Department of Dermatology, University of California Davis School of Medicine, UC Davis Comprehensive Cancer Center, Sacramento, California, United States of America.
PLoS Pathog. 2013;9(8):e1003506. doi: 10.1371/journal.ppat.1003506. Epub 2013 Aug 22.
The small ubiquitin-like modifier (SUMO) is a protein that regulates a wide variety of cellular processes by covalent attachment of SUMO moieties to a diverse array of target proteins. Sumoylation also plays an important role in the replication of many viruses. Previously, we showed that Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a SUMO-ligase, K-bZIP, which catalyzes sumoylation of host and viral proteins. We report here that this virus also encodes a gene that functions as a SUMO-targeting ubiquitin-ligase (STUbL) which preferentially targets sumoylated proteins for degradation. K-Rta, the major transcriptional factor which turns on the entire lytic cycle, was recently found to have ubiquitin ligase activity toward a selected set of substrates. We show in this study that K-Rta contains multiple SIMs (SUMO interacting motif) and binds SUMOs with higher affinity toward SUMO-multimers. Like RNF4, the prototypic cellular STUbL, K-Rta degrades SUMO-2/3 and SUMO-2/3 modified proteins, including promyelocytic leukemia (PML) and K-bZIP. PML-NBs (nuclear bodies) or ND-10 are storage warehouses for sumoylated proteins, which negatively regulate herpesvirus infection, as part of the intrinsic immune response. Herpesviruses have evolved different ways to degrade or disperse PML bodies, and KSHV utilizes K-Rta to inhibit PML-NBs formation. This process depends on K-Rta's ability to bind SUMO, as a K-Rta SIM mutant does not effectively degrade PML. Mutations in the K-Rta Ring finger-like domain or SIM significantly inhibited K-Rta transactivation activity in reporter assays and in the course of viral reactivation. Finally, KSHV with a mutation in the Ring finger-like domain or SIM of K-Rta replicates poorly in culture, indicating that reducing SUMO-conjugates in host cells is important for viral replication. To our knowledge, this is the first virus which encodes both a SUMO ligase and a SUMO-targeting ubiquitin ligase that together may generate unique gene regulatory programs.
小泛素样修饰物（SUMO）是一种通过将 SUMO 部分共价连接到各种靶蛋白上来调节多种细胞过程的蛋白质。Sumoylation 也在许多病毒的复制中起着重要作用。以前，我们表明卡波济肉瘤相关疱疹病毒（KSHV）编码一种 SUMO 连接酶，K-bZIP，它催化宿主和病毒蛋白的 sumoylation。我们在这里报告，这种病毒还编码一种作为 SUMO 靶向泛素连接酶（STUbL）的基因，该基因优先靶向 sumoylated 蛋白进行降解。K-Rta，打开整个裂解周期的主要转录因子，最近被发现对一组选定的底物具有泛素连接酶活性。我们在这项研究中表明，K-Rta 包含多个 SIM（SUMO 相互作用基序），并以更高的亲和力结合 SUMO 多聚体。与原型细胞 STUbL RNF4 一样，K-Rta 降解 SUMO-2/3 和 SUMO-2/3 修饰的蛋白，包括早幼粒细胞白血病（PML）和 K-bZIP。PML-NBs（核体）或 ND-10 是 sumoylated 蛋白的储存仓库，作为固有免疫反应的一部分，它们负调节疱疹病毒感染。疱疹病毒已经进化出不同的方法来降解或分散 PML 体，而 KSHV 则利用 K-Rta 来抑制 PML-NBs 的形成。这个过程依赖于 K-Rta 结合 SUMO 的能力，因为 K-Rta SIM 突变体不能有效地降解 PML。K-Rta 环指样结构域或 SIM 中的突变显著抑制了 K-Rta 在报告基因检测和病毒再激活过程中的转录激活活性。最后，KSHV 中 K-Rta 的环指样结构域或 SIM 突变在培养中复制能力较差，表明减少宿主细胞中的 SUMO 缀合物对病毒复制很重要。据我们所知，这是第一个编码 SUMO 连接酶和 SUMO 靶向泛素连接酶的病毒，它们可能共同产生独特的基因调控程序。
