Epstein-Barr virus-specific DNase activity in nonproducer Raji cells after treatment with 12-o-tetradecanoylphorbol-13-acetate and sodium butyrate

A Distinct Anti-EBV DNase Profile in Patients with Undifferentiated Nasopharyngeal Carcinoma Compared to Classical Antigens

Nasopharyngeal cancer (NPC) is a prevalent type of cancer that often takes the form of undifferentiated carcinoma in the Maghreb region. It affects people of all ages. NPC diagnosis, mainly based on detecting Epstein-Barr virus (EBV), has not been well evaluated in North Africa. We compared the classical EBV serological tests using indirect immunofluorescence to the detection of EBV DNase antibodies by immunoblot in Algerian NPC patients. Significant variations were observed among different age groups of patients regarding the presence of VCA-IgA antibodies (0-14 and ≥30 years old, p < 0.0001; 15-19 and ≥30 years old, p < 0.01) and EA-IgA (0-14 and ≥30 years old, p < 0.01; 15-29 and ≥30 years old, p < 0.05). Differences were also noted in the titers of IgA anti-VCA and anti-EA antibodies across the three age groups. Some patients under the age of 30 with detectable IgG anti-VCA antibodies had undetectable IgA anti-VCA antibodies. These patients had a strong anti-DNase IgA response. However, older individuals had a higher level of anti-DNase IgG. Before treatment, children had strong DNase reactivity as indicated by specific IgA antibodies. Young adults had high IgA anti-DNase response, but the elderly (90.9%) had a lower response for these antibodies. Following therapy, the children retained high levels of IgA anti-DNase antibodies, and 66% of the young adults demonstrated robust antibody reactivity against DNase. In contrast, IgG responses to anti-DNase were low in children. This study demonstrated the utility of anti-DNase responses in the diagnosis and prognosis of NPC.

Diversity of Epstein-Barr virus BamHI-A rightward transcripts and their expression patterns in lytic and latent infections

Epstein-Barr virus (EBV) BamHI-A rightward transcripts (BARTs; also designated complementary strand transcripts or CSTs) have been demonstrated to contain several splicing forms in EBV-infected cells. To date, however, little is known about the actual full-length splicing form and its functions. In the present study, we proved that six forms of BARTs were present in EBV-positive cell lines and various tissue specimens with different EBV infection patterns. Of the BART-encoded genes, mRNA of four major splicing forms, including BARF0, RPMS1, RPMS1A and A73, were expressed in all EBV-infected cells. On the other hand, mRNA of two minor splicing forms, RK-BARF0 and RB3, was rarely detected, or if at all, at very low expression levels. Both RPMS1A and RPMS1 mRNA was transcribed at higher levels in EBV-infected cells. In particular, RPMS1 mRNA was expressed abundantly in epithelial carcinoma cells, including gastric carcinoma and nasopharyngeal carcinoma, in association with a lytic infection signal, BZLF1 mRNA. The four major splicing forms were expressed much less in B-cell lines with an integrated EBV genome than in those with episomal EBV genomes. These data indicate that at least six splicing forms can be expressed by EBV-infected cells or tissues, although the expression patterns or levels differ for different infection states such as lytic and latent infections.

Interactions of Epstein-Barr virus origins of replication with nuclear matrix in the latent and in the lytic phases of viral infection

Eukaryotic DNA is organized into domains or loops generated by the attachment of chromatin fibers to the nuclear matrix via specific regions called scaffold or matrix attachment regions. The role of these regions in DNA replication is currently under investigation since they have been found in close association with origins of replication. Also, viral DNA sequences, containing the origins of replication, have been found attached to the nuclear matrix. To investigate the functional role of this binding we have studied, in Raji cells, the interaction between Epstein-Barr virus (EBV) origins of replication and the nuclear matrix in relation to the viral cycle of infection. We report here that both the latent (ori P) and the lytic (ori Lyt) EBV origins of replication are attached to the nuclear matrix, the first during the latent cycle of infection and the second after induction of the lytic cycle. These findings suggest that the binding of the origins of replication with the nuclear matrix modulates viral replication and expression in the two different phases of infection.

A major DNA binding protein encoded by BALF2 open reading frame of Epstein-Barr virus (EBV) forms a complex with other EBV DNA-binding proteins: DNAase, EA-D, and DNA polymerase

A major 135-kDa DNA binding protein (mDBP) encoded by the BALF2 open reading frame of Epstein-Barr Virus (EBV) is known to be an essential protein for the induction of the lytic cycle. The present investigation was carried out to know whether this protein forms a complex in vivo with other viral DNA binding proteins (DBP) involved in DNA replication: DNA polymerase, EA-D (diffused early antigen), and DNAase. Immunoprecipitation assays followed by mono- and two-dimensional electrophoresis showed that mDBP forms a complex with these three DBP. Other complexes were also found such as EA-D/DNAase, DNA polymerase/DNAase, and DNA polymerase/EA-D. The complexed forms already exist in the early stage of EBV cycle before DNA synthesis is induced in the EBV producer P3HR-1 cell line. The exonuclease activity encoded by DNAase was found to be inhibited when this enzyme complexed with mDBP, while the EBV DNA polymerase retained its activity in the complexed form with mDBP. Our results suggest that these complexes already present before DNA synthesis are necessary for EBV DNA synthesis.

Branched structures in the intracellular DNA of herpes simplex virus type 1

Herpes simplex virus type 1 (HSV-1) replication produces large intracellular DNA molecules that appear to be in a head-to-tail concatemeric arrangement. We have previously suggested (A. Severini, A.R. Morgan, D.R. Tovell, and D.L.J. Tyrrell, Virology 200:428-435, 1994) that these DNA species may have a complex branched structure. We now provide direct evidence for the presence of branches in the high-molecular-weight DNA produced during HSV-1 replication. On neutral agarose two-dimensional gel electrophoresis, a technique that allows separation of branched restriction fragments from linear fragments, intracellular HSV-1 DNA produces arches characteristic of Y junctions (such as replication forks) and X junctions (such as merging replication forks or recombination intermediates). Branched structures were resolved by T7 phage endonuclease I (gene 3 endonuclease), an enzyme that specifically linearizes Y and X structures. Resolution was detected by the disappearance of the arches on two-dimensional gel electrophoresis. Branched structures were also visualized by electron microscopy. Molecules with a single Y junction were observed, as well as large tangles containing two or more consecutive Y junctions. We had previously shown that a restriction enzyme which cuts the HSV-1 genome once does not resolve the large structure of HSV-1 intracellular DNA on pulsed-field gel electrophoresis. We have confirmed that result by using sucrose gradient sedimentation, in which both undigested and digested replicative intermediates sediment to the bottom of the gradient. Taken together, our experiments show that the intracellular HSV-1 DNA is held together in a large complex by frequent branches that create a network of replicating molecules. The fact that most of these branches are Y structures suggests that the network is held together by frequent replication forks and that it resembles the replicative intermediates of bacteriophage T4. Our findings add complexity to the simple model of rolling-circle DNA replication, and they pose interesting questions as to how the network is formed and how it is resolved for packaging into progeny virions.

The lytic cycle of Epstein-Barr virus in the nonproducer Raji line can be rescued by the expression of a 135-kilodalton protein encoded by the BALF2 open reading frame

In Epstein-Barr virus (EBV)-carrying nonproducer Raji cells, the induction of the viral replicative cycle by chemical treatment is limited to only the early stage and viral DNA synthesis is totally inhibited. We previously showed the absence of two messenger RNAs that are encoded by the BamHI-A fragment of the EBV genome and that correspond to open reading frames BALF2 and BARF1 in chemically induced Raji cells. Since the BALF2 gene encodes a 135-kDa DNA-binding protein which was immunoprecipitated by antibody against ICP8 protein, a key protein in herpes simplex virus replication, we asked whether the lack of productive cycle in Raji cells is due to the absence of expression of the BALF2 gene. We transfected the Raji cell line with the BALF2 gene. After chemical induction, the BALF2-transfected cells expressed not only early antigens but also late antigens. In these cultures, the viral particles were detected by electron microscopy. The expression of late antigens was completely inhibited by arabinofuranosylthymine, which is a specific inhibitor of viral DNA replication. The BALF2 gene might play an essential role in the induction of the EBV-lytic cycle.

Use of bacterially-expressed antigen for detection of antibodies to the EBV-specific deoxyribonuclease in sera from patients with nasopharyngeal carcinoma

A cDNA clone, BG9, corresponding to the open reading frame BGLF5 of Epstein-Barr virus (EBV) DNase was inserted into an E. coli expression vector, pET3a, to generate a recombinant plasmid, pDNase 5. High level of expression of a DNase activity was detected in the E. coli transformed with pDNase 5 following induction with IPTG. The enzyme activity was purified using DEAE-cellulose, phosphocellulose and DNA-cellulose column chromatography. The purified protein appeared to be nearly homogeneous in SDS-PAGE using Coomassie blue staining. The requirement for divalent cations and optimum pH as well as inhibitory concentrations of ionic strength and polyamines for the purified enzyme activity were determined and seemed to be very similar to those of the enzyme activity purified from an EBV producing lymphoblastoid cell line. Using the purified enzyme as an antigen and anti-IgA as the secondary antibody, 82% (64/78) and 91% (71/78) of sera from patients with nasopharyngeal carcinoma (NPC) were shown to be positive by dot immunobinding assay and ELISA, respectively. The results suggest that purified E. coli expressed EBV DNase may be useful for preparing specific test for large scale screening of patients with NPC.

Quantitative analysis of the Epstein-Barr virus-inducing properties of short-chain fatty acids present in the culture fluids of oral bacteria

The culture fluids of various anaerobic bacteria induced the synthesis of early antigens (EA) in Epstein-Barr virus (EBV) carrying lymphoblastoid cells. The culture fluids of Corynebacterium butyricum and Fusobacterium nucleatum were the effective inducer on EA. The inducing activity was, to some extent, dependent on their n-butyric acid content, but appeared to be regulated by yet unidentified materials.

Characterization of 3'-to 5'-exonuclease activity associated with Epstein-Barr virus DNA polymerase

Epstein-Barr virus (EBV) DNA polymerase mediates viral DNA replication during the lytic phase of the EB virus life cycle. In order to characterize its enzymatic activities EBV DNA polymerase was purified more than 1200-fold from chemically induced B95-8 cells. One polypeptide with molecular weight of 110,000 corresponded to the predicted EBV DNA polymerase, whereas the other polypeptides did not. A 3'-to-5' exonuclease activity was copurified with the EBV DNA polymerase through the course of the purification. Unlike HSV DNA DNA polymerase, 5'-to-3' exonuclease activity was not associated with the EBV DNA polymerase on the final step chromatography of single-stranded DNA agarose column. The associated 3'-to-5' exonuclease activity was stimulated by ammonium sulfate like the polymerase activity. It exhibited DNA-dependent nucleotide turnover activity and preferentially excised a terminal mismatched nucleotide on hybridized polynucleotides compared to the correctly paired substrate, indicating that the 3'-to-5' exonuclease may play a role in proofreading in the polymerization process.

Chromatographic purification and characterization of EBV DNase from chemically induced lymphoid cells

Epstein-Barr virus-associated deoxyribonuclease (EBV-DNase) was purified to homogeneity, as determined by silver staining, sequential column chromatography, and FPLC from Raji and P3HR-1 cells treated with 12-O-tetradecanoyl-phorbol-13-acetate and sodium butyrate. This viral protein was immunogenic and elicited high neutralization titer sera in rabbits. By silver staining of SDS-PAGE, Western immunoblot, and radioimmunoprecipitation using NPC patient sera and both polyclonal and monoclonal antibodies, the EBV DNase was identified as a 58K protein. The potential presence of two EBV DNases was also discussed.

Purification and properties of Epstein-Barr virus DNase expressed in Escherichia coli

A cDNA corresponding to the BGLF5 open reading frame of the Epstein-Barr virus (EBV) genome and coding for an early DNase was inserted into the procaryotic expression vector pKK223-3. One bacterial clone producing the expected 52-kilodalton DNase was used as a source of EBV DNase. The 52-kilodalton Dnase was purified in the active form to near homogeneity by ammonium sulfate precipitation and successive chromatographies on phosphocellulose, DNA-cellulose, and gel filtration columns. The purified enzyme exhibited both exonuclease and endonuclease activities, an absolute requirement for divalent cations, an alkaline pH preference, and a typical residual activity in presence of 300 mM KCl. Moreover, the enzyme was specifically inhibited by human sera with high antibody titers to EBV early antigens. These properties are similar to those observed for EBV-induced DNase from lymphoblastoid cell extracts. In addition, the enzyme was recognized by both immunoglobulin G and A serum fractions from patients with nasopharyngeal carcinoma (NPC). From these results and previous studies which demonstrated the value of antibody titers to this viral DNase as an NPC marker, it appears that EBV-encoded DNase produced in a heterologous expression system could be used in the development of a specific and early NPC diagnosis test.

Characterization of two newly established EBV-containing lymphoblastoid cell lines from patients with myeloid leukemias

Two spontaneous outgrowing Epstein-Barr virus (EBV)-carrying lymphoblastoid cell lines (LCLs), CG2 and CG3, have been established from bone marrow cells of myeloid leukemia patients. CG2 was derived from a patient with chronic myelomonocytic leukemia (CMMoL) and who has a 45 XO karyotype. CG3 was derived from a patient with juvenile chronic myeloid leukemia (CML) and who carries a hypotetraploid karyotype, 91XXYY. Both CG2 and CG3 cells carry the same type of translocation; t(1;19)(q23;p13). Both cell lines are of an early B cell lineage as shown by their reactivities with monoclonal antibodies OKIa, B1, B2 and B4. The combination of horizontal discontinuous agarose slab gel and Southern hybridization results show CG2 and CG3 cells are of monoclonal origin and harbor episomal EBV genomes. Approximately 50 EBV genome equivalents were contained in CG2 and CG3 cells. Immunofluorescence studies demonstrate the expression of EBV-encoded antigen (EBNA) in almost all cells of these two lines. The expression of EA and VCA is only observed in a small percentage of cells and cannot be induced by treatment with TPA and SB. Therefore, CG2 and CG3 cells are probably nonproducer cell lines for EBV. The serum samples from both patients have been shown to contain elevated IgG antibody titers to EBV antigens. Both cells are found to be nontumorigenic in nude mice. These cells may provide an important tool in analyzing molecular epidemiological aspects of EBV infections in diseases such as CMMoL and juvenile CML.

Antibody to Epstein-Barr virus-specific DNase as a marker for field survey of patients with nasopharyngeal carcinoma in Taiwan

A serological survey using antibody to Epstein-Barr virus (EBV)-specific DNase activity as a marker for the identification of patients with nasopharyngeal carcinoma (NPC) has been carried out on healthy subjects who visited Government Employees' Clinic Center (GECC) for routine health examination and on individuals residing in NPC high-risk areas (HRA) in Taiwan. During a 3-year prospective study, 22,596 and 9,869 sera were collected from the GECC and HRA groups, respectively. Taking neutralization of 2 or more units of EBV DNase activity as a positive response, the positivity rates in the GECC and HRA groups were 5.4% and 11.92%, respectively. Among the antibody-positive individuals, three cases of NPC were found in the GECC group (detection rate 0.63%) and 11 in the HRA group (detection rate 1.32%). A further patient at stage III of the disease was found in the first year of following up of 1,005 antibody-positive individuals. Among the 12 NPC patients in the HRA, five were newly diagnosed as having stage II (three patients) and stage III (two patients) NPC. These results support the hypothesis that antibody against EBV-specific DNase activity may be a useful marker for detection of patients with NPC, and they imply that individuals having high levels of antibody to EBV DNase activity may have an increased risk of development of NPC.

Relationship between nasopharyngeal carcinoma and high antibody titers to Epstein-Barr virus-specific thymidine kinase

Epstein-Barr virus (EBV) has long been implicated in nasopharyngeal carcinoma (NPC). Recent studies in our and other laboratories have shown a correlation between the disease and high antibody titers to EBV-specific DNase. These data led us to also examine serial sera from healthy adults and patients with infectious mononucleosis or NPC, for their capacity to neutralize the EBV-specific thymidine kinase (TK) activity from chemically induced EBV-carrying human lymphoblastoid cells. Our results were the following: (i) sera were found that efficiently blocked the EBV-specific TK activity of induced-Raji TK- cell extracts, but not the host-cell TK activity from EBV-negative BJAB cells; (ii) a relationship appeared between high levels of EBV-specific TK-neutralizing activity in sera and NPC pathology, even though in this preliminary study the degrees of EBV-induced TK-blocking activity detected in sera were not significantly correlated with EBV-specific antibody titers; (iii) the EBV-induced TK-neutralizing activity was found in the main IgG fraction derived from NPC sera. These data must be compared with other known antibody responses to EBV for their clinical interest in NPC control.

Antigenic variation in alkaline deoxyribonuclease induced by three different strains of Epstein-Barr virus

To determine whether biological and/or biochemical variants exist between strains of Epstein-Barr virus (EBV), we superinfected Raji cells with the nontransforming lytic strain of EBV (HR-1), and two isolates that both transform B-lymphocytes and superinfect Raji cells, B95-8, and NPC-EBV. The superinfected cells were assayed for EBV specific DNase. A new electrophoretic form of DNase was observed in cells superinfected with B95-8 EBV as compared to the enzymes induced by the HR-1 and NPC-EBV isolates. There were antigenic differences in the DNase induced by the EBV strains. Since antibody to EBV DNase is a marker for nasopharyngeal carcinoma (NPC), these data may have implications for EBV-associated disease.

Specific immune serum to the Epstein-Barr virus DNA polymerase

Epstein-Barr virus (EBV) DNA polymerase was released from phorbol ester-treated tamarin (Saguinus oedipus) cells (B95-8) and prepared for use as an antigen by sequential column chromatography with DEAE-Sephadex A-25, DEAE-cellulose, phosphocellulose, and single-stranded DNA cellulose. Proteins from single-stranded DNA cellulose with DNA polymerase activity in 100 mM ammonium sulfate were mixed with complete Freund adjuvant and injected intradermally into rats and rabbits. Immune sera that were screened for specific antibody by indirect immunofluorescence procedures reacted with approximately 3% of the cells in EBV-producer cultures (B95-8 and P3HR-1) but not with EBV genome-negative cells (BJAB). In functional enzyme assays, immune sera or the immunoglobulin fraction inhibited the activity of purified EBV DNA polymerase 90%. Inhibition of enzyme activity was not affected by absorption of immune sera with insoluble matrices of proteins prepared with tamarin and human cells which lacked the EBV genome. Cellular DNA polymerase alpha was not inhibited by immune sera to the EBV enzyme.

Identification of an Epstein-Barr virus-specific desoxyribonuclease gene using complementary DNA

We have recently obtained 18 distinct cDNA clones representing different genes expressed in the early phase of EBV infection. One of them, c37, which is situated at the position 12907-122451 in the B95-8 viral genome, is shown here to code for a viral desoxyribonuclease [DNase]. Cell free translation of c37-selected messenger RNA yielded a protein of about 52 KDa which was immunoprecipitated by a high EA titer serum from nasopharyngeal carcinoma patient. This protein showed a DNase activity which was resistant to high salt concentrations (150 to 300 mM KCl) and was specifically neutralized by EA positive serum. These properties are typical of the EBV-specific DNase activity that we recently described in chemically induced EBV-transformed lymphoid cells. The same results were obtained on cell-free translation of the native RNA synthesized in vitro from pGEM-37 plasmid containing the entire c37 cDNA sequence (1.53 Kb). These data indicate that the BGLF5 open reading frame contained in c37 encodes for the EBV-specific DNase.

Epstein-Barr virus-specific DNA polymerase in virus-nonproducer Raji cells

Virus-nonproducer Raji cells, when induced to early antigen synthesis by 12-O-tetradecanoyl-phorbol-13-acetate and sodium butyrate, showed an increase in DNA polymerase activity. This enzyme has the characteristics of a typical Epstein-Barr virus DNA polymerase with regard to chromatographical pattern and biological properties: it is eluted from DEAE-cellulose at 0.08 M NaCl, has a high salt resistance, is sensitive to phosphonoacetic acid and phosphonoformate, and shows a substrate preference for poly(dC)-oligo(dG12-18). The resistance of Epstein-Barr virus polymerase activity to aphidicolin is a property distinct from that of HSV DNA polymerase. Viral DNA polymerase activity increases in the absence of Epstein-Barr virus DNA replication, indicating that this enzyme is an early viral protein.

Characterization of an Epstein-Barr virus-induced thymidine kinase

Previous work from our laboratory suggested that the selective inhibition of Epstein-Barr virus (EBV) replication by 1-beta-D-arabinofuranosylthymine in human lymphoid cell lines involved the induction of a new thymidine kinase (TK) able to phosphorylate the thymidine analog. We further characterized this enzyme induced in various EBV-positive cell lines after viral genome activation with a combination of sodium butyrate and 12-O-tetradecanoylphorbol-13-acetate. The following results confirmed the existence of an EBV-specific deoxypyrimidine kinase: induction of EBV-related TK was connected with the appearance of viral early antigens in EBV-carrying cells; unexpected behaviors of the enzyme activity upon different fractionating treatments led to the conclusion that EBV-induced TK was extracted as a complex molecular form, larger than other known cellular or viral isozymes; enzymatic properties distinguished EBV-induced TK from host lymphoid cell isozymes but made it resemble other herpesvirus-specific deoxypyrimidine kinases, i.e., by partial inhibition by dTTP or ammonium sulfate, insensitiveness to dCTP, and nonstringent specificity for normal TK substrates. Genetic evidence is required to definitively ensure that EBV-specific TK actually is virus coded in EBV-transformed human lymphoid cells.