K-Rta as a Novel SUMO and Epigenetic Regulator

摘要： 基因表达的表观遗传调控在许多基础生物学中起着关键作用， 真核生物中的过程。我们已经集中在定义表观遗传机制，涉及翻译后 在卡波西肉瘤疱疹病毒（KSHV）的生命周期中，染色质蛋白的修饰，这是一种 卡波西肉瘤（KS），一种艾滋病相关的恶性肿瘤的病原体。这种病毒有潜伏期 在感染的细胞中，只有少数病毒基因表达。细胞信号通路可以重新激活潜在的 细胞通过调节近100个病毒基因表达的时间级联产生病毒。因此，本发明的目的是， KSHV是研究影响染色质结构和动力学的表观遗传机制的一个非常有吸引力的模型， 其是调节真核细胞中转录的关键过程。 小泛素样修饰物（SUMO）是一种调节多种细胞过程的蛋白质， 包括异染色质形成，通过共价连接（即，类小泛素化）作用于多种靶点 proteins.类小泛素化和磷酸化一样，作为翻译后信号分子传递信号 下游含有SUMO相互作用基序（SIM）的目标;这些目标包括影响蛋白质， 通常沉默转录的染色质结构。我们最近的研究表明， 转录反式激活因子K-Rta是一种靶向SUMO的泛素（Ub）连接酶，可降解SUMO- 改性蛋白质我们假设这种靶向SUMO的Ub连接酶功能对于K-Rta很重要， 通过破坏周围的抑制环境，启动KSHV复制的裂解（生产）阶段 潜伏感染细胞中的病毒附加体。这种压抑的环境是由病毒潜伏期建立的- 相关核抗原（拉娜），其是一种SUMO结合蛋白，其将病毒附加体系在 病毒可以在宿主细胞染色体的异染色质区域中复制，从而维持病毒的潜伏状态。这 该提案将验证SUMO修饰的调节在KSHV生命中起关键作用的假设 通过调节病毒的结构， 染色质在第一个目标中，我们将研究K-Rta作为SUMO依赖性泛素连接酶在以下方面的作用： KSHV复制。在第二个目标中，K-Rta在SUMO依赖性中发挥作用的潜在机制 方式和影响病毒染色质的表观遗传特征将被分析。综合来看，这些研究 将定义K-Rta以及拉娜在KSHV复制中的新角色，并将提供对后 翻译修饰和染色质重塑控制潜伏期和再激活。

Abstract: Epigenetic regulation of gene expression plays a critical role in many fundamental biological processes in eukaryotes. We have focused on defining epigenetic mechanisms, involving post-translation modification of chromatin proteins, in the life cycle of Kaposi's sarcoma herpesvirus (KSHV), which is an etiological agent of Kaposi's sarcoma (KS), an AIDS-associated malignancy. This virus exhibits a latent phase in infected cells in which only a few viral genes are expressed. Cell signaling pathways can reactivate latent cells to produce virus through a temporal cascade that regulates expression of nearly 100 viral genes. Thus, KSHV is a very attractive model to study epigenetic mechanisms that affect chromatin structure and dynamics, which are key processes regulating transcription in eukaryotic cells. The small ubiquitin-like modifier (SUMO) is a protein that regulates a wide variety of cellular processes, including heterochromatin formation, by covalent attachment (i.e., sumoylation) to a diverse array of target proteins. Sumoylation, like phosphorylation, serves as a post-translational signal molecule to transmit signals to down-stream targets containing a SUMO-interacting motif (SIM); these targets include proteins that impact chromatin structure that generally silence transcription. Our recent studies show that the main viral transcriptional transactivator, K-Rta, is a SUMO-targeting ubiquitin (Ub) ligase, which degrades SUMO- modified proteins. We hypothesize that this SUMO-targeting Ub ligase function is important for K-Rta to initiate the lytic (productive) phase of KSHV replication by disrupting the repressive environment surrounding of the viral episome in latently infected cells. This repressive environment is established by the viral latency- associated nuclear antigen (LANA), which is a SUMO-binding protein that tethers viral episomes to heterochromatic regions of host cell chromosomes and thereby maintains the latent state of the virus. This proposal will test the hypothesis that the regulation of SUMO modification plays a key role in the KSHV life cycle in both establishment of latency and reactivation of this virus by modulating the structure of viral chromatin. In the first Aim, we will investigate the role of K-Rta as a SUMO-dependent ubiquitin ligase in KSHV replication. In the second Aim, the potential mechanisms whereby K-Rta acts in a SUMO-dependent manner and affects the epigenetic signature of viral chromatin will be analyzed. Taken together, these studies will define a new role of K-Rta, as well as LANA, in KSHV replication, and will provide insights into the post- translational modifications and chromatin remodeling that govern latency and reactivation.