Tropberger Philipp, Mercier Alexandre, Robinson Margaret, Zhong Weidong, Ganem Don E, Holdorf Meghan
Department of Infectious Diseases, Novartis Institutes for BioMedical Research, Emeryville, CA 94608
Department of Infectious Diseases, Novartis Institutes for BioMedical Research, Emeryville, CA 94608.
Proc Natl Acad Sci U S A. 2015 Oct 20;112(42):E5715-24. doi: 10.1073/pnas.1518090112. Epub 2015 Oct 5.
Chronic hepatitis B virus (HBV) infection affects 240 million people worldwide and is a major risk factor for liver failure and hepatocellular carcinoma. Current antiviral therapy inhibits cytoplasmic HBV genomic replication, but is not curative because it does not directly affect nuclear HBV closed circular DNA (cccDNA), the genomic form that templates viral transcription and sustains viral persistence. Novel approaches that directly target cccDNA regulation would therefore be highly desirable. cccDNA is assembled with cellular histone proteins into chromatin, but little is known about the regulation of HBV chromatin by histone posttranslational modifications (PTMs). Here, using a new cccDNA ChIP-Seq approach, we report, to our knowledge, the first genome-wide maps of PTMs in cccDNA-containing chromatin from de novo infected HepG2 cells, primary human hepatocytes, and from HBV-infected liver tissue. We find high levels of PTMs associated with active transcription enriched at specific sites within the HBV genome and, surprisingly, very low levels of PTMs linked to transcriptional repression even at silent HBV promoters. We show that transcription and active PTMs in HBV chromatin are reduced by the activation of an innate immunity pathway, and that this effect can be recapitulated with a small molecule epigenetic modifying agent, opening the possibility that chromatin-based regulation of cccDNA transcription could be a new therapeutic approach to chronic HBV infection.
慢性乙型肝炎病毒（HBV）感染影响着全球2.4亿人，是肝衰竭和肝细胞癌的主要危险因素。目前的抗病毒疗法可抑制细胞质中的HBV基因组复制，但无法治愈，因为它不会直接影响核内的HBV共价闭合环状DNA（cccDNA），而cccDNA是作为病毒转录模板并维持病毒持续存在的基因组形式。因此，非常需要直接针对cccDNA调控的新方法。cccDNA与细胞组蛋白组装成染色质，但关于组蛋白翻译后修饰（PTM）对HBV染色质的调控却知之甚少。在此，我们使用一种新的cccDNA染色质免疫沉淀测序（ChIP-Seq）方法，据我们所知，首次绘制了来自从头感染的HepG2细胞、原代人肝细胞以及HBV感染肝组织中含cccDNA染色质的全基因组PTM图谱。我们发现，与活跃转录相关的高水平PTM富集于HBV基因组内的特定位点，而且令人惊讶的是，即使在沉默的HBV启动子处，与转录抑制相关的PTM水平也非常低。我们表明，激活先天免疫途径会降低HBV染色质中的转录和活跃PTM，并且这种效应可以用一种小分子表观遗传修饰剂来重现，这为基于染色质的cccDNA转录调控可能成为慢性HBV感染的一种新治疗方法开辟了可能性。
