Isolation of Epstein-Barr virus (EBV)-negative cell clones from the EBV-positive Burkitt's lymphoma (BL) line Akata: malignant phenotypes of BL cells are dependent on EBV

Evaluation of epstein-barr virus DNA load in gastric mucosa with chronic atrophic gastritis using a real-time quantitative PCR assay

PURPOSE

It is hypothesized that Epstein-Barr virus (EBV) has already infected the noncarcinomatous gastric mucosa before carcinogenesis of EBV-associated gastric carcinoma. However, the frequency and distribution of EBV infection in the gastric mucosa of chronic atrophic gastritis (CAG) are still unclear. To clarify these points, we evaluated the EBV DNA load in gastric mucosa with CAG.

METHODS

We tested samples from 35 CAG cases. Paired biopsy specimens from five sites of the stomach were obtained according to the Updated Sydney System. One of each pair of specimens was subjected to areal-time quantitative polymerase chain reaction (Q-PCR) assay to detect EBV. Q-PCR was performed using the LightCycler System (Roche, Mannheim, Germany). The other was subjected to hematoxylin and eosin (H&E) and Giemsa staining. The histological degree of CAG was graded according to the Updated Sydney System. To evaluate the surface distribution of gastric mucosal atrophic changes of CAG, we modified the endoscopic classification of Kimura and Takemoto.

RESULT

EBV DNA was detected in 65.7% (23 of 35 cases) of the gastric biopsy specimens of the cases examined. EBV DNA was detected most frequently (92.3%; 12 of 13 cases) in the cases with endoscopically moderate CAG (p < 0.01). There was a significant association between EBV detection and the presence of inflammatory cell infiltration and atrophy in the stomach with endoscopically moderate CAG.

CONCLUSION

EBV mainly infects the gastric mucosa of patients with moderate CAG.

Induction of Epstein-Barr virus latent membrane protein 1 by a lytic transactivator Rta

Latent membrane protein 1 (LMP1) of Epstein-Barr virus (EBV) is a transforming protein that affects multiple cell signaling pathways and contributes to EBV-associated oncogenesis. LMP1 can be expressed in some states of EBV latency, and significant induction of full-length LMP1 is also observed frequently during virus reactivation into the lytic cycle. It is still unknown how LMP1 expression is regulated during the lytic stage and whether any EBV lytic protein is involved in the induction of LMP1. In this study, we first identified that LMP1 expression is associated with the spontaneous virus reactivation in EBV-infected 293 cells and that its expression is a downstream event of the lytic cycle. We further found that LMP1 can be induced by ectopic expression of Rta, an EBV immediate-early lytic protein. The Rta-mediated LMP1 induction is independent of another immediate-early protein, Zta. Northern blotting and reverse transcription-PCR analysis revealed that Rta upregulates LMP1 at the RNA level. Reporter gene assays further demonstrated that Rta activates both the proximal and distal promoters of the LMP1 gene in EBV-negative cells. Both the amino and carboxyl termini of the Rta protein are required for the induction of LMP1. In addition, Rta transactivates LMP1 not only in epithelial cells but also in B-lymphoid cells. This study reveals a new mechanism to upregulate LMP1 expression, expanding the knowledge of LMP1 regulation in the EBV life cycle. Considering an equivalent case of Kaposi's sarcoma-associated herpesvirus, induction of a transforming membrane protein by a key lytic transactivator during virus reactivation is likely to be a conserved event for gammaherpesviruses.

Characterization of Epstein-Barr virus infection in a human signet ring cell gastric carcinoma cell line, HSC-39

In order to study the mechanism of Epstein-Barr virus (EBV) infection in gastric carcinoma cells, we characterized the EBV infection in signet ring cell line HSC-39, derived from a human gastric carcinoma. HSC-39 cells were highly susceptible to cell-free EBV infection by Akata and P3HR-1 EBV strains. EBV nuclear antigen (EBNA) and EBV-encoded small RNA (EBER) were detected in the infected cells. Akata and P3HR-1 EBV-infected cell clones were isolated by a limiting dilution technique. The Akata and P3HR-1 EBV-infected clones differed from each other in morphology and growth patterns. Akata EBV-infected clones had lower growth rates than did P3HR-1 EBV-infected clones in both liquid and soft agar mediums. Both the infected HSC-39 cells and the clones expressed EBNA1 and EBER, but did not express EBNA2, latent membrane protein (LMP) 1 and LMP2A. The Q promoter (p), but not the Cp/Wp for EBNA transcription, was active in the infected HSC-39 cells and all clones. No lytic infection was observed in either infected parental cells or any clones. Uninfected HSC-39 cells did not express a principal EBV receptor CD21; however, Akata but not P3HR-1 EBV-infected clones expressed low levels of CD21 mRNA. These results demonstrate that the cellular phenotypes of HSC-39 cells are altered by EBV infection in strain-specific manner. We propose the HSC-39 cell line as a model target for the study of the mechanism and significance of EBV infection in gastric carcinoma.

Epstein-Barr virus and cancer

EBV was the first human virus to be directly implicated in carcinogenesis. It infects >90% of the world's population. Although most humans coexist with the virus without serious sequelae, a small proportion will develop tumors. Normal host populations can have vastly different susceptibility to EBV-related tumors as demonstrated by geographical and immunological variations in the prevalence of these cancers. EBV has been implicated in the pathogenesis of Burkitt's lymphoma, Hodgkin's disease, non-Hodgkin's lymphoma, nasopharyngeal carcinoma, and lymphomas, as well as leiomyosarcomas arising in immunocompromised individuals. The presence of this virus has also been associated with epithelial malignancies arising in the gastric region and the breast, although some of this work remains in dispute. EBV uses its viral proteins, the actions of which mimic several growth factors, transcription factors, and antiapoptotic factors, to usurp control of the cellular pathways that regulate diverse homeostatic cellular functions. Recent advances in antiviral therapeutics, application of monoclonal antibodies, and generation of EBV-specific CTLs are beginning to show promise in the treatment of EBV-related disorders.

Epstein-Barr virus (EBV) SM protein induces and recruits cellular Sp110b to stabilize mRNAs and enhance EBV lytic gene expression

Promyelocytic leukemia protein (PML) nuclear bodies or nuclear domain 10s (ND10s) are multiprotein nuclear structures implicated in transcriptional and posttranscriptional gene regulation that are disrupted during replication of many DNA viruses. Interferon increases the size and number of PML nuclear bodies and stimulates transcription of several genes encoding PML nuclear body proteins. Moreover, some PML nuclear body proteins colocalize at sites of viral DNA synthesis and transcription. In this study, the relationship between lytic Epstein-Barr virus (EBV) replication and Sp110b, a PML nuclear body protein, was investigated. Sp110b is shown to physically and functionally interact with the EBV protein SM. SM is expressed early in the EBV replicative cycle and posttranscriptionally increases the level of target EBV lytic transcripts. SM bound to Sp110b via two distinct sites in Sp110b in an RNA-independent manner. SM also specifically induced expression of Sp110b during lytic EBV replication and in several cell types. Exogenous expression of Sp110b synergistically enhanced SM-mediated accumulation of intronless and lytic viral transcripts. This synergistic effect was shown to be promoter independent, posttranscriptional, and the result of increased stabilization of target transcripts. Finally, inhibiting Sp110b expression decreased accumulation of an SM-responsive lytic EBV transcript in EBV-infected cells. These findings imply that SM induces Sp110b expression, binds to Sp110b, and utilizes the recruited Sp110b protein to increase the stability of lytic EBV transcripts, indicating that Sp110b is a component of the cellular machinery that EBV utilizes to enhance lytic EBV replication.

Mechanism for induction of hydroxyurea resistance and loss of latent EBV genome in hydroxyurea-treated Burkitt's lymphoma cell line Raji

Hydroxyurea (HU), as an inhibitor of ribonucleotide reductase (RR) through interaction with the R2 component, has been used in the treatment of malignancies. Recently, therapeutic strategies in Epstein-Barr Virus (EBV)-targeted lymphoma have been reported. In order to study the effect of HU on EBV, infected Burkitt's lymphoma (BL) Raji cells were passaged in medium containing 50 microM HU for more than 2 months. EBV DNA was eliminated in about 40% of the cells in the HU-treated cultures. The cells were cloned from such cultures, and only EBV-positive clones could be isolated in 102 examined clones. No differences were observed in the EBV-latent state, EBV-gene expression, or cell growth between HU-untreated Raji cells and HU-treated clones. However, relative to parental Raji cells, the HU-treated Raji clones were almost eight times resistant to growth inhibition by HU according to the ID50 value, and the expression of the R2 component of RR increased more than two to three times. These results indicate that HU not only efficiently eliminates the EBV genome from Raji cells but also induces HU resistance. HU resistance was accompanied by over-expression of the R2 component of RR. However, the HU-resistant clones were sensitive to gemcitabine, another inhibitor of RR, and this seems highly relevant to chemotherapeutic combination in the use of these drugs.

Production of high-titer Epstein-Barr virus recombinants derived from Akata cells by using a bacterial artificial chromosome system

An Epstein-Barr virus (EBV) genome in Burkitt's lymphoma-derived cell line Akata was cloned into a bacterial artificial chromosome (BAC) vector. The BAC clone, designated AK-BAC, was rapidly and precisely modified by means of efficient homologous recombination in Escherichia coli. This system was used to produce recombinant EBVs with transgenes. An expression cassette of green fluorescent protein (GFP) was inserted into AK-BAC, and the resultant BAC clone, AK-BAC-GFP, was transfected into Akata cells. We found that transfected BAC plasmids efficiently formed episomes in EBV-positive Akata cells. Mixtures of wild-type and AK-BAC-GFP viruses were then produced and used to infect EBV-negative Akata cells. We obtained cell clones that harbored only AK-BAC-GFP but no wild-type episome. These cell clones produced infectious viruses after stimulating virus production, and the recombinant viruses of AK-BAC-GFP efficiently immortalized primary B lymphocytes. We further revised the method so that any kind of cDNA could be rapidly inserted into the unique I-PpoI site that had been artificially introduced into AK-BAC. The AK-BAC system will have a broad range of applications, such as genetic analyses of various viral gene products and development of viral vectors for human gene therapy.

Epstein-Barr virus association is rare in esophageal squamous cell carcinoma

BACKGROUND

A critical role of Epstein-Barr virus (EBV) in carcinogenesis of nasopharyngeal squamous cell carcinoma and gastric adenocarcinoma is strongly suspected. We analyzed the possible EBV association for Japanese squamous cell carcinoma (SCC)-dominant esophageal cancer cases.

METHODS

We retrospectively screened 36 surgically resected esophageal cancer lesions from 36 patients mainly with SCC using in situ hybridization (ISH) for EBV-encoded small RNA1 (EBER-1). EBV DNA analysis using real-time quantitative polymerase chain reaction (Q-PCR) was performed for three recent cases.

RESULTS

We found no EBER-1-positive cancer cell in any tested esophageal cancer lesion. There were many EBER-1-positive tumor-infiltrating lymphocytes in the basaloid SCC lesion and a small number of positive lymphocytes in the other five advanced SCC lesions (14.7% of SCC). One SCC lesion with a highcopy number of EBV DNA had EBER-1-positive lymphocytes.

CONCLUSIONS

EBV is rarely associated with esophageal SCC, and may appear through tumorinfiltrating lymphocytes in some advanced lesions.

Epstein-Barr virus, the TCL-1 oncogene and Burkitt's lymphoma

Epstein-Barr virus (EBV) is strongly implicated in the pathogenesis of several human malignancies, but notably in all endemic and some sporadic cases of Burkitt's lymphoma (BL). Although the virus's contribution to the development of BL remains unclear, evidence now suggests that a common feature of all BL tumours is the expression of the TCL-1 oncogene. A recent report shows that TCL-1 expression in virus-positive BL tumour cells is dependent on the presence of EBV. This finding suggests that the ability of EBV to induce TCL-1 would circumvent the need for the additional genetic or epigenetic changes that lead to the constitutive expression of this oncogene in EBV-negative BL tumours.

EBV-associated neoplasms: alternative pathogenetic pathways

We propose that there are two main classes of Epstein-Barr virus (EBV) associated lymphomas: primarily malignant Burkitt's Lymphoma (BL) and Hodgkin's Disease (HD), on one hand, and primarily benign lymphoproliferations, e.g., post-transplant lymphoproliferative disease (PTLD) on the other hand. PTLD may start as a benign lymphoproliferation which becomes malignant if out of T cell control for too long. Our discovery of a binding site for the oncoprotein c-Myc at a central position of the EBV genome favours a distinction of pathogenetic pathways or scenarios for the proposed lymphoma classes. In the first scenario nuclear maintenance of the EBV genome and activation of viral anti-apoptotic functions with the help of c-Myc are indispensable for the origin of malignant tumours (BL, HD) from the germinal centre B-cell. In the second scenario expression of the main viral transforming protein EBNA2 is essential for immortalisation and non-malignant morphological transformation of any (germinal centre derived or non-germinal centre) B-cell in the absence of T cell control. Although EBNA2 expression is permissible, under specific circumstances, in malignant B-cells, it is not required for oncogenesis.

Epstein-Barr virus provides a survival factor to Burkitt's lymphomas

Epstein-Barr virus (EBV) has been causally associated with at least five human malignancies. The exact contributions made by EBV to these cancers remain unknown. We demonstrate that one viral protein found in all EBV-associated malignancies, Epstein-Barr nuclear antigen 1 (EBNA-1), is required for survival of one of these cancers, EBV-positive Burkitt's lymphoma. Inhibition of EBNA-1 decreases survival of these tumor cells by inducing apoptosis. Expression of EBNA-1 in uninfected cells also can inhibit apoptosis induced by expression of p53 in the absence of the EBV genome. Our findings demonstrate that EBNA-1 is critical for the continued survival of EBV-associated Burkitt's lymphoma, and, by extension, for the other B cell tumors with which EBV is associated. Efficient inhibitors of EBNA-1's functions would likely prove useful in the therapy of EBV-associated malignancies.

Epstein-Barr virus nuclear antigen-1 and Myc cooperate in lymphomagenesis

The lymphomagenic action of myc genes in conjunction with Epstein-Barr virus nuclear antigen-1 (EBNA-1) have been examined using transgenic mice in several separate tests. Synergy between Myc and EBNA-1 in lymphomagenesis was revealed in a cross breed study where co-expression of transgenic myc and EBNA-1 led to a tumor latency period reduced significantly in some crosses. In the resulting bitransgenic tumors, expression of the Emu-myc genes was not affected by EBNA-1 expression. MoMLV was utilized as a transposon tag to activate cellular oncogenes by infection of EmuEBNA-1 mice. Rearrangement at the c-myc locus in B cell tumors from these mice again suggests a cooperative action between myc and EBNA-1. Tumors arising in EmuEBNA-1 mice typically showed a trisomy of chromosome 15, upon which the c-myc locus resides. Bitransgenic tumors (EBNA-1/c-myc) did not show trisomy 15. This raises the possibility that amplification of c-myc is factorial in the selection of trisomy 15 in these tumors. These data indicate that myc and EBNA-1 act cooperatively and are not redundant in lymphomagenesis. Expression of EBNA-1 by EBV may provide a selection pressure in addition to translocation of the c-myc locus in the genesis of endemic Burkitt's lymphoma (BL).

Rabbit model for human EBV-associated hemophagocytic syndrome (HPS): sequential autopsy analysis and characterization of IL-2-dependent cell lines established from herpesvirus papio-induced fatal rabbit lymphoproliferative diseases with HPS

Epstein-Barr virus-associated hemophagocytic syndrome (EBV-AHS) is often associated with fatal infectious mononucleosis or T-cell lymphoproliferative diseases (LPD). To elucidate the true nature of fatal LPD observed in Herpesvirus papio (HVP)-induced rabbit hemophagocytosis, reactive or neoplastic, we analyzed sequential development of HVP-induced rabbit LPD and their cell lines. All of the seven Japanese White rabbits inoculated intravenously with HVP died of fatal LPD 18 to 27 days after inoculation. LPD was also accompanied by hemophagocytic syndrome (HPS) in five of these seven rabbits. Sequential autopsy revealed splenomegaly and swollen lymph nodes, often accompanied by bleeding, which developed in the last week. Atypical lymphoid cells infiltrated many organs with a "starry sky" pattern, frequently involving the spleen, lymph nodes, and liver. HVP-small RNA-1 expression in these lymphoid cells was clearly demonstrated by a newly developed in situ hybridization (ISH) system. HVP-ISH of immunomagnetically purified lymphoid cells from spleen or lymph nodes revealed HVP-EBER1+ cells in each CD4+, CD8+, or CD79a+ fraction. Hemophagocytic histiocytosis was observed in the lymph nodes, spleen, bone marrow, and thymus. HVP-DNA was detected in the tissues and peripheral blood from the infected rabbits by PCR or Southern blot analysis. Clonality analysis of HVP-induced LPD by Southern blotting with TCR gene probe revealed polyclonal bands, suggesting polyclonal proliferation. Six IL-2-dependent rabbit T-cell lines were established from transplanted scid mouse tumors from LPD. These showed latency type I/II HVP infection and had normal karyotypes except for one line, and three of them showed tumorigenicity in nude mice. These data suggest that HVP-induced fatal LPD in rabbits is reactive polyclonally in nature.

T cell leukemia I oncogene expression depends on the presence of Epstein-Barr virus in the virus-carrying Burkitt lymphoma lines

We used a modified subtractive suppression hybridization to identify cellular genes that show altered expression in Burkitt lymphomas (BLs) in the presence of Epstein-Barr virus (EBV). Comparison of the gene expression patterns of an EBV-negative clone of the originally EBV-positive BL line Akata, with its Neo(R)-EBV derivative, revealed a significant difference in the expression of the T cell leukemia 1 oncogene (TCL-1). Subsequent expression studies showed that the original EBV-positive Akata line and the EBV-reconstituted derivative expressed high levels of TCL-1, whereas the EBV-negative variant showed only a low level of expression. Two other independently established EBV-positive BLs (Mutu and OMA) that have also thrown off EBV showed a similar decrease in TCL-1 expression after virus loss. Reinfection with Neo(R)-EBV restored the TCL-1 expression levels in the EBV loss variants to as high a level as the originally EBV-positive lines. High-resolution immunostaining showed that TCL-1 was localized in both the cytoplasm and the nucleus. Our findings suggest that high expression of TCL-1 is necessary for the development of the BL phenotype. In view of the fact that germinal center B cells, regarded as the progenitors of BL, do not express TCL-1, we suggest that constitutive expression of this oncogene occurs by genetic or epigenetic changes in the EBV-negative BLs. In the originally EBV-positive BLs, the ability of the virus to switch on TCL-1 expression would obviate this need.

Proteome analysis of Epstein-Barr virus-transformed B-lymphoblasts and the proteome database

The proteome is the entire protein complement of the genome expressed in a particular cell, tissue, or organism at a given time under a specific set of environmental conditions. Proteomics is a combinatorial methodology to comprehensively analyze the proteome. The general protocol of the expression proteomics consists of advanced methods of high-resolution protein separation, high-quality image analysis and high-throughput protein identification. Although Epstein-Barr virus-transformed B-lymphoblastoid cell lines (LCLs) have long been believed to be immortalized, recent studies have provided ample evidence that a large proportion of LCLs have limited life spans due to shortening of telomeres, and that part of them are truly immortalized by developing strong telomerase activity to maintain telomeres. Differential proteome analysis of pre- and post-immortal LCLs would provide a powerful tool to analyze proteins participating in the process of immortalization. We focus in this review on cumulative data of proteomic information on pre- and post-immortal LCLs.

The role of Epstein-Barr virus-encoded small RNAs (EBERs) in oncogenesis

Epstein-Barr virus (EBV)-encoded RNAs (EBERs) are the most abundant viral transcripts in latently EBV-infected cells. Recently, we found that EBERs play a key role in the maintenance of malignant phenotypes of Burkitt's lymphoma (BL) cells. They confer clonability in soft agarose, tumorigenicity in immunodeficient mice, resistance to apoptosis and induction of interleukin (IL)-10, which acts as an autocrine growth factor of BL cells. Furthermore, we demonstrated that EBERs confer resistance to interferon (IFN)-alpha-induced apoptosis by inhibition of double-stranded (ds) RNA-activated protein kinase (PKR), which is the key mediator of the antiviral effect of IFN-alpha. These studies provide a new notion that RNA molecules contribute to oncogenesis.

SH2D1A expression in Burkitt lymphoma cells is restricted to EBV positive group I lines and is downregulated in parallel with immunoblastic transformation

The SH2 domain containing SH2D1A protein has been characterized in relation to the X-linked lymphoproliferative disease (XLP), a primary immunodeficiency that leads to serious clinical conditions after Epstein-Barr virus (EBV) infection. The SH2D1A gene is mutated in the majority of XLP patients. We previously detected SH2D1A in activated T and NK cells, but not in B lymphocytes. We have found SH2D1A protein in Burkitt lymphoma (BL) lines, but only in those that carried EBV and had a Group I (germinal center) phenotype. All the EBV-carrying Group III (immunoblastic) and the EBV-negative BL lines tested were SH2D1A-negative. Motivated by these differences, we studied the impact of EBV and the cellular phenotype on SH2D1A expression. We approached the former question with BL sublines after both the loss of the virus and subsequent reinfection. We also tested original EBV-negative BL lines carrying transfected EBV genes, such as EBNA1, EBNA2, EBNA6, EBER1, 2 and LMP1, respectively. In our experiments, no direct relationship could be seen between EBV and SH2D1A expression. We modified the phenotype of the Group I BL cells by LMP1 transfection or CD40 ligation. The phenotypic changes, indicated by expression of immunoblastic markers, e.g., SLAM, were accompanied by downregulation of SH2D1A. It seems, therefore, that the presence of EBV and the phenotype of the cell together regulate SH2D1A expression in the BL cells. It is possible that SH2D1A is expressed in a narrow window of B cell development represented by germinal center cells.

Role of Epstein-Barr virus in Burkitt's lymphoma

We established an in vitro system representing BL-type EBV infection, which is characterized by expression of EBNA1, EBER, BARF0, and LMP2A, and absence of EBNA2 and LMP1 expression (Shimizu et al. 1994; Komano et al. 1998). Comparison of EBV-positive and -negative Akata cell clones revealed that EBV contributes to the malignant phenotype and resistance to apoptosis. This is clear evidence that EBV is not a passenger and plays a role in BL. Moreover, we found that EBERs are responsible for these phenotypes (Komano et al. 1999). In the transfection study, EBER-expressing Akata cell clones restored the malignant phenotype, resistance to apoptosis and upregulated expression of bcl-2 protein to a level comparable to the restoration rate of EBER expression compared with EBV-reinfected cell clones. Many RNAs are known to have catalytic functions; however, there has been no report describing an oncogenic RNA. This is the first paper that provides evidence that RNA polymerase III-transcribed virus-encoded small RNAs affect the malignant phenotype and resistance to apoptosis. Like Akata cells (Takada et al. 1991), all the BL cells possess a chromosomal translocation involving the c-myc locus, which results in constitutive activation of the c-myc gene (Klein 1981). In mammalian cells, deregulated expression of c-myc has been shown to contribute not only to tumorigenesis (Land et al. 1983) but also to induce apoptosis (Askew et al. 1991; Evan et al. 1992; Milner et al. 1993). Therefore, BL cells are predisposed to c-myc-induced apoptosis. Our data imply that EBV infection would upregulate expression of bcl-2 protein to protect cells from c-myc-induced apoptosis, and to allow c-myc to exert its oncogenic functions (Vaux et al. 1988; Brito-Babapulle et al. 1991; Bissonnette et al. 1992; Fanidi et al. 1992; Karsan et al. 1993; Mohammad et al. 1993; Oltvai et al. 1993; Marin et al. 1995). In this way bcl-2 might cooperate with c-myc in the development of BL (Fig. 5).

Epstein-Barr virus RNA confers resistance to interferon-alpha-induced apoptosis in Burkitt's lymphoma

We investigated whether Epstein--Barr virus (EBV) infection could counteract the antitumor effect of interferon (IFN)-alpha. EBV-negative subclones isolated from EBV-positive Burkitt's lymphoma (BL) cell lines Akata, Daudi and Mutu were found to fall into apoptosis after IFN-alpha treatment. On the other hand, EBV-positive counterparts exhibited striking resistance against IFN-alpha-induced apoptosis. Transfection of an individual EBV latent gene into EBV-negative BL cells revealed that EBV-encoded poly(A)(-) RNAs (EBERs) were responsible for IFN resistance. EBERs bound double-stranded (ds) RNA-activated protein kinase (PKR), a key mediator of the antiviral effect of IFN-alpha, and inhibited its phosphorylation. Transfection of dominant-negative PKR, which was catalytically inactive and could block phosphorylation of endogenous PKR, made EBV-negative BL cells resistant to IFN-alpha-induced apoptosis. Furthermore, EBERs did not bind mutant PKR, which was catalytically active but lacked dsRNA-binding activity, nor did they inhibit its phosphorylation. These results indicate that EBERs confer resistance to IFN-alpha-induced apoptosis via binding to PKR and inhibition of its phosphorylation. This is the first report that the virus counteracts IFN-induced apoptosis in virus-associated tumors.

The role of EBERs in oncogenesis

Epstein-Barr virus (EBV)-encoded small non-polyadenylated RNAs (EBERs) are the most abundant viral transcripts in latently EBV-infected cells. However, until recently, their roles in viral infection were totally unknown. It now appears that EBERs play a key role in maintaining the malignant phenotypes of Burkitt's lymphoma (BL) cells. The EBERs confer clonability in soft agarose, tumourigenicity in mice, and resistance to apoptosis against various stimuli in BL. Furthermore, EBERs induce transcription of interleukin-10, which acts as an autocrine growth factor of BL. These studies open the way toward the new concept that RNA molecules can act in oncogenesis.

Spontaneous reduction in Epstein-Barr virus (EBV) DNA copy number in EBV-infected epithelial cell lines

We found that spontaneous and 12-0-tetradecanoylphorbol-13-acetate-induced Epstein-Barr virus (EBV) reactivation occurred in short-term (ST)-cultured EBV-infected epithelial cell lines GT38 and GT39 after their establishment; however, it diminished in the long-term (LT)-cultured cells passaged for more than 2 years from ST-cultured cells. We hypothesized that the EBV reactivation may be related to the EBV DNA copy number in the cells. A higher level of EBV DNA content was detected in ST-cultured cells than in LT-cultured cells by Southern hybridization using an EBV DNA XhoI probe. Fluorescence in situ hybridization using EBV DNA BamHI W fragments showed that ST-cultured cells contained a higher EBV DNA copy number than that of LT-cultured cells. EBV DNA-negative cells were detected in small proportions in LT-cultured cells, but were undetected in ST-cultured cells. These results demonstrate that EBV genomes are not maintained stably in the cell lines, and some of them are lost in continuous passages of the cells. We discuss the mechanisms of reduction of EBV reactivation and EBV DNA in the cell lines.

From Burkitt's lymphoma to chronic active Epstein-Barr virus (EBV) infection: an expanding spectrum of EBV-associated diseases

Epstein-Barr virus (FBV) is one of 8 known human herpesviruses. EBV infection usually occurs in early childhood and is subclinical. However, primary infection in adolescence or adulthood causes infectious mononucleosis in approximately half of infected individuals. Recently, the spectrum of human diseases associated with EBV injection has increased, primarily due to methodological advances in EBV detection. Initially, EBV was isolated from a cultured Burkitt lymphoma cell line, and has been felt to be etiologically linked to the development of Burkitt lymphoma, as well as other human malignancies. This review mainly focuses on pathogenetic mechanisms, many of which remain enigmatic, for the various human diseases, which are considered to be associated with EBV injection.

Analysis of single EBER-positive and negative tumour cells in EBV-harbouring B-cell non-Hodgkin lymphomas

In situ hybridization for Epstein-Barr virus (EBV) encoded small nuclear RNAs (EBERs) is the method of choice for the detection of EBV infection at the single cell level. With the application of this technique it was shown that non-Hodgkin's lymphomas of B-cell type may be associated with an EBV infection of tumour cells. Interestingly, in many EBV-positive cases, only a proportion of the tumour cell population has been found to be EBER-positive. To clarify whether EBV is absent or whether EBER gene expression is downregulated in EBER-negative tumour cells, single EBER-positive and negative tumour cells were isolated from paraffin sections from four B-cell non-Hodgkin's lymphoma cases with partial EBER expression in the neoplastic cells. These single cells were then screened for the presence of EBV DNA by a nested single cell PCR. EBV DNA was undetectable in all but one of the 86 EBER-negative cells, whereas in the EBER-positive cells EBV-specific DNA amplificates could be generated following single cell PCR. This finding prompts the conclusion that the inability to detect EBERs in a proportion of tumour cells is not due to a down-regulation of gene expression but to a real absence of EBV from these cells. This partial absence of EBV is thought to be caused by a loss of the EBV episomes during cell division, rather than by infection of only a proportion of the tumour cells.

Replacement of the Epstein-Barr virus plasmid with the EBER plasmid in Burkitt's lymphoma cells

Transfection of an Epstein-Barr virus (EBV)-encoded plasmid containing EBER caused a substantial decrease in the level of plasmid containing EBV in Akata and Mutu Burkitt's lymphoma (BL) lines, but failed to do so in other BL lines. The results suggest that EBER could replace the role of EBV, but other EBV products also play a role in the growth of BL.

Roles of Epstein-Barr virus glycoproteins gp350 and gp25 in the infection of human epithelial cells

Epstein-Barr virus (EBV) is associated with various epithelial malignancies such as nasopharyngeal carcinoma and gastric carcinoma, and causes oral hairy leukoplakia, a productive EBV infection of the differentiated epithelium of the tongue. However, it is not clear by what mechanism EBV infects epithelial cells. We generated a recombinant EBV that expresses enhanced green fluorescent protein in order to monitor EBV entrance into epithelial cells quickly and quantitatively. Using this monitoring system, we examined the roles of gp350 and gp25 in EBV infection of epithelial cells by utilizing soluble forms of the gp350 and gp25 proteins. EBV infection of three of four examined epithelial cell lines, 293, NU-GC-3 and Lovo, was almost completely blocked by pretreatment of cells with a soluble form of gp350 (designated gp350Ig), and this blockage was dependent on the CD21-binding region of gp350. On the other hand, infection of the other epithelial cell line, AGS, was not inhibited at all by pretreatment with gp350Ig. Moreover, we found that a soluble form of gp25 (designated gp25Ig) preferentially bound to epithelial cells rather than B cells, and pretreatment of cells with gp25Ig substantially blocked EBV infection of some epithelial cells. These results indicate the existence of two distinct pathways in EBV infection of epithelial cells, a gp350-dependent pathway and a gp350-independent pathway, and that gp25 can play a role in the infection of some epithelial cells.

Growth transformation of primary epithelial cells with a NPC-derived Epstein-Barr virus strain

The Epstein-Barr virus (EBV) is associated with two major human epithelial malignancies, where it is likely to play a role in the malignant phenotype: undifferentiated nasopharyngeal carcinoma (100% of cases) and gastric carcinomas (about 10% of cases). We and others have obtained growth transformation of monkey kidney primary epithelial cells by transfection of viral DNA, especially with the BARF1 gene of EBV (Wei et al., 1997). We now report that the same type of primary epithelial cells can be growth-transformed using EBV particles derived from a nasopharyngeal carcinoma tumor line. Not only can these EBV-infected cells grow over 100 passages, escaping senescence, in contrast to their noninfected counterparts, but they can also survive and proliferate at very low cell density. Several subclones were characterized in terms of viral gene expression. All these clones gave a similar pattern, with detection of EBNA1 and BARF1 proteins but absence of LMP1. CD21, which is the main EBV receptor on B lymphocytes, was not expressed on parental monkey kidney epithelial cells nor on EBV-infected cell clones. This model of epithelial cell transformation will be useful for a better investigation of EBV functions critical for oncogenesis of epithelial cells.

Epstein-Barr virus infection and human malignancies

The Epstein-Barr virus (EBV) is a herpes virus which establishes a life-long persistent infection in over 90% of the human adult population world-wide. Based on its association with a variety of lymphoid and epithelial malignancies, EBV has been classified as a group 1 carcinogen by the International Agency for Research on Cancer. In this article we discuss the evidence supporting an aetiological role for EBV in the pathogenesis of human tumours. The biology of EBV infection will be described with special emphasis on viral transforming gene products. A brief survey of EBV-associated tumours is followed by a discussion of specific problems. Evidence is presented which suggests that failures of the EBV-specific immunity may play a role in the pathogenesis of EBV-associated tumours also in patients without clinically manifest immunodeficiencies. Finally, the timing of EBV infection in the pathogenesis of virus-associated malignancies is discussed. There is good evidence that EBV infection precedes expansion of the malignant cell populations in some virus-associated tumours. However, this is clearly not always the case and for some of these tumours there are indications that clonal genetic alterations may occur prior to EBV infection. Thus, whilst there is good evidence to suggest that EBV is a human carcinogen, its precise role(s) in the development of virus-associated human tumours requires clarification.

Role of Epstein-Barr virus-encoded latent membrane protein 2A on virus-induced immortalization and virus activation

To quantitatively evaluate the role of Epstein-Barr virus (EBV)-encoded latent membrane protein 2A (LMP2A) in immortalization of peripheral B-lymphocytes, we used the Akata cell system to generate an EBV recombinant in which the first exon of the LMP2A gene was disrupted. The results indicated that deletion of the LMP2A gene did not affect the immortalization efficiency of EBV in B-lymphocytes. Deletion of the LMP2A gene made EBV-transformed lymphocytes more permissive for virus replication in response to surface immunoglobulin cross-linking. On the other hand Akata cells, in which LMP2A expression was much lower than in EBV-transformed lymphocytes, were equally permissive for virus replication whether they were infected with wild EBV or LMP2A-knockout EBV. The results raise a question as to the role of LMP2A in inhibition of disruption of virus latency in vivo, where LMP2A expression has been expected to be low as in Akata cells.

Activation of TRAF5 and TRAF6 signal cascades negatively regulates the latent replication origin of Epstein-Barr virus through p38 mitogen-activated protein kinase

Latent Epstein-Barr virus (EBV) is maintained by the virus replication origin oriP that initiates DNA replication with the viral oriP-binding factor EBNA1. However, it is not known whether oriP's replicator activity is regulated by virus proteins or extracellular signals. By using a transient replication assay, we found that a low level of expression of viral signal transduction activator latent membrane protein 1 (LMP1) suppressed oriP activity. The binding site of the tumor necrosis factor receptor-associated factor (TRAF) of LMP1 was essential for this suppressive effect. Activation of the TRAF signal cascade by overexpression of TRAF5 and/or TRAF6 also suppressed oriP activity. Conversely, blocking of TRAF signaling with dominant negative mutants of TRAF5 and TRAF6, as well as inhibition of a downstream signal mediator p38 MAPK, released the LMP1-induced oriP suppression. Furthermore, activation of TRAF6 signal cascade by lipopolysaccharides (LPS) resulted in loss of EBV from Burkitt's lymphoma cell line Akata, and inhibition of p38 MAPK abolished the suppressive effect of LPS. These results suggested that the level of oriP activity is regulated by LMP1 and extracellular signals through TRAF5- and TRAF6-mediated signal cascades.

Epstein-Barr virus infection and human malignancies

The Epstein-Barr virus (EBV) is a herpes virus which establishes a life-long persistent infection in over 90% of the human adult population world-wide. Based on its association with a variety of lymphoid and epithelial malignancies, EBV has been classified as a group 1 carcinogen by the International Agency for Research on Cancer. In this article we discuss the evidence supporting an aetiological role for EBV in the pathogenesis of human tumours. The biology of EBV infection will be described with special emphasis on viral transforming gene products. A brief survey of EBV-associated tumours is followed by a discussion of specific problems. Evidence is presented which suggests that failures of the EBV-specific immunity may play a role in the pathogenesis of EBV-associated tumours also in patients without clinically manifest immunodeficiencies. Finally, the timing of EBV infection in the pathogenesis of virus-associated malignancies is discussed. There is good evidence that EBV infection precedes expansion of the malignant cell populations in some virus-associated tumours. However, this is clearly not always the case and for some of these tumours there are indications that clonal genetic alterations may occur prior to EBV infection. Thus, whilst there is good evidence to suggest that EBV is a human carcinogen, its precise role(s) in the development of virus-associated human tumours requires clarification.

Epstein-Barr virus infection and human malignancies

The Epstein-Barr virus (EBV) is a herpes virus which establishes a life-long persistent infection in over 90% of the human adult population world-wide. Based on its association with a variety of lymphoid and epithelial malignancies, EBV has been classified as a group 1 carcinogen by the International Agency for Research on Cancer. In this article we discuss the evidence supporting an aetiological role for EBV in the pathogenesis of human tumours. The biology of EBV infection will be described with special emphasis on viral transforming gene products. A brief survey of EBV-associated tumours is followed by a discussion of specific problems. Evidence is presented which suggests that failures of the EBV-specific immunity may play a role in the pathogenesis of EBV-associated tumours also in patients without clinically manifest immunodeficiencies. Finally, the timing of EBV infection in the pathogenesis of virus-associated malignancies is discussed. There is good evidence that EBV infection precedes expansion of the malignant cell populations in some virus-associated tumours. However, this is clearly not always the case and for some of these tumours there are indications that clonal genetic alterations may occur prior to EBV infection. Thus, whilst there is good evidence to suggest that EBV is a human carcinogen, its precise role(s) in the development of virus-associated human tumours requires clarification.

Possible involvement of EBV-mediated alpha-fodrin cleavage for organ-specific autoantigen in Sjogren's syndrome

A cleavage product of alpha-fodrin may be an important organ-specific autoantigen in the pathogenesis of Sjogren's syndrome (SS), but the mechanisms of alpha-fodrin cleavage remain unclear. Since EBV has been implicated in the pathogenesis of SS, we determined whether EBV activation could induce the SS-specific 120-kDa autoantigen alpha-fodrin. ZEBRA mRNA expression, a marker for activation of the lytic cycle of EBV, was found in the salivary gland tissues from SS patients, but not in those from control individuals. ZEBRA-expressing lymphoid cells were also found in the SS glands in double-stained immunohistochemistry. Furthermore, a significant link between production of Abs against 120-kDa alpha-fodrin and reactivated EBV Ag was found in sera from patients with SS, but not in those from control individuals. EBV-activated lymphoid cells showed specific alpha-fodrin cleavage to the expected 120-kDa fragments in vitro. Pretreatment with caspase inhibitors inhibited cleavage of alpha-fodrin. Thus, an increase in apoptotic protease activities induced by EBV reactivation may be involved in the progression of alpha-fodrin proteolysis in the development of SS.

Differential regulation of Epstein-Barr virus (EBV) latent gene expression in Burkitt lymphoma cells infected with a recombinant EBV strain

Epstein-Barr virus (EBV)-negative Burkitt lymphomas (BLs) can be infected in vitro with prototype EBV strains to study how the virus may affect the phenotype of tumor cells. Studies thus far have concentrated on the use of transforming B95-8 and nontransforming P3HR1 strains. Immunological and phenotypic differences between the sublines infected with these two strains were reported. The majority of these differences, if not all, can be attributed to the lack of EBNA-2 coding sequences in the P3HR1 strain. The recent development of a selectable Akata strain has opened up new possibilities for infecting epithelial and T cells as well. We infected five EBV-negative BL lines with the recombinant Akata virus. Our results indicate that the infected cell lines BL28, Ramos, and DG75 express EBNA-1, EBNA-2, and LMP1, the viral proteins associated with type III latency, and use both YUK and QUK splices. In contrast, two EBV-negative variants of Akata and Mutu when reinfected displayed restricted type I latency and expressed only EBNA-1. All clones of infected Mutu cells used the QUK splice exclusively. The usage of Qp was observed in a majority of Akata clones. Some Akata clones, however, were found to have double promoter usage (Qp and C/Wp) but at 4 months after infection did not express EBNA-2. The results demonstrate differential regulation of EBV latency in BLs with the same recombinant viral strain and suggest that the choice of latency type may be cell dependent. The restricted latency observed for infected Akata and Mutu cells indicates that a BL may opt for type I latency in the absence of immune pressure as well.

Activators of the Epstein-Barr virus lytic program concomitantly induce apoptosis, but lytic gene expression protects from cell death

Expression of the lytic cycle genes of Epstain-Barr virus (EBV) is induced in type I Burkitt's lymphoma-derived cells by treatment with phorbol esters (e.g., phorbol myristate acetate [PMA]), anti-immunoglobulin, or the cytokine transforming growth factor beta (TGF-beta). Concomitantly, all these agents induce apoptosis as judged by a sub-G1 fluorescence-activated cell sorter (FACS) profile, proteolytic cleavage of poly(ADP-ribose) polymerase (PARP) and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) staining. However, caspase activation is not required for induction of the lytic cycle since the latter is not blocked by the caspase inhibitor ZVAD. Furthermore, not all agents that induce apoptosis in these cultures (for example, cisplatin and ceramide) induce the EBV lytic programme. Although it is closely associated with the lytic cycle, apoptosis is neither necessary nor sufficient for its activation. Multiparameter FACS analysis of cultures treated with PMA, anti-Ig, or TGF-beta revealed BZLF1-expressing cells distributed in different phases of the cell cycle according to which inducer was used. However, BZLF1-positive cells did not appear to undergo apoptosis and accumulate with a sub-G1 DNA content, irrespective of the inducer used. This result, which suggests that lytic gene expression is protective, was confirmed and extended by immunofluorescence staining doubled with TUNEL analysis. BZLF1- and also gp350-expressing cells were almost always shown to be negative for TUNEL staining. Similar experiments using EBV-positive and -negative subclones of Akata BL cells carrying an episomal BZLF1 reporter plasmid confirmed that protection from apoptosis was associated with the presence of the EBV genome. Finally, treatment with phosphonoacetic acid or acyclovir prior to induction with PMA, anti-Ig, or TGF-beta blocked the protective effect in Mutu-I cells. These data suggest that a late gene product(s) may be particularly important for protection against caspase activity and cell death.

Role of bcl-2 in Epstein-Barr virus-induced malignant conversion of Burkitt's lymphoma cell line Akata

We have demonstrated that Epstein-Barr virus (EBV) confers enhanced growth capability in soft agarose, tumorigenesis in the SCID mouse, and resistance to apoptosis in the Burkitt's lymphoma cell line Akata. Subsequently, we have shown that EBV-encoded small RNAs (EBERs) are responsible for these phenotypes. We constantly observed the upregulation of bcl-2 oncoprotein expression upon EBV infection and expression of EBERs. To test whether these phenotypes were due to the upregulation of bcl-2 expression, we introduced bcl-2 into EBV-negative Akata cells at various levels encompassing the range at which EBV-positive cells expressed it. As cells expressed bcl-2 at higher levels, they became more capable of growing in soft agarose and became resistant to apoptosis. However, clones expressing bcl-2 at a higher level than EBV-positive Akata cells were negative in the tumorigenesis assay in the SCID mouse. On the other hand, introduction of bax into EBV-positive Akata cells reduced the resistance to apoptosis; however, it failed to reduce the growth capability in soft agarose. These data indicate that EBV targets not only bcl-2, but also an unknown pathway(s) to enhance the oncogenic potential of Akata cells.

Epstein-Barr virus-encoded poly(A)(-) RNA supports Burkitt's lymphoma growth through interleukin-10 induction

Akata and Mutu cell lines are derived from Burkitt's lymphoma (BL) and retain the in vivo phenotype of Epstein-Barr virus (EBV) expression that is characterized by expression of EBV-determined nuclear antigen 1 (EBNA1), EBV-encoded RNAs (EBERs) and transcripts from the BAM:HI A region (BARF0). We found that EBV-positive Akata and Mutu cell clones expressed higher levels of interleukin (IL)-10 than their EBV-negative subclones at the transcriptional level. Transfection of an individual EBV latent gene into EBV-negative Akata cells revealed that EBERs were responsible for IL-10 induction. Recombinant IL-10 enabled EBV-negative Akata cells to grow in low (0.1%) serum conditions. On the other hand, growth of EBV-positive Akata cells was blocked by treatment either with an anti-IL-10 antibody or antisense oligonucleotide against IL-10. EBV-positive BL biopsies consistently expressed IL-10, but EBV-negative BL biopsies did not. These results suggest that IL-10 induced by EBERs acts as an autocrine growth factor for BL. EBERs, EBER1 and EBER2, are non-polyadenylated RNAs and are 166 and 172 nucleotides long, respectively. The present findings indicate that RNA molecules could regulate cell growth.

Epstein-Barr virus small RNAs potentiate tumorigenicity of Burkitt lymphoma cells independently of an effect on apoptosis

The tumorigenic potential of the Burkitt lymphoma (BL) cell line Akata is dependent on the restricted latency program of Epstein-Barr virus (EBV) that is characteristically maintained in BL tumors. Within these cells, EBV-mediated inhibition of apoptosis correlates with an up-regulation of BCL-2 levels in concert with a down-regulation in c-MYC expression that occurs under growth-limiting conditions. Here we addressed whether EBV's effects on apoptosis and tumorigenicity are mediated by the EBV small RNAs EBER-1 and EBER-2. Stable expression of the EBERs in EBV-negative Akata BL cells, at levels comparable to those in EBV-positive cells, significantly enhanced the tumorigenic potential of EBV-negative BL cells in SCID mice, but did not fully restore tumorigenicity relative to EBV-positive Akata cells. Furthermore, wild-type or greater levels of EBER expression in EBV-negative Akata cells did not promote BL cell survival. These data therefore suggest that EBV can contribute to BL through at least two avenues: an EBER-dependent mechanism that enhances tumorigenic potential independent of a direct effect on apoptosis, and a second mechanism, mediated by an as-yet-unidentified EBV gene(s), that offsets the proapoptotic consequences of deregulated c-MYC in BL.

Latent membrane protein 2A-mediated effects on the phosphatidylinositol 3-Kinase/Akt pathway

Epstein-Barr virus (EBV) latent membrane protein 2A (LMP2A) is expressed on the membranes of B lymphocytes and blocks B-cell receptor (BCR) signaling in EBV-transformed B lymphocytes in vitro. The phosphotyrosine motifs at positions 74 or 85 and 112 within the LMP2A amino-terminal domain are essential for the LMP2A-mediated block of B-cell signal transduction. In vivo studies indicate that LMP2A allows B-cell survival in the absence of normal BCR signals. A possible role for Akt in the LMP2A-mediated B-cell survival was investigated. The protein kinase Akt is a crucial regulator of cell survival and is activated within B lymphocytes upon BCR cross-linking. LMP2A expression resulted in the constitutive phosphorylation of Akt, and this LMP2A effect is dependent on phosphatidylinositol 3-kinase activity. In addition, recruitment of Syk and Lyn protein tyrosine kinases (PTKs) to tyrosines 74 or 85 and 112, respectively, are critical for LMP2A-mediated Akt phosphorylation. However, the ability of LMP2A to mediate a survival phenotype downstream of Akt could not be detected in EBV-negative Akata cells. This would indicate that LMP2A is not responsible for EBV-dependent Burkitt's lymphoma cell survival.

Epstein-Barr virus lacking glycoprotein gp85 cannot infect B cells and epithelial cells

To evaluate whether the BXLF2 gene of Epstein-Barr virus (EBV), which codes gp85 protein, is essential for infection of B cells and epithelial cells, we analyzed the infectivity of an EBV recombinant lacking gp85. The cells that were infected with the BXLF2-disrupted virus were unable to express gp85 proteins that could be detected by mouse monoclonal antibody E1D1, specific for gp85/gp25 complexes. The BXLF2-disrupted EBV had the ability to attach to, but not infect, B cells. On the other hand, the same virus failed to bind to and infect NU-GC-3, a human gastric adenocarcinoma cell line that is susceptible to EBV infection. The results indicate that the gp85 is used for infection of not only B cells but also epithelial cells and suggest that the gp85 is necessary for attaching the virus to epithelial cells.

Epstein-Barr virus and gastric carcinoma

The Epstein-Barr virus (EBV) is detected in the tissue of about 10% of gastric carcinoma cases throughout the world. In each case, 100% of carcinoma cells are infected with EBV. Analysis of EBV in carcinoma biopsies indicates that carcinoma is formed by the proliferation of a single EBV infected cell. These findings suggest that EBV plays an important role in the development of EBV positive gastric carcinomas. The EBV genes expressed are EBV determined nuclear antigen 1 (EBNA1), two small non-polyadenylated RNAs known as EBER1 and EBER2, and the transcripts from the BamHI-A region (BARF0); in addition, some cases also express a small amount of latent membrane protein 2A (LMP2A). Epithelial cells are refractory to EBV infection in vitro. This has hampered the study of the role of EBV in epithelial malignancies. The use of recombinant EBV carrying a selectable marker has enabled this difficulty to be overcome. EBV infected cell clones can be obtained from most carcinoma cell lines examined, and it was found that cell to cell contact was an efficient mode of EBV infection. Furthermore, it was possible to immortalize primary gastric epithelial cells by EBV infection. The cells expressed identical EBV genes to those typically seen in EBV positive gastric carcinoma, and showed accelerated malignant properties, including growth in soft agarose and tumorigenicity in severe combined immunodeficient (SCID) mice. These results suggest that EBV contributes to the maintenance of the malignant phenotype of EBV positive gastric carcinoma.

Discrepancies in Epstein-Barr virus association at presentation and relapse of classical Hodgkin's disease: impact on pathogenesis

BACKGROUND

Though Epstein-Barr virus (EBV) has been linked to classical Hodgkin's disease (cHD), only a proportion of cHD cases show EBV-association. While there has been evidence to suggest a crucial role for EBV in the early phase of cHD evolution, we are unclear whether continued presence of EBV is essential for the maintenance of the neoplasm. We have addressed this issue by investigating the EBV-association in paired samples of cHD obtained at presentation and relapse.

MATERIALS AND METHODS

We have analysed lymph node biopsy samples from 23 cases of cHD at presentation and relapse. In situ hybridization with EBER-1 probe and immunostaining with anti latent membrane protein-1 (LMP-1) antibody was performed on the paraffin sections. PCR for EBNA 3C gene was performed for EBV subtype analysis on the DNA extracted from paraffin sections.

RESULTS

EBV-association was documented in both the presentation and relapse samples of 14 cases. One case showed loss of EBV-association at relapse. PCR analysable DNA was obtained from both presentation and relapse samples in four of the EBV-associated cases. The EBNA 3C amplimer corresponded to type A strain of EBV in all the samples.

CONCLUSION

Loss of EBV-association between presentation and relapse seen in one case implies a hit and run mechanism in EBV-induced lymphomagenesis. Though EBV may be essential early in the evolution of cHD, it may not be required for maintenance of the neoplastic clone. Our study also brings out a speculation that a proportion of EBV-negative cHD could represent loss of EBV in the tumour prior to clinical presentation. Alternatively, an unidentified lymphotropic virus other than EBV might play a pathogenetic role in EBV-negative cHD.

Cutaneous lymphoproliferative disorders associated with Epstein-Barr virus infection: a clinical overview

Epstein Barr virus (EBV) infection is implicated in various kinds of neoplasms including certain types of cutaneous T or natural killer (NK) cell proliferative disorders. Although a pathogenic role of EBV infection is not clear, some EBV gene products expressed during a latency phase were found to have biological properties leading to cellular gene expression and immortalization. Furthermore, EBV can use an array of strategies to evade host immune responses, and maintain the latent infection. EBV-associated cutaneous lymphoproliferative disorders are prevalent in Asia, and less frequent in western countries where infectious mononucleosis is common in adolescents and young adults. This review introduces recent advances on the mechanism of EBV infection, highlighting unique clinicopathologic manifestations of EBV-associated cutaneous lymphoproliferative disorders.

Epstein-Barr virus and Hodgkin's disease

Approximately 40% to 50% of cases of Hodgkin's disease occurring in Western populations are associated with the Epstein-Barr virus (EBV). In these cases, EBV is found in the neoplastic elements, the Reed-Sternberg and Hodgkin's cells. EBV is probably not present in all cases, but neither have any other viruses been found in the cases that are EBV-negative. EBV may play a role in the pathogenesis of Hodgkin's disease by the activation of anti-apoptotic factors in a premalignant germinal center B-lymphocyte. Regardless of their role in etiology or pathogenesis, EBV-latent antigens may represent a target for possible immune therapy.

An animal model for Epstein-Barr virus (EBV)-associated lymphomagenesis in the human: malignant lymphoma induction of rabbits by EBV-related herpesvirus from cynomolgus

It is very important to develop and analyze animal models of Epstein-Barr virus (EBV)-associated tumors in the human. However, only a few reports on the animal models of EBV infection have been reported. Here we review those previous models and describe the details on our newly developed rabbit model of malignant lymphoma induced by EBV-related virus from cynomolgus. In brief, Si-IIA-EBV or Cyno-EBV induced T-cell lymphomas in rabbits inoculated intravenously (77-90%), orally (82-89%), subcutaneously (3/3) and intraperitoneally (2/3) about 2-5 months later. EBV-DNA was detected in peripheral blood by polymerase chain reaction 2 days after oral inoculation of Cyno-EBV while antiviral capsid antigen immunoglobulin G (IgG) was raised 3 weeks after the inoculation. Rabbit lymphomas and their cell lines contained EBV-DNA and expressed EBV-encoded small RNA-1 and EBV-associated nuclear antigen. Rabbit lymphoma cell lines, some of which have specific chromosomal abnormality, showed tumorigenicity in nude mice. The significance and further research subjects of this animal model will be discussed. We believe that the present rabbit model of lymphoma with specific chromosomal abnormalities is very useful for clarifying the role of EBV in human EBV-associated lymphoma and provides a means for studying prophylactic and therapeutic regimens.

Interferon regulatory factor 7 is induced by Epstein-Barr virus latent membrane protein 1

Infection by Epstein-Barr virus (EBV) generates several types of latency with different profiles of gene expression but with expression of Epstein-Barr nuclear antigen 1 (EBNA-1) in common. The BamHI Q promoter (Qp) is used for the transcription of EBNA-1 mRNA in type I latency, which is an EBV infection state exemplified by Burkitt's lymphoma (BL). However, Qp is inactive in type III latency, and other promoters (C/Wp) are used for transcription of EBNA-1, which raises the question of how usage of these promoters is governed. Interferon (IFN) regulatory factor 7 (IRF-7) was identified first as a negative regulator of Qp. Expression of IRF-7 is associated with EBV type III latency, where Qp is inactive, but not with type I latency, raising the possibility that a viral gene product(s) expressed in type III latency might induce IRF-7 and repress Qp. Here, detailed analysis of the expression of IRF-7 revealed that it is associated with the expression of EBV latent membrane protein 1 (LMP-1) and that LMP-1 stimulates the expression of IRF-7 in type III latency in which Qp is inactive. In contrast, LMP-1 is not expressed in type I latency cells in which Qp is active. LMP-1 represses the constitutive activity of Qp reporter constructs. Mutational analysis of Qp reporter constructs revealed that the Qp IFN-stimulated response element (ISRE) is essential for the repression by LMP-1. Furthermore, LMP-1 reduced EBNA-1 mRNA derived from Qp only in type I cells in which IRF-7 could be induced. Finally, IFN-alpha, but not IFN-gamma, repressed endogenous Qp activity, which is consistent with the ability of IFN-alpha to induce IRF-7. Thus, IRF-7 may mediate repression of Qp by LMP-1. The induction of IRF-7 by LMP-1 may be relevant to the silencing of Qp in EBV type III latency.

Histone acetylation and reactivation of Epstein-Barr virus from latency

Induction of the viral BZLF1 gene has previously been shown to be one of the first steps in the reactivation of Epstein-Barr virus (EBV). Using an EBV oriP episomal vector system, we have reconstituted the regulation of the promoter for BZLF1 on stably transfected episomes, mapped promoter elements required for that regulation, and investigated mechanisms that may control the switch between latency and the lytic cycle. Changes in histone acetylation at the promoter for the BZLF1 gene appear to be a key part of the reactivation mechanism of this herpesvirus.