Key Laboratory of Medical Molecular Virology, Ministry of Education and Health, School of Basic Medical Sciences, Shanghai Medical College, Fudan University, Shanghai, China.
Shanghai Public Health Clinical Center, Fudan University, Shanghai, China.
Hepatology. 2017 Aug;66(2):398-415. doi: 10.1002/hep.29133. Epub 2017 Jun 19.
Chronic hepatitis B virus (HBV) infection remains a major health problem worldwide. The covalently closed circular DNA (cccDNA) minichromosome, which serves as the template for the transcription of viral RNAs, plays a key role in viral persistence. While accumulating evidence suggests that cccDNA transcription is regulated by epigenetic machinery, particularly the acetylation of cccDNA-bound histone 3 (H3) and H4, the potential contributions of histone methylation and related host factors remain obscure. Here, by screening a series of methyltransferases and demethylases, we identified protein arginine methyltransferase 5 (PRMT5) as an effective restrictor of HBV transcription and replication. In cell culture-based models for HBV infection and in liver tissues of patients with chronic HBV infection, we found that symmetric dimethylation of arginine 3 on H4 on cccDNA was a repressive marker of cccDNA transcription and was regulated by PRMT5 depending on its methyltransferase domain. Moreover, PRMT5-triggered symmetric dimethylation of arginine 3 on H4 on the cccDNA minichromosome involved an interaction with the HBV core protein and the Brg1-based human SWI/SNF chromatin remodeler, which resulted in down-regulation of the binding of RNA polymerase II to cccDNA. In addition to the inhibitory effect on cccDNA transcription, PRMT5 inhibited HBV core particle DNA production independently of its methyltransferase activity. Further study revealed that PRMT5 interfered with pregenomic RNA encapsidation by preventing its interaction with viral polymerase protein through binding to the reverse transcriptase-ribonuclease H region of polymerase, which is crucial for the polymerase-pregenomic RNA interaction.
PRMT5 restricts HBV replication through a two-part mechanism including epigenetic suppression of cccDNA transcription and interference with pregenomic RNA encapsidation; these findings improve the understanding of epigenetic regulation of HBV transcription and host-HBV interaction, thus providing new insights into targeted therapeutic intervention. (Hepatology 2017;66:398-415).
慢性乙型肝炎病毒（HBV）感染仍然是全球的一个主要健康问题。共价闭合环状 DNA（cccDNA）微染色体作为病毒 RNA 转录的模板，在病毒持续存在中起着关键作用。虽然越来越多的证据表明 cccDNA 转录受表观遗传机制调控，特别是 cccDNA 结合组蛋白 3（H3）和 H4 的乙酰化，但组蛋白甲基化和相关宿主因子的潜在贡献仍然不清楚。在这里，通过筛选一系列甲基转移酶和去甲基酶，我们鉴定了蛋白质精氨酸甲基转移酶 5（PRMT5）作为 HBV 转录和复制的有效抑制剂。在基于细胞培养的 HBV 感染模型和慢性 HBV 感染患者的肝组织中，我们发现 cccDNA 上组蛋白 H4 上精氨酸 3 的对称二甲基化是 cccDNA 转录的抑制性标记，并且受 PRMT5 调控，这取决于其甲基转移酶结构域。此外，PRMT5 触发的 cccDNA 微染色体上组蛋白 H4 上精氨酸 3 的对称二甲基化涉及与 HBV 核心蛋白和基于 Brg1 的人 SWI/SNF 染色质重塑酶的相互作用，导致 RNA 聚合酶 II 与 cccDNA 的结合下调。除了对 cccDNA 转录的抑制作用外，PRMT5 还通过阻止其与病毒聚合酶蛋白的相互作用来抑制 HBV 核心颗粒 DNA 的产生，这一过程独立于其甲基转移酶活性。进一步的研究表明，PRMT5 通过与聚合酶的逆转录酶-核糖核酸酶 H 区域结合，阻止前基因组 RNA 与聚合酶的相互作用，从而干扰前基因组 RNA 的封装，这对于聚合酶-前基因组 RNA 的相互作用至关重要。
PRMT5 通过包括 cccDNA 转录的表观遗传抑制和干扰前基因组 RNA 封装在内的两部分机制来限制 HBV 复制；这些发现提高了对 HBV 转录和宿主-HBV 相互作用的表观遗传调控的理解，从而为靶向治疗干预提供了新的见解。（《肝脏病学》2017；66：398-415）。
