Department of Pediatrics, The University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA.
J Virol. 2014 Jun;88(11):6355-67. doi: 10.1128/JVI.00219-14. Epub 2014 Mar 26.
Kaposi's sarcoma-associated herpesvirus (KSHV) establishes persistent latent infection in immunocompetent hosts. Disruption of KSHV latency results in viral lytic replication, which promotes the development of KSHV-related malignancies in immunocompromised individuals. While inhibitors of classes I and II histone deacetylases (HDACs) potently reactivate KSHV from latency, the role of class III HDAC sirtuins (SIRTs) in KSHV latency remains unclear. Here, we examined the effects of inhibitors of SIRTs, nicotinamide (NAM) and sirtinol, on KSHV reactivation from latency. Treatment of latently KSHV-infected cells with NAM or sirtinol induced transcripts and proteins of the master lytic transactivator RTA (ORF50), early lytic genes ORF57 and ORF59, and late lytic gene ORF65 and increased the production of infectious virions. NAM increased the acetylation of histones H3 and H4 as well as the level of the active histone H3 trimethyl Lys4 (H3K4me3) mark but decreased the level of the repressive histone H3 trimethyl Lys27 (H3K27me3) mark in the RTA promoter. Consistent with these results, we detected SIRT1 binding to the RTA promoter. Importantly, knockdown of SIRT1 was sufficient to increase the expression of KSHV lytic genes. Accordingly, the level of the H3K4me3 mark in the RTA promoter was increased following SIRT1 knockdown, while that of the H3K27me3 mark was decreased. Furthermore, SIRT1 interacted with RTA and inhibited RTA transactivation of its own promoter and that of its downstream target, the viral interleukin-6 gene. These results indicate that SIRT1 regulates KSHV latency by inhibiting different stages of viral lytic replication and link the cellular metabolic state with the KSHV life cycle.
Kaposi's sarcoma-associated herpesvirus (KSHV) is the causal agent of several malignancies, including Kaposi's sarcoma, commonly found in immunocompromised patients. While latent infection is required for the development of KSHV-induced malignancies, viral lytic replication also promotes disease progression. However, the mechanism controlling KSHV latent versus lytic replication remains unclear. In this study, we found that class III histone deacetylases (HDACs), also known as SIRTs, whose activities are linked to the cellular metabolic state, mediate KSHV replication. Inhibitors of SIRTs can reactivate KSHV from latency. SIRTs mediate KSHV latency by epigenetically silencing a key KSHV lytic replication activator, RTA. We found that one of the SIRTs, SIRT1, binds to the RTA promoter to mediate KSHV latency. Knockdown of SIRT1 is sufficient to induce epigenetic remodeling and KSHV lytic replication. SIRT1 also interacts with RTA and inhibits RTA's transactivation function, preventing the expression of its downstream genes. Our results indicate that SIRTs regulate KSHV latency by inhibiting different stages of viral lytic replication and link the cellular metabolic state with the KSHV life cycle.
卡波氏肉瘤相关疱疹病毒（KSHV）在免疫功能正常的宿主中建立持续潜伏感染。破坏 KSHV 潜伏期会导致病毒裂解复制，从而促进免疫功能低下个体中 KSHV 相关恶性肿瘤的发展。虽然 I 类和 II 类组蛋白去乙酰化酶（HDACs）抑制剂能强有力地从潜伏状态重新激活 KSHV，但 III 类 HDACs 沉默调节蛋白（SIRTs）在 KSHV 潜伏中的作用仍不清楚。在这里，我们研究了 SIRTs 抑制剂烟酰胺（NAM）和 sirtinol 对 KSHV 从潜伏中重新激活的影响。用 NAM 或 sirtinol 处理潜伏感染的 KSHV 细胞，诱导主裂解转录激活物 RTA（ORF50）、早期裂解基因 ORF57 和 ORF59 以及晚期裂解基因 ORF65 的转录物和蛋白的表达，并增加感染性病毒粒子的产生。NAM 增加了组蛋白 H3 和 H4 的乙酰化以及活性组蛋白 H3 三甲基赖氨酸 4（H3K4me3）标记的水平，但降低了 RTA 启动子中抑制性组蛋白 H3 三甲基赖氨酸 27（H3K27me3）标记的水平。与这些结果一致，我们检测到 SIRT1 与 RTA 启动子结合。重要的是，SIRT1 的敲低足以增加 KSHV 裂解基因的表达。因此，在 SIRT1 敲低后，RTA 启动子中的 H3K4me3 标记增加，而 H3K27me3 标记减少。此外，SIRT1 与 RTA 相互作用并抑制 RTA 对其自身启动子和病毒白细胞介素-6 基因的转录激活。这些结果表明，SIRT1 通过抑制病毒裂解复制的不同阶段来调节 KSHV 潜伏，并将细胞代谢状态与 KSHV 生命周期联系起来。
卡波氏肉瘤相关疱疹病毒（KSHV）是几种恶性肿瘤的致病因子，包括卡波氏肉瘤，常见于免疫功能低下的患者。虽然潜伏感染是 KSHV 诱导恶性肿瘤发展所必需的，但病毒裂解复制也促进了疾病的进展。然而，控制 KSHV 潜伏与裂解复制的机制仍不清楚。在这项研究中，我们发现，III 类组蛋白去乙酰化酶（HDACs），也称为 SIRTs，其活性与细胞代谢状态有关，介导 KSHV 复制。SIRTs 抑制剂可使 KSHV 从潜伏中重新激活。SIRTs 通过表观遗传沉默关键的 KSHV 裂解复制激活物 RTA 来介导 KSHV 潜伏。我们发现，SIRTs 之一 SIRT1 结合 RTA 启动子来介导 KSHV 潜伏。SIRT1 的敲低足以诱导表观遗传重塑和 KSHV 裂解复制。SIRT1 还与 RTA 相互作用并抑制 RTA 的转录激活功能，从而阻止其下游基因的表达。我们的结果表明，SIRTs 通过抑制病毒裂解复制的不同阶段来调节 KSHV 潜伏，并将细胞代谢状态与 KSHV 生命周期联系起来。
