Deletion of the nontransforming Epstein-Barr virus strain P3HR-1 causes fusion of the large internal repeat to the DSL region

The DNA loop release factor WAPL suppresses Epstein-Barr virus latent membrane protein expression to maintain the highly restricted latency I program

Epstein-Barr virus (EBV) uses latency programs to colonize the memory B-cell reservoir, and each program is associated with human malignancies. However, knowledge remains incomplete of epigenetic mechanisms that maintain the highly restricted latency I program, present in memory and Burkitt lymphoma cells, in which EBNA1 is the only EBV-encoded protein expressed. Given increasing appreciation that higher order chromatin architecture is an important determinant of viral and host gene expression, we investigated roles of Wings Apart-Like Protein Homolog (WAPL), a host factor that unloads cohesins to control DNA loop size and that was discovered as an EBNA2-associated protein. WAPL knockout (KO) in Burkitt cells de-repressed LMP1 and LMP2A expression but not other EBV oncogenes to yield a viral program reminiscent of EBV latency II, which is rarely observed in B-cells. WAPL KO also increased LMP1/2A levels in latency III lymphoblastoid cells. WAPL KO altered EBV genome architecture, triggering formation of DNA loops between the LMP promoter region and the EBV origins of lytic replication (oriLyt). Hi-C analysis further demonstrated that WAPL KO reprograms EBV genomic DNA looping. LMP1 and LMP2A de-repression correlated with decreased histone repressive marks at their promoters. We propose that EBV coopts WAPL to negatively regulate latent membrane protein expression to maintain Burkitt latency I.

Author Summary

EBV is a highly prevalent herpesvirus etiologically linked to multiple lymphomas, gastric and nasopharyngeal carcinomas, and multiple sclerosis. EBV persists in the human host in B-cells that express a series of latency programs, each of which is observed in a distinct type of human lymphoma. The most restricted form of EBV latency, called latency I, is observed in memory cells and in most Burkitt lymphomas. In this state, EBNA1 is the only EBV-encoded protein expressed to facilitate infected cell immunoevasion. However, epigenetic mechanisms that repress expression of the other eight EBV-encoded latency proteins remain to be fully elucidated. We hypothesized that the host factor WAPL might have a role in restriction of EBV genes, as it is a major regulator of long-range DNA interactions by negatively regulating cohesin proteins that stabilize DNA loops, and WAPL was found in a yeast 2-hybrid screen for EBNA2-interacting host factors. Using CRISPR together with Hi-ChIP and Hi-C DNA architecture analyses, we uncovered WAPL roles in suppressing expression of LMP1 and LMP2A, which mimic signaling by CD40 and B-cell immunoglobulin receptors, respectively. These proteins are expressed together with EBNA1 in the latency II program. We demonstrate that WAPL KO changes EBV genomic architecture, including allowing the formation of DNA loops between the oriLyt enhancers and the LMP promoter regions. Collectively, our study suggests that WAPL reinforces Burkitt latency I by preventing the formation of DNA loops that may instead support the latency II program.

Epstein-Barr virus-encoded EBNA2 downregulates ICOSL by inducing miR-24 in B-cell lymphoma

ABSTRACT

Hematological malignancies such as Burkitt lymphoma (BL), Hodgkin lymphoma (HL), and diffuse large B-cell lymphoma (DLBCL) cause significant morbidity in humans. A substantial number of these lymphomas, particularly HL and DLBCLs have poorer prognosis because of their association with Epstein-Barr virus (EBV). Our earlier studies have shown that EBV-encoded nuclear antigen (EBNA2) upregulates programmed cell death ligand 1 in DLBCL and BLs by downregulating microRNA-34a. Here, we investigated whether EBNA2 affects the inducible costimulator (ICOS) ligand (ICOSL), a molecule required for efficient recognition of tumor cells by T cells through the engagement of ICOS on the latter. In virus-infected and EBNA2-transfected B-lymphoma cells, ICOSL expression was reduced. Our investigation of the molecular mechanisms revealed that this was due to an increase in microRNA-24 (miR-24) by EBNA2. By using ICOSL 3' untranslated region-luciferase reporter system, we validated that ICOSL is an authentic miR-24 target. Transfection of anti-miR-24 molecules in EBNA2-expressing lymphoma cells reconstituted ICOSL expression and increased tumor immunogenicity in mixed lymphocyte reactions. Because miR-24 is known to target c-MYC, an oncoprotein positively regulated by EBNA2, we analyzed its expression in anti-miR-24 transfected lymphoma cells. Indeed, the reduction of miR-24 in EBNA2-expressing DLBCL further elevated c-MYC and increased apoptosis. Consistent with the in vitro data, EBNA2-positive DLBCL biopsies expressed low ICOSL and high miR-24. We suggest that EBV evades host immune responses through EBNA2 by inducing miR-24 to reduce ICOSL expression, and for simultaneous rheostatic maintenance of proproliferative c-MYC levels. Overall, these data identify miR-24 as a potential therapeutically relevant target in EBV-associated lymphomas.

Co-Expression of the Epstein-Barr Virus-Encoded Latent Membrane Proteins and the Pathogenesis of Classic Hodgkin Lymphoma

The Epstein-Barr virus (EBV) is present in the tumour cells of a subset of patients with classic Hodgkin lymphoma (cHL), yet the contribution of the virus to the pathogenesis of these tumours remains only poorly understood. The EBV genome in virus-associated cHL expresses a limited subset of genes, restricted to the non-coding Epstein-Barr virus-encoded RNAs (EBERs) and viral miRNA, as well as only three virus proteins; the Epstein-Barr virus nuclear antigen-1 (EBNA1), and the two latent membrane proteins, known as LMP1 and LMP2, the latter of which has two isoforms, LMP2A and LMP2B. LMP1 and LMP2A are of particular interest because they are co-expressed in tumour cells and can activate cellular signalling pathways, driving aberrant cellular transcription in infected B cells to promote lymphomagenesis. This article seeks to bring together the results of recent studies of the latent membrane proteins in different B cell systems, including experiments in animal models as well as a re-analysis of our own transcriptional data. In doing so, we summarise the potentially co-operative and antagonistic effects of the LMPs that are relevant to B cell lymphomagenesis.

Epstein-Barr virus large tegument protein BPLF1 contributes to innate immune evasion through interference with toll-like receptor signaling

Viral infection triggers an early host response through activation of pattern recognition receptors, including Toll-like receptors (TLR). TLR signaling cascades induce production of type I interferons and proinflammatory cytokines involved in establishing an anti-viral state as well as in orchestrating ensuing adaptive immunity. To allow infection, replication, and persistence, (herpes)viruses employ ingenious strategies to evade host immunity. The human gamma-herpesvirus Epstein-Barr virus (EBV) is a large, enveloped DNA virus persistently carried by more than 90% of adults worldwide. It is the causative agent of infectious mononucleosis and is associated with several malignant tumors. EBV activates TLRs, including TLR2, TLR3, and TLR9. Interestingly, both the expression of and signaling by TLRs is attenuated during productive EBV infection. Ubiquitination plays an important role in regulating TLR signaling and is controlled by ubiquitin ligases and deubiquitinases (DUBs). The EBV genome encodes three proteins reported to exert in vitro deubiquitinase activity. Using active site-directed probes, we show that one of these putative DUBs, the conserved herpesvirus large tegument protein BPLF1, acts as a functional DUB in EBV-producing B cells. The BPLF1 enzyme is expressed during the late phase of lytic EBV infection and is incorporated into viral particles. The N-terminal part of the large BPLF1 protein contains the catalytic site for DUB activity and suppresses TLR-mediated activation of NF-κB at, or downstream of, the TRAF6 signaling intermediate. A catalytically inactive mutant of this EBV protein did not reduce NF-κB activation, indicating that DUB activity is essential for attenuating TLR signal transduction. Our combined results show that EBV employs deubiquitination of signaling intermediates in the TLR cascade as a mechanism to counteract innate anti-viral immunity of infected hosts.

Epstein-Barr virus (EBV) is a human herpesvirus that persistently infects >90% of adults worldwide. One factor underlying the ability of EBV to establish such widespread and lifelong infections is its capacity to escape elimination by the human immune system. Among the first lines of defense against viral infection is the human Toll-like receptor (TLR) system. These receptors can detect the presence of viruses and initiate an intracellular protein signaling cascade that leads to the expression of immune response genes. The activation status of many proteins in this signaling cascade is regulated by the addition of ubiquitin tags. EBV has previously been reported to encode enzymes, called deubiquitinases (DUBs), which are capable of removing such ubiquitin tags from substrate proteins. In our study, we found that one of these enzymes, BPLF1, functions as an active DUB during EBV production in infected cells before being packaged into newly produced viral particles. Furthermore, our study provides insight into the way in which EBV can subvert the human immune response, as we show that BPLF1 can remove ubiquitin tags from proteins in the TLR signaling cascade. This inhibits TLR signaling and decreases the expression of immune response genes.

Latency type-dependent modulation of Epstein-Barr virus-encoded latent membrane protein 1 expression by type I interferons in B cells

We report that type I interferons (IFNs) upregulate latent membrane protein 1 (LMP-1) expression by direct activation of the ED-L1 promoter in several Epstein-Barr virus (EBV)-carrying Burkitt's lymphoma lines. In EBV-infected primary B cells, IFN-α transiently upregulates LMP-1 mRNA, but not protein levels, followed by downregulation of both, suggesting a novel antiproliferative mechanism of type I IFNs. Furthermore, our results may explain the expression of LMP-1 in memory B cells of systemic lupus erythematosus patients.

Epithelial cell retention of transcriptionally active, P3HR-1-derived heterogeneous Epstein-Barr virus DNA with concurrent loss of parental virus

Deleted, rearranged, heterogeneous (het) Epstein-Barr virus (EBV) DNA with the distinctive capability of disrupting EBV latency has been reported in biopsy samples of EBV-associated tumors whose onset in immunocompetent hosts is characteristically preceded by an antibody response indicative of EBV reactivation. Using the EBV P3HR-1 strain, we have reproduced in long-term culture of SVK epithelial cells an unusual pattern of infection previously observed in a subset of tumor biopsy samples: the persistence of het DNA in the absence of the parental helper virus. Fluorescence in situ hybridization (FISH) of infected cell subclones indicated the retention of het DNA in an integrated form. Incorporation of an intact het DNA molecule was confirmed by PCR, using primers that framed junctions of the four rearranged EBV DNA segments comprising P3HR-1-derived het DNA. Structural analysis of EBV terminal repeats revealed a banding pattern consistent with the integration of het DNA as a concatemer. Linkage of concatemeric monomers was defined at a nucleotide level, and that junctional sequence was detected in cell-free P3HR-1 virion DNA, confirming that subgenomic het DNA was packaged into infectious particles in a concatemeric configuration. Stable integration into cells having lost the standard viral genome allowed the unambiguous designation of het DNA as the source for viral gene products potentially encoded by both. Continuous expression of the latency-to-lytic switch protein Zta and detection of the BALF4 gene product gB, known to expand the target cell range of standard virus when incorporated at augmented levels into infectious progeny, add to a presumption of het DNA-enhanced pathogenesis in diseases of EBV reactivation.

Viral hit and run-oncogenesis: genetic and epigenetic scenarios

It is well documented that viral genomes either inserted into the cellular DNA or co-replicating with it in episomal form can be lost from neoplastic cells. Therefore, "hit and run"-mechanisms have been a topic of longstanding interest in tumor virology. The basic idea is that the transient acquisition of a complete or incomplete viral genome may be sufficient to induce malignant conversion of host cells in vivo, resulting in neoplastic development. After eliciting a heritable change in the gene expression pattern of the host cell (initiation), the genomes of tumor viruses may be completely lost, i.e. in a hit and run-scenario they are not necessary for the maintenance of the malignant state. The expression of viral oncoproteins and RNAs may interfere not only with regulators of cell proliferation, but also with DNA repair mechanisms. DNA recombinogenic activities induced by tumor viruses or activated by other mechanisms may contribute to the secondary loss of viral genomes from neoplastic cells. Viral oncoproteins can also cause epigenetic dysregulation, thereby reprogramming cellular gene expression in a heritable manner. Thus, we expect that epigenetic scenarios of viral hit and run-tumorigenesis may facilitate new, innovative experiments and clinical studies in spite of the fact that the regular presence of a suspected human tumor virus in an early phase of neoplastic development and its subsequent regular loss have not been demonstrated yet. We propose that virus-specific "epigenetic signatures", i.e. alterations of the host cell epigenome, especially altered DNA methylation patterns, may help to identify viral hit and run-oncogenic events, even after the complete loss of tumor viruses from neoplastic cells.

KSHV-infected PEL cell lines exhibit a distinct gene expression profile

We analyzed the gene expression profiles of lymphocyte-originated tumor cell lines - primary effusion lymphoma (PEL) cell lines, T-cell leukemia (TCL) cell lines, Burkitt lymphoma (BL) cell lines - and two sets of normal peripheral blood mononuclear cells (PBMCs) - in order to determine characteristic gene expression profiles for each of the former three groups. And we found that these cell lines showed respective typical gene expression profiles and classified into clear four groups, PEL, TCL, BL, and normal PBMCs. Two B lymphocyte-originated tumor cell lines, PEL and BL cell lines, clearly exhibited distinct gene expression profiles, respectively. Even though there was only one line that was co-infected with both Kaposi's sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV), KSHV seemed to govern the gene expression profile of the co-infected line. These data suggested not only that established typical tumor cell lines show a distinct gene expression profile but also that this profile may be governed by certain viruses.

Epstein-Barr virus-encoded Bcl-2 homologue functions as a survival factor in Wp-restricted Burkitt lymphoma cell line P3HR-1

Burkitt lymphoma (BL) is etiologically associated with Epstein-Barr virus (EBV). EBV-positive BL tumors display two latent forms of infection. One is referred to as latency I infection, in which EBV expresses the virus genome maintenance protein EBNA1 as the only viral protein. The other is referred to as Wp-restricted latency and was recently identified in a subset of BL tumors. In these tumors, EBV expresses EBNA1, EBNA3A, EBNA3B, EBNA3C, a truncated form of EBNA-LP, and the viral Bcl-2 homologue BHRF1, all of which are driven by the BamHI W promoter (Wp). To investigate the role of EBV in Wp-restricted BL, we conditionally expressed a dominant-negative EBNA1 (dnEBNA1) mutant which interrupts the virus genome maintenance function of EBNA1 in the P3HR-1 BL cell line. Induction of dnEBNA1 expression caused loss of the EBV genome and resulted in apoptosis of P3HR-1 cells in the absence of exogenous apoptosis inducers, indicating that P3HR-1 cells cannot survive without EBV. Stable transfection of the BHRF1 gene into P3HR-1 cells rescued the cells from the apoptosis induced by dnEBNA1 expression, whereas stable transfection of truncated EBNA-LP, EBNA3A, or EBNA3C did not. Moreover, knockdown of BHRF1 expression in P3HR-1 cells resulted in increased cell death. These results indicate that EBV is essential for the survival of P3HR-1 cells and that BHRF1 functions as a survival factor. Our finding implies a critical contribution of BHRF1 to the pathogenesis of Wp-restricted BLs.

Points of recombination in Epstein-Barr virus (EBV) strain P3HR-1-derived heterogeneous DNA as indexes to EBV DNA recombinogenic events in vivo

Deletions and rearrangements in the genome of Epstein-Barr virus (EBV) strain P3HR-1 generate subgenomic infectious particles that, unlike defective interfering particles in other viral systems, enhance rather than restrict EBV replication in vitro. Reports of comparable heterogeneous (het) DNA in EBV-linked human diseases, based on detection of an abnormal juxtaposition of EBV DNA fragments BamHI W and BamHI Z that disrupts viral latency, prompted us to determine at the nucleotide level all remaining recombination joints formed by the four constituent segments of P3HR-1-derived het DNA. Guided by endonuclease restriction maps, we chose PCR primer pairs that approximated and framed junctions creating the unique BamHI M/B1 and E/S fusion fragments. Sequencing of PCR products revealed points of recombination that lacked regions of extensive homology between constituent fragments. Identical recombination junctions were detected by PCR in EBV-positive salivary samples from human immunodeficiency virus-infected donors, although the W/Z rearrangement that induces EBV reactivation was frequently found in the absence of the other two. In vitro infection of lymphoid cells similarly indicated that not all three het DNA rearrangements need to reside on a composite molecule. These results connote a precision in the recombination process that dictates both composition and regulation of gene segments altered by genomic rearrangement. Moreover, the apparent frequency of het DNA at sites of EBV replication in vivo is consistent with a likely contribution to the pathogenesis of EBV reactivation.

Loss of expression of Epstein-Barr virus nuclear antigen-2 correlates with a poor prognosis in cases of pyothorax-associated lymphoma

Pyothorax-associated lymphoma (PAL) is a non-Hodgkin's lymphoma, which develops in the pleural cavity of patients who have had pyothorax for over 20 years, and is strongly associated with Epstein-Barr virus (EBV) infection. The expression of latent genes, especially EBV nuclear antigen-2 (EBNA-2), influences the growth characteristics and malignant features of EBV-infected cells. Here, the effect of EBNA-2 expression on clinical features was examined in 13 cases of PAL. The EBNA-2 transcript was detected in 8 cases but was absent in 5. There was a significant difference in survival between patients with the transcripts and those without: the 1-year survival rate was 87.5 and 0%, respectively (p < 0.01). There was a discrepancy between EBNA-2 expression and EBNA promoter usage in 6 cases. The Cp/Wp promoter was used in 3 EBNA-2-negative cases, whereas the Qp promoter or multiple promoters were used in 3 EBNA-2-positive cases. Analysis of PAL cell lines provided a clue as to the mechanism underlying the discrepancy between EBNA-2 expression and EBNA promoter usage. Loss of EBNA-2 expression, irrespective of the latency pattern, is correlated with a poor prognosis, suggesting that down-regulation of the EBNA-2 expression could be selection pressure for the progression of PAL.

Epstein-Barr virus nuclear antigen 2 (EBNA2) gene deletion is consistently linked with EBNA3A, -3B, and -3C expression in Burkitt's lymphoma cells and with increased resistance to apoptosis

Most Epstein-Barr virus (EBV)-positive Burkitt's lymphomas (BLs) carry a wild-type EBV genome and express EBV nuclear antigen 1 (EBNA1) selectively from the BamHI Q promoter (latency I). Recently we identified a distinct subset of BLs carrying both wild-type and EBNA2 gene-deleted (transformation-defective) viral genomes. The cells displayed an atypical "BamHI W promoter (Wp)-restricted" form of latency where Wp (rather than Qp) was active and EBNA1, -3A, -3B, -3C, and -LP were expressed in the absence of EBNA2 or latent membrane proteins 1 and 2. Here we present data strongly supporting the view that the EBNA2-deleted genome is transcriptionally active in these cells and the wild-type genome is silent. Single-cell cloning of three parental Wp-restricted BL lines generated clones carrying either both viral genomes or the EBNA2-deleted genome only, never clones with the wild-type genome only. All rescued clones displayed the Wp-restricted form of latency characteristic of the parent line and retained the original parent cell phenotype. Interestingly, Wp-restricted parent lines and derived clones were markedly more resistant to inducers of apoptosis than standard latency I BL lines. Furthermore, in vitro infection of EBV-negative BL lines with an EBNA2 gene-deleted virus generated EBV-positive converts with Wp-restricted latency and a similarly marked apoptosis resistance. We postulate that, in the subset of BLs displaying Wp-restricted latency, infection of a tumor progenitor cell with an EBNA2 gene-deleted virus has provided that cell with a survival advantage through broadening antigen expression to include the EBNA3 proteins.

A 30 kb region of the Epstein-Barr virus genome is colinear with the rearranged human immunoglobulin gene loci: implications for a "ping-pong evolution" model for persisting viruses and their hosts. A review

The left part of the Epstein-Barr virus (EBV) genome exhibits a strong colinearity of structural and functional elements with the immunoglobulin (Ig) gene loci which is only partially reflected in nucleotide sequence homologies. We propose that this colinearity may be the result of an inter-dependent co-evolution of the immunoglobulin loci together with EBV. Our observation could help elucidating the mechanisms of somatic hypermutation, explaining the ability of EBV to accidentally cause tumors, and shedding more light on the general mechanisms of viral and organismal evolution. We suggest that persisting viruses served as a complement for the organismal germline like in a ping-pong game and outline The Ping-Pong Evolution Hypothesis.

Epstein-Barr virus latent membrane protein LMP-2A is sufficient for transactivation of the human endogenous retrovirus HERV-K18 superantigen

Superantigens are microbial proteins that strongly stimulate T cells. We described previously that the Epstein-Barr virus (EBV) transactivates a superantigen encoded by the human endogenous retrovirus, HERV-K18. We now report that the transactivation is dependent upon the EBV latent cycle proteins. Moreover, LMP-2A is sufficient for induction of HERV-K18 superantigen activity.

EBV-associated neoplasms: alternative pathogenetic pathways

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

Epstein-Barr virus-associated Burkitt lymphomagenesis selects for downregulation of the nuclear antigen EBNA2

Epstein-Barr virus (EBV) is etiologically linked to endemic Burkitt lymphoma (BL), but its contribution to lymphomagenesis, versus that of the chromosomal translocation leading to c-myc gene deregulation, remains unclear. The virus's growth-transforming (Latency III) program of gene expression is extinguished in tumor cells, and only a single viral protein, the EBV nuclear antigen (EBNA)1, is expressed via the alternative Latency I program. It is not known if BL arises from a B-cell subset in which EBV naturally adopts a Latency I infection or if a clone with limited antigen expression has been selected from an EBV-transformed Latency III progenitor pool. Here we identify a subset of BL tumors in which the Latency III-associated EBNA promoter Wp is active and most EBNAs are expressed, but where a gene deletion has specifically abrogated the expression of EBNA2. This implies that BL can be selected from a Latency III progenitor and that the principal selection pressure is for downregulation of the c-Myc antagonist EBNA2.

EBNA2 and Notch signalling in Epstein-Barr virus mediated immortalization of B lymphocytes

Epstein-Barr virus (EBV) has the ability to immortalize B cells. A viral key protein for immortalization is the transactivator EBNA2 that controls expression of several viral and cellular genes. EBNA2 is tethered to promoters by interacting with the cellular repressor RBP-J. This resembles the physiological activation of RBP-J-repressed promoters by activated Notch receptors (Notch-IC). Since EBNA2 and Notch-IC have been shown to be partially interchangeable in regard to activation of target genes in B cell lines and modulation of differentiation processes it is conceivable that EBNA2 is a biological equivalent of an activated Notch receptor.

Molecular virology of Epstein-Barr virus

Epstein-Barr virus (EBV) interacts with its host in three distinct ways in a highly regulated fashion: (i) EBV infects human B lymphocytes and induces proliferation of the infected cells, (ii) it enters into a latent phase in vivo that follows the proliferative phase, and (iii) it can be reactivated giving rise to the production of infectious progeny for reinfection of cells of the same type or transmission of the virus to another individual. In healthy people, these processes take place simultaneously in different anatomical and functional compartments and are linked to each other in a highly dynamic steady-state equilibrium. The development of a genetic system has paved the way for the dissection of those processes at a molecular level that can be studied in vitro, i.e. B-cell immortalization and the lytic cycle leading to production of infectious progeny. Polymerase chain reaction analyses coupled to fluorescent-activated cell sorting has on the other hand allowed a descriptive analysis of the virus-host interaction in peripheral blood cells as well as in tonsillar B cells in vivo. This paper is aimed at compiling our present knowledge on the process of B-cell immortalization in vitro as well as in vivo latency, and attempts to integrate this knowledge into the framework of the viral life cycle in vivo.

Immune modulation of human B lymphocytes by gene transfer with recombinant Epstein-Barr virus amplicons

We described previously a novel mode of gene transfer by infection of human B lymphocytes with recombinant Epstein-Barr virus (EBV) amplicons. This system was explored for its potential use in expressing various recombinant genes, including the cytokine IL-4, the HIV envelope glycoprotein (gp120) and a suicide and gag gene. Recombinant genes were present as multiple copy episomes and stable, high level recombinant gene expression could be detected by antigenic and functional assays. Amplicon-infected B cells secreted high levels of recombinant cytokine and efficiently presented recombinant antigens through classes I and II MHC-restricted antigen processing pathways. Thus, recombinant EBV amplicons can be used to express components of the immune system or heterologous genes for immune recognition in human B cells. Combining gene transfer with EBV infection may provide unique advantages for in vitro and in vivo gene transfer.

Early detection of the lytic LMP-1 protein in EBV-infected B-cells suggests its presence in the virion

The Epstein-Barr virus (EBV)-positive B958 cell line expresses two related membrane proteins encoded by BNLF-1 open reading frames. One protein (LMP-1) has been shown to be essential for the growth transforming properties of EBV. The second protein (the lytic LMP-1) is an amino-terminally truncated form of LMP-1 whose expression is associated with induction of EBV's lytic cycle. We have investigated the expression of full-length and lytic forms of LMP-1 immediately after infection of the EBV-negative, B-lymphoma cell line BJAB. Only the lytic LMP-1 protein is present in BJAB cells early (within minutes following addition of virus) after infection with virus derived from either uninduced or tetradecanoyl phorbol acetate and sodium butyrate-induced B958 cells. Lytic LMP-1 protein levels begin to decline by 48 hr after infection, whereas levels of full-length LMP-1 increase between 24 and 48 hr after infection and then remain constant. The presence of the lytic LMP-1 protein in infected cells is independent of both protein synthesis and virus internalization. We also find the lytic LMP-1 protein in BJAB cells early after infection (within 3 hr of addition of virus) with the HH514 strain of EBV, and HH514 cells treated with tetradecanoyl phorbol acetate and sodium butyrate, express high levels of both the lytic LMP-1 and full-length LMP-1 proteins. The lytic LMP-1 protein is enriched in purified virion preparations, and immunoelectron microscopic analysis indicates that EBV virions can be specifically labeled with anti-LMP-1 antisera. Together, these results are consistent with a model in which the lytic LMP-1 protein is present in the EBV virion and is carried into the B-cell upon infection and suggest a role for this protein in early infection events and/or in EBV's lytic cycle.

Tissue distribution of Epstein-Barr virus genotypes

The genome of naturally occurring Epstein-Barr virus contains either two or three copies of a 29-bp tandem repeat sequence in the first intron of the BZLF gene. These genotypes differ markedly in their distribution between blood and epithelial tissues, presumably because they have adapted to separate life cycles in these sites. The genotype prevalent in the blood also appears to be better able to transform B lymphocytes.

Epstein-Barr virus nuclear antigen 2 is a transcriptional suppressor of the immunoglobulin mu gene: implications for the expression of the translocated c-myc gene in Burkitt's lymphoma cells

A conditional mutant of Epstein-Barr virus nuclear antigen 2 (EBNA2) regulated by estrogen was employed to study the effect of EBNA2 on the cellular phenotype. Activation of EBNA2 in lymphoblastoid cell lines (LCLs) and in B cell lymphoma lines resulted in down-regulation of cell surface IgM and Ig-mu steady-state RNA expression. In LCLs, activation of EBNA2 is required for maintaining proliferation, whereas in Burkitt's lymphoma (BL) cell lines with t(8;14) translocations, activation of EBNA2 induces growth arrest. In these cells, Northern and nuclear run-on analyses revealed rapid simultaneous repression of Ig-mu and c-myc transcription as early as 30 min after activation of EBNA2. Since c-myc expression is under the control of the Ig heavy chain locus in BL cell lines with a t(8;14) translocation, we propose that Ig-mu and c-myc are down-regulated by EBNA2 through a common mechanism.

Epstein-Barr virus induction of recombinase-activating genes RAG1 and RAG2

In experimental B-cell infections, Epstein-Barr virus induced sustained expression of V(D)J recombinase-activating genes RAG1 and RAG2, whose aberrant activity has been implicated in chromosomal translocations in B-cell neoplasms. In cell lines in which RAG1 and RAG2 were detected, virus integrated into cellular DNA rather than assumed the configuration of extrachromosomal episomes. Expression of the Epstein-Barr virus nuclear antigen 1 in transient transfection assays was sufficient to induce both recombinase-activating genes.

Geographic sequence variation of latent membrane protein 1 gene of Epstein-Barr virus in Hodgkin's lymphomas

To assess the role of the Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) gene in the development of Hodgkin's lymphoma (HL), the polymorphism of this gene in EBV isolates from different geographic locations was analyzed. A 497 bp fragment spanning LMP1 gene exons 1 and 2 was amplified by polymerase chain reaction (PCR), using a primer pair bracketing a Xhol restriction site. PCR products were subjected to Xhol digestion and to DNA sequencing analysis. Twenty-five HL biopsy specimens from the United States and five HL and four non-Hodgkin's lymphoma (NHL) biopsy specimens from Italy were examined. Eighty percent of LMP1-positive samples (12 of 15) from the United States maintained the Xhol restriction site and the remaining 20% partially lost the Xhol site. One of four EBV-positive HL and one of the three EBV-positive NHL specimens from Italy lost the restriction site. The other three EBV-positive HL DNAs were partially cut by Xhol. Direct DNA sequencing analysis revealed that those Italian samples not digested by Xhol were due to a G to C transversion at the first base of codon 18, resulting in the change of glycine to arginine. Those DNA samples partially cut by Xhol were due to a mixture of G/C at the same location. In contrast, those partially digested American HL DNAs had a mixture of G/T at the second base of codon 17.(ABSTRACT TRUNCATED AT 250 WORDS)

A strategy for precision of genotyping of Epstein-Barr virus by polymerase chain reaction: application for studying Hodgkin's lymphoma

Previous studies on the genotyping of Epstein-Barr virus (EBV) have been based on the analysis of a single gene locus. The assignment of genotype of an isolate could easily be over-looked with this assay. Our strategy for precision of EBV genotyping has exploited the existence of two families of EBV strains (type A and B) that can be distinguished at three divergent gene loci (EBNA-2, EBNA-3C, and EBER). To precisely determine the genotype of EBV in Hodgkin's disease (HD), we designed primers and simultaneously analysed these three gene loci that distinguish type A and B viruses by the polymerase chain reaction (PCR) technique. The primers designed to amplify these three gene loci encompass either type-specific deletion sequences (EBNA-2 and EBNA-3C) or type-specific point mutations (EBER) that identify the virus strain based on the sizes of PCR-amplified products or the mobility shifts in single-strand conformation polymorphism (SSCP) analysis. The locations of point mutations were identified by direct sequencing of the PCR-amplified DNA. Fifteen EBV-infected cell lines were analysed and a good correlation between EBNA-2 and EBNA-3C typing results was found. In contrast, approximately 33% of the cell lines analysed maintained type A sequences in EBNA-2 and EBNA-3C genes while carrying type B sequences in the EBER region. Data obtained from analysis of cell lines served as a reference for studying HD samples. EBV DNA was detected in about 70% of HD. Among the EBV-positive samples, 56% were associated with type A virus, 13% with type B, and 31% with dual viral sequences.(ABSTRACT TRUNCATED AT 250 WORDS)

Crucial sequences within the Epstein-Barr virus TP1 promoter for EBNA2-mediated transactivation and interaction of EBNA2 with its responsive element

EBNA2 is one of the few genes of Epstein-Barr virus which are necessary for immortalization of human primary B lymphocytes. The EBNA2 protein acts as a transcriptional activator of several viral and cellular genes. For the TP1 promoter, we have shown previously that an EBNA2-responsive element (EBNA2RE) between -258 and -177 relative to the TP1 RNA start site is necessary and sufficient for EBNA2-mediated transactivation and that it binds EBNA2 through a cellular factor. To define the critical cis elements within this region, we cloned EBNA2RE mutants in front of the TP1 minimal promoter fused to the reporter gene for luciferase. Transactivation by EBNA2 was tested by transfection of these mutants in the absence and presence of an EBNA2 expression vector into the established B-cell line BL41-P3HR-1. The analysis revealed that two identical 11-bp motifs and the region 3' of the second 11-bp motif are essential for transactivation by EBNA2. Methylation interference experiments indicated that the same cellular factor in the absence of EBNA2 binds either one (complex I) or both (complex III) 11-bp motifs with different affinities, giving rise to two different specific protein-DNA complexes within the left-hand 54 bp of EBNA2RE. A third specific complex was shown previously to be present only in EBNA2-expressing cells and to contain EBNA2. Analysis of this EBNA2-containing complex revealed the same protection pattern as for complex III, indicating that EBNA2 interacts with DNA through binding of the cellular protein to the 11-bp motifs. Mobility shift assays with the different mutants demonstrated that one 11-bp motif is sufficient for binding the cellular factor, whereas for binding of EBNA2 as well as for efficient transactivation by EBNA2, both 11-bp motifs are required.

Autoantigenic proteins that bind recombinogenic sequences in Epstein-Barr virus and cellular DNA

We have identified conserved autoantigenic cellular proteins that bind to G-rich sequence motifs in recombinogenic regions of Epstein-Barr virus (EBV) DNA. This binding activity, called TRBP, recognizes the EBV terminal repeats, a locus responsible for interconversion of linear and circular EBV DNA. We found that TRBP also binds to EBV DNA sequences involved in deletion of EBNA2, a gene product required for immortalization. We show that TRBP binds sequences present in repetitive cellular DNA, such as variable-number tandem repeats (VNTR) and immunoglobulin heavy-chain class switch regions. We propose that EBV utilizes cellular DNA recombination systems to mediate several types of viral genome alterations. These findings may lead to an understanding of the mechanism of rearrangements of EBV DNA that are a central feature of the biology of the virus.

The Epstein-Barr virus latent membrane protein-1 (LMP1) induces interleukin-10 production in Burkitt lymphoma lines

Human interleukin-10 (h-IL-10) is a pleiotropic cytokine with stimulatory activity on B-lymphocytes. Recent evidence indicates that infection with Epstein-Barr virus (EBV) induces h-IL-10 production in B-cells and that this cytokine may contribute to EBV-induced B-cell transformation. It is not known whether h-IL-10 induction by EBV correlates with distinct phenotypic features of the infected cells or with the expression of particular viral genes. We have approached these questions by investigating the expression of h-IL-10 mRNA in a panel of B-cell lines including: in vitro EBV-transformed lymphoblastoid cell lines (LCLs), EBV-carrying Burkitt lymphoma (BL) lines, EBV-negative BL lines and their sublines infected with different EBV strains, or transfected with the transformation-associated viral gene. h-IL-10 mRNA was detected by reverse-transcriptase-assisted (RT)-PCR in a subset of EBV-negative BLs and in all EBV-positive BL lines and LCLs investigated except Daudi. This cell line carries an EBV nuclear antigen (EBNA)-2 gene-defective virus strain. h-IL-10 mRNA was induced by conversion of 3 EBV-negative and h-IL-10-negative BL lines (BL41, BL47 and BL49) with the transforming, B95.8-derived EBV strain. P3HR-I virus convertants that do not express the viral EBNA-2 and the EBV latent membrane protein (LMP)-1, and fail to progress towards a LCL-like cell phenotype, showed no evidence of h-IL-10 up-regulation. Expression of LMP1 was sufficient to induce h-IL-10 mRNA in transfected sublines of the EBV-negative DG75 and BL41 cell lines, whereas expression of EBNA1, 2, 5, or 6 had no effect. h-IL-10 was detected in the culture supernatants of the LMP1 transfectants by specific ELISA assays. The present findings confirm the role of LMP1 in the transactivation of a wide variety of cellular genes which may be involved in EBV-induced B-cell transformation.

Epstein-Barr virus and the lacrimal gland pathology of Sjögren's syndrome

The lacrimal gland (LG) immunopathology of Sjögren's syndrome (SS) consists of a proliferation of B and CD4 lymphocytes surrounding epithelial structures (Pepose JS, et al: Ophthalmology 1990, 97:1599-1605). Based on the detection of EBV genomes in a greater percentage of SS than normal LG biopsies, we previously postulated that Epstein-Barr virus (EBV) is a risk factor for LG lymphoproliferation in SS (Pflugfelder SC, et al: Ophthalmology 1990, 97:976-984). The purpose of this study was to determine the cellular site(s) of infection, virus type, and antigen expression of EBV infecting normal and SS LGs. EBV DNA was detected by in situ hybridization in intraductal epithelia in 13-33% of lobules in 21% of normal LGs and in cells in areas of B lymphoproliferation as well as the majority of epithelia in 86% of SS LGs. EBV genomic sequences were amplified from 36% of normal and 88% of SS LG biopsies by polymerase chain reaction. Only type 1 EBV sequences were amplified in SS LGs; in contrast EBV nuclear antigen 2-deleted but not type 1 sequences were amplified in normal LGs. Immunohistochemistry with EBV-specific monoclonal antibodies was performed on normal and SS LGs. No EBV antigens were detected in normal LGs. In contrast, latent antigens (latent membrane protein, EBV nuclear antigen 2) were detected in lymphocytes in areas of B lymphoproliferation, and early and late lytic cycle antigens were observed in epithelia in SS LGs. These studies suggest that EBV may play a role in the LG B lymphoproliferation and epithelial pathologic changes observed in SS.

Epstein-Barr virus nuclear antigen 2 transactivates the long terminal repeat of human immunodeficiency virus type 1

Human immunodeficiency virus type 1 (HIV-1)-infected subjects show a high incidence of Epstein-Barr virus (EBV) infection. This suggests that EBV may function as a cofactor that affects HIV-1 activation and may play a major role in the progression of AIDS. To test this hypothesis, we generated two EBV-negative human B-cell lines that stably express the EBNA2 gene of EBV. These EBNA2-positive cell lines were transiently transfected with plasmids that carry either the wild type or deletion mutants of the HIV-1 long terminal repeat (LTR) fused to the chloramphenicol acetyltransferase (CAT) gene. There was a consistently higher HIV-1 LTR activation in EBNA2-expressing cells than in control cells, which suggested that EBNA2 proteins could activate the HIV-1 promoter, possibly by inducing nuclear factors binding to HIV-1 cis-regulatory sequences. To test this possibility, we used CAT-based plasmids carrying deletions of the NF-kappa B (pNFA-CAT), Sp1 (pSpA-CAT), or TAR (pTAR-CAT) region of the HIV-1 LTR and retardation assays in which nuclear proteins from EBNA2-expressing cells were challenged with oligonucleotides encompassing the NF-kappa B or Sp1 region of the HIV-1 LTR. We found that both the NF-kappa B and the Sp1 sites of the HIV-1 LTR are necessary for EBNA2 transactivation and that increased expression resulted from the induction of NF-kappa B-like factors. Moreover, experiments with the TAR-deleted pTAR-CAT and with the tat-expressing pAR-TAT plasmids indicated that endogenous Tat-like proteins could participate in EBNA2-mediated activation of the HIV-1 LTR and that EBNA2 proteins can synergize with the viral tat transactivator. Transfection experiments with plasmids expressing the EBNA1, EBNA3, and EBNALP genes did not cause a significant HIV-1 LTR activation. Thus, it appears that among the latent EBV genes tested, EBNA2 was the only EBV gene active on the HIV-1 LTR. The transactivation function of EBNA2 was also observed in the HeLa epithelial cell line, which suggests that EBV and HIV-1 infection of non-B cells may result in HIV-1 promoter activation. Therefore, a specific gene product of EBV, EBNA2, can transactivate HIV-1 and possibly contribute to the clinical progression of AIDS.

Epstein-Barr virus nuclear proteins EBNA-3A and EBNA-3C are essential for B-lymphocyte growth transformation

Recombinant Epstein-Barr viruses (EBV) with a translation termination codon mutation inserted into the nuclear protein 3A (EBNA-3A) or 3C (EBNA-3C) open reading frame were generated by second-site homologous recombination. These mutant viruses were used to infect primary B lymphocytes to assess the requirement of EBNA-3A or -3C for growth transformation. The frequency of obtaining transformants infected with a wild-type EBNA-3A recombinant EBV was 10 to 15%. In contrast, the frequency of obtaining transformants infected with a mutant EBNA-3A recombinant EBV was only 1.4% (9 mutants in 627 transformants analyzed). Transformants infected with mutant EBNA-3A recombinant virus could be obtained only by coinfection with another transformation-defective EBV which provided wild-type EBNA-3A in trans. Cells infected with mutant EBNA-3A recombinant virus lost the EBNA-3A mutation with expansion of the culture. The decreased frequency of recovery of the EBNA-3A mutation, the requirement for transformation-defective EBV coinfection, and the inability to maintain the EBNA-3A mutation indicate that EBNA-3A is essential or critical for lymphocyte growth transformation and that the EBNA-3A mutation has a partial dominant negative effect. Five transformants infected with mutant EBNA-3C recombinant virus EBV were also identified and expanded. All five also required wild-type EBNA-3C in trans. Serial passage of the mutant recombinant virus into primary B lymphocytes resulted in transformants only when wild-type EBNA-3C was provided in trans by coinfection with a transformation-defective EBV carrying a wild-type EBNA-3C gene. A secondary recombinant virus in which the mutated EBNA-3C gene was replaced by wild-type EBNA-3C was able to transform B lymphocytes. Thus, EBNA-3C is also essential or critical for primary B-lymphocyte growth transformation.

Epstein-Barr virus (EBV) nuclear-antigen-2-induced up-regulation of CD21 and CD23 molecules is dependent on a permissive cellular context

The Epstein-Barr virus (EBV) induces unlimited growth of B lymphocytes in vitro, a phenomenon known as immortalization. The elucidation of the mechanisms by which EBV de-regulates B-cell proliferation in vitro will permit an understanding of how the virus contributes in vivo to the genesis of Burkitt's lymphoma (BL) and of lymphoproliferations in immunosuppressed patients. At present, no single EBV immortalizing gene has been identified, and the hypothesis has been made that many viral genes cooperate in establishing an autocrine loop of secretion leading to immortalization. Constitutive expression of B-cell surface molecules such as CD21 and CD23, specifically implicated in the control of B-cell proliferation, is indeed induced at the surface of immortalized B lymphocytes. The expression of the viral nuclear antigen 2 (EBNA2) has been shown to be in part responsible for CD21 and CD23 up-regulation, and EBNA2 is suspected to be a transactivator of cellular genes, although this point remains to be demonstrated. The role of EBNA2 gene, independently of other viral genes, has been investigated by transfection into B-lymphoma lines, but conflicting results have been reported. To further investigate its role in the regulation of CD21 and CD23 molecules, we have compared the effects of EBNA2 expression in 2 sets of B-lymphoma lines infected with P3HR1 EBV strain, and/or transfected with EBNA2 gene. We report here that: (i) EBNA2 expression is not a sufficient condition to induce CD21 and CD23 upregulation, EBNA2's effects are highly dependent on the cellular context, and moreover can be modified by infection with P3HR1 virus; (ii) EBNA2 induces activation of CD23 expression in a very particular way, namely, an increased quantity of CD23 steady-state RNA coding for the form A of the protein, which is not detectable at the cell surface but directly secreted.

Expression of the Epstein-Barr virus (EBV) latent membrane protein is tightly regulated, independently of EB nuclear antigen 2 and of EBV integration or copy number

In vivo, Epstein-Barr virus (EBV) is associated with human tumours and with lymphoproliferations in immunosuppressed patients. In vitro, EBV induces unlimited growth of normal B-lymphocytes, a phenomenon known as immortalization. A limited number of viral genes is expressed during this phenomenon and their relative role concerning the deregulation of cellular proliferation is still unclear. At present, the nuclear antigen EBNA2 and the membrane protein LMP are the two EBV proteins considered to be implicated in the immortalization process. Moreover, many data support the hypothesis that EBNA2 is the major inducer of LMP expression by transactivation; however, in some instances, expression of the two proteins is not correlated, suggesting the existence of complex interactions between EBV and its host-cell that influence viral gene regulation. In an attempt to study thoroughly these EBNA2/LMP interactions, it is important to evaluate whether EBNA2 is or is not a major inducer of LMP expression, and which other parameters can influence LMP expression. By analysing two sets of B-lymphoma lines either infected in vitro with EBV or stably transfected with EBNA2, we have demonstrated that (1) LMP expression can be absolutely independent of EBNA2 expression, (2) the level of LMP expression is very tightly regulated, and is independent of EBV genome status (integrated or episomal) and copy number. Our findings provide compelling evidence that LMP expression has to be related to that of cellular factors that remain to be identified.

The only domain which distinguishes Epstein-Barr virus latent membrane protein 2A (LMP2A) from LMP2B is dispensable for lymphocyte infection and growth transformation in vitro; LMP2A is therefore nonessential

Using second-site homologous recombination, Epstein-Barr virus (EBV) recombinants were constructed which carry an LMP2A mutation terminating translation at codon 19. Despite the absence of LMP2A or LMP2A cross-reactive protein, the recombinants were able to initiate and maintain primary B-lymphocyte growth transformation in vitro. EBNA1, EBNA2, and LMP1 expression was unaffected by the LMP2A mutation. The LMP2A mutant recombinant EBV-infected lymphoblastoid cell lines (LCLs) were identical to wild-type recombinant EBV-infected control LCLs with respect to initial outgrowth, subsequent growth, sensitivity to limiting cell dilution, sensitivity to low serum, and growth in soft agarose. The permissivity of LCLs for lytic EBV infection and virus replication was also unaffected by the LMP2A mutation.

Use of second-site homologous recombination to demonstrate that Epstein-Barr virus nuclear protein 3B is not important for lymphocyte infection or growth transformation in vitro

Recombinant Epstein-Barr viruses with a stop codon inserted into the nuclear protein 3B (EBNA 3B) open reading frame were generated by second-site homologous recombination. These mutant viruses infected and growth transformed primary B lymphocytes, resulting in the establishment of lymphoblastoid cell lines (LCLs). Polymerase chain reaction analysis and Southern hybridizations with infected cell DNA demonstrated the presence of the mutant EBNA 3B and the absence of wild-type EBNA 3B. Immunoblot analysis of the LCLs with affinity-purified EBNA 3B antibodies confirmed the absence of EBNA 3B cross-reactive protein. Virus was reactivated from two of these infected LCLs and serially passaged through primary B lymphocytes. The newly infected cells contained only the mutant recombinant virus. No difference was noted between mutant and wild-type recombinants, derived in parallel, in latent (other than EBNA 3B) or lytic cycle-infected cell virus protein expression or in the growth of the latently infected transformed cell lines. These data indicate that the EBNA 3B protein is not critical for primary B-lymphocyte infection, growth transformation, or lytic virus infection in vitro.

Host cell and EBNA-2 regulation of Epstein-Barr virus latent-cycle promoter activity in B lymphocytes

The six latent-cycle nuclear antigens (EBNAs) of Epstein-Barr virus (EBV), whose genes share 5' leader exons and two promoters (Cp and Wp), are differentially expressed by cells of the B lineage. To examine the possibility that EBNA gene expression is regulated through selective use of Cp and Wp, we monitored the activity of promoter-chloramphenicol acetyltransferase (CAT) gene constructs transfected into EBV-positive and EBV-negative B lymphocytes and Burkitt's lymphoma cells. Wp was a much stronger promoter than Cp in EBV genome-negative B-cell lines and was used exclusively in primary B cells. When B cells were infected with transforming EBV, Cp became the stronger promoter. This switch was not observed when B cells were infected with an immortalization-deficient virus, P3HR-1, which lacks the EBNA-2 open reading frame and expresses a mutant leader protein (EBNA-LP). Cp function was transactivated when EBV-negative or P3HR-1-infected B cells were cotransfected with Cp and a 12-kb fragment of DNA (BamHI-WWYH) that spanned the P3HR-1 deletion. This activity was mapped to the EBNA-2 gene within WWYH; constructs expressing EBNA-LP did not induce Cp function, and the deletion of 405 bp from the EBNA-2 open reading frame abolished transactivation. This research demonstrates host cell and EBNA-2 regulation of latent-cycle promoter activity in B lymphocytes, a mechanism with implications for persistence of EBV-infected lymphoid cells in vivo.

Identification of the gene product encoded by the PstI repeats (IR4) of the Epstein-Barr virus genome

The Epstein-Barr virus (EBV) genome contains several clusters of internal repeats (IR). Here we report the identification of the repetitive protein encoded by the IR4 region (PstI repeats). This IR4 protein is inducible by TPA and n-butyrate and belongs to the EA-D subgroup of the EBV-encoded early antigens. Its molecular size varies between different EBV strains. Furthermore, several human EBV-positive sera reacted with a part of the IR4 protein expressed as a fusion protein. These data indicate the in vivo expression of this protein during the course of an EBV infection.

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.

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.

Sequence and transcription of Raji Epstein-Barr virus DNA spanning the B95-8 deletion region

The DNA sequence of Raji DNA spanning the deletion found in B95-8 cells has been determined. Three open reading frames and a region of homology with the BamHI-H fragment are found within the deletion. The deletion contains a region of 102-bp repeats which is transcribed into an mRNA. The Raji sequence reported here varies slightly from a smaller M-ABA sequence reported previously. This paper completes the sequence of all parts of the wild-type Epstein-Barr virus genome.

Modulation of cellular gene expression in B lymphoma cells following in vitro infection by Epstein-Barr virus (EBV)

In vitro infection of EBV-negative lymphoma cell lines with immortalizing strains of Epstein-Barr virus induces the cell-surface expression of B-cell markers, such as the EBV receptor/CR2 (CD21) and the CD23 antigen. The non-immortalizing EBV variant, P3HRI, which carries a deletion encompassing the EBV nuclear antigen 2 (EBNA2) gene, fails to induce any such expression. We show here that the EBV-mediated up-regulation of cell-surface expression of these molecules is associated with an increased level of the specific steady-state RNA corresponding to these 2 genes. These results suggest that the role of EBNA2 in B-cell growth and immortalization may be related to its role in transactivation of cellular genes. In order to identify other cellular genes whose expression may be modulated by EBV, we analyzed the level of transcription of a set of genes possibly involved in Burkitt's lymphoma pathogenesis. The level of the c-myc oncogene transcript was not significantly affected by in vitro EBV infection. The c-fgr oncogene, thought to be specifically activated in EBV-infected cells, was found to be expressed in some EBV-negative lymphoma cells and also to be activated by both non-immortalizing and immortalizing strains of EBV. The expression of vimentin, the major 56-kDa polypeptide of mesenchymal cell intermediate filaments, was altered by all EBV isolates, in either a negative or a positive way, depending on the cell line. Expression of lymphocyte-function-associated antigens, LFA-1 alpha/beta (CD11 a/18) and LFA-3 (CD58), involved in intercellular adhesion and the T-cytotoxic pathway, were differentially regulated by EBV; a crucial observation was the activation by immortalizing EBV isolates of LFA-1 beta chain (CD18) and of LFA-3 (CD58). The EBV-and possibly EBNA2-associated modulation of cellular genes, such as CR2 (CD21), CD23 and LFAs, probably represents key events for EBV-induced B-cell proliferation, and also for in vivo immune control of EBV-infected B cells.

Epstein-Barr virus types 1 and 2 differ in their EBNA-3A, EBNA-3B, and EBNA-3C genes

The two Epstein-Barr virus (EBV) types, EBV-1 and EBV-2, are known to differ in their EBNA-2 genes, which are 64 and 53% identical in their nucleotide and predicted amino acid sequences, respectively. Restriction endonuclease maps and serologic analyses detect few other differences between EBV-1 and EBV-2 except in the EBNA-3 gene family. We determined the DNA sequence of the AG876 EBV-2 EBNA-3 coding region and have compared it with known B95-8 EBV-1 EBNA-3 sequences to delineate the extent of divergence between EBV-1 and EBV-2 isolates in their EBNA-3 genes. The B95-8 and AG876 EBV isolates had nucleotide and amino acid identity levels of 90 and 84%, 88 and 80%, and 81 and 72% for the EBNA-3A, -3B, and -3C genes, respectively. In contrast, nucleotide sequence identity in the noncoding DNA adjacent to the B95-8 and AG876 EBNA-3 open reading frames was 96%. We used the polymerase chain reaction to demonstrate that five additional EBV-1 isolates and six additional EBV-2 isolates have the type-specific differences in their EBNA-3 genes predicted from the B95-8 or AG876 sequences. Thus, EBV-1 and EBV-2 are two distinct wild-type EBV strains that have significantly diverged at four genetic loci and have maintained type-characteristic differences at each locus. The delineation of these sequence differences between EBV-1 and EBV-2 is essential to ongoing molecular dissection of the biologic properties of EBV and of the human immune response to EBV infection. The application of these data to the delineation of epitopes recognized in the EBV-immune T-cell response is also discussed.

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.

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.

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.