Recognition of dsRNA by Toll-like receplor 3

Toll 样受体 3 (TLR3) 识别 dsRNA 并传递信号以激活 NF-κB 和 IFN-β 启动子，独立于衔接分子 MyD88 和 Mal/TIRAP。我们已经鉴定出一种替代接头，命名为含有 Toll-白细胞介素 1 受体结构域 (TIR) 的接头分子 (TICAM)-1，它可以物理结合 TLR3 的 TIR 结构域，并响应 dsRNA 的合成类似物 Poly(I:C) 激活 IFN-β 启动子。 TICAM-1 过度表达时，会激活 NF-κB 和干扰素调节因子 (IRF)-3，后者是 IFN-β 基因表达的极其重要的转录因子。 RNA 干扰介导的 TLR3 或 TICAM-1 敲低（而非 MyD88 或 Mal/TIRAP）显着减少了人成纤维细胞和 HeLa 细胞中由聚 (I:C) 诱导的 IFN-β 产生。因此，dsRNA-TLR3 依赖性 IFN-β 的产生主要由 TICAM-1 介导。此外，我们克隆了一个额外的接头分子 TICAM-2，它在物理上桥接 TLR4 和 TICAM-1，并在功能上将 LPS-TLR4 信号传导至 TICAM-1，TICAM-1 反过来激活 IRF-3，从而产生 IFN-β。这种 TICAM-1 依赖性途径构成 MyD88 独立细胞免疫反应的一部分。使用抗人 TLR3 mAb (TLR3.7) 进行的免疫荧光染色和共聚焦显微镜分析表明，TLR3 定位于单核细胞来源的未成熟 DC 和 CD11c^ 血液 DC 中特定的未识别细胞内囊泡。 TLR3 介导的信号传导需要内体成熟。这些结果表明 TLR3-TICAM-1 通路在感知细胞外 dsRNA 方面发挥着重要作用，细胞外 dsRNA 参与抗病毒免疫反应。

Toll-like receptor 3(TLR3) recognizes dsRNA and transmits signals to activate NF-κB and the IFN-β promoter independent of the adaptor molecules MyD88 and Mal/TIRAP. We have identified an alternative adaptor, designated Toll-interleukin 1 receptor domain(TIR)-containing adaptor molecule (TICAM)-1, that can physically bind the TIR domain of TLR3 and activate the IFN-β promoter in response to poly(I:C), a syntetic analog of dsRNA. TICAM-1, when overexpressed, activated NF-κB and interferon regulatory factor(IRF)-3, a critically important transcription factor for IFN-β gene expression. RNA interference-mediated knockdown of TLR3 or TICAM-1, but not of MyD88 or Mal/TIRAP, significantly reduced IFN-β production induced by poly(I:C) in human fibloblasts and HeLa cells. Thus, dsRNA-TLR3-dependent production of IFN-β is mediated mainly by TICAM-1. Furthermore, we cloned an additional adaptor molecule, TICAM-2, that physically bridges TLR4 and TICAM-1 and functionally transmits LPS-TLR4 signaling to TICAM-1, which in turn activates IRF-3 leading to produce IFN-β. This TICAM-1-dependent pathway forms part of the MyD88-independent cellular immune response. Immunofluorescence staining and con focal microscopic analysis using anti-human TLR3 mAb (TLR3.7) revealed that TLR3 localized to specific unidentified intracellular vesicles in both monocyte-derived immature DCs and CD11c^+ blood DCs. TLR3-mediated signaling required endosomal maturation. These results suggest that the TLR3-TICAM-1 pathway plays an important role in sensing the extracellular dsRNA, which participates in an antiviral immune response.