An EBV membrane protein expressed in immortalized lymphocytes transforms established rodent cells

Biochemical characterization of Epstein-Barr virus nuclear antigen 2A

The Epstein-Barr virus nuclear antigen 2A (EBNA-2A) was immunoprecipitated from latently Epstein-Barr virus-infected lymphocytes with a polyclonal serum raised against the EBNA-2A C terminus. The nucleus contained three subfractions of EBNA-2A which could be distinguished by their resistance to salt extraction: (i) a nucleoplasmatic fraction that was solubilized at 50 mM NaCl, (ii) a chromatin-associated fraction extractable at 1.5 M NaCl, and (iii) a nuclear matrix-associated fraction solubilized only by boiling with buffer containing 2% sodium dodecyl sulfate. The three subfractions were phosphorylated; it was demonstrated that the nucleoplasmatic and the chromatin-associated fractions were phosphorylated at serine and threonine residues. The half-life of the EBNA-2A protein was determined by cycloheximide treatment and by pulse-chase experiments and was found to be at least 24 h. The turnover of the phosphate residues bound to the two salt-soluble subfractions was determined to be approximately 6 to 9 h, suggesting a possible role of the phosphorylation in the regulation of the biological activity of EBNA-2A. Dephosphorylation of EBNA-2A resulted in an increased mobility of the protein during sodium dodecyl sulfate-polyacrylamide gel electrophoresis and indicated the presence of differentially phosphorylated subclasses of the protein. Analysis of EBNA-2A by sucrose gradient centrifugation revealed the existence of two subclasses of complexed molecules which exhibited sedimentation coefficients of approximately 13S and 34S.

An Epstein-Barr virus protein associated with cell growth transformation interacts with a tyrosine kinase

Epstein-Barr virus (EBV) encodes two integral membrane proteins in latently infected growth-transformed cells. One of these, LMP1, can transform rodent fibroblasts and induce markers of B-lymphocyte activation. The second, LMP2, colocalizes with LMP1 in a constitutive patch in the EBV-transformed B-lymphocyte plasma membrane. The experiments reported here demonstrate that LMP2 may biochemically interact with LMP1 and that LMP2 closely associates with and is an important substrate for a B-lymphocyte tyrosine kinase in EBV-transformed B lymphocytes or in B-lymphoma cells in which LMP2 is expressed by gene transfer. LMP2 is also serine and threonine phosphorylated. LMP2 localizes to a peripheral membrane (presumably plasma membrane) patch in transfected B-lymphoma cells and colocalizes with much of the cellular tyrosine-phosphorylated proteins. LMP2 undergoes tyrosine phosphorylation in anti-LMP2 or antiphosphotyrosine immunoprecipitates from transfected B-lymphoma cells or EBV-transformed B lymphocytes. The first 167 of the 497 amino acids of LMP2 retain full ability to associate with and act as a substrate for a tyrosine kinase. A 70-kDa phosphotyrosine cell protein associates with LMP2 in transfected cells or in EBV-transformed B lymphocytes and could be a mediator of the effects of LMP2.

The latent membrane protein-1 in Epstein-Barr virus-transformed lymphoblastoid cells is found with ubiquitin-protein conjugates and heat-shock protein 70 in lysosomes oriented around the microtubule organizing centre

Immunofluorescence studies on Epstein-Barr virus (EBV)-transformed lymphoblastoid cells have previously shown that the latent membrane transforming protein (LMP-1) is found in patch-like inclusions which also immunostain for vimentin. We now show that EBV transformation causes a major reorganization of intermediate filaments, microtubules, mitochondria, and lysosomal elements, which generally become oriented around the microtubule organizing centre. Immunogold electron microscopy shows that LMP-1 is primarily concentrated in secondary lysosomes together with ubiquitin-protein conjugates and heat-shock protein 70. Intermediate filament inclusion formation with the above characteristics may be a general response triggered by other membrane glycoproteins; as seen, for example, in major human neurodegenerative diseases such as diffuse Lewy body disease.

The prototypical Epstein-Barr virus-transformed lymphoblastoid cell line IB4 is an unusual variant containing integrated but no episomal viral DNA

IB4 is a prototype, latently Epstein-Barr virus (EBV)-infected, lymphoblastoid cell line. We show here that IB4 contains only integrated EBV genomes. Episomal EBV DNA is not detected by Gardella gel analysis or in situ hybridization. Restriction enzyme mapping indicates that the EBV genomes first circularized and then integrated into and deleted part of the BamHI C fragment. IB4 is therefore the only lymphoblastoid cell line described to date that lacks episomal EBV and has integrated EBV genomes with joined ends. Thus, the detection of joined EBV termini on Southern blots is not as reliable as the Gardella gel system for detecting episomal EBV DNA, and IB4 is not an ideal prototype cell line for the study of latent infection by EBV.

Induction of bcl-2 expression by Epstein-Barr virus latent membrane protein 1 protects infected B cells from programmed cell death

Epstein-Barr virus (EBV) not only induces growth transformation in human B lymphocytes, but has more recently been shown to enhance B cell survival under suboptimal conditions where growth is inhibited; both effects are mediated through the coordinate action of eight virus-coded latent proteins. The effect upon cell survival is best recognized in EBV-positive Burkitt's lymphoma cell lines where activation of full virus latent gene expression protects the cells from programmed cell death (apoptosis). Here we show by DNA transfection into human B cells that protection from apoptosis is conferred through expression of a single EBV latent protein, the latent membrane protein LMP 1. Furthermore, we demonstrate that LMP 1 mediates this effect by up-regulating expression of the cellular oncogene bcl-2. The interplay between EBV infection and expression of this cellular oncogene has important implications for virus persistence and for the pathogenesis of virus-associated malignant disease.

Transformation by the oncogenic latent membrane protein correlates with its rapid turnover, membrane localization, and cytoskeletal association

The latent membrane protein (LMP) of Epstein-Barr virus (EBV) has a short half-life (V. R. Baichwal and B. Sugden, J. Virol, 61:866-875, 1987; K.P. Mann and D. Thorley-Lawson, J. Virol, 61:2100-2108, 1987), is localized in patches in the membrane (D. Liebowitz, D. Wang, and E, Kieff, J. Virol, 58:233-237, 1986), and associates with the cytoskeleton in EBV-immortalized B lymphocytes (D. Liebowitz, R. Kopan, E. Fuchs, J. Sample, and E. Kieff, Mol. Cell. Biol. 7:2299-2308, 1987; K. P. Mann and D. Thorley-Lawson, J. Virol. 61:2100-2108, 1987). Deletion mutants of LMP that are either positive or negative in the induction both of anchorage-independent growth of BALB/c 3T3 cells (V. R. Baichwal and B. Sugden, Oncogene 4:67-74, 1989) and of cytotoxicity in a variety of cells (W. Hammerschmidt, B. Sugden, and V. R. Baichwal, J. Virol. 63:2469-2475, 1989) have been studied to identify the biochemical properties of this protein that correlate with its effects on cell growth. Mutant LMP proteins that are metabolically stable, do not associate with the cytoskeleton, and exhibit a diffuse plasma membrane localization also do not induce anchorage-independent growth in rodent cells or cytotoxicity in B lymphoblastoid cells. In contrast, a mutant of LMP that is functionally identical to the wild-type protein has a half-life, membrane localization, and cytoskeletal association similar or identical to those of LMP. These results are consistent with the hypothesis that LMP's rapid turnover, association with the cytoskeleton, and patching in the membrane are required for it to affect cell growth.

Epstein-Barr virus latent membrane protein expression in Hodgkin and Reed-Sternberg cells

Cryostat sections from lymph nodes of 47 Hodgkin disease patients were examined by immunohistology for the Epstein-Barr virus (EBV)-encoded latent membrane protein (LMP), nuclear antigen 2, and late viral glycoprotein gp350/250. A distinct LMP-specific membrane and cytoplasmic staining was detected exclusively in Hodgkin and Reed-Sternberg cells in 18 patients (38%); EBV nuclear antigen 2 and gp350/250 immunoreactivity was absent in all instances. Thirty-two of 47 (68%) cases contained EBV-specific DNA sequences as detected by PCR, all LMP-positive cases being in this category. Our results confirm previous studies establishing the presence of EBV genomes in Hodgkin and Reed-Sternberg cells by demonstrating expression of an EBV-encoded protein in the tumor-cell population. The finding of LMP expression in the absence of EBV nuclear antigen 2 suggests a pattern of EBV gene expression different from that of B-lymphoblastoid cell lines and Burkitt lymphoma, whereas this finding shows similarities with that seen in undifferentiated nasopharyngeal carcinoma. Because the LMP gene has transforming potential, our findings support the concept of a pathoetiological role of EBV in many cases of Hodgkin disease.

Differential expression of Epstein Barr viral transcripts for two proteins (TP1 and LMP) in lymphocyte and epithelial cells

Studies presented here show that some functions of the human herpesvirus, EBV, may be transcriptionally differentially expressed in two cell types which carry the same (C15) isolate of this virus. Of the 'latent' viral functions investigated, only one (TP2) of the episomally-specific genes that encode terminal proteins (TP1 and TP2) is found to be expressed in the C15 epithelial cell tumour environment, whereas both are transcribed--as different, but related, messengers--in a B-cell line generated with virus from the C15 tumour. The other gene investigated is that for latent membrane protein (LMP), which is found in the same region of the EBV genome but on the opposite strand. This gene, apparently transcriptionally silent in B-cell (Burkitt's) lymphomas, is expressed in the C15 epithelial tumour, as well as in other nasopharyngeal carcinomas investigated. Promoter usage in the carcinomas and B-cells appears, in some cases at least, to be cell-type specific. Expression may also be governed by methylation since a chromosomally silent region in the carcinoma (that encompassing TP1) is highly methylated on CpG residues, whereas the active region (encoding TP2 and LMP) is virtually free of such methylation. Our data suggest that there may be selective transcriptional regulation of EBV genes in the two types of cells investigated. Thus, it may be unnecessary to invoke different virus genotypes to account for the two distinct malignancies--Burkitt's lymphoma and nasopharyngeal carcinoma--associated with EBV.

Epstein-Barr virus nuclear protein 2 mutations define essential domains for transformation and transactivation

Epstein-Barr virus (EBV) nuclear protein 2 (EBNA-2) is essential for B-lymphocyte growth transformation. EBNA-2 transactivates expression of the EBV latent membrane protein (LMP-1) and also transactivates expression of the B-lymphocyte proteins CD21 and CD23. In order to analyze the functional domains of EBNA-2, we constructed 11 linker-insertion and 15 deletion mutations. Each of the mutant EBNA-2 proteins localized to the nucleus, and each was expressed at levels similar to wild-type EBNA-2. Deletion of both EBNA-2 basic domains was required to prevent nuclear localization, indicating that either is sufficient for nuclear translocation. The mutant EBNA-2 genes were assayed for lymphocyte transformation after recombination with the EBNA-2-deleted P3HR-1 EBV genome and for LMP-1 transactivation following transfection into P3HR-1-infected B-lymphoma cells. Cell lines transformed by recombinant EBV carrying EBNA-2 mutations were assayed for growth properties and LMP-1, CD21, and CD23 expression. The mutational analysis indicates that at least four separate EBNA-2 domains are essential for lymphocyte transformation. Two other domains are necessary for the full transforming phenotype. Two deletion and eight linker-insertion mutations did not reduce transforming activity. Mutations which diminish or abolish lymphocyte transformation also diminish or abolish LMP-1 transactivation, respectively. Cells transformed by recombinant EBV carrying EBNA-2 genes with diminished or normal transforming activity all expressed high levels of LMP-1, CD23, and CD21. These findings suggest that transactivation of these viral and cellular genes by EBNA-2 plays a critical role in lymphocyte transformation by EBV. Furthermore, these results indicate that the transformation and transactivation functions of EBNA-2 may not be separable.

When Epstein-Barr virus persistently infects B-cell lines, it frequently integrates

In this study we used Gardella gel analysis of intact DNA, Southern blotting of digested DNA, and fluorescence in situ hybridization to provide complementary and unequivocal information on the state of the Epstein-Barr virus (EBV) genome in persistently infected cells. The fluorescence in situ hybridization technique allowed us to directly visualize both integrated and episomal EBV DNA at the single-cell level. We show here that circularization of the EBV genome is rarely detected upon infecting activated normal B cells. The virus can persist upon infection of a different proliferating B-cell target, EBV-negative Burkitt's lymphoma tumor cell lines. Analysis of 16 such lines reveal again, that the virus infrequently persists as covalently closed episomes; rather, the virus preferentially persists by integrating into the host DNA (10 of 16 clones). The integrated virus is linear and usually intact, although 3 of 10 isolates have deletions from the left-hand end including the latent origin of replication. At the level of our analysis, no obvious relationship was seen between the integration sites. These studies provide, for the first time, a reproducible in vitro model system to study integration by EBV.

Variable expression of latent membrane protein in nasopharyngeal carcinoma can be related to methylation status of the Epstein-Barr virus BNLF-1 5'-flanking region

Seven virus-coded proteins, the nuclear proteins EBNA-1 to EBNA-6 and the latent membrane protein (LMP), are regularly expressed in Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines. In nasopharyngeal carcinoma (NPC), only EBNA-1 is regularly expressed; LMP is detected in about 65% of the tumors. In Burkitt's lymphoma tumors only EBNA-1 is expressed. We have recently shown that the methylation patterns of the EBV genome varied between these cell types. In virally transformed lymphoblastoid cell lines of normal origin, the EBV DNA is completely unmethylated. In contrast, in the Burkitt's lymphoma-derived cell line Rael and in a nude mouse-passaged NPC tumor, C15, there was an extensive methylation of CpG pairs. The methylation extended into the coding regions of the two expressed genes, EBNA-1 (in both tumor types) and LMP (in C15). Two presumptive control regions were exempted from this overall methylation: the oriP that contains both an origin of DNA replication and an EBNA-1-dependent enhancer and the 5'-flanking region of the BNLF-1 open reading frame that codes for LMP. The latter was only exempted in the LMP expressing NPC. We have now investigated the relation between expression of LMP and methylation of DNA in the 5'-flanking 1 kb region of BNLF-1, coding for LMP. LMP was methylated in 3 of 12 NPC biopsies that did not express LMP but was partially or totally unmethylated in the remaining 9 that expressed the protein. The three BNLF-1 exons were highly methylated in all the tumors. The oriP region was unmethylated in all the tumors, as in the previously studied Rael cell line and nude mouse-passaged NPC. Also, the BamHI W enhancer region involved in the expression of EBNA nuclear proteins was methylated. None of the biopsies expressed EBNA-2. Our data show that the EBV genomes are highly methylated in NPC tumors. The strong reverse correlation between the methylation of the putative control region of the LMP gene and the expression of LMP suggests that methylation has a role in the regulation of this gene.

Expression of Epstein-Barr virus latent gene products in tumour cells of Hodgkin's disease

The Epstein-Barr virus (EBV)-encoded latent gene products, latent membrane protein (LMP) and EBV nuclear antigen 2 (EBNA 2), seem to have important roles in EBV-induced cell transformation in vitro, and have been implicated as important effector molecules in EBV-associated lymphomagenesis. Because up to 35% of Hodgkin's disease (HD) samples have been reported to contain EBV genomes, the expression of LMP and EBNA 2 in these tumours was investigated. 84 cases of HD were studied with monoclonal antibodies and immunohistochemical labelling of acetone-fixed cryostat sections. LMP, but not EBNA 2, was demonstrated in Reed-Sternberg (RS) cells of 40 cases (48%); the two proteins were easily detected in transformed lymphocytes of positive control acute infectious mononucleosis tonsils. LMP expression in RS cells varied according to the histological subtype of HD (1/10 cases [10%] of lymphocyte predominance subtype, 16/50 cases [32%] of nodular sclerosis, 23/24 [96%] cases of mixed cellularity type). That the LMP antibodies showed no substantial cross-reactivity with negative control tissues shows that they are useful probes for the diagnosis of latent EBV infection in tissue sections. The findings suggest that EBV is associated with more cases of HD than was previously recognised, that in positive cases RS cells express a latent infection protein phenotype (LMP+, EBNA 2-) which differs from that of other EBV-associated lymphomas, and that LMP expression is related to histologically aggressive subtypes of HD.

Effect of transforming growth factor-beta 1 and -beta 2 on the proliferation of Burkitt lymphoma and lymphoblastoid cell lines

We tested the effect of transforming growth factor (TGF)-beta 1 and TGF-beta 2 on the proliferation of human B cell lines. The panel was selected to give information whether (1) their origin, (2) their phenotype, (3) their Epstein-Barr virus (EBV) carrier state, influence their responsiveness. The growth of lymphoblastoid cell lines (LCL) was not inhibited by TGF-beta 1. The EBV-carrying Burkitt lymphoma (BL) lines, Daudi, Jijoye, Rael but not Raji were inhibited. Three EBV-negative BL lines and the majority of their converted sublines were sensitive. The cell lines tested expressed TGF-beta receptors and TGF-beta 1 transcripts. The proliferation of EBV-infected B cells was inhibited by TGF-beta, their sensitivity decreased, however, after 3 days. The results suggest that the activation state of the B cells is decisive for TGF-beta sensitivity and EBV influences it indirectly by changing the cell phenotype.

Epstein-Barr virus (EBV) genome carrying monoclonal B-cell lymphoma in a patient with adult T-cell leukemia-lymphoma

A Japanese patient with adult T-cell leukemia-lymphoma (ATL) showed a disease progression from the smoldering type to the chronic type and finally to the acute type. The patient was variously treated, including 2'-deoxycoformycin, with some beneficial effects. During the chronic type he developed a composite lymphoma consisting of T-cell lymphoma (ATL) of medium-sized cells and B-cell lymphoma of diffuse large cell type. At that time, he also suffered from miliary tuberculosis and adenovirus type 11-induced hemorrhagic cystitis, indicating that he was in a marked immunodeficient state. Southern-blot analysis revealed that the two malignancies have distinct clonal origin on the basis of the following results: (1) clonally rearranged T-cell receptor beta-chain gene (TcR-beta gene) and germline configuration of immunoglobulin heavy chain gene (IgH gene) in ATL leukemic cells, (2) clonal rearrangement of IgH gene in lymphoma cells, indicating a monoclonal B-cell lymphoma, (3) monoclonal integration of HTLV-I provirus in ATL leukemic cells, (4) definite presence and monoclonal origin of EBV genome in lymphoma cells. This is the first report of secondary EBV genome carrying monoclonal B-cell lymphoma in an ATL patient. It is suggested that the immunodeficient state in the patient with ATL allows the emergence of EBV-related B-cell lymphoma.

Immortalizing genes of Epstein-Barr virus

EBV immortalizes human B lymphocytes efficiently. Ten of its approximately 100 genes are expressed in these proliferating lymphoblasts and are candidates for mediating the changes central to the immortalization of the cell. Enough has been learned now about three of these viral genes to indicate that they are likely to be required for immortalization. As more is learned, additional genes of EBV will probably be found to support the process of immortalization of the host cell. EBNA-2 has been shown genetically to be required for EBV to immortalize an infected B lymphocyte. The biochemical activities of EBNA-2 that constitute this requirement have not been identified. Many experiments indicate that EBNA-2 affects the accumulation of specific viral and cellular RNAs. These effects, however, can be detected only in certain EBV-negative B-lymphoblastoid cells. It is, therefore, not clear that the known effects of EBNA-2 adequately explain its ubiquitous requirement in the immortalization of primary human B lymphocytes. LMP is likely to be required for immortalization because it can affect the growth properties of established human lymphoid and epithelial cells and can transform at least two established rodent cells to proliferate in an anchorage-independent manner. The structure of this viral protein, its position in the plasma membrane, many of its biochemical properties, as well as studies of its mutant derivatives are consistent with its acting as a growth factor receptor or affecting the activity of such a receptor. However, no biochemical activity has been assigned directly to LMP, and both its mechanism of action and its possible contribution to immortalization by EBV remain enigmatic. EBNA-1 presumably is required for EBV to immortalize a B lymphocyte because it is essential for the initiation of plasmid DNA replication by EBV. Circumstantial observations indicate also that EBNA-1 is probably necessary for sustaining viral DNA replication in the proliferating cell population. EBNA-1 may well affect the regulation of transcription of viral genes that themselves are required for immortalization. These roles of EBNA-1 are performed in part by its site-specific binding to the elements of oriP required in cis for the replication of EBV plasmid DNAs. It is probable that EBNA-1 also binds both to a set of cellular proteins that function in transcription and to a nonidentical set of cellular proteins that function in replication. EBV effects a fascinating phenotypic change in B lymphocytes it infects. It does so by using several viral genes that alter the physiology of the cell by different means.(ABSTRACT TRUNCATED AT 400 WORDS)

Isolation and partial characterization of a transformation-associated sequence from human nasopharyngeal carcinoma

A transforming activity associated with Chinese nasopharyngeal carcinoma (NPC) cell line CNE2 DNA has been identified by transfer into nontransformed promotion-sensitive mouse JB6(P+) C141 cells. To clone this transformation-associated sequence, we carried out three cycles of transfection, followed by cloning of anchorage-independent transformants in soft agar. A tertiary CNE/JB6 clonal transfectant cell line 625 whose DNA showed transforming activity, as indicated in both soft-agar assay and nude-mice implantation, was used to make a genomic library in the vector lambda dash. Using the human repeated sequence Blur 8 to screen the library, we obtained 10 human Alu-positive clones. A cloned Alu-positive insert of 16 kbp, CNE 323, was characterized in detail. CNE 323 transferred moderate transforming activity when introduced into JB6 P+ cells and showed no homology to Ha-, Ki-, or N-ras genes; human promotion sensitivity genes; src, myb, jun, myc, fos, raf, or int-2 oncogenes; or epidermal growth factor receptor. The isolated CNE 323 DNA sequence appeared to preserve the genomic structure of the original sequence found in CNE2 cells and in nude mouse tumors induced by CNE2 cells or by CNE/JB6 transfectant cells, indicating that the cloned NPC sequence was activated during NPC carcinogenesis and not during transfection or construction of the library, and that the cloned sequence or a larger sequence of which it was part played a role in tumor formation. Finally, we identified a 1.3-kb mRNA that hybridizes to a subclone of the 16-kb NPC sequence in CNE2 cell poly (A)+ RNA.

Epstein-Barr virus nuclear antigen 2 activates transcription of the terminal protein gene

Transcription of the terminal protein (TP) gene of Epstein-Barr virus (EBV) in Burkitt's lymphoma cells, in EBV-negative Burkitt's lymphoma cells converted with transformation-defective (P3HR1) and transformation-competent (B95-8, AG876) EBV strains, and in EBV-immortalized cell lines was studied. A TP1 cDNA probe spanning the boundary between exons 1 and 2 and discriminating between TP1 and TP2 transcripts was used for S1 analysis. TP RNA expression varied widely in Burkitt's lymphoma cells. TP-specific transcripts were not detectable or only hardly detectable in Burkitt's lymphoma cells with the group I phenotype (CD10+ CD77+ CD21- CD23- CD30- CDw70-) as well as in P3HR1 virus-converted Burkitt's lymphoma lines. TP expression was high in Burkitt's lymphoma lines with the group II and group III phenotypes (CD21+ CD23+ CD30+ CDw70+), in B95-8 and AG876 virus-converted lines, and in EBV-immortalized cells. Detection of TP1 RNA correlated with EBNA2 expression. TP1 transcription was shown to be dependent on EBNA2 expression by stable transfection of an EBNA2 expression vector into P3HR1 virus-converted BL41 cells. EBNA2 is activating the TP1 as well as the TP2 promoter, as shown by the analysis of TP promoter-chloramphenicol acetyltransferase constructs transiently transfected into EBNA2-positive and EBNA2-negative Burkitt's lymphoma cells.

Expression of the Epstein-Barr virus genome in a nasopharyngeal carcinoma epithelial tumor cell line

An epithelial tumor cell line was recently established from a biopsy specimen of a nasopharyngeal carcinoma (NPC), and designated HONE-I. Uncloned (parental) HONE-I and HONE-I clone (C)-40 cells were found to contain latent Epstein-Barr virus (EBV). Expression of the latent EBV genome in HONE-I C-40 cells has been examined. It was possible to detect a small percentage of cells spontaneously synthesizing EBV early antigen (EA) and virus capsid antigen (VCA) by immunofluorescence (IF). In addition, the EBV nuclear antigens (EBNA-I and EBNA-2), as well as the EBV latent membrane protein (LMP) were detected in the HONE-I cells. Attempts were made to induce the latent EBV genome in these cells with iododeoxyuridine (IUdR). We observed a significant increase in the number of EA/VCA-positive cells, an increase in EBV DNA, the synthesis of virus particles, and the rescue of infectious virus after treatment of HONE-I C-40 cells with IUdR. The HONE-I C-40 cells should facilitate studies of the expression and regulation of the EBV genome in NPC epithelial tumor cells, which have not previously been available.

Up regulation of the Epstein-Barr virus (EBV)-encoded membrane protein LMP in the Burkitt's lymphoma line Daudi after exposure to n-butyrate and after EBV superinfection

The Burkitt's lymphoma line Daudi carries a nontransforming Epstein-Barr virus (EBV) strain that has a deletion in the BamHI WYH region of the genome coding for the EBV nuclear antigen 2 (EBNA-2). Daudi cells fail to express the EBV-encoded latent membrane protein (LMP) (D. Ghosh and E. Kieff, J. Virol. 64:1855-1858, 1990). We show that LMP expression can be up regulated by exposure to n-butyrate and by superinfection with the B95-8 (B virus)- and P3HR1 (P virus)-derived EBV strains. Two LMP polypeptides of 60 and 48 kilodaltons (kDa) were detected in immunoblots of Daudi cells that had been exposed to 3 mM n-butyrate for 24 h. The intensity of the 48-kDa LMP increased during 72 h, in parallel with the appearance of early antigen-positive cells. The 60-kDa LMP was expressed at a low level and remained constant. Superinfection of Daudi cells with B and P virus induced the 60-kDa LMP within 3 h. In addition, P virus induced the 48-kDa LMP at a low level. The B virus-encoded EBNA-2 and EBNA-5 were detected 12 h after superinfection. The B virus-encoded 63-kDa LMP was coexpressed with the endogenous LMP after 48 h. Inactivation of the virus by UV illumination abolished the expression of the B virus-encoded antigens but did not affect the induction of the endogenous LMP. The B-cell activation marker CD23 was up regulated by B virus superinfection but not by n-butyrate exposure. CD23 was also expressed at a higher level in a stable B virus-converted subline, E95A-Daudi, that was EBNA-2 positive and coexpressed the Daudi virus- and B virus-encoded LMP. The results suggest that LMP expression is regulated by the interaction of cellular and viral factors. Binding of the virus to its membrane receptor might be involved in the triggering of cellular control mechanisms. Viral gene products are not directly involved in this function but may contribute to create a permissive cellular environment for LMP expression.

Epstein-Barr virus small nuclear RNAs are not expressed in permissively infected cells in AIDS-associated leukoplakia

Epstein-Barr virus (EBV) DNA structure and gene expression were analyzed in tissue specimens from oral hairy leukoplakia (HLP), a mucocutaneous lesion that develops in patients infected with human immunodeficiency virus (HIV). The structure of the terminal restriction enzyme fragments of EBV revealed that HLP is a permissive infection without a predominant, detectable population of EBV episomal DNA. In RNA preparations from this uniquely permissive infection, EBV replicative mRNAs could be identified by Northern analysis; however, the virally encoded small nuclear RNAs, the EBERs, were not detected in most HLP RNA preparations. In situ hybridization detected EBER expression in very rare cells. These data indicate that unlike other viral small nuclear RNAs, the EBERs are not expressed during viral replication and must participate in the complex maintenance of latent EBV infection.

High frequency of Epstein-Barr virus genome detection in Hodgkin's disease of HIV-positive patients

Lymph nodes obtained from 7 HIV-positive and 20 HIV-negative patients with Hodgkin's disease were examined for the presence of Epstein-Barr virus antigens and genome. EBV antigens were observed in only 2 out of 20 HIV-negative patients, whereas lymph nodes of HIV-positive patients did not reveal evidence of EBV antigens. By in situ hybridization and Southern blot analysis, EBV genome was found in 5 out of 7 HIV-positive patients; the EBV genome was detected in the nucleus of Reed-Sternberg and Hodgkin's cells. EBV DNA was observed by in situ hybridization and Southern blot analysis in only 3 out of 20 HIV-negative patients with Hodgkin's disease. In both groups, Reed-Sternberg and Hodgkin's cells were negative for C3d EBV receptor. Our results show a statistically significant increased expression of EBV DNA in HIV-positive patients with Hodgkin's disease, as compared with HIV-negative patients with HD.

Novel transcription from the Epstein-Barr virus terminal EcoRI fragment, DIJhet, in a nasopharyngeal carcinoma

Transcription of Epstein-Barr virus (EBV) genes in epithelial tissue, one of the two principal cell types infected by EBV, is not well characterized. EBV transcription in a nasopharyngeal carcinoma established in nude mice, C15, has been analyzed by using strand-specific RNA probes and sequence analysis of a C15 cDNA library. In C15, two equally abundant mRNAs of 3.7 and 2.8 kilobases (kb) are encoded by the sequences that encode latent membrane protein (LMP). Hybridization with probes specific for the 3' end of the LMP mRNA to Northern (RNA) blots and sequence analysis of cDNAs representing the messages indicated that the 3.7- and 2.8-kb mRNAs are 3' coterminal. Sequence analysis of additional cDNAs revealed an mRNA that is spliced identically to the LMP mRNA but is initiated 5' to the promoter for LMP. A probe representing the sequences contained within the cDNA which are 5' to the LMP promoter identified the 3.7-kb mRNA in C15 and a low-abundance 3.7-kb mRNA in B95-8 RNA. These data indicate that transcription of the LMP-encoding sequences is complex and that LMP can be expressed from an additional RNA in both nasopharyngeal carcinoma and lymphoid cells. Hybridization with BamHI-A identified a predominant 4.8-kb mRNA and two less abundant larger-molecular-weight mRNAs transcribed in C15. These mRNAs are consistently expressed in all passages in nude mice of the C15 tumor. Hybridization with strand-specific probes and sequence analysis of three cDNAs revealed that these mRNAs are transcribed from left to right. Sequence analysis of cDNAs representing the 3' end of the mRNAs identified an open reading frame that could potentially encode a protein of 174 amino acids. In situ hybridization of a 35S-labeled RNA probe homologous to the BamHI-A cDNA to tissue sections revealed that the BamHI-A mRNA is not focally expressed and is transcribed in all cells within the C15 tumor. Linear forms of EBV DNA were not detected in any of the C15 tumors, and replicative viral antigens have not been detected. These data suggest that the C15 tumor represents a latently infected tumor and that the transcription from BamHI-A, which is expressed in all cells, is not associated with virus replication.

Expression of the Epstein-Barr virus (EBV)-encoded membrane antigen (LMP) increases the stimulatory capacity of EBV-negative B lymphoma lines in allogeneic mixed lymphocyte cultures

Epstein-Barr virus (EBV)-negative Burkitt lymphoma (BL) lines are poor stimulators in allogeneic mixed lymphocyte cultures compared to EBV-transformed lymphoblastoid cell lines derived from the same individuals. We have previously shown that the stimulatory capacity of the tumor cells is increased after EBV conversion (Avila-Carino et al., Int. J. Cancer 1987. 40: 691). As a first step towards the identification of the viral gene product responsible for this change we have studied the influence of the EBV latent membrane protein (LMP) on the stimulatory capacity of the EBV-negative BL lines BL41 and DG75 and the B lymphoma line BJAB. Four LMP-transfected sublines of BL41, four DG75 LMP transfectants and one LMP-transfected subline of BJAB showed a significantly stronger stimulatory capacity than the original line. The effect was directly proportional to the amount of LMP detected in each transfectant but was not due to reactivation of LMP-specific memory cells since lymphocytes from EBV-seropositive and -seronegative individuals responded equally. In order to define the relation between LMP expression and induction of stimulatory capacity, DG75 was transfected with constructs containing the LMP gene under the control of an heat-shock promoter. The peak of LMP expression in heat shock-treated cells preceded the appearance of stimulatory capacity by 6-12 h suggesting that critical amounts of the protein may be required to induce the phenotypic change recognized by the T cells. LMP influenced in a dose-dependent manner the expression of the adhesion molecules LFA-1, LFA-3 and ICAM-1 and B cell activation markers CD23 and CD39 in transfected sublines of BL41, but did not affect the expression of these markers in the DG75 and BJAB cell line. All LMP-expressing transfectants showed an increased capacity to form conjugates with unprimed allogeneic lymphocytes.

Epstein-Barr virus gene expression in interferon-treated cells. Implications for the regulation of protein synthesis and the antiviral state

This paper presents data on the effects of interferon treatment on Epstein-Barr virus (EBV) gene expression in latently infected Daudi Burkitt's lymphoma cells, and reviews the possible role of viral gene products in the regulation of translation. In Daudi cells the main virally coded RNAs are the small untranslated RNAs EBER-1 and EBER-2, two mRNAs for the DNA binding protein EBNA-1, and a number of small RNAs containing sequences from the BamHI W repeat region of the viral genome. Interferon treatment does not change the qualitative pattern of EBV gene expression but decreases the levels of the EBNA-1 mRNAs. The chromatographic behaviour of EBV-encoded RNAs on CF11-cellulose indicates that many contain double-stranded regions; these RNAs co-purify with RNA that activates the interferon-induced, dsRNA-sensitive protein kinase DAI. Computer analysis indicates that the exons transcribed from the BamHI W repeats have the potential for formation of very stable secondary structures. Many viruses can counteract the inhibition of protein synthesis mediated by the DAI-catalysed phosphorylation of initiation factor eIF-2 and our data suggest that the small RNA EBER-1 may fulfil this function in the EBV system. During the infection and immortalization of B lymphocytes by EBV the synthesis of large amounts of EBER-1 RNA might thus allow the virus to circumvent one of the interferon-mediated mechanisms of host cell defence.

Epstein-Barr virus nuclear antigen 2 transactivates latent membrane protein LMP1

Several lines of evidence are compatible with the hypothesis that Epstein-Barr virus (EBV) nuclear antigen 2 (EBNA-2) or leader protein (EBNA-LP) affects expression of the EBV latent infection membrane protein LMP1. We now demonstrate the following. (i) Acute transfection and expression of EBNA-2 under control of simian virus 40 or Moloney murine leukemia virus promoters resulted in increased LMP1 expression in P3HR-1-infected Burkitt's lymphoma cells and the P3HR-1 or Daudi cell line. (ii) Transfection and expression of EBNA-LP alone had no effect on LMP1 expression and did not act synergistically with EBNA-2 to affect LMP1 expression. (iii) LMP1 expression in Daudi and P3HR-1-infected cells was controlled at the mRNA level, and EBNA-2 expression in Daudi cells increased LMP1 mRNA. (iv) No other EBV genes were required for EBNA-2 transactivation of LMP1 since cotransfection of recombinant EBNA-2 expression vectors and genomic LMP1 DNA fragments enhanced LMP1 expression in the EBV-negative B-lymphoma cell lines BJAB, Louckes, and BL30. (v) An EBNA-2-responsive element was found within the -512 to +40 LMP1 DNA since this DNA linked to a chloramphenicol acetyltransferase reporter gene was transactivated by cotransfection with an EBNA-2 expression vector. (vi) The EBV type 2 EBNA-2 transactivated LMP1 as well as the EBV type 1 EBNA-2. (vii) Two deletions within the EBNA-2 gene which rendered EBV transformation incompetent did not transactivate LMP1, whereas a transformation-competent EBNA-2 deletion mutant did transactivate LMP1. LMP1 is a potent effector of B-lymphocyte activation and can act synergistically with EBNA-2 to induce cellular CD23 gene expression. Thus, EBNA-2 transactivation of LMP1 amplifies the biological impact of EBNA-2 and underscores its central role in EBV-induced growth transformation.

Expression of the BNLF-1 oncogene of Epstein-Barr virus in the skin of transgenic mice induces hyperplasia and aberrant expression of keratin 6

The BNLF-1 gene of Epstein-Barr virus (EBV) encodes the latent membrane protein (LMP), one of the putative oncogene products of the virus. This gene has been expressed from two different enhancer-promoter constructs in transgenic mice, to determine its biological activity and possible contribution to oncogenesis. While transgenic mice expressing LMP in many tissues demonstrated poor viability, expression of LMP specifically in the epidermis induces a phenotype of hyperplastic dermatosis. Concomitant with the expression of LMP in this tissue (and in the esophagus) is an induction of the expression of a hyperproliferative keratin, K6, at aberrant locations within the epidermis. The epithelial hyperplastic phenotype caused by the LMP-encoding transgenes implies that the LMP plays a role in the acanthotic condition of the tongue epithelium in the human EBV- and HIV-associated syndrome oral hairy leukoplakia, as well as possibly predisposing the nasopharyngeal epithelium to carcinogenesis.

CpG methylation of viral DNA in EBV-associated tumours

In EBV-immortalized lymphoblastoid cell lines (LCLs) a small number of "latent" proteins are expressed. These are the EBV nuclear antigens, EBNAs 1-6, and a latent membrane protein, LMP. We have investigated the expression of these proteins in a variety of EBV-associated tumours and cell lines. Whereas transplant and B-cell lymphomas from cotton-top tamarins appear to express the full range of antigens found in LCLs, we and others have found that in Burkitt's lymphomas (BL) and a nasopharyngeal carcinoma (NPC) isolate, EBNA expression is restricted to EBNA-I. (In NPC, but not in BL, LMP may also be expressed). In order to ask what restricts the expression of EBNA 2-6 in NPC and BL cells it seemed reasonable to consider the possibility that the DNA sequences normally regulating expression of these antigens could be chemically modified. In this analysis, a tight inverse correlation between methylation of CpG dinucleotides in the 5' flanking region of the EBNA-2 gene and the expression of EBNAs 2-6 has been revealed. In the NPC tumour, CpG methylation within the gene is also observed, as is specific methylation over the EBNA-I region I and II binding sites (in oriP). The significance of these observations is considered.

Identification of the Epstein-Barr virus terminal protein gene products in latently infected lymphocytes

The terminal protein (TP) gene produces two overlapping mRNAs in latently infected lymphocytes that are predicted to encode the similar polypeptides TP1 (497 amino acids) and TP2 (378 amino acids), with TP1 exon 1 providing 119 extra unique residues at the N terminus. Rabbit antisera were raised to procaryotic fusion proteins and used to detect expression of a predicted 53-kilodalton (kDa) TP product in transfected 293 cells and latently infected lymphocytes. Fractionation of transfected 293 cells showed this protein to be localized to an integral membrane preparation. The same fraction of latently infected lymphocytes contained proteins of 53 and 27 to 39 kDa as determined by Western immunoblotting with the TP-specific rabbit antisera. Immunoprecipitation of TP products from 35S-labeled human lymphoblastoid cells (CR/B95-8) was used in pulse-chase experiments and showed that TP1 was a labile protein with a half-life of approximately 2 to 4 h. The anti-fusion protein serum detected a 53-kDa TP1 and degradation products in the range of 25 to 35 kDa. A panel of Burkitt's lymphoma cell lines and cell lines established with virus recovered from the BL cells were analyzed by Western immunoblotting and found to contain the 53-kDa TP1 product, its degradation products, or both. Only two EBV-positive BL cell lines (BL72 and Wewak II) were negative in this assay. The results suggest that a labile TP1 protein may be expressed by most, if not all, EBV-infected cell lines.

The divergence between two oncogenic Herpesvirus saimiri strains in a genomic region related to the transforming phenotype

Herpesvirus saimiri strains can be divided into at least three subgroups (A, B, C) based on sequence divergence at the left end of viral unique sequence DNA. Strains of subgroups A and C are highly oncogenic and readily transform simian T-lymphocytes in vitro to interleukin-2 independent growth, while subgroup B strains do not. A left terminal reading frame of a H. saimiri subgroup A strain was shown previously to correlate with the oncogenic phenotype and in vitro transforming potential; the deduced polypeptide was termed STP-A. Furthermore, this same region contains an open reading frame (ORF) for dihydrofolate reductase (DHFR) and genes for five virus-specific U RNAs (HSURs). We now show by sequence analysis of the corresponding region in a subgroup C strain that DHFR and HSUR genes are present in both virus subgroups; however, no sequence homologous to the STP-A reading frame was found in this subgroup C virus. At a position and orientation similar to STP-A, two ORFs were found for peptides sharing a putative transmembrane domain. One of them encodes a peptide with collagen-like repetitions. In addition to the lack of similarity to STP-A, these two reading frames also did not show any similarity to known oncogenes. The organization of sequences at the left junction of unique L- and repetitive H-DNA of H. saimiri suggests frequent recombinational events, possibly accelerating the uptake of foreign genes by the virus.

Subnuclear localization and phosphorylation of Epstein-Barr virus latent infection nuclear proteins

Functions of the six Epstein-Barr virus latent infection nuclear proteins (EBNA-1, -2, -3A, -3B, -3C, or -LP) in maintaining latent infection or cell growth transformation are only partially understood. Using antibodies specific for each EBNA in immunofluorescence microscopy, EBNA-2, -3A, and -3C localized to subnuclear granules which fill much of the nucleus, excluding nucleoli. EBNA-LP localized to a small number of discrete subnuclear particles, also excluding nucleoli. Only EBNA-1 associated with metaphase chromosomes. Concordantly, in biochemical nuclear fractionation studies, EBNA-1 was the major chromatin-associated EBNA. EBNA-1 also differed from the other EBNAs in the extent of its association with the nucleoplasm and in its lack of nuclear matrix association. EBNA-LP, -2, -3A, and -3C were associated with the nuclear matrix, although they were also found in the nucleoplasm and to a lesser extent in the chromatin fractions. Metabolic 32Pi-labeling of cells followed by two-dimensional gel electrophoresis showed that EBNA-LP could be resolved into multiple phosphorylated isoforms. EBNA-2 was also phosphorylated and many isoforms were detected by isoelectric focusing.

The level of c-fgr RNA is increased by EBNA-2, an Epstein-Barr virus gene required for B-cell immortalization

The efficient immortalization of primary resting human B lymphocytes by Epstein-Barr virus (EBV) requires several viral genes and presumably the altered expression of an unknown number of cellular genes as well. In this paper, I show that infection of primary human B cells with EBV increased the transcript level of the proto-oncogene, c-fgr, 10-fold. This effect on the level of c-fgr transcripts in B cells was not secondary to blast formation, because levels of c-fgr RNA were also increased 10-fold in two proliferating EBV-negative Burkitt's lymphoma-derived cell lines, Ramos and BJAB, 2 days after infection with EBV. Two lines of evidence indicated that EBV nuclear antigen 2 (EBNA-2) mediates this increase in c-fgr RNA levels: acute infection of BJAB and Ramos cells by a mutant strain of EBV that lacked the EBNA-2 open reading frame, P3HR1, did not affect c-fgr RNA levels; and cell lines constitutively expressing only the EBNA-2 gene of EBV had increased levels of c-fgr RNA relative to those in the parental cell lines. Since P3HR1, a nonimmortalizing strain of EBV, failed to affect c-fgr RNA levels and since a viral gene required for B-cell immortalization was responsible for the induction of c-fgr, the data indicate a possible role of c-fgr expression in B-lymphocyte immortalization by EBV and a mechanism by which EBNA-2 contributes to the immortalizing activity of EBV.

Epstein-Barr virus latent membrane protein (LMP1) and nuclear proteins 2 and 3C are effectors of phenotypic changes in B lymphocytes: EBNA-2 and LMP1 cooperatively induce CD23

Latent Epstein-Barr virus (EBV) infection and growth transformation of B lymphocytes is characterized by EBV nuclear and membrane protein expression (EBV nuclear antigen [EBNA] and latent membrane protein [LMP], respectively). LMP1 is known to be an oncogene in rodent fibroblasts and to induce B-lymphocyte activation and cellular adhesion molecules in the EBV-negative Burkitt's lymphoma cell line Louckes. EBNA-2 is required for EBV-induced growth transformation; it lowers rodent fibroblast serum dependence and specifically induces the B-lymphocyte activation antigen CD23 in Louckes cells. These initial observations are now extended through an expanded study of EBNA- and LMP1-induced phenotypic effects in a different EBV-negative B-lymphoma cell line, BJAB. LMP1 effects were also evaluated in the EBV-negative B-lymphoma cell line BL41 and the EBV-positive Burkitt's lymphoma cell line, Daudi (Daudi is deleted for EBNA-2 and does not express LMP). Previously described EBNA-2- and LMP1-transfected Louckes cells were studied in parallel. EBNA-2, from EBV-1 strains but not EBV-2, induced CD23 and CD21 expression in transfected BJAB cells. In contrast, EBNA-3C induced CD21 but not CD23, while no changes were evident in vector control-, EBNA-1-, or EBNA-LP-transfected clones. EBNAs did not affect CD10, CD30, CD39, CD40, CD44, or cellular adhesion molecules. LMP1 expression in all cell lines induced growth in large clumps and expression of the cellular adhesion molecules ICAM-1, LFA-1, and LFA-3 in those cell lines which constitutively express low levels. LMP1 expression induced marked homotypic adhesion in the BJAB cell line, despite the fact that there was no significant increase in the high constitutive BJAB LFA-1 and ICAM-1 levels, suggesting that LMP1 also induces an associated functional change in these molecules. LMP1 induction of these cellular adhesion molecules was also associated with increased heterotypic adhesion to T lymphocytes. The Burkitt's lymphoma marker, CALLA (CD10), was uniformly down regulated by LMP1 in all cell lines. In contrast, LMP1 induced unique profiles of B-lymphocyte activation antigens in the various cell lines. LMP1 induced CD23 and CD39 in BJAB; CD23 in Louckes; CD39 and CD40 in BL41; and CD21, CD40, and CD44 in Daudi. In BJAB, CD23 surface and mRNA expression were markedly increased by EBNA-2 and LMP1 coexpression, compared with EBNA-2 or LMP1 alone. This cooperative effect was CD23 specific, since no such effect was observed on another marker, CD21.(ABSTRACT TRUNCATED AT 400 WORDS)

A second Epstein-Barr virus membrane protein (LMP2) is expressed in latent infection and colocalizes with LMP1

Recent cDNA cloning and sequencing of two Epstein-Barr virus (EBV)-specific mRNAs from latently infected cultures revealed that these RNAs are encoded across the fused terminal repeats of the viral genome and that they are likely to encode two nearly identical proteins with the same transmembrane domains. The smaller predicted protein (LMP2B) lacks 119 amino-terminal amino acids found in the larger one (LMP2A). To test whether these proteins are expressed in latently infected lymphocytes, antibodies to the LMP2 proteins were derived by immunizing rabbits with TrpE-LMP2A fusion proteins. Affinity-purified LMP2-specific antibodies recognized 54- and 40-kilodalton proteins, corresponding to LMP2A and LMP2B, in immunoblots of rodent fibroblasts stably transfected with eucaryotic expression plasmids containing either the LMP2A or LMP2B cDNA. Similar-size proteins were also identified in immunoblots of latently infected lymphocytes. LMP2A localized to membranes in cellular fractionation studies. In immunofluorescent studies, LMP2 localized in the plasma membrane of EBV-infected lymphocytes, with the majority of reactivity confined to the region of the LMP1 patch. This reactivity was detected in almost all lymphoblastoid cells latently infected with EBV.

Epstein-Barr virus nuclear antigen 2 induces expression of the virus-encoded latent membrane protein

Infection of Epstein-Barr virus-negative human B-lymphoma cell lines with the fully transforming B95.8 Epstein-Barr virus strain was associated with complete virus latent gene expression and a change in the cell surface and growth phenotype toward that of in vitro-transformed lymphoblastoid cell lines. In contrast, the cells infected with the P3HR1 Epstein-Barr virus strain, a deletion mutant that cannot encode Epstein-Barr nuclear antigen 2 (EBNA2) or a full-length EBNA-LP, expressed EBNAs1, 3a, 3b, and 3c but were negative for the latent membrane protein (LMP) and showed no change in cellular phenotype. This suggests that EBNA2 and/or EBNA-LP may be required for subsequent expression of LMP in Epstein-Barr virus-infected B cells. Recombinant vectors capable of expressing the B95.8 EBNA2A protein were introduced by electroporation into two P3HR1-converted B-lymphoma cell lines, BL30/P3 and BL41/P3. In both cases, stable expression of EBNA2A was accompanied by activation of LMP expression from the resident P3HR1 genome; control transfectants that did not express the EBNA2A protein never showed induction of LMP. In further experiments, a recombinant vector capable of expressing the full-length B95.8 EBNA-LP was introduced into the same target lines. Strong EBNA-LP expression was consistently observed in the transfected clones but was never accompanied by induction of LMP. The EBNA2A gene transfectants expressing EBNA2A and LMP showed a dramatic change in cell surface and growth phenotype toward a pattern like that of lymphoblastoid cell lines; some but not all of these changes could be reproduced in the absence of EBNA2A by transfection of P3HR1-converted cell lines with a recombinant vector expressing LMP. These studies suggest that EBNA2 plays an important dual role in the process of B-cell activation to the lymphoblastoid phenotype; the protein can have a direct effect upon cellular gene expression and is also involved in activating the expression of a second virus-encoded effector protein, LMP.

Epstein-Barr virus latent membrane protein inhibits human epithelial cell differentiation

Epstein-Barr virus (EBV), a human herpesvirus, is strongly linked with two relatively rare forms of B-cell lymphoma and with a much more prevalent epithelial malignancy, undifferentiated nasopharyngeal carcinoma (NPC). The availability of suitable culture systems has allowed detailed analysis of EBV-induced growth transformation in B lymphocytes, but little is known about the virus--epithelial cell interaction or about the possible effector role of viral proteins in the pathogenesis of NPC. Here we describe an experimental system to monitor the effects of introduced viral or cellular genes upon human epithelial cell growth and differentiation. We transfected a human epithelial cell line, which retains several features of normal keratinocyte behaviour in vitro, with the EBV gene encoding latent membrane protein (LMP), one of only two viral proteins known to be expressed in NPC cells in vivo. LMP expression was accompanied by changes in the epithelial cell surface phenotype, mimicking surface changes observed in NPC cells, and by severe impairment of the cellular response to differentiation signals. The ability of LMP to inhibit terminal differentiation indicates a mechanism whereby EBV infection of squamous epithelium could contribute to the multi-step pathogenesis of NPC.

Establishment of immortalized primate epithelial cells with sub-genomic EBV DNA

The genetic information in a sub-fragment of EBV DNA, designated p31 (containing less than a quarter of the viral genome and derived from a recombinant DNA cosmid library) allows epithelial cells from primary monkey and human kidney cultures to escape senescence under standard tissue culture conditions. A number of epithelial cell lines, designated M1/31, 483/31, 199/31 and HK/31, have been established and characterized following transfection of primary cells with p31 DNA. They share many properties, although morphologically they are not all identical. The cultures are immortalized but not fully transformed or tumorigenic. They appear to be phenotypically stable, although DNA hybridization studies indicate that genotypic alterations, including amplification, occur subsequent to transfection with p31 DNA and the establishment of a continuously proliferating epithelium. All cell lines consistently express high levels of cytokeratin 18 and varying amounts of cytokeratin 7, demonstrating their epithelial origin. From a single marmoset kidney (designated 199) a series of related immortalized cells, with subtle phenotypic differences, have been generated by p31 or sub-fragments of it. Although hallmarks of a "hit-and-run" mechanism are apparent in all of our studies, 2 different techniques (in situ hybridization or selection for cell survival in semi-solid media, followed by nucleic acid hybridization) show that, in late-passaged cultures, a small proportion of the cells still contain some viral DNA. The studies focus on genetic information within the BamHI A and I regions as being relevant to immortalization. The role of the EBV DNA fragment in the genesis of epithelial cell lines is considered.

cis-acting regulatory elements near the Epstein-Barr virus latent-infection membrane protein transcriptional start site

Epstein-Barr virus (EBV) latent-infection membrane protein (LMP) gene cis-acting regulatory sequences were assayed in human B lymphocytes by using chloramphenicol acetyltransferase (cat) gene expression as a reporter. The activities of progressively longer upstream elements from bases -55 to -2350 were compared. At least two positive cis-activating regulatory components (-155 to -147 and -234 to -205) upstream of the LMP promoter were defined. LMP promoter cat gene constructs were more active in a Burkitt's lymphoma cell line latently infected with the B95 EBV strain than in the same cells latently infected with the P3HR1 EBV strain. Since the P3HR1- and B95-infected cells differ in EBNA-2 and EBNA-LP expression, EBNA-2 or EBNA-LP is a likely transactivator of the LMP promoter. Probable cognate sequences for known transcription factors in the LMP promoter are discussed.

Stable transfection of Epstein-Barr virus (EBV) nuclear antigen 2 in lymphoma cells containing the EBV P3HR1 genome induces expression of B-cell activation molecules CD21 and CD23

A set of B-cell activation molecules, including the Epstein-Barr virus (EBV) receptor CR2 (CD21) and the B-cell activation antigen CD23 (Blast2/Fc epsilon RII), is turned on by infecting EBV-negative B-lymphoma cell lines with immortalizing strains of the viruslike B95-8 (BL/B95 cells). This up regulation may represent one of the mechanisms involved in EBV-mediated B-cell immortalization. The P3HR1 nonimmortalizing strain of the virus, which is deleted for the entire Epstein-Barr nuclear antigen 2 (EBNA2) protein open reading frame, is incapable of inducing the expression of CR2 and CD23, suggesting a crucial role for EBNA2 in the activation of these molecules. In addition, lymphoma cells containing the P3HR1 genome (BL/P3HR1 cells) do not express the viral latent membrane protein (LMP), which is regularly expressed in cells infected with immortalizing viral strains. Using electroporation, we have transfected the EBNA2 gene cloned in an episomal vector into BL/P3HR1 cells and have obtained cell clones that stably express the EBNA2 protein. In these clones, EBNA2 expression was associated with an increased amount of CR2 and CD23 steady-state RNAs. Of the three species of CD23 mRNAs described, the Fc epsilon RIIa species was preferentially expressed in these EBNA2-expressing clones. An increased cell surface expression of CR2 but not of CD23 was observed, and the soluble form of CD23 molecule (SCD23) was released. We were, however, not able to detect any expression of LMP in these cell clones. These data demonstrate that EBNA2 gene is able to complement P3HR1 virus latent functions to induce the activation of CR2 and CD23 expression, and they emphasize the role of EBNA2 protein in the modulation of cellular gene implicated in B-cell proliferation and hence in EBV-mediated B-cell immortalization. Nevertheless, EBNA2 expression in BL/P3HR1 cells is not able to restore the level of CR2 and CD23 expression observed in BL/B95 cells, suggesting that other cellular or viral proteins may also have an important role in the activation of these molecules: the viral LMP seems to be a good candidate.

Regulation of c-fgr proto-oncogene expression in Epstein-Barr virus infected B-cell lines

We and others have previously shown that in vitro conversion of Epstein-Barr virus (EBV)-negative Burkitt lymphoma (BL) cell lines with the immortalizing B95-8 strain of EBV results in a marked elevation in levels of c-fgr proto-oncogene mRNA. We now show, using a nuclear run-off assay, that this induction results from an increase in the rate of transcription of the c-fgr gene. We also show that BL cell lines freshly converted with the non-immortalizing HR-I strain of EBV do not accumulate higher levels of c-fgr mRNA, suggesting that EBNA-2 and/or LMP, the genes which are deleted in the HR-I strain, may be involved in the pathway which leads to changes in c-fgr gene expression. In order to assess the generality of a role for the c-fgr gene in the response of B-lymphocytes to EBV-infection, which is controversial, we have analysed c-fgr expression in 6 freshly immortalized cell lines established by EBV (B95-8) infection of B-lymphocytes from the peripheral blood of normal adults and of adults with rheumatoid arthritis, from cord blood, and from foetal liver. All 6 cell lines expressed c-fgr mRNA at elevated levels compared to EBV-negative BL cell lines.

Regulated expression of Epstein-Barr virus nuclear antigen 3-encoding gene carried on stable episomal vectors in human cells

Recently a small number of Epstein-Barr viral (EBV) genes, characteristically expressed in latently infected, growth-transformed B-lymphocytes, have been cloned and several have been transiently expressed by DNA transfection. Here we demonstrate production of stable human cell lines containing episomal EBV vectors and expressing EBV nuclear antigen 3 from the adenovirus major late promoter or the mouse metallothionein promoter, which retains metal-regulation in the episomal state. This system has proved useful in an analysis of the role of these and other EBV genes implicated in immortalization and/or oncogenic transformation of human cells.

Processing of the Epstein-Barr virus-encoded latent membrane protein p63/LMP

We have analyzed the processing of the Epstein-Barr virus-encoded latent membrane protein (p63/LMP) in lymphoblastoid cell lines, Burkitt's lymphoma cell lines, and rodent fibroblasts transfected with the p63/LMP gene. Pulse-chase analysis by immunoprecipitation, under denaturing conditions, reveals a half-life of 2 h. This is due to turnover in the plasma membrane with cleavage of the protein, resulting in a 25,000-molecular-weight (p25) fragment derived from the carboxy-terminal portion of LMP. This fragment is rich in proline and acidic amino acids and sheds into the cytoplasm, where it appears to accumulate, being present in a six- to sevenfold molar excess over p63/LMP in immunoprecipitation analyses. p25 is, like p63/LMP, also phosphorylated (pp25) on serine and threonine residues, in the same ratio and to approximately the same extent as the intact p63/LMP molecule. Amino acid sequence analysis and carboxy-terminal labeling suggest that p25 is derived through a single cleavage adjacent to the sequence LGAPGGGPDNGPQDPD.

Epstein-Barr virus in nasal T-cell lymphomas in patients with lethal midline granuloma

Five cases of lethal midline granuloma were identified histologically and phenotypically as peripheral T-cell lymphomas. Epstein-Barr virus (EBV) DNA was detected in the nasal tumour biopsy specimens by Southern blotting and in-vitro hybridisation with simultaneous detection of EBV-determined nuclear antigen (EBNA) and T-cell surface markers by two-colour immunofluorescence. Further immunofluorescence and northern blotting revealed that EBNA2 gene and also latent membrane protein gene were expressed in the nasal tumour cells. The patients had high titres of antibodies to EBV. These findings suggest that lethal midline granuloma is causally associated with EBV.

Levels of Epstein-Barr virus DNA in lymphoblastoid cell lines are correlated with frequencies of spontaneous lytic growth but not with levels of expression of EBNA-1, EBNA-2, or latent membrane protein

The process of Epstein-Barr virus (EBV)-induced transformation of human B lymphocytes results in a cell line that is a mixture of latently and lytically infected cells, with the lytic cells composing roughly 5% to less than 0.0001% of the overall population. A set of nine normal lymphoblastoid cell lines that span a 100- to 200-fold range in average EBV DNA content were studied, and the frequency with which these cells entered a lytic phase of viral growth correlated with their EBV DNA copy number (as a population average). However, neither factor correlated with the levels of expression of transcript for the viral genes EBNA-1, EBNA-2, and latent membrane protein, nor did they correlate with the levels of EBNA-2 protein and latent membrane protein. The rate at which a cell line enters into lytic growth spontaneously is therefore not dependent on the overall steady-state levels of expression of these latent-phase genes.