Epigenomic Control of KSHV Latency

KSHV是所有形式卡波西肉瘤（KS）的病原体。KS是撒哈拉以南非洲地区男性和艾滋病患者中最常见的癌症。KSHV还可导致多种淋巴系统疾病，包括胸腔积液淋巴瘤（PEL）和Castleman病。B淋巴细胞的长期潜伏感染和内皮细胞的持续感染被认为是KSHV肿瘤发生的主要驱动力。KSHV的发病机制取决于潜伏感染期间病毒的持久性和高度调控的基因表达。我们关注的是在KSHV感染的肿瘤细胞中调节病毒基因表达和维持稳定潜伏期的表观遗传和染色质组织因子。在这里，我们扩展了对KSHV编码LANA的X射线晶体结构的研究，以探索其形成高阶寡聚复合物的倾向，这是维持片段所必需的。我们通过细胞因子，包括染色质组织因子CTCF和内聚素以及异染色质调节因子DAXX和EZH2，研究了LANA寡聚化与染色质组织的关系。我们还研究了溴域蛋白BRD2和BRD4如何结合到LANA DNA结合域的基本斑块上，以及这些β -蛋白如何促进LANA染色质结合和表观基因组结构。我们发现BET蛋白的小分子抑制剂，如JQ1，是KSHV裂解基因表达的有效激活剂，并研究BRD2或BRD4功能的破坏如何改变KSHV表观基因组。最后，我们分析了KS病变的转录组学数据，揭示了未折叠蛋白反应（UPR）在调节KSHV潜伏期中的核心作用。我们发现UPR诱导剂通过一种机制破坏KSHV潜伏期，该机制涉及内聚蛋白亚基RAD21的快速蛋白水解裂解。我们提出RAD21的裂解作为裂解再激活的快速释放触发器，因此代表了一种新的染色质-构象传感器机制。UPR与RAD21-BRD2/4-LANA轴之间的潜在机制关系将被研究。最后，我们探讨了UPR的药理抑制如何调节KSHV基因表达以改善KS的进展和发病机制。这些研究将提高我们对KSHV感染的认识，为KSHV相关疾病的治疗干预提供机会。

KSHV is the causative agent of all forms of Kaposi’s sarcoma (KS). KS is the most common form of cancer in males in sub-Saharan Africa and HIV-AIDS patients. KSHV is also responsible for several lymphoid disorders, including pleural effusion lymphoma (PEL) and Castleman’s disease. Long-term latent infection in B- lymphocytes and persistent infection in endothelial cells is thought to be a major driving force for KSHV oncogenesis. KSHV pathogenesis depends on viral persistence and highly regulated gene expression during latent infection. We have focused on epigenetic and chromatin organizing factors that regulate viral gene expression and maintain stable latency in KSHV infected tumor cells. Here, we expand our studies on the X- ray crystal structures of KSHV encoded LANA to explore its propensity to form higher-order oligomeric complexes that are necessary for episome maintenance. We investigate the relationship between LANA oligomerization and chromatin organization mediated by cellular factors, including the chromatin organizing factors CTCF and cohesins and the heterochromatin regulatory factors DAXX and EZH2. We also investigate how the bromodomain proteins BRD2 and BRD4 bind to the basic patch of the LANA DNA binding domain, and how these BET-proteins function to facilitate LANA chromatin binding, and epigenome architecture. We discovered that small molecule inhibitors of BET proteins, like JQ1, are potent activators of KSHV lytic gene expression, and investigate how disruption of BRD2 or BRD4 function alters the KSHV epigenome. Finally, we analyze transcriptomic data from KS lesions to reveal a central role of the Unfolded Protein Response (UPR) in regulating KSHV latency. We find that inducers of the UPR disrupt KSHV latency through a mechanism involving the rapid proteolytic cleavage of the Cohesin subunit RAD21. We propose that RAD21 cleavage functions as a rapid release trigger for lytic reactivation, and therefore represents a novel chromatin- conformation sensor mechanism for UPR stress. The potential mechanistic relationship between UPR and the RAD21-BRD2/4-LANA axis will be investigated. Finally, we explore how pharmacological inhibition of UPR may modulate KSHV gene expression to ameliorate KS progression and pathogenesis. These studies will advance our knowledge of KSHV infection opportunities for therapeutic intervention in KSHV-associated disease.