Recognition of dsRNA by Toll-like receplor 3

Toll样受体3（TLR 3）识别dsRNA并传递信号以激活NF-κB和IFN-β启动子，而不依赖于接头分子MyD 88和Mal/TIRAP。我们已经鉴定了一种替代衔接子，命名为Toll-白细胞介素1受体结构域（TIR）-含有衔接子分子（TICAM）-1，其可以物理结合TLR 3的TIR结构域并响应于poly（I：C）（dsRNA的合成类似物）激活IFN-β启动子。当TICAM-1过表达时，激活NF-κB和干扰素调节因子（IRF）-3，这是IFN-β基因表达的一个至关重要的转录因子。RNA干扰介导的TLR 3或TICAM-1的敲低，而不是MyD 88或Mal/TIRAP的敲低，显著降低了人成纤维细胞和HeLa细胞中poly（I：C）诱导的IFN-β产生。因此，IFN-β的dsRNA-TLR 3依赖性产生主要由TICAM-1介导。此外，我们克隆了另外的衔接子分子TICAM-2，其物理上桥接TLR 4和TICAM-1，并在功能上将LPS-TLR 4信号传导至TICAM-1，TICAM-1进而激活IRF-3，从而产生IFN-β。这种TICAM-1依赖性途径形成了MyD 88非依赖性细胞免疫应答的一部分。免疫荧光染色和使用抗人TLR 3 mAb（TLR3.7）的共聚焦显微镜分析显示，TLR 3定位于单核细胞来源的未成熟DC和CD 11 c ^+血液DC中的特异性未识别胞内囊泡。TLR 3介导的信号传导需要内体成熟。这些结果表明，TLR 3-TICAM-1途径在感知参与抗病毒免疫应答的细胞外dsRNA中起重要作用。

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.