Induction of the early growth response 1 gene by Epstein-Barr virus lytic transactivator Zta

Egr-1 is a key regulator of the blood-brain barrier damage induced by meningitic Escherichia coli

Bacterial meningitis remains a leading cause of infection-related mortality worldwide. Although Escherichia coli (E. coli) is the most common etiology of neonatal meningitis, the underlying mechanisms governing bacterial blood-brain barrier (BBB) disruption during infection remain elusive. We observed that infection of human brain microvascular endothelial cells with meningitic E. coli triggers the activation of early growth response 1 (Egr-1), a host transcriptional activator. Through integrated chromatin immunoprecipitation sequencing and transcriptome analysis, we identified Egr-1 as a crucial regulator for maintaining BBB integrity. Mechanistically, Egr-1 induced cytoskeletal changes and downregulated tight junction protein expression by directly targeting VEGFA, PDGFB, and ANGPTL4, resulting in increased BBB permeability. Meanwhile, Egr-1 also served as a master regulator in the initiation of neuroinflammatory response during meningitic E. coli infection. Our findings support an Egr-1-dependent mechanism of BBB disruption by meningitic E. coli, highlighting a promising therapeutic target for bacterial meningitis.

Streptolysin S induces pronounced calcium-ion influx-dependent expression of immediate early genes encoding transcription factors

Anginosus group streptococci (AGS) are opportunistic human pathogens of the oral cavity. The β-hemolytic subgroup of Streptococcus anginosus subsp. anginosus secretes streptolysin S (SLS) and exhibits not only hemolytic activity but also cytotoxicity toward cultured human cell lines. However, the detailed mechanism of action of SLS and the cellular responses of host cells have not yet been fully clarified. To determine the pathogenic potential of SLS-producing β-hemolytic S. anginosus subsp. anginosus, the SLS-dependent response induced in the human oral squamous cell carcinoma HSC-2 cells was investigated to determine the pathogenic potential of SLS-producing β-hemolytic S. anginosus subsp. anginosus. This study revealed that the Ca2+ influx and the expression of immediate early genes (IEGs) encoding transcription factors such as early growth responses (EGRs) and activator protein-1 (AP-1) were greatly increased in HSC-2 cells incubated with the culture supernatant of SLS-producing β-hemolytic S. anginosus subsp. anginosus. Moreover, this SLS-dependent increase in expression was significantly suppressed by Ca2+ chelation, except for jun. These results suggest that SLS caused Ca2+ influx into the cells following greatly enhanced expression of IEG-encoding transcription factors. The results of this study may help in understanding the pathogenicity of SLS-producing AGS.

Dendrosomal nanocurcumin prevents EBV-associated cell transformation by targeting the lytic cycle genes of the Epstein-Barr virus in the generation of lymphoblastoid cell line

Objectives

Targeting the lytic cycle of the Epstein-Barr virus (EBV) has been considered a new treatment strategy for malignancies caused by this virus. This study aimed to investigate the effect of Dendrosomal NanoCurcumin (DNC) to prevent cell transformation and inhibit the expression of viral lytic gene expression in the generation of lymphoblastoid cell line (LCL).

Materials and Methods

Cell viability of LCLs and PBMCs was performed by MTT assay, and flow cytometry (Annexin/PI) was used for evaluation of apoptosis. CD markers on the surface of generated LCL (CD19) cells were examined for cell validation. The effect of DNC on transformation was evaluated by examining cell morphology and determining the expression level of lytic genes BZLF1, Zta, BHRF1, and BRLF1 of EBV using Real-time PCR. Student's t-test was used for statistical analysis.

Results

The MTT assay showed that DNC can inhibit the proliferation of LCL in a dose-dependent manner. The 50% cytotoxic concentration (CC50) of DNC and curcumin for LCL was determined 38.8 µg/ml and 75 µg/ml, respectively after 72 hr. Also, Real-time PCR data analysis showed that DNC in 30 µg/ml concentration significantly inhibited cell transformation in the LCL and significantly reduced viral lytic genes such as BZLF1, Zta, BHRF1, and BRLF1expression compared to control.

Conclusion

Overall, these findings show that DNC reduces the expression of the viral lytic cycle genes and also the induction of cell apoptosis and finally prevents the generation of LCL.

Examining the role of EGR1 during viral infections

Early growth response 1 (EGR1) is a multifunctional mammalian transcription factor capable of both enhancing and/or inhibiting gene expression. EGR1 can be activated by a wide array of stimuli such as exposure to growth factors, cytokines, apoptosis, and various cellular stress states including viral infections by both DNA and RNA viruses. Following induction, EGR1 functions as a convergence point for numerous specialized signaling cascades and couples short-term extracellular signals to influence transcriptional regulation of genes required to initiate the appropriate biological response. The role of EGR1 has been extensively studied in both physiological and pathological conditions of the adult nervous system where it is readily expressed in various regions of the brain and is critical for neuronal plasticity and the formation of memories. In addition to its involvement in neuropsychiatric disorders, EGR1 has also been widely examined in the field of cancer where it plays paradoxical roles as a tumor suppressor gene or oncogene. EGR1 is also associated with multiple viral infections such as Venezuelan equine encephalitis virus (VEEV), Kaposi's sarcoma-associated herpesvirus (KSHV), herpes simplex virus 1 (HSV-1), human polyomavirus JC virus (JCV), human immunodeficiency virus (HIV), and Epstein-Barr virus (EBV). In this review, we examine EGR1 and its role(s) during viral infections. First, we provide an overview of EGR1 in terms of its structure, other family members, and a brief overview of its roles in non-viral disease states. We also review upstream regulators of EGR1 and downstream factors impacted by EGR1. Then, we extensively examine EGR1 and its roles, both direct and indirect, in regulating replication of DNA and RNA viruses.

Epstein-Barr Virus Enhances Cancer-Specific Aberrant Splicing of TSG101 Pre-mRNA

Tumor viruses gain control of cellular functions when they infect and transform host cells. Alternative splicing is one of the cellular processes exploited by tumor viruses to benefit viral replication and support oncogenesis. Epstein-Barr virus (EBV) participates in a number of cancers, as reported mostly in nasopharyngeal carcinoma (NPC) and Burkitt lymphoma (BL). Using RT-nested-PCR and Northern blot analysis in NPC and BL cells, here we demonstrate that EBV promotes specific alternative splicing of TSG101 pre-mRNA, which generates the TSG101∆154-1054 variant though the agency of its viral proteins, such as EBNA-1, Zta and Rta. The level of TSG101∆154-1054 is particularly enhanced upon EBV entry into the lytic cycle, increasing protein stability of TSG101 and causing the cumulative synthesis of EBV late lytic proteins, such as VCA and gp350/220. TSG101∆154-1054-mediated production of VCA and gp350/220 is blocked by the overexpression of a translational mutant of TSG101∆154-1054 or by the depletion of full-length TSG101, which is consistent with the known role of the TSG101∆154-1054 protein in stabilizing the TSG101 protein. NPC patients whose tumor tissues express TSG101∆154-1054 have high serum levels of anti-VCA antibodies and high levels of viral DNA in their tumors. Our findings highlight the functional importance of TSG101∆154-1054 in allowing full completion of the EBV lytic cycle to produce viral particles. We propose that targeting EBV-induced TSG101 alternative splicing has broad potential as a therapeutic to treat EBV-associated malignancies.

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.

Epstein-Barr Virus Lytic Replication Induces ACE2 Expression and Enhances SARS-CoV-2 Pseudotyped Virus Entry in Epithelial Cells

Understanding factors that affect the infectivity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is central to combatting coronavirus disease 2019 (COVID-19). The virus surface spike protein of SARS-CoV-2 mediates viral entry into cells by binding to the ACE2 receptor on epithelial cells and promoting fusion. We found that Epstein-Barr virus (EBV) induces ACE2 expression when it enters the lytic replicative cycle in epithelial cells. By using vesicular stomatitis virus (VSV) particles pseudotyped with the SARS-CoV-2 spike protein, we showed that lytic EBV replication enhances ACE2-dependent SARS-CoV-2 pseudovirus entry. We found that the ACE2 promoter contains response elements for Zta, an EBV transcriptional activator that is essential for EBV entry into the lytic cycle of replication. Zta preferentially acts on methylated promoters, allowing it to reactivate epigenetically silenced EBV promoters from latency. By using promoter assays, we showed that Zta directly activates methylated ACE2 promoters. Infection of normal oral keratinocytes with EBV leads to lytic replication in some of the infected cells, induces ACE2 expression, and enhances SARS-CoV-2 pseudovirus entry. These data suggest that subclinical EBV replication and lytic gene expression in epithelial cells, which is ubiquitous in the human population, may enhance the efficiency and extent of SARS-CoV-2 infection of epithelial cells by transcriptionally activating ACE2 and increasing its cell surface expression. IMPORTANCE SARS-CoV-2, the coronavirus responsible for COVID-19, has caused a pandemic leading to millions of infections and deaths worldwide. Identifying the factors governing susceptibility to SARS-CoV-2 is important in order to develop strategies to prevent SARS-CoV-2 infection. We show that Epstein-Barr virus, which infects and persists in >90% of adult humans, increases susceptibility of epithelial cells to infection by SARS-CoV-2. EBV, when it reactivates from latency or infects epithelial cells, increases expression of ACE2, the cellular receptor for SARS-CoV-2, enhancing infection by SARS-CoV-2. Inhibiting EBV replication with antivirals may therefore decrease susceptibility to SARS-CoV-2 infection.

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

Epstein-Barr virus (EBV), a herpes virus also termed HHV 4 and the first identified human tumor virus, establishes a stable, long-term latent infection in human B cells, its preferred host. Upon induction of EBV's lytic phase, the latently infected cells turn into a virus factory, a process that is governed by EBV. In the lytic, productive phase, all herpes viruses ensure the efficient induction of all lytic viral genes to produce progeny, but certain of these genes also repress the ensuing antiviral responses of the virally infected host cells, regulate their apoptotic death or control the cellular transcriptome. We now find that EBV causes previously unknown massive and global alterations in the chromatin of its host cell upon induction of the viral lytic phase and prior to the onset of viral DNA replication. The viral initiator protein of the lytic cycle, BZLF1, binds to >105 binding sites with different sequence motifs in cellular chromatin in a concentration dependent manner implementing a binary molar switch probably to prevent noise-induced erroneous induction of EBV's lytic phase. Concomitant with DNA binding of BZLF1, silent chromatin opens locally as shown by ATAC-seq experiments, while previously wide-open cellular chromatin becomes inaccessible on a global scale within hours. While viral transcripts increase drastically, the induction of the lytic phase results in a massive reduction of cellular transcripts and a loss of chromatin-chromatin interactions of cellular promoters with their distal regulatory elements as shown in Capture-C experiments. Our data document that EBV's lytic cycle induces discrete early processes that disrupt the architecture of host cellular chromatin and repress the cellular epigenome and transcriptome likely supporting the efficient de novo synthesis of this herpes virus.

Epstein-Barr Virus Limits the Accumulation of IPO7, an Essential Gene Product

Epstein-Barr virus (EBV) encodes more than 40 miRNAs that target cellular mRNAs to aid its infection, replication, and maintenance in individual cells and in its human host. Importin-7 (IPO7), also termed Imp7 or RanBPM7, is a nucleocytoplasmic transport protein that has been frequently identified as a target for two of these viral miRNAs. How the viral life cycle might benefit from regulating IPO7 has been unclear, though. We demonstrate with CRISPR-Cas9 mutagenesis that IPO7 is essential in at least three cells lines and that increasing its levels of expression inhibits growth of infected cells. EBV thus regulates the level of IPO7 to limit its accumulation consistent with its being required for survival of its host cell.

Ubiquitin Modification of the Epstein-Barr Virus Immediate Early Transactivator Zta

The Epstein-Barr virus (EBV) immediate early transactivator Zta plays a key role in regulating the transition from latency to the lytic replication stages of EBV infection. Regulation of Zta is known to be controlled through a number of transcriptional and posttranscriptional events. Here, we show that Zta is targeted for ubiquitin modification and that this can occur in EBV-negative and in EBV-infected cells. Genetic studies show critical roles for both an amino-terminal region of Zta and the basic DNA binding domain of Zta in regulating Zta ubiquitination. Pulse-chase experiments demonstrate that the bulk population of Zta is relatively stable but that at least a subset of ubiquitinated Zta molecules are targeted for degradation in the cell. Mutation of four out of a total of nine lysine residues in Zta largely abrogates its ubiquitination, indicating that these are primary ubiquitination target sites. A Zta mutant carrying mutations at these four lysine residues (lysine 12, lysine 188, lysine 207, and lysine 219) cannot induce latently infected cells to produce and/or release infectious virions. Nevertheless, this mutant can induce early gene expression, suggesting a possible defect at the level of viral replication or later in the lytic cascade. As far as we know, this is the first study that has investigated the targeting of Zta by ubiquitination or its role in Zta function.IMPORTANCE Epstein-Barr virus (EBV) is a ubiquitous human pathogen and associated with various human diseases. EBV undergoes latency and lytic replication stages in its life cycle. The transition into the lytic replication stage, at which virus is produced, is mainly regulated by the viral gene product, Zta. Therefore, the regulation of Zta function becomes a central issue regarding viral biology and pathogenesis. Known modifications of Zta include phosphorylation and sumoylation. Here, we report the role of ubiquitination in regulating Zta function. We found that Zta is subjected to ubiquitination in both EBV-infected and EBV-negative cells. The ubiquitin modification targets 4 lysine residues on Zta, leading to both mono- and polyubiquitination of Zta. Ubiquitination of Zta affects the protein's stability and likely contributes to the progression of viral lytic replication. The function and fate of Zta may be determined by the specific lysine residue being modified.

Early Growth Response Gene Upregulation in Epstein-Barr Virus (EBV)-Associated Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a chronic multisystem disease exhibiting a variety of symptoms and affecting multiple systems. Psychological stress and virus infection are important. Virus infection may trigger the onset, and psychological stress may reactivate latent viruses, for example, Epstein-Barr virus (EBV). It has recently been reported that EBV induced gene 2 (EBI2) was upregulated in blood in a subset of ME/CFS patients. The purpose of this study was to determine whether the pattern of expression of early growth response (EGR) genes, important in EBV infection and which have also been found to be upregulated in blood of ME/CFS patients, paralleled that of EBI2. EGR gene upregulation was found to be closely associated with that of EBI2 in ME/CFS, providing further evidence in support of ongoing EBV reactivation in a subset of ME/CFS patients. EGR1, EGR2, and EGR3 are part of the cellular immediate early gene response and are important in EBV transcription, reactivation, and B lymphocyte transformation. EGR1 is a regulator of immune function, and is important in vascular homeostasis, psychological stress, connective tissue disease, mitochondrial function, all of which are relevant to ME/CFS. EGR2 and EGR3 are negative regulators of T lymphocytes and are important in systemic autoimmunity.

Dysregulation of Dual-Specificity Phosphatases by Epstein-Barr Virus LMP1 and Its Impact on Lymphoblastoid Cell Line Survival

The strongest evidence of the oncogenicity of Epstein-Barr virus (EBV) in vitro is its ability to immortalize human primary B lymphocytes into lymphoblastoid cell lines (LCLs). Yet the underlying mechanisms explaining how the virus tempers the growth program of the host cells have not been fully elucidated. The mitogen-activated protein kinases (MAPKs) are implicated in many cellular processes and are constitutively activated in LCLs. We questioned the expression and regulation of the dual-specificity phosphatases (DUSPs), the main negative regulator of MAPKs, during EBV infection and immortalization. Thirteen DUSPs, including 10 typical and 3 atypical types of DUSPs, were tested. Most of them were downregulated after EBV infection. Here, a role of viral oncogene latent membrane protein 1 (LMP1) in limiting DUSP6 and DUSP8 expression was identified. Using MAPK inhibitors, we found that LMP1 activates extracellular signal-regulated kinase (ERK) or p38 to repress the expression of DUSP6 and DUSP8, with corresponding substrate specificity. Morphologically, overexpression of DUSP6 and DUSP8 attenuates the ability of EBV-immortalized LCL cells to clump together. Mechanistically, apoptosis induced by restoring DUSP6 and DUSP8 in LCLs indicated a novel mechanism for LMP1 to provide a survival signal during EBV immortalization. Collectively, this report provides the first description of the interplay between EBV genes and DUSPs and contributes considerably to the interpretation of MAPK regulation in EBV immortalization.IMPORTANCE Infections by the ubiquitous Epstein-Barr virus (EBV) are associated with a wide spectrum of lymphomas and carcinomas. It has been well documented that activation levels of MAPKs are found in cancer cells to translate various external or intrinsic stimuli into cellular responses. Physiologically, the dual-specificity phosphates (DUSPs) exhibit great ability in regulating MAPK activities with respect to their capability of dephosphorylating MAPKs. In this study, we found that DUSPs were generally downregulated after EBV infection. EBV oncogenic latent membrane protein 1 (LMP1) suppressed DUSP6 and DUSP8 expression via MAPK pathway. In this way, LMP1-mediated MAPK activation was a continuous process. Furthermore, DUSP downregulation was found to contribute greatly to prevent apoptosis of EBV-infected cells. To sum up, this report sheds light on a novel molecular mechanism explaining how EBV maintains the unlimited proliferation status of the immortalized cells and provides a new link to understand EBV-induced B cell survival.

Screening of Cellular Stress Responses Induced by Ambient Aerosol Ultrafine Particle Fraction PM0.5 in A549 Cells

Effects of airborne particles on the expression status of markers of cellular toxic stress and on the release of eicosanoids, linked with inflammation and oxidative damage, remain poorly characterized. Therefore, we proposed a set of various methodological approaches in order to address complexity of PM0.5-induced toxicity. For this purpose, we used a well-characterized model of A549 pulmonary epithelial cells exposed to a non-cytotoxic concentration of ambient aerosol particle fraction PM0.5 for 24 h. Electron microscopy confirmed accumulation of PM0.5 within A549 cells, yet, autophagy was not induced. Expression profiles of various cellular stress response genes that have been previously shown to be involved in early stress responses, namely unfolded protein response, DNA damage response, and in aryl hydrocarbon receptor (AhR) and p53 signaling, were analyzed. This analysis revealed induction of GREM1, EGR1, CYP1A1, CDK1A, PUMA, NOXA and GDF15 and suppression of SOX9 in response to PM0.5 exposure. Analysis of eicosanoids showed no oxidative damage and only a weak anti-inflammatory response. In conclusion, this study helps to identify novel gene markers, GREM1, EGR1, GDF15 and SOX9, that may represent a valuable tool for routine testing of PM0.5-induced in vitro toxicity in lung epithelial cells.

Host signaling and EGR1 transcriptional control of human cytomegalovirus replication and latency

Sustained phosphotinositide3-kinase (PI3K) signaling is critical to the maintenance of alpha and beta herpesvirus latency. We have previously shown that the beta-herpesvirus, human cytomegalovirus (CMV), regulates epidermal growth factor receptor (EGFR), upstream of PI3K, to control states of latency and reactivation. How signaling downstream of EGFR is regulated and how this impacts CMV infection and latency is not fully understood. We demonstrate that CMV downregulates EGFR early in the productive infection, which blunts the activation of EGFR and its downstream pathways in response to stimuli. However, CMV infection sustains basal levels of EGFR and downstream pathway activity in the context of latency in CD34+ hematopoietic progenitor cells (HPCs). Inhibition of MEK/ERK, STAT or PI3K/AKT pathways downstream of EGFR increases viral reactivation from latently infected CD34⁺ HPCs, defining a role for these pathways in latency. We hypothesized that CMV modulation of EGFR signaling might impact viral transcription important to latency. Indeed, EGF-stimulation increased expression of the UL138 latency gene, but not immediate early or early viral genes, suggesting that EGFR signaling promotes latent gene expression. The early growth response-1 (EGR1) transcription factor is induced downstream of EGFR signaling through the MEK/ERK pathway and is important for the maintenance of hematopoietic stemness. We demonstrate that EGR1 binds the viral genome upstream of UL138 and is sufficient to promote UL138 expression. Further, disruption of EGR1 binding upstream of UL138 prevents the establishment of latency in CD34⁺ HPCs. Our results indicate a model whereby UL138 modulation of EGFR signaling feeds back to promote UL138 gene expression and suppression of replication for latency. By this mechanism, the virus has hardwired itself into host cell biology to sense and respond to changes in homeostatic host cell signaling.

Host signaling is important for regulating states of cytomegalovirus (CMV) replication and latency. We have shown that human cytomegalovirus regulates EGFR levels and trafficking and that sustained EGFR or downstream PI3K signaling is a requirement for viral latency. Changes in host signaling have the ability to alter viral and host gene expression to impact the outcome of infection. Here we show that EGFR signaling through MEK/ERK pathway induces the host EGR1 transcription factor that is highly expressed in hematopoietic stem cells and necessary for the maintenance of hematopoietic stemness. Downregulation of EGR1 promotes stem cell mobilization and differentiation, known stimuli for CMV reactivation. We identified functional EGR1 binding sites upstream of the UL138 CMV latency gene and EGR1 stimulated UL138 expression to reinforce the latent infection. Mutant viruses where the regulation of UL138 by EGR1 is disrupted are unable to establish latency in CD34⁺ HPCs. This study advances our understanding of how host signaling impacts decisions to enter into or exit from latency. The regulation of viral gene expression by host signaling allows the virus to sense and respond to changes in host stress or differentiation.

Oct4 upregulates osteopontin via Egr1 and is associated with poor outcome in human lung cancer

BACKGROUND

Roles of cancer stem cells and early growth response gene 1 (Egr1) in carcinogenesis have been extensively studied in lung cancer. However, the role of Egr1 in the metastasis of lung cancer remains undetermined, especially in regard to stem cell-related pathways.

METHODS

Egr1, osteopontin (OPN) and Oct4 expression in human lung cancer was determined by performing immunohistochemistry. Immunoblotting, ELISA, luciferase reporter assay, chromatin immunoprecipitation assay and RT-PCR were performed to validate the regulation of Oct4-Egr1-OPN axis. Moreover, the effect of Oct4-Egr1-OPN axis on lung cancer progression was evaluated by cell migration assay and mice study.

RESULTS

We detected Oct4, Egr1, and OPN expression in clinical specimens from 79 lung cancer patients, including 72 adenocarcinomas and 7 squamous cell carcinomas. High expression of Oct4, Egr1, and OPN accounted for 53, 51, and 57% of the patients, respectively. All of the three biomarkers were positively correlated in clinical human lung cancer. Patients with high expression of OPN were significantly associated with shorter disease-free survivals than those with low expression of OPN (p < 0.05). In lung cancer cells, Oct4 transactivated the Egr1 promoter and upregulated Egr1 expression. In a human lung cancer xenograft model, Oct4-overexpressing tumors expressed elevated levels of Egr1. Furthermore, overexpression of Oct4 in lung cancer cells increased the metastatic potential.

CONCLUSIONS

Egr1 exerts a promoting effect on cancer metastasis in Oct4-overexpressing lung cancer. Thus, therapeutic strategies targeting the Oct4/Egr1/OPN axis may be further explored for the treatment of lung cancer, especially when lung cancer is refractory to conventional treatment due to cancer stem cells.

Cellular microRNA bta-miR-2361 inhibits bovine herpesvirus 1 replication by directly targeting EGR1 gene

Bovine herpesvirus 1 (BHV-1) is an economically important pathogen of cattle and has led to significant consequences on the cattle industry worldwide. MicroRNAs (miRNAs) are a class of regulators that play critical roles in virus and host interaction. However, the roles of host miRNAs in BHV-1 infection remain largely unclear. In this study, a set of differentially expressed miRNAs by small RNA deep sequencing were analyzed in the Madin-Darby Bovine Kidney Cells (MDBK) infected with BHV-1 after 12 h, 24 h and 48 h post-infection compared to mock infection, and it was confirmed that bta-miR-2361 was significantly down-regulated. Moreover, bta-miR-2361 mimics transfection could inhibit BHV-1 replication. Combined with up-regulated genes from BHV-1-infected MDBK cells by deep RNA-sequencing and predicted by bioinformatics tools, early growth response 1 (EGR1) was putative target of bta-miR-2361. Furthermore, EGR1 was up-regulated during BHV-1 infection, and overexpression of EGR1 promoted BHV-1 replication whereas knockdown of EGR1 had the opposite effects. Subsequently, the target association between bta-miR-2361 and 3'UTR of EGR1 was further validated using a dual-luciferase reporter assay. In addition, overexpression of bta-miR-2361 resulted in decreased EGR1 mRNA and protein levels. Further mechanistic study showed that EGR1 stimulated BHV-1 UL46 promoter activity, but overexpression of bta-miR-2361 suppressed the production of UL46 gene. Collectively, this is the first study to reveal that bta-miR-2361 as a novel host factor regulates BHV-1 replication via directly targeting the EGR1 gene, which is a transcription factor that regulates viral UL46 gene of BHV-1. These results provide further insight into the study of BHV-1 pathogenesis.

Egr-1 regulates RTA transcription through a cooperative involvement of transcriptional regulators

Kaposi's sarcoma associated herpesvirus (KSHV) regulates the host cellular environment to establish life-long persistent infection by manipulating cellular signaling pathways, with approximately 1- 5% of cells undergoing lytic reactivation during the course of infection. Egr-1 (Early Growth Response Factor-1) is one such cellular transcription factor, which gets phosphorylated during the lytic phase of viral life cycle to perpetrate its function. This study demonstrates the mechanism of how Egr-1 mediates transcription of the immediate early gene, RTA (Replication and transcription activator), which is the lytic switch gene of KSHV. Egr-1 depleted KSHV infected cells exhibited reduced expression of RTA. Also, an increase in Egr-1 phosphorylation led to a higher virion production, which was suppressed in the presence of p38 and Raf inhibitors. Reporter assays showed that coexpression of Egr-1 and CBP (CREB-binding protein) enhances RTA promoter activity as compared to the expression of either Egr-1 or CBP alone. Binding of Egr-1 and CBP at RTA promoter was analyzed by chromatin immunoprecipitation assay (ChIP), which showed an enhanced accumulation during viral reactivation. Mutation in Egr-1 binding site of the RTA promoter eliminated Egr-1 response on promoter activation. Furthermore, de novo infection of THP-1 (monocytic) and HUVECs (endothelial) cells showed an upregulation of Egr-1 phosphorylation, whereas depletion of Egr-1 reduced the mRNA levels of RTA during primary infection. Together, these results demonstrate a cooperative role of Egr-1 and CBP in mediating RTA transcription, which significantly improves our understanding of the involvement of cellular factors controlling RTA transcription in KSHV pathogenesis.

Epstein-Barr virus (EBV)-associated epithelial and non-epithelial lesions of the oral cavity

Epstein–Barr virus (EBV) is known to be associated with the development of malignant lymphoma and lymphoproliferative disorders (LPDs) in immunocompromised patients. EBV, a B-lymphotropic gamma-herpesvirus, causes infectious mononucleosis and oral hairy leukoplakia, as well as various pathological types of lymphoid malignancy. Furthermore, EBV is associated with epithelial malignancies such as nasopharyngeal carcinoma (NPC), salivary gland tumor, gastric carcinoma and breast carcinoma. In terms of oral disease, there have been several reports of EBV-related oral squamous cell carcinoma (OSCC) worldwide. However, the role of EBV in tumorigenesis of human oral epithelial or lymphoid tissue is unclear. This review summarizes EBV-related epithelial and non-epithelial tumors or tumor-like lesions of the oral cavity. In addition, we describe EBV latent genes and their expression in normal epithelium, inflamed gingiva, epithelial dysplasia and SCC, as well as considering LPDs (MTX- and age-related) and DLBCLs of the oral cavity.

Epstein-Barr virus lytic reactivation regulation and its pathogenic role in carcinogenesis

Epstein-Barr virus (EBV) has been associated with several types of human cancers. In the host, EBV can establish two alternative modes of life cycle, known as latent or lytic and the switch from latency to the lytic cycle is known as EBV reactivation. Although EBV in cancer cells is found mostly in latency, a small number of lytically-infected cells promote carcinogenesis through the release of growth factors and oncogenic cytokines. This review focuses on the mechanisms by which EBV reactivation is controlled by cellular and viral factors, and discusses how EBV lytic infection contributes to human malignancies.

Fresh Insights into Disease Etiology and the Role of Microbial Pathogens

Pathogens have been implicated in the initiation and/or promotion of systemic sclerosis (scleroderma, SSc); however, no evidence was found to substantiate the direct contribution to this disease in past years. Recently, significant advances have been made in understanding the role of the innate immune system in SSc pathogenesis, supporting the idea that pathogens might interact with host innate immune-regulatory responses in SSc. In light of these findings, we review the studies that identified the presence of pathogens in SSc, along with studies on pathogens implicated in driving the innate immune dysregulation in SSc. The goal of this review is to illustrate how these pathogens, specifically viruses, may play important role both as triggers of the innate immune system, and critical players in the development of SSc disease.

Valpromide Inhibits Lytic Cycle Reactivation of Epstein-Barr Virus

Reactivation of Epstein-Barr virus (EBV) from latency into the lytic phase of its life cycle allows the virus to spread among cells and between hosts. Valproic acid (VPA) inhibits initiation of the lytic cycle in EBV-infected B lymphoma cells. While VPA blocks viral lytic gene expression, it induces expression of many cellular genes, because it is a histone deacetylase (HDAC) inhibitor. Here we show, using derivatives of VPA, that blockade of EBV reactivation is separable from HDAC inhibition. Valpromide (VPM), an amide derivative of valproic acid that is not an HDAC inhibitor, prevented expression of two EBV genes, BZLF1 and BRLF1, that mediate lytic reactivation. VPM also inhibited expression of a viral late gene, but not early genes, when BZLF1 was exogenously expressed. Unlike VPA, VPM did not activate lytic expression of Kaposi's sarcoma-associated herpesvirus. Expression of cellular immediate-early genes, such as FOS and EGR1, is kinetically upstream of the EBV lytic cycle. VPM did not activate expression of these cellular immediate-early genes but decreased their level of expression when induced by butyrate, an HDAC inhibitor. VPM did not alter expression of several other cellular immediate-early genes, including STAT3, which were induced by the HDAC inhibitors in cells refractory to lytic induction. Therefore, VPM selectively inhibits both viral and cellular gene expression. VPA and VPM represent a new class of antiviral agents. The mechanism by which VPA and VPM block EBV reactivation may be related to their anticonvulsant activity.

IMPORTANCE

Epstein-Barr virus, (EBV), a human tumor virus, establishes a life-long latent infection. Reactivation of EBV into the lytic phase of its life cycle allows the virus to spread. Previously, we showed that EBV reactivation was blocked by valproic acid (VPA), an inhibitor of cellular histone deacetylases (HDACs). VPA alters the expression of thousands of cellular genes. In this study, we demonstrate that valpromide (VPM), an amide derivative of valproic acid that is not an HDAC inhibitor, prevented initiation of the EBV lytic cycle. VPA induced lytic reactivation of Kaposi's sarcoma-associated herpesvirus (KSHV), but VPM did not. Unlike VPA, VPM did not activate cellular immediate-early gene expression. VPM is a new type of antiviral agent. VPM will be useful in probing the mechanism of EBV lytic reactivation and may have therapeutic application.

Epstein-Barr virus transcription factor Zta acts through distal regulatory elements to directly control cellular gene expression

Lytic replication of the human gamma herpes virus Epstein-Barr virus (EBV) is an essential prerequisite for the spread of the virus. Differential regulation of a limited number of cellular genes has been reported in B-cells during the viral lytic replication cycle. We asked whether a viral bZIP transcription factor, Zta (BZLF1, ZEBRA, EB1), drives some of these changes. Using genome-wide chromatin immunoprecipitation coupled to next-generation DNA sequencing (ChIP-seq) we established a map of Zta interactions across the human genome. Using sensitive transcriptome analyses we identified 2263 cellular genes whose expression is significantly changed during the EBV lytic replication cycle. Zta binds 278 of the regulated genes and the distribution of binding sites shows that Zta binds mostly to sites that are distal to transcription start sites. This differs from the prevailing view that Zta activates viral genes by binding exclusively at promoter elements. We show that a synthetic Zta binding element confers Zta regulation at a distance and that distal Zta binding sites from cellular genes can confer Zta-mediated regulation on a heterologous promoter. This leads us to propose that Zta directly reprograms the expression of cellular genes through distal elements.

Overexpression of Activation-Induced Cytidine Deaminase in MTX- and Age-Related Epstein-Barr Virus-Associated B-Cell Lymphoproliferative Disorders of the Head and Neck

Recent research has shown that activation-induced cytidine deaminase (AID) triggers somatic hypermutation and recombination, in turn contributing to lymphomagenesis. Such aberrant AID expression is seen in B-cell leukemia/lymphomas, including Burkitt lymphoma which is associated with c-myc translocation. Moreover, Epstein-Barr virus (EBV) latent membrane protein-1 (LMP-1) increases genomic instability through early growth transcription response-1 (Egr-1) mediated upregulation of AID in B-cell lymphoma. However, few clinicopathological studies have focused on AID expression in lymphoproliferative disorders (LPDs). Therefore, we conducted an immunohistochemical study to investigate the relationship between AID and LMP-1 expression in LPDs (MTX-/Age-related EBV-associated), including diffuse large B-cell lymphomas (DLBCLs). More intense AID expression was detected in LPDs (89.5%) than in DLBCLs (20.0%), and the expression of LMP-1 and EBER was more intense in LPDs (68.4% and 94.7%) than in DLBCLs (10.0% and 20.0%). Furthermore, stronger Egr-1 expression was found in MTX/Age-EBV-LPDs (83.3%) than in DLBCLs (30.0%). AID expression was significantly constitutively overexpressed in LPDs as compared with DLBCLs. These results suggest that increased AID expression in LPDs may be one of the processes involved in lymphomagenesis, thereby further increasing the survival of genetically destabilized B-cells. AID expression may be a useful indicator for differentiation between LPDs and DLBCLs.

Inhibition of mTORC1 inhibits lytic replication of Epstein-Barr virus in a cell-type specific manner

BACKGROUND

Epstein-Barr virus is a human herpesvirus that infects a majority of the human population. Primary infection of Epstein-Barr virus (EBV) causes the syndrome infectious mononucleosis. This virus is also associated with several cancers, including Burkitt's lymphoma, post-transplant lymphoproliferative disorder and nasopharyngeal carcinoma. As all herpesvirus family members, EBV initially replicates lytically to produce abundant virus particles, then enters a latent state to remain within the host indefinitely.

METHODS

Through a genetic screen in Drosophila, we determined that reduction of Drosophila Tor activity altered EBV immediate-early protein function. To further investigate this finding, we inhibited mTOR in EBV-positive cells and investigated subsequent changes to lytic replication via Western blotting, flow cytometry, and quantitative PCR. The student T-test was used to evaluate significance.

RESULTS

mTOR, the human homolog of Drosophila Tor, is an important protein at the center of a major signaling pathway that controls many aspects of cell biology. As the EBV immediate-early genes are responsible for EBV lytic replication, we examined the effect of inhibition of mTORC1 on EBV lytic replication in human EBV-positive cell lines. We determined that treatment of cells with rapamycin, which is an inhibitor of mTORC1 activity, led to a reduction in the ability of B cell lines to undergo lytic replication. In contrast, EBV-positive epithelial cell lines underwent higher levels of lytic replication when treated with rapamycin.

CONCLUSIONS

Overall, the responses of EBV-positive cell lines vary when treated with mTOR inhibitors, and this may be important when considering such inhibitors as anti-cancer therapeutic agents.

Regulation of the latent-lytic switch in Epstein-Barr virus

Epstein-Barr virus (EBV) infection contributes to the development of several different types of human malignancy, including Burkitt lymphoma, Hodgkin lymphoma, and nasopharyngeal carcinoma. As a herpesvirus, EBV can establish latent or lytic infection in cells. EBV-positive tumors are composed almost exclusively of cells with latent EBV infection. Strategies for inducing the lytic form of EBV infection in tumor cells are being investigated as a potential therapy for EBV-positive tumors. In this article, we review how cellular and viral proteins regulate the latent-lytic EBV switch in infected B cells and epithelial cells, and discuss how harnessing lytic viral reactivation might be used therapeutically.

Epstein-Barr virus infection induces aberrant TLR activation pathway and fibroblast-myofibroblast conversion in scleroderma

Scleroderma (SSc) is a complex and heterogeneous connective tissue disease mainly characterized by autoimmunity, vascular damage, and fibrosis that mostly involve the skin and lungs. Epstein–Barr virus (EBV) is a lymphotropic γ-herpesvirus that has co-evolved with human species, infecting >95% of the adult population worldwide, and has been a leading candidate in triggering several autoimmune diseases. Here we show that EBV establishes infection in the majority of fibroblasts and endothelial cells in the skin of SSc patients, characterized by the expression of the EBV noncoding small RNAs (EBERs) and the increased expression of immediate-early lytic and latency mRNAs and proteins. We report that EBV is able to persistently infect human SSc fibroblasts in vitro, inducing an aberrant innate immune response in infected cells. EBV–Toll-like receptor (TLR) aberrant activation induces the expression of selected IFN-regulatory factors (IRFs), IFN-stimulated genes (ISGs), transforming growth factor-β1 (TGFβ1), and several markers of fibroblast activation, such as smooth muscle actin and Endothelin-1, and all of these genes play a key role in determining the profibrotic phenotype in SSc fibroblasts. These findings imply that EBV infection occurring in mesenchymal, endothelial, and immune cells of SSc patients may underlie the main pathological features of SSc including autoimmunity, vasculopathy, and fibrosis, and provide a unified disease mechanism represented by EBV reactivation.

Magnetically-controllable zigzag structures as cell microgripper

We designed and fabricated a micro-scaled cell gripper based on two highly flexible magnetic zigzag structures that can be actuated by a magnetic field. Elongated single domain magnetic thin films with high magnetic shape anisotropy were deposited on the zigzag structures. By adjusting the external magnetic field we were able to control the torque applied on the magnetic films that was responsible for the actuation. We measured and discussed the displacement of the zigzag structures under different magnetic fields, and we observed a hysteresis characteristic in the actuation. Furthermore, we demonstrated the ability of gripping a single cell in water solution using the designed cell microgripper. The cell microgripper proposed in this study can provide important information for future biochip and biomedical applications.

Epstein-Barr virus Zta upregulates matrix metalloproteinases 3 and 9 that synergistically promote cell invasion in vitro

Zta is a lytic transactivator of Epstein-Barr virus (EBV) and has been shown to promote migration and invasion of epithelial cells. Although previous studies indicate that Zta induces expression of matrix metalloproteinase (MMP) 9 and MMP1, direct evidence linking the MMPs to Zta-induced cell migration and invasion is still lacking. Here we performed a series of in vitro studies to re-examine the expression profile and biologic functions of Zta-induced MMPs in epithelial cells derived from nasopharyngeal carcinoma. We found that, in addition to MMP9, MMP3 was a new target gene upregulated by Zta. Ectopic Zta expression in EBV-negative cells increased both mRNA and protein production of MMP3. Endogenous Zta also contributed to induction of MMP3 expression, migration and invasion of EBV-infected cells. Zta activated the MMP3 promoter through three AP-1 elements, and its DNA-binding domain was required for the promoter binding and MMP3 induction. We further tested the effects of MMP3 and MMP9 on cell motility and invasiveness in vitro. Zta-promoted cell migration required MMP3 but not MMP9. On the other hand, both MMP3 and MMP9 were essential for Zta-induced cell invasion, and co-expression of the two MMPs synergistically increased cell invasiveness. Therefore, this study provides integrated evidence demonstrating that, at least in the in vitro cell models, Zta drives cell migration and invasion through MMPs.

Disease progression mediated by egr-1 associated signaling in response to oxidative stress

When cellular reducing enzymes fail to shield the cell from increased amounts of reactive oxygen species (ROS), oxidative stress arises. The redox state is misbalanced, DNA and proteins are damaged and cellular transcription networks are activated. This condition can lead to the initiation and/or to the progression of atherosclerosis, tumors or pulmonary hypertension; diseases that are decisively furthered by the presence of oxidizing agents. Redox sensitive genes, like the zinc finger transcription factor early growth response 1 (Egr-1), play a pivotal role in the pathophysiology of these diseases. Apart from inducing apoptosis, signaling partners like the MEK/ERK pathway or the protein kinase C (PKC) can activate salvage programs such as cell proliferation that do not ameliorate, but rather worsen their outcome. Here, we review the currently available data on Egr-1 related signal transduction cascades in response to oxidative stress in the progression of epidemiologically significant diseases. Knowing the molecular pathways behind the pathology will greatly enhance our ability to identify possible targets for the development of new therapeutic strategies.

Suppression of transcription factor early growth response 1 reduces herpes simplex virus 1-induced corneal disease in mice

Herpes simplex virus 1 replication initiates angiogenesis and inflammation in the cornea. This can result in herpetic stromal keratitis (HSK), which is a leading cause of infection-induced corneal blindness. Host cellular factors mediate the progression of HSK, but little is known about these cellular factors and their mechanisms of action. We show here that the expression of the cellular transcription factor early growth response 1 (Egr-1) in HSV-1-infected mouse corneas was enhanced. Enhanced Egr-1 expression aggravated HSK by increasing viral replication and subsequent neovascularization with high levels of potent angiogenic factors, fibroblast growth factor 2, and vascular endothelial growth factor. Furthermore, Egr-1 deficiency due to a targeted disruption of the gene or knockdown of Egr-1 expression topically using a DNA-based enzyme significantly reduced HSK by decreasing both viral replication and the angiogenic response. The present study provides the first evidence that endogenous Egr-1 aggravates HSK and that blocking Egr-1 reduces corneal damage.

Epigenetic control of viral life-cycle by a DNA-methylation dependent transcription factor

Epstein-Barr virus (EBV) encoded transcription factor Zta (BZLF1, ZEBRA, EB1) is the prototype of a class of transcription factor (including C/EBPalpha) that interact with CpG-containing DNA response elements in a methylation-dependent manner. The EBV genome undergoes a biphasic methylation cycle; it is extensively methylated during viral latency but is reset to an unmethylated state following viral lytic replication. Zta is expressed transiently following infection and again during the switch between latency and lytic replication. The requirement for CpG-methylation at critical Zta response elements (ZREs) has been proposed to regulate EBV replication, specifically it could aid the activation of viral lytic gene expression from silenced promoters on the methylated genome during latency in addition to preventing full lytic reactivation from the non-methylated EBV genome immediately following infection. We developed a computational approach to predict the location of ZREs which we experimentally assessed using in vitro and in vivo DNA association assays. A remarkably different binding motif is apparent for the CpG and non-CpG ZREs. Computational prediction of the location of these binding motifs in EBV revealed that the majority of lytic cycle genes have at least one and many have multiple copies of methylation-dependent CpG ZREs within their promoters. This suggests that the abundance of Zta protein coupled with the methylation status of the EBV genome act together to co-ordinate the expression of lytic cycle genes at the majority of EBV promoters.

Lytic HSV-1 infection induces the multifunctional transcription factor Early Growth Response-1 (EGR-1) in rabbit corneal cells

BACKGROUND

Herpes simplex virus type-1 (HSV-1) infections can cause a number of diseases ranging from simple cold sores to dangerous keratitis and lethal encephalitis. The interaction between virus and host cells, critical for viral replication, is being extensively investigated by many laboratories. In this study, we tested the hypothesis that HSV-1 lytic infection triggers the expression of important multi-functional transcription factor Egr1. The mechanisms of induction are mediated, at least in part, by signaling pathways such as NFκB and CREB.

METHODS

SIRC, VERO, and 293HEK cell lines were infected with HSV-1, and the Egr-1 transcript and protein were detected by RT-PCR and Western blot, respectively. The localization and expression profile of Egr-1 were investigated further by immunofluorescence microscopy analyses. The recruitment of transcription factors to the Egr-1 promoter during infection was studied by chromatin immunoprecipitation (ChIP). Various inhibitors and dominant-negative mutant were used to assess the mechanisms of Egr-1 induction and their effects were addressed by immunofluorescence microscopy.

RESULTS

Western blot analyses showed that Egr-1 was absent in uninfected cells; however, the protein was detected 24-72 hours post treatment, and the response was directly proportional to the titer of the virus used for infection. Using recombinant HSV-1 expressing EGFP, Egr-1 was detected only in the infected cells. ChIP assays demonstrated that NFкB and cAMP response element binding protein (CREB) were recruited to the Egr-1 promoter upon infection. Additional studies showed that inhibitors of NFкB and dominant-negative CREB repressed the Egr-1 induction by HSV-1 infection.

CONCLUSION

Collectively, these results demonstrate that Egr-1 is expressed rapidly upon HSV-1 infection and that this novel induction could be due to the NFкB/CREB-mediated transactivation. Egr-1 induction might play a key role in the viral gene expression, replication, inflammation, and the disease progression.

Enterovirus-induced miR-141 contributes to shutoff of host protein translation by targeting the translation initiation factor eIF4E

Viruses rely on the host translation machinery to complete their life cycles. Picornaviruses use an internal ribosome entry site to initiate cap-independent protein translation and in parallel host cap-dependent translation is shut off. This process is thought to occur primarily via cleavage of host translation initiation factors eIF4GI and eIF4GII by viral proteases. Here we describe another mechanism whereby miR-141 induced upon enterovirus infection targets the cap-dependent translation initiation factor, eIF4E, for shutoff of host protein synthesis. Knockdown of miR-141 reduces viral propagation, and silencing of eIF4E can completely reverse the inhibitory effect of the miR-141 antagomiR on viral propagation. Ectopic expression of miR-141 promotes the switch from cap-dependent to cap-independent translation. Moreover, we identified a transcription factor, EGR1, which is partly responsible for miR-141 induction in response to enterovirus infection. Our results suggest that upregulation of miR-141 upon enterovirus infection can facilitate viral propagation by expediting the translational switch.

Virus reactivation: a panoramic view in human infections

Viruses are obligate intracellular parasites, relying to a major extent on the host cell for replication. An active replication of the viral genome results in a lytic infection characterized by the release of new progeny virus particles, often upon the lysis of the host cell. Another mode of virus infection is the latent phase, where the virus is 'quiescent' (a state in which the virus is not replicating). A combination of these stages, where virus replication involves stages of both silent and productive infection without rapidly killing or even producing excessive damage to the host cells, falls under the umbrella of a persistent infection. Reactivation is the process by which a latent virus switches to a lytic phase of replication. Reactivation may be provoked by a combination of external and/or internal cellular stimuli. Understanding this mechanism is essential in developing future therapeutic agents against viral infection and subsequent disease. This article examines the published literature and current knowledge regarding the viral and cellular proteins that may play a role in viral reactivation. The focus of the article is on those viruses known to cause latent infections, which include herpes simplex virus, varicella zoster virus, Epstein-Barr virus, human cytomegalovirus, human herpesvirus 6, human herpesvirus 7, Kaposi's sarcoma-associated herpesvirus, JC virus, BK virus, parvovirus and adenovirus.

Epigenetic mechanisms in virus-induced tumorigenesis

About 15–20% of human cancers worldwide have viral etiology. Emerging data clearly indicate that several human DNA and RNA viruses, such as human papillomavirus, Epstein–Barr virus, Kaposi’s sarcoma-associated herpesvirus, hepatitis B virus, hepatitis C virus, and human T-cell lymphotropic virus, contribute to cancer development. Human tumor-associated viruses have evolved multiple molecular mechanisms to disrupt specific cellular pathways to facilitate aberrant replication. Although oncogenic viruses belong to different families, their strategies in human cancer development show many similarities and involve viral-encoded oncoproteins targeting the key cellular proteins that regulate cell growth. Recent studies show that virus and host interactions also occur at the epigenetic level. In this review, we summarize the published information related to the interactions between viral proteins and epigenetic machinery which lead to alterations in the epigenetic landscape of the cell contributing to carcinogenesis.

Getting the message direct manipulation of host mRNA accumulation during gammaherpesvirus lytic infection

The Gammaherpesvirinae subfamily of herpesviruses comprises lymphotropic viruses, including the oncogenic human pathogens Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus. During lytic infection, gammaherpesviruses manipulate host gene expression to optimize the cellular environment for viral replication and to evade the immune response. Additionally, although a lytically infected cell will itself be killed in the process of viral replication, lytic infection can contribute to pathogenesis by inducing the secretion of paracrine factors with functions in cell survival and proliferation, and angiogenesis. The mechanisms by which these viruses manipulate host gene expression are varied and target the accumulation of cellular mRNAs and their translation, signaling pathways, and protein stability. Here, we discuss how gammaherpesviral proteins directly influence host mRNA biogenesis and stability, either selectively or globally, in order to fine-tune the cellular environment to the advantage of the virus. Appreciation of the mechanisms by which these viruses interface with and adapt normal cellular processes continues to inform our understanding of gammaherpesviral biology and the regulation of mRNA accumulation and turnover in our own cells.

Suppression of osteosarcoma cell invasion by chemotherapy is mediated by urokinase plasminogen activator activity via up-regulation of EGR1

BACKGROUND

The cellular and molecular mechanisms of tumour response following chemotherapy are largely unknown. We found that low dose anti-tumour agents up-regulate early growth response 1 (EGR1) expression. EGR1 is a member of the immediate-early gene group of transcription factors which modulate transcription of multiple genes involved in cell proliferation, differentiation, and development. It has been reported that EGR1 act as either tumour promoting factor or suppressor. We therefore examined the expression and function of EGR1 in osteosarcoma.

METHODS

We investigated the expression of EGR1 in human osteosarcoma cell lines and biopsy specimens. We next examined the expression of EGR1 following anti-tumour agents treatment. To examine the function of EGR1 in osteosarcoma, we assessed the tumour growth and invasion in vitro and in vivo.

RESULTS

Real-time PCR revealed that EGR1 was down-regulated both in osteosarcoma cell lines and osteosarcoma patients' biopsy specimens. In addition, EGR1 was up-regulated both in osteosarcoma patient' specimens and osteosarcoma cell lines following anti-tumour agent treatment. Although forced expression of EGR1 did not prevent osteosarcoma growth, forced expression of EGR1 prevented osteosarcoma cell invasion in vitro. In addition, forced expression of EGR1 promoted down-regulation of urokinase plasminogen activator, urokinase receptor, and urokinase plasminogen activity. Xenograft mice models showed that forced expression of EGR1 prevents osteosarcoma cell migration into blood vessels.

CONCLUSIONS

These findings suggest that although chemotherapy could not prevent osteosarcoma growth in chemotherapy-resistant patients, it did prevent osteosarcoma cell invasion by down-regulation of urokinase plasminogen activity via up-regulation of EGR1 during chemotherapy periods.

Analysis of global methylation using a Zta-expressing nasopharyngeal carcinoma cell line

EBV infects more than 90% of the human population and persists in most individuals as a latent infection where the viral genome is silenced by host-driven methylation. The lytic cycle is initiated when the viral protein Zta binds to methylated BRLF1 and BRRF1 promoters. Although studies reveal the role of Zta and methylation changes in the viral genome upon EBV infection to reactivation, whether Zta plays any role in alteration of methylation in the host genome remains unknown. Using an inducible model, we demonstrate that global DNA methylation, based on whole-genome 5-methylcytosine content, and regional DNA methylation in repetitive elements, imprinting genes and the X chromosome, remains unchanged in response to Zta expression. Expression of DNA methyltransferases was also unaffected by ectopically expressed Zta. Our data imply that alteration of host gene expression following EBV reactivation may reflect methylation-independent Zta-mediated gene activation and not epigenetic modification of the host genome.

Interplay between PKCδ and Sp1 on histone deacetylase inhibitor-mediated Epstein-Barr virus reactivation

Epstein-Barr virus (EBV) undergoes latent and lytic replication cycles, and its reactivation from latency to lytic replication is initiated by expression of the two viral immediate-early transactivators, Zta and Rta. In vitro, reactivation of EBV can be induced by anti-immunoglobulin, tetradecanoyl phorbol acetate, and histone deacetylase inhibitor (HDACi). We have discovered that protein kinase C delta (PKCδ) is required specifically for EBV reactivation by HDACi. Overexpression of PKCδ is sufficient to induce the activity of the Zta promoter (Zp) but not of the Rta promoter (Rp). Deletion analysis revealed that the ZID element of Zp is important for PKCδ activation. Moreover, the Sp1 putative sequence on ZID is essential for PKCδ-induced Zp activity, and the physiological binding of Sp1 on ZID has been confirmed. After HDACi treatment, activated PKCδ can phosphorylate Sp1 at serine residues and might result in dissociation of the HDAC2 repressor from ZID. HDACi-mediated HDAC2-Sp1 dissociation can be inhibited by the PKCδ inhibitor, Rotterlin. Furthermore, overexpression of HDAC2 can suppress the HDACi-induced Zp activity. Consequently, we hypothesize that HDACi induces PKCδ activation, causing phosphorylation of Sp1, and that the interplay between PKCδ and Sp1 results in the release of HDAC2 repressor from Zp and initiation of Zta expression.

Cell membrane-bound Kaposi's sarcoma-associated herpesvirus-encoded glycoprotein B promotes virus latency by regulating expression of cellular Egr-1

One of the important questions in the field of virus research is about the balance between latent and lytic cycles of replication. Kaposi's sarcoma-associated herpesvirus (KSHV) remains predominantly in a latent state, with only 1-3% of cells supporting a lytic replication at any time. KSHV glycoprotein B (gB) is expressed not only on the virus envelope but also on the surfaces of the few cells supporting lytic replication. Using co-culture experiments, we determined that expression of KSHV gB on as few as 1-2% of human dermal microvascular endothelial cells resulted in a 10-fold inhibition of expression of ORF50, a viral gene critical for the onset of lytic replication. Also, we demonstrate that such a profound inhibitory effect of gB on the lytic cycle of virus replication is by repressing the ability of Egr-1 (early growth response-1) to bind and activate the ORF50 promoter. In general, virus-encoded late stage structural proteins, such as gB, are said to play major roles in virus entry and egress. The present report provides initial evidence supporting a role for membrane-associated gB expressed in a minimal number of cells to promote virus latency. These findings may have ramifications leading to a better understanding of the role of virus-encoded structural proteins not only in KSHV-related diseases but also in other viruses causing latent infections.

Cellular immediate-early gene expression occurs kinetically upstream of Epstein-Barr virus bzlf1 and brlf1 following cross-linking of the B cell antigen receptor in the Akata Burkitt lymphoma cell line

The Epstein-Barr virus (EBV) lytic activator genes bzlf1 and brlf1 are conventionally referred to as immediate-early (IE) genes. However, previous studies showed that the earliest expression of these genes was blocked by cycloheximide when the EBV lytic cycle was induced by histone deacetylase (HDAC) inhibitors and protein kinase C agonists. Anti-IgG activates a complex signal transduction pathway that leads to EBV lytic activation in the Akata cell line. Here we demonstrate that in Akata cells, where lytic cycle activation occurs very rapidly after anti-IgG treatment, de novo protein synthesis is also required for induction of bzlf1 and brlf1 expression. New protein synthesis is required up to 1.25 h after application of anti-IgG; bzlf1 and brlf1 mRNAs can be detected 1.5 h after anti-IgG. Five cellular IE genes were shown to be expressed by 1 h after addition of anti-IgG, and their expression preceded that of bzlf1 and brlf1. These include early growth response genes (egr1, egr2, and egr3) and nuclear orphan receptors (nr4a1 and nr4a3). These genes were activated by anti-IgG treatment of Akata cells with and without the EBV genome; therefore, their expression was not dependent on expression of any EBV gene product. EGR1, EGR2, and EGR3 proteins were kinetically upstream of ZEBRA and Rta proteins. Expression of EGR1, ZEBRA, and Rta proteins were inhibited by bisindolylmaleimide X, a selective inhibitor of PKC. The findings suggest a revised model in which the signal transduction cascade activated by cross-linking of the B cell receptor induces expression of cellular IE genes, such as early growth response and nuclear orphan receptor genes, whose products, in turn, regulate bzlf1 and brlf1 expression.

Evaluation of a prediction protocol to identify potential targets of epigenetic reprogramming by the cancer associated Epstein Barr virus

Background

Epstein Barr virus (EBV) infects the majority of the human population, causing fatal diseases in a small proportion in conjunction with environmental factors. Following primary infection, EBV remains latent in the memory B cell population for life. Recurrent reactivation of the virus occurs, probably due to activation of the memory B-lymphocytes, resulting in viral replication and re-infection of B-lymphocytes. Methylation of the viral DNA at CpG motifs leads to silencing of viral gene expression during latency. Zta, the key viral protein that mediates the latency/reactivation balance, interacts with methylated DNA. Zta is a transcription factor for both viral and host genes. A sub-set of its DNA binding sites (ZREs) contains a CpG motif, which is recognised in its methylated form. Detailed analysis of the promoter of the viral gene BRLF1 revealed that interaction with a methylated CpG ZRE (RpZRE3) is key to overturning the epigenetic silencing of the gene.

Methodology and Principal Findings

Here we question whether we can use this information to identify which host genes contain promoters with similar response elements. A computational search of human gene promoters identified 274 targets containing the 7-nucleotide RpZRE3 core element. DNA binding analysis of Zta with 17 of these targets revealed that the flanking context of the core element does not have a profound effect on the ability of Zta to interact with the methylated sites. A second juxtaposed ZRE was observed for one promoter. Zta was able to interact with this site, although co-occupancy with the RpZRE3 core element was not observed.

Conclusions/Significance

This research demonstrates 274 human promoters have the potential to be regulated by Zta to overturn epigenetic silencing of gene expression during viral reactivation from latency.

Cellular factors associated with latency and spontaneous Epstein-Barr virus reactivation in B-lymphoblastoid cell lines

EBV-immortalized B-lymphoblastoid cell lines are used as models for cellular transformation and as antigen-presenting cells in immunological assays. LCLs vary in surface markers and other phenotypic properties, but it is not known how this heterogeneity relates to the EBV life cycle. To explore correlations, we examined 62 LCLs for cellular and viral phenotypes. LCLs generated from pediatric and adult donors could similarly be categorized as either low in EBV copy number or fluctuating within a high range. High-copy status accompanied higher lytic viral gene expression and lower latent gene expression. Inhibiting lytic EBV replication did not affect cellular phenotype or lytic switch protein expression, indicating that an LCL's lytic permissivity was a stable property. Among the cellular genes overexpressed in permissive LCLs were unfolded protein response genes and plasma cell markers. Among genes overexpressed in non-permissive LCLs were transcription factors involved in maintaining B cell lineage, in particular EBF1. This study suggests previously undetected mechanisms by which cellular pathways influence the lytic reactivation of EBV.

Viral epigenomes in human tumorigenesis

Viruses are associated with 15-20% of human cancers worldwide. In the last century, many studies were directed towards elucidating the molecular mechanisms and genetic alterations by which viruses cause cancer. The importance of epigenetics in the regulation of gene expression has prompted the investigation of virus and host interactions not only at the genetic level but also at the epigenetic level. In this study, we summarize the published epigenetic information relating to the genomes of viruses directly or indirectly associated with the establishment of tumorigenic processes. We also review aspects such as viral replication and latency associated with epigenetic changes and summarize what is known about epigenetic alterations in host genomes and the implications of these for the tumoral process. The advances made in characterizing epigenetic features in cancer-causing viruses have improved our understanding of their functional mechanisms. Knowledge of the epigenetic changes that occur in the genome of these viruses should provide us with markers for following cancer progression, as well as new tools for cancer therapy.

Initiation of lytic DNA replication in Epstein-Barr virus: search for a common family mechanism

Herpesviruses are a complex family of dsDNA viruses that are a major cause of human disease. All family members share highly related viral replication proteins, such as DNA polymerase, ssDNA-binding proteins and processivity factors. Consequently, it is generally thought that lytic replication occurs through a common and conserved mechanism. However, considerable evidence indicates that proteins controlling initiation of DNA replication vary greatly among the herepesvirus subfamilies. In this article, we focus on some of the known mechanisms that regulate Epstein-Barr virus lytic-cycle replication, and compare this to other herpesvirus family members. Our reading of the literature leads us to conclude that diverse viral mechanisms generate a common nucleoprotein prereplication structure that can be recognized by a highly conserved family of viral replication enzymes.

Quantitative evaluation of the role of Epstein-Barr virus immediate-early protein BZLF1 in B-cell transformation

The Epstein-Barr virus (EBV) immediate-early transactivator BZLF1 plays a key role in switching EBV infection from the latent to the lytic form by stimulating the expression cascade of lytic genes; it also regulates the expression of several cellular genes. Recently, we reported that BZLF1 is expressed in primary human B cells early after EBV infection. To investigate whether this BZLF1 expression early after infection plays a role in the EBV-induced growth transformation of primary B cells, we generated BZLF1-knockout EBV and quantitatively evaluated its transforming ability compared with that of wild-type EBV. We found that the 50% transforming dose of BZLF1-knockout EBV was quite similar to that of wild-type EBV. Established lymphoblastoid cell lines (LCLs) harbouring BZLF1-knockout EBV were indistinguishable from LCLs harbouring wild-type EBV in their pattern of latent gene expression and in their growth in vitro. Furthermore, the copy numbers of EBV episomes were very similar in the LCLs harbouring BZLF1-knockout EBV and in those harbouring wild-type EBV. These data indicate that disrupting BZLF1 expression in the context of the EBV genome, and the resultant inability to enter lytic replication, have little impact on the growth of LCLs and the steady-state copy number of EBV episomes in established LCLs.

Endoplasmic reticulum stress triggers XBP-1-mediated up-regulation of an EBV oncoprotein in nasopharyngeal carcinoma

Endoplasmic reticulum (ER) stress-activated unfolded protein response (UPR) plays multiple roles in cancer development, but its specific roles for virus-associated cancers have not been fully understood. It is still unknown whether ER stress/UPR occurs in and contributes to nasopharyngeal carcinoma (NPC), an epithelial malignancy closely associated with EBV. Here, we report that UPR proteins are frequently detected in NPC biopsies. In addition, we reveal that, in EBV-infected NPC cells, ER stress inducers up-regulate a potent EBV oncoprotein latent membrane protein 1 (LMP1), and the ER stress-induced LMP1 enhances production of interleukin-8. ER stress triggers LMP1 expression at a transcriptional level, activating a distal LMP1 promoter TR-L1. TR-L1 contains an ER stress-responsive element, which is targeted by an UPR protein XBP-1. Ectopic expression of XBP-1 induces LMP1 expression, and knockdown of XBP-1 blocks ER stress-triggered up-regulation of LMP1 in NPC cells. Furthermore, XBP-1 significantly correlates with LMP1 expression in NPC tumor biopsies. Therefore, this study not only provides a novel clue linking ER stress/UPR to EBV-associated NPC but also suggests that ER stress/UPR can promote virus-associated cancer in a unique way by driving expression of a viral oncogene.

EBV Zta protein induces the expression of interleukin-13, promoting the proliferation of EBV-infected B cells and lymphoblastoid cell lines

Epstein-Barr virus (EBV) infection can modify the cytokine expression profiles of host cells and determine the fate of those cells. Of note, expression of interleukin-13 (IL-13) may be detected in EBV-associated Hodgkin lymphoma and the natural killer (NK) cells of chronic active EBV-infected patients, but its biologic role and regulatory mechanisms are not understood. Using cytokine antibody arrays, we found that IL-13 production is induced in B cells early during EBV infection. Furthermore, the EBV lytic protein, Zta (also known as the BZLF-1 product), which is a transcriptional activator, was found to induce IL-13 expression following transfection. Mechanistically, induction of IL-13 expression by Zta is mediated directly through its binding to the IL-13 promoter, via a consensus AP-1 binding site. Blockade of IL-13 by antibody neutralization showed that IL-13 is required at an early stage of EBV-induced proliferation and for long-term maintenance of the growth of EBV immortalized lymphoblastoid cell lines (LCLs). Thus, Zta-induced IL-13 production facilitates B-cell proliferation and may contribute to the pathogenesis of EBV-associated lymphoproliferative disorders, such as posttransplantation lymphoproliferative disease (PTLD) and Hodgkin lymphoma.

The Epstein-Barr virus lytic cycle activator Zta interacts with methylated ZRE in the promoter of host target gene egr1

Activation of the host gene egr1 is essential for the lytic replication of Epstein–Barr virus (EBV). egr1 is activated by Zta (BZLF1, ZEBRA). Zta interacts directly with DNA through a series of closely related Zta-response elements (ZREs). Here we dissect the mechanism used by Zta to interact with the egr1 promoter and identify a weak interaction with egr1ZRE that is dependent on the distal part of egr1ZRE. Furthermore, we demonstrate that the ability of Zta to interact with egr1ZRE is enhanced at least tenfold by methylation. The ability of Zta to transactivate a reporter construct driven by the egr1 promoter can be enhanced by methylation. As the ability of Zta to interact with a methylated ZRE in the EBV genome correlates with its ability to activate the expression of the endogenous viral gene BRLF1, this suggests that Zta may also have the capability to overturn epigenetic control of egr1.