Han Mingyuan, Ke Hanzhong, Zhang Qingzhan, Yoo Dongwan
Department of Pathobiology, University of Illinois at Urbana-Champaign, 2001 South Lincoln Avenue, Urbana, IL 61802, USA.
Department of Pathobiology, University of Illinois at Urbana-Champaign, 2001 South Lincoln Avenue, Urbana, IL 61802, USA.
Virology. 2017 May;505:42-55. doi: 10.1016/j.virol.2017.02.004. Epub 2017 Feb 20.
Positive-strand RNA genomes function as mRNA for viral protein synthesis which is fully reliant on host cell translation machinery. Competing with cellular protein translation apparatus needs to ensure the production of viral proteins, but this also stifles host innate defense. In the present study, we showed that porcine reproductive and respiratory syndrome virus (PRRSV), whose replication takes place in the cytoplasm, imprisoned host cell mRNA in the nucleus, which suggests a novel mechanism to enhance translation of PRRSV genome. PRRSV nonstructural protein (nsp) 1β was identified as the nuclear protein playing the role for host mRNA nuclear retention and subversion of host protein synthesis. A SAP (SAF-A/B, Acinus, and PIAS) motif was identified in nsp1β with the consensus sequence of -LQxxLxxxGL-. In situ hybridization unveiled that SAP mutants were unable to cause nuclear retention of host cell mRNAs and did not suppress host protein synthesis. In addition, these SAP mutants reverted PRRSV-nsp1β-mediated suppression of interferon (IFN) production, IFN signaling, and TNF-α production pathway. Using reverse genetics, a series of SAP mutant PRRS viruses, vK124A, vL126A, vG134A, and vL135A were generated. No mRNA nuclear retention was observed during vL126A and vL135A infections. Importantly, vL126A and vL135A did not suppress IFN production. For other arteriviruses, mRNA nuclear accumulation was also observed for LDV-nsp1β and SHFV-nsp1β. EAV-nsp1 was exceptional and did not block the host mRNA nuclear export.
正链RNA基因组作为病毒蛋白合成的mRNA，完全依赖宿主细胞的翻译机制。与细胞蛋白翻译装置竞争需要确保病毒蛋白的产生，但这也抑制了宿主的先天防御。在本研究中，我们发现猪繁殖与呼吸综合征病毒（PRRSV）在细胞质中复制，将宿主细胞mRNA囚禁在细胞核中，这提示了一种增强PRRSV基因组翻译的新机制。PRRSV非结构蛋白（nsp）1β被鉴定为在宿主mRNA核滞留和宿主蛋白合成颠覆中起作用的核蛋白。在nsp1β中鉴定出一个SAP（SAF-A/B、Acinus和PIAS）基序，其共有序列为-LQxxLxxxGL-。原位杂交显示，SAP突变体无法导致宿主细胞mRNA的核滞留，也不抑制宿主蛋白合成。此外，这些SAP突变体恢复了PRRSV-nsp1β介导的对干扰素（IFN）产生、IFN信号传导和TNF-α产生途径的抑制。利用反向遗传学，构建了一系列SAP突变的PRRS病毒，vK124A、vL126A、vG134A和vL135A。在vL126A和vL135A感染期间未观察到mRNA核滞留。重要的是，vL126A和vL135A不抑制IFN产生。对于其他动脉炎病毒，LDV-nsp1β和SHFV-nsp1β也观察到mRNA核积累。EAV-nsp1是例外，不阻断宿主mRNA的核输出。
