Genome-Scale Biology Program, Biomedicum Helsinki & Institute of Biomedicine, University of Helsinki, Helsinki, Finland.
PLoS Pathog. 2010 Mar 19;6(3):e1000818. doi: 10.1371/journal.ppat.1000818.
Nucleophosmin (NPM) is a multifunctional nuclear phosphoprotein and a histone chaperone implicated in chromatin organization and transcription control. Oncogenic Kaposi's sarcoma herpesvirus (KSHV) is the etiological agent of Kaposi's sarcoma, primary effusion lymphoma (PEL) and multicentric Castleman disease (MCD). In the infected host cell KSHV displays two modes of infection, the latency and productive viral replication phases, involving extensive viral DNA replication and gene expression. A sustained balance between latency and reactivation to the productive infection state is essential for viral persistence and KSHV pathogenesis. Our study demonstrates that the KSHV v-cyclin and cellular CDK6 kinase phosphorylate NPM on threonine 199 (Thr199) in de novo and naturally KSHV-infected cells and that NPM is phosphorylated to the same site in primary KS tumors. Furthermore, v-cyclin-mediated phosphorylation of NPM engages the interaction between NPM and the latency-associated nuclear antigen LANA, a KSHV-encoded repressor of viral lytic replication. Strikingly, depletion of NPM in PEL cells leads to viral reactivation, and production of new infectious virus particles. Moreover, the phosphorylation of NPM negatively correlates with the level of spontaneous viral reactivation in PEL cells. This work demonstrates that NPM is a critical regulator of KSHV latency via functional interactions with v-cyclin and LANA.
核仁磷酸蛋白（Nucleophosmin，NPM）是一种多功能核磷蛋白，也是一种组蛋白伴侣，参与染色质组织和转录调控。致瘤性卡波西肉瘤疱疹病毒（Kaposi's sarcoma herpesvirus，KSHV）是卡波西肉瘤、原发性渗出性淋巴瘤（primary effusion lymphoma，PEL）和多中心卡斯特曼病（multicentric Castleman disease，MCD）的病原体。在受感染的宿主细胞中，KSHV 显示出两种感染模式，潜伏和有活力的病毒复制阶段，涉及广泛的病毒 DNA 复制和基因表达。潜伏和重新激活到有活力的感染状态之间的持续平衡对于病毒持续存在和 KSHV 发病机制至关重要。我们的研究表明，KSHV 的 v-cyclin 和细胞周期蛋白依赖性激酶 6（CDK6）激酶在从头和自然感染 KSHV 的细胞中使 NPM 的苏氨酸 199（Thr199）磷酸化，并且 NPM 在原发性 KS 肿瘤中被磷酸化至相同的位点。此外，v-cyclin 介导的 NPM 磷酸化使 NPM 与潜伏相关核抗原 LANA 相互作用，LANA 是 KSHV 编码的病毒裂解复制抑制剂。引人注目的是，PEL 细胞中 NPM 的耗竭导致病毒重新激活和新的感染性病毒颗粒的产生。此外，NPM 的磷酸化与 PEL 细胞中自发病毒重新激活的水平呈负相关。这项工作表明，NPM 通过与 v-cyclin 和 LANA 的功能相互作用，是 KSHV 潜伏的关键调节剂。
