Transcriptional regulation of Toll-like receptor signaling

描述(申请人提供)：Toll样受体(TLRs)是微生物产品的关键感受器，对于发展对病原体的天然免疫力是必不可少的。TLR激活诱导数百个基因的表达，这些基因编码炎症细胞因子、抗菌蛋白以及再生和代谢调节因子；这些分子反过来介导感染疾病患者的炎症、抗菌免疫和组织再生。然而，不受控制的或长时间激活TLRs可能会产生毁灭性的后果，包括发展为感染性休克和致命的炎症性疾病。幸运的是，TLR的激活受到两类负调控因子的严格控制：a)抑制TLR信号转导的信号特异性调控因子；b)抑制TLR靶基因转录的基因特异性调控因子。这些调节剂确保TLRs长时间或重复暴露于其配体不会导致受体的持续激活；相反，它会使它们对随后的配体刺激不敏感或反应迟钝。这种现象被称为TLR耐受性，或当内毒素(LPS)是参与的配体时的耐受性。最近对内毒素反应的基因组图谱显示，内毒素耐受是一种基因特异性现象，即它选择性地针对一组基因(例如炎症基因)，而不是其他基因(例如抗菌素基因)；事实上，在内毒素耐受的细胞中，抗菌素基因的表达进一步上调。由于引起有害炎症反应的是炎症基因，而不是抗菌基因，因此，即使在慢性或长期感染的情况下，内毒素耐受性也能确保宿主能够不断增强其抗微生物免疫能力，而不会导致致命的炎症性疾病。然而，长时间接触脂多糖激活抗菌基因，但矛盾地抑制炎症基因的分子机制尚不清楚。我们最近发现，B细胞白血病(Bcl3)通过抑制内毒素激活的三大转录因子之一的核因子-βB来介导内毒素耐受。本研究的目的是阐明Bcl3调节TLR激活和耐受的分子机制。具体地说，我们将确定1)基因启动子的NF-B结合位点在TLR耐受中的作用，2)p50泛素化在TLR信号转导中的作用，以及3)Bcl-3抑制p50泛素化的机制。这些研究产生的信息不仅可能带来关于TLR信号转导机制的重要的概念性进展，而且还有助于开发基于Bcl3的新的感染性疾病治疗策略。 公共卫生相关性拟议的实验将结合使用遗传学、生物信息学和免疫学工具，研究Toll样受体(TLR)信号转导所必需的关键基因特异性调控机制。这种跨学科的方法可能会导致在TLR耐受机制方面取得概念上的突破，这一现象得到了广泛的承认，但人们对此知之甚少。此外，拟议的研究还将有助于开发基于Bcl-3的治疗传染病的新策略。

DESCRIPTION (provided by applicant): Toll-like receptors (TLRs) are key sensors of microbial products and are essential for the development of innate immunity to pathogens. TLR activation induces the expression of hundreds of genes that encode inflammatory cytokines, antimicrobial proteins, and regeneration and metabolic regulators; these molecules in turn mediate inflammation, antimicrobial immunity and tissue regeneration seen in patients with infectious diseases. However, uncontrolled or prolonged activation of TLRs can have devastating consequences, which include the development of septic shock and fatal inflammatory diseases. Fortunately, TLR activation is tightly controlled by two classes of negative regulators: a) signal-specific regulators that inhibit TLR signaling, and b) gene-specific regulators that suppress TLR target gene transcription. These regulators ensure that prolonged or repeated exposure of TLRs to their ligands does not lead to sustained activation of the receptors; instead, it renders them insensitive or hyporesponsive to subsequent ligand stimulation. This phenomenon is referred to as TLR tolerance, or lipopolysaccharide (LPS) tolerance when LPS is the ligand involved. Recent genomic profiling of LPS responses reveals that LPS tolerance is a gene-specific phenomenon, i.e., it selectively targets one set of genes (e.g., inflammatory genes) but not others (e.g., antimicrobial genes); in fact, the expression of antimicrobial genes is further upregulated in LPS tolerized cells. Because it is the inflammatory genes, not the antimicrobial genes, that cause deleterious inflammatory responses, LPS tolerance ensures that the host is able to continuously build up its antimicrobial immunity without causing fatal inflammatory diseases even with chronic or prolonged infections. However, the molecular mechanisms through which prolonged LPS exposure activates antimicrobial genes, but paradoxically suppresses inflammatory genes are unknown. We recently discovered that B cell leukemia (Bcl)-3 mediates LPS tolerance by inhibiting nuclear factor (NF)-??B, one of the three major transcription factors activated by LPS. The goal of this investigation is to elucidate the molecular mechanisms through which Bcl-3 regulates TLR activation and tolerance. Specifically, we will define 1) the roles of NF-?B binding sites of gene promoters in TLR tolerance, 2) the roles of p50 ubiquitination in TLR signaling, and 3) the mechanisms through which Bcl-3 inhibits p50 ubiquitination. Information generated from these studies may not only bring about an important conceptual advance with regard to mechanisms of TLR signaling but also aid in the development of novel Bcl-3-based strategies for the treatment of infectious diseases. PUBLIC HEALTH RELEVANCE The proposed experiments will examine a key gene-specific regulatory mechanism essential for Toll-like receptor (TLR) signaling using combined genetic, bioinformatic and immunologic tools. This inter-disciplinary approach, will likely lead to a conceptual breakthrough with regard to the mechanism of TLR tolerance, a phenomenon widely recognized but poorly understood. Additionally, the proposed studies will also help develop novel Bcl-3-based strategies for the treatment of infectious diseases.