Isolation and characterization of cDNA clones corresponding to transcripts from the BamHI H and F regions of the Epstein-Barr virus genome

The roles of miRNAs and lncRNAs in Epstein-Barr virus associated epithelial cell tumors

Epstein-Barr virus (EBV) infection is highly prevalent in the population and is known to be associated with a variety of human tumors, such as nasopharyngeal carcinoma, gastric cancer, and lymphoma; however, the mechanisms of EBV carcinogenesis remain unclear. Recent studies have revealed that many non-coding RNAs participate in the regulation of proliferation, migration, invasion, and other processes in EBV-associated tumor, and the interaction between ncRNAs and the potential target genes has gradually become a research hotspot. Therefore, here, we discuss the expression and roles of ncRNAs in EBV-associated epithelial tumors.

Translational profiling of B cells infected with the Epstein-Barr virus reveals 5' leader ribosome recruitment through upstream open reading frames

The Epstein-Barr virus (EBV) genome encodes several hundred transcripts. We have used ribosome profiling to characterize viral translation in infected cells and map new translation initiation sites. We show here that EBV transcripts are translated with highly variable efficiency, owing to variable transcription and translation rates, variable ribosome recruitment to the leader region and coverage by monosomes versus polysomes. Some transcripts were hardly translated, others mainly carried monosomes, showed ribosome accumulation in leader regions and most likely represent non-coding RNAs. A similar process was visible for a subset of lytic genes including the key transactivators BZLF1 and BRLF1 in cells infected with weakly replicating EBV strains. This suggests that ribosome trapping, particularly in the leader region, represents a new checkpoint for the repression of lytic replication. We could identify 25 upstream open reading frames (uORFs) located upstream of coding transcripts that displayed 5′ leader ribosome trapping, six of which were located in the leader region shared by many latent transcripts. These uORFs repressed viral translation and are likely to play an important role in the regulation of EBV translation.

The Epstein-Barr virus miR-BHRF1 microRNAs regulate viral gene expression in cis

The Epstein-Barr virus (EBV) miR-BHRF1 microRNA (miRNA) cluster has been shown to facilitate B-cell transformation and promote the rapid growth of the resultant lymphoblastoid cell lines (LCLs). However, we find that expression of physiological levels of the miR-BHRF1 miRNAs in LCLs transformed with a miR-BHRF1 null mutant (∆123) fails to increase their growth rate. We demonstrate that the pri-miR-BHRF1-2 and 1-3 stem-loops are present in the 3'UTR of transcripts encoding EBNA-LP and that excision of pre-miR-BHRF1-2 and 1-3 by Drosha destabilizes these mRNAs and reduces expression of the encoded protein. Therefore, mutational inactivation of pri-miR-BHRF1-2 and 1-3 in the ∆123 mutant upregulates the expression of not only EBNA-LP but also EBNA-LP-regulated mRNAs and proteins, including LMP1. We hypothesize that this overexpression causes the reduced transformation capacity of the ∆123 EBV mutant. Thus, in addition to regulating cellular mRNAs in trans, miR-BHRF1-2 and 1-3 also regulate EBNA-LP mRNA expression in cis.

Differential expression of EBV proteins LMP1 and BHFR1 in EBV‑associated gastric and nasopharyngeal cancer tissues

Epstein-Barr virus (EBV) infection is associated with the development of T cell lymphoma, nasopharyngeal cancer (NPC), and EBV-associated gastric cancer (EBVaGC). This study assessed the expression of the EBV-associated proteins latent membrane protein 1 (LMP1) and BamHI-A rightward frame 1 (BARF1) in NPC and EBVaGC tissue specimens and determined their association with clinicopathological data, microvessel density (MVD) and micro-lymphatic vessel density (MLVD). This study collected 600 gastric cancer and 75 NPC tissue samples. EBV infection was assessed using in situ hybridization, and LMP1 and BARF1 expression was assessed using immunohistochemistry. The levels of MVD and MLVD were assessed using immunostaining of vascular endothelial growth factor (VEGF)-C, CD34, and lymphatic vessel endothelial receptor 1 (LYVE-1). Among the 600 gastric cancer cases, 30 were positive for EBV infection, which was shown to be associated with the age of patients (P=0.073), tumor differentiation (P<0.0001), tumor location (P<0.0001) and lymph node metastasis (P<0.0001). In these 30 EBVaGC cases, only one case was weakly positive for LMP1, but 17 cases were BARF1 positive. BARF1 expression was associated with lymph node metastasis of EBVaGC and the level of MLVD. Furthermore, 61 (81%) of 75 NPC patients were EBV positive, among which 38 cases were LMP-1 positive (62.3%) and LMP1 expression was associated with tumor-node-metastasis stage (P=0.011) and lymph node metastasis (P=0.041). MLVD was significantly higher in LMP1-positive cases than LMP1-negative cases. There were only 8 (13.3%) cases positive for BARF1 expression. In conclusion, EBV infection exhibits a role in gastric cancer and NPC development; however, expression of EBV-associated proteins LMP1 and BARF1 have differential functions during tumorigenesis of these two types of cancer.

A Viral microRNA Cluster Regulates the Expression of PTEN, p27 and of a bcl-2 Homolog

The Epstein-Barr virus (EBV) infects and transforms B-lymphocytes with high efficiency. This process requires expression of the viral latent proteins and of the 3 miR-BHRF1 microRNAs. Here we show that B-cells infected by a virus that lacks these non-coding RNAs (Δ123) grew more slowly between day 5 and day 20, relative to wild type controls. This effect could be ascribed to a reduced S phase entry combined with a moderately increased apoptosis rate. Whilst the first phenotypic trait was consistent with an enhanced PTEN expression in B-cells infected with Δ123, the second could be explained by very low BHRF1 protein and RNA levels in the same cells. Indeed, B-cells infected either by a recombinant virus that lacks the BHRF1 protein, a viral bcl-2 homolog, or by Δ123 underwent a similar degree of apoptosis, whereas knockouts of both BHRF1 microRNAs and protein proved transformation-incompetent. We find that that the miR-BHRF1-3 seed regions, and to a lesser extent those of miR-BHRF1-2 mediate these stimulatory effects. After this critical period, B-cells infected with the Δ123 mutant recovered a normal growth rate and became more resistant to provoked apoptosis. This resulted from an enhanced BHRF1 protein expression relative to cells infected with wild type viruses and correlated with decreased p27 expression, two pro-oncogenic events. The upregulation of BHRF1 can be explained by the observation that large BHRF1 mRNAs are the source of BHRF1 protein but are destroyed following BHRF1 microRNA processing, in particular of miR-BHRF1-2. The BHRF1 microRNAs are unlikely to directly target p27 but their absence may facilitate the selection of B-cells that express low levels of this protein. Thus, the BHRF1 microRNAs allowed a time-restricted expression of the BHRF1 protein to innocuously expand the virus B-cell reservoir during the first weeks post-infection without increasing long-term immune pressure.

Downregulation of the polyamine regulator spermidine/spermine N(1)-acetyltransferase by Epstein-Barr virus in a Burkitt's lymphoma cell line

Transition of Akata Burkitt's lymphoma (BL) from a malignant to nonmalignant phenotype upon loss of Epstein-Barr virus (EBV) is evidence for a viral contribution to tumorigenesis despite the tight restriction of EBV gene expression in BL. Examination of global cellular gene expression in Akata subclones that retained or lost EBV identified spermidine/spermine N(1)-acetyltransferase (SAT1), an inducible enzyme whose catabolism of polyamines affects both apoptosis and cell growth, as one of a limited number of cellular genes downregulated by EBV. Re-infection of the EBV-negative Akata clone reduced SAT1 mRNA to a level comparable with the parental EBV-positive Akata. EBV-positive Akata cells demonstrated decreased SAT1 enzyme activity concomitant with altered intracellular polyamine constituents. Reduction of SAT1 in EBV-positive BL was a transcriptional effect. Forced expression of the viral BCL2 homologue, BHRF1, in an EBV-negative Akata clone reduced SAT1 mRNA. Thus, EBV repression of polyamine catabolism becomes a complementary alteration to dysregulated c-myc enhancement of polyamine synthesis in BL and favorable to BL lymphomagenesis.

cis-Acting effects on RNA processing and Drosha cleavage prevent Epstein-Barr virus latency III BHRF1 expression

In Epstein-Barr virus (EBV) latency III (LTIII) infection, BHRF1 encodes three microRNAs (miRNAs). Herein we report that Drosha cleavage of LTIII BHRF1 RNA and cis-acting splicing effects inhibit splicing and inhibit BHRF1 RNA and protein expression. Evidence shown here supports the view that Drosha cleavage to generate mature miRNAs and cis-acting sequences that prevent mRNA maturation are independent processes that prevent LTIII BHRF1 expression in lymphoblastoid cell lines.

Initiation of Epstein-Barr virus lytic replication requires transcription and the formation of a stable RNA-DNA hybrid molecule at OriLyt

The genetic elements of herpesvirus origins of lytic replication have been characterized in detail; however, much remains to be elucidated concerning their functional role in replication initiation. In the case of the Epstein-Barr virus (EBV), we have found that in addition to the two well-defined critical elements required for lytic replication (the upstream and downstream essential elements, UEE and DEE), the origin of lytic replication (OriLyt) also requires the presence of a GC-rich RNA in cis. The BHLF1 transcript is similar to the essential K5 transcript identified at the Kaposi's sarcoma-associated herpesvirus OriLyt. We have found that truncation of the BHLF1 transcript or deletion of the TATA box, but not the putative ATG initiation codon, reduce OriLyt function to background levels. By using an antibody specific for RNA-DNA hybrid molecules, we found the BHLF1 RNA stably annealed to its DNA template during the early steps of lytic reactivation. Furthermore, expression of human RNase H1, which degrades RNA in RNA-DNA hybrids, drastically reduces OriLyt-dependent DNA replication as well as recruitment of the viral single-stranded DNA binding protein BALF2 to OriLyt. These studies suggest that a GC-rich OriLyt transcript is an important component of gammaherpesvirus lytic origins and is required for initial strand separation and loading of core replication proteins.

Negative autoregulation of Epstein-Barr virus (EBV) replicative gene expression by EBV SM protein

The Epstein-Barr virus (EBV) SM protein is essential for lytic EBV DNA replication and virion production. When EBV replication is induced in cells infected with an SM-deleted recombinant EBV, approximately 50% of EBV genes are expressed inefficiently. When EBV replication is rescued by transfection of SM, SM enhances expression of these genes by direct and indirect mechanisms. While expression of most EBV genes is either unaffected or enhanced by SM, expression of several genes is decreased in the presence of SM. Expression of BHRF1, a homolog of cellular bcl-2, is particularly decreased in the presence of SM. Investigation of the mechanism of BHRF1 downregulation revealed that SM downregulates expression of the immediate-early EBV transactivator R. In EBV-infected cells, R-responsive promoters, including the BHRF1 and SM promoters, were less active in the presence of SM, consistent with SM inhibition of R expression. SM decreased spliced R mRNA levels, supporting a posttranscriptional mechanism of R inhibition. R and BHRF1 expression were also found to decrease during later stages of EBV lytic replication in EBV-infected lymphoma cells. These data indicate that feedback regulation of immediate-early and early genes occurs during the lytic cycle of EBV regulation.

An Epstein-Barr virus anti-apoptotic protein constitutively expressed in transformed cells and implicated in burkitt lymphomagenesis: the Wp/BHRF1 link

Two factors contribute to Burkitt lymphoma (BL) pathogenesis, a chromosomal translocation leading to c-myc oncogene deregulation and infection with Epstein-Barr virus (EBV). Although the virus has B cell growth–transforming ability, this may not relate to its role in BL since many of the transforming proteins are not expressed in the tumor. Mounting evidence supports an alternative role, whereby EBV counteracts the high apoptotic sensitivity inherent to the c-myc–driven growth program. In that regard, a subset of BLs carry virus mutants in a novel form of latent infection that provides unusually strong resistance to apoptosis. Uniquely, these virus mutants use Wp (a viral promoter normally activated early in B cell transformation) and express a broader-than-usual range of latent antigens. Here, using an inducible system to express the candidate antigens, we show that this marked apoptosis resistance is mediated not by one of the extended range of EBNAs seen in Wp-restricted latency but by Wp-driven expression of the viral bcl2 homologue, BHRF1, a protein usually associated with the virus lytic cycle. Interestingly, this Wp/BHRF1 connection is not confined to Wp-restricted BLs but appears integral to normal B cell transformation by EBV. We find that the BHRF1 gene expression recently reported in newly infected B cells is temporally linked to Wp activation and the presence of W/BHRF1-spliced transcripts. Furthermore, just as Wp activity is never completely eclipsed in in vitro–transformed lines, low-level BHRF1 transcripts remain detectable in these cells long-term. Most importantly, recognition by BHRF1-specific T cells confirms that such lines continue to express the protein independently of any lytic cycle entry. This work therefore provides the first evidence that BHRF1, the EBV bcl2 homologue, is constitutively expressed as a latent protein in growth-transformed cells in vitro and, in the context of Wp-restricted BL, may contribute to virus-associated lymphomagenesis in vivo.

Cancer almost always develops through the cumulative effects of several independent changes in the target cell. For certain tumors, one step in the chain involves infection of the cell with a particular type of virus. The best example is Burkitt lymphoma (BL), a tumor of B lymphocytes which develops through the combined action of a genetic accident leading to uncontrolled expression of the c-myc oncogene and infection with a common herpesvirus, the Epstein-Barr virus (EBV). Recent evidence suggests that, although latent EBV infection can itself drive B cell growth, the virus plays a different role in the context of BL, namely to counteract the naturally poor survival ability of c-myc–expressing cells while leaving their c-myc–driven growth intact. Here we show that EBV achieves this by unexpectedly switching on a viral protein that was thought never to be seen in latent infection; this viral protein resembles one of the cell's own key survival proteins called bcl2. Furthermore, the work has led us to realise that this virally encoded bcl2-like protein is not only important in the context of BL but, contrary to conventional wisdom, is actually part of EBV's natural strategy for B cell growth transformation.

Epstein-Barr virus BHRF1 micro- and stable RNAs during latency III and after induction of replication

Epstein-Barr virus (EBV) microRNAs miR-BHRF1-1, -2, and -3 have been detected in latency III-infected lymphoblasts, where they are encoded within EBNA transcripts (X. Cai, A. Schafer, S. Lu, J. P. Bilello, R. C. Desrosiers, R. Edwards, N. Raab-Traub, and B. R. Cullen, PLoS Pathog. 2:e23, 2006). In latency III-infected lymphoblasts, we have also identified a stable 1.3-kb RNA, which begins 3' to miR-BHRF1-1, includes the BHRF1 open reading frame, and ends near miR-BHRF1-2. This 1.3-kb RNA is the residue of Drosha cleavage of the BHRF1 microRNAs from EBNA transcripts. Early after induction of EBV replication in latency I-infected Akata lymphoblasts, BHRF1 spliced 1.4-kb mRNA accumulated along with low levels of miR-BHRF1-2 and -3 and a 0.9-kb Drosha or miR-BHRF1-2 cleavage product of BHRF1 mRNA. The turning on of latency III infection at 48 to 72 h after induction of EBV replication was associated with higher miR-BHRF1-1, -2, and -3 levels; accumulation of the 1.3-kb RNA residue in the nucleus; abundant BHRF1 spliced 1.4-kb mRNA in the cytoplasm; and more abundant 0.9-kb mRNA cleavage product in the cytoplasm. These findings implicate miR-BHRF1-2 in 3' cleavage of BHRF1 mRNA in the cytoplasm and Drosha in cleavage of latency III EBNA and EBV replication-associated BHRF1 transcripts in the nucleus.

Multiple roles of Epstein-Barr virus SM protein in lytic replication

The effect of Epstein-Barr virus (EBV) SM protein on EBV gene expression was examined using a recombinant EBV strain with the SM gene deleted and DNA microarrays representing all known EBV coding regions. Induction of lytic EBV replication in the absence of SM led to expression of approximately 40% of EBV genes, but a block in expression of over 50% of EBV genes. Contrary to previous findings, several early genes were SM dependent, and lytic EBV DNA replication did not occur in the absence of SM. Notably, two genes essential for lytic EBV DNA replication, BSLF1 and BALF5, encoding EBV DNA primase and polymerase, respectively, were SM dependent. Lytic DNA replication was partially rescued by ectopic expression of EBV primase and polymerase, but virion production was not. Rescue of DNA replication only enhanced expression of a subset of late genes, consistent with a direct requirement for SM for late gene expression in addition to its contribution to DNA replication. Therefore, while SM is essential for most late gene expression, the proximate block to virion production by the EBV SM deletion strain is an inability to replicate linear DNA. The block to DNA replication combined with the direct effect of SM on late gene expression leads to a global deficiency of late gene expression. SM also inhibited BHRF1 expression during productive replication in comparison to that of cells induced into lytic replication in the absence of SM. Thus, SM plays a role in multiple steps of lytic cycle EBV gene expression and that it is transcript-specific in both activation and repression functions.

Epstein-Barr virus BHRF1 functions downstream of Bid cleavage and upstream of mitochondrial dysfunction to inhibit TRAIL-induced apoptosis in BJAB cells

We have previously reported that TNF-related apoptosis inducing ligand (TRAIL) causes cleavage of Bid via activation of caspase-8 and the loss of mitochondrial membrane potential (DeltaPsim), resulting in apoptosis. Experiments with BJAB clones expressing Epstein-Barr virus (EBV) anti-apoptotic protein BHRF1 showed that BHRF1 drastically inhibited TRAIL-mediated apoptosis. Although Western blot analysis demonstrated that TRAIL-induced Bid cleavage was not inhibited by BHRF1, the decrease in DeltaPsim caused by TRAIL was effectively blocked by BHRF1. These findings suggest that in BJAB cells, BHRF1 acts downstream of Bid cleavage and upstream of mitochondrial damage, resulting in inhibition of TRAIL-induced apoptosis.

The UL34 gene product of herpes simplex virus type 2 is a tail-anchored type II membrane protein that is significant for virus envelopment

The UL34 gene of herpes simplex virus type 2 (HSV-2) is highly conserved in the herpesvirus family. The UL34 gene product was identified In lysates of HSV-2-infected cells as protein species with molecular masses of 31 and 32.5 kDa, the latter being a phosphorylated product. Synthesis of these proteins occurred at late times post-infection and was highly dependent on viral DNA synthesis. Immunofluorescence assays revealed that the UL34 protein was localized in the cytoplasm in a continuous net-like structure, closely resembling the staining pattern of the endoplasmic reticulum (ER), in both HSV-2-infected cells and in cells transiently expressing UL34 protein. Deletion mutant analysis showed that this colocalization required the C terminus of the UL34 protein. The UL34 protein associated with virions but not with A, B or C capsids. We treated virions, HSV-2-infected cells and cells expressing the UL34 protein with a protease in order to examine the topology of the UL34 protein. In addition, we constructed UL34 deletion mutant proteins and examined their intracellular localization. Our data strongly support the hypothesis that the UL34 protein is inserted into the viral envelope as a tail-anchored type II membrane protein and is significant for virus envelopment.

The Us9 gene product of pseudorabies virus, an alphaherpesvirus, is a phosphorylated, tail-anchored type II membrane protein

The Us9 gene is highly conserved among the alphaherpesviruses sequenced to date, yet its function remains unknown. In this report, we demonstrate that the pseudorabies virus (PRV) Us9 protein is present in infected cell lysates as several phosphorylated polypeptides ranging from 17 to 20 kDa. Synthesis is first detected at 6 h postinfection and is sensitive to the DNA synthesis inhibitor phosphonoacetic acid. Unlike the herpes simplex virus type 1 Us9 homolog, which was reported to be associated with nucleocapsids in the nuclei of infected cells (M. C. Frame, D. J. McGeoch, F. J. Rixon, A. C. Orr, and H. S. Marsden, Virology 150:321-332, 1986), PRV Us9 localizes to the secretory pathway (predominately to the Golgi apparatus) and not to the nucleus. By fusing the enhanced green fluorescent protein (EGFP) reporter molecule to the carboxy terminus of Us9, we demonstrated that Us9 not only is capable of targeting a Us9-EGFP fusion protein to the Golgi compartment but also is able to direct efficient incorporation of such chimeric molecules into infectious viral particles. Moreover, through protease digestion experiments with Us9-EGFP-containing viral particles, we demonstrated that the Us9 protein is inserted into the viral envelope as a type II, tail-anchored membrane protein.

Epstein-Barr virus BHRF1 protein protects intestine 407 epithelial cells from apoptosis induced by tumor necrosis factor alpha and anti-Fas antibody

Tumor necrosis factor (TNF) and cytotoxic T lymphocytes, which utilize Fas to induce apoptosis in target cells, are known to play a critical role in the host defense against viral infection. In this study, the Epstein-Barr virus BHRF1 protein was stably expressed in intestine 407 cells which were susceptible to cell death mediated through both the TNF receptor and Fas. WST-1 conversion assays and acridine orange staining showed that vector-transfected control cells were killed by TNF-alpha or anti-Fas antibody in a dose-dependent manner, whereas BHRF1-expressing cells were resistant to apoptosis induced by these mediators. DNA fragmentation, a characteristic of apoptosis induced by TNF-alpha and the anti-Fas antibody, was suppressed in BHRF1-expressing cells. These results indicate that the BHRF1 protein protects cells from apoptosis mediated by the TNF receptor and Fas. The role of BHRF1 as an inhibitor of cytokine-induced apoptosis during the Epstein-Barr virus lytic cycle in vivo is discussed.

Marked, transient inhibition of expression of the Epstein-Barr virus latent membrane protein gene in Burkitt's lymphoma cell lines by electroporation

The Raji, EB1, and EB2 cell lines are derived from Epstein-Barr virus (EBV)-positive Burkitt's lymphomas. EBV gene products associated with viral latency, including latent membrane protein (LMP) and Epstein-Barr nuclear antigen 2 (EBNA-2), are expressed in these cell lines. We have found that transfection of all three of these cell lines by electroporation in both the presence and the absence of foreign DNA resulted in a marked decrease in expression of the endogenous EBV gene encoding LMP. An analysis of this response in Raji cells revealed that the level of RNA of this gene was decreased transiently and returned to normal levels by 7 days after transfection. The level of LMP protein was also reduced after transfection. No difference in survival was detected in electroporated versus unperturbed Raji cells. The level of mRNA encoding a modulator of the LMP gene, EBNA-2, was unchanged by electroporation. However, the level of another EBV transcript, BHLF-I, was reduced. The effect of electroporation could not be attributed to flux of Ca2+, Na+, K+, or Cl- ions across the plasma membrane. Expression of LMP in several lymphoblastoid cell lines was unaffected by electroporation.

Apoptosis in the development of the immune system: growth factors, clonal selection and bcl-2

The mammalian immune system is essential for surviving challenge infections with a great range of potential pathogens. The protective effect produced is dependent on many different types of cells which require flexible and independent production and regulation. In particular, many important responses are carried out by lymphocytes, which recognise foreign antigen through exquisitely specific receptors: i.e. surface immunoglobulin (sIg) on B lymphocytes and the T cell receptor (TCR) on T lymphocytes. Each lymphocyte displays receptors with a single specificity, allowing cells with particular specificities to be regulated independently. Since millions of different Igs and TCRs are expressed, the precise selection and regulation of each T and B cell population to produce a useful self-tolerant repertoire is a very complex process. Control of cell populations can, in theory, be exercised at a number of levels, including modulation of active cell death by apoptosis. Recent research has demonstrated that regulation of apoptosis is indeed a crucial element in the control of the immune system in general, and in the development of the TCR and Ig repertoires in particular. The molecular analysis of apoptosis now takes a high priority and the proto-oncogene bcl-2 appears to be responsible for specific suppression of apoptosis in several important situations. It is also clear that malfunctions affecting apoptosis, and in particular bcl-2, can result in significant progression towards malignancy.

BHRF1, the Epstein-Barr virus gene with homology to Bc12, is dispensable for B-lymphocyte transformation and virus replication

The Epstein-Barr virus (EBV) BHRF1 open reading frame is abundantly expressed early in the lytic replication cycle. BHRF1 is also transiently expressed in some latently infected cell lines in the absence of expression of other lytic cycle proteins. BHRF1 shares distant, but significant, colinear primary amino acid sequence homology to Bc12, a cellular gene strongly implicated in the evolution of follicular lymphoma. The experiments reported here used a molecular genetic approach to examine the role of BHRF1 in EBV infection. Isogenic EBV recombinants having either wild-type BHRF1 or a null mutation due to a translational stop signal in place of the 24th BHRF1 codon were used to infect primary B lymphocytes. The BHRF1 mutant recombinants did not differ from the wild type in their ability to infect and transform the growth of primary B lymphocytes, to replicate in the resultant lymphoblastoid cell lines, or to initiate a second round of primary cell transformation. Deletion of the entire BHRF1 open reading frame did not destroy the ability of the mutant virus to maintain cell growth transformation. The significance of these findings with regard to the role of BHRF1 in EBV infection is discussed.

A novel IL-1 receptor, cloned from B cells by mammalian expression, is expressed in many cell types

cDNA clones corresponding to an Mr approximately 80,000 receptor (type I receptor) for interleukin-1 (IL-1) have been isolated previously by mammalian expression. Here, we report the use of an improved expression cloning method to isolate human and murine cDNA clones encoding a second type (Mr approximately 60,000) of IL-1 receptor (type II receptor). The mature type II IL-1 receptor consists of (i) a ligand binding portion comprised of three immunoglobulin-like domains; (ii) a single transmembrane region; and (iii) a short cytoplasmic domain of 29 amino acids. This last contrasts with the approximately 215 amino acid cytoplasmic domain of the type I receptor, and suggests that the two IL-1 receptors may interact with different signal transduction pathways. The type II receptor is expressed in a number of different tissues, including both B and T lymphocytes, and can be induced in several cell types by treatment with phorbol ester. Both IL-1 receptors appear to be well conserved in evolution, and map to the same chromosomal location. Like the type I receptor, the human type II IL-1 receptor can bind all three forms of IL-1 (IL-1 alpha, IL-1 beta and IL-1ra). Vaccinia virus contains an open reading frame bearing strong resemblance to the type II IL-1 receptor.

Epstein-Barr virus BHRF1 gene but not the cellular protooncogene bcl-2 is expressed in ataxia-telangiectasia lymphoblastoid lines

The expression of both the Epstein-Barr virus (EBV) ORF BHRF1 and the cellular protooncogene bcl-2 was studied in EBV-transformed lymphoblastoid B cells from patients with the human genetic disorder ataxia-telangiectasia (A-T). Using the Northern blot technique, it was found that the pattern of transcription of the BHRF1 gene in A-T lymphoblastoids resembled that in EBV-transformed normal lymphoblastoid lines and Burkitt lymphoma (BL) lymphocytes. However, the 1.5-kb mature BHRF1 mRNA species present in normal lymphoblastoid cells and in BL cells was not found in the A-T lymphoblastoid cell lines. Treatment of the A-T lymphoblastoid lines with phorbol ester caused changes in the pattern of the synthesis and quantity of BHRF1-related RNA transcripts. The bcl-2 protooncogene probe did not detect bcl-2-related mRNA in the A-T lymphoblastoid lines.

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.

Identification of phorbol ester response elements in the promoter of Epstein-Barr virus putative lytic switch gene BZLF1

The product of the Epstein-Barr virus BZLF1 gene encodes a protein which is related to c-fos, it has been shown to bind specifically to a consensus AP-1 site, and its expression in latently Epstein-Barr virus-infected lymphocytes is sufficient to trigger the viral lytic cycle. We identified several elements within the BZLF1 promoter (Zp) which are responsive to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), an inducer of the viral lytic cycle. These elements fall into two classes based on the factors which bind to these sequences and their resulting functional behavior. Four of the elements are homologous (ZI elements) and share homology to a protein-binding domain in the promoter region of the coordinately expressed BRLF1 gene. When cloned upstream of heterologous promoters, the ZI elements function as silencers which exhibit TPA-inducible enhancer activity. A distinct TPA-responsive element (ZII) is located near the TATA box and shares homology with the AP-1-binding site in the c-jun promoter. A synthetic oligonucleotide with a sequence corresponding to the ZII element effectively competes for binding of nuclear factors to the c-jun AP-1 site. Furthermore, we found that a complex of c-jun and c-fos bound to the ZII domain.

Effect of the EBNA-2 gene on the surface antigen phenotype of transfected EBV-negative B-lymphoma lines

Two EBV-negative B-lymphoma cell lines with different phenotypes were transfected with the Epstein-Barr virus EBNA-2 gene. The effects on the expression of 8 B-cell surface markers were analyzed by immunofluorescence methods. In one of the EBNA-2 transfected cell lines, the expression of the CR2 receptor CD21 was induced and the expression of CD23 was enhanced. The results suggest that the EBNA-2 gene is involved in the regulation of CD21 and CD23 in EBV-carrying cells.

An Epstein-Barr virus immortalization associated gene segment interferes specifically with the IFN-induced anti-proliferative response in human B-lymphoid cell lines

Immortalization of human B-lymphocytes by Epstein-Barr virus (EBV) is associated with a decreased anti-proliferative response to interferon (IFN). In the present investigation we show that the resistance to the anti-proliferative effect of IFN class I on certain EBV-carrying Burkitt lymphoma cell lines is connected to the presence of the EBNA-2 gene and parts of the EBNA-5 gene of the EBV genome. Transfection of the genomic segment comprising these open reading frames into an IFN-sensitive lymphoma cell line demonstrated that it is sufficient to make cells resistant towards the antiproliferative effect of IFN class I. Expression of the EBNA-2 gene seems to be correlated with the IFN-resistant phenotype. The antiviral function of IFN, as tested by inhibition by vesicular stomatitis virus (VSV) infection, and the IFN-receptor binding are not suppressed. The present results suggest that the neutralization of the anti-proliferative effect of IFN-alpha is involved in the EBV-mediated immortalization of B-cells and that the anti-proliferative action of IFN class I does not necessarily recruit the same mechanism as the antiviral effect.

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.

Identification and characterization of an Epstein-Barr virus early antigen that is encoded by the NotI repeats

The Epstein-Barr virus (EBV) genome is characterized by two regions carrying partially homologous clusters of short tandem repeats (NotI and PstI repeats) flanked by 1,044 and 1,045 base pairs with almost perfect homology (DL and DR, left and right duplications, respectively). Both repetitive regions are transcribed into poly(A)+ mRNA after induction of the productive EBV cycle with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate and contain open reading frames. To identify the potential protein encoded by the NotI repeat open reading frame (BHLF1), two repeat units of EBV strain M-ABA were expressed using the tryptophan-regulated Escherichia coli expression vector pATH11. Rabbit antisera generated against the resulting fusion protein reacted specifically with a protein varying in molecular size between 70,000 and 90,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, found after 12-O-tetradecanoyl-phorbol-13-acetate or n-butyrate induction in various cell lines harboring EBV. In immunofluorescence tests with the BHLF1-specific antiserum, an immunofluorescence with EA-D specificity could be observed. In addition, the BHLF1 protein is exhibiting polyanion-binding activity with a maximum for single-stranded DNA. Furthermore, the fusion protein is recognized by a number of human EBV-positive sera.

Relative rates of RNA synthesis across the genome of Epstein-Barr virus are highest near oriP and oriLyt

The rates of Epstein-Barr virus transcription were measured in isolated nuclei from marmoset and human lymphoblasts transformed in vitro. In B95-8, a marmoset B-lymphoid cell line, the most frequently transcribed viral genes are the EBERs (small nuclear RNAs) and BHLF-1 (encoding a lytic-phase gene product). The EBERs and BHLF-1 genes are separated by nearly 50 kilobase pairs on the Epstein-Barr virus genome and lie adjacent to (less than 300 base pairs from) oriP and oriLyt, respectively. oriP and oriLyt are putative origins of viral DNA replication, and each is associated with a transcriptional enhancer element. Among the human B-lymphoblastoid cell lines tested, only the transcription of EBERs predominates.

Identification of an enhancer-type sequence that is responsive to Z and R trans-activators of Epstein-Barr virus

We studied the regulatory region of the open reading frame BHRF1 of Epstein-Barr virus (EBV) DNA that was responsive to two trans-activators (Z and R) encoded by the BZLF1 and BRLF1, respectively. The 200-bp sequence, nucleotide numbers 53,617 to 53,817 on the EBV map, was sufficient for conferring responsiveness to Z and R. This 200-bp sequence also enhanced expression of the chloramphenicol acetyltransferase (CAT) gene from the simian virus 40 promoter in response to both Z and R, even when inserted downstream of the cat gene. The results indicate that the Z and R response sequence upstream of the BHRF1 has the properties of an enhancer.

Identification of proteins encoded by Epstein-Barr virus trans-activator genes

Specific antisera were generated to characterize Epstein-Barr virus proteins reported to have trans-activating properties. Open reading frame BRLF1 was found to be expressed in two modifications in vivo, with molecular sizes ranging from 94 to 98 kilodaltons (kDa) depending on the cell line, whereas only one protein (Raji cells, 96 kDa) was detected by in vitro translation. Open reading frame BZLF1 encoded polypeptides of 38 and 35 kDa and additional smaller forms. A BZLF1-encoded 30-kDa protein could be detected under conditions in which expression was restricted to immediate early genes. Nuclear localization could be detected under conditions in which expression was restricted to immediate early genes. Nuclear localization could be shown for the proteins derived from reading frames BZLF1 and BMLF1. BMLF1 expression gave a heterogeneous protein pattern, with molecular sizes between 45 and 70 kDa, including a predominant 60-kDa protein detected in different B-cell lines.

A new Epstein-Barr virus transactivator, R, induces expression of a cytoplasmic early antigen

Several Epstein-Barr virus (EBV) early promoters respond to a new EBV transactivator encoded by BRLF1, designated R. Transactivation was measured in chloramphenicol acetyltransferase assays on Raji, BHK, and Vero cells that were cotransfected with the transactivator and target promoters linked to the cat gene. The divergent promoter of BamHI-H was particularly responsive to R transactivation. This large promoter region consists of a leftward TATA box for the NotI repeat gene (BHLF1) and a probable rightward TATA box for the EA-R gene (BHRF1) separated by 940 base pairs of unusual sequence complexity. Sequences within this divergent promoter region appear to confer inducibility by EBV transactivators R and Z (BZLF1). The Z transactivator stimulated expression in both the leftward and rightward directions, and R stimulated expression primarily in the rightward direction, but the MS transactivator (BMLF1) had no activity in either direction. The adenovirus E3 promoter also responded to the R transactivator, but several other herpesvirus and human promoters were nonresponsive. When the divergent promoter was linked to the EA-R gene as it is in the EBV genome, the R and Z transactivators also induced the expression of EA-R in cotransfected cells. This cytoplasmic early antigen is encoded by BHRF1 and may be anchored in intracellular membranes by a carboxy-terminal transmembrane region.

Complex transcription of the Epstein-Barr virus BamHI fragment H rightward open reading frame 1 (BHRF1) in latently and lytically infected B lymphocytes

Several cDNA clones containing the Epstein-Barr virus BamHI fragment H rightward open reading frame 1 (BHRF1) have been recovered from the tightly latent lymphoblastoid cell line IB4. These clones contain the 5' leader exons encoded in the major internal repeat 1 and the viral BamHI fragment Y, identified in the rightwardly transcribed viral mRNAs associated with the latent viral life cycle. In addition, a cDNA clone containing BHRF1 from the Burkitt lymphoma cell line Jijoye was also recovered and exhibits a distinctive splicing pattern. In vitro transcription and translation of BHRF1, followed by immunoprecipitation with Epstein-Barr virus-positive human sera, indicates that this viral antigen is expressed during infection. RNA blot analyses with a wide panel of lymphoblastoid and Burkitt lymphoma cell lines revealed a complex pattern of transcription. Hybridization data obtained with several probes is presented.