LMP1-Induced Sumoylation Influences the Maintenance of Epstein-Barr Virus Latency through KAP1

TRIM28 in cancer and cancer therapy

TRIM28 (tripartite motif protein 28) was initially believed to be a transcription inhibitor that plays an important role in DNA damage repair (DDR) and in maintaining cancer cellular stemness. As research has continued to deepen, several studies have found that TRIM28 not only has ubiquitin E3 ligase activity to promote degradation of substrates, but also can promote SUMOylation of substrates. Although TRIM28 is highly expressed in various cancer tissues and has oncogenic effects, there are still a few studies indicating that TRIM28 has certain anticancer effects. Additionally, TRIM28 is subject to complex upstream regulation. In this review, we have elaborated on the structure and regulation of TRIM28. At the same time, highlighting the functional role of TRIM28 in tumor development and emphasizing its impact on cancer treatment provides a new direction for future clinical antitumor treatment.

Characterization of target gene regulation by the two Epstein-Barr virus oncogene LMP1 domains essential for B-cell transformation

IMPORTANCE

Epstein-Barr virus (EBV) causes multiple human cancers, including B-cell lymphomas. In cell culture, EBV converts healthy human B-cells into immortalized ones that grow continuously, which model post-transplant lymphomas. Constitutive signaling from two cytoplasmic tail domains of the EBV oncogene latent membrane protein 1 (LMP1) is required for this transformation, yet there has not been systematic analysis of their host gene targets. We identified that only signaling from the membrane proximal domain is required for survival of these EBV-immortalized cells and that its loss triggers apoptosis. We identified key LMP1 target genes, whose abundance changed significantly with loss of LMP1 signals, or that were instead upregulated in response to switching on signaling by one or both LMP1 domains in an EBV-uninfected human B-cell model. These included major anti-apoptotic factors necessary for EBV-infected B-cell survival. Bioinformatics analyses identified clusters of B-cell genes that respond differently to signaling by either or both domains.

Adenovirus E1B-55K controls SUMO-dependent degradation of antiviral cellular restriction factors

IMPORTANCE

Human adenoviruses (HAdVs) generally cause mild and self-limiting diseases of the upper respiratory and gastrointestinal tracts but pose a serious risk to immunocompromised patients and children. Moreover, they are widely used as vectors for vaccines and vector-based gene therapy approaches. It is therefore vital to thoroughly characterize HAdV gene products and especially HAdV virulence factors. Early region 1B 55 kDa protein (E1B-55K) is a multifunctional HAdV-encoded oncoprotein involved in various viral and cellular pathways that promote viral replication and cell transformation. We analyzed the E1B-55K dependency of SUMOylation, a post-translational protein modification, in infected cells using quantitative proteomics. We found that HAdV increases overall cellular SUMOylation and that this increased SUMOylation can target antiviral cellular pathways that impact HAdV replication. Moreover, we showed that E1B-55K orchestrates the SUMO-dependent degradation of certain cellular antiviral factors. These results once more emphasize the key role of E1B-55K in the regulation of viral and cellular proteins in productive HAdV infections.

Characterization of Target Gene Regulation by the Two Epstein-Barr Virus Oncogene LMP1 Domains Essential for B-cell Transformation

The Epstein-Barr virus (EBV) oncogene latent membrane protein 1 (LMP1) mimics CD40 signaling and is expressed by multiple malignancies. Two LMP1 C-terminal cytoplasmic tail regions, termed transformation essential sites (TES) 1 and 2, are critical for EBV transformation of B lymphocytes into immortalized lymphoblastoid cell lines (LCL). However, TES1 versus TES2 B-cell target genes have remained incompletely characterized, and whether both are required for LCL survival has remained unknown. To define LCL LMP1 target genes, we profiled transcriptome-wide effects of acute LMP1 CRISPR knockout (KO) prior to cell death. To then characterize specific LCL TES1 and TES2 roles, we conditionally expressed wildtype, TES1 null, TES2 null or double TES1/TES2 null LMP1 alleles upon endogenous LMP1 KO. Unexpectedly, TES1 but not TES2 signaling was critical for LCL survival. The LCL dependency factor cFLIP, which plays obligatory roles in blockade of LCL apoptosis, was highly downmodulated by loss of TES1 signaling. To further characterize TES1 vs TES2 roles, we conditionally expressed wildtype, TES1 and/or TES2 null LMP1 alleles in two Burkitt models. Systematic RNAseq analyses revealed gene clusters that responded more strongly to TES1 versus TES2, that respond strongly to both or that are oppositely regulated. Robust TES1 effects on cFLIP induction were again noted. TES1 and 2 effects on expression of additional LCL dependency factors, including BATF and IRF4, and on EBV super-enhancers were identified. Collectively, these studies suggest a model by which LMP1 TES1 and TES2 jointly remodel the B-cell transcriptome and highlight TES1 as a key therapeutic target.

Changes in SUMO-modified proteins in Epstein-Barr virus infection identifies reciprocal regulation of TRIM24/28/33 complexes and the lytic switch BZLF1

SUMO modifications regulate the function of many proteins and are important in controlling herpesvirus infections. We performed a site-specific proteomic analysis of SUMO1- and SUMO2-modified proteins in Epstein-Barr virus (EBV) latent and lytic infection to identify proteins that change in SUMO modification status in response to EBV reactivation. Major changes were identified in all three components of the TRIM24/TRIM28/TRIM33 complex, with TRIM24 being rapidly degraded and TRIM33 being phosphorylated and SUMOylated in response to EBV lytic infection. Further experiments revealed TRIM24 and TRIM33 repress expression of the EBV BZLF1 lytic switch gene, suppressing EBV reactivation. However, BZLF1 was shown to interact with TRIM24 and TRIM33, resulting in disruption of TRIM24/TRIM28/TRIM33 complexes, degradation of TRIM24 and modification followed by degradation of TRIM33. Therefore, we have identified TRIM24 and TRIM33 as cellular antiviral defence factors against EBV lytic infection and established the mechanism by which BZLF1 disables this defence.

Immunity and Immune Evasion Mechanisms of Epstein-Barr Virus

Epstein-Barr virus (EBV) is the first human oncogenic virus to be identified, which evades the body's immune surveillance through multiple mechanisms that allow long-term latent infection. Under certain pathological conditions, EBVs undergo a transition from the latent phase to the lytic phase and cause targeted dysregulation of the host immune system, leading to the development of EBV-related diseases. Therefore, an in-depth understanding of the mechanism of developing an immune response to EBV and the evasion of immune recognition by EBV is important for the understanding of the pathogenesis of EBV, which is of great significance for finding strategies to prevent EBV infection, and developing a therapy to treat EBV-associated diseases. In this review, we will discuss the molecular mechanisms of host immunological responses to EBV infection and the mechanisms of EBV-mediated immune evasion during chronic active infection.

Survey of genomic and physiological characteristics for survival in lymphoma: The NCI genomic data portal

Lymphoma represents a myriad collection of neoplasms that impact lymphocytes. This cancer often involves disrupted cytokine, immune surveillance, and gene regulatory signaling, sometimes with expression of Epstein Barr Virus (EBV). We explored mutation patterns for People experiencing Lymphoma (PeL) in the National Cancer Institute (NCI) Genomic Data Commons (GDC), which contains detailed, deidentified genomic data on 86,046 people who have/had cancer with 2,730,388 distinctive mutations in 21,773 genes. The database included information on 536 (PeL), with the primary focal sample being the n = 30 who had complete mutational genomic data. We used correlations, independent samples t-tests, and linear regression to compare PeL demographics and vital status on mutation numbers, BMI, and mutation deleterious score across functional categories of 23 genes. PeL demonstrated varied patterns of mutated genes, consistent with most other cancer types. The primary PeL gene mutations clustered around five functional protein groups: transcriptional regulatory proteins, TNF/NFKB and cell signaling regulators, cytokine signaling proteins, cell cycle regulators, and immunoglobulins. Diagnosis Age, Birth Year, and BMI negatively (P < 0.05) correlated with Days to Death, and cell cycle mutations negatively correlated (P = 0.004) with survival days (R² = 0.389). There were commonalities in some PeL for mutations across other cancer types based upon large sequence length, but also for 6 small cell lung cancer genes. Immunoglobulin mutations were prevalent but not for all cases. Research indicates a need for greater personalized genomics and multi-level systems analysis to evaluate facilitators and barriers for lymphoma survival.

The role of tripartite motif-containing 28 in cancer progression and its therapeutic potentials

Tripartite motif-containing 28 (TRIM28) belongs to tripartite motif (TRIM) family. TRIM28 not only binds and degrades its downstream target, but also acts as a transcription co-factor to inhibit gene expression. More and more studies have shown that TRIM28 plays a vital role in tumor genesis and progression. Here, we reviewed the role of TRIM28 in tumor proliferation, migration, invasion and cell death. Moreover, we also summarized the important role of TRIM28 in tumor stemness sustainability and immune regulation. Because of the importance of TRIM28 in tumors, TIRM28 may be a candidate target for anti-tumor therapy and play an important role in tumor diagnosis and treatment in the future.

Functional diversity: update of the posttranslational modification of Epstein-Barr virus coding proteins

Epstein-Barr virus (EBV), a human oncogenic herpesvirus with a typical life cycle consisting of latent phase and lytic phase, is associated with many human diseases. EBV can express a variety of proteins that enable the virus to affect host cell processes and evade host immunity. Additionally, these proteins provide a basis for the maintenance of viral infection, contribute to the formation of tumors, and influence the occurrence and development of related diseases. Posttranslational modifications (PTMs) are chemical modifications of proteins after translation and are very important to guarantee the proper biological functions of these proteins. Studies in the past have intensely investigated PTMs of EBV-encoded proteins. EBV regulates the progression of the latent phase and lytic phase by affecting the PTMs of its encoded proteins, which are critical for the development of EBV-associated human diseases. In this review, we summarize the PTMs of EBV-encoded proteins that have been discovered and studied thus far with focus on their effects on the viral life cycle.

N6-methyladenosine modification of the Aedes aegypti transcriptome and its alteration upon dengue virus infection in Aag2 cell line

The N⁶-methyladenosine (m⁶A) modification of RNA has been reported to affect viral infections. Studies have confirmed the role of m⁶A in replication of several vector-borne flaviviruses, including dengue virus (DENV), in mammalian cells. Here, we explored the role of m⁶A in DENV replication in the mosquito Aedes aegypti Aag2 cell line. We first determined the presence of m⁶A on the RNAs from mosquito cells and using methylated RNA immunoprecipitation and sequencing (MeRIP-Seq) identified m⁶A modification of the mosquito transcriptome and those that changed upon DENV infection. Depletion of m⁶A methyltransferases and the m⁶A binding protein YTHDF3 RNAs decreased the replication of DENV. In particular, we found that the Ae. aegypti ubiquitin carrier protein 9 (Ubc9) is m⁶A modified and its expression increases after DENV infection. Silencing of the gene and ectopic expression of Ubc9 led to reduced and increased DENV replication, respectively. The abundance of Ubc9 mRNA and its stability were reduced with the inhibition of m⁶A modification, implying that m⁶A modification of Ubc9 might enhance expression of the gene. We also show that the genome of DENV is m⁶A modified at five sites in mosquito cells. Altogether, this work reveals the involvement of m⁶A modification in Ae. aegypti-DENV interaction.

Analysis of m⁶A RNA modifications in the mosquito transcriptome and their changes upon dengue virus infection provides insight into the role of epigenetics in regulating viral replication in mosquitoes.

SUMOylation in Viral Replication and Antiviral Defense

SUMOylation is a ubiquitination-like post-translational modification that plays an essential role in the regulation of protein function. Recent studies have shown that proteins from both RNA and DNA virus families can be modified by SUMO conjugation, which facilitates viral replication. Viruses can manipulate the entire process of SUMOylation through interplay with the SUMO pathway. By contrast, SUMOylation can eliminate viral infection by regulating host antiviral immune components. A deeper understanding of how SUMOylation regulates viral proteins and cellular antiviral components is necessary for the development of effective antiviral therapies. In the present review, the regulatory mechanism of SUMOylation in viral replication and infection and the antiviral immune response, and the consequences of this regulation for viral replication and engagement with antiviral innate immunity are summarized. The potential therapeutic applications of SUMOylation in diseases caused by viruses are also discussed.

KAP1/TRIM28: Transcriptional Activator and/or Repressor of Viral and Cellular Programs?

Several transcriptional and epigenetic regulators have been functionally linked to the control of viral and cellular gene expression programs. One such regulator is Krüppel-associated box (KRAB)-associated protein 1 (KAP1: also named TRIM28 or TIF1β), which has been extensively studied in the past three decades. Here we offer an up-to date review of its various functions in a diversity of contexts. We first summarize the discovery of KAP1 repression of endogenous retroviruses during development. We then deliberate evidence in the literature suggesting KAP1 is both an activator and repressor of HIV-1 transcription and discuss experimental differences and limitations of previous studies. Finally, we discuss KAP1 regulation of DNA and RNA viruses, and then expand on KAP1 control of cellular responses and immune functions. While KAP1 positive and negative regulation of viral and cellular transcriptional programs is vastly documented, our mechanistic understanding remains narrow. We thus propose that precision genetic tools to reveal direct KAP1 functions in gene regulation will be required to not only illuminate new biology but also provide the foundation to translate the basic discoveries from the bench to the clinics.

Epstein-Barr Virus BGLF2 commandeers RISC to interfere with cellular miRNA function

The Epstein-Barr virus (EBV) BGLF2 protein is a tegument protein with multiple effects on the cellular environment, including induction of SUMOylation of cellular proteins. Using affinity-purification coupled to mass-spectrometry, we identified the miRNA-Induced Silencing Complex (RISC), essential for miRNA function, as a top interactor of BGLF2. We confirmed BGLF2 interaction with the Ago2 and TNRC6 components of RISC in multiple cell lines and their co-localization in cytoplasmic bodies that also contain the stress granule marker G3BP1. In addition, BGLF2 expression led to the loss of processing bodies in multiple cell types, suggesting disruption of RISC function in mRNA regulation. Consistent with this observation, BGLF2 disrupted Ago2 association with multiple miRNAs. Using let-7 miRNAs as a model, we tested the hypothesis that BGLF2 interfered with the function of RISC in miRNA-mediated mRNA silencing. Using multiple reporter constructs with 3’UTRs containing let-7a regulated sites, we showed that BGLF2 inhibited let-7a miRNA activity dependent on these 3’UTRs, including those from SUMO transcripts which are known to be regulated by let-7 miRNAs. In keeping with these results, we showed that BGLF2 increased the cellular level of unconjugated SUMO proteins without affecting the level of SUMO transcripts. Such an increase in free SUMO is known to drive SUMOylation and would account for the effect of BGLF2 in inducing SUMOylation. We further showed that BGLF2 expression inhibited the loading of let-7 miRNAs into Ago2 proteins, and conversely, that lytic infection with EBV lacking BGLF2 resulted in increased interaction of let-7a and SUMO transcripts with Ago2, relative to WT EBV infection. Therefore, we have identified a novel role for BGLF2 as a miRNA regulator and shown that one outcome of this activity is the dysregulation of SUMO transcripts that leads to increased levels of free SUMO proteins and SUMOylation.

Epstein-Barr virus (EBV) infects most people worldwide, persists for life and is associated with several kinds of cancer. In order to undergo efficient lytic infection, EBV must manipulate multiple cellular pathways. BGLF2 is an EBV lytic protein known to modulate several cellular processes including increasing the modification of cellular proteins with the Small Ubiquitin-Like Modifier (SUMO), a process referred to as SUMOylation. Here we show for the first time that BGLF2 interacts with a cellular complex (RISC) required for miRNA function and interferes with the function of some cellular miRNAs by sequestering this complex. One of the consequences of this effect is the increased expression of SUMO proteins, due to inhibition of the miRNAs that normally downregulate their expression. The resulting increase in SUMO proteins drives SUMOylation, providing a mechanism for the previously reported BGLF2-induced SUMOylation of cellular proteins. In addition, the discovery of BGLF2 as a miRNA regulator suggests that this EBV protein can control many cellular pathways by interfering with cellular miRNAs that normally regulate them.

EBV Genome Mutations and Malignant Proliferations

The Epstein-Barr virus (EBV) is a DNA virus with a relatively stable genome. Indeed, genomic variability is reported to be around 0.002%. However, some regions are more variable such as those carrying latency genes and specially EBNA1, -2, -LP, and LMP1. Tegument genes, particularly BNRF1, BPLF1, and BKRF3, are also quite mutated. For a long time, it has been considered for this ubiquitous virus, which infects a very large part of the population, that particular strains could be the cause of certain diseases. However, the mutations found, in some cases, are more geographically restricted rather than associated with proliferation. In other cases, they appear to be involved in oncogenesis. The objective of this chapter is to provide an update on changes in viral genome sequences in malignancies associated with EBV. We focused on describing the structure and function of the proteins corresponding to the genes mentioned above in order to understand how certain mutations of these proteins could increase the tumorigenic character of this virus. Mutations described in the literature for these proteins were identified by reporting viral and/or cellular functional changes as they were described.

A Tale of Usurpation and Subversion: SUMO-Dependent Integrity of Promyelocytic Leukemia Nuclear Bodies at the Crossroad of Infection and Immunity

Promyelocytic leukemia nuclear bodies (PML NBs) are multi-protein assemblies representing distinct sub-nuclear structures. As phase-separated molecular condensates, PML NBs exhibit liquid droplet-like consistency. A key organizer of the assembly and dynamics of PML NBs is the ubiquitin-like SUMO modification system. SUMO is covalently attached to PML and other core components of PML NBs thereby exhibiting a glue-like function by providing multivalent interactions with proteins containing SUMO interacting motifs (SIMs). PML NBs serve as the catalytic center for nuclear SUMOylation and SUMO-SIM interactions are essential for protein assembly within these structures. Importantly, however, formation of SUMO chains on PML and other PML NB-associated proteins triggers ubiquitylation and proteasomal degradation which coincide with disruption of these nuclear condensates. To date, a plethora of nuclear activities such as transcriptional and post-transcriptional regulation of gene expression, apoptosis, senescence, cell cycle control, DNA damage response, and DNA replication have been associated with PML NBs. Not surprisingly, therefore, SUMO-dependent PML NB integrity has been implicated in regulating many physiological processes including tumor suppression, metabolism, drug-resistance, development, cellular stemness, and anti-pathogen immune response. The interplay between PML NBs and viral infection is multifaceted. As a part of the cellular antiviral defense strategy, PML NB components are crucial restriction factors for many viruses and a mutual positive correlation has been found to exist between PML NBs and the interferon response. Viruses, in turn, have developed counterstrategies for disarming PML NB associated immune defense measures. On the other end of the spectrum, certain viruses are known to usurp specific PML NB components for successful replication and disruption of these sub-nuclear foci has recently been linked to the stimulation rather than curtailment of antiviral gene repertoire. Importantly, the ability of invading virions to manipulate the host SUMO modification machinery is essential for this interplay between PML NB integrity and viruses. Moreover, compelling evidence is emerging in favor of bacterial pathogens to negotiate with the SUMO system thereby modulating PML NB-directed intrinsic and innate immunity. In the current context, we will present an updated account of the dynamic intricacies between cellular PML NBs as the nuclear SUMO modification hotspots and immune regulatory mechanisms in response to viral and bacterial pathogens.

SUMO: a novel target for anti-coronavirus therapy

Over the past 20 years, humankind has encountered three severe coronavirus outbreaks. Currently ongoing, COVID-19 (coronavirus disease 2019) was declared a pandemic due to its massive impact on global health and the economy. Numerous scientists are working to identify efficacious therapeutic agents for COVID-19, although treatment ability has yet to be demonstrated. The SUMO (small ubiquitin-like modifier) system has diverse roles in viral manipulation, but the function of SUMO in coronaviruses is still unknown. The objective of this review article is to present recently published data suggesting contributions of the host SUMO system to coronavirus infection. These findings underscore the potential of SUMO as a novel target for anti-coronavirus therapy, and the need for a deeper understanding of coronavirus pathology to prepare and prevail against the current and emerging coronavirus outbreaks.

Targeting Host Cellular Factors as a Strategy of Therapeutic Intervention for Herpesvirus Infections

Herpesviruses utilize various host factors to establish latent infection, survival, and spread disease in the host. These factors include host cellular machinery, host proteins, gene expression, multiple transcription factors, cellular signal pathways, immune cell activation, transcription factors, cytokines, angiogenesis, invasion, and factors promoting metastasis. The knowledge and understanding of host genes, protein products, and biochemical pathways lead to discovering safe and effective antivirals to prevent viral reactivation and spread infection. Here, we focus on the contribution of pro-inflammatory, anti-inflammatory, and resolution lipid metabolites of the arachidonic acid (AA) pathway in the lifecycle of herpesvirus infections. We discuss how various herpesviruses utilize these lipid pathways to their advantage and how we target them to combat herpesvirus infection. We also summarize recent development in anti-herpesvirus therapeutics and new strategies proposed or under clinical trials. These anti-herpesvirus therapeutics include inhibitors blocking viral life cycle events, engineered anticancer agents, epigenome influencing factors, immunomodulators, and therapeutic compounds from natural extracts.

Effects of targeting sumoylation processes during latent and induced Epstein-Barr virus infections using the small molecule inhibitor ML-792

As the second leading cause of death in the United States, cancer has a considerable impact on society, and one cellular process that is commonly dysregulated in many cancers is the post-translational modification of proteins by the Small Ubiquitin-like Modifier (SUMO; sumoylation). We documented that sumoylation processes are up-regulated in lymphoma tissues in the presence of Latent Membrane Protein-1 (LMP1), the principal oncoprotein of Epstein-Barr virus (EBV). LMP1-mediated dysregulation of cellular sumoylation processes contributes to oncogenesis, modulates innate immune responses, and aids the maintenance of viral latency. Manipulation of protein sumoylation has been proposed for anti-cancer and anti-viral therapies; however, known inhibitors of sumoylation do not only target sumoylation processes. Recently, a specific and selective small-molecule inhibitor of sumoylation (ML-792) was identified; however, nothing is known about the effect of ML-792 on LMP1-mediated dysregulation of cellular sumoylation or the EBV life-cycle. We hypothesized that ML-792 modulates viral replication and the oncogenic potential of EBV LMP1 by inhibiting protein sumoylation. Results showed that ML-792 inhibited sumoylation processes in multiple EBV-positive B cell lines and EBV-positive nasopharyngeal carcinoma cell lines but not in their EBV-negative counterparts. Focusing on its effect on B cells, ML-792 inhibited B-cell growth and promoted cell death at very low doses. ML-792 also modulated LMP1-induced cell migration and cell adhesion, which suggests the abrogation of the oncogenic potential of LMP1. Finally, while higher concentrations of ML-792 were sufficient to induce low levels EBV spontaneous reactivation, they decreased the production of new infectious virus following an induced reactivation and the infection of new cells, suggesting that ML-792 has anti-viral potential. Together, these findings suggest that ML-792 may be a potential therapeutic drug to treat EBV-associated lymphoid malignancies by targeting oncogenesis and the EBV life-cycle.

Herpesvirus latency

Herpesviruses infect virtually all humans and establish lifelong latency and reactivate to infect other humans. Latency requires multiple functions: maintaining the herpesvirus genome in the nuclei of cells; partitioning the viral genome to daughter cells in dividing cells; avoiding recognition by the immune system by limiting protein expression; producing noncoding viral RNAs (including microRNAs) to suppress lytic gene expression or regulate cellular protein expression that could otherwise eliminate virus-infected cells; modulating the epigenetic state of the viral genome to regulate viral gene expression; and reactivating to infect other hosts. Licensed antivirals inhibit virus replication, but do not affect latency. Understanding of the mechanisms of latency is leading to novel approaches to destroy latently infected cells or inhibit reactivation from latency.

Merkel Cell Polyomavirus DNA Replication Induces Senescence in Human Dermal Fibroblasts in a Kap1/Trim28-Dependent Manner

Merkel cell polyomavirus (MCPyV) is the only polyomavirus known to be associated with tumorigenesis in humans. Similarly to other polyomaviruses, MCPyV expresses a large tumor antigen (LT-Ag) that, together with a small tumor antigen (sT-Ag), contributes to cellular transformation and that is of critical importance for the initiation of the viral DNA replication. Understanding the cellular protein network regulated by MCPyV early proteins will significantly contribute to our understanding of the natural MCPyV life cycle as well as of the mechanisms by which the virus contributes to cellular transformation. We here describe KRAB-associated protein 1 (Kap1), a chromatin remodeling factor involved in cotranscriptional regulation, as a novel protein interaction partner of MCPyV T antigens sT and LT. Kap1 knockout results in a significant increase in the level of viral DNA replication that is highly suggestive of Kap1 being an important host restriction factor during MCPyV infection. Differently from other DNA viruses, MCPyV gene expression is unaffected in the absence of Kap1 and Kap1 does not associate with the viral genome. Instead, we show that in primary normal human dermal fibroblast (nHDF) cells, MCPyV DNA replication, but not T antigen expression alone, induces ataxia telangiectasia mutated (ATM) kinase-dependent Kap1 S824 phosphorylation, a mechanism that typically facilitates repair of double-strand breaks in heterochromatin by arresting the cells in G2 We show that MCPyV-induced inhibition of cell proliferation is mainly conferred by residues within the origin binding domain and thereby by viral DNA replication. Our data suggest that phosphorylation of Kap1 and subsequent Kap1-dependent G2 arrest/senescence represent host defense mechanisms against MCPyV replication in nHDF cells.IMPORTANCE We here describe Kap1 as a restriction factor in MCPyV infection. We report a novel, indirect mechanism by which Kap1 affects MCPyV replication. In contrast with from other DNA viruses, Kap1 does not associate with the viral genome in MCPyV infection and has no impact on viral gene expression. In MCPyV-infected nHDF cells, Kap1 phosphorylation (pKap1 S824) accumulates because of genomic stress mainly induced by viral DNA replication. In contrast, ectopic expression of LT or LT MCPyV mutants, previously shown to be important for induction of genotoxic stress, does not result in a similar extent of pKap1 accumulation. We show that cells actively replicating MCPyV accumulate pKap1 (in a manner dependent on the presence of ATM) and display a senescence phenotype reflected by G2 arrest. These results are supported by transcriptome analyses showing that LT antigen, in a manner dependent on the presence of Kap1, induces expression of secreted factors, which is known as the senescence-associated secretory phenotype (SASP).

Identification of ARKL1 as a Negative Regulator of Epstein-Barr Virus Reactivation

Epstein-Barr virus (EBV) maintains a life-long infection due to the ability to alternate between latent and lytic modes of replication. Lytic reactivation starts with derepression of the Zp promoter controlling BZLF1 gene expression, which binds and is activated by the c-Jun transcriptional activator. Here, we identified the cellular Arkadia-like 1 (ARKL1) protein as a negative regulator of Zp and EBV reactivation. Silencing of ARKL1 in the context of EBV-positive gastric carcinoma (AGS) cells, nasopharyngeal carcinoma (NPC43) cells, and B (M81) cells led to increased lytic protein expression, whereas overexpression inhibited BZLF1 expression. Similar effects of ARKL1 modulation were seen on BZLF1 transcripts as well as on Zp activity in Zp reporter assays, showing that ARKL1 repressed Zp. Proteomic profiling of ARKL1-host interactions identified c-Jun as an ARKL1 interactor, and reporter assays for Jun transcriptional activity showed that ARKL1 inhibited Jun activity. The ARKL1-Jun interaction required ARKL1 sequences that we previously showed mediated binding to the CK2 kinase regulatory subunit CK2β, suggesting that CK2β might mediate the ARKL1-Jun interaction. This model was supported by the findings that silencing of CK2β, but not the CK2α catalytic subunit, abrogated the ARKL1-Jun interaction and phenocopied ARKL1 silencing in promoting EBV reactivation. Additionally, ARKL1 was associated with Zp in reporter assays and this was increased by additional CK2β. Together, the data indicate that ARKL1 is a negative regulator of Zp and EBV reactivation that acts by inhibiting Jun activity through a CK2β-mediated interaction.IMPORTANCE Epstein-Barr virus (EBV) maintains a life-long infection due to the ability to alternate between latent and lytic modes of replication and is associated with several types of cancer. We have identified a cellular protein (ARKL1) that acts to repress the reactivation of EBV from the latent to the lytic cycle. We show that ARKL1 acts to repress transcription of the EBV lytic switch protein by inhibiting the activity of the cellular transcription factor c-Jun. This not only provides a new mechanism of regulating EBV reactivation but also identifies a novel cellular function of ARKL1 as an inhibitor of Jun-mediated transcription.

Pathogenesis of Human Gammaherpesviruses: Recent Advances

PURPOSE OF THIS REVIEW

Human gammaherpesviruses have complex lifecycles that drive their pathogenesis. KSHV and EBV are the etiological agents of multiple cancers worldwide. There is no FDA-approved vaccine for either KSHV or EBV. This review will describe recent progress in understanding EBV and KSHV lifecycles during infection.

RECENT FINDINGS

Determining how latency is established, particularly how non-coding RNAs influence latent and lytic infection, is a rapidly growing area of investigation into how gammaherpesviruses successfully persist in the human population. Many factors have been identified as restrictors of reactivation from latency, especially innate immune antagonism. Finally, new host proteins that play a role in lytic replication have been identified.

SUMMARY

In this review we discuss recent findings over the last 5 years on both host and viral factors that are involved in EBV and KSHV pathogenesis.

The Epstein-Barr Virus Oncoprotein, LMP1, Regulates the Function of SENP2, a SUMO-protease

Epstein-Barr virus (EBV) latent membrane protein-1 (LMP1) activates numerous signal transduction pathways using its C-terminal activating regions. We reported that LMP1 increased global levels of sumoylated proteins, which aided the oncogenic nature of LMP1. Because increased protein sumoylation is detected in numerous cancers, we wanted to elucidate additional mechanisms by which LMP1 modulates the sumoylation machinery. Results indicated that SUMO-protease activity decreased in a LMP1-dependent manner, so we hypothesized that LMP1 inhibits SUMO-protease activity, resulting in reduced de-sumoylation of cellular proteins, which contributes to the detected accumulation of sumoylated proteins in EBV-positive lymphomas. Focusing on SENP2, findings revealed that LMP1 expression corresponded with increased sumoylation of SENP2 at K48 and K447 in a CTAR-dependent manner. Interestingly, independent of LMP1-induced sumoylation of SENP2, LMP1 also decreased SENP2 activity, decreased SENP2 turnover, and altered the localization of SENP2, which led us to investigate if LMP1 regulated the biology of SENP2 by a different post-translational modification, specifically ubiquitination. Data showed that expression of LMP1 inhibited the ubiquitination of SENP2, and inhibition of ubiquitination was sufficient to mimic LMP1-induced changes in SENP2 activity and trafficking. Together, these findings suggest that LMP1 modulates different post-translational modifications of SENP2 in order to modulate its biology and identify a third member of the sumoylation machinery that is manipulated by LMP1 during latent EBV infections, which can affect oncogenesis.

Using glycyrrhizic acid to target sumoylation processes during Epstein-Barr virus latency

Cellular sumoylation processes are proposed targets for anti-viral and anti-cancer therapies. We reported that Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) dysregulates cellular sumoylation processes, contributing to its oncogenic potential in EBV-associated malignancies. Ginkgolic acid and anacardic acid, known inhibitors of sumoylation, inhibit LMP1-induced protein sumoylation; however, both drugs have adverse effects in hosts. Here we test the effects of glycyrrhizic acid, a medicinal botanical extract with anti-inflammatory, anti-carcinogenic, and anti-viral properties, on cellular sumoylation processes. While glycyrrhizic acid is known to inhibit EBV penetration, its affect on cellular sumoylation processes remains to be documented. We hypothesized that glycyrrhizic acid inhibits cellular sumoylation processes and may be a viable treatment for Epstein-Barr virus-associated malignancies. Results showed that glycyrrhizic acid inhibited sumoylation processes (without affecting ubiquitination processes), limited cell growth, and induced apoptosis in multiple cell lines. Similar to ginkgolic acid; glycyrrhizic acid targeted the first step of the sumoylation process and resulted in low levels of spontaneous EBV reactivation. Glycyrrhizic acid did not affect induced reactivation of the virus, but the presence of the extract did reduce the ability of the produced virus to infect additional cells. Therefore, we propose that glycyrrhizic acid may be a potential therapeutic drug to augment the treatment of EBV-associated lymphoid malignancies.

Epstein-Barr Virus Latent Membrane Protein-1 Induces the Expression of SUMO-1 and SUMO-2/3 in LMP1-positive Lymphomas and Cells

Epstein-Barr Virus latent membrane protein-1 (LMP1) interacts with the SUMO-conjugating enzyme Ubc9, which induces protein sumoylation and may contribute to LMP1-mediated oncogenesis. After analyzing human lymphoma tissues and EBV-positive cell lines, we now document a strong correlation between LMP1 and sumo-1/2/3 or SUMO-1/2/3 levels, and show that LMP1-induced sumo expression requires the activation of NF-κB signaling through CTAR1 and CTAR2. Together, these results point to a second mechanism by which LMP1 dysregulates sumoylation processes and adds EBV-associated lymphomas to the list of malignancies associated with increased SUMO expression.

The Epstein-Barr virus LMP1 interactome: biological implications and therapeutic targets

The oncogenic potential of Epstein-Barr virus (EBV) is mostly attributed to latent membrane protein 1 (LMP1), which is essential and sufficient for transformation of fibroblast and primary lymphocytes. LMP1 expression results in the activation of multiple signaling cascades like NF-ΚB and MAP kinases that trigger cell survival and proliferative pathways. LMP1 specific signaling events are mediated through the recruitment of a number of interacting proteins to various signaling domains. Based on these properties, LMP1 is an attractive target to develop effective therapeutics to treat EBV-related malignancies. In this review, we focus on LMP1 interacting proteins, associated signaling events, and potential targets that could be exploited for therapeutic strategies.

A genome-wide screen of Epstein-Barr virus proteins that modulate host SUMOylation identifies a SUMO E3 ligase conserved in herpesviruses

Many cellular processes pertinent for viral infection are regulated by the addition of small ubiquitin-like modifiers (SUMO) to key regulatory proteins, making SUMOylation an important mechanism by which viruses can commandeer cellular pathways. Epstein-Barr virus (EBV) is a master at manipulating of cellular processes, which enables life-long infection but can also lead to the induction of a variety of EBV-associated cancers. To identify new mechanisms by which EBV proteins alter cells, we screened a library of 51 EBV proteins for global effects on cellular SUMO1 and SUMO2 modifications (SUMOylation), identifying several proteins not previously known to manipulate this pathway. One EBV protein (BRLF1) globally induced the loss of SUMOylated proteins, in a proteasome-dependent manner, as well as the loss of promeylocytic leukemia nuclear bodies. However, unlike its homologue (Rta) in Kaposi's sarcoma associated herpesvirus, it did not appear to have ubiquitin ligase activity. In addition we identified the EBV SM protein as globally upregulating SUMOylation and showed that this activity was conserved in its homologues in herpes simplex virus 1 (HSV1 UL54/ICP27) and cytomegalovirus (CMV UL69). All three viral homologues were shown to bind SUMO and Ubc9 and to have E3 SUMO ligase activity in a purified system. These are the first SUMO E3 ligases discovered for EBV, HSV1 and CMV. Interestingly the homologues had different specificities for SUMO1 and SUMO2, with SM and UL69 preferentially binding SUMO1 and inducing SUMO1 modifications, and UL54 preferentially binding SUMO2 and inducing SUMO2 modifications. The results provide new insights into the function of this family of conserved herpesvirus proteins, and the conservation of this SUMO E3 ligase activity across diverse herpesviruses suggests the importance of this activity for herpesvirus infections.

New Insights from Elucidating the Role of LMP1 in Nasopharyngeal Carcinoma

Latent membrane protein 1 (LMP1) is an Epstein-Barr virus (EBV) oncogenic protein that has no intrinsic enzymatic activity or sequence homology to cellular or viral proteins. The oncogenic potential of LMP1 has been ascribed to pleiotropic signaling properties initiated through protein-protein interactions in cytosolic membrane compartments, but the effects of LMP1 extend to nuclear and extracellular processes. Although LMP1 is one of the latent genes required for EBV-immortalization of B cells, the biology of LMP1 in the pathogenesis of the epithelial cancer nasopharyngeal carcinoma (NPC) is more complex. NPC is prevalent in specific regions of the world with high incidence in southeast China. The epidemiology and time interval from seroconversion to NPC onset in adults would suggest the involvement of multiple risk factors that complement the establishment of a latent and persistent EBV infection. The contribution of LMP1 to EBV pathogenesis in polarized epithelia has only recently begun to be elucidated. Furthermore, the LMP1 gene has emerged as one of the most divergent sequences in the EBV genome. This review will discuss the significance of recent advances in NPC research from elucidating LMP1 function in epithelial cells and lessons that could be learned from mining LMP1 sequence diversity.

(-)-Epigallocatechin-3-gallate inhibition of Epstein-Barr virus spontaneous lytic infection involves downregulation of latent membrane protein 1

The Epstein-Barr virus (EBV) lytic cycle contributes to the development of EBV-associated diseases. EBV-encoded latent membrane protein 1 (LMP1) is key to EBV lytic replication, and our previous work indicated that epigallocatechin-3-gallate (EGCG) inhibited constitutive EBV lytic infection through the suppression of LMP1-activated phosphoinositide 3-kinase/Akt and mitogen-activated protein kinase kinase/extracellular signal-related protein kinase 1/2 signaling. The present study demonstrated that LMP1 in CNE-LMP1 constructed cells significantly induced the expression of the EBV lytic proteins BZLF1 (P<0.001) and BMRF1 (P<0.05) compared with CNE1 cells. Following treatment with a specific DNAzyme that targets LMP1, significantly reduced protein expression levels of BZLF1 and BMRF1 in EBV-associated epithelial carcinoma CNE1-LMP1 cells (P<0.001 and P<0.01, respectively) and lymphoma B95.8 cells (both P<0.01) were observed. Furthermore, EGCG significantly inhibited the mRNA and protein expression levels of LMP1 (P<0.05) in an apparent dose-dependent manner in CNE1-LMP1 and B95.8 cells. Thus, the present findings indicated that the molecular mechanism underlying EGCG inhibition of EBV lytic infection involves downregulation of LMP1.

Epstein-Barr Virus LMP1-Mediated Oncogenicity

Epstein-Barr virus latent membrane protein 1 (LMP1) is expressed in multiple human malignancies, including nasopharyngeal carcinoma and Hodgkin and immunosuppression-associated lymphomas. LMP1 mimics CD40 signaling to activate multiple growth and survival pathways, in particular, NF-κB. LMP1 has critical roles in Epstein-Barr virus (EBV)-driven B-cell transformation, and its expression causes fatal lymphoproliferative disease in immunosuppressed mice. Here, we review recent developments in studies of LMP1 signaling, LMP1-induced host dependency factors, mouse models of LMP1 lymphomagenesis, and anti-LMP1 immunotherapy approaches.

Epigenetics and Genetics of Viral Latency

Viral latency can be considered a metastable, nonproductive infection state that is capable of subsequent reactivation to repeat the infection cycle. Viral latent infections have numerous associated pathologies, including cancer, birth defects, neuropathy, cardiovascular disease, chronic inflammation, and immunological dysfunctions. The mechanisms controlling the establishment, maintenance, and reactivation from latency are complex and diversified among virus families, species, and strains. Yet, as examined in this review, common properties of latent viral infections can be defined. Eradicating latent virus has become an important but elusive challenge and will require a more complete understanding of the mechanisms controlling these processes.

Viral Interplay with the Host Sumoylation System

Viruses have evolved elaborate means to regulate diverse cellular pathways in order to create a cellular environment that facilitates viral survival and reproduction. This includes enhancing viral macromolecular synthesis and assembly, as well as preventing antiviral responses, including intrinsic, innate, and adaptive immunity. There are numerous mechanisms by which viruses mediate their effects on the host cell, and this includes targeting various cellular post-translational modification systems, including sumoylation. The wide-ranging impact of sumoylation on cellular processes such as transcriptional regulation, apoptosis, stress response, and cell cycle control makes it an attractive target for viral dysregulation. To date, proteins from both RNA and DNA virus families have been shown to be modified by SUMO conjugation, and this modification appears critical for viral protein function. More interestingly, members of the several viral families have been shown to modulate sumoylation, including papillomaviruses, adenoviruses, herpesviruses, orthomyxoviruses, filoviruses, and picornaviruses. This chapter will focus on mechanisms by which sumoylation both impacts human viruses and is used by viruses to promote viral infection and disease.

Viral manipulation of the cellular sumoylation machinery

Viruses exploit various cellular processes for their own benefit, including counteracting anti-viral responses and regulating viral replication and propagation. In the past 20 years, protein sumoylation has emerged as an important post-translational modification that is manipulated by viruses to modulate anti-viral responses, viral replication, and viral pathogenesis. The process of sumoylation is a multi-step cascade where a small ubiquitin-like modifier (SUMO) is covalently attached to a conserved ΨKxD/E motif within a target protein, altering the function of the modified protein. Here we review how viruses manipulate the cellular machinery at each step of the sumoylation process to favor viral survival and pathogenesis.

Tripartite motif-containing 28 bridges endothelial inflammation and angiogenic activity by retaining expression of TNFR-1 and -2 and VEGFR2 in endothelial cells

Angiogenesis and inflammation are regarded as important factors in the pathogenesis of chronic inflammation, cancer, and wound healing. Recent studies have supported prior evidence that common signaling pathways are involved in angiogenesis and inflammatory responses; however, key factors controlling both processes remain unclear. Although tripartite motif-containing (TRIM)-28 is known to have an immunosuppressive role in immune cells, its expression level and role in endothelial cells (ECs) are still unclear. In this study, we investigated the role of TRIM28 in inflammatory responses and angiogenic activity of ECs for the first time. We showed that TRIM28 is the most abundant TRIM family member and is localized in nuclei of ECs. Small interfering RNA-mediated knockdown of TRIM28 strikingly suppressed expression of TNF receptor (TNFR)-1 and -2, decreased TNF-α-induced phosphorylation of IKKα/β and IκBα and degradation of IκBα and nuclear translocation of p65, and suppressed basal level and TNF-α-induced expression of chemokines and adhesion molecules, including VCAM-1, IL-6, ICAM-1, E-selectin, and monocyte chemoattractant protein (MCP)-1. Unexpectedly, IL-8 was potentiated by TRIM28 knockdown in ECs in an NF-κB-inducing kinase-dependent manner. Meanwhile, knockdown of TRIM28 inhibited expression of VEGF receptor 2 and suppressed VEGF-induced proliferation and tube formation by ECs. Finally, knockdown of TRIM28 suppressed recruitment of ECs in vivo in a murine synthetic basement membrane model. In summary, we found that TRIM28 acts as a central factor in controlling endothelial inflammatory responses and angiogenic activities by retaining expression of TNFR-1 and -2 and VEGF receptor 2 in ECs.-Wang, Y., Li, J., Huang Y., Dai, X., Liu, Y., Liu, Z., Wang, Y., Wang, N., Zhang, P. Tripartite motif-containing 28 bridges endothelial inflammation and angiogenic activity by retaining expression of TNFR1 and -2 and VEGFR2 in endothelial cells.

The Epstein-Barr virus miR-BHRF1-1 targets RNF4 during productive infection to promote the accumulation of SUMO conjugates and the release of infectious virus

Post-translational modification by the Small Ubiquitin-like Modifier (SUMO) regulates a variety of cellular functions, and is hijacked by viruses to remodel the host cell during latent and productive infection. Here we have monitored the activity of the SUMO conjugation machinery in cells productively infected with Epstein-Barr virus (EBV). We found that SUMO2/3 conjugates accumulate during the late phase of the productive virus cycle, and identified several viral proteins as bone fide SUMOylation substrates. Analysis of the mechanism involved in the accumulation of SUMOylated proteins revealed upregulation of several components of the SUMO-conjugation machinery and post-transcriptional downregulation of the SUMO-targeted ubiquitin ligase RNF4. The latter effect was mediated by selective inhibition of RNF4 protein expression by the viral miR-BHRF1-1. Reconstitution of RNF4 in cells expressing an inducible miR-BHRF1-1 sponge or a miR-BHRF1-1 resistant RNF4 was associated with reduced levels of early and late viral proteins and impaired virus release. These findings illustrate a novel strategy for viral interference with the SUMO pathway, and identify the EBV miR-BHRF1-1 and the cellular RNF4 as regulators of the productive virus cycle.

We have investigated the activity of the SUMOylation machinery in cells infected with Epstein-Barr virus (EBV), a human herpesvirus that infects B-lymphocytes and is associated with malignancies. We found that activation of the productive virus cycle is accompanied by accumulation of SUMO conjugates, upregulation of components of the SUMO conjugation machinery, and downregulation of the SUMO-targeted ubiquitin ligase RNF4. The decrease of RNF4 is due to post-transcriptional downregulation by miR-BHRF1-1, a member of the BHRF1 microRNA cluster that is upregulated during productive infection. The effect of miR-BHRF1-1 was confirmed in luciferase reported assays, by mutation of the RNF4 3’UTR seed site, by transfection of a synthetic miR-BHRF1-1 mimic, by ectopic expression of miR-BHRF1-1 and by the reversal of RNF4 downregulation in cells expressing a miR-BHRF1-1 sponge. We also found that several early and late viral proteins are bona fide SUMOylation substrates. Reconstitution of RNF4 in productively infected cells was accompanied by proteasome-dependent degradation of the SUMOylated viral protein and by a significantly reduced virus yield. These findings illustrate a new strategy for viral interference with the SUMO pathway, an unexpected contribution of miR-BHRF1-1 to the productive cycle of EBV and a previously unrecognized role of the RNF4 ligase in the regulation of virus production.

Viral gene products actively promote latent infection by epigenetic silencing mechanisms

Many viruses undergo an acute infection in the host organism and then are cleared by the ensuing host immune response, but other viruses establish a persistent infection involving a latent infection or a chronic infection. Latent infection by the herpesviruses or human immunodeficiency virus involves epigenetic silencing of the DNA genome or proviral genome, respectively. Latent infection was previously thought to be a default pathway resulting from infection of a nonpermissive cell, but recent studies have shown that viral gene products can promote epigenetic silencing and latent infection. This review will summarize the viral gene products that have been shown to promote epigenetic silencing of the genomes and their potential for therapeutics to target these viral gene products and disrupt or lock in latent infection.

Differentiation-Dependent LMP1 Expression Is Required for Efficient Lytic Epstein-Barr Virus Reactivation in Epithelial Cells

Epstein-Barr virus (EBV)-associated diseases of epithelial cells, including tumors that have latent infection, such as nasopharyngeal carcinoma (NPC), and oral hairy leukoplakia (OHL) lesions that have lytic infection, frequently express the viral latent membrane protein 1 (LMP1). In lytically infected cells, LMP1 expression is activated by the BRLF1 (R) immediate early (IE) protein. However, the mechanisms by which LMP1 expression is normally regulated in epithelial cells remain poorly understood, and its potential roles in regulating lytic reactivation in epithelial cells are as yet unexplored. We previously showed that the differentiation-dependent cellular transcription factors KLF4 and BLIMP1 induce lytic EBV reactivation in epithelial cells by synergistically activating the two EBV immediate early promoters (Zp and Rp). Here we show that epithelial cell differentiation also induces LMP1 expression. We demonstrate that KLF4 and BLIMP1 cooperatively induce the expression of LMP1, even in the absence of the EBV IE proteins BZLF1 (Z) and R, via activation of the two LMP1 promoters. Furthermore, we found that differentiation of NOKs-Akata cells by either methylcellulose suspension or organotypic culture induces LMP1 expression prior to Z and R expression. We show that LMP1 enhances the lytic infection-inducing effects of epithelial cell differentiation, as well as 12-O-tetradecanoylphorbol-13-acetate (TPA) and sodium butyrate treatment, in EBV-infected epithelial cells by increasing expression of the Z and R proteins. Our results suggest that differentiation of epithelial cells activates a feed-forward loop in which KLF4 and BLIMP1 first activate LMP1 expression and then cooperate with LMP1 to activate Z and R expression.IMPORTANCE The EBV protein LMP1 is expressed in EBV-associated epithelial cell diseases, regardless of whether these diseases are due to lytic infection (such as oral hairy leukoplakia) or latent infection (such as nasopharyngeal carcinoma). However, surprisingly little is known about how LMP1 expression is regulated in epithelial cells, and there are conflicting reports about whether it plays any role in regulating viral lytic reactivation. In this study, we show that epithelial cell differentiation induces LMP1 expression by increasing expression of two cellular transcription factors (KLF4 and BLIMP1) which cooperatively activate the two LMP1 promoters. We also demonstrate that LMP1 promotes efficient lytic reactivation in EBV-infected epithelial cells by enhancing expression of the Z and R proteins. Thus, in EBV-infected epithelial cells, LMP1 expression is promoted by differentiation and positively regulates lytic viral reactivation.

Chloroquine triggers Epstein-Barr virus replication through phosphorylation of KAP1/TRIM28 in Burkitt lymphoma cells

Trials to reintroduce chloroquine into regions of Africa where P. falciparum has regained susceptibility to chloroquine are underway. However, there are long-standing concerns about whether chloroquine increases lytic-replication of Epstein-Barr virus (EBV), thereby contributing to the development of endemic Burkitt lymphoma. We report that chloroquine indeed drives EBV replication by linking the DNA repair machinery to chromatin remodeling-mediated transcriptional repression. Specifically, chloroquine utilizes ataxia telangiectasia mutated (ATM) to phosphorylate the universal transcriptional corepressor Krüppel-associated Box-associated protein 1/tripartite motif-containing protein 28 (KAP1/TRIM28) at serine 824 -a mechanism that typically facilitates repair of double-strand breaks in heterochromatin, to instead activate EBV. Notably, activation of ATM occurs in the absence of detectable DNA damage. These findings i) clarify chloroquine's effect on EBV replication, ii) should energize field investigations into the connection between chloroquine and endemic Burkitt lymphoma and iii) provide a unique context in which ATM modifies KAP1 to regulate persistence of a herpesvirus in humans.

Novel roles and therapeutic targets of Epstein-Barr virus-encoded latent membrane protein 1-induced oncogenesis in nasopharyngeal carcinoma

Epstein-Barr virus (EBV) was first discovered 50 years ago as an oncogenic gamma-1 herpesvirus and infects more than 90% of the worldwide adult population. Nasopharyngeal carcinoma (NPC) poses a serious health problem in southern China and is one of the most common cancers among the Chinese. There is now strong evidence supporting a role for EBV in the pathogenesis of NPC. Latent membrane protein 1 (LMP1), a primary oncoprotein encoded by EBV, alters several functional and oncogenic properties, including transformation, cell death and survival in epithelial cells in NPC. LMP1 may increase protein modification, such as phosphorylation, and initiate aberrant signalling via derailed activation of host adaptor molecules and transcription factors. Here, we summarise the novel features of different domains of LMP1 and several new LMP1-mediated signalling pathways in NPC. When then focus on the potential roles of LMP1 in cancer stem cells, metabolism reprogramming, epigenetic modifications and therapy strategies in NPC.