Graduate School of Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China.
National Institute of Biological Sciences, Beijing, China.
J Virol. 2023 Jul 27;97(7):e0032823. doi: 10.1128/jvi.00328-23. Epub 2023 Jun 20.
Hepatitis B virus (HBV) chronically infects approximately 300 million people worldwide, and permanently repressing transcription of covalently closed circular DNA (cccDNA), the episomal viral DNA reservoir, is an attractive approach toward curing HBV. However, the mechanism underlying cccDNA transcription is only partially understood. In this study, by illuminating cccDNA of wild-type HBV (HBV-WT) and transcriptionally inactive HBV that bears a deficient HBV X gene (HBV-ΔX), we found that the HBV-ΔX cccDNA more frequently colocalizes with promyelocytic leukemia (PML) bodies than that of HBV-WT cccDNA. A small interfering RNA (siRNA) screen targeting 91 PML body-related proteins identified SMC5-SMC6 localization factor 2 (SLF2) as a host restriction factor of cccDNA transcription, and subsequent studies showed that SLF2 mediates HBV cccDNA entrapment in PML bodies by interacting with the SMC5/6 complex. We further showed that the region of SLF2 comprising residues 590 to 710 interacts with and recruits the SMC5/6 complex to PML bodies, and the C-terminal domain of SLF2 containing this region is necessary for repression of cccDNA transcription. Our findings shed new light on cellular mechanisms that inhibit HBV infection and lend further support for targeting the HBx pathway to repress HBV activity. Chronic HBV infection remains a major public health problem worldwide. Current antiviral treatments rarely cure the infection, as they cannot clear the viral reservoir, cccDNA, in the nucleus. Therefore, permanently silencing HBV cccDNA transcription represents a promising approach for a cure of HBV infection. Our study provides new insights into the cellular mechanisms that restrict HBV infection, revealing the role of SLF2 in directing HBV cccDNA to PML bodies for transcriptional repression. These findings have important implications for the development of antiviral therapies against HBV.
乙型肝炎病毒（HBV）在全球范围内慢性感染约 3 亿人，永久抑制共价闭合环状 DNA（cccDNA）的转录，cccDNA 是病毒的 episomal DNA 储存库，是治愈 HBV 的一种有吸引力的方法。然而，cccDNA 转录的机制仅部分被理解。在这项研究中，通过照亮野生型 HBV（HBV-WT）和转录失活的 HBV 的 cccDNA，该 HBV 携带缺陷的 HBV X 基因（HBV-ΔX），我们发现 HBV-ΔX 的 cccDNA 比 HBV-WT cccDNA 更频繁地与早幼粒细胞白血病（PML）体共定位。针对 91 个 PML 体相关蛋白的小干扰 RNA（siRNA）筛选鉴定出 SMC5-SMC6 定位因子 2（SLF2）作为 cccDNA 转录的宿主限制因子，随后的研究表明，SLF2 通过与 SMC5/6 复合物相互作用介导 HBV cccDNA 困在 PML 体中。我们进一步表明，SLF2 的包含残基 590 至 710 的区域与 SMC5/6 复合物相互作用并募集到 PML 体，并且包含该区域的 SLF2 的 C 末端结构域对于抑制 cccDNA 转录是必需的。我们的发现为抑制 HBV 感染的细胞机制提供了新的见解，并进一步支持针对 HBx 途径来抑制 HBV 活性的方法。慢性 HBV 感染仍然是全球主要的公共卫生问题。目前的抗病毒治疗很少能治愈感染，因为它们不能清除核内的病毒储存库 cccDNA。因此，永久沉默 HBV cccDNA 转录代表了治愈 HBV 感染的一种很有前途的方法。我们的研究提供了新的见解，了解限制 HBV 感染的细胞机制，揭示了 SLF2 在将 HBV cccDNA 引导到 PML 体进行转录抑制中的作用。这些发现对开发针对 HBV 的抗病毒治疗具有重要意义。
