Effects of adenine arabinoside on lymphocytes infected with Epstein-Barr virus.

Low concentrations of adenine arabinoside inhibited growth of two Epstein-Barr virus producer cell lines in culture, while not significantly affecting a nonproducer cell line and a B-cell-negative line. These observations were extended to include freshly infected cells. Mitogen-stimulated human umbilical cord blood lymphocytes were unaffected by the drug at concentration levels that inhibited [3H]thymidine incorporation into the DNA of Epstein-Barr virus-stimulated cells. DNA synthesis in Epstein-Barr virus-superinfected Raji cells was also adversely affected by adenine arabinoside. However, these same low concentrations of adenine arabinoside in the triphosphate form produced less effect on DNA synthesis in nuclear systems and DNA polymerase assays than on growth or DNA synthesis in whole cells. Therefore the effects reported here of low concentrations of the drug on whole cells may be only in part related to DNA polymerase inhibition. The work reported here suggests that adenine arabinoside has multiple sites of action in infected cells.     

Inhibition of Epstein-Barr virus DNA synthesis and late gene expression by phosphonoacetic acid.

Growth of lymphoblastoid cells (B95-8, Raji) is not inhibited by the presence of 0.4 mM phosphonoacetic acid. The synthesis of Epstein-Barr virus (EBV) in the producer line B95-8 is completely inhibited, as shown by the total inhibition of viral capsid antigen synthesis. Early viral antigens are made normally in the presence of phosphonoacetic acid, but EBV DNA synthesis is blocked in cells entering the productive cycle. Nonproducer cells in the population replicate the resident EBV DNA by a mechanism that is resistant to phosphonoacetic acid. These results are consistant with the hypotheses that EBV DNA is replicated by two mechanisms, one in the noninduced cell and a different mechanism in the producer cell, and that prior replication of EBV DNA, probably by the second mode, is a prerequisite for late gene expression.     

Synthesis of Epstein-Barr virus DNA in vitro: effects of phosphonoacetic acid, N-ethylmaleimide, and ATP.

Nuclei from superinfected Raji cells synthesized Epstein-Barr Virus (EBV) DNA in vitro in the absence of cell DNA synthesis. The synthesis of EBV DNA in vitro was inhibited by phosphonoacetic acid and N-ethylmaleimide, and maximum synthesis was achieved in the absence of an ATP-regenerating system. Nuclei from mock-infected cells required an ATP-regenerating system for maximum DNA synthesis.     

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

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

Herpes simplex virus resistance and sensitivity to phosphonoacetic acid.

Phosphonoacetic acid (PAA) inhibited the synthesis of herpes simplex virus DNA in infected cells and the activity of the virus-specific DNA polymerase in vitro. In the presence of concentrations of PAA sufficient to prevent virus growth and virus DNA synthesis, normal amounts of early virus proteins (alpha- and beta-groups) were made, but late virus proteins (gamma-group) were reduced to less than 15% of amounts made in untreated infected cells. This residual PAA-insensitive synthesis of gamma-polypeptides occurred early in the virus growth cycle when rates were identical in PAA-treated and untreated infected cells. Passage of virus in the presence of PAA resulted in selection of mutants resistant to the drug. Stable clones of mutant viruses with a range of drug sensitivities were isolated and the emergence of variants resistant to high concentrations of PAA involved the sequential selection of mutants progressively better adapted to growth in the presence of the drug. Increased drug resistance of virus yield or plaque formation was correlated with increased resistance of virus DNA synthesis, gamma-protein synthesis, and resistance of the virus DNA polymerase reaction in vitro to the inhibitory effects of the drug. PAA-resistant strains of herpes simplex virus type 1 (HSV-1) complemented the growth of sensitive strains of homologous and heterologous types in mixed infections in the presence of the drug. Complementation was markedly dependent upon the proportions of the resistant and sensitive partners participating in the mixed infection. Intratypic (HSV-1A X HSV-1B) recombination of the PAA resistance marker(s), Pr, occurred at high frequency relative to plaque morphology (syn) and bromodeoxyuridine resistance (Br, thymidine kinase-negative phenotype) markers, with the most likely order being syn-Br-Pr. Recombinant viruses were as resistant or sensitive to PAA as the parental viruses, and viruses recombinant for their PAA resistance phenotype were also recombinant for the PAA resistance character of the virus DNA polymerase. The results provide additional evidence that the herpesvirus DNA polymerase is the site of action of PAA and illustrate the potential usefulness of PAA-resistant mutants in genetic studies of herpesviruses.     

Phosphonoacetic acid: inhibition of transformation of human cord blood lymphocytes by Epstein-Barr virus.

Phosphonoacetic acid disodium salt (PAA) inhibited the transformation of human cord blood lymphocytes by Epstein-Barr virus (EBV) at concentrations of 50-100 microgram/ml. At these concentrations, PAA had no effect on the multiplication of EBV transformed human lymphoblastoid cells or on the survival of human cord blood lymphocytes. The transformation of human cord blood lymphocytes by the B95-8 strain of EBV was measured by 3H-thymidine uptake, 5 days or more after infection. The degree of inhibition of transformation was correlated with the relation between the input of EBV and the concentration of PAA in the experiment. PAA inhibited the transformation even when added 24 h after EBV infection, but had no effect when added 48 h after EBV infection. The inhibitory effect of PAA could be overcome by its removal and normal 3H-thymidine uptake was restored even after 6 days of inhibition. The specificity of the inhibitory effect on EBV induced transformation of human cord blood lymphocytes is discussed.     

A bicistronic Epstein-Barr virus mRNA encodes two nuclear proteins in latently infected, growth-transformed lymphocytes.

EBNA2 is a nuclear protein expressed in all cells latently infected with and growth transformed by Epstein-Barr virus (EBV) infection (K. Hennessy and E. Kieff, Science 227:1230-1240, 1985). The nucleotide sequence of the EBNA2 mRNA (J. Sample, M. Hummel, D. Braun, M. Birkenbach, and E. Kieff, Proc. Natl. Acad. Sci. USA 83:5096-5100, 1986) revealed that it begins with a 924-base open reading frame that has an unusual potential translational initiation site (CAAATGG). This open reading frame is followed by 138 nucleotides with only one highly unlikely translational initiation site (TACATGC), which would translate a pentapeptide before the next stop codon. The last part of the mRNA is the open reading frame which encodes EBNA2. In this paper, we demonstrate that the 924-base open reading frame translates a 40-kilodalton protein in vitro or in murine cells transfected with the EBNA2 cDNA under control of the murine leukemia virus long terminal repeat. A protein of identical size was detected in EBV-transformed, latently infected human lymphocyte nuclei by using antibody specific for the leader open reading frame expressed in bacteria. Therefore, this is a rare example of a mRNA which translates two proteins from nonoverlapping open reading frames. Since the protein encoded by the leader of the EBNA mRNA is expressed in all nuclei of a latently infected cell line, it was designated EBNA-LP. EBNA-LP localizes to small intranuclear particles and differs in this respect from EBNA1, EBNA2, or EBNA3. EBNA-LP is not expressed in an EBV-transformed marmoset lymphocyte cell (B95-8) or in one EBV-infected Burkitt tumor cell line (Raji) but is expressed in three other Burkitt tumor cell lines (Namalwa, P3HR-1, and Daudi).     

An Epstein-Barr virus transforming protein associates with vimentin in lymphocytes.

The Epstein-Barr virus (EBV) latent infection membrane protein (LMP) is likely to be an important mediator of EBV-induced cell proliferation, since it is one of the few proteins encoded by the virus in latent infection and since production of this protein in Rat-1 cells results in their conversion to a fully transformed phenotype. LMP was previously noted to localize to patches at the cell periphery. In this paper we examine the basis of LMP patching in EBV-infected, transformed lymphocytes. Our data indicate that LMP is associated with the cytoskeletal protein vimentin. Although LMP is fully soluble in isotonic Triton X-100 buffer, only 50% of it is extracted from cells in this solution. The rest remains bound to the cytoskeleton. LMP undergoes phosphorylation, and phosphorylated LMP is preferentially associated with the cytoskeleton. As judged by both immunofluorescence and immunoelectron microscopy, the vimentin network in EBV-transformed lymphocytes or EBV-infected Burkitt tumor lymphocytes is abnormal. Vimentin and LMP often colocalize in a single patch near the plasma membrane. In response to Colcemid treatment of EBV-infected cells, vimentin reorganizes into perinuclear rings, as it does in uninfected cells. LMP is associated with these perinuclear rings. Vimentin (or a vimentin-associated protein) may be a transducer of an LMP transmembrane effect in lymphoproliferation.     

Effect of tumor necrosis factor alpha and infliximab on apoptosis of B lymphocytes infected or not with Epstein-Barr virus

Chronic inflammation and immunosuppressive therapies increase the risk of non-Hodgkin's lymphoma associated or not with Epstein-Barr virus (EBV) infection. A possible link between infliximab treatment and increased risk of lymphoma has been suggested. Indeed, infliximab induces apoptosis of monocytes and activated T lymphocytes, but its effect on B lymphocytes infected or not with EBV is unknown. Secreted tumor necrosis factor (TNF) alpha and the expression level of TNF receptor 1 (TNFR1) and TNFR2 were compared in EBV-positive and negative B-cell lines. The impact of TNFalpha and infliximab on apoptosis of EBV-positive cells was analyzed regarding the activity of NF-kappaB. Increased expression of TNFalpha in EBV-positive cells suggested that infliximab could affect their survival. However, TNFalpha or infliximab incubation had no effect on apoptosis of EBV-positive cells. Loss of NF-kappaB activity sensitized lymphoblastoid cell lines to TNFalpha-induced apoptosis, but no direct effect of infliximab on apoptosis was detected. On the basis of our in vitro data, neither TNFalpha nor infliximab has a direct effect on apoptosis of B lymphocytes and EBV-positive cell lines. Thus, if an increased incidence of lymphoma were induced by TNFalpha blockers, it would not involve a direct effect on B cells but rather an impaired immune surveillance by T cells.     

Iridescent virus replication: patterns of nucleic acid synthesis in insect cells infected with iridescent virus types 2 and 6

The patterns of nucleic acid synthesis in insect cells infected with iridescent virus types 2 and 6 has been examined using nucleic acid hybridization techniques. Virus-specific RNA synthesis was detected 24 hr after infection. Virus-specific DNA synthesis was detected 96 hr after infection. Host-specific nucleic acid synthesis declined throughout infection, and host-specific nucleic acid synthesis was detected only in the first 48 hr of infection. The synthesis of iridescent virus progeny DNA molecules precedes the appearance of mature iridescent virus particles.     

Epstein-Barr virus DNA is amplified in transformed lymphocytes.

Leukocytes isolated from two adult donors who lacked detectable antibodies to antigens associated with Epstein-Barr virus were exposed to an average of 0.02 to 0.1 DNA-containing particles of Epstein-Barr virus per cell and immediately clones in agarose. Within about 30 generations all transformed cell clones contained between 5 and 800 copies of viral DNA per cell. Only 1 in 10(4) to less than 1 in 10(5) of the cells of each clone release virus, and the frequency of release did not correlate with the average number of copies of viral DNA in the cells of each clone. One clone that had an average of five copies of viral DNA per cell was recloned, and the average number of copies in four of six subclones increased 15-to 50-fold while the subclones were being propagated sufficiently to study them. These results indicate that Epstein-Barr virus DNA can undergo amplification relative to cell DNA at different times after it transforms cells.     

Virion nucleic acid of Ebola virus.

The virion nucleic acid of Ebola virus consists of a single-stranded RNA with a molecular weight of approximately 4.0 x 10(6). The virion RNA did not bind to oligodeoxythymidylic acid-cellulose under conditions known to bind RNAs rich in polyadenylic acid and was not infectious under conditions which yielded infectious RNA from Sindbis virus, suggesting that Ebola virus virion nucleic acid is a negative-stranded RNA.     

A fifth Epstein-Barr virus nuclear protein (EBNA3C) is expressed in latently infected growth-transformed lymphocytes.

Three distantly homologous neighboring long open reading frames in the Epstein-Barr virus (EBV) genome are preceded by short open reading frames. The leftmost short and long open reading frames encode EBNA3, a nuclear protein which is slightly smaller (145 kilodaltons [kDa]) than two other nuclear proteins (150 to 155 kDa) detected in Western blots (immunoblots) of latently infected cell protein (K. Hennessy, F. Wang, E. Woodland-Bushman, and E. Kieff, Proc. Natl. Acad. Sci. USA 83:5693-5697, 1986; I. Joab, D. T. Rowe, M. Bodescot, J.-C. Nicolas, P. J. Farrell, and M. Perricaudet, J. Virol. 61:3340-3344, 1987). We have demonstrated that the most rightward short (BERF3) and long (BERF4) open reading frames are spliced in frame at the 3' end of a 5-kilobase latently infected cell RNA and that this RNA begins within or upstream of the EBV long internal repeat. EBV-immune human antibodies specific for the long open reading frame translation product identified a 155-kDa protein on Western blots of latently infected cell protein and specifically reacted with large nonnucleolar nuclear granules in every latently infected cell. Expression of the cDNA in BALB/c 3T3 cells resulted in translation of full-size EBNA3C but had no effect on cell morphology, contact inhibition, or serum independence.