Evaluating the Clinical Utility of Epstein-Barr Virus Antibodies as Biomarkers in Multiple Sclerosis: A Systematic Review

BACKGROUND

EBV is a necessary but not sufficient factor in the pathophysiology of multiple sclerosis (MS). EBV antibodies to the nuclear antigen (EBNA1) and viral capsid antigen (VCA) rise rapidly prior to MS disease manifestations, and their absence has clinical utility with a high negative predictive value. It remains unclear whether EBV levels act as prognostic, monitoring, or pharmacodynamic/response biomarkers. Substantial literature on this topic exists but has not been systematically reviewed. We hypothesized that EBV levels against EBNA1 and VCA are potential prognostic and monitoring biomarkers in MS, and that patient population, MS clinical phenotype, and EBV assay method may play important roles in explaining variation among study outcomes.

METHODS

We systematically searched PubMed and EMBASE from inception to April 1, 2022. After removal of duplicates, records were screened by abstract. Remaining full-text articles were reviewed. Clinical and MRI data were extracted from full-text articles for comparison and synthesis.

RESULTS

Searches yielded 696 unique results; 285 were reviewed in full, and 36 met criteria for data extraction. Heterogeneity in sample population, clinical outcome measures, assay methods and statistical analyses precluded a meta-analysis. EBV levels were not consistently associated with clinical disease markers including conversion from CIS to RRMS, neurological disability, or disease phenotype. Studies using repeated-measures design suggest that EBNA1 levels may temporarily reflect inflammatory disease activity as assessed by gadolinium-enhancing Magnetic Resonance Imaging (MRI) lesions. Limited data also suggest a decrease in EBV levels following initiation of certain disease-modifying therapies.

CONCLUSION

Heterogeneous methodology limited generalization and meta-analysis. EBV antibody levels are unlikely to represent prognostic biomarkers in MS. The areas of highest ongoing promise relate to diagnostic exclusion and pharmacodynamic/disease response. Use of EBV antibodies as biomarkers in clinical practice remains additionally limited by lack of methodological precision, reliability, and validation.

The Level of Anti-Viral Antigen-Specific Antibodies to EBNA-1 in the Serum of MS Patients Does not Depend on the Severity of the Disease

Multiple sclerosis (MS) is an autoimmune neurodegenerative disease leading to inevitable disability and primarily affecting the young and middle-aged population. Recent studies have shown a direct correlation between the risk of MS development and Epstein-Barr virus (EBV) infection. Analysis of the titer of EBV-specific antibodies among patients with MS and healthy donors among Russian population confirmed that MS is characterized by an increased level of serum IgG binding EBNA-1 (EBV nuclear antigen 1). The number of patients with elevated levels of EBNA-1-specific antibodies does not differ statistically significantly between two groups with diametrically opposite courses of MS: benign MS or highly active MS. It can be assumed that the primary link between EBV and the development of MS is restricted to the initiation of the disease and does not impact its severity.

Epstein-Barr virus induces germinal center light zone chromatin architecture and promotes survival through enhancer looping at the BCL2A1 locus

IMPORTANCE

Epstein-Barr virus has evolved with its human host leading to an intimate relationship where infection of antibody-producing B cells mimics the process by which these cells normally recognize foreign antigens and become activated. Virtually everyone in the world is infected by adulthood and controls this virus pushing it into life-long latency. However, immune-suppressed individuals are at high risk for EBV+ cancers. Here, we isolated B cells from tonsils and compare the underlying molecular genetic differences between these cells and those infected with EBV. We find similar regulatory mechanism for expression of an important cellular protein that enables B cells to survive in lymphoid tissue. These findings link an underlying relationship at the molecular level between EBV-infected B cells in vitro with normally activated B cells in vivo. Our studies also characterize the role of a key viral control mechanism for B cell survival involved in long-term infection.

Humoral response to Epstein-Barr virus in patients with multiple sclerosis treated with B cell depletion therapy

BACKGROUND

B cell depletion therapy is highly effective in relapsing-remitting multiple sclerosis (RRMS). However, the precise underlying mechanisms of action for its biological effects in MS have still not been clarified. Epstein-Barr virus (EBV) is a known risk factor for MS and seems to be a prerequisite for disease development. EBV resides latently in the memory B cells, and may not only increase the risk of developing MS, but also contribute to disease activity and disability progression. Therefore, the effects of B cell depletion in MS could be associated with the depletion of EBV-infected cells and the altered immune response to the virus. In this study, we investigate the impact of B cell depletion on the humoral immune response specific to EBV in patients with MS.

METHODS

Newly diagnosed, treatment-naïve patients with RRMS were followed up to 18 months after initiation of B-cell depletion therapy in the Overlord-MS study, a phase III trial (NCT04578639). We analyzed serum sampled before treatment and after 3, 6, 12 and 18 months for immunoglobulin γ (IgG) against Epstein-Barr nuclear antigen 1 (EBNA1) and Epstein-Barr viral capsid antigen (VCA). We analyzed antibodies to cytomegalovirus (CMV) and total IgG in serum, as controls for viral and overall humoral immunity. The risk allele, HLA-DRB1*15:01, and the protective allele, HLA-A*02:01, were determined in all participants. In addition, polymerase chain reaction (PCR) for circulating EBV-DNA was performed in the first 156 samples drawn. The associations between time on B cell-depletion therapy and serum anti-EBV antibody levels were estimated using linear mixed-effects models.

RESULTS

A total of 290 serum samples from 99 patients were available for analysis. After 6, 12 and 18 months, the EBNA1 IgG levels decreased by 12.7 % (95 % CI -18.8 to -6.60, p < 0.001), 12.1 % (95 % CI -19.8 to -3.7, p = 0.006) and 14.6 % (95 % CI to -25.3 to -2.4, p = 0.02) respectively, compared to baseline level. Carriers of the HLA-DRB1*15:01 allele had higher EBNA1 IgG levels at baseline (p = 0.02). The VCA IgG levels significantly increased by 13.7 % (95 % CI 9.4 to 18.1, p < 0.001) after 3 months, compared to baseline, and persisted at this level throughout the follow-up. CMV IgG levels decreased, but to a lesser extent than the decrease of EBNA1 IgG, and total IgG levels decreased during therapy. Circulating EBV-DNA was found in only three of 156 samples from 64 patients.

CONCLUSIONS

EBNA1 IgG levels decreased, while VCA IgG levels increased, during B cell depletion therapy. This supports the hypothesis that the mechanism of action for B cell depletion therapy might be mediated by effects on EBV infection, which, in turn, mitigate immune cross-reactivity and disease perpetuation.

EBNA1 Inhibitors Block Proliferation of Spontaneous Lymphoblastoid Cell Lines From Patients With Multiple Sclerosis and Healthy Controls

BACKGROUND AND OBJECTIVES

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus that establishes lifelong latency in memory B cells and has been identified as a major risk factor of multiple sclerosis (MS). B cell depletion therapies have disease-modifying benefit in MS. However, it is unclear whether this benefit is partly attributable to the elimination of EBV+ B cells. Currently, there are no EBV-specific antiviral therapies available for targeting EBV latent infection in MS and limited experimental models to study EBV in MS.

METHODS

In this study, we describe the establishment of spontaneous lymphoblastoid cell lines (SLCLs) generated ex vivo with the endogenous EBV of patients with MS and controls and treated with either an Epstein-Barr virus nuclear antigen 1 (EBNA1) inhibitor (VK-1727) or cladribine, a nucleoside analog that eliminates B cells.

RESULTS

We showed that a small molecule inhibitor of EBNA1, a critical regulator of the EBV life cycle, blocks the proliferation and metabolic activity of these SLCLs. In contrast to cladribine, a highly cytotoxic B cell depleting therapy currently used in MS, the EBNA1 inhibitor VK-1727 was cytostatic rather than cytotoxic and selective for EBV+ cells, while having no discernible effects on EBV- cells. We validate that VK-1727 reduces EBNA1 DNA binding at known viral and cellular sites by ChIP-qPCR.

DISCUSSION

This study shows that patient-derived SLCLs provide a useful tool for interrogating the role of EBV+ B cells in MS and suggests that a clinical trial testing the effect of EBNA1 inhibitors in MS may be warranted.

Effect of Epstein-Barr Virus Infection on Selected Immunological Parameters in Children with Type 1 Diabetes

Diabetes mellitus is a group of metabolic disorders with different etiologies, pathogeneses and clinical pictures, characterized by chronic hyperglycemia due to abnormal insulin secretion or action. Type 1 diabetes mellitus is the most common type of diabetes mellitus in children and adolescents, accounting for about 90% of diabetes in the population under the age of 18. The etiopathogenesis of type 1 diabetes is multifactorial. The disease occurs as a result of the interaction of three factors: genetic predisposition, environmental factors and the immune response. Research in recent years has focused on the involvement of Epstein-Barr virus (EBV) in the pathogenesis of type I diabetes. The goals of treating type 1 diabetes include maintaining blood-glucose, fructosamine and glycated hemoglobin (HbA1c) levels; therefore, the main purpose of this study was to evaluate the effect of EBV infection on the activation of selected immune cells, fructosamine levels and HbA1c levels in children with type I diabetes. Based on our study, we found a lower percentage of CD8+ T lymphocytes with expression of the CD69 molecule in patients with anti-VCA antibodies in the IgG class, and a lower percentage of CD8+ T lymphocytes with expression of the CD25+ molecule in patients with anti-EBNA-1 antibodies in the IgG class, which may indicate limited control of the immune system during EBV infection in patients. There was a lower percentage of CD3+CD4+ T lymphocytes secreting IL-4 in the study group, indicating that a deficiency in IL-4 production may be related to the development of type 1 diabetes. There was an increase in the percentage of CD4+CD3+IL-10 lymphocytes in the study group with anti-VCA antibodies present in the IgG class and anti-EBNA-1 antibodies in the IgG class compared to the patients without antibodies. In addition, there was a significant increase in fructosamine levels and higher glycated hemoglobin levels in the study group with antibodies to EBV antigens. In addition, an increase in the percentage of T lymphocytes with a CD4+CD3+IL-17+ phenotype in the patients with anti-VCA IgG antibodies was confirmed, and higher HbA1c levels may suggest that EBV infection is accompanied by an increase in IL-17 secretion.

Combined assessment of Epstein-Barr virus viral capsid antigen and Epstein-Barr virus nuclear antigen-1 serology for post-transplant lymphoproliferative disorder risk stratification in adult solid organ transplant recipients

BACKGROUND

Epstein-Barr virus (EBV) seronegative solid organ transplant recipients (SOTRs) are at increased risk for post-transplant lymphoproliferative disorder (PTLD). Assays for EBV serostatus assess antibody to both EBV viral capsid antigen (VCA) and Epstein-Barr nuclear antigen-1 (EBNA-1), but PTLD risk among SOT recipients with discordant VCA and EBNA-1 results is unknown.

METHODS

We performed a retrospective, single-center cohort study to determine the risk of PTLD among adult (≥ 18 years) SOTRs with discordant pre-transplant VCA and EBNA-1 IgG compared to that of SOTRs with concordantly negative or concordantly positive serology using univariable and multivariable Cox-proportional hazards models.

RESULTS

Of 4106 SOTRs, the number (%) who were concordantly positive, concordantly negative, and discordant was 3787 (92.2%), 149 (3.6%), and 170 (4.2%), respectively. The adjusted hazard of PTLD was significantly higher among discordant SOTRs compared to concordantly positive SOTRs (aHR 2.6, 95% CI 1.04-6.6, p =.04) and lower compared to concordantly negative SOTRs (aHR 0.27, 95% CI 0.10-0.76, p <.001). The adjusted hazard of EBV+ PTLD among those with discordant serology was also significantly higher compared to the concordantly positive cohort (aHR 3.53, 95% CI 1.04-12.0, p =.04) and significantly lower compared to the concordantly negative cohort (aHR 0.23, 95% CI 0.06-0.82, p =.02).

CONCLUSIONS

Risk of PTLD among SOTRs with discordant VCA and EBNA-1 may be intermediate between those with concordantly positive and negative serology. If confirmed in future studies, revision of national EBV serology reporting to include both VCA and EBNA results may be needed to optimize PTLD risk stratification.

Evolution of functional antibodies following acute Epstein-Barr virus infection

While Epstein-Barr virus causes mostly asymptomatic infection, associated malignancies, and autoimmune and lymphoproliferative diseases occur. To dissect the evolution of humoral immune responses over the course of EBV infection and to gain a better understanding of the potential contribution of antibody (Ab) function to viral control, we comprehensively profiled Ab specificities and Fc-functionalities using systems serology and VirScan. Ab functions against latent (EBNA1), early (p47/54) and two late (gp350/220 and VCA-p18) EBV proteins were overall modest and/or short-lived, differing from humoral responses induced during acute infection by other viruses such as HIV. In the first year post infection, only p18 elicited robust IgM-driven complement deposition and IgG-driven neutrophil phagocytosis while responses against EBNA-1 were largely Fc-functionally silent and only matured during chronic infection to drive phagocytosis. In contrast, Abs against Influenza virus readily mediated broad Fc-activity in all participants. These data suggest that EBV evades the induction of robust Fc-functional Abs, potentially due to the virus’ life cycle, switching from lytic to latent stages during infection.

While previously thought to be largely innocuous, emerging data clearly highlight the pathological role of lifelong EBV infection in driving autoimmunity and malignancies in a small, but not insignificant portion of the population. We therefore aimed to define potential humoral mechanisms associated with viral control, beyond neutralizing Abs, by systematically focusing on antibody Fc-functional activities during acute to convalescent EBV infection applying technologies such as systems serology and VirScan. We found that functions against EBV proteins were overall only modest and either short-lived or delayed, differing from functional antibody responses induced during acute infection by other viruses such as HIV. These data suggest that EBV evades the induction of robust Fc-functional Abs thereby potentially facilitating lifelong, persistent infection with all its consequences.

Virus-Mediated Inhibition of Apoptosis in the Context of EBV-Associated Diseases: Molecular Mechanisms and Therapeutic Perspectives

Epstein-Barr virus (EBV), the representative of the Herpesviridae family, is a pathogen extensively distributed in the human population. One of its most characteristic features is the capability to establish latent infection in the host. The infected cells serve as a sanctuary for the dormant virus, and therefore their desensitization to apoptotic stimuli is part of the viral strategy for long-term survival. For this reason, EBV encodes a set of anti-apoptotic products. They may increase the viability of infected cells and enhance their resistance to chemotherapy, thereby contributing to the development of EBV-associated diseases, including Burkitt’s lymphoma (BL), Hodgkin’s lymphoma (HL), gastric cancer (GC), nasopharyngeal carcinoma (NPC) and several other malignancies. In this paper, we have described the molecular mechanism of anti-apoptotic actions of a set of EBV proteins. Moreover, we have reviewed the pro-survival role of non-coding viral transcripts: EBV-encoded small RNAs (EBERs) and microRNAs (miRNAs), in EBV-carrying malignant cells. The influence of EBV on the expression, activity and/or intracellular distribution of B-cell lymphoma 2 (Bcl-2) protein family members, has been presented. Finally, we have also discussed therapeutic perspectives of targeting viral anti-apoptotic products or their molecular partners.

DNA methylation enzymes and PRC1 restrict B-cell Epstein-Barr virus oncoprotein expression

To accomplish the remarkable task of lifelong infection, the Epstein-Barr virus (EBV) switches between four viral genome latency and lytic programmes to navigate the B-cell compartment and evade immune responses. The transforming programme, consisting of highly immunogenic EBV nuclear antigen (EBNA) and latent membrane proteins (LMPs), is expressed in newly infected B lymphocytes and in post-transplant lymphomas. On memory cell differentiation and in most EBV-associated Burkitt's lymphomas, all but one viral antigen are repressed for immunoevasion. To gain insights into the epigenetic mechanisms that restrict immunogenic oncoprotein expression, a genome-scale CRISPR-Cas9 screen was performed in EBV and Burkitt's lymphoma cells. Here, we show that the ubiquitin ligase ubiquitin-like PHD and RING finger domain-containing protein 1 (UHRF1) and its DNA methyltransferase partner DNA methyltransferase I (DNMT1) are critical for the restriction of EBNA and LMP expression. All UHRF1 reader and writer domains were necessary for silencing and DNMT3B was identified as an upstream viral genome CpG methylation initiator. Polycomb repressive complex I exerted a further layer of control over LMP expression, suggesting a second mechanism for latency programme switching. UHRF1, DNMT1 and DNMT3B are upregulated in germinal centre B cells, the Burkitt's lymphoma cell of origin, providing a molecular link between B-cell state and the EBV latency programme. These results suggest rational therapeutic targets to manipulate EBV oncoprotein expression.

B cells infected with Type 2 Epstein-Barr virus (EBV) have increased NFATc1/NFATc2 activity and enhanced lytic gene expression in comparison to Type 1 EBV infection

Humans are infected with two distinct strains (Type 1 (T1) and Type 2 (T2)) of Epstein-Barr virus (EBV) that differ substantially in their EBNA2 and EBNA 3A/B/C latency genes and the ability to transform B cells in vitro. While most T1 EBV strains contain the "prototype" form of the BZLF1 immediate-early promoter ("Zp-P"), all T2 strains contain the "Zp-V3" variant, which contains an NFAT binding motif and is activated much more strongly by B-cell receptor signalling. Whether B cells infected with T2 EBV are more lytic than cells infected with T1 EBV is unknown. Here we show that B cells infected with T2 EBV strains (AG876 and BL5) have much more lytic protein expression compared to B cells infected with T1 EBV strains (M81, Akata, and Mutu) in both a cord blood-humanized (CBH) mouse model and EBV-transformed lymphoblastoid cell lines (LCLs). Although T2 LCLs grow more slowly than T1 LCLs, both EBV types induce B-cell lymphomas in CBH mice. T1 EBV strains (M81 and Akata) containing Zp-V3 are less lytic than T2 EBV strains, suggesting that Zp-V3 is not sufficient to confer a lytic phenotype. Instead, we find that T2 LCLs express much higher levels of activated NFATc1 and NFATc2, and that cyclosporine (an NFAT inhibitor) and knockdown of NFATc2 attenuate constitutive lytic infection in T2 LCLs. Both NFATc1 and NFATc2 induce lytic EBV gene expression when combined with activated CAMKIV (which is activated by calcium signaling and activates MEF2D) in Burkitt Akata cells. Together, these results suggest that B cells infected with T2 EBV are more lytic due to increased activity of the cellular NFATc1/c2 transcription factors in addition to the universal presence of the Zp-V3 form of BZLF1 promoter.

New Agents Designed to Fight EBV+ Cancers

Researchers report using structure-based design to create small molecules capable of preventing the viral protein Epstein-Barr Nuclear Antigen 1 from binding to DNA, thus blocking viral replication. The molecules inhibited the growth of tumors in cell lines and in patient-derived xenografts of Epstein-Barr virus-positive cancers.

[The following-up study of high-risk and moderate-risk groups defined by EB virus serology test at the nasopharyngeal carcinoma screening programme]

OBJECTIVE

To investigate the relationship between changes in high-risk populations and screening detected nasopharyngeal carcinoma (NPC) during the three-year follow-up of high-risk and moderate-risk groups at initial EB virus serology screening.

METHODS

We tested EB virus VCA-IgA and EBNA1-IgA antibody to identify the probability of suffering from NPC of the crowd. The high-risk and moderate-risk groups at initial screening in one county during 2009 to 2010 were followed-up once a year with EB virus serology testing. All the high-risk people during initial screening and follow-up were conducted with nasopharyngeal fiber endoscopy. Through the follow-up of three years, we analyzed changes in the number of high-risk group, detection rate of NPC in high-risk group, and tumor staging. Firstly detected NPC by screening was defined as screening group, and detected by following-up was defined as following-up group.

RESULTS

A total of 404 participants were at high-risk and 1 041 participants were at moderate-risk group, 1 445 persons were in the group. All 404 persons were at high-risk at initial screening, the number of high-risk people during follow-up decreased from 371 to 187, 853 people of the all high-risk group were conducted with nasopharyngeal fiber endoscopy, and 38 cases of NPC were detected. NPC detection rate of high-risk group was 6.2% (25/404), 3.2% (12/371), 0.5% (1/188) and 0 (0/187) during the initial screening and three years follow-up respectively. The cumulative incidence of NPC in the high-risk and moderate-risk group were 7.7% (31/404) ,0.8% (8/1 041) . The early diagnosis rate of NPC in screening group and following-up group was 80% (20/25)and 11/13, respectively. With the primary tumor, the rate of T1 in screening group was higher than following-up group (80% to 38%, 20/25 to 5/13; P = 0.028). However, compared with following-up group, the rate of regional lymph node metastasis in screening group was higher (19/25 to 5/13; P = 0.035 ).

CONCLUSION

Along with the high detection rate of early staging NPC in screening group and following-up group, the detection of NPC in high risk people is mainly at initial screening and the first year following-up and NPC detection rate thereafter is dropping significantly.

Characterization of Epstein-Barr virus type 1 nuclear antigen 3C sequence patterns of nasopharyngeal and gastric carcinomas in northern China

Epstein-Barr virus nuclear antigen protein 3C (EBNA3C) is a 992-amino-acid protein that has been shown to play a complex regulatory role in the transcription of viral and cellular genes. In this study, we successfully amplified 26 Epstein-Barr virus (EBV)-associated gastric carcinomas (EBVaGCs), 50 nasopharyngeal carcinomas (NPCs) and 27 throat washing (TW) samples from healthy donors. Based on a phylogenetic tree, the samples could be divided into three patterns. 3C-6 was the predominant subtype in northern China, and the variations between the strains sequenced in our study and those from southern China and Japan were similar, but differences were also identified. The distribution of EBNA3C subtypes among EBVaGCs, NPCs and healthy donors was not significantly different. These data suggest that EBNA3C gene variations are geographically restricted rather than tumor-specific polymorphisms.

E2F1 mediated apoptosis induced by the DNA damage response is blocked by EBV nuclear antigen 3C in lymphoblastoid cells

EBV latent antigen EBNA3C is indispensible for in vitro B-cell immortalization resulting in continuously proliferating lymphoblastoid cell lines (LCLs). EBNA3C was previously shown to target pRb for ubiquitin-proteasome mediated degradation, which facilitates G1 to S transition controlled by the major transcriptional activator E2F1. E2F1 also plays a pivotal role in regulating DNA damage induced apoptosis through both p53-dependent and -independent pathways. In this study, we demonstrate that in response to DNA damage LCLs knocked down for EBNA3C undergo a drastic induction of apoptosis, as a possible consequence of both p53- and E2F1-mediated activities. Importantly, EBNA3C was previously shown to suppress p53-induced apoptosis. Now, we also show that EBNA3C efficiently blocks E2F1-mediated apoptosis, as well as its anti-proliferative effects in a p53-independent manner, in response to DNA damage. The N- and C-terminal domains of EBNA3C form a stable pRb independent complex with the N-terminal DNA-binding region of E2F1 responsible for inducing apoptosis. Mechanistically, we show that EBNA3C represses E2F1 transcriptional activity via blocking its DNA-binding activity at the responsive promoters of p73 and Apaf-1 apoptosis induced genes, and also facilitates E2F1 degradation in an ubiquitin-proteasome dependent fashion. Moreover, in response to DNA damage, E2F1 knockdown LCLs exhibited a significant reduction in apoptosis with higher cell-viability. In the presence of normal mitogenic stimuli the growth rate of LCLs knockdown for E2F1 was markedly impaired; indicating that E2F1 plays a dual role in EBV positive cells and that active engagement of the EBNA3C-E2F1 complex is crucial for inhibition of DNA damage induced E2F1-mediated apoptosis. This study offers novel insights into our current understanding of EBV biology and enhances the potential for development of effective therapies against EBV associated B-cell lymphomas.

Aberrant cellular proliferation due to deregulation of E2F1 transcriptional activity as a result of either genetic or functional alterations of its upstream components is a hallmark of human cancer. Interestingly, E2F1 can also promote cellular apoptosis regardless of p53 status by activating a number of pro-apoptotic genes in response to DNA damage stimuli. Epstein-Barr virus (EBV) encoded essential latent antigen EBNA3C can suppress p53-mediated apoptotic activities. This study now demonstrates that EBNA3C can further impede E2F1 mediated apoptosis by inhibiting its transcriptional ability, as well as by facilitating its degradation in an ubiquitin-proteasome dependent manner. This is the first evidence, which shows through targeting EBNA3C function linked to the E2F1-mediated apoptotic pathway, an additional therapeutic platform could be implemented against EBV-associated human B-cell lymphomas.

Epstein-Barr virus nuclear antigen 3C stabilizes Gemin3 to block p53-mediated apoptosis

The Epstein-Barr nuclear antigen 3C (EBNA3C), one of the essential latent antigens for Epstein-Barr virus (EBV)-induced immortalization of primary human B lymphocytes in vitro, has been implicated in regulating cell proliferation and anti-apoptosis via interaction with several cellular and viral factors. Gemin3 (also named DDX20 or DP103) is a member of DEAD RNA helicase family which exhibits diverse cellular functions including DNA transcription, recombination and repair, and RNA metabolism. Gemin3 was initially identified as a binding partner to EBNA2 and EBNA3C. However, the mechanism by which EBNA3C regulates Gemin3 function remains unclear. Here, we report that EBNA3C directly interacts with Gemin3 through its C-terminal domains. This interaction results in increased stability of Gemin3 and its accumulation in both B lymphoma cells and EBV transformed lymphoblastoid cell lines (LCLs). Moreover, EBNA3C promotes formation of a complex with p53 and Gemin3 which blocks the DNA-binding affinity of p53. Small hairpin RNA based knockdown of Gemin3 in B lymphoma or LCL cells remarkably attenuates the ability of EBNA3C to inhibit the transcription activity of p53 on its downstream genes p21 and Bax, as well as apoptosis. These findings provide the first evidence that Gemin3 may be a common target of oncogenic viruses for driving cell proliferation and anti-apoptotic activities.

Gemin3 (DDX20 or DP103) is a member of the DEAD-box family of RNA helicases involved in various cellular processes including DNA transcription and RNA processing. The Epstein-Barr virus (EBV) encoded nuclear antigen 3C (EBNA3C) is essential for EBV-induced immortalization of primary human B-lymphocytes in vitro. In this study, we discovered that Gemin3 directly binds to the tumor suppressor p53, and acts as a negative regulator blocking p53 functions. Importantly, EBNA3C induces Gemin3 accumulation and enhances the formation of the complex of Gemin3 and p53 in EBV- transformed primary human B lymphocytes. Remarkably, inhibition of Gemin3 production leads to cell death of B lymphoma cells, particularly EBNA3C positive cells. This is the first evidence which shows that Gemin3 directly impairs p53 function in EBV positive cells, and that Gemin3 could be a potential target for EBV-associated cancer therapy.

Epstein-Barr virus nuclear antigen 3C facilitates G1-S transition by stabilizing and enhancing the function of cyclin D1

EBNA3C, one of the Epstein-Barr virus (EBV)-encoded latent antigens, is essential for primary B-cell transformation. Cyclin D1, a key regulator of G1 to S phase progression, is tightly associated and aberrantly expressed in numerous human cancers. Previously, EBNA3C was shown to bind to Cyclin D1 in vitro along with Cyclin A and Cyclin E. In the present study, we provide evidence which demonstrates that EBNA3C forms a complex with Cyclin D1 in human cells. Detailed mapping experiments show that a small N-terminal region which lies between amino acids 130-160 of EBNA3C binds to two different sites of Cyclin D1- the N-terminal pRb binding domain (residues 1-50), and C-terminal domain (residues 171-240), known to regulate Cyclin D1 stability. Cyclin D1 is short-lived and ubiquitin-mediated proteasomal degradation has been targeted as a means of therapeutic intervention. Here, we show that EBNA3C stabilizes Cyclin D1 through inhibition of its poly-ubiquitination, and also increases its nuclear localization by blocking GSK3β activity. We further show that EBNA3C enhances the kinase activity of Cyclin D1/CDK6 which enables subsequent ubiquitination and degradation of pRb. EBNA3C together with Cyclin D1-CDK6 complex also efficiently nullifies the inhibitory effect of pRb on cell growth. Moreover, an sh-RNA based strategy for knock-down of both cyclin D1 and EBNA3C genes in EBV transformed lymphoblastoid cell lines (LCLs) shows a significant reduction in cell-growth. Based on these results, we propose that EBNA3C can stabilize as well as enhance the functional activity of Cyclin D1 thereby facilitating the G1-S transition in EBV transformed lymphoblastoid cell lines.

EBNA3C can modulate the activities of the transcription factor Necdin in association with metastasis suppressor protein Nm23-H1

Previous studies have demonstrated the interaction between the Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA3C) and the metastatic suppressor Nm23-H1 both in vitro and in vivo (C. Subramanian, M. A. Cotter II, and E. S. Robertson, Nat. Med. 7:350-355, 2001). Importantly EBNA3C can reverse the ability of Nm23-H1 to suppress migration of human cells in vitro. EBNA3C contributes to EBV-associated human cancers by regulating transcription of a number of cellular and viral promoters as well as targeting and altering the transcription activities of the metastasis suppressor Nm23-H1. Furthermore, Necdin is a cellular protein which is highly induced in terminally differentiated cells; it contributes to the regulation of cell growth and is also known to interact with viral oncoproteins. In this report, we show that Nm23-H1 and EBNA3C can modulate the biological functions of Necdin in the context of EBV infection and transformation. The levels of Necdin were consistently lower in EBV-positive cells, and EBNA3C could change the subcellular localization of Necdin as well as rescue cells from the antiangiogenic and antiproliferative effects mediated by Necdin. We also show that Necdin directly interacts with Nm23-H1, resulting in modulation of the biochemical function of Nm23-H1 as well as the biological function of Necdin. Both EBNA3C and Nm23-H1 were able to rescue not only Necdin-mediated transcriptional repression of the downstream vascular endothelial growth factor promoter but also Necdin-mediated growth suppression and antiangiogenic effects on cancer cells. The majority of this response was mediated through amino acid residues 191 to 222 of Necdin, which are also known to be important for nuclear matrix targeting. These studies suggest a role for Necdin in the regulation of downstream cellular targets in a hypoxic environment in virus-associated human cancers.

Two-step Epstein-Barr virus immunoglobulin A enzyme-linked immunosorbent assay system for serological screening and confirmation of nasopharyngeal carcinoma

Undifferentiated nasopharyngeal carcinoma (NPC; WHO type III) is 100% associated with Epstein-Barr virus (EBV) infection and the fourth most prevalent cancer in Indonesian males. Therapy failure is high, since most patients come to the hospital at an advanced stage of disease. Screening for early-stage NPC is needed. Here, a simple and economical two-step enzyme-linked immunosorbent assay (ELISA) system is proposed for diagnosing NPC in high-risk populations, employing the peptide-based immunoglobulin A (IgA) EBNA1 plus viral capsid antigen p18 ELISA as an initial screening test and the IgA early antigen (EA) ELISA using a different set of EBV antigens as a confirmation test. A total of 151 NPC patients and 199 regional healthy EBV carriers were used to evaluate the two-step ELISA approach. Routinely, EBV IgG immunoblotting is used as a standard confirmation test. The sensitivity and specificity for diagnosing NPC by the two-step ELISA approach increased from 85.4% to 96.7% and 90.1% to 98%, respectively, with positive predictive values and negative predictive values increasing from 78.7 and 93.9% to 97.3 and 97.5%, respectively, relative to the immunoblotting confirmation system. On discrepant samples, additional testing was done by EBV DNA load quantification in blood. Results showed that 5/11 discrepant NPC samples with an elevated IgA EA ELISA also had elevated an EBV DNA load in the circulation (range, 3,200 to 25,820 copies/ml). Therefore, the IgA EA ELISA is proposed as a confirmation test in first-line NPC serological screening studies. This two-step EBV ELISA system provides a standardized approach for NPC screening and may be used in combination with dried blood sampling in future field studies for identification of early-stage NPC in high-risk regions.

A peptide-based inhibitor for prevention of B cell hyperproliferation induced by Epstein–Barr virus

Epstein-Barr virus (EBV) infects and transforms resting B lymphocytes in vitro. The virus can also cause B cell lymphomas in immunosuppressed humans. Indeed, EBV-mediated post-transplant lymphoproliferative disease causes significant complications in transplant recipients, including loss of the transplanted organ and even death. The limited treatment options include, nonspecific targeting of B cell surface antigens with monoclonal antibodies or withdrawal of immunosuppression. These therapies fail in approximately 50% of patients. Clearly, treatments that specifically target EBV-infected cells are desirable. The EBV antigen EBNA3C regulates cell cycle by targeting critical cellular complexes such as cyclin A/cdk2, SCF(Skp2), and Rb. Here, we use a 20-amino-acid EBNA3C-derived peptide, fused to an HIV TAT tag for efficient delivery, to disrupt cell cycle regulation by EBNA3C. The peptide inhibited hyperproliferation of EBV-infected B cell lines and reduced in vitro immortalization of primary B lymphocytes by EBV. Importantly, the peptide inhibited lymphoblastoid outgrowth from the blood of an EBV-positive transplant patient in vitro.

Structure and function of the Epstein-Barr virus transcription factor, EBNA 3C

EBNA 3C is one of only nine proteins expressed by the tumourigenic gamma-herpesvirus Epstein-Barr virus (EBV) during the infection and immortalization of human B lymphocytes. In fact, the expression of EBNA 3C has been shown to be essential for the B-cell transformation process to take place. The mechanism by which EBNA 3C contributes to viral pathogenicity has therefore been the subject of intensive research over many years. The first clues on the function of EBNA 3C came from analysis of the primary amino acid sequence of EBNA 3C which identified a number of domains commonly found in transcriptional regulatory proteins. These domains include a proline-rich and a glutamine-proline-rich domain and a putative bZIP domain located in the N-terminus of the protein. EBNA 3C has subsequently been shown to function as a regulator of both viral and cellular transcription and to have potent effects on normal cell-cycle regulatory pathways. This review will discuss our current knowledge of the functions of EBNA 3C, the roles played by the different domains of EBNA 3C in these functions, and summarize some recent work from our laboratory that provides the first structural and functional analysis of the putative bZIP domain of EBNA 3C.

Expression of alpha V integrin is modulated by Epstein-Barr virus nuclear antigen 3C and the metastasis suppressor Nm23-H1 through interaction with the GATA-1 and Sp1 transcription factors

Epstein-Barr virus (EBV) is a lymphotrophic herpesvirus infecting most of the world's population. It is associated with a number of human lymphoid and epithelial tumors and lymphoproliferative diseases in immunocompromised patients. A subset of latent EBV antigens is required for immortalization of primary B-lymphocytes. The metastatic suppressor Nm23-H1 which is downregulated in human invasive breast carcinoma reduces the migration and metastatic activity of breast carcinoma cells when expressed from a heterologous promoter. Interestingly, the EBV nuclear antigen 3C (EBNA3C) reverses these activities of Nm23-H1. The alpha V integrins recognize a variety of ligands for signaling and are involved in cell migration and proliferation and also serve as major receptors for extracellular-matrix-mediated cell adhesion and migration. The goal of this study was to determine if Nm23-H1 and EBNA3C can modulate alpha V integrin expression and downstream activities. The results of our studies indicate that Nm23-H1 downregulates alpha V intregrin expression in a dose responsive manner. In contrast, EBNA3C can upregulate alpha V integrin expression. Furthermore, the study showed that the association of the Sp1 and GATA transcription factors with Nm23-H1 is required for modulation of the alpha V integrin activity. Thus, these results suggest a direct correlation between the alpha V integrin expression and the interaction of Nm23-H1 with EBNA3C.

Epstein-Barr virus protein can upregulate cyclo-oxygenase-2 expression through association with the suppressor of metastasis Nm23-H1

Previous studies have demonstrated the interaction between the Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA3C) and the metastatic suppressor Nm23-H1 both in vitro and in vivo (C. Subramanian, M. A. Cotter II, and E. S. Robertson, Nat. Med. 7:350-355, 2001). EBNA3C can reverse the ability of Nm23-H1 to suppress migration of Burkitt's lymphoma and breast carcinoma cell lines in vitro. EBNA3C contributes to EBV-associated human cancers by regulating transcription of a number of cellular and viral promoters and by targeting and altering the transcription activities of the metastasis suppressor Nm23-H1. Cyclo-oxygenase-2 (COX-2), an inducible enzyme important in inflammation, is overexpressed in a variety of cancers and can influence cell migration. In this report we show that Nm23-H1 and EBNA3C can modulate expression of COX-2 in the context of EBV infection and transformation. The levels of COX-2 were consistently higher in EBV-positive cells than in EBV-negative cells. Additionally, we show that Nm23-H1 can upregulate the COX-2 promoter element in luciferase reporter assays, whereas EBNA3C alone did not affect the level of response but clearly contributed to an additive increase when coexpressed with Nm23-H1. The downstream effect of COX-2 expression was also evaluated and showed that prostaglandin E(2) levels increased with Nm23-H1 and that there was some level of cooperativity in the presence of EBNA3C. The majority of this response was mediated through the cyclic AMP response element and NF-kappaB sites. These studies suggest a potential role for COX-2 in EBV-associated human cancers.

Conserved cell cycle regulatory properties within the amino terminal domain of the Epstein-Barr virus nuclear antigen 3C

The gammaherpesviruses Rhesus lymphocryptovirus (LCV) and Epstein-Barr virus (EBV) are closely related phylogenetically. Rhesus LCV efficiently immortalizes Rhesus B cells in vitro. However, despite a high degree of conservation between the Rhesus LCV and EBV genomes, Rhesus LCV fails to immortalize human B cells in vitro. This species restriction may, at least in part, be linked to the EBV nuclear antigens (EBNAs) and latent membrane proteins (LMPs), known to be essential for B cell transformation. We compared specific properties of EBNA3C, a well-characterized and essential EBV protein, with its Rhesus counterpart to determine whether EBNA3C phenotypes which contribute to cell cycle regulation are conserved in the Rhesus LCV. We show that both EBNA3C and Rhesus EBNA3C bind to a conserved region of mammalian cyclins, regulate pRb stability, and modulate SCF(Skp2)-dependent ubiquitination. These results suggest that Rhesus LCV restriction from human B cell immortalization is independent of the conserved cell cycle regulatory functions of the EBNA3C protein.

Epstein-Barr virus latent antigen 3C can mediate the degradation of the retinoblastoma protein through an SCF cellular ubiquitin ligase

Epstein-Barr virus (EBV) stimulates the proliferation of latently infected B cells and promotes lymphoid malignancies in humans. To address the role of EBV latency protein Epstein-Barr nuclear antigen 3C (EBNA3C) in regulation of the retinoblastoma protein (Rb), we transfected EBNA3C into 293, BJAB, and SAOS-2 cells. In this context, a dominant effect of EBNA3C is to decrease Rb protein levels. EBNA3C also rescues an Rb-induced flat cell phenotype and targets Rb for proteasome- and ubiquitin-dependent degradation. Further, EBNA3C forms a stable complex with Rb in cells when the proteasome machinery is inhibited and interacts with Rb in vitro, mapping to a conserved domain at the terminus of EBNA3C. Deletion analysis of EBNA3C identified a motif within amino acids 140-149 important for both the binding and regulation of Rb. This motif is of particular interest, because it has also been linked to regulation of the Skp1/Cul1/F-box complex, SCF(Skp2). Indeed, inhibition of Skp2 function with a dominant-negative molecule reduces the ability of EBNA3C to degrade Rb. Skp2 has no detectable effect on Rb levels in the absence of EBNA3C, suggesting that SCF(Skp2) is specifically usurped by EBNA3C for the enhancement of Rb degradation. That EBNA3C has exploited this association suggests that other human malignancies might use a similar strategy to regulate the Rb protein.

Epstein-Barr virus EBNA3 proteins bind to the C8/alpha7 subunit of the 20S proteasome and are degraded by 20S proteasomes in vitro, but are very stable in latently infected B cells

A yeast two-hybrid screen using EBNA3C as bait revealed an interaction between this Epstein-Barr virus (EBV)-encoded nuclear protein and the C8 (alpha7) subunit of the human 20S proteasome. The interaction was confirmed by glutathione S-transferase (GST) pull-down experiments and these also revealed that the related proteins EBNA3A and EBNA3B can bind similarly to C8/alpha7. The interaction between these viral proteins and GST-C8/alpha7 was shown to be significantly more robust than the previously reported interaction between C8/alpha7 and the cyclin-dependent kinase inhibitor p21(WAF1/CIP1). Co-immunoprecipitation of the EBNA3 proteins with C8/alpha7 was also demonstrated after transfection of expression vectors into B cells. Consistent with this ability to bind directly to an alpha-subunit of the 20S proteasome, EBNAs 3A, 3B and 3C were all degraded in vitro by purified 20S proteasomes. However, surprisingly, no sign of proteasome-mediated turnover of these latent viral proteins in EBV-immortalized B cells could be detected, even in the presence of gamma interferon. In actively proliferating lymphoblastoid cell lines, EBNAs 3A, 3B and 3C appear to be remarkably stable, with no evidence of either de novo synthesis or proteasome-mediated degradation.

Epstein-Barr virus nuclear antigen 3C regulates cyclin A/p27 complexes and enhances cyclin A-dependent kinase activity

Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA3C) is essential for primary B-cell transformation. In this report we show that cyclin A, an activator of S phase progression, bound tightly to EBNA3C. EBNA3C interacted with cyclin A in vitro and associated with cyclin A complexes in EBV-transformed lymphoblastoid cell lines. Importantly, EBNA3C stimulated cyclin A-dependent kinase activity and rescued p27-mediated inhibition of cyclin A/Cdk2 kinase activity by decreasing the molecular association between cyclin A and p27 in cells. Additionally, phosphorylation of the retinoblastoma protein, a major regulator of cell cycle progression, was enhanced both in vitro and in vivo in the presence of EBNA3C. Cyclin A interacted with a region of the carboxy terminus of EBNA3C, shown to be important both for stimulation of cyclin A-dependent kinase activity and for cell cycle progression. This provides the first evidence of an essential EBV latent antigen's directly targeting a cell cycle regulatory protein and suggests a novel mechanism by which EBV deregulates the mammalian cell cycle, which is of critical importance in B-cell transformation.

Transcriptional regulatory properties of Epstein-Barr virus nuclear antigen 3C are conserved in simian lymphocryptoviruses

Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA-3C) is a large transcriptional regulator essential for EBV-mediated immortalization of B lymphocytes. We previously identified interactions between EBNA-3C and two cellular transcription factors, J kappa and Spi proteins, through which EBNA-3C regulates transcription. To better understand the contribution of these interactions to EBNA-3C function and EBV latency, we examined whether they are conserved in the homologous proteins of nonhuman primate lymphocryptoviruses (LCVs), which bear a strong genetic and biological similarity to EBV. The homologue of EBNA-3C encoded by the LCV that infects baboons (BaLCV) was found to be only 35% identical in sequence to its EBV counterpart. Of particular significance, this homology localized predominantly to the N-terminal half of the molecule, which encompasses the domains in EBNA-3C that interact with J kappa and Spi proteins. Like EBNA-3C, both BaLCV and rhesus macaque LCV (RhLCV) 3C proteins bound to J kappa and repressed transcription mediated by EBNA-2 through its interaction with J kappa. Both nonhuman primate 3C proteins were also able to activate transcription mediated by the Spi proteins in the presence of EBNA-2. Like EBNA-3C, a domain encompassing the putative basic leucine zipper motif of the BaLCV-3C protein directly interacted with both Spi-1 and Spi-B. Surprisingly, a recently identified motif in EBNA-3C that mediates repression was not identifiable in the BaLCV-3C protein. Finally, although the C terminus of BaLCV-3C bears minimal homology to EBNA-3C, it nonetheless contains a C-terminal domain rich in glutamine and proline that was able to function as a potent transcriptional activation domain, as does the C terminus of EBNA-3C. The conservation of these functional motifs despite poor overall homology among the LCV 3C proteins strongly suggests that the interactions of EBNA-3C with J kappa and Spi do indeed play significant roles in the life cycle of EBV.

Protein interactions provide new insight into Nm23/nucleoside diphosphate kinase functions

Nm23-NDPKs besides contributing to the maintenance of the cellular nucleoside triphosphate pool, exert regulatory properties in a variety of cellular events including proliferation, invasiveness, development, differentiation, and gene regulation. This review focuses on recently discovered protein-protein interactions involving the Nm23 proteins. The findings herein summarized provide new and intriguing suggestions for a more extensive understanding of the biological functions of the Nm23 proteins.

Association of EBV infection with lymphomas

The diagnostic reliability of the IgA immunoblot test in the diagnosis of EBV associated lymphomas was examined. Serum samples from patients with clinically diagnosed lymphomas were tested for the presence of EBV specific IgG and IgA antibodies and based on test results the EBV association with lymphoma was estimated. Obtained results indicated that EBV IgA testing may be helpful in diagnosis of EBV association with lymphomas.

Serum nm23-H1 protein as a prognostic factor in hematological malignancies

A nondifferentiating mouse myeloid leukemia cell line produces differentiation-inhibiting factors. One of these factors was purified as a homologue of nm23. The nm23 gene was isolated as a metastasis-suppressor gene that exhibits low expression in high-level metastatic cancer cells. The nm23 gene was overexpressed in acute myelogenous leukemia (AML) cells and a higher level of nm23-H1 expression was correlated with a poor prognosis in AML. Multivariate analysis of putative prognostic factors revealed that elevated nm23-H1 mRNA levels significantly contributed to the prognosis of patients with AML. The overexpression of nm23-H1 was also observed in various hematological neoplasms. To use nm23 overexpression to determine the prognosis for lymphoma, we established an enzyme-linked immunosorbent assay (ELISA) technique to determine the serum level of nm23-H1 protein. This assay is far simpler than that used to determine nm23 mRNA by reverse transcriptase-polymerase chain reaction (RT-PCR). Using this system, we measured nm23-H1 protein levels in many hematological malignancies. Serum nm23-HI levels were significantly higher in patients with all of the hematological neoplasms tested (AML, chronic myelogenous leukemia, acute lymphoblastic leukemia, (ALL) myelodysplastic syndrome (MDS) and malignant lymphomas) than in normal controls. An elevated serum nm23-H1 protein concentration predicted a poor outcome for AML and non-Hodgkin's lymphoma. Especially in diffuse large B-cell lymphoma (DLBCL), seram nm23-H1 protein levels were an important prognostic factor in planning an appropriate treatment strategy for DLBCL. The serum nm23-H I protein levels probably depend on the total mass of malignant cells overexpressing nm23-H1.

Promoter-specific targeting of human SWI-SNF complex by Epstein-Barr virus nuclear protein 2

The multiprotein human SWI-SNF (hSWI-SNF) complex is a chromatin-remodeling machine that facilitates transcription by overcoming chromatin-mediated gene repression. We had previously shown that hSNF5/INI1, an intrinsic, consistent component of the hSWI/SNF complex, is associated with Epstein-Barr nuclear antigen 2 (EBNA2) and have proposed that EBNA2 directs this complex to key EBNA2-responsive viral and cellular genes. Using chromatin immunoprecipitation and quantitative PCR, we show that antibodies directed against components of the hSWI-SNF complex preferentially precipitate chromatin-associated DNA that contains a targeted EBNA2-responsive element in the context of both episomal and cellular chromatin. This enrichment does not occur in EBNA2-negative cells or when the EBNA2-responsive element is mutated. The stable association of the hSWI-SNF complex with the EBNA2-responsive promoter can also be disrupted by deletion of the TATA element, suggesting that EBNA2 in itself is insufficient to mediate stable targeting of the hSWI-SNF complex. These results demonstrate that recruitment of the hSWI-SNF complex to selected promoters can occur in vivo through its interaction with site-specific activator proteins and that stable targeting may require the presence of basal transcription factors.

Polymorphism analysis of Epstein-Barr virus isolates from patients with cutaneous natural killer/T-cell lymphoproliferative disorders: A possible relation to the endemic occurrence of these diseases in Japan

Certain forms of cutaneous lymphomas in Asia are associated frequently with Epstein-Barr virus (EBV) infection, whereas such cases are less common in western countries. The virus-related peptides, EBV-determined nuclear antigen (EBNA)-2 and the latent membrane protein (LMP)-1, play an essential role in cell transformation. The polymorphisms of these EBV genes may be related to their transforming abilities. In order to clarify the viral subtype that may be involved in the incidence of EBV-associated lymphomas, we analyzed the EBNA-2 and LMP-1 gene polymorphisms and mutations in healthy adults and in patients with EBV-associated cutaneous natural killer(NK)/T-cell lymphoproliferative disorders in Japan. In EBV-related cutaneous lymphoproliferative disorders, EBV subtype 1 was found in all 15 cases, and 1 sample contained a dual infection with subtypes 1 and 2. All EBV isolates from our patients lost a Xho-1 site in exon 1 of the LMP-1 gene, and 7 of 13 cases had a Nco-1 site within the promoter region. All isolates without the LMP-1-Xho-1 site had a 30 bp deletion in the carboxy terminus of the LMP-1 gene, except for the isolate from a patient with angioimmunoblastic lymphadenophathy-like T-cell lymphoma in which a novel Nco-1 site was present in exon 1. Eleven of fourteen throat washings from healthy adults which contained EBV-DNA harbored EBV subtype 1, and the EBNA2 region was not amplified in the other 3 samples. The Xho-1 site was lost in 12 (86%) of 14 isolates and the 30 bp deletion was present in 11 (78%) of 14 isolates from the throat washings. The findings indicate that the predominant EBV isolate from Japanese healthy adults and patients with cutaneous NK/T-cell lymphoproliferative disorders is subtype 1 with a 30 bp deletion and loss of a Xho-1 site in the LMP-1 gene. Since previous data indicated that either subtype 1 or the 30 bp deletion variant possesses high tumorigenic activity, the prevalence of subtype 1 containing these mutations might be responsible for the high incidence of EBV-associated lymphoproliferative disorders in Japan.

A reporter gene assay for high-throughput screening of G-protein-coupled receptors stably or transiently expressed in HEK293 EBNA cells grown in suspension culture

We describe in detail a robust, sensitive, and versatile functional assay for G-protein-coupled receptors (GPCRs) expressed in human embryonic kidney (HEK) 293-EBNA (Epstein-Barr virus nuclear antigen) (designated 293E) cells. The ability to grow these cells in suspension, in conjunction with the use of the secreted form of the human placental alkaline phosphatase (SEAP) as the reporter enzyme transcriptionally regulated by 5-cyclic AMP (cAMP) response elements (CREs) (Chen et al., Anal. Biochem. 226, 349-354 (1995)), makes this CRE-SEAP assay potentially attractive for high-throughput screening (HTS). A 293E clonal cell line, stably transfected with the CRE-SEAP plasmid, was initially characterized with compounds known to activate intracellular signal transduction pathways similar to those activated by GPCRs. Forskolin and cAMP analogues were potent at inducing SEAP expression but calcium ionophores (A23187 and ionomycin) were without effect. The forskolin response was also potentiated by the protein kinase C activator phorbol myristate acetate as well as the phosphodiesterase inhibitor isobutylmethylxanthine. Previously established cell lines expressing the G(alphas)-coupled DP or the G(alphaq)-coupled-EP(1) prostanoid receptors were stably transfected with the reporter gene construct and clones were selected based on their ability to secrete SEAP upon agonist challenge. Pharmacological characterization of the DP and EP(1) receptors displayed a similar rank order of potency for several known prostanoids and related compounds to that previously reported using classical binding assays or other functional assays. The CRE-SEAP assay was also used to characterize the EP(1) receptor antagonists SC-51322, SC-51089, and AH6809. In summary, we have established a reporter gene assay for GPCRs that couple to both G(alphas) and G(alphaq) and is amenable to HTS of both agonists and antagonists.

Regulation of the Epstein-Barr virus C promoter by AUF1 and the cyclic AMP/protein kinase A signaling pathway

EBNA2 is an Epstein-Barr virus (EBV)-encoded protein that regulates the expression of viral and cellular genes required for EBV-driven B-cell immortalization. Elucidating the mechanisms by which EBNA2 regulates viral and cellular gene expression is necessary to understand EBV-induced B-cell immortalization and viral latency in humans. EBNA2 targets to the latency C promoter (Cp) through an interaction with the cellular DNA binding protein CBF1 (RBPJk). The EBNA2 enhancer in Cp also binds another cellular factor, C promoter binding factor 2 (CBF2), whose protein product(s) has not yet been identified. Within the EBNA2 enhancer in Cp, we have previously identified the DNA sequence required for CBF2 binding and also determined that this element is required for efficient activation of Cp by EBNA2. In this study, the CBF2 activity was biochemically purified and microsequenced. The peptides sequenced were identical to the hnRNP protein AUF1. Antibodies against AUF1 but not antibodies to related hnRNP proteins reacted with CBF2 in gel mobility shift assays. In addition, stimulation of the cellular cyclic AMP (cAMP)/protein kinase A (PKA) signal transduction pathway results in an increase in detectable CBF2/AUF1 binding activity extracted from stimulated cells. Furthermore, the CBF2 binding site was able to confer EBNA2 responsiveness to a heterologous promoter when transfected cells were treated with compounds that activate PKA or by cotransfection of plasmids expressing a constitutively active catalytic subunit of PKA. EBNA2-mediated stimulation of the latency Cp is also increased in similar cotransfection assays. These results further support an important role for CBF2 in mediating EBNA2 transactivation; they identify the hnRNP protein AUF1 as a major component of CBF2 and are also the first evidence of a cis-acting sequence other than a CBF1 binding element that is able to confer responsiveness to EBNA2.

Cell growth and matrix invasion of EBV-immortalized human B lymphocytes is regulated by expression of alpha(v) integrins

alpha(v) integrins have been shown to play an important role in epithelial-derived cell migration, cell growth and tumor invasion/metastasis, however their role on cells of hematopoietic origin is less clear. Epstein-Barr virus (EBV), a human herpesvirus associated with several lymphoproliferative disorders in man, induces expression of alpha(v) integrins on transformed B lymphocytes. In the studies reported here, we show that EBV infection increases alpha(v), beta3 and beta5 integrin subunit mRNAs as well as upregulates the expression of the alphavbeta3 integrin protein on human B cells. Among the nine different EBV proteins expressed in latently infected B cells (nuclear and plasma membrane-associated), only LMP1, LMP2A and EBNA2 were shown to selectively transactivate the alpha(v) integrin promoter. Treatment of EBV-transformed B cells with alpha(v) antisense oligonucleotides specifically reduced cell surface expression of alpha(v) integrins, inhibited cell growth in low serum, reduced cell invasion in matrigels and decreased expression of metalloprotease, MMP9. These studies indicate that alpha(v) integrins play a significant role in EBV-induced B-lymphocyte proliferation and invasion. Strategies to interfere with alphav integrin expression and/or function may therefore be of potential value in the treatment of EBV-associated lymphoproliferative disorders.

Epstein-Barr virus (EBV) genes expression in cervical intraepithelial neoplasia and invasive cervical cancer: a comparative study with human papillomavirus (HPV) infection

To elucidate a causative role of Epstein-Barr virus (EBV) for cervical cancer, presence and expression of EBV genes were examined in 31 cervical carcinomas (ICC), 23 cervical intraepithelial neoplasias (CIN), and 35 normal cervices (NCX). In reverse transcription polymerase chain reaction (RT-PCR) analysis, EBER-1 mRNAwas expressed in 74% (23/31) of ICC, 83% (19/23) of CIN, 37% (13/35) of NCX. LMP-1 was expressed in 52% (16/31) of ICC, 70% (16/23) of CIN, and 23% (8/35) of NCX, and EBNA-2 was expressed in 32% (10/31) of ICC, in 48% (11/23) of CIN, and in 11% (4/35) of NCX. Expression rates of these genes were significantly higher in ICC and CIN than in NCX (P < .05). RNA in situ hybridization analysis showed that EBER-1 was expressed in half (7/14) of ICC and 35% (6/17) of CIN, and BamH-W, which is a leader sequence of EBNA genes, was expressed in 86% (12/14) of ICC and 71% (12/17) of CIN. LMP-1 and EBNA-2 proteins also were detected in ICC and CIN cells by inmunofluorescence staining. PCR analysis showed that EBV genome was detected in 55% (17 of 31) of ICC and in 26% (9/35) of NCX. In contrast, human papillomavirus (HPV) DNA was detected in 84% (26/31) of ICC, whereas none of NCX had HPV DNA. Either EBV or HPV was detected in 61% (19/31) of ICC, whereas both EBV and HPV was detected in 39% (12/31) of ICC. EBV infection may be involved in the development of cervical cancer, although further study should be performed to elucidate a causative role of EBV for the cancer.

Infection of primary human monocytes by Epstein-Barr virus

Previous studies have reported that infection of monocytes by viruses such as cytomegalovirus and human immunodeficiency virus weakens host natural immunity. In the present study, we demonstrated the capability of Epstein-Barr virus (EBV) to infect and replicate in freshly isolated human monocytes. Using electron microscopy analysis, we observed the presence of EBV virions in the cytoplasm and nuclei of approximately 20% of monocytes. This was confirmed by Southern blot analysis of EBV genomic DNA sequences in isolated nuclei from monocytes. Infection of monocytes by EBV leads to the activation of the replicative cycle. This was supported by the detection of immediate-early lytic mRNA BZLF-1 transcripts, and by the presence of two early lytic transcripts (BALF-2, which appears to function in DNA replication, and BHRF-1, also associated with the replicative cycle). The late lytic BcLF-1 transcripts, which code for the major nucleocapsid protein, were also detected, as well as EBNA-1 transcripts. However, attempts to detect EBNA-2 transcripts have yielded negative results. Viral replication was also confirmed by the release of newly synthesized infectious viral particles in supernatants of EBV-infected monocytes. EBV-infected monocytes were found to have significantly reduced phagocytic activity, as evaluated by the quantification of ingested carboxylated fluoresceinated latex beads. Taken together, our results suggest that EBV infection of monocytes and alteration of their biological functions might represent a new mechanism to disrupt the immune response and promote viral propagation during the early stages of infection.

A role for SKIP in EBNA2 activation of CBF1-repressed promoters

EBNA2 is essential for Epstein-Barr virus (EBV) immortalization of B lymphocytes. EBNA2 functions as a transcriptional activator and targets responsive promoters through interaction with the cellular DNA binding protein CBF1. We have examined the mechanism whereby EBNA2 overcomes CBF1-mediated transcriptional repression. A yeast two-hybrid screen performed using CBF1 as the bait identified a protein, SKIP, which had not previously been recognized as a CBF1-associated protein. Protein-protein interaction assays demonstrated contacts between SKIP and the SMRT, CIR, Sin3A, and HDAC2 proteins of the CBF1 corepressor complex. Interestingly, EBNA2 also interacted with SKIP in glutathione S-transferase affinity and mammalian two-hybrid assays and colocalized with SKIP in immunofluorescence assays. Interaction with SKIP was not affected by mutation of EBNA2 conserved region 6, the CBF1 interaction region, but was abolished by mutation of conserved region 5. Mutation of conserved region 5 also severely impaired EBNA2 activation of a reporter containing CBF1 binding sites. Thus, interaction with both CBF1 and SKIP is necessary for efficient promoter activation by EBNA2. A model is presented in which EBNA2 competes with the SMRT-corepressor complex for contacts on SKIP and CBF1.

Epstein-Barr virus nuclear protein 2 interacts with p300, CBP, and PCAF histone acetyltransferases in activation of the LMP1 promoter

The Epstein-Barr virus (EBV) nuclear protein 2 (EBNA2) and herpes simplex virion protein 16 (VP16) acidic domains that mediate transcriptional activation now are found to have affinity for p300, CBP, and PCAF histone acetyltransferases (HATs). Transcriptionally inactive point mutations in these domains lack affinity for p300, CBP, or PCAF. P300 and CBP copurify with the principal HAT activities that bind to EBNA2 or VP16 acidic domains through velocity sedimentation and anion-exchange chromatography. EBNA2 binds to both the N- and C-terminal domains of p300 and coimmune-precipitates from transfected 293T cells with p300. In EBV-infected Akata Burkitt's tumor cells that do not express the EBV encoded oncoproteins EBNA2 or LMP1, p300 expression enhances the ability of EBNA2 to up-regulate LMP1 expression. Through its intrinsic HAT activity, PCAF can further potentiate the p300 effect. In 293 T cells, P300 and CBP (but not PCAF) can also coactivate transcription mediated by the EBNA2 or VP16 acidic domains and HAT-negative mutants of p300 have partial activity. Thus, the EBNA2 and VP16 acidic domains can utilize the intrinsic HAT or scaffolding properties of p300 to activate transcription.

Intracellular forms of human NOTCH1 interact at distinctly different levels with RBP-jkappa in human B and T cells

The cellular transcriptional repressor RBP-Jkappa associates with the Epstein-Barr virus nuclear antigens (EBNAs) determined to be essential for transformation of human primary B lymphocytes. It was demonstrated through genetic analysis that interaction between the viral transactivator EBNA2 and RBP-Jkappa is essential for EBV immortalization of primary B lymphocytes. We have shown that the association of RBP-Jkappa with intracellular NOTCH1 differs significantly in B and T cells. Immunoprecipitation analyses with antibodies to both the intracellular forms of NOTCH1 and to RBP-Jkappa demonstrated that little or no RBP-Jkappa is associated with NOTCH1 in B cell lines compared to the RBP-Jkappa associated with NOTCH1 in T cell lines and was further demonstrated in human primary lymphocytes. Additionally, EBNA2 can compete with intracellular NOTCH1 for binding to GST-RBP-Jkappa in vitro. Northern blot for the cellular gene hairy enhancer of split (HES1) demonstrated that HES1 is upregulated in the EBV transformed lymphoblastoid cells expressing high levels of EBNA2 and in a T cell line SupT1 overexpressing intracellular activated NOTCH1. Hence, EBNA2 may be able to compete for the available pool of RBP-Jkappa more effectively in human B cells than in T cells and provides a possible explanation for the ability of EBV to potently and efficiently infect and immortalize human B cells. Leukemia (2000) 14, 84-92.

Sequence and functional analysis of EBNA-LP and EBNA2 proteins from nonhuman primate lymphocryptoviruses

The Epstein-Barr virus (EBV) EBNA-LP and EBNA2 proteins are the first to be synthesized during establishment of latent infection in B lymphocytes. EBNA2 is a key transcriptional regulator of both viral and cellular gene expression and is essential for EBV-induced immortalization of B lymphocytes. EBNA-LP is also important for EBV-induced immortalization of B lymphocytes, but far less is known about the functional domains and cellular cofactors that mediate EBNA-LP function. While recent studies suggest that serine phosphorylation of EBNA-LP and coactivation of EBNA2-mediated transactivation are important, more detailed mutational and genetic studies are complicated by the repeat regions that comprise the majority of the EBNA-LP sequence. Therefore, we have used a comparative approach by studying the EBNA-LP homologues from baboon and rhesus macaque lymphocryptoviruses (LCVs) (baboon LCV and rhesus LCV). The predicted baboon and rhesus LCV EBNA-LP amino acid sequences are 61 and 64% identical to the EBV EBNA-LP W1 and W2 exons and 51% identical to the EBV EBNA-LP Y1 and Y2 exons. Five evolutionarily conserved regions can be defined, and four of eight potential serine residues are conserved among all three EBNA-LPs. The major internal repeat sequence also revealed a highly conserved Wp EBNA promoter with strong conservation of upstream activating sequences important for Wp transcriptional regulation. To test whether transcriptional coactivating properties were common to the rhesus LCV EBNA-LP, a rhesus LCV EBNA2 homologue was cloned and expressed. The rhesus LCV EBNA2 transcriptionally transactivates EBNA2-responsive promoters through a CBF1-dependent mechanism. The rhesus LCV EBNA-LP was able to further enhance rhesus LCV or EBV EBNA2 transactivation 5- to 12-fold. Thus, there is strong structural and functional conservation among the simian EBNA-LP homologues. Identification of evolutionarily conserved serine residues and regions in EBNA-LP homologues provides important clues for identifying the cellular cofactors and molecular mechanisms mediating these conserved viral functions.

The residues between the two transformation effector sites of Epstein-Barr virus latent membrane protein 1 are not critical for B-lymphocyte growth transformation

Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) is essential for EBV-mediated transformation of primary B lymphocytes. LMP1 spontaneously aggregates in the plasma membrane and enables two transformation effector sites (TES1 and TES2) within the 200-amino-acid cytoplasmic carboxyl terminus to constitutively engage the tumor necrosis factor receptor (TNFR)-associated factors TRAF1, TRAF2, TRAF3, and TRAF5 and the TNFR-associated death domain proteins TRADD and RIP, thereby activating NF-kappaB and c-Jun N-terminal kinase (JNK). To investigate the importance of the 60% of the LMP1 carboxyl terminus that lies between the TES1-TRAF and TES2-TRADD and -RIP binding sites, an EBV recombinant was made that contains a specific deletion of LMP1 codons 232 to 351. Surprisingly, the deletion mutant was similar to wild-type (wt) LMP1 EBV recombinants in its efficiency in transforming primary B lymphocytes into lymphoblastoid cell lines (LCLs). Mutant and wt EBV-transformed LCLs were similarly efficient in long-term outgrowth and in regrowth after endpoint dilution. Mutant and wt LMP1 proteins were also similar in their constitutive association with TRAF1, TRAF2, TRAF3, TRADD, and RIP. Mutant and wt EBV-transformed LCLs were similar in steady-state levels of Bcl2, JNK, and activated JNK proteins. The wt phenotype of recombinants with LMP1 codons 232 to 351 deleted further demarcates TES1 and TES2, underscores their central importance in B-lymphocyte growth transformation, and provides a new perspective on LMP1 sequence variation between TES1 and TES2.

Requirement of replication licensing for the dyad symmetry element-dependent replication of the Epstein-Barr virus oriP minichromosome

Latent Epstein-Barr virus genome is maintained in cells by the viral oriP-binding factor EBNA1 and cellular replication factors. EBNA1 binds to the dyad symmetry (DS) element in oriP and initiates DNA replication once in a single S phase, but the mechanism by which this DS-dependent replication is initiated is unknown. Replication licensing of cellular chromatins occurs during early G1 phase. Because licensing is essential for the next round of replication in S phase, it facilitates once-in-a-cell-cycle replication of the cellular genome. Using the transient replication assay with HeLa/EB1 cell, we demonstrate that the oriP plasmid required a cell cycle window including early G1 phase for replication in the next S phase. The plasmid containing only the DS element had a similar requirement of early G1 phase for replication. Analysis using sucrose density gradient centrifugation revealed that the oriP minichromosome existed in two distinct states: one formed at late G1 and the other formed at G2/M. These results suggest that the DS-dependent DNA replication from oriP requires the replication licensing, implying a possible involvement of the cellular licensing factor MCM in the DNA replication from oriP.

A system for shuttling 200-kb BAC/PAC clones into human cells: stable extrachromosomal persistence and long-term ectopic gene activation

A novel shuttle vector, pBH140, has been constructed that allows stable maintenance of large genomic inserts as human artificial episomal chromosomes (HAECs) in mammalian cells. The vector, essentially a hybrid BAC-HAEC, contains an F-based replication system as in a bacterial artificial chromosome (BAC) and the Epstein-Barr virus (EBV) latent origin of replication system, oriP, for replication in human cells. A 185-kb DNA insert containing the entire human beta-globin locus, including its locus control region (LCR), was retrofitted into this vector. The resulting beta-globin BAC-HAEC clone, p148BH, was transfected into human cells and analyzed for episomal maintenance and expression of the beta-globin gene. FISH revealed an association of the vector with different human chromosomes but no integration. The beta-globin BAC-HAECs were present at an average copy number of 11-15 per nucleus in the stably transformed human cells. After 1 year of continuous in vitro cultivation, the HAECs persisted as structurally intact 200-kb episomes. While no beta-globin transcription could be detected in the parental D98/Raji cells, correctly spliced RT-PCR products were produced at significant levels in long-term cultures of the BAC-HAEC-transduced cells. The wide availability of BAC and PAC libraries, the ease in manipulating cloned DNA in bacteria, and the episomal stability of the pBH140 vector make this system ideal for studies on gene expression and other genomic functions in human cells. The potential significance of large, functionally active episomes for gene therapy is discussed.