require a functional TLR4 signaling (TIR) domain, or any of its associated adaptor proteins. Rather TLR4 is cargo for an endocytosis pathway that is activated by the LPS-binding protein CD14. While TLR4 does not direct its own endocytosis, this process is essential for TLR4 to induce TRIF-dependent signal transduction from endosomes. This discovery provides an example of how TLR4-dependent and -independent responses to LPS can be interdependent. In this grant application, we propose to 1) determine if a common signaling pathway is activated by CD14 to elicit diverse cell type-specific innate immune responses, 2) determine if common or distinct protein complexes exist that regulate diverse LPS inducible signaling pathways, and 3) identify the cell populations that directly respond to LPS produced by pathogenic bacterial infections in animal models of infection. Collectively, this work will provide important insight into the means by which diverse cellular responses to LPS are interconnected.