Epstein-Barr virus inactivates the transcriptome and disrupts the chromatin architecture of its host cell in the first phase of lytic reactivation

Multiple sclerosis and infection: history, EBV, and the search for mechanism

SUMMARYInfection has long been hypothesized as the cause of multiple sclerosis (MS), and recent evidence for Epstein-Barr virus (EBV) as the trigger of MS is clear and compelling. This clarity contrasts with yet uncertain viral mechanisms and their relation to MS neuroinflammation and demyelination. As long as this disparity persists, it will invigorate virologists, molecular biologists, immunologists, and clinicians to ascertain how EBV potentiates MS onset, and possibly the disease's chronic activity and progression. Such efforts should take advantage of the diverse body of basic and clinical research conducted over nearly two centuries since the first clinical descriptions of MS plaques. Defining the contribution of EBV to the complex and multifactorial pathology of MS will also require suitable experimental models and techniques. Such efforts will broaden our understanding of virus-driven neuroinflammation and specifically inform the development of EBV-targeted therapies for MS management and, ultimately, prevention.

Identifying Safeguards Disabled by Epstein-Barr Virus Infections in Genomes From Patients With Breast Cancer: Chromosomal Bioinformatics Analysis

Background

The causes of breast cancer are poorly understood. A potential risk factor is Epstein-Barr virus (EBV), a lifelong infection nearly everyone acquires. EBV-transformed human mammary cells accelerate breast cancer when transplanted into immunosuppressed mice, but the virus can disappear as malignant cells reproduce. If this model applies to human breast cancers, then they should have genome damage characteristic of EBV infection.

Objective

This study tests the hypothesis that EBV infection predisposes one to breast cancer by causing permanent genome damage that compromises cancer safeguards.

Methods

Publicly available genome data from approximately 2100 breast cancers and 25 ovarian cancers were compared to cancers with proven associations to EBV, including 70 nasopharyngeal cancers, 90 Burkitt lymphomas, 88 diffuse large B-cell lymphomas, and 34 gastric cancers. Calculation algorithms to make these comparisons were developed.

Results

Chromosome breakpoints in breast and ovarian cancer clustered around breakpoints in EBV-associated cancers. Breakpoint distributions in breast and EBV-associated cancers on some chromosomes were not confidently distinguished (P>.05), but differed from controls unrelated to EBV infection. Viral breakpoint clusters occurred in high-risk, sporadic, and other breast cancer subgroups. Breakpoint clusters disrupted gene functions essential for cancer protection, which remain compromised even if EBV infection disappears. As CRISPR (clustered regularly interspaced short palindromic repeats)-like reminders of past infection during evolution, EBV genome fragments were found regularly interspaced between Piwi-interacting RNA (piRNA) genes on chromosome 6. Both breast and EBV-associated cancers had inactivated genes that guard piRNA defenses and the major histocompatibility complex (MHC) locus. Breast and EBV-associated cancer breakpoints and other variations converged around the highly polymorphic MHC. Not everyone develops cancer because MHC differences produce differing responses to EBV infection. Chromosome shattering and mutation hot spots in breast cancers preferentially occurred at incorporated viral sequences. On chromosome 17, breast cancer breakpoints that clustered around those in EBV-mediated cancers were linked to estrogen effects. Other breast cancer breaks affected sites where EBV inhibits JAK-STAT and SWI-SNF signaling pathways. A characteristic EBV-cancer gene deletion that shifts metabolism to favor tumors was also found in breast cancers. These changes push breast cancer into metastasis and then favor survival of metastatic cells.

Conclusions

EBV infection predisposes one to breast cancer and metastasis, even if the virus disappears. Identifying this pathogenic viral damage may improve screening, treatment, and prevention. Immunizing children against EBV may protect against breast, ovarian, other cancers, and potentially even chronic unexplained diseases.

Epstein-Barr virus induces host shutoff extensively via BGLF5-independent mechanisms

Epstein-Barr virus (EBV) is a ubiquitous oncogenic virus associated with multiple cancers and autoimmune diseases. Unlike most herpesviruses, EBV reactivation from latency occurs asymptomatically, allowing it to spread efficiently to other hosts. However, available models are limited by the inefficient and asynchronous reactivation from latency into lytic replication. To address this problem, we develop a dual-fluorescent lytic reporter (DFLR) EBV that specifically labels cells in the early and late stages of replication. Using lymphoblastoid cell lines transformed by DFLR EBV as a model for EBV reactivation in B cells, we observe extensive reprogramming of the host cell transcriptome during lytic cycle progression. This includes widespread shutoff of host gene expression and disruption of mRNA processing. Unexpectedly, host shutoff remains extensive even in cells infected with DFLR EBV deleted for the BGLF5 nuclease. These findings implicate BGLF5-independent mechanisms as the primary drivers of host transcriptome remodeling during EBV lytic replication.

Epstein-Barr virus reactivation induces divergent abortive, reprogrammed, and host shutoff states by lytic progression

Viral infection leads to heterogeneous cellular outcomes ranging from refractory to abortive and fully productive states. Single cell transcriptomics enables a high resolution view of these distinct post-infection states. Here, we have interrogated the host-pathogen dynamics following reactivation of Epstein-Barr virus (EBV). While benign in most people, EBV is responsible for infectious mononucleosis, up to 2% of human cancers, and is a trigger for the development of multiple sclerosis. Following latency establishment in B cells, EBV reactivates and is shed in saliva to enable infection of new hosts. Beyond its importance for transmission, the lytic cycle is also implicated in EBV-associated oncogenesis. Conversely, induction of lytic reactivation in latent EBV-positive tumors presents a novel therapeutic opportunity. Therefore, defining the dynamics and heterogeneity of EBV lytic reactivation is a high priority to better understand pathogenesis and therapeutic potential. In this study, we applied single-cell techniques to analyze diverse fate trajectories during lytic reactivation in three B cell models. Consistent with prior work, we find that cell cycle and MYC expression correlate with cells refractory to lytic reactivation. We further found that lytic induction yields a continuum from abortive to complete reactivation. Abortive lytic cells upregulate NFκB and IRF3 pathway target genes, while cells that proceed through the full lytic cycle exhibit unexpected expression of genes associated with cellular reprogramming. Distinct subpopulations of lytic cells further displayed variable profiles for transcripts known to escape virus-mediated host shutoff. These data reveal previously unknown and promiscuous outcomes of lytic reactivation with broad implications for viral replication and EBV-associated oncogenesis.

Epstein-Barr virus reactivation induces divergent abortive, reprogrammed, and host shutoff states by lytic progression

Viral infection leads to heterogeneous cellular outcomes ranging from refractory to abortive and fully productive states. Single cell transcriptomics enables a high resolution view of these distinct post-infection states. Here, we have interrogated the host-pathogen dynamics following reactivation of Epstein-Barr virus (EBV). While benign in most people, EBV is responsible for infectious mononucleosis, up to 2% of human cancers, and is a trigger for the development of multiple sclerosis. Following latency establishment in B cells, EBV reactivates and is shed in saliva to enable infection of new hosts. Beyond its importance for transmission, the lytic cycle is also implicated in EBV-associated oncogenesis. Conversely, induction of lytic reactivation in latent EBV-positive tumors presents a novel therapeutic opportunity. Therefore, defining the dynamics and heterogeneity of EBV lytic reactivation is a high priority to better understand pathogenesis and therapeutic potential. In this study, we applied single-cell techniques to analyze diverse fate trajectories during lytic reactivation in two B cell models. Consistent with prior work, we find that cell cycle and MYC expression correlate with cells refractory to lytic reactivation. We further found that lytic induction yields a continuum from abortive to complete reactivation. Abortive lytic cells upregulate NFκB and IRF3 pathway target genes, while cells that proceed through the full lytic cycle exhibit unexpected expression of genes associated with cellular reprogramming. Distinct subpopulations of lytic cells further displayed variable profiles for transcripts known to escape virus-mediated host shutoff. These data reveal previously unknown and promiscuous outcomes of lytic reactivation with broad implications for viral replication and EBV-associated oncogenesis.

Viral reprogramming of host transcription initiation

Viruses are master remodelers of the host cell environment in support of infection and virus production. For example, viruses typically regulate cell gene expression through modulating canonical cell promoter activity. Here, we show that Epstein Barr virus (EBV) replication causes 'de novo' transcription initiation at 29674 new transcription start sites throughout the cell genome. De novo transcription initiation is facilitated in part by the unique properties of the viral pre-initiation complex (vPIC) that binds a TATT[T/A]AA, TATA box-like sequence and activates transcription with minimal support by additional transcription factors. Other de novo promoters are driven by the viral transcription factors, Zta and Rta and are influenced by directional proximity to existing canonical cell promoters, a configuration that fosters transcription through existing promoters and transcriptional interference. These studies reveal a new way that viruses interact with the host transcriptome to inhibit host gene expression and they shed light on primal features driving eukaryotic promoter function.

Differential carbonic anhydrase activities control EBV-induced B-cell transformation and lytic cycle reactivation

Epstein-Barr virus (EBV) contributes to ~1% of all human cancers including several B-cell neoplasms. A characteristic feature of EBV life cycle is its ability to transform metabolically quiescent B-lymphocytes into hyperproliferating B-cell blasts with the establishment of viral latency, while intermittent lytic cycle induction is necessary for the production of progeny virus. Our RNA-Seq analyses of both latently infected naïve B-lymphocytes and transformed B-lymphocytes upon lytic cycle replication indicate a contrasting expression pattern of a membrane-associated carbonic anhydrase isoform CA9, an essential component for maintaining cell acid-base homeostasis. We show that while CA9 expression is transcriptionally activated during latent infection model, lytic cycle replication restrains its expression. Pharmacological inhibition of CA-activity using specific inhibitors retards EBV induced B-cell transformation, inhibits B-cells outgrowth and colony formation ability of transformed B-lymphocytes through lowering the intracellular pH, induction of cell apoptosis and facilitating degradation of CA9 transcripts. Reanalyses of ChIP-Seq data along with utilization of EBNA2 knockout virus, ectopic expression of EBNA2 and sh-RNA mediated knockdown of CA9 expression we further demonstrate that EBNA2 mediated CA9 transcriptional activation is essential for EBV latently infected B-cell survival. In contrast, during lytic cycle reactivation CA9 expression is transcriptionally suppressed by the key EBV lytic cycle transactivator, BZLF1 through its transactivation domain. Overall, our study highlights the dynamic alterations of CA9 expression and its activity in regulating pH homeostasis act as one of the major drivers for EBV induced B-cell transformation and subsequent B-cell lymphomagenesis.

Five families of diverse DNA viruses comprehensively restructure the nucleus

Many viruses have evolved ways to restructure their host cell's nucleus profoundly and unexpectedly upon infection. In particular, DNA viruses that need to commandeer their host's cellular synthetic functions to produce their progeny can induce the condensation and margination of host chromatin during productive infection, a phenomenon known as virus-induced reorganization of cellular chromatin (ROCC). These ROCC-inducing DNA viruses belong to 5 families (herpesviruses, baculoviruses, adenoviruses, parvoviruses, and geminiviruses) that infect a wide range of hosts and are important for human and ecosystem health, as well as for biotechnology. Although the study of virus-induced ROCC is in its infancy, investigations are already raising important questions, such as why only some DNA viruses that replicate their genomes in the nucleus elicit ROCC. Studying the shared and distinct properties of ROCC-inducing viruses will provide valuable insights into viral reorganization of host chromatin that could have implications for future therapies that target the viral life cycle.

Epstein-Barr virus and host cell 3D genome organization

The human genome is organized in an extremely complexed yet ordered way within the nucleus. Genome organization plays a critical role in the regulation of gene expression. Viruses manipulate the host machinery to influence host genome organization to favor their survival and promote disease development. Epstein-Barr virus (EBV) is a common human virus, whose infection is associated with various diseases, including infectious mononucleosis, cancer, and autoimmune disorders. This review summarizes our current knowledge of how EBV uses different strategies to control the cellular 3D genome organization to affect cell gene expression to transform normal cells into lymphoblasts.

SARS-CoV-2 and Epstein-Barr Virus-like Particles Associate and Fuse with Extracellular Vesicles in Virus Neutralization Tests

The successful development of effective viral vaccines depends on well-known correlates of protection, high immunogenicity, acceptable safety criteria, low reactogenicity, and well-designed immune monitoring and serology. Virus-neutralizing antibodies are often a good correlate of protective immunity, and their serum concentration is a key parameter during the pre-clinical and clinical testing of vaccine candidates. Viruses are inherently infectious and potentially harmful, but we and others developed replication-defective SARS-CoV-2 virus-like-particles (VLPs) as surrogates for infection to quantitate neutralizing antibodies with appropriate target cells using a split enzyme-based approach. Here, we show that SARS-CoV-2 and Epstein-Barr virus (EBV)-derived VLPs associate and fuse with extracellular vesicles in a highly specific manner, mediated by the respective viral fusion proteins and their corresponding host receptors. We highlight the capacity of virus-neutralizing antibodies to interfere with this interaction and demonstrate a potent application using this technology. To overcome the common limitations of most virus neutralization tests, we developed a quick in vitro diagnostic assay based on the fusion of SARS-CoV-2 VLPs with susceptible vesicles to quantitate neutralizing antibodies without the need for infectious viruses or living cells. We validated this method by testing a set of COVID-19 patient serum samples, correlated the results with those of a conventional test, and found good sensitivity and specificity. Furthermore, we demonstrate that this serological assay can be adapted to a human herpesvirus, EBV, and possibly other enveloped viruses.

The autophagy machinery interacts with EBV capsids during viral envelope release

Autophagy serves as a defense mechanism against intracellular pathogens, but several microorganisms exploit it for their own benefit. Accordingly, certain herpesviruses include autophagic membranes into their infectious virus particles. In this study, we analyzed the composition of purified virions of the Epstein-Barr virus (EBV), a common oncogenic γ-herpesvirus. In these, we found several components of the autophagy machinery, including membrane-associated LC3B-II, and numerous viral proteins, such as the capsid assembly proteins BVRF2 and BdRF1. Additionally, we showed that BVRF2 and BdRF1 interact with LC3B-II via their common protein domain. Using an EBV mutant, we identified BVRF2 as essential to assemble mature capsids and produce infectious EBV. However, BdRF1 was sufficient for the release of noninfectious viral envelopes as long as autophagy was not compromised. These data suggest that BVRF2 and BdRF1 are not only important for capsid assembly but together with the LC3B conjugation complex of ATG5-ATG12-ATG15L1 are also critical for EBV envelope release.

EBV Reactivation from Latency Is a Degrading Experience for the Host

During reactivation from latency, gammaherpesviruses radically restructure their host cell to produce virion particles. To achieve this and thwart cellular defenses, they induce rapid degradation of cytoplasmic mRNAs, suppressing host gene expression. In this article, we review mechanisms of shutoff by Epstein-Barr virus (EBV) and other gammaherpesviruses. In EBV, canonical host shutoff is accomplished through the action of the versatile BGLF5 nuclease expressed during lytic reactivation. We explore how BGLF5 induces mRNA degradation, the mechanisms by which specificity is achieved, and the consequences for host gene expression. We also consider non-canonical mechanisms of EBV-induced host shutoff. Finally, we summarize the limitations and barriers to accurate measurements of the EBV host shutoff phenomenon.

How Epstein-Barr Virus Induces the Reorganization of Cellular Chromatin

We have discovered how Epstein-Barr virus (EBV) induces the reorganization of cellular chromatin (ROCC), in which host chromatin is compacted and marginated within the nucleus, with viral DNA replication occurring in the chromatin-free regions. Five families of DNA viruses induce ROCC: herpesviruses, adenoviruses, parvoviruses, baculoviruses, and geminiviruses. These families infect a variety of hosts, including vertebrates, insects, and plants. They also share several characteristics: they replicate and encapsidate their genomes in the host nucleus and package their genomes unbound by histones. We have identified the viral genes and processes required for EBV's ROCC. Each of EBV's seven core DNA synthesis genes and its origin of lytic replication (oriLyt), in trans, are required, while its protein kinase, BGLF4, and its true late genes are not. Following these findings, we tested the role of EBV lytic DNA amplification in driving ROCC. Surprisingly, the inhibition of EBV's lytic DNA synthesis still supports chromatin compaction but blocks its margination. We propose a two-step model for ROCC. First, the initiation of viral lytic DNA synthesis induces a cellular response that results in global chromatin compaction. Second, the histone-free, productive viral DNA synthesis leads to the margination of compacted chromatin to the nuclear periphery. We have tested this model by asking if the histone-associated simian virus 40 (SV40) DNA synthesis could substitute for oriLyt-mediated synthesis and found that EBV's ROCC is incompatible with SV40 DNA replication. Elucidating EBV's induction of ROCC both illuminates how other viruses can do so and indicates how this spatial control of cellular chromatin benefits them. IMPORTANCE Five families of viruses support the reorganization of cellular chromatin (ROCC), the compaction and margination of host chromatin, upon their productive infection. That they all share this phenotype implies the importance of ROCC in viral life cycles. With Epstein-Barr virus (EBV), a herpesvirus, we show that the viral replication complex and origin of lytic replication (oriLyt) are essential for ROCC. In contrast, its protein kinase and true late genes are not. We show that, unexpectedly, the viral lytic amplification is not required for chromatin compaction but is required for its margination. We propose a two-step model for ROCC: first, global chromatin compaction occurs as a cellular response to the initiation of viral DNA synthesis; then, the accumulation of newly synthesized, histone-free viral DNA leads to cellular chromatin margination. Taken together, our findings provide insights into a process contributing to the productive phase of five families of viruses.

A comprehensive single cell data analysis of lymphoblastoid cells reveals the role of super-enhancers in maintaining EBV latency

We probed the lifecycle of Epstein-Barr virus (EBV) on a cell-by-cell basis using single cell RNA sequencing (scRNA-seq) data from nine publicly available lymphoblastoid cell lines (LCLs). While the majority of LCLs comprised cells containing EBV in the latent phase, two other clusters of cells were clearly evident and were distinguished by distinct expression of host and viral genes. Notably, both were high expressors of EBV LMP1/BNLF2 and BZLF1 compared to another cluster that expressed neither gene. The two novel clusters differed from each other in their expression of EBV lytic genes, including glycoprotein gene GP350. The first cluster, comprising GP350- LMP1hi cells, expressed high levels of HIF1A and was transcriptionally regulated by HIF1-α. Treatment of LCLs with Pevonedistat, a drug that enhances HIF1-α signaling, markedly induced this cluster. The second cluster, containing GP350+ LMP1hi cells, expressed EBV lytic genes. Host genes that are controlled by super-enhancers (SEs), such as transcription factors MYC and IRF4, had the lowest expression in this cluster. Functionally, the expression of genes regulated by MYC and IRF4 in GP350+ LMP1hi cells were lower compared to other cells. Indeed, induction of EBV lytic reactivation in EBV+ AKATA reduced the expression of these SE-regulated genes. Furthermore, CRISPR-mediated perturbation of the MYC or IRF4 SEs in LCLs induced the lytic EBV gene expression, suggesting that host SEs and/or SE target genes are required for maintenance of EBV latency. Collectively, our study revealed EBV-associated heterogeneity among LCLs that may have functional consequence on host and viral biology.

Strategies of Epstein-Barr virus to evade innate antiviral immunity of its human host

Epstein-Barr virus (EBV) is a double-stranded DNA virus of the Herpesviridae family. This virus preferentially infects human primary B cells and persists in the human B cell compartment for a lifetime. Latent EBV infection can lead to the development of different types of lymphomas as well as carcinomas such as nasopharyngeal and gastric carcinoma in immunocompetent and immunocompromised patients. The early phase of viral infection is crucial for EBV to establish latency, but different viral components are sensed by cellular sensors called pattern recognition receptors (PRRs) as the first line of host defense. The efficacy of innate immunity, in particular the interferon-mediated response, is critical to control viral infection initially and to trigger a broad spectrum of specific adaptive immune responses against EBV later. Despite these restrictions, the virus has developed various strategies to evade the immune reaction of its host and to establish its lifelong latency. In its different phases of infection, EBV expresses up to 44 different viral miRNAs. Some act as viral immunoevasins because they have been shown to counteract innate as well as adaptive immune responses. Similarly, certain virally encoded proteins also control antiviral immunity. In this review, we discuss how the virus governs innate immune responses of its host and exploits them to its advantage.

Epigenetic control of the Epstein-Barr lifecycle

Epstein-Barr virus (EBV) infects 95% of adults worldwide, causes infectious mononucleosis, is etiologically linked to multiple sclerosis and is associated with 200 000 cases of cancer each year. EBV manipulates host epigenetic pathways to switch between a series of latency programs and to reactivate from latency in order to colonize the memory B-cell compartment for lifelong infection and to ultimately spread to new hosts. Here, we review recent advances in the understanding of epigenetic mechanisms that control EBV latency and lytic gene expression in EBV-transformed B and epithelial cells. We highlight newly appreciated roles of DNA methylation epigenetic machinery, host histone chaperones, the Hippo pathway, m6A RNA modification and nonsense mediated decay in control of the EBV lifecycle.

Interaction sites of the Epstein-Barr virus Zta transcription factor with the host genome in epithelial cells

Epstein-Barr virus (EBV) is present in a state of latency in infected memory B-cells and EBV-associated lymphoid and epithelial cancers. Cell stimulation or differentiation of infected B-cells and epithelial cells induces reactivation to the lytic replication cycle. In each cell type, the EBV transcription and replication factor Zta (BZLF1, EB1) plays a role in mediating the lytic cycle of EBV. Zta is a transcription factor that interacts directly with Zta response elements (ZREs) within viral and cellular genomes. Here we undertake chromatin-precipitation coupled to DNA-sequencing (ChIP-Seq) of Zta-associated DNA from cancer-derived epithelial cells. The analysis identified over 14 000 Zta-binding sites in the cellular genome. We assessed the impact of lytic cycle reactivation on changes in gene expression for a panel of Zta-associated cellular genes. Finally, we compared the Zta-binding sites identified in this study with those previously identified in B-cells and reveal substantial conservation in genes associated with Zta-binding sites.

Structural basis of DNA methylation-dependent site selectivity of the Epstein-Barr virus lytic switch protein ZEBRA/Zta/BZLF1

In infected cells, Epstein-Barr virus (EBV) alternates between latency and lytic replication. The viral bZIP transcription factor ZEBRA (Zta, BZLF1) regulates this cycle by binding to two classes of ZEBRA response elements (ZREs): CpG-free motifs resembling the consensus AP-1 site recognized by cellular bZIP proteins and CpG-containing motifs that are selectively bound by ZEBRA upon cytosine methylation. We report structural and mutational analysis of ZEBRA bound to a CpG-methylated ZRE (meZRE) from a viral lytic promoter. ZEBRA recognizes the CpG methylation marks through a ZEBRA-specific serine and a methylcytosine-arginine-guanine triad resembling that found in canonical methyl-CpG binding proteins. ZEBRA preferentially binds the meZRE over the AP-1 site but mutating the ZEBRA-specific serine to alanine inverts this selectivity and abrogates viral replication. Our findings elucidate a DNA methylation-dependent switch in ZEBRA's transactivation function that enables ZEBRA to bind AP-1 sites and promote viral latency early during infection and subsequently, under appropriate conditions, to trigger EBV lytic replication by binding meZREs.