Department of Virology, Faculty of Medicine, Imperial College London, Norfolk Place, London W2 1PG, UK.
Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK.
J Gen Virol. 2012 Oct;93(Pt 10):2098-2108. doi: 10.1099/vir.0.045070-0. Epub 2012 Jul 12.
Vaccinia virus (VACV) strain Western Reserve protein C4 has been characterized and its function and contribution to virus virulence assessed. Bioinformatic analysis showed that C4 is conserved in six orthopoxvirus species and shares 43 % amino acid identity with VACV protein C16, a known virulence factor. A recombinant VACV expressing a C-terminally tagged version of C4 showed that, like C16, this 37 kDa protein is expressed early during infection and localizes to both the cytoplasm and the nucleus. Functional assays using a firefly luciferase reporter plasmid under the control of a nuclear factor kappa B (NF-κB)-dependent promoter demonstrated that C4 inhibits NF-κB activation at, or downstream of, the inhibitor of kappa kinase (IKK) complex. Consistent with this, C4 inhibited interleukin-1β-induced translocation of p65 into the nucleus. A VACV lacking the C4L gene (vΔC4) showed no significant differences from wild-type virus in growth kinetics or spread in cell culture, but had reduced virulence in a murine intranasal model of infection. vΔC4-infected mice exhibited fewer symptoms, lost less weight and recovered 7 days earlier than animals infected with control viruses expressing C4. Furthermore, bronchoalveolar lavage fluid from vΔC4-infected mice had increased cell numbers at day 5 post-infection, which correlated with reduced lung virus titres from this time onward. C4 represents the ninth VACV protein to inhibit NF-κB activation and remarkably, in every case examined, loss of each protein individually caused an alteration in virus virulence, despite the presence of other NF-κB inhibitors.
牛痘病毒（VACV）菌株西部储备蛋白 C4 已被鉴定，其功能及其对病毒毒力的贡献也已得到评估。生物信息学分析表明，C4 在六种正痘病毒物种中保守，与 VACV 蛋白 C16 （一种已知的毒力因子）共享 43%的氨基酸同一性。表达 C4 末端标记版本的重组 VACV 表明，与 C16 一样，这种 37 kDa 蛋白在感染早期表达，并定位于细胞质和细胞核。使用核因子 kappa B （NF-κB）依赖性启动子控制的萤火虫荧光素酶报告质粒进行的功能测定表明，C4 在 IKK 复合物或其下游抑制 NF-κB 激活。与此一致，C4 抑制白细胞介素-1β诱导的 p65 向核内易位。缺乏 C4L 基因的 VACV （vΔC4）在细胞培养物中的生长动力学或传播方面与野生型病毒没有明显差异，但在感染的小鼠鼻腔模型中毒力降低。vΔC4 感染的小鼠表现出较少的症状，体重减轻较少，并且比感染表达 C4 的对照病毒的动物早 7 天恢复。此外，vΔC4 感染的小鼠在感染后第 5 天的支气管肺泡灌洗液中细胞数量增加，这与从那时起肺病毒滴度降低有关。C4 是第九种抑制 NF-κB 激活的 VACV 蛋白，值得注意的是，在每种情况下，单独失去每种蛋白都会导致病毒毒力发生变化，尽管存在其他 NF-κB 抑制剂。
