3D landscape of Hepatitis B virus interactions with human chromatins

Viral remodeling of the 4D nucleome

The dynamic spatial organization of genomes across time, referred to as the four-dimensional nucleome (4DN), is a key component of gene regulation and biological fate. Viral infections can lead to a reconfiguration of viral and host genomes, impacting gene expression, replication, latency, and oncogenic transformation. This review provides a summary of recent research employing three-dimensional genomic methods such as Hi-C, 4C, ChIA-PET, and HiChIP in virology. We review how viruses induce changes in gene loop formation between regulatory elements, modify chromatin accessibility, and trigger shifts between A and B compartments in the host genome. We highlight the central role of cellular chromatin organizing factors, such as CTCF and cohesin, that reshape the 3D structure of both viral and cellular genomes. We consider how viral episomes, viral proteins, and viral integration sites can alter the host epigenome and how host cell type and conditions determine viral epigenomes. This review consolidates current knowledge of the diverse host-viral interactions that impact the 4DN.

Genome-wide chromatin interaction profiling reveals a vital role of super-enhancers and rearrangements in host enhancer contacts during BmNPV infection

As influential regulatory elements in the genome, enhancers control gene expression under specific cellular conditions, and such connections are dynamic under different conditions. However, because of the lack of a genome-wide enhancer-gene connection map, the roles and regulatory pattern of enhancers were poorly investigated in insects, and the dynamic changes of enhancer contacts and functions under different conditions remain elusive. Here, combining Hi-C, ATAC-seq, and H3K27ac ChIP-seq data, we generate the genome-wide enhancer-gene map of silkworm and identify super-enhancers with a role in regulating the expression of vital genes related to cell state maintenance through a sophisticated interaction network. Additionally, a radical attenuation of chromatin interactions is found after infection of Bombyx mori nucleopolyhedrovirus (BmNPV), the main pathogen of silkworm, which directly rearranges the enhancer contacts. Such a rearrangement disturbs the intrinsic enhancer-gene connections in several antiviral genes, resulting in reduced expression of these genes, which accelerates viral infection. Overall, our results reveal the regulatory role of super-enhancers and shed new light on the mechanisms and dynamic changes of the genome-wide enhancer regulatory network.

Human tumor viruses: induction of three-dimensional alterations in the host genome structure

Certain viruses called tumor viruses or oncoviruses are capable to change the gene expression pattern of distinct human or animal cell types in tissue culture, resulting in uncontrolled proliferation as well as a change in the social behavior of the infected cells: the oncovirus-transformed, immortalized cells are capable to form malignant neoplasms in suitable animal models. At present, seven human viruses are categorized as causative agents of distinct human malignancies. The genomes of human tumor viruses, typically encode viral oncoproteins and non- translated viral RNAs that affect the gene expression pattern of their target cells or induce genetic and epigenetic alterations contributing to oncogenesis. Recently, the application of chromatin conformation capture technologies and three-dimensional (3D) molecular imaging techniques revealed how the gene products or genomes of certain human tumor viruses interact with and induce alterations in the 3D host genome structure. This Mini Review aims to cover selected aspects of these developments. The papers, discussed briefly, describe how insertion of a novel viral binding site for the 3D genome organizer cellular protein CCCTC-binding factor (CTCF) into the DNA of T cells infected by human T-cell lymphotropic virus type 1 (HTLV-1) may contribute to lymphomagenesis, as well as how integration of high risk human papillomavirus genome into the host cell DNA may facilitate cervical carcinogenesis. Recent results regarding the interactions of cellular genomes with the episomal, chromatinized DNA genomes of oncogenic human herpesvirus, Epstein-Barr virus (EBV) will also be summarized, similarly to available data regarding contacts formed by episomal or integrated hepatitis B virus (HBV) DNA with host chromatin. Finally, a putative mechanism of hepatitis C virus (HCV) induced chromatin alterations will be presented, which may solve the riddle, how a cytoplasmic RNA virus without a viral oncogene could induce malingnant transfrormation of hepatocytes.

A CRISPR-based rapid DNA repositioning strategy and the early intranuclear life of HSV-1

The relative positions of viral DNA genomes to the host intranuclear environment play critical roles in determining virus fate. Recent advances in the application of chromosome conformation capture-based sequencing analysis (3 C technologies) have revealed valuable aspects of the spatiotemporal interplay of viral genomes with host chromosomes. However, to elucidate the causal relationship between the subnuclear localization of viral genomes and the pathogenic outcome of an infection, manipulative tools are needed. Rapid repositioning of viral DNAs to specific subnuclear compartments amid infection is a powerful approach to synchronize and interrogate this dynamically changing process in space and time. Herein, we report an inducible CRISPR-based two-component platform that relocates extrachromosomal DNA pieces (5 kb to 170 kb) to the nuclear periphery in minutes (CRISPR-nuPin). Based on this strategy, investigations of herpes simplex virus 1 (HSV-1), a prototypical member of the human herpesvirus family, revealed unprecedently reported insights into the early intranuclear life of the pathogen: (I) Viral genomes tethered to the nuclear periphery upon entry, compared with those freely infecting the nucleus, were wrapped around histones with increased suppressive modifications and subjected to stronger transcriptional silencing and prominent growth inhibition. (II) Relocating HSV-1 genomes at 1 hr post infection significantly promoted the transcription of viral genes, termed an 'Escaping' effect. (III) Early accumulation of ICP0 was a sufficient but not necessary condition for 'Escaping'. (IV) Subnuclear localization was only critical during early infection. Importantly, the CRISPR-nuPin tactic, in principle, is applicable to many other DNA viruses.

Three-dimensional genome structure and function

Linear DNA undergoes a series of compression and folding events, forming various three-dimensional (3D) structural units in mammalian cells, including chromosomal territory, compartment, topologically associating domain, and chromatin loop. These structures play crucial roles in regulating gene expression, cell differentiation, and disease progression. Deciphering the principles underlying 3D genome folding and the molecular mechanisms governing cell fate determination remains a challenge. With advancements in high-throughput sequencing and imaging techniques, the hierarchical organization and functional roles of higher-order chromatin structures have been gradually illuminated. This review systematically discussed the structural hierarchy of the 3D genome, the effects and mechanisms of cis-regulatory elements interaction in the 3D genome for regulating spatiotemporally specific gene expression, the roles and mechanisms of dynamic changes in 3D chromatin conformation during embryonic development, and the pathological mechanisms of diseases such as congenital developmental abnormalities and cancer, which are attributed to alterations in 3D genome organization and aberrations in key structural proteins. Finally, prospects were made for the research about 3D genome structure, function, and genetic intervention, and the roles in disease development, prevention, and treatment, which may offer some clues for precise diagnosis and treatment of related diseases.

Multiomics analyses reveal pathological mechanisms of HBV infection and integration in liver cancer

Hepatitis B virus (HBV) infection and integration are important for hepatocellular carcinoma (HCC) initiation and progression, while disease mechanisms are still largely elusive. Here, we combined bulk and single-cell sequencing technologies to tackle the disease mechanisms of HBV-related HCC. We observed high HBV mutation rate and diversity only in tumors without HBV integration. We identified human somatic risk loci for HBV integration (VIMs). Transcription factors (TFs) enriched in VIMs were involved in DNA repair and androgen receptor (AR) signaling. Aberration of AR signaling was further observed by single-cell regulon analysis in HBV-infected hepatocytes, which showed remarkable interactions between AR and the complement system that, together with the X-linked ZXDB regulon that contains albumin (ALB), probably contribute to HCC male predominance. Complement system dysregulation caused by HBV infection was further confirmed by analyses of single-cell copy numbers and cell-cell communications. Finally, HBV infection-associated immune cells presented critical defects, including TXNIP in T cells, TYROBP in NK cells, and the X-linked TIMP1 in monocytes. We further experimentally validated our findings in multiple independent patient cohorts. Collectively, our work shed light on the pathogenesis of HBV-related HCC and other liver diseases that affect billions of people worldwide.

Multiomic analysis of cohesin reveals that ZBTB transcription factors contribute to chromatin interactions

One bottleneck in understanding the principles of 3D chromatin structures is caused by the paucity of known regulators. Cohesin is essential for 3D chromatin organization, and its interacting partners are candidate regulators. Here, we performed proteomic profiling of the cohesin in chromatin and identified transcription factors, RNA-binding proteins and chromatin regulators associated with cohesin. Acute protein degradation followed by time-series genomic binding quantitation and BAT Hi-C analysis were conducted, and the results showed that the transcription factor ZBTB21 contributes to cohesin chromatin binding, 3D chromatin interactions and transcriptional repression. Strikingly, multiomic analyses revealed that the other four ZBTB factors interacted with cohesin, and double degradation of ZBTB21 and ZBTB7B led to a further decrease in cohesin chromatin occupancy. We propose that multiple ZBTB transcription factors orchestrate the chromatin binding of cohesin to regulate chromatin interactions, and we provide a catalog of many additional proteins associated with cohesin that warrant further investigation.

Three-dimensional and single-cell sequencing of liver cancer reveals comprehensive host-virus interactions in HBV infection

Backgrounds

Hepatitis B virus (HBV) infection is a major risk factor for chronic liver diseases and liver cancer (mainly hepatocellular carcinoma, HCC), while the underlying mechanisms and host-virus interactions are still largely elusive.

Methods

We applied HiC sequencing to HepG2 (HBV-) and HepG2-2.2.15 (HBV+) cell lines and combined them with public HCC single-cell RNA-seq data, HCC bulk RNA-seq data, and both genomic and epigenomic ChIP-seq data to reveal potential disease mechanisms of HBV infection and host-virus interactions reflected by 3D genome organization.

Results

We found that HBV enhanced overall proximal chromatin interactions (CIs) of liver cells and primarily affected regional CIs on chromosomes 13, 14, 17, and 22. Interestingly, HBV altered the boundaries of many topologically associating domains (TADs), and genes nearby these boundaries showed functional enrichment in cell adhesion which may promote cancer metastasis. Moreover, A/B compartment analysis revealed dramatic changes on chromosomes 9, 13 and 21, with more B compartments (inactive or closed) shifting to A compartments (active or open). The A-to-B regions (closing) harbored enhancers enriched in the regulation of inflammatory responses, whereas B-to-A regions (opening) were enriched for transposable elements (TE). Furthermore, we identified large HBV-induced structural variations (SVs) that disrupted tumor suppressors, NLGN4Y and PROS1. Finally, we examined differentially expressed genes and TEs in single hepatocytes with or without HBV infection, by using single-cell RNA-seq data. Consistent with our HiC sequencing findings, two upregulated genes that promote HBV replication, HNF4A and NR5A2, were located in regions with HBV-enhanced CIs, and five TEs were located in HBV-activated regions. Therefore, HBV may promote liver diseases by affecting the human 3D genome structure.

Conclusion

Our work promotes mechanistic understanding of HBV infection and host-virus interactions related to liver diseases that affect billions of people worldwide. Our findings may also have implications for novel immunotherapeutic strategies targeting HBV infection.

Illuminating the Live-Cell Dynamics of Hepatitis B Virus Covalently Closed Circular DNA Using the CRISPR-Tag System

The covalently closed circular DNA (cccDNA) of hepatitis B virus (HBV) is the major obstacle to curing chronic hepatitis B (CHB). Current cccDNA detection methods are mostly based on biochemical extraction and bulk measurements. They nevertheless generated a general sketch of its biological features. However, an understanding of the spatiotemporal features of cccDNA is still lacking. To achieve this, we established a system combining CRISPR-Tag and recombinant HBV minicircle technology to visualize cccDNA at single-cell level in real time. Using this system, we found that the observed recombinant cccDNA (rcccDNA) correlated quantitatively with its active transcripts when a low to medium number of foci (<20) are present, but this correlation was lost in cells harboring high copy numbers (≥20) of rcccDNA. The disruption of HBx expression seems to displace cccDNA from the dCas9-accessible region, while HBx complementation restored the number of observable cccDNA foci. This indicated regulation of cccDNA accessibility by HBx. Second, observable HBV and duck HBV (DHBV) cccDNA molecules are substantially lost during cell division, and the remaining ones were distributed randomly to daughter cells. In contrast, Kaposi's sarcoma-associated herpesvirus (KSHV)-derived episomes can be retained in a LANA (latency-associated nuclear antigen)-dependent manner. Last, the dynamics of rcccDNA episomes in nuclei displayed confined diffusion at short time scales, with directional transport over longer time scales. In conclusion, this system enables the study of physiological kinetics of cccDNA at the single-cell level. The differential accessibility of rcccDNA to dCas9 under various physiological conditions may be exploited to elucidate the complex transcriptional and epigenetic regulation of the HBV minichromosome. IMPORTANCE Understanding the formation and maintenance of HBV cccDNA has always been a central issue in the study of HBV pathobiology. However, little progress has been made due to the lack of robust assay systems and its resistance to genetic modification. Here, a live-cell imaging system by grafting CRISPR-Tag into the recombinant cccDNA was established to visualize its molecular behavior in real time. We found that the accessibility of rcccDNA to dCas9-based imaging is related to HBx-regulated mechanisms. We also confirmed the substantial loss of observable rcccDNA in one-round cell division and random distribution of the remaining molecules. Molecular dynamics analysis revealed the confined movement of the rcccDNA episome, suggesting its juxtaposition to chromatin domains. Overall, this novel system offers a unique platform to investigate the intranuclear dynamics of cccDNA within live cells.

Topological implications of DNA tumor viral episomes

A persistent DNA tumor virus infection transforms normal cells into cancer cells by either integrating its genome into host chromosomes or retaining it as an extrachromosomal entity called episome. Viruses have evolved mechanisms for attaching episomes to infected host cell chromatin to efficiently segregate the viral genome during mitosis. It has been reported that viral episome can affect the gene expression of the host chromosomes through interactions between viral episomes and epigenetic regulatory host factors. This mini review summarizes our current knowledge of the tethering sites of viral episomes, such as EBV, KSHV, and HBV, on host chromosomes analyzed by three-dimensional genomic tools. [BMB Reports 2022; 55(12): 587-594].

Safeguarding genome integrity during gene-editing therapy in a mouse model of age-related macular degeneration

Ensuring genome safety during gene editing is crucial for clinical translation of the high-efficient CRISPR-Cas9 toolbox. Therefore, the undesired events including chromosomal translocations, vector integrations, and large deletions arising during therapeutic gene editing remain to be adequately addressed or tackled in vivo. Here, we apply CRISPR-Cas9TX in comparison to CRISPR-Cas9 to target Vegfa for the treatment of age-related macular degeneration (AMD) disease in a mouse model. AAV delivery of both CRISPR-Cas9 and CRISPR-Cas9TX can efficiently inhibit laser-induced neovascularization. Importantly, Cas9TX almost eliminates chromosomal translocations that occur at a frequency of approximately 1% in Cas9-edited mouse retinal cells. Strikingly, the widely observed AAV integration at the target Vegfa site is also greatly reduced from nearly 50% of edited events to the background level during Cas9TX editing. Our findings reveal that chromosomal structural variations routinely occur during in vivo genome editing and highlight Cas9TX as a superior form of Cas9 for in vivo gene disruption.

When 3D genome technology meets viral infection, including SARS-CoV-2

Mammalian chromosomes undergo varying degrees of compression to form three-dimensional genome structures. These three-dimensional structures undergo dynamic and precise chromatin interactions to achieve precise spatial and temporal regulation of gene expression. Most eukaryotic DNA viruses can invade their genomes into the nucleus. However, it is still poorly understood how the viral genome is precisely positioned after entering the host cell nucleus to find the most suitable location and whether it can specifically interact with the host genome to hijack the host transcriptional factories or even integrate into the host genome to complete its transcription and replication rapidly. Chromosome conformation capture technology can reveal long-range chromatin interactions between different chromosomal sites in the nucleus, potentially providing a reference for viral DNA-host chromatin interactions. This review summarized the research progress on the three-dimensional interaction between virus and host genome and the impact of virus integration into the host genome on gene transcription regulation, aiming to provide new insights into chromatin interaction and viral gene transcription regulation, laying the foundation for the treatment of infectious diseases.

Potential multi-modal effects of provirus integration on HIV-1 persistence: lessons from other viruses

Despite antiretroviral therapy (ART), HIV-1 persists as proviruses integrated into the genomic DNA of CD4⁺ T cells. The mechanisms underlying the persistence and clonal expansion of these cells remain incompletely understood. Cases have been described in which proviral integration can alter host gene expression to drive cellular proliferation. Here, we review observations from other genome-integrating human viruses to propose additional putative modalities by which HIV-1 integration may alter cellular function to favor persistence, such as by altering susceptibility to cytotoxicity in virus-expressing cells. We propose that signals implicating such mechanisms may have been masked thus far by the preponderance of defective and/or nonreactivatable HIV-1 proviruses, but could be revealed by focusing on the integration sites of intact proviruses with expression potential.

PRKDC promotes hepatitis B virus transcription through enhancing the binding of RNA Pol II to cccDNA

Hepatitis B virus infection remains a major health problem worldwide due to its high risk of liver failure and hepatocellular carcinoma. Covalently closed circular DNA (cccDNA), which is present as an individual minichromosome, serves as the template for transcription of all viral RNAs and pla ays critical role in viral persistence. Therefore, there is an urgent need to gain broader insight into the transcription regulation of cccDNA. Here, we combined a modified Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) with an engineered ascorbate peroxidase 2 (APEX2) to identify cccDNA associated proteins systematically in living cells. By functional screening, we verified that protein kinase, DNA-activated, catalytic subunit (PRKDC) was an effective activator of HBV cccDNA transcription in HBV-infected HepG2-NTCP cells and primary human hepatocytes. Mechanismly, PRKDC interacted with POLR2A and POLR2B, the two largest subunits of RNA polymerase II (Pol II) and recruited Pol II to HBV cccDNA minichromosome in a kinase-dependent manner. PRKDC knockdown or inhibitor treatment significantly decreased the enrichment of POLR2A and POLR2B on cccDNA, as well as reducing the levels of cccDNA associated Pol II Ser5 and Ser2 phosphorylation, which eventually inhibited the HBV cccDNA activity. Collectively, these findings give us new insights into cccDNA transcription regulation, thus providing new potential targets for HBV treatment in patients.

Crosstalk between Hepatitis B Virus and the 3D Genome Structure

Viruses that transcribe their DNA within the nucleus have to adapt to the existing cellular mechanisms that govern transcriptional regulation. Recent technological breakthroughs have highlighted the highly hierarchical organization of the cellular genome and its role in the regulation of gene expression. This review provides an updated overview on the current knowledge on how the hepatitis B virus interacts with the cellular 3D genome and its consequences on viral and cellular gene expression. We also briefly discuss the strategies developed by other DNA viruses to co-opt and sometimes subvert cellular genome spatial organization.

ViMIC: a database of human disease-related virus mutations, integration sites and cis-effects

Molecular mechanisms of virus-related diseases involve multiple factors, including viral mutation accumulation and integration of a viral genome into the host DNA. With increasing attention being paid to virus-mediated pathogenesis and the development of many useful technologies to identify virus mutations (VMs) and viral integration sites (VISs), much research on these topics is available in PubMed. However, knowledge of VMs and VISs is widely scattered in numerous published papers which lack standardization, integration and curation. To address these challenges, we built a pilot database of human disease-related Virus Mutations, Integration sites and Cis-effects (ViMIC), which specializes in three features: virus mutation sites, viral integration sites and target genes. In total, the ViMIC provides information on 31 712 VMs entries, 105 624 VISs, 16 310 viral target genes and 1 110 015 virus sequences of eight viruses in 77 human diseases obtained from the public domain. Furthermore, in ViMIC users are allowed to explore the cis-effects of virus-host interactions by surveying 78 histone modifications, binding of 1358 transcription regulators and chromatin accessibility on these VISs. We believe ViMIC will become a valuable resource for the virus research community. The database is available at http://bmtongji.cn/ViMIC/index.php.

Advances in Multi-Omics Applications in HBV-Associated Hepatocellular Carcinoma

Hepatitis B virus (HBV) specifically infects liver cells, leading to progressive liver cirrhosis and significantly increasing the risk of hepatocellular carcinoma (HCC). The maturity of sequencing technology, improvement in bioinformatics data analysis and progress of omics technologies had improved research efficiency. The occurrence and progression of HCC are affected by multisystem and multilevel pathological changes. With the application of single-omics technologies, including genomics, transcriptomics, metabolomics and proteomics in tissue and body fluid samples, and even the novel development of multi-omics analysis on a single-cell platform, HBV-associated HCC changes can be better analyzed. The review summarizes the application of single omics and combined analysis of multi-omics data in HBV-associated HCC and proposes the importance of multi-omics analysis in the type of HCC, which provide the possibility for the precise diagnosis and therapy of HBV-associated HCC.

Viral Manipulation of the Host Epigenome as a Driver of Virus-Induced Oncogenesis

Tumorigenesis due to viral infection accounts for a high fraction of the total global cancer burden (15–20%) of all human cancers. A comprehensive understanding of the mechanisms by which viral infection leads to tumor development is extremely important. One of the main mechanisms by which viruses induce host cell proliferation programs is through controlling the host’s epigenetic machinery. In this review, we dissect the epigenetic pathways through which oncogenic viruses can integrate their genome into host cell chromosomes and lead to tumor progression. In addition, we highlight the potential use of drugs based on histone modifiers in reducing the global impact of cancer development due to viral infection.