Naik Nenavath Gopal, Lee See-Chi, Alonso Juan D, Toth Zsolt
Department of Oral Biology, University of Florida College of Dentistry, 1395 Center Drive, Gainesville, FL 32610, USA.
Department of Oral Biology, University of Florida College of Dentistry, 1395 Center Drive, Gainesville, FL 32610, USA
J Virol. 2021 May 10;95(11). doi: 10.1128/JVI.00331-21. Epub 2021 Mar 10.
It is still largely unknown what host factors are involved in controlling the expression of the lytic viral gene RTA during primary infection, which determines if Kaposi's sarcoma-associated herpesvirus (KSHV) establishes latent or lytic infection. We have recently identified the histone demethylase KDM2B as a repressor of RTA expression during both KSHV infection and latency based on an epigenetic factor siRNA screen. Here, we report that surprisingly, KDM2B overexpression can promote lytic infection by using a mechanism that differs from what is needed for its repressor function. Our study revealed that while the DNA-binding and demethylase activities of KDM2B linked to its transcription repressive function are dispensable, its C-terminal F-box and LRR domains are required for the lytic infection-inducing function of KDM2B. We found that overexpressed KDM2B increases the half-life of the AP-1 subunit c-Jun protein and induces the AP-1 signaling pathway. This effect is dependent upon the binding of KDM2B to the SKP1-CUL1-F-box (SCF) E3 ubiquitin ligase complex via its F-box domain. Importantly, the inhibition of AP-1 reduces KDM2B-mediated lytic KSHV infection. Overall, our findings indicate that KDM2B may induce the degradation of some host factors by using the SCF complex resulting in the enrichment of c-Jun. This leads to increased AP-1 transcriptional activity, which facilitates lytic gene expression following infection interfering with the establishment of viral latency.The expression of epigenetic factors is often dysregulated in cancers or upon specific stress signals, which often results in a display of non-canonical functions of the epigenetic factors that are independent from their chromatin-modifying roles. We have previously demonstrated that KDM2B normally inhibits KSHV lytic cycle using its histone demethylase activity. Surprisingly, we found that KDM2B overexpression can promote lytic infection, which does not require its histone demethylase or DNA-binding functions. Instead, KDM2B uses the SKP1-CUL1-F-box (SCF) E3 ubiquitin ligase complex to induce AP-1 transcriptional activity, which promotes lytic gene expression. This is the first report that demonstrates a functional link between SFC and AP-1 in the regulation of KSHV lytic cycle.
在初次感染期间，哪些宿主因素参与控制裂解性病毒基因RTA的表达在很大程度上仍不清楚，而RTA的表达决定了卡波西肉瘤相关疱疹病毒（KSHV）是建立潜伏感染还是裂解感染。基于表观遗传因子siRNA筛选，我们最近鉴定出组蛋白去甲基化酶KDM2B在KSHV感染和潜伏期间均为RTA表达的抑制剂。在此，我们报告令人惊讶的是，KDM2B过表达可通过一种与其抑制功能所需机制不同的机制促进裂解感染。我们的研究表明，虽然与KDM2B转录抑制功能相关的DNA结合和去甲基化酶活性并非必需，但其C端F盒和LRR结构域是KDM2B诱导裂解感染功能所必需的。我们发现过表达的KDM2B增加了AP-1亚基c-Jun蛋白的半衰期并诱导AP-1信号通路。这种效应依赖于KDM2B通过其F盒结构域与SKP1-CUL1-F盒（SCF）E3泛素连接酶复合物的结合。重要的是，抑制AP-1可减少KDM2B介导的KSHV裂解感染。总体而言，我们的研究结果表明，KDM2B可能通过利用SCF复合物诱导某些宿主因素的降解，从而导致c-Jun富集。这导致AP-1转录活性增加，这有利于感染后裂解基因的表达，干扰病毒潜伏的建立。表观遗传因子的表达在癌症中或在特定应激信号作用下常常失调，这通常导致表观遗传因子展现出与其染色质修饰作用无关的非经典功能。我们之前已经证明，KDM2B通常利用其组蛋白去甲基化酶活性抑制KSHV裂解周期。令人惊讶的是，我们发现KDM2B过表达可促进裂解感染，这并不需要其组蛋白去甲基化酶或DNA结合功能。相反，KDM2B利用SKP1-CUL1-F盒（SCF）E3泛素连接酶复合物诱导AP-1转录活性，从而促进裂解基因表达。这是第一份证明SFC与AP-1在KSHV裂解周期调控中存在功能联系的报告。
