Department of Molecular & Cellular Biochemistry, Indiana University, Bloomington, Indiana, United States of America.
PLoS One. 2011;6(10):e25837. doi: 10.1371/journal.pone.0025837. Epub 2011 Oct 10.
Toll-like Receptor 3 (TLR3) detects double-stranded (ds) RNAs to activate innate immune responses. While poly(I:C) is an excellent agonist for TLR3 in several cell lines and in human peripheral blood mononuclear cells, viral dsRNAs tend to be poor agonists, leading to the hypothesis that additional factor(s) are likely required to allow TLR3 to respond to viral dsRNAs. TLR3 signaling was examined in a lung epithelial cell line by quantifying cytokine production and in human embryonic kidney cells by quantifying luciferase reporter levels. Recombinant 1b hepatitis C virus polymerase was found to enhance TLR3 signaling in the lung epithelial BEAS-2B cells when added to the media along with either poly(I:C) or viral dsRNAs. The polymerase from the genotype 2a JFH-1 HCV was a poor enhancer of TLR3 signaling until it was mutated to favor a conformation that could bind better to a partially duplexed RNA. The 1b polymerase also co-localizes with TLR3 in endosomes. RNA-binding capsid proteins (CPs) from two positive-strand RNA viruses and the hepadenavirus hepatitis B virus (HBV) were also potent enhancers of TLR3 signaling by poly(I:C) or viral dsRNAs. A truncated version of the HBV CP that lacked an arginine-rich RNA-binding domain was unable to enhance TLR3 signaling. These results demonstrate that several viral RNA-binding proteins can enhance the dsRNA-dependent innate immune response initiated by TLR3.
Toll 样受体 3（TLR3）可识别双链（ds）RNA 并激活先天免疫反应。聚肌苷酸-聚胞苷酸（poly(I:C)）是几种细胞系和人外周血单核细胞中 TLR3 的优秀激动剂，而病毒 dsRNA 往往是较差的激动剂，这导致了一种假说，即可能需要其他因素来使 TLR3 能够对病毒 dsRNA 产生反应。通过定量细胞因子产生的方法在肺上皮细胞系中，通过定量荧光素酶报告基因水平的方法在人胚肾细胞中检测 TLR3 信号通路。发现重组 1b 型丙型肝炎病毒聚合酶与 poly(I:C)或病毒 dsRNA 一起添加到培养基中时，可增强肺上皮细胞 BEAS-2B 中的 TLR3 信号通路。来自基因型 2a 的 JFH-1 HCV 聚合酶在突变为有利于与部分双链 RNA 更好结合的构象之前，对 TLR3 信号通路的增强作用较差。1b 型聚合酶也与 TLR3 在内涵体中共定位。两种正链 RNA 病毒和肝 DNA 病毒乙型肝炎病毒（HBV）的 RNA 结合衣壳蛋白（CP）也可增强 TLR3 信号通路，无论是通过 poly(I:C)还是病毒 dsRNA。缺乏富含精氨酸的 RNA 结合结构域的 HBV CP 的截断版本无法增强 TLR3 信号通路。这些结果表明，几种病毒 RNA 结合蛋白可增强 TLR3 引发的 dsRNA 依赖性先天免疫反应。
