Shugoshin 1 is dislocated by KSHV-encoded LANA inducing aneuploidy

Shugoshin-1 (Sgo1) protects the integrity of the centromeres, and H2A phosphorylation is critical for this process. The mitotic checkpoint kinase Bub1, phosphorylates H2A and ensures fidelity of chromosome segregation and chromosome number. Oncogenic KSHV induces genetic alterations through chromosomal instability (CIN), and its essential antigen LANA regulates Bub1. We show that LANA inhibits Bub1 phosphorylation of H2A and Cdc20, important for chromosome segregation and mitotic signaling. Inhibition of H2A phosphorylation at residue T120 by LANA resulted in dislocation of Sgo1, and cohesin from the centromeres. Arrest of Cdc20 phosphorylation also rescued degradation of Securin and Cyclin B1 at mitotic exit, and interaction of H2A, and Cdc20 with Bub1 was inhibited by LANA. The N-terminal nuclear localization sequence domain of LANA was essential for LANA and Bub1 interaction, reversed LANA inhibited phosphorylation of H2A and Cdc20, and attenuated LANA-induced aneuploidy and cell proliferation. This molecular mechanism whereby KSHV-induced CIN, demonstrated that the NNLS of LANA is a promising target for development of anti-viral therapies targeting KSHV associated cancers.着丝粒保护蛋白1（Shugoshin-1, Sgo1）可维持着丝粒的结构完整性，而组蛋白H2A磷酸化对此过程发挥关键调控作用。有丝分裂检验点激酶Bub1能够磷酸化组蛋白H2A，保障染色体分离的保真度与染色体数目稳定。致瘤性卡波西肉瘤相关疱疹病毒（KSHV）可通过诱导染色体不稳定性（CIN）引发遗传改变，其核心抗原LANA可对Bub1进行调控。本研究发现，LANA能够抑制Bub1对组蛋白H2A与Cdc20的磷酸化修饰，该调控过程对染色体分离及有丝分裂信号转导具有重要意义。LANA对T120位点组蛋白H2A磷酸化的抑制，会导致着丝粒处Sgo1与黏连蛋白（cohesin）发生解离。阻断Cdc20的磷酸化，同样可挽救有丝分裂退出阶段的分离酶抑制蛋白（Securin）与细胞周期蛋白B1（Cyclin B1）的降解过程；同时LANA可抑制组蛋白H2A、Cdc20与Bub1的相互结合。LANA的N端核定位序列（NLS）结构域是LANA与Bub1相互作用的必需元件，该结构域可逆转LANA对组蛋白H2A与Cdc20磷酸化的抑制作用，并缓解LANA诱导的非整倍体与细胞增殖异常。本研究阐明了KSHV诱导染色体不稳定性的分子机制，证实LANA的核定位序列（NLS）可作为靶向KSHV相关癌症的抗病毒治疗的潜在靶点。