Division of Infection and Immunity, Department of Electromagnetic and Laser Biology, Beijing Institute of Radiation Medicine, Beijing, 100850, China.
Protein Cell. 2014 May;5(5):369-81. doi: 10.1007/s13238-014-0026-3. Epub 2014 Mar 14.
SARS coronavirus (SARS-CoV) develops an antagonistic mechanism by which to evade the antiviral activities of interferon (IFN). Previous studies suggested that SARS-CoV papain-like protease (PLpro) inhibits activation of the IRF3 pathway, which would normally elicit a robust IFN response, but the mechanism(s) used by SARS PLpro to inhibit activation of the IRF3 pathway is not fully known. In this study, we uncovered a novel mechanism that may explain how SARS PLpro efficiently inhibits activation of the IRF3 pathway. We found that expression of the membrane-anchored PLpro domain (PLpro-TM) from SARS-CoV inhibits STING/TBK1/IKKε-mediated activation of type I IFNs and disrupts the phosphorylation and dimerization of IRF3, which are activated by STING and TBK1. Meanwhile, we showed that PLpro-TM physically interacts with TRAF3, TBK1, IKKε, STING, and IRF3, the key components that assemble the STING-TRAF3-TBK1 complex for activation of IFN expression. However, the interaction between the components in STING-TRAF3-TBK1 complex is disrupted by PLpro-TM. Furthermore, SARS PLpro-TM reduces the levels of ubiquitinated forms of RIG-I, STING, TRAF3, TBK1, and IRF3 in the STING-TRAF3-TBK1 complex. These results collectively point to a new mechanism used by SARS-CoV through which PLpro negatively regulates IRF3 activation by interaction with STING-TRAF3-TBK1 complex, yielding a SARS-CoV countermeasure against host innate immunity.
严重急性呼吸综合征冠状病毒（SARS-CoV）通过一种拮抗机制来逃避干扰素（IFN）的抗病毒活性。先前的研究表明，SARS-CoV 木瓜蛋白酶样蛋白酶（PLpro）抑制了 IRF3 途径的激活，该途径通常会引发强烈的 IFN 反应，但 SARS PLpro 抑制 IRF3 途径激活所使用的机制尚不完全清楚。在这项研究中，我们揭示了一种可能解释 SARS PLpro 如何有效地抑制 IRF3 途径激活的新机制。我们发现，来自 SARS-CoV 的膜锚定 PLpro 结构域（PLpro-TM）的表达抑制了 STING/TBK1/IKKε 介导的 I 型 IFN 的激活，并破坏了 STING 和 TBK1 激活的 IRF3 的磷酸化和二聚化。同时，我们表明，PLpro-TM 与 TRAF3、TBK1、IKKε、STING 和 IRF3 发生物理相互作用，这些是组装 STING-TRAF3-TBK1 复合物以激活 IFN 表达的关键成分。然而，PLpro-TM 破坏了 STING-TRAF3-TBK1 复合物中各成分之间的相互作用。此外，SARS PLpro-TM 降低了 STING-TRAF3-TBK1 复合物中 RIG-I、STING、TRAF3、TBK1 和 IRF3 的泛素化形式的水平。这些结果共同指出了 SARS-CoV 通过与 STING-TRAF3-TBK1 复合物相互作用来负调控 IRF3 激活的新机制，从而产生 SARS-CoV 对抗宿主固有免疫的对策。
