Stewart Hazel, Lu Yongxu, O'Keefe Sarah, Valpadashi Anusha, Cruz-Zaragoza Luis Daniel, Michel Hendrik A, Nguyen Samantha K, Carnell George W, Lukhovitskaya Nina, Milligan Rachel, Adewusi Yasmin, Jungreis Irwin, Lulla Valeria, Matthews David A, High Stephen, Rehling Peter, Emmott Edward, Heeney Jonathan L, Davidson Andrew D, Edgar James R, Smith Geoffrey L, Firth Andrew E
Department of Pathology, University of Cambridge, Cambridge, UK.
Faculty of Biology, Medicine and Health, School of Biological Sciences, University of Manchester, Manchester, UK.
iScience. 2023 Sep 28;26(11):108080. doi: 10.1016/j.isci.2023.108080. eCollection 2023 Nov 17.
The SARS-CoV-2 genome encodes a multitude of accessory proteins. Using comparative genomic approaches, an additional accessory protein, ORF3c, has been predicted to be encoded within the ORF3a sgmRNA. Expression of ORF3c during infection has been confirmed independently by ribosome profiling. Despite ORF3c also being present in the 2002-2003 SARS-CoV, its function has remained unexplored. Here we show that ORF3c localizes to mitochondria, where it inhibits innate immunity by restricting IFN-β production, but not NF-κB activation or JAK-STAT signaling downstream of type I IFN stimulation. We find that ORF3c is inhibitory after stimulation with cytoplasmic RNA helicases RIG-I or MDA5 or adaptor protein MAVS, but not after TRIF, TBK1 or phospho-IRF3 stimulation. ORF3c co-immunoprecipitates with the antiviral proteins MAVS and PGAM5 and induces MAVS cleavage by caspase-3. Together, these data provide insight into an uncharacterized mechanism of innate immune evasion by this important human pathogen.
严重急性呼吸综合征冠状病毒2（SARS-CoV-2）基因组编码多种辅助蛋白。通过比较基因组学方法，预测在开放阅读框3a（ORF3a）亚基因组mRNA（sgmRNA）内编码一种额外的辅助蛋白，即ORF3c。感染期间ORF3c的表达已通过核糖体图谱分析独立得到证实。尽管ORF3c也存在于2002 - 2003年的严重急性呼吸综合征冠状病毒（SARS-CoV）中，但其功能仍未被探索。在此，我们表明ORF3c定位于线粒体，在那里它通过限制干扰素-β（IFN-β）的产生来抑制先天免疫，但不影响核因子κB（NF-κB）的激活或I型干扰素刺激下游的JAK-STAT信号传导。我们发现，在用细胞质RNA解旋酶视黄酸诱导基因I（RIG-I）或黑色素瘤分化相关基因5（MDA5）或衔接蛋白线粒体抗病毒信号蛋白（MAVS）刺激后，ORF3c具有抑制作用，但在用TIR结构域衔接蛋白诱导干扰素β（TRIF）、TANK结合激酶1（TBK1）或磷酸化干扰素调节因子3（IRF3）刺激后则没有抑制作用。ORF3c与抗病毒蛋白MAVS和磷酸甘油酸变位酶5（PGAM5）共免疫沉淀，并诱导MAVS被半胱天冬酶-3切割。总之，这些数据为这种重要的人类病原体逃避先天免疫的未知机制提供了见解。
