Coupled transcription of Epstein-Barr virus latent membrane protein (LMP)-1 and LMP-2B genes in nasopharyngeal carcinomas

Dexamethasone prevents the Epstein-Barr virus induced epithelial-mesenchymal transition in A549 cells

Clinical data have shown that pulmonary interstitial fibrosis is likely to occur in the later stages of viral pneumonia. While viral infections are thought to cause chronic pulmonary interstitial inflammation and pulmonary fibrosis, it remains unclear if they promote pulmonary fibrosis by epithelial-mesenchymal transition (EMT). In this study, human epithelial cell line A549 has been used to model the infection of the Epstein-Barr virus (EBV) and the respiratory syncytial virus (RSV). Their differences were compared and the possible infection mechanisms analyzed by randomly assigning cells to one of five treatments. Exposure of the LMP1 is thought to be the key gene during EBV-induced EMT in the A549 cells. Enzyme-linked immunosorbent assay analysis revealed that the EBV infection was associated with the induction of a number of cytokines (interleukin-8 [IL-8], IL-13, tumor necrosis factor-α, and transforming growth factor-β) and dexamethasone (DXM) could significantly prevent the phenotypic changes, and partly the mechanisms related with the IL-13 pathway. Surprisingly, different results were seen with the RSV infection as the A549 cells still displayed an epithelial morphology but the levels of E-cadherin, α-SMA, vimentin, and fibronectin did not change. This is the first study demonstrating the different reactions induced by different viruses, and the protective effects of DXM on the EBV-induced EMT in the A549 cells by partially inhibiting the IL-13 pathway. These findings suggest a novel mechanism, by which DXM or anti-IL-13 may delay the progression of pulmonary fibrosis by preventing the progress of EBV-induced EMT.

Epstein-Barr virus latent infection and BAFF expression in B cells in the multiple sclerosis brain: implications for viral persistence and intrathecal B-cell activation

A cardinal feature of multiple sclerosis (MS) is the persistent intrathecal synthesis of antibodies. Our previous finding that a large fraction of B cells infiltrating the MS brain are infected with Epstein-Barr virus (EBV) raises the possibility that this virus, because of its ability to establish a latent infection in B cells and interfere with their differentiation, contributes to B-cell dysregulation in MS. The aim of this study was to gain further insight into EBV latency programs and their relationship to B-cell activation in the MS brain. Immunohistochemical analysis of postmortem MS brain samples harboring large EBV deposits revealed that most B cells in white matter lesions, meninges, and ectopic B-cell follicles are CD27+ antigen-experienced cells and coexpress latent membrane protein 1 and latent membrane protein 2A, 2 EBV-encoded proteins that provide survival and maturation signals to B cells. By combining laser-capture microdissection with preamplification reverse transcription-polymerase chain reaction techniques, EBV latency transcripts (latent membrane protein 2A, EBV nuclear antigen 1) were detected in all MS brain samples analyzed. We also found that B cell-activating factor of the tumor necrosis factor family is expressed in EBV-infected B cells in acute MS lesions and ectopic B-cell follicles. These findings support a role for EBV infection in B-cell activation in the MS brain and suggest that B cell-activating factor of the tumor necrosis factor family produced by EBV-infected B cells may contribute to this process resulting in viral persistence and, possibly, disruption of B-cell tolerance.

Analysis of Epstein-Barr virus latent gene expression in endemic Burkitt's lymphoma and nasopharyngeal carcinoma tumour cells by using quantitative real-time PCR assays

Studies of Epstein-Barr virus (EBV)-positive cell lines have identified several forms of virus latency, but the patterns of virus gene expression in EBV-positive tumour cells appear more variable. However, it is unclear to what extent these differences merely reflect the increased sensitivities of different detection methods. Here, the design and validation of novel real-time RT-PCR assays to quantify relative levels of EBV transcripts are described. When the new assays were used to screen a collection of endemic Burkitt's lymphoma tumours, abundant Qp-driven EBNA1 expression was found, whereas the other latent transcripts (with the exception of LMP2A) were either absent or detectable only at trace levels. Analysis of 12 nasopharyngeal carcinoma biopsies revealed significant levels of EBNA1 and LMP2A transcripts in almost every case but, in contrast to previous reports, LMP1 expression was undetectable. These new quantitative assays may help to provide a clearer picture of EBV gene expression in tumour material.

Epigenotypes of latent herpesvirus genomes

Epigenotypes are modified cellular or viral genotypes which differ in transcriptional activity in spite of having an identical (or nearly identical) DNA sequence. Restricted expression of latent, episomal herpesvirus genomes is also due to epigenetic modifications. There is no virus production (lytic viral replication, associated with the expression of all viral genes) in tight latency. In vitro experiments demonstrated that DNA methylation could influence the activity of latent (and/or crucial lytic) promoters of prototype strains belonging to the three herpesvirus subfamilies (alpha-, beta-, and gamma-herpesviruses). In vivo, however, DNA methylation is not a major regulator of herpes simplex virus type 1 (HSV-1, a human alpha-herpesvirus) latent gene expression in neurons of infected mice. In these cells, the promoter/enhancer region of latency-associated transcripts (LATs) is enriched with acetyl histone H3, suggesting that histone modifications may control HSV-1 latency in terminally differentiated, quiescent neurons. Epstein-Barr virus (EBV, a human gamma-herpesvirus) is associated with a series of neoplasms. Latent, episomal EBV genomes are subject to host cell-dependent epigenetic modifications (DNA methylation, binding of proteins and protein complexes, histone modifications). The distinct viral epigenotypes are associated with distinct EBV latency types, i.e., cell type-specific usage of latent EBV promoters controlling the expression of latent, growth transformation-associated EBV genes. The contribution of major epigenetic mechanisms to the regulation of latent EBV promoters is variable. DNA methylation contributes to silencing of Wp and Cp (alternative promoters for transcripts coding for the nuclear antigens EBNA 1-6) and LMP1p, LMP2Ap, and LMP2Bp (promoters for transcripts encoding transmembrane proteins). DNA methylation does not control, however, Qp (a promoter for EBNA1 transcripts only) in lymphoblastoid cell lines (LCLs), although in vitro methylated Qp-reporter gene constructs are silenced. The invariably unmethylated Qp is probably switched off by binding of a repressor protein in LCLs.

High frequency of latent membrane protein-1 30-bp deletion variant with specific single mutations in Epstein-Barr virus-associated nasopharyngeal carcinoma in Moroccan patients

Latent membrane protein 1 (LMP-1) is an Epstein-Barr virus-encoded oncoprotein expressed in approximately 50-70% of nasopharyngeal carcinoma (NPC). Previous studies have shown that NPC-derived LMP-1 variants carrying 30 bp deletion and specific mutations in the 3'C-terminal region confer high oncogenic potential and a weak immunogenicity. Although numerous polymorphism studies of LMP-1 have been carried out so far in the Asian population with NPC, very little is known in this regard on NPC patients from Northern Africa where there is a significantly high occurrence of this tumor. In our study, we examined the frequency of different LMP-1 sequence variants derived from Moroccan NPC patients. As compared to healthy donors, NPC patients showed a high prevalence of the 30bp deletion variant of LMP-1 (i.e. 84% vs. 36%; p<0.0005). Moreover, the del-LMP-1 variant derived from NPC tumors shared identical amino acid substitutions at positions 322, 334, 338, 352 and 366 with the Mediterranean (Med) variant, whereas those derived from peripheral blood mononuclear cells (PBMC) had similar mutation pattern as China1 variant. Additional mutations within the 342-352 regions (identified in LMP-1 variants without deletion derived from NPC tumors) were not found in healthy donors' PBMC. Our results support the assumption that the distribution of LMP-1 variants in NPC tumors co-segregate with geographic regions. Indeed, Med variant is found more frequently in tumors from NPC Moroccan patients, whereas China1 variant is more prevalent in tumors from NPC patients in endemic regions for NPC.

EBV latent membrane protein 1 abundance correlates with patient age but not with metastatic behavior in north African nasopharyngeal carcinomas

Background

Undifferentiated nasopharyngeal carcinomas are rare in a majority of countries but they occur at a high incidence in South China and to a lesser extent in North Africa. They are constantly associated with the Epstein-Barr virus (EBV) regardless of patient geographic origin. In North Africa, the distribution of NPC cases according to patient age is bi-modal with a large group of patients being around 50 years old (80%) and a smaller group below 25 years old. We and others have previously shown that the juvenile form of NPC has distinct biological characteristics including a low amount of p53 and Bcl2 in the tumor tissue and a low level of anti-EBV IgG and IgA in the peripheral blood.

Results

To get more insight on potential oncogenic mechanisms specific of these two forms, LMP1 abundance was assessed in 82 NPC patients of both groups, using immuno-histochemistry and semi-quantitative evaluation of tissue staining. Serum levels of anti-EBV antibodies were simultaneously assessed. For LMP1 staining, we used the S12 antibody which has proven to be more sensitive than the common anti-LMP1 CS1-4 for analysis of tissue sections. In all NPC biopsies, at least a small fraction of cells was positively stained by S12. LMP1 abundance was strongly correlated to patient age, with higher amounts of the viral protein detected in specimens of the juvenile form. In contrast, LMP1 abundance was not correlated to the presence of lymph node or visceral metastases, nor to the risk of metastatic recurrence. It was also independent of the level of circulating anti-EBV antibodies.

Conclusion

The high amount of LMP1 recorded in tumors from young patients confirms that the juvenile form of NPC has specific features regarding not only cellular but also viral gene expression.

Expression of Epstein-Barr virus genes in EBV-associated gastric carcinomas

AIM: To understand the expression of latent and lytic genes of Epstein-Barr virus (EBV) in EBV-associated gastric carcinoma (EBVaGC) and to explore the relationship between EBV-encoded genes and development of EBVaGC at molecular level.

METHODS: One hundred and seventy-two gastric carcinoma tissues and 172 corresponding para-carcinoma tissues were tested for EBV genome by polymerase chain reaction (PCR)-Southern blotting. EBV-encoded small RNA (EBER) 1 of the PCR positive specimens was detected by in situ hybridization (ISH). Gastric carcinomas with positive EBER1 signals were classified as EBVaGCs. RT-PCR and Southern hybridization were applied to the detection of expression of nuclear antigen (EBNA) promoters (Qp, Wp and Cp), EBNA 1 and EBNA 2, latent membrane proteins (LMP) 1, 2A and 2B and lytic genes (immediate early genes BZLF1 and BRLF1, early genes BARF1 and BHRF1, late genes BcLF1 and BLLF1) in EBVaGCs.

RESULTS: Eleven EBV positive samples existed in gastric carcinoma tissues (6.39%). No EBV positive sample was found in corresponding para-carcinoma tissues. The difference between EBV positivity in carcinoma tissues and corresponding para-carcinoma tissues was significant (χ² = 9.0909, P = 0.0026). Transcripts of Qp and EBNA1 were detected in all the 11 EBVaGCs, while both Wp and Cp were silent. EBNA2, LMP1 and LMP2B mRNA were absent in all the cases, while LMP2A mRNA was detected in 4 of the 11 cases. Of the 11 EBVaGCs, 7 exhibited BcLF1 transcripts and 2 exhibited BHRF1 transcripts. The transcripts of BZLF1 and BARF1 were detected in 5 cases, respectively. No BLLF1 and BRLF mRNA were detected.

CONCLUSION: The latent pattern of EBV in gastric carcinoma corresponds to the latency I/II. Some lytic infection genes are expressed in EBVaGCs tissues. BARF1 and BHRF1 genes may play an important role in tumorigenesis of gastric carcinoma.

The Epstein-Barr virus-encoded LMP2A and LMP2B proteins promote epithelial cell spreading and motility

The frequent expression of latent membrane proteins LMP2A and LMP2B in Epstein Barr virus (EBV)-associated tumors suggests that these proteins play a role in EBV-induced epithelial cell growth transformation. Expression of LMP2A and LMP2B had no effect on the morphology of squamous epithelial cells in monolayer culture, but their expression was associated with an increased capacity to spread and migrate on extracellular matrix. Although the mechanisms by which LMP2A and LMP2B promote cell spreading and motility are unclear, the use of selective pharmacological inhibitors has established a role for tyrosine kinases in this phenotype but ruled out contributions of phosphatidylinositol 3-kinase, extracellular signal-regulated kinase/mitogen-activated protein kinase, and protein kinase C. The ability of LMP2B to induce a phenotype that is virtually indistinguishable from that of LMP2A suggests that regions of the LMP2 protein in addition to the cytosolic amino terminus are capable of inducing phenotypic effects in epithelial cells. Thus, rather than serving to modulate the activity of LMP2A, LMP2B may directly engage signaling pathways to influence epithelial cell behavior such as cell adhesion and motility.

C-terminal domain of the Epstein-Barr virus LMP2A membrane protein contains a clustering signal

The latency-regulated transmembrane protein LMP2A interferes with signaling from the B-cell antigen receptor by recruiting the tyrosine kinases Lyn and Syk and by targeting them for degradation by binding the cellular E3 ubiquitin ligase AIP4. It has been hypothesized that this constitutive activity of LMP2A requires clustering in the membrane, but molecular evidence for this has been lacking. In the present study we show that LMP2A coclusters with chimeric rat CD2 transmembrane molecules carrying the 27-amino-acid (aa) intracellular C terminus of LMP2A and that this C-terminal domain fused to the glutathione-S-transferase protein associates with LMP2A in cell lysates. This molecular association requires neither the cysteine-rich region between aa 471 and 480 nor the terminal three aa 495 to 497. We also show that the juxtamembrane cysteine repeats in the LMP2A C terminus are the major targets for palmitoylation but that this acylation is not required for targeting of LMP2A to detergent-insoluble glycolipid-enriched membrane microdomains.

Epigenetics of latent Epstein-Barr virus genomes: high resolution methylation analysis of the bidirectional promoter region of latent membrane protein 1 and 2B genes

We analysed the methylation patterns of CpG dinucleotides in a bidirectional promoter region (LRS, LMP 1 regulatory sequences) of latent Epstein-Barr virus (EBV) genomes using automated fluorescent genomic sequencing after bisulfite-induced modification of DNA. Transcripts for two latent membrane proteins, LMP 1 (a transforming protein) and LMP 2B, are initiated in this region in opposite directions. We found that B cell lines and a clone expressing LMP 1 carried EBV genomes with unmethylated or hypomethylated LRS, while highly methylated CpG dinucleotides were present at each position or at discrete sites and within hypermethylated regions in LMP 1 negative cells. Comparison of high resolution methylation maps suggests that CpG methylation-mediated direct interference with binding of nuclear factors LBF 2, 3, 7, AML1/LBF1, LBF5 and LBF6 or methylation of CpGs within an E-box sequence (where activators as well as repressors can bind) is not the major mechanism in silencing of the LMP 1 promoter. Although a role for CpG methylation within binding sites of Sp1 and 3, ATF/CRE and a sis-inducible factor (SIF) cannot be excluded, hypermethylation of LRS or regions within LRS in LMP 1 negative cells suggests a role for an indirect mechanism, via methylcytosine binding proteins, in silencing of the LMP 1 promoter.

Expression of the Epstein-Barr virus BHRF1 gene, a homologue of Bcl-2, in nasopharyngeal carcinoma tissue

Epstein-Barr virus (EBV) infection is associated closely with the pathogenesis of nasopharyngeal carcinoma (NPC). The EBV gene product, BHRF1, has been demonstrated in vitro and is structurally and functionally similar to the oncogene bcl-2, that is able to protect cells from programmed cell death. To determine whether the BHRF1 gene is expressed in vivo, BHRF1 mRNA or protein were sought in tissues from NPC and non-NPC patients. BHRF1 transcripts were specifically detected in the NPC tumours (32 out of 44, 72.7%) rather than the non-NPC tissues (0 out of 25) by reverse transcription, polymerase chain reaction and Southern hybridization. Other EBV genes, such as the lytic gene BZLF1 and latent genes EBNA1 and LMP2A, were also investigated. BZLF1 transcripts also were found specifically in NPC tumours (33 out of 44, 75%). EBNA1 was expressed in 79.5% of NPC, and 28% of non- NPC, tissues and LMP2A was expressed in 70.5% of NPC, and 88% of non-NPC, tissues. BHRF1 protein was detected by immunohistochemistry in 4 metastatic NPC, of 36 NPC tissue sections available. The BHRF1 protein was distributed in both the nucleus and cytoplasm of the neoplastic epithelial cells. IgG antibody against the BHRF1 protein was detected in 6 of 17 (35. 3%) NPC plasma, but the protein and IgG were both absent from the non-NPC controls. BHRF1 DNA sequences were determined for 11 NPC and 3 non-NPC samples. No sequence was specific for the EBV isolates from NPC tissue. Amino acids 79 and 88 always appeared in the same form, however, for every tested isolate and both were valine or leucine. This particular characteristic was not present in the B95-8 strain or in the corresponding regions of homologues, Bcl-2 and Bcl-XL, and was regarded as unique to Oriental EBV strains.

Nasopharyngeal carcinoma cell line (C666-1) consistently harbouring Epstein-Barr virus

We have established a cell line (C666-1) from undifferentiated nasopharyngeal carcinoma (NPC). This cell line consistently carries the Epstein-Barr virus (EBV) in long-term cultures. C666-1 is a subclone of its parental cell line, C666, derived from an NPC xenograft of southern Chinese origin. It grows as an adherent culture and lacks contact inhibition. In addition, it is tumorigenic in athymic nude mice. The cells consistently express EBV-encoded RNAs and are positively stained for cytokeratin, an epithelial marker. In addition, they express EBNA1 protein, LMP1 and LMP2 transcripts and thus resemble the EBV latency II pattern. The virus genotype is EBV-1 with the latent membrane protein 1 gene showing a 30-bp deletion at the carboxyl terminus, both consistent with findings in southern Chinese NPC tumours. Cytogenetic analysis revealed a sub-diploid status with a chromosomal modal number of 45. C666-1 is unique among NPC cell lines in that it carries EBV. These cells may serve as a good investigative tool as the viral latency pattern and genotype are observed in the majority of primary NPC biopsies from Chinese patients.

Specific latent membrane protein 1 gene sequences in type 1 and type 2 Epstein-Barr virus from nasopharyngeal carcinoma in Hong Kong

We reported previously that a characteristic Epstein-Barr virus latent membrane protein 1 (EBV-LMP1) gene was associated with nasopharyngeal carcinoma (NPC) in Hong Kong. It showed a 30 bp deletion at the carboxyl terminus with specific amino acid substitution Asp at codon 335 with reference to Gly in B95-8 LMP1. This deletion variant Asp335 was present in over 90% of NPC biopsy specimens. The present study attempted to determine the whole encoding sequence of the LMP1 gene in different EBV isolates from NPC, and its relation with EBV types. We found that 92% (34/37) of primary NPC tumours harboured EBV-1 and possessed the LMP1 deletion variant, of which 86% were Asp335 and 6% were Gly335. EBV-2 was present in 8% (3/37) of tumours and all contained the retention variant of the LMP1 gene. Sequencing of the whole encoding region of the LMP1 gene revealed that the deletion variant Asp335 and deletion variant Gly335 carried similar sequences. They showed 43 common nucleotide substitutions in 41 codons with reference to B95-8. The retention variant showed 52 base changes in 46 codons compared with B95-8. The amino acid alterations in both the deletion and retention variants were mostly clustered at the transmembrane domain of the protein. Furthermore, half of the substitutions were common to both variants, suggesting a common evolutionary selection pressure. Nonetheless, the 2 LMP1 variants showed differences in nucleotide alterations and were associated with different EBV types, suggesting the presence of 2 distinct EBV strains in Hong Kong NPC.

Site-specific localization of Epstein-Barr virus in pharyngeal carcinomas

In this study, the correlations of factors with Epstein-Barr virus (EBV)-association were investigated in 50 patients with nasopharyngeal carcinoma (NPC), 61 with oropharyngeal carcinoma (OPC), and 55 with hypopharyngeal carcinoma (HPC) in Okinawa and Osaka prefectures in Japan. The incidence of pharyngeal carcinoma in Okinawa was previously found to be higher than that in Osaka; the incidence of OPC was approximately 6 times higher and that of HPC was two times higher. The EBV genome was detected in the tumor cells of the present patients; 83% of the Okinawa and 92% of the Osaka NPC patients. The EBV genome was not detected in OPC or HPC. A univariate analysis showed that sex, the location of the tumor, histology, and the degree of lymphocytic infiltration correlated with the EBV-positive rate. A multivariate analysis revealed that only the location of the tumor was independently correlated with the EBV-positive rate. Histology and tumor size were factors affecting the prognosis of the patients with NPC. The NPC of poorly differentiated type frequently showed the EBV genome, and NPC with lymphocytic infiltration showed a more favorable prognosis compared to the other NPC types. These findings suggest that latent genes of EBV expressed in cancer cells might trigger a cytotoxic T cell reaction against the cancer.

Cell-to-cell contact as an efficient mode of Epstein-Barr virus infection of diverse human epithelial cells

We show clear evidence for direct infection of various human epithelial cells by Epstein-Barr virus (EBV) in vitro. The successful infection was achieved by using recombinant EBV (Akata strain) carrying a selective marker gene but without any other artificial operations, such as introduction of the known EBV receptor (CD21) gene or addition of polymeric immunoglobulin A against viral gp350 in culture. Of 21 human epithelial cell lines examined, 18 became infected by EBV, as ascertained by the detection of EBV-determined nuclear antigen (EBNA) 1 expression in the early period after virus exposure, and the following selection culture easily yielded a number of EBV-infected clones from 15 cell lines. None of the human fibroblasts and five nonhuman-derived cell lines examined was susceptible to the infection. By comparison, cocultivation with virus producers showed approximately 800-fold-higher efficiency of infection than cell-free infection did, suggesting the significance of direct cell-to-cell contact as a mode of virus spread in vivo. Most of the epithelial cell lines infectable with EBV were negative for CD21 expression at the protein and mRNA levels. The majority of EBV-infected clones established from each cell line invariably expressed EBNA1, EBV-encoded small RNAs, rightward transcripts from the BamHI-A region of the virus genome, and latent membrane protein (LMP) 2A, but not the other EBNAs or LMP1. This restricted form of latent viral gene expression, which is a central issue for understanding epithelial oncogenesis by EBV, resembled that seen in EBV-associated gastric carcinoma and LMP1-negative nasopharyngeal carcinoma. The results indicate that direct infection of epithelial cells by EBV may occur naturally in vivo, and this could be mediated by an unidentified, epithelium-specific binding receptor for EBV. The EBV convertants are viewed, at least in terms of viral gene expression, as in vitro analogs of EBV-associated epithelial tumor cells, thus facilitating analysis of an oncogenic role(s) for EBV in epithelial cells.

Specific methylation patterns in two control regions of Epstein-Barr virus latency: the LMP-1-coding upstream regulatory region and an origin of DNA replication (oriP)

The Epstein-Barr virus (EBV) can establish at least four different forms of latent infection. Previously, we have shown that the level of methylation of the EBV genome varies, depending on the form of latency. The methylation status of CpGs was analyzed by the bisulfite genomic sequencing technique in four different cell types representing different forms of latency. The dyad symmetry element of the origin of replication (oriP) region and the latent membrane protein 1 (LMP-1) regulatory sequence (LRS) were studied. The dyad symmetry element has four binding sites for EBNA-1. In a cell with type I latency, a region upstream of the dyad symmetry element was highly methylated, whereas the dyad symmetry element was unmethylated in the EBNA-1-binding region. The LRS was extensively methylated in the LMP-1-negative cell line Rael, in contrast to a LMP-1-expressing nasopharyngeal carcinoma tumor (NPC C15), which was almost completely unmethylated. The methylation pattern of LRS in type I and type III Burkitt lymphoma cells of similar parental origins confirmed that demethylation of some regions takes place upon phenotypic drift.

Deletion variants within the NF-kappaB activation domain of the LMP1 oncogene in acquired immunodeficiency syndrome-related large cell lymphomas, in prelymphomas and atypical lymphoproliferations

The latent membrane protein 1 (LMP1) oncogene of Epstein Barr virus (EBV) is expressed in tumor cells of acquired immunodeficiency syndrome (AIDS) related lymphomas, HIV-negative, EBV-associated malignant lymphoproliferations, nasopharyngeal carcinoma, as well as in reactive immunoblasts of infectious mononucleosis. Naturally occurring LMP1 deletion variants (LMP1-del), characterized by clustered mutations and a distinct 30 base pair deletion within the carboxy terminal domain of LMP1, essential for maximal NF-kappaB stimulation, have been identified in the same conditions. These variants prevail in AIDS-related lymphomas, and are associated with clinically aggressive behaviour in HIV-negative lymphomas, and are frequent in prelymphomatous and reactive states. Functional studies showing a growth advantage of cells infected by these variants may explain the accumulation of LMP1-del in these entities. In the carboxy terminal NF-kappaB activation domain of LMP1, evidence of a hypervariable region close to the highly conserved 23 outermost amino acids essential for malignant transformation, may reflect the natural selection of growth promoting variants involved in signalling pathways. The prevalence of the same mutational pattern in AIDS-related lymphoma as well as in hyperplastic reactive states and prelymphomas supports the hypothesis that these variants confer a growth advantage manifested under impaired cellular immunity.

Epstein-Barr virus (EBV) gene expression in lymphoid B cells during acute infectious mononucleosis (IM) and clonality of the directly growing cell lines

We examined the patterns of viral gene expression in acute infectious mononucleosis (IM) patients and the clonality of the directly growing EBV-carrying cell lines. Both low- and high-density EBV-carrying B cells obtained from the patients' tonsils expressed EBNA1, EBNA2 and LMP1. Like LCLs and immunoblastic B-cell lymphomas, the in vivo EBV-carrying low-density cells used only the latency III program for viral gene expression. The in vivo EBV-carrying high-density B cells used both the latency I program, as indicated by the QUK-, and the latency III program, as indicated by the YUK-EBNA1. This suggests that the lymphoid tissues contained not only proliferating immunoblasts but also cells programmed for latent viral persistence in vivo. EBV-carrying cells that grew directly into permanent cell lines in the presence of virus-neutralizing antibody and a late viral inhibitor were polyclonal, as indicated by JH rearrangement. Two of the high-density-derived lines had identical JH and TR patterns, indicating a common parental origin. Our investigation indicates that EBV-carrying cells divide and survive in a fully competent immune system during the outbreak of acute IM.

Differential immunogenicity of Epstein-Barr virus (EBV) encoded growth transformation-associated antigens in a murine model system

The strong immunosurveillance of humans against EBV transformed immunoblasts, mediated by CD8+ cytotoxic T cells, is based on the recognition of peptides derived from eight of the nine growth transformation-associated proteins, the nuclear antigens EBNA2-6 and the membrane proteins LMP1, -2A and -2B. The ninth protein, EBNA1, required for maintenance of the viral episomes, and expressed in a cell phenotype independent manner, has not been found to generate a cytotoxic lymphocyte (CTL) response in humans. We tested whether EBNA1 has a similar immunologically privileged status in a species that has not encountered the virus in nature, the mouse. Non-immunogenic murine mammary carcinoma cells were transfected with the appropriate viral gene. Rejection responses were assayed in syngeneic mice following repeated immunisation with irradiated cells. Previously, we found that LMP1 expression in S6C, a murine mammary carcinoma of ACA (H-2f) origin, induces high rejectability, whereas corresponding EBNA1 transfectants remained non-immunogenic. In order to test whether this finding could be reproduced on another MHC class 1 background, we expressed LMP1 and EBNA1 in another non-immunogenic mammary carcinoma, SBfnHd of CBA (H-2k) origin. LMP1 but not EBNA1 transfectants were immunogenic in this system. In order to investigate whether other growth transformation-associated EBV proteins were immunogenic in the mouse, we also transfected the S6C cells with EBNA4, EBNA5, LMP2A and -2B. All four proteins induced strong rejection reactions. These findings are fully consistent with corresponding findings in the human system. They also show that the immunologically privileged status of EBNA1 is not due to some peculiarity of the long-standing co-existence between EBV and the human species, nor to any specific features of the human MHC class I system. They are consistent with the suggestion that EBNA1 may not be properly processed and/or transported, due to specific features of the protein itself.

Transcriptional analysis of Epstein-Barr virus gene expression in EBV-positive gastric carcinoma: unique viral latency in the tumour cells

Although case-oriented evidence for an association of Epstein-Barr virus (EBV) with gastric carcinoma has been accumulating recently, the interaction(s) between EBV and gastric epithelial cells is/are largely unknown. In this study, we examined seven EBV-positive gastric carcinoma tissues for viral gene expression at the mRNA level, from which studies on the EBV oncogenicity in human epithelial cells will benefit. Reverse transcription-PCR analysis showed that all seven EBV-positive tumour tissues constitutively expressed EBV nuclear antigen (EBNA) 1 mRNA, but not EBNA2 mRNA. The EBNA transcription was initiated from one of three EBNA promoters, Qp: by contrast, both Cp and Wp were silent, thus resulting in the lack of EBNA2 mRNA. Latent membrane protein (LMP) 2A mRNA was detected in three of seven cases; however, neither LMP1 nor LMP2B mRNA was detected in any of the tumours tested. Transcripts from the BamHI-A region of the viral genome were detectable in all cases. BZLF1 mRNA and the product, an immediate-early gene for EBV replication, was not expressed in any of them, thereby suggesting that the tumour cells carried EBV genomes in a tightly latent form. These findings further extended our previous data regarding EBV latency in gastric carcinoma cells at the protein level, and have affirmed that the programme of viral gene expression in the tumour more closely resembles 'latency I' represented by Burkitt's lymphoma than 'latency II' represented by the majority of nasopharyngeal carcinomas.

Epstein Barr virus (EBV)-carrying cells of a chronic lymphocytic leukemia (CLL) subpopulation express EBNA1 and LMPs but not EBNA2 in vivo

We have previously described an exceptional CLL patient, P.G., whose leukemic cell population contained a small fraction of Epstein-Barr virus (EBV)-carrying cells. These cells grow directly into permanent cell lines in vitro. Using RT-PCR analysis, we now show that the in vivo EBV-carrying CLL cells expressed EBNAI, LMPI, LMP2a and 2b, but not EBNA2, in 4 of 4 blood samples obtained during the last 3 years of the patient's life. Our data also show that the CLL cells used a promoter in the F/Q, but not the W or C, region. This is consistent with the fact that CLL cells resemble resting lymphocytes rather than immunoblasts. Expression of LMP1 and LMP2b differs from the exclusive EBNAI and LMP2a expression of normal resting B cells, however, and corresponds to the state defined as latency II. This form of latency was until now detected only in EBV-carrying non-B cells in vivo. Our data show that a B-cell subtype can also show this expression pattern in vivo.

Antibodies to LMP2A/2B in EBV-carrying malignancies

Antibodies to the Epstein-Barr virus (EBV)-encoded membrane proteins, LMP2A and LMP2B, were assayed in 540 individuals, including 154 patients with nasopharyngeal carcinoma, 16 with African Burkitt's lymphoma, 113 with Hodgkin's disease, 14 with EBV-carrying gastric carcinoma, 14 with oral hairy leucoplakia (HIV+ patients), 37 with non-Hodgkin's lymphoma, 49 with tumours of the head/neck, 19 with infectious mononucleosis, 62 with chronic illnesses with EBV titres consistent with re-activations, and 62 healthy controls. A novel assay, mouse monoclonal enhanced indirect immunofluorescence assay (MIFA) was designed and used to test the sera for antibodies to the LMP2A and 2B proteins, expressed in human keratinocytes. Antibody to both LMP2A and LMP2B was strikingly specific to NPC. Virtually all (99 of 101) of the LMP2 antibody positive individuals were NPC patients, 95% of whom had antibodies that reacted both with the LMP2A- and LMP2B-transfected indicator cells, while the remaining 5% reacted only with the LMP2B expressing cells.