Department of Molecular Biophysics, Yale University School of Medicine, New Haven, Connecticut, USA.
Department of Biochemistry, Yale University School of Medicine, New Haven, Connecticut, USA.
J Virol. 2018 Sep 26;92(20). doi: 10.1128/JVI.01254-18. Print 2018 Oct 15.
Profound alterations in host cell nuclear architecture accompany the lytic phase of Epstein-Barr virus (EBV) infection. Viral replication compartments assemble, host chromatin marginalizes to the nuclear periphery, cytoplasmic poly(A)-binding protein translocates to the nucleus, and polyadenylated mRNAs are sequestered within the nucleus. Virus-induced changes to nuclear architecture that contribute to viral host shutoff (VHS) must accommodate selective processing and export of viral mRNAs. Here we describe additional previously unrecognized nuclear alterations during EBV lytic infection in which viral and cellular factors that function in pre-mRNA processing and mRNA export are redistributed. Early during lytic infection, before formation of viral replication compartments, two cellular pre-mRNA splicing factors, SC35 and SON, were dispersed from interchromatin granule clusters, and three mRNA export factors, Y14, ALY, and NXF1, were depleted from the nucleus. During late lytic infection, virus-induced nodular structures (VINORCs) formed at the periphery of viral replication compartments. VINORCs were composed of viral (BMLF1 and BGLF5) and cellular (SC35, SON, SRp20, and NXF1) proteins that mediate pre-mRNA processing and mRNA export. BHLF1 long noncoding RNA was invariably found in VINORCs. VINORCs did not contain other nodular nuclear cellular proteins (PML or coilin), nor did they contain viral proteins (BRLF1 or BMRF1) found exclusively within replication compartments. VINORCs are novel EBV-induced nuclear structures. We propose that EBV-induced dispersal and depletion of pre-mRNA processing and mRNA export factors during early lytic infection contribute to VHS; subsequent relocalization of these pre-mRNA processing and mRNA export proteins to VINORCs and viral replication compartments facilitates selective processing and export of viral mRNAs. In order to make protein, mRNA transcribed from DNA in the nucleus must enter the cytoplasm. Nuclear export of mRNA requires correct processing of mRNAs by enzymes that function in splicing and nuclear export. During the Epstein-Barr virus (EBV) lytic cycle, nuclear export of cellular mRNAs is blocked, yet export of viral mRNAs is facilitated. Here we report the dispersal and dramatic reorganization of cellular (SC35, SON, SRp20, Y14, ALY, and NXF1) and viral (BMLF1 and BGLF5) proteins that play key roles in pre-mRNA processing and export of mRNA. These virus-induced nuclear changes culminate in formation of VINORCs, novel nodular structures composed of viral and cellular RNA splicing and export factors. VINORCs localize to the periphery of viral replication compartments, where viral mRNAs reside. These EBV-induced changes in nuclear organization may contribute to blockade of nuclear export of host mRNA, while enabling selective processing and export of viral mRNA.
宿主细胞核结构的深刻改变伴随着 Epstein-Barr 病毒 (EBV) 感染的裂解期。病毒复制隔间组装，宿主染色质边缘化到核周，细胞质多聚(A)结合蛋白易位到核内，多聚腺苷酸化的 mRNAs 被隔离在核内。病毒诱导的核结构改变有助于病毒宿主关闭 (VHS)，必须适应病毒 mRNA 的选择性加工和输出。在这里，我们描述了 EBV 裂解感染过程中另外一些以前未被识别的核改变，其中参与前体 mRNA 加工和 mRNA 输出的病毒和细胞因子重新分布。在裂解感染早期，在形成病毒复制隔间之前，两个细胞前体 mRNA 剪接因子 SC35 和 SON 从染色质间颗粒簇中分散，三个 mRNA 输出因子 Y14、ALY 和 NXF1 从核内耗尽。在晚期裂解感染期间，病毒诱导的结节状核结构 (VINORCs) 形成于病毒复制隔间的外围。VINORCs 由病毒 (BMLF1 和 BGLF5) 和细胞 (SC35、SON、SRp20 和 NXF1) 蛋白组成，这些蛋白介导前体 mRNA 加工和 mRNA 输出。BHLF1 长非编码 RNA 始终存在于 VINORCs 中。VINORCs 不包含其他结节状核细胞蛋白 (PML 或 coilin)，也不包含仅存在于复制隔间内的病毒蛋白 (BRLF1 或 BMRF1)。VINORCs 是新型 EBV 诱导的核结构。我们提出，在早期裂解感染过程中，前体 mRNA 加工和 mRNA 输出因子的分散和耗竭有助于 VHS；随后，这些前体 mRNA 加工和 mRNA 输出蛋白重新定位到 VINORCs 和病毒复制隔间中，促进了病毒 mRNAs 的选择性加工和输出。为了合成蛋白质，从细胞核中的 DNA 转录的 mRNA 必须进入细胞质。mRNA 的核输出需要由在剪接和核输出中起作用的酶正确加工 mRNAs。在 Epstein-Barr 病毒 (EBV) 裂解周期中，细胞 mRNA 的核输出被阻断，但病毒 mRNA 的输出却得到促进。在这里，我们报告了细胞 (SC35、SON、SRp20、Y14、ALY 和 NXF1) 和病毒 (BMLF1 和 BGLF5) 蛋白的分散和显著重组，这些蛋白在 mRNA 的前体加工和输出中起着关键作用。这些病毒诱导的核变化最终导致 VINORCs 的形成，VINORCs 是由病毒和细胞 RNA 剪接和输出因子组成的新型结节状结构。VINORCs 定位于病毒复制隔间的外围，病毒 mRNAs 就位于那里。这些 EBV 诱导的核组织变化可能有助于阻断宿主 mRNA 的核输出，同时允许病毒 mRNA 的选择性加工和输出。
