RSV dsRNA binds TLR3

Viral infections, including those by single-stranded (ss) DNA viruses, positive (+)- and negative (-)-sense RNA viruses, produce immunostimulatory double-stranded RNA intermediates during viral replication cycle (reviewed by Chen YG & Hur S 2022). The presence of dsRNA is sensed by pattern recognition receptors (PRR) such as Toll-like receptor 3 (TLR3) which detects viral dsRNA in the lumen of the endosome (Alexopoulou L et al. 2001; Liu L et al. 2008; reviewed by Chen Y et al. 2021). Human respiratory syncytial virus (hRSV or RSV) induces TLR3 activity to mediate production of inflammatory cytokines and chemokines in RSV-infected human epithelial cells and fibroblasts (Rudd BD et al. 2005; Groskreutz DJ et al. 2006; Dou Y et al. 2013; Liu D et al. 2018). Increased TLR3 expression was detected in sputum samples from RSV-positive patients with acute exacerbations of chronic obstructive pulmonary disease (Liu D et al. 2018). In vivo studies in mice further confirm that TLR3 mediates host immune responses upon RSV infection (Rudd BD et al. 2006; Huang S et al. 2009; Aeffner F et al. 2011; Qi F et al. 2015).<p>The replication/transcription process of RSV, a (−)-sense ssRNA virus, is coordinated by nucleoprotein (N), large protein (L), phosphoprotein (P), and M2-1 protein. Viral N, L, P , M2-1 and RSV RNA form the RNA synthesis ribonucleoprotein (RNP) complex (reviewed by Cao D et al. 2021). This complex serves as a template for RNA replication, generating the (+) RNA antigenome and the (-) RNA genome, as well as for RNA transcription, producing capped and poly-adenylated mRNAs. Within this complex, the catalytic core L polypeptide performs various enzymatic activities including RNA-dependent RNA polymerase (RdRp) activity, polyribonucleotidyl transferase activity, which is essential for mRNA 5' cap addition, and methyltransferase activity to catalyze the cap methylation at both N7- and 2′-O-positions (reviewed by Sutto-Ortiz P et al. 2023). The interaction of the cofactor P with multiple proteins, including L and M2-1, enables conformational changes necessary to perform various enzymatic activities during the viral replication/transcription process. The M2-1 protein is required for RSV transcription to prevent premature transcription termination by increasing the processivity of the RdRp complex. Further, during RNA replication, the viral RNA polymerase activity can generate both standard (such as genomic) viral RNA and nonstandard viral RNA (reviewed by Vignuzzi M & López CB 2019; González Aparicio LJ et al. 2022). <p>One type of nonstandard viral genome is known as copy-back viral genomes (cbVGs). These cbVGs are produced when the polymerase enzyme dissociates from the template strand at a specific breakpoint and then resumes elongation at a downstream rejoin point (reviewed by Vignuzzi M  & López CB 2019; González Aparicio LJ et al. 2022). This process creates a complementary end to the 5' end of the nascent genomic RNA, resulting in the formation of double-stranded cbVG structures. RSV infection has been shown to generate cbVGs in vitro and in vivo (Sun Y et al. 2015; 2019; Felt SA et al. 2022). The accumulation of cbVGs is thought to modulate the viral replication and stimulate host immune responses via PRRs including TLR3 and RIG-I-like receptors (DDX58 and IFIH1) (reviewed by Vignuzzi M  & López CB 2019; González Aparicio LJ et al. 2022).<p>This Reactome event shows binding of RSV dsRNA species to TLR3. Upon ligand recognition, TLR3 recruits Toll/interleukin-1 receptor (TIR)-domain-containing adapter-inducing interferon-β (TRIF or TICAM1) to induce the activation of transcription factors interferon receptor factor 3 (IRF-3) and nuclear factor kappa B (NF-kappa-B), which ultimately results in the induction of type I interferons (IFN-α, β).

病毒感染，包括单链（ss）DNA病毒、正链（+）和负链（-）RNA病毒，在病毒复制周期中产生免疫刺激性的双链RNA中间体（参见Chen YG & Hur S，2022年综述）。双链RNA的存在被模式识别受体（PRR）如Toll样受体3（TLR3）所感知，该受体检测内体腔内的病毒双链RNA（参见Alexopoulou L等，2001年；Liu L等，2008年；Chen YG等，2021年综述）。人类呼吸道合胞病毒（hRSV或RSV）诱导TLR3活性，介导RSV感染的人上皮细胞和成纤维细胞产生炎症细胞因子和趋化因子（参见Rudd BD等，2005年；Groskreutz DJ等，2006年；Dou Y等，2013年；Liu D等，2018年）。在慢性阻塞性肺疾病急性加重期RSV阳性患者的痰样本中检测到TLR3表达增加（参见Liu D等，2018年）。在体内的老鼠研究中进一步证实，TLR3介导宿主对RSV感染的免疫反应（参见Rudd BD等，2006年；Huang S等，2009年；Aeffner F等，2011年；Qi F等，2015年）。RSV作为一种负链单链RNA病毒，其复制/转录过程由核蛋白（N）、大蛋白（L）、磷酸蛋白（P）和M2-1蛋白协同调节。病毒N、L、P、M2-1和RSV RNA形成RNA合成核糖核蛋白（RNP）复合体（参见Cao D等，2021年综述）。此复合体作为RNA复制的模板，生成正链RNA抗原体和负链RNA基因组，以及RNA转录的模板，产生加帽和多聚腺苷酸化的mRNA。在此复合体中，催化核心L多肽执行多种酶促活性，包括RNA依赖性RNA聚合酶（RdRp）活性、多核糖核苷酸转移酶活性，这对于mRNA 5'帽的添加至关重要，以及甲基转移酶活性，催化N7-和2′-O位置的帽甲基化（参见Sutto-Ortiz P等，2023年综述）。辅因子P与L和M2-1等多种蛋白的相互作用，使得在病毒复制/转录过程中进行各种酶促活性所需的构象变化成为可能。M2-1蛋白对于RSV转录是必需的，它通过增加RdRp复合体的进程性来防止转录提前终止。此外，在RNA复制过程中，病毒RNA聚合酶活性可以生成标准病毒RNA（如基因组病毒RNA）和非标准病毒RNA（参见Vignuzzi M & López CB，2019年综述；González Aparicio LJ等，2022年）。一种非标准病毒基因组被称为复制回病毒基因组（cbVGs）。当聚合酶酶从模板链的特定断点解离并在下游重接点重新延长时，产生这些cbVGs（参见Vignuzzi M & López CB，2019年综述；González Aparicio LJ等，2022年）。此过程在5'端新生基因组RNA上创建一个互补末端，从而形成双链cbVG结构。体外和体内研究表明，RSV感染可以产生cbVGs（参见Sun Y等，2015年；2019年；Felt SA等，2022年）。cbVGs的积累被认为可以通过PRR（包括TLR3和RIG-I样受体DDX58和IFIH1）调节病毒复制并刺激宿主免疫反应（参见Vignuzzi M & López CB，2019年综述；González Aparicio LJ等，2022年）。此Reactome事件显示了RSV双链RNA物种与TLR3的结合。在配体识别后，TLR3募集Toll/白细胞介素-1受体（TIR）结构域含有的适配体诱导干扰素-β（TRIF或TICAM1）以激活转录因子干扰素受体因子3（IRF-3）和核因子κB（NF-kappa-B），最终导致I型干扰素（IFN-α、β）的诱导。