Epstein-Barr virus BNRF1 destabilizes SMC5/6 cohesin complexes to evade its restriction of replication compartments. Yiu et al.

Epstein-Barr virus (EBV) persistently infects most people worldwide. Delivery of ~170 kilobase EBV genomes to nuclei, and use of nuclear membrane-less replication compartments (RC) for their lytic cycle amplification, necessitate evasion of intrinsic antiviral responses. Proteomic analysis identified that upon B-cell infection or lytic reactivation, EBV depletes the chromosome maintenance cohesin SMC5/6, which has major chromosome maintenance roles and DNA damage repair. The major tegument protein BNRF1 targeted SMC5/6 complexes by a ubiquitin proteasome pathway dependent on calpain proteolysis and cullin-7. In the absence of BNRF1, SMC5/6 associated with R-loop structures, including at the viral lytic origin of replication, and interfered with RC formation and encapsidation. CRISPR analysis highlighted RC restriction roles of SMC5/6 components involved in DNA entrapment and SUMOylation. Our studies highlight SMC5/6 as a key intrinsic immune sensor and restriction factor for a human herpesvirus RC and have implications for the pathogenesis of EBV-associated cancers.

爱泼斯坦-巴尔病毒(Epstein-Barr virus, EBV)可在全球绝大多数人群中建立持续性感染。将约170千碱基(kilobase)的EBV基因组递送至细胞核，并利用无核膜复制区室(replication compartments, RC)完成其裂解周期的扩增，这一过程需逃逸固有抗病毒免疫应答。蛋白质组学分析(proteomic analysis)显示，在B细胞(B-cell)感染或病毒裂解性激活(lytic reactivation)后，EBV会降解染色体维持型黏连素SMC5/6(cohesin SMC5/6)——该复合物在染色体维持与DNA损伤修复中发挥关键作用。该病毒的主要被膜蛋白BNRF1通过依赖于钙蛋白酶水解(calpain proteolysis)与Cullin-7(cullin-7)的泛素蛋白酶体通路(ubiquitin proteasome pathway)靶向SMC5/6复合物。在缺失BNRF1的情况下，SMC5/6会与包括病毒裂解复制起点(viral lytic origin of replication)在内的R环结构(R-loop structures)结合，并干扰RC的形成与病毒衣壳化(encapsidation)。CRISPR分析(CRISPR analysis)证实，参与DNA捕获(DNA entrapment)与类泛素化修饰(SUMOylation)的SMC5/6组分对RC具有限制作用。本研究明确了SMC5/6作为人类疱疹病毒(human herpesvirus)RC的关键固有免疫感受器与限制因子，其研究结果可为阐释EBV相关癌症(EBV-associated cancers)的致病机制(pathogenesis)提供重要理论参考。