Toll-like receptor 9 proteolytic processing and signaling

描述(申请人提供)：治疗靶向先天免疫引起的炎症有可能减少疾病相关的病理；然而，将潜在转化为临床现实的第一步是定义对调节先天免疫至关重要的分子途径，并确定这些途径中可以调节的靶点。在描述调节Toll样受体(TLRs)核酸敏感家族中的一个成员的分子通路方面取得了重大进展，TLRs与自身免疫性疾病的发生有关。最近的研究表明，其中一种TLR，TLR9，是一种被酸性内体中的蛋白酶激活的前受体。这种切割去除了一个N-末端片段，留下了一个称为p80的C-末端片段，它被认为是TLR9的功能形式。这一途径被吹捧为减少自身免疫性炎症的新的、潜在的重要药物靶点。然而，我们的初步结果表明，TLR9的蛋白水解性切割并不发生在对TLR9配体反应强烈的B细胞中。此外，我们发现TLR9的p80形式不足以支持高度相关的巨噬细胞和树突状细胞中的信号传递。我们回顾了显示N-末端片段具有DNA结合活性的数据，该片段在蛋白降解过程中被移除。因此，我们提出的假设是，N-末端片段在决定受体的配基特异性和反应中起着关键作用。我们将在两个目标上检验这一假说，这两个目标定义了N末端在调节受体的特异性中的作用，以及切割事件在调节包括B细胞、巨噬细胞和树突状细胞在内的各种细胞类型的信号和运输中的作用。虽然我们使用TLR9作为一个模型系统，但最近发表的研究表明，其他核酸感应TLRs也受到类似机制的调控。这项研究将提供关键的新信息，有助于澄清该领域的争议。但更重要的是，这将决定蛋白质分解实际上是一种很有前途的药物开发新途径，还是与其他调控机制相比意义较小。

DESCRIPTION (provided by applicant): Therapeutically targeting inflammation induced by innate immunity has the potential to reduce disease associated pathology; however, the first step in translating potential to clinical reality is defining the molecular pathways critical for regulating innate immunity, and identifying targets within these pathways that can be modulated. Significant progress has been made in delineating the molecular pathways regulating one member of the nucleic acids-sensing family of Toll-like receptors (TLRs), which have been implicated in development of autoimmune disease. Recent studies suggest that one of these TLRs, TLR9, is a pro-receptor that is activated by proteases in acidic endosomes. This cleavage removes an N-terminal fragment, leaving a C-terminal fragment, called p80, which is proposed to be the functional form of TLR9. This pathway has been touted as a new and potentially important drug target to reduce autoimmune inflammation. However, our preliminary results demonstrate that proteolytic cleavage of TLR9 does not occur in B cells, which respond robustly to TLR9 ligands. Moreover, we show that the p80 form of TLR9 is insufficient to support signaling in highly relevant macrophages, and dendritic cells. We review data that shows the N-terminal fragment, which is removed during the proteolytic event, has DNA binding activity. Therefore, we propose the hypothesis that the N-terminal fragment plays a critical role in determining the ligand specificity and response of the receptor. We will test this hypothesis in two aims, which define the role of the N-terminus in regulating specificity of the receptor, and the role of the cleavage event in regulating signaling and trafficking in various cell types including B cells, macrophages and dendritic cells. While we use TLR9 as a model system, recent published studies showed that other nucleic acid sensing TLRs are regulated by similar mechanisms. This study will provide critical new information that will help clarify controversies i the field. But more importantly, will determine whether proteolysis is, in fact, a promising new pathway for drug development, or of lesser significance compared with other regulatory mechanisms.