Two distant clusters of partially homologous small repeats of Epstein-Barr virus are transcribed upon induction of an abortive or lytic cycle of the virus

The BHLF1 Locus of Epstein-Barr Virus Contributes to Viral Latency and B-Cell Immortalization

The Epstein-Barr virus (EBV) BHLF1 gene encodes an abundant linear and several circular RNAs believed to perform noncoding functions during virus replication, although an open reading frame (ORF) is retained among an unknown percentage of EBV isolates. Evidence suggests that BHLF1 is also transcribed during latent infection, which prompted us to investigate the contribution of this locus to latency. Analysis of transcripts transiting BHLF1 revealed that its transcription is widespread among B-cell lines supporting the latency I or III program of EBV protein expression and is more complex than originally presumed. EBV-negative Burkitt lymphoma cell lines infected with either wild-type or two different BHLF1 mutant EBVs were initially indistinguishable in supporting latency III. However, cells infected with BHLF1 ^- virus ultimately transitioned to the more restrictive latency I program, whereas cells infected with wild-type virus either sustained latency III or transitioned more slowly to latency I. Upon infection of primary B cells, which require latency III for growth in vitro, both BHLF1 ^- viruses exhibited variably reduced immortalization potential relative to the wild-type virus. Finally, in transfection experiments, efficient protein expression from an intact BHLF1 ORF required the EBV posttranscriptional regulator protein SM, whose expression is limited to the replicative cycle. Thus, one way in which BHLF1 may contribute to latency is through a mechanism, possibly mediated or regulated by a long noncoding RNA, that supports latency III critical for the establishment of EBV latency and lifelong persistence within its host, whereas any retained protein-dependent function of BHLF1 may be restricted to the replication cycle.IMPORTANCE Epstein-Barr virus (EBV) has significant oncogenic potential that is linked to its latent infection of B lymphocytes, during which virus replication is not supported. The establishment of latent infection, which is lifelong and can precede tumor development by years, requires the concerted actions of nearly a dozen EBV proteins and numerous small non-protein-coding RNAs. Elucidating how these EBV products contribute to latency is crucial for understanding EBV's role in specific malignancies and, ultimately, for clinical intervention. Historically, EBV genes that contribute to virus replication have been excluded from consideration of a role in latency, primarily because of the general incompatibility between virus production and cell survival. However, here, we provide evidence that the genetic locus containing one such gene, BHLF1, indeed contributes to key aspects of EBV latency, including its ability to promote the continuous growth of B lymphocytes, thus providing significant new insight into EBV biology and oncogenic potential.

Genetic diversity: frameshift mechanisms alter coding of a gene (Epstein-Barr virus LF3 gene) that contains multiple 102-base-pair direct sequence repeats

Frameshift mutations provide recognized mechanisms for changing the coding potential of an organism. Here, multiple frameshifts are identified in repetitive sequences within an Epstein-Barr virus unspliced early gene, LF3, which is associated with the viral replicative cycle and also transcriptionally expressed in many virally associated tumors. On the DNA strand encoding LF3, there are three open reading frames, only one of which contains an initiation codon. Most (>95%) of the gene consists of numerous (>20, varying with cell source) GC-rich copies of a 102-bp direct repeat (called IR 4) flanked by small unique sequences. LF3 may express a protein if its initiation and termination codons reside in the same reading frame, but this is not always the case. Frameshifting events, occurring in short runs of pyrimidines (mainly C residues) in the repeats, give rise to mutations which may provide a mechanism for escape of an LF3 function from host surveillance. Sequence studies link these frameshifts to DNA replication errors. Notably, the number of sites in LF3 at which such mutations can occur permits a very large amount of diversity in this gene. Our data also suggest a second degeneracy mechanism within the protein itself, which influences its stability and may reflect a host defense mechanism. LF3 thus provides a potentially important model for studying the quest for supremacy between a virus and its host.

Expression of two related viral early genes in Epstein-Barr virus-associated tumors

The transcription of two early "leftwardly" expressed genes carrying repetitive sequences, IR2 and IR4, has been studied for Epstein-Barr virus-associated tumors, and for established B-cell lines, using sequence-specific probes generated for this purpose. Whereas the IR4 transcript was identified in every tumor and cell line assessed (except B95-8, with a deletion that removes the gene), expression of the IR2 gene was restricted to B lymphocytes. Though the promoters for both transcripts lie within homologous regions (D(L) and D(R)) in the viral genome, the IR2 promoter appears more tightly regulated. Detailed characterization of the IR4 transcript from a nasopharyngeal carcinoma tumor, C15, identifies a sequence variant of this gene that differs from those reported for B cells; in situ hybridization methods show transcription to be restricted to a subset of cells, with the strongest signals seen adjacent to host stroma. As with B cells in culture (Y. Gao, P. R. Smith, L. Karran, Q. L. Lu, and B. E. Griffin, J. Virol. 71:84-94, 1997), chemical induction enhanced transcriptional expression of the IR4 gene in the C15 tumor, although staining for both the IR4 antigen and that of the virus lytic switch, Zta, gave negative results. In a Burkitt's lymphoma biopsy specimen, however, both proteins were found expressed, notably in the same subset of cells. The data here and elsewhere (Gao et al., J. Virol., 1997) are consistent with a block to intracellular transport of the transcript(s) and suggest nuclear roles for it in tumors, possibly in RNA processing and viral lytic replication. Both roles could be fulfilled in the absence of translation.

Analysis of Epstein-Barr virus in Hodgkin's disease: experience of a single university hospital in Korea

Hodgkin's disease is known to be associated with Epstein-Barr virus (EBV) infection in Western countries, and viral nucleic acids and proteins have been identified within Reed-Sternberg (RS) cells, which are the histopathologic hallmark of the disease process. Twenty-five cases of Hodgkin's disease from a single university hospital in Korea were studied for evidence of EBV by in situ hybridization for EBV DNA and RNA and immunohistochemistry for an EBV latent protein. EBV nucleic acids were studied by a rapid (60 minutes) in situ hybridization procedure, which utilized biotinylated DNA probes specific for the following nucleic acid sequences: (1) EBV EBER1 RNA (an abundant RNA sequence expressed during latent EBV infection), (2) EBV NotI repeats (a tandemly repeated DNA sequence, which has been established to identify amplified EBV genome in lytic EBV infection), and (3) BAM HI W (a DNA sequence reiterated 11 times within the viral genome). In addition, immunohistochemistry for EBV latent membrane protein, a protein that is capable of inducing cellular transformation in cell culture, was also performed. EBV was identified within the neoplastic RS cells by at least one method in 19/25 cases (76%). The mixed cellularity subtype was the most common subtype associated with EBV infection (11/13-85%). In situ hybridization for EBV EBER1 RNA was the most sensitive method for EBV detection and was present in 17/25 cases. A significant proportion of Korean Hodgkin's disease cases is associated with EBV infection.

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.

Short-term assays for detection of conditional cancerogens. I. Construction of DR-CAT Raji cells and some of their characteristics as tester cells

A number of agents including the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA) (TPA) can induce an abortive virus cycle in the EBV-non-producer Burkitt's-lymphoma line Raji. Two distant regions, DL and DR, of the EBV genome with almost complete homology carry strong promoters which are induced in an abortive or lytic cycle and additionally function as lytic origins of viral DNA replication. To set up a system in which the activity of EBV-inducing agents can be measured in a quantitative and reproducible fashion, we generated a cell line which carries multiple copies of a DR-promoter chloramphenicol-acetyltransferase (CAT) construct on an episomal vector. CAT activity is low in untreated cells, but high upon treatment of the cells with various EBV-inducing agents. Combinations of different agents can produce an over-additive effect. The Raji-DR-CAT cell line may provide a simple quantitative and reproducible test system for EBV-inducing agents, especially for tumor promoters which activate protein kinases C.

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.

Immunogenetic markers as probes for polymorphism, gene regulation and gene transfer in man--the Gm system in perspective

The genetic markers of immunoglobulins (Ig) demonstrable by immunological methods have shown their usefulness as genetic probes. The study of these allotypes originally proved that Ig production is under conventional genetic control and also established that allelic exclusion is valid for the key molecules of the immune response. The codons responsible for the G1m(a) marker and their position in the human genome are precisely known. This knowledge implies that Gm typing may be used as a convenient and reliable means of following the fate of IgG constant gene segments. Anti-Gm's are common in rheumatoid arthritis. They appear early in the disease and may persist throughout life. The stimulus for their appearance has not yet been established. The anti-Gm's in the allegedly autoimmune disease rheumatoid arthritis are commonly and apparently paradoxically specific for Gm gene products of other persons. Another apparent paradox brought to light by Ig allotype research is the occasional appearance of non-nominal allotypes in contradiction to Mendelian laws. It is proposed that a plausible explanation for these two paradoxes is Ig gene transfer between individuals with viral vectors. Reasons for this proposal and some possible consequences of gene transfer in a polymorphic species are delineated. Immunogenetics and DNA technology in combination provide powerful tools to elucidate the fate of genes. A method allowing the assignment of G1m(a+) and G1m(a-) at the gene level by polymerase chain reaction analysis has recently been established and is briefly described.

Identification of the lytic origin of DNA replication in human cytomegalovirus by a novel approach utilizing ganciclovir-induced chain termination

Infection with human cytomegalovirus in the presence of the antiviral nucleotide analog ganciclovir results in continuing low-level viral DNA synthesis and the accumulation of relatively small fragments of double-stranded progency DNA. These fragments consistently proved to represent amplification of sequences from only one small section of the viral genome (EcoRI-V) lying near the center of the unique L segment. Further mapping revealed that the viral sequences represented in these fragments occurred in gradients of abundance that decreased in both directions from a point near 0.35 to 0.4 map unit. The proportion of amplified sequences increased with both time after infection and dosage of ganciclovir used. We conclude that the primary lytic cycle replication origin of human cytomegalovirus lies within a 3- to 4-kb region immediately upstream and to the right of the promoter for the single-stranded DNA-binding protein (DB140). The amplified origin-containing DNA molecules appeared to arise by continuing rounds of bidirectional initiation on truncated fragments of the genome that were generated as a result of chain termination effects induced by the incorporation of ganciclovir into the viral DNA. Inspection of the DNA sequence in the vicinity of ori-Lyt revealed a large complex upstream region that may be a noncoding intergenic domain and that bears no homology to any previously described herpesvirus origin. This 2.5-kb region includes many duplicated and inverted sequences, together with consensus CRE/ATF and other transcription factor-binding sites, and an interesting set of 23 copies of an interspersed decamer consensus element AAAACACCGT that is also conserved at the equivalent locus in simian cytomegalovirus. This work represents the first identification of an origin domain in a cytomegalovirus genome and is the first demonstration of a bidirectional mechanism for any herpesvirus lytic cycle origin.

The Epstein-Barr virus (EBV) ORI1yt enhancer is not B-cell specific and does not respond synergistically to the EBV transcription factors R and Z

The Epstein-Barr virus DR promoter is located upstream of the PstI repeats, and in addition to the TATA box, it contains an upstream region (positions -69 to -220) responsive to EB1 (Z) (the BZLF1-encoded transcription factor) and an enhancer with two functionally distinct domains, A and B. Domain B has been described as a B-cell-specific EB1-responsive element (P. M. Lieberman, J. M. Hardwick, and S. D. Hayward, J. Virol. 63:3040-3050, 1989) activated synergistically by EB1 and R, an EBV early product encoded by the open reading frame BRLF1 (M. A. Cox, J. Leahy, and J. M. Hardwick, J. Virol. 64:313-321, 1990). We show here that domain B is an R-responsive element in HeLa cells and is therefore not an EB1-responsive B-cell-specific element. However, there is an EB1-binding site (ZRE-B) located within the R-responsive enhancer region. ZRE-B can be deleted without affecting the R-dependent enhancer activity. Moreover, there is no cooperation or synergy between R and EB1 when activating the B domain (ZRE-B plus the R-responsive element) positioned as an enhancer. ZRE-B is therefore not part of the R-inducible enhancer. We have tested several subregions of the DR enhancer B domain, either alone or in combination, for their capacity to transmit the R-activating signal to the rabbit beta-globin promoter. We found that the R-responsive element is composed of four protoenhancers that span the whole B domain. These protoenhancers alone are weakly or not responsive to R. One of the protoenhancers contains the overlapping palindromes 5'-TTGTCCcgtGGACAAaTGTCC-3'. However, one palindrome, either alone or duplicated, or the overlapping palindromes did not respond to R.

The zta transactivator involved in induction of lytic cycle gene expression in Epstein-Barr virus-infected lymphocytes binds to both AP-1 and ZRE sites in target promoter and enhancer regions

The BZLF1 or zta immediate-early gene of Epstein-Barr virus (EBV) encodes a 33-kilodalton phosphorylated nuclear protein that is a specific transcriptional activator of the EBV lytic cycle when introduced into latently infected B lymphocytes. We have shown previously that the divergent EBV DSL target promoter contains two zta-response regions, one within the minimal promoter and the other in an upstream lymphocyte-dependent enhancer region. In this study, we used footprinting and gel mobility retardation assays to reveal that bacterially synthesized Zta fusion proteins bound directly to six TGTGCAA-like motifs within DSL. Four of the Zta-binding sites lay adjacent to cellular TATA and CAAT factor-binding sites within the minimal promoter, and two mapped within the enhancer region. Single-copy oligonucleotides containing these Zta-binding sites conferred Zta responsiveness to heterologous promoters. In addition, the Zta protein, which possesses a similar basic domain to the conserved DNA-binding region of the c-Fos, c-Jun, GCN4, and CREB protein family, proved to bind directly to the consensus AP-1 site in the collagenase 12-O-tetradecanoylphorbol-13-acetate response element. Cotransfection with zta also trans activated a target reporter gene containing inserted wild-type 12-O-tetradecanoylphorbol-13-acetate response element oligonucleotides. Cellular AP-1 binding activity proved to be low in latently EBV-infected Raji cells but was induced (together with the Zta protein) after activation of the lytic cycle with 12-O-tetradecanoylphorbol-13-acetate. We conclude that EBV may have captured and modified a cellular gene encoding a c-jun-like DNA-binding protein during its evolutionary divergence from other herpesviruses and that this protein is used to specifically redirect transcriptional activity toward expression of EBV lytic-cycle genes in infected cells.

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.

Responsiveness of the Epstein-Barr virus NotI repeat promoter to the Z transactivator is mediated in a cell-type-specific manner by two independent signal regions

Cells latently infected with Epstein-Barr virus (EBV) can be activated to express lytic-cycle polypeptides by the introduction of the EBV-encoded Z transactivator, indicating that this protein has a pivotal role in virus reactivation. We examined the target specificity of the Z transactivator in short-term contransfection assays and found that the most responsive target to Z transactivation was the divergent NotI repeat promoter, located within the EBV BamHI H fragment. In contrast, target plasmids containing the cat gene linked to heterologous viral promoters were not activated by cotransfection with the Z gene. S1 nuclease analysis of RNA from chemically induced B95-8 cells and from Vero cells cotransfected with NotI repeat promoter-CAT and Z showed that Z transactivation increased the level of correctly initiated, stable RNA transcripts. The NotI repeat gene (ntr) gives rise to a highly abundant mRNA species after chemical induction of lytic virus replication, but no protein product had been previously identified. Using monospecific antiserum raised against a synthetic peptide from the BHLF1 open reading frame, we demonstrated that the ntr gene encodes a protein product that is found in nuclear patches colocalizing with nucleoli. A series of deletions introduced into the upstream sequences of the NotI-repeat-promoter revealed two separate Z-response regions. The minimal promoter region between -7 and -155 of the leftward RNA cap site and an upstream region between -644 and -902 were both independently capable of conferring Z responsiveness. However, the minimal region, which was activated by Z cotransfection in Vero cells, was poorly responsive in lymphocytes, whereas the response of the far-upstream region to Z cotransfection was lymphocyte specific. In its human host, EBV infects both epithelial and lymphocyte populations. This dual lifestyle may have led to the evolution of multiple Z-response signals that enable the Z transactivator to interact with both cell-specific promoter and enhancer factors.

The Epstein-Barr virus (EBV) DR enhancer contains two functionally different domains: domain A is constitutive and cell specific, domain B is transactivated by the EBV early protein R

The Epstein-Barr virus (EBV) DR promoter is located upstream of the PstI repeats, and besides the TATA box, it contains two cis-acting regulatory elements. One of them has enhancer properties. To define more precisely the functional region(s) in the DR enhancer, we generated 5' and 3' deletion mutants. These deletion mutants, which were transfected into various recipient cells of different origins, allowed us to identify two functionally distinct domains, A and B. Domain A was constitutively active in all cell lines tested, except in lymphoid B cells. Domain B was active in lymphoid B cells, and its activity required both EB1 (the BZLF1-encoded EBV trans-acting factor) and the presence of the EBV genome. This suggested that an EBV-encoded, EB1-inducible factor was activating the enhancer B domain. In effect, the B domain was trans-activated by R, an EBV early product encoded by the open reading frame BRLF1, and the activation by R occurred in epithelial, fibroblastic, and lymphoid cells. The R-responsive element has been reduced to 28 base pairs containing the double palindromic sequence TTGTCCCGTGGACAATGTCC. Both domains A and B act by increasing the initiation of specific RNAs.

Synchronous and sequential activation of latently infected Epstein-Barr virus genomes

A lymphoid cell system was established that can induce the prompt and synchronous activation of latent Epstein-Barr virus (EBV) genomes and thus allows the identification of viral genes that are activated sequentially depending on their functions. With this system, we proved that disruption of EBV latency is initiated by activation of four EBV genes and that protein synthesis is not required prior to activation of latent EBV. The system should be an in vitro model for studying the mechanism of herpesvirus latency.

Genetic polymorphism of natural Epstein-Barr virus isolates from infectious mononucleosis patients and healthy carriers

We analyzed Epstein-Barr virus (EBV) genomes from lymphoblastoid cell lines isolated from patients with infectious mononucleosis and from healthy subjects from California, Hawaii, and Hong Kong between 1970 and 1987. Using genetic polymorphism as epidemiological markers, we found that several genotypes of EBV cocirculate in a community and that although most EBV strains isolated from California and Southern China may be differentiated genotypically, there was no specific association between genotype and disease or time of isolation.

Allelic sequence variation of the HLA-DQ loci: relationship to serology and to insulin-dependent diabetes susceptibility

Analysis of sequence variation in the polymorphic second exon of the major histocompatibility complex genes HLA-DQ alpha and -DQ beta has revealed 8 allelic variants at the alpha locus and 13 variants at the beta locus. Correlation of sequence variation with serologic typing suggests that the DQw2, DQw3, and DQ(blank) types are determined by the DQ beta subunit, while the DQw1 specificity is determined by DQ alpha. The nature of the amino acid at position 57 in the DQ beta subunit is correlated with susceptibility to insulin-dependent diabetes mellitus. This region of the DQ beta chain contains shared peptides with Epstein-Barr virus and rubella virus.

TPA-inducible Epstein-Barr virus genes in Raji cells and their regulation

A number of agents including the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) can induce an abortive virus cycle in the EBV nonproducer Burkitt's lymphoma line Raji. We describe the pattern of viral RNAs transcribed in uninduced cells and in cells treated with TPA for 8 hr, as analyzed by Northern blotting. By comparing the patterns of RNAs observed in cells treated with TPA, TPA plus cycloheximide, or cycloheximide alone, we have tested whether any EBV gene in TPA-treated Raji cells would be inducible directly by TPA in the presence of protein synthesis inhibitors, similarly to immediate-early genes induced by superinfection of Raji cells with P3HR-1 virus in the presence of cycloheximide. We demonstrate here that induction of all early EBV genes is dependent on ongoing protein synthesis. The experiments do not provide an answer to whether TPA acts by activating an initial step in the cascade of virus production or whether TPA has a simultaneous pleiotropic effect on the regulation of a large number of viral genes.

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

The Epstein-Barr virus (EBV) mutant P3HR1 is incapable of immortalizing B lymphocytes because of a 6.8-kilobase deletion in the BamHI W, Y, and H regions of the viral genome (M. Rabson, L. Gradoville, L. Heston, and G. Miller, J. Virol. 44:834-844, 1982). To characterize transcripts that are encoded in this region, poly(A)+ RNA from the EBV-transformed lymphoblastoid cell line JY was isolated, and this RNA was used to generate a cDNA library in lambda gt10. By screening 500,000 recombinant bacteriophages with the BamHI H fragment, we isolated 10 cDNA clones and characterized them in detail. One group of six cDNA clones was derived from a 2.9-kilobase early transcript encoded by the IR2 repeat element and showed restriction site polymorphism for the enzyme SmaI. The second group consisted of four cDNA clones, all of which contained the BamHI-H right reading frame (BHRF1), and used the polyadenylation signal at base pair 662 in the BamHI F fragment. Computer analysis of the hydrophobicity of the BHRF1 protein revealed that it is likely to be a membrane protein. Northern blotting experiments with RNA from an EBV producer line, B95-8, and a tightly latent lymphoblastoid B-cell line, IB4, revealed that BHRF1 is contained in at least two different mRNA species which can be detected during the latent cycle of EBV. These data and the recent characterization of a spliced transcript (containing five exons in common with other known latent messages [M. Bodescot and M. Perricaudet, Nucleic Acids Res. 14:7103-7113, 1986]) suggest that alternative splicing is used to generate transcripts containing BHRF1, as for the EBV nuclear antigen 1 transcripts. Furthermore, the observation that a potential oncogene activated in human follicular lymphomas is homologous to the BHRF1-encoded polypeptide (M. L. Cleary, S.D. Smith, and J. Sklar, Cell 47:19-28, 1986) suggests a possible role for this putative viral protein in EBV-induced growth transformation of B lymphocytes.

Papillomavirus sequences integrate near cellular oncogenes in some cervical carcinomas

The chromosomal locations of cellular sequences flanking integrated papillomavirus DNA in four cervical carcinoma cell lines and a primary cervical carcinoma have been determined. The two human papillomavirus (HPV) 16 flanking sequences derived from the tumor were localized to chromosome regions 20pter----20q13 and 3p25----3qter, regions that also contain the protooncogenes c-src-1 and c-raf-1, respectively. The HPV 16 integration site in the SiHa cervical carcinoma-derived cell line is in chromosome region 13q14----13q32. The HPV 18 integration site in SW756 cervical carcinoma cells is in chromosome 12 but is not closely linked to the Ki-ras2 gene. Finally, in two cervical carcinoma cell lines, HeLa and C4-I, HPV 18 DNA is integrated in chromosome 8, 5' of the c-myc gene. The HeLa HPV 18 integration site is within 40 kilobases 5' of the c-myc gene, inside the HL60 amplification unit surrounding and including the c-myc gene. Additionally, steady-state levels of c-myc mRNA are elevated in HeLa and C4-I cells relative to other cervical carcinoma cell lines. Thus, in at least some genital tumors, cis-activation of cellular oncogenes by HPV may be involved in malignant transformation of cervical cells.

Geographical prevalence of two types of Epstein-Barr virus

The Jijoye EBV strain is characterized by a substitution of 1.8 kb in the C-terminal part of the EBNA 2 gene compared to B95-8 or M-ABA virus. This made it possible to construct hybridization probes specific for M-ABA (type A) and Jijoye viruses (type B), which have been used to type the EBV genomes in 38 spontaneously established cell lines. Type A is more prevalent being found in 31 of 38 cases; type B virus was found in five cell lines (Jijoye, LY 67, QIMR-GOR, BL 16, and BL 29); and two cell lines, Daudi and EB-3, contained neither the M-ABA- nor the Jijoye-specific sequences. EBV type B appears to be less ubiquitous, since all type B isolates, including AG 876 virus, originated from Central Africa, La Réunion, and New Guinea. All the other cell lines, carrying EBV type A, were established from patients from Central Africa (4), North Africa (7), New Guinea (1), and Asia (6) and from white individuals (13). The restricted geographical localization of EBV type B in parts of the southern hemisphere and its similarity to herpesvirus papio (T. Dambaugh, K. Hennessy, L. Chamnankit, and E. Kieff (1984) Proc. Natl. Acad. Sci. USA 81, 7632-7636) could suggest that such viruses may have evolved by recombination of EBV with a related Old World monkey virus, alternatively, evolution of virus variants within the human species also being conceivable.

Different human cervical carcinoma cell lines show similar transcription patterns of human papillomavirus type 18 early genes

Transcription of human papillomavirus type 18 (HPV18) DNA in the human cervical carcinoma cell lines HeLa, C4-1 and SW756 was studied by nucleotide sequence analysis of HPV18-positive cDNA clones isolated from a HeLa, C4-1 and SW756 cDNA library, respectively, and the cDNA sequences were used to predict the potential encoded proteins. The cDNA clones from all three cell lines were found to be derived from virus-cell fusion transcripts in which 3'-terminal host cell sequences (different for each cell line) were spliced to 5'-terminal exon sequences from the HPV18 E6-E7-E1 region. Three different types of cDNA clones can be distinguished according to the splicing patterns observed in the 5' terminal HPV18 sequences. They carry as potential protein-coding regions the HPV18 specific open reading frames E6 and E6* (generated by splicing and identical with E6 up to the E6* splice junction), E7 and E1 (only in HeLa). Translation of specific cellular genes from the chimeric viral-cellular transcripts seems to be unlikely. The mapping of the 5'-ends of the virus-cell fusion transcripts indicates that transcription is initiated at a viral promoter. The similar patterns of HPV18 transcription in the three different cervical carcinoma cell lines suggest a functional role of HPV18 early genes for the malignant phenotype of these cells.

trans activation of the latent Epstein-Barr virus (EBV) genome after transfection of the EBV DNA fragment

Transfection of Epstein-Barr virus (EBV)-nonproducer Raji cells with the BamHI Z fragment of EBV DNA induced antigens that were detected with human antiserum against EBV-specific early antigens. Northern blot analysis of transfected cells revealed that one intense RNA band hybridized with the BamHI H and F fragments but not with the BamHI Z fragment. Cooperation between the BamHI H, F, and BamHI Z regions was also confirmed in baby hamster kidney cells that were cotransfected with both fragments. These results indicate that the transfected BamHI Z fragment of EBV DNA induces a trans-acting factor which activates the gene expression of the BamHI H and F region and that the BamHI Z region possibly plays an important role in the latency of EBV.

Structure and evolution of two related transcription units of Epstein-Barr virus carrying small tandem repeats

Two regions of the Epstein-Barr virus (EBV) genome carrying partially homologous clusters of short tandem repeats (NotI and PstI repeats) flanked by 1044 and 1045 base pairs with almost complete homology (DL and DR, left and right duplication, respectively) were most abundantly transcribed into poly(A)+ mRNA after induction with the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate. The nucleotide sequence of both repeat clusters and the conserved upstream regulatory sequences from the M-ABA EBV strain are presented. Nearly the whole part of the sequences coding for the RNAs is covered by the NotI and PstI repeats, respectively. The regulatory sequences for these genes are located in the homologous regions of 1044 and 1045 base pairs (DL and DR, respectively). A CAAT box, a TATA box, and other herpes simplex virus-like elements were identified for both transcription units. The initiation points and the 3' ends of both inducible RNAs were mapped by S1 nuclease analysis. Both genes have open reading frames and may potentially code for proteins with repetitive amino acid compositions. The structure of these two inducible EBV genes is discussed, and an evolutionary model is proposed for the generation of gene duplication in the M-ABA strain of EBV.

Identification of the coding region for a second Epstein-Barr virus nuclear antigen (EBNA 2) by transfection of cloned DNA fragments

Cell lines were established by co-transfection of cloned M-ABA Epstein-Barr virus (EBV) DNA fragments with plasmids conferring resistance to dominant selective markers. A baby hamster kidney cell line carrying the HindIII-I1 fragment exhibits a nuclear antigen of 82 000 daltons, serologically defined as EBV-determined nuclear antigen (EBNA) 1. Furthermore, a Rat-1 cell line transfected with DNA of the clone pM 780-28 containing three large internal repeats (BglII-U) and the adjacent BglII-C fragment expresses a nuclear antigen of 82 000 daltons which can be visualized only by a subset of anti EBNA-positive human sera. Sera recognizing the 82 000-dalton protein of the transfected cell line reacted with a protein of the same size in the non-producer line Raji, designated as EBNA 2. Conversely, sera without reactivity to the 82 000-dalton protein failed to react with EBNA 2 of Raji cells. P3HR-1 and Daudi cells with large deletions in BglII-U and -C are devoid of EBNA 2. The data presented provide evidence that a second EBNA protein is encoded by the region of the EBV genome which is deleted in the non-transforming P3HR-1 strain.

Construction and use of cDNA clones for the mapping and identification of Epstein-Barr virus early P3HR-1 mRNAs

cDNA clones, specific for early Epstein-Barr virus (EBV) RNAs, were constructed from total cytoplasmic RNA of P3HR-1 TK- cells. From 10,000 cDNA clones screened, 22 virus-specific cDNA clones were selected by hybridization with a total EBV DNA. These clones were then precisely mapped on the EBV genome and the corresponding mRNAs were identified by Northern blot hybridizations. Most of them are clearly related to some of the open reading frames described by Baer et al. (Nature [London] 310:207-211, 1984). They represent at least 18 different genes active during the early viral cycle. The transcriptional activity of the virus during the early stage was also studied by dot blot hybridization of total early cDNA probe to EBV genomic fragments. Three main regions showed very strong hybridization with the cDNA probe: BamHI a, M, and L fragments, BamHI K, B, and G fragments, and BamHI B1 fragment (deleted in strain B95-8) and the adjacent right end of the DNA molecule. Seventeen of the cDNA clones were localized in these highly transcribed regions. The five others were dispersed all along the EBV genome.

Structure of the Epstein-Barr virus nuclear antigen as probed with monoclonal antibodies

Five hybridoma cell lines secreting antibodies directed against an Epstein-Barr virus (EBV) nuclear antigen (BamHI K antigen) have been isolated. All five antibodies detect this antigen in a variety of EBV-positive lymphoblastoid cell lines. The reaction of these antibodies with several mutant forms of this protein has allowed the antibody binding site(s) to be predicted.

Structure and transcription of human papillomavirus sequences in cervical carcinoma cells

DNA of human papillomavirus (HPV) types 16 and 18 has been found closely associated with human genital cancer, supporting the concept that members of this virus group are key factors in the aetiology of genital cancer. HPV 18 DNA sequences were also detected in cell lines derived from cervical cancer. We have now analysed these cell lines, HeLa, C4-1 and 756, for the structural organization and transcription of the HPV 18 genome and we find that the HPV 18 DNA is integrated into the cellular genome and is amplified in HeLa and 756 cells. Almost the complete HPV 18 genome seems to be present in 756 cells, with the early region being disrupted into two portions in each integrated copy. In HeLa and C4-1 cells, a 2-3 kilobase (kb) segment of HPV 18-specific sequences is missing from the E2 to L2 region. HPV 18 sequences are specifically transcribed from the E6-E7-E1 region into poly(A)+ RNAs of 1.5-6.5 kb. Hybridization analysis of cDNA clones indicated that some of the transcripts are composed of HPV 18 and cellular sequences. In addition, poly(A)+ RNA hybridizing with HPV 16 DNA was found in two out of three cervical carcinoma biopsies.

No evidence for differences in the Epstein-Barr virus genome carried in Burkitt lymphoma cells and nonmalignant lymphoblastoid cells from the same patients

Epstein-Barr virus (EBV), although not an indispensable factor for the development of Burkitt lymphoma, is apparently associated with the 20-fold higher incidence of the disease in Equatorial Africa compared to the incidence in other parts of the world. To determine whether different EBV subtypes are associated with the appearance of the malignant phenotype, we have compared the EBV genomes carried in the Burkitt tumor cells with those carried in the nonmalignant lymphoblastoid cells from the same individuals. From three patients with EBV -associated Burkitt lymphoma, tumor cell lines as well as spontaneously established lymphoblastoid cell lines representing the nonmalignant counterparts were obtained. The viral DNA in these cell lines was analyzed by Southern blot hybridization, using a set of cloned EBV DNA fragments as probes that recognize polymorphic regions in the viral genome. Using a number of different polymorphic markers to distinguish one isolate from another, the virus genome found in the tumor cells could also be identified in the nonmalignant cells of the same patient. In one case, in which two independent lymphoblastoid cell lines were established, evidence was obtained that this patient was infected by at least two distinct EBV subtypes. These results strongly suggest that in Burkitt lymphoma, the risk associated with EBV is related to cofactors such as chronic malaria and the mode of infection rather than to peculiar viral subtypes. The situation seems to be totally different from papillomavirus-associated diseases, in which the risk of progression to malignancy appears to be associated with particular viral strains.

A complete set of overlapping cosmid clones of M-ABA virus derived from nasopharyngeal carcinoma and its similarity to other Epstein-Barr virus isolates

DNA of the transforming, nondefective Epstein-Barr virus (EBV) strain M-ABA, which is derived from nasopharyngeal carcinoma cells, was cloned as large overlapping pieces into the cosmid pHC79 . The termini were cloned from closed circular virus DNA molecules out of M-ABA cell DNA in phage lambda L47 . The large overlapping clones were used to prepare a library of subclones with inserts of 1-15 kb. A detailed restriction enzyme map of M-ABA virus DNA reveals the close similarity to isolates from other sources. The high number of tandem repeats in EBV DNA stresses the importance of using cloning vectors that can be propagated in recA- Escherichia coli hosts.

Two deletions in the Epstein-Barr virus genome of the Burkitt lymphoma nonproducer line Raji

The Epstein-Barr virus genome carried in the Burkitt lymphoma nonproducer cell line Raji was characterized by partial denaturation mapping and by hybridization of cloned viral fragments to filters containing separated Raji DNA fragments. Partial denaturation mapping revealed that the EBV DNA population of Raji cells is homogeneous and that two deletions are observed in distant parts of the genome compared to linear DNA isolated from virus particles of different strains. These deletions were characterized by blot analysis. One deletion of 3.15 kb lies within HindIII-E; the second is 2.4 kb and is located close to the right terminus of linear viral DNA. The two deletions were observed in several cell lines derived from the Raji line. These deletions might contribute to the inability of Raji cells to produce EBV either spontaneously or upon induction.