Department of Biochemical Science and Technology, College of Life Science, National Taiwan University, Taipei City, Taiwan.
Division of Infectious Disease, Department of Internal Medicine, Kaohsiung Medical University Chung-Ho Memorial Hospital, Kaohsiung Medical University, Kaohsiung City, Taiwan; Center for Tropical Medicine and Infectious Disease Research, Kaohsiung Medical University, Kaohsiung City, Taiwan.
J Mol Biol. 2020 Sep 4;432(19):5227-5243. doi: 10.1016/j.jmb.2020.07.011. Epub 2020 Jul 23.
Rta of Epstein-Barr virus (EBV) is thought to be expressed only during the lytic cycle to promote the transcription of lytic genes. However, we found that Rta is expressed in EBV-infected B cells during viral latency, at levels detectable by immunoblot analysis. Latent Rta expression cannot be attributed to spontaneous lytic activation, as we observed that more than 90% of Akata, P3HR1, and 721 cells latently infected by EBV express Rta. We further found that Rta is sequestered in the nucleolus during EBV latency through its interaction with MCRS2, a nucleolar protein. When Rta is sequestered in the nucleolus, it no longer activates RNA polymerase II-driven transcription, thus explaining why Rta expression during latency does not transactivate EBV lytic genes. Additional experiments showed that Rta can bind to 18S rRNA and become incorporated into ribosomes, and a transient transfection experiment showed that Rta promotes translation from an mRNA reporter. These findings reveal that Rta has novel functions beyond transcriptional activation during EBV latency and may have interesting implications for the concept of EBV latency.
Epstein-Barr 病毒 (EBV) 的 Rta 被认为仅在裂解周期中表达，以促进裂解基因的转录。然而，我们发现 Rta 在 EBV 感染的 B 细胞中在病毒潜伏期间表达，通过免疫印迹分析可检测到水平。潜伏 Rta 的表达不能归因于自发的裂解激活，因为我们观察到超过 90%的 Akata、P3HR1 和 721 细胞潜伏感染 EBV 表达 Rta。我们进一步发现，Rta 通过与核仁蛋白 MCRS2 的相互作用在 EBV 潜伏期间被隔离在核仁中。当 Rta 被隔离在核仁中时，它不再激活 RNA 聚合酶 II 驱动的转录，从而解释了为什么潜伏期间 Rta 的表达不会反式激活 EBV 裂解基因。额外的实验表明，Rta 可以与 18S rRNA 结合并整合到核糖体中，瞬时转染实验表明 Rta 促进 mRNA 报告基因的翻译。这些发现表明，Rta 在 EBV 潜伏期间具有超越转录激活的新功能，这可能对 EBV 潜伏的概念具有有趣的意义。
