Key Laboratory of Animal Virology of Ministry of Agriculture, Department of Veterinary Medicine, College of Animal Science, Zhejiang University, 866 Yuhangtang Road, Hangzhou, People's Republic of China.
Yinhe Biomedical Investment Co., Ltd, Beihai, Guangxi, People's Republic of China.
Arch Virol. 2021 Aug;166(8):2173-2185. doi: 10.1007/s00705-021-05073-3. Epub 2021 May 26.
Infectious bronchitis virus (IBV) is the only coronavirus known to infect poultry. The replication and pathogenesis of IBV are poorly understood, mainly because of the unavailability of a robust cell culture system. Here, we report that an active ubiquitin proteasome system (UPS) is necessary for efficient replication of IBV in Vero cells. Synthesis of IBV-specific RNA as well as viral protein is hampered in the presence of chemical inhibitors specific for the UPS. Like other coronaviruses, IBV encodes a papain-like protease (PLpro) that exhibits in vitro deubiquitinase activity in addition to proteolytically processing the replicase polyprotein. Our results show that the IBV PLpro enzyme inhibits the synthesis of interferon beta (IFNβ) in infected chicken embryonic fibroblast (DF-1) cells and that this activity is enhanced in the presence of melanoma differentiation-associated protein 5 (MDA5) and TANK binding kinase 1 (TBK1). IBV PLpro, when overexpressed in DF-1 cells, deubiquitinates MDA5 and TBK1. Both of these proteins, along with other adapter molecules such as MAVS, IKKε, and IRF3, form a signaling cascade for the synthesis of IFNβ. Ubiquitination of MDA5 and TBK1 is essential for their activation, and their deubiquitination by IBV PLpro renders them unable to participate in antiviral signaling. This study shows for the first time that there is cross-talk between the UPS and the innate immune response during IBV infection and that the deubiquitinase activity of IBV PLpro is involved in its activity as an IFN antagonist. This insight will be useful for designing better antivirals targeting the catalytic activity of the IBV PLpro enzyme.
传染性支气管炎病毒（IBV）是唯一已知感染家禽的冠状病毒。IBV 的复制和发病机制尚未得到充分了解，主要是因为缺乏强大的细胞培养系统。在这里，我们报告说，有效的泛素蛋白酶体系统（UPS）对于 IBV 在 Vero 细胞中的有效复制是必需的。在存在针对 UPS 的化学抑制剂的情况下，IBV 特异性 RNA 的合成以及病毒蛋白的合成受到阻碍。与其他冠状病毒一样，IBV 编码一种木瓜蛋白酶样蛋白酶（PLpro），该蛋白酶除了对复制酶多蛋白进行蛋白水解加工外，还具有体外去泛素化酶活性。我们的结果表明，IBV PLpro 酶抑制感染鸡胚成纤维细胞（DF-1）细胞中干扰素β（IFNβ）的合成，并且在黑色素瘤分化相关蛋白 5（MDA5）和 TANK 结合激酶 1（TBK1）存在下，这种活性增强。IBV PLpro 在 DF-1 细胞中过表达时，去泛素化 MDA5 和 TBK1。这两种蛋白以及其他衔接分子（如 MAVS、IKKε 和 IRF3）形成 IFNβ 合成的信号级联。MDA5 和 TBK1 的泛素化对于它们的激活是必需的，而 IBV PLpro 对它们的去泛素化使它们无法参与抗病毒信号转导。这项研究首次表明，在 IBV 感染过程中 UPS 和先天免疫反应之间存在串扰，并且 IBV PLpro 的去泛素化酶活性参与其作为 IFN 拮抗剂的活性。这一见解将有助于设计针对 IBV PLpro 酶催化活性的更好抗病毒药物。
