Recognition of dsRNA by Toll-like receplor 3

toll样受体3（TLR3）识别dsRNA并传递信号激活NF-κB和IFN-β启动子，而不依赖于接头分子MyD88和Mal/TIRAP。我们已经确定了另一种适配器，称为含有toll -白细胞介素1受体结构域（TIR）的适配器分子(TICAM)-1，它可以物理结合TLR3的TIR结构域并激活IFN-β启动子，以响应poly(I:C)，一种合成的dsRNA类似物。当TICAM-1过表达时，可激活NF-κB和干扰素调节因子(IRF)-3， IRF -3是IFN-β基因表达的重要转录因子。RNA干扰介导的TLR3或TICAM-1的下调，而不是MyD88或Mal/TIRAP的下调，显著降低了聚（I:C）在人成纤维细胞和HeLa细胞中诱导的IFN-β的产生。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适配器分子，TICAM-2，它在物理上连接TLR4和TICAM-1，并在功能上将LPS-TLR4信号传递给TICAM-1，进而激活IRF-3导致产生IFN-β。这种依赖于ticam -1的途径形成了不依赖于myd88的细胞免疫应答的一部分。免疫荧光染色和使用抗人TLR3单抗（TLR3.7）共聚焦显微镜分析显示，在单核细胞来源的未成熟dc和CD11c^+血液dc中，TLR3定位于特定的未识别的细胞内囊泡。tlr3介导的信号需要内体成熟。这些结果表明，TLR3-TICAM-1通路在感知细胞外dsRNA中发挥重要作用，参与抗病毒免疫应答。

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.