Toll-like receptor 9 proteolytic processing and signaling

描述（由申请人提供）：治疗性靶向由先天免疫诱导的炎症具有减少疾病相关病理的潜力；然而，将潜力转化为临床现实的第一步是确定调节先天免疫的关键分子途径，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）核酸感应家族成员的分子途径方面取得了重大进展，TLRs与自身免疫性疾病的发展有关。最近的研究表明，其中一种tlr， TLR9，是一种被酸性内体蛋白酶激活的前受体。这种切割去除一个n端片段，留下一个c端片段，称为p80，这被认为是TLR9的功能形式。这一途径已被吹捧为一个新的和潜在的重要药物靶点，以减少自身免疫性炎症。然而，我们的初步结果表明，TLR9的蛋白水解裂解并不发生在B细胞中，B细胞对TLR9配体反应强烈。此外，我们发现p80形式的TLR9不足以支持高度相关的巨噬细胞和树突状细胞的信号传导。我们回顾了显示在蛋白水解过程中被移除的n端片段具有DNA结合活性的数据。因此，我们提出假设，n端片段在决定受体的配体特异性和反应中起着关键作用。我们将通过两个目标来验证这一假设，即定义n端在调节受体特异性中的作用，以及切割事件在调节各种细胞类型（包括B细胞、巨噬细胞和树突状细胞）的信号传导和运输中的作用。虽然我们使用TLR9作为模型系统，但最近发表的研究表明，其他核酸感知tlr也受到类似机制的调节。这项研究将提供关键的新信息，这将有助于澄清该领域的争议。但更重要的是，它将决定蛋白质水解实际上是一种有希望的药物开发新途径，还是与其他调节机制相比意义较小。

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. PUBLIC HEALTH RELEVANCE: Innate immune receptors contribute to the development of inflammatory and autoimmune disease, and there is great promise to modulate their function for therapeutic benefit. However, a critical barrier to progress in this field is contradictory data on the importance of a newly discovered regulatory pathway for one family of innate immune receptors. At the completion of these studies we will have provided key data that will lead to paradigmatic shift in the current model of how these receptors are regulated and permit development of new therapeutic targets to treat autoimmune disease.