Three Epstein-Barr virus (EBV)-determined nuclear antigens induced by the BamHI E region of EBV DNA

Detection of Epstein-Barr virus in synovial fluid of rheumatoid arthritis patients

INTRODUCTION

Rheumatoid arthritis (RA) is one of the most common chronic inflammatory disorders. Genes and environmental factors contribute to RA. Epstein-Barr Virus (EBV) has been considered as one the RA pathogeneses. The aim of this study was to detect of the EBV genome in patients with RA.

METHODS

In this cross-sectional study, 50 samples of synovial fluid were obtained from patients with RA from 2010-2012. Using a standard of the EBV genome and EBNA-1-specific primers, the method of PCR was set up. Then, all of the samples of synovial fluids separately were subjected to DNA extraction and Polymerase Chain Reaction (PCR) amplification. Data were analyzed using SPSS version 18.0. The statistical analysis was performed by the t-test.

RESULTS

The demographic and laboratory characteristic assay revealed that the mean age of patients was 49, and the patients were 60% males and 40% females. In addition, in all cases, the mean rheumatoid factor (RF) levels of the patients were below the normal level. The results of this study showed that the PCR was able to detect EBV DNA in > 60% of the cases.

CONCLUSION

The results of this study indicated that EBV was frequently detected in the synovial fluid of RA patients. Thus, EBV may be a strong candidate that can act at several levels of the pathophysiology of RA. However, these findings also indicated that EBV may play a role in the pathogenesis of RA. However, the possible relationship between RA and EBV must be determined by further research.

Epstein-Barr virus nuclear protein EBNA3C is required for cell cycle progression and growth maintenance of lymphoblastoid cells

Epstein-Barr virus (EBV) infection converts primary human B cells into continuously proliferating lymphoblastoid cell lines (LCLs). To examine the role of EBV nuclear antigen (EBNA) 3C in the proliferation of LCLs, we established LCLs infected with an EBV recombinant that expresses EBNA3C with a C-terminal fusion to a 4-hydroxytamoxifen (4HT)-dependent mutant estrogen receptor, E3C-HT. In the presence of 4HT, LCLs expressed the E3C-HT protein and grew like WT LCLs. When E3C-HT EBV-infected LCLs were transferred to medium without 4HT, E3C-HT protein slowly disappeared, and the LCLs gradually ceased growing. WT EBNA3C expression from an oriP plasmid transfected into E3C-HT LCLs protected the LCLs from growth arrest in medium without 4HT, whereas expression of EBNA3A or EBNA3B did not. The expression of other EBNA proteins and of LMP1, CD21, CD23, and c-myc was unaffected by EBNA3C inactivation. However, EBNA3C inactivation resulted in the accumulation of p16INK4A, a decrease in the hyperphosphorylated form of the retinoblastoma protein, and a decrease in the proportion of cells in S or G2/M phase. These results indicate that EBNA3C has an essential role in cell cycle progression and the growth maintenance of LCLs.

Epstein-Barr virus and rheumatoid arthritis: is there a link?

Rheumatoid arthritis is a systemic autoimmune disease characterized by chronic, destructive, debilitating arthritis. Its etiology is unknown; it is presumed that environmental factors trigger development in the genetically predisposed. Epstein–Barr virus, a nearly ubiquitous virus in the human population, has generated great interest as a potential trigger. This virus stimulates polyclonal lymphocyte expansion and persists within B lymphocytes for the host's life, inhibited from reactivating by the immune response. In latent and replicating forms, it has immunomodulating actions that could play a role in the development of this autoimmune disease. The evidence linking Epstein–Barr virus and rheumatoid arthritis is reviewed.

Decreased expression of signaling lymphocytic-activation molecule-associated protein (SAP) transcripts in T cells from patients with rheumatoid arthritis

The function of Epstein-Barr virus (EBV)-specific cytotoxic T cells is disturbed in rheumatoid arthritis (RA) patients but the mechanism for this disturbance has remained unknown. In a recent study searching for the causative gene of X-linked lymphoproliferative syndrome, the gene possibly linked to EBV-specific cytotoxic T cells or NK cell-mediated cytotoxic activity to EBV-infected cells was discovered, and its product is now referred to as signaling lymphocytic-activation molecule-associated protein (SAP) or Src homology 2 domain-containing protein (SH2D1A). In the present study, we attempted to investigate the involvement of the SAP gene in RA using a quantitative real-time PCR; the expression level of SAP transcripts in peripheral leukocytes or T cells was examined for patients with RA. The expression level of SAP transcripts in peripheral leukocytes of 21 RA patients was significantly lower than that of 13 normal individuals (P = 0.0007), four patients with palindromic RA, 11 with inactive systemic lupus erythematosus (SLE) or 17 with chronic renal diseases. The decreased expression of SAP transcripts in RA patients was also observed in peripheral CD2(+) T cells compared with normal individuals. There was no mutation in the coding region of SAP cDNAs derived from peripheral leukocytes of five RA patients. The decreased expression of SAP transcripts in peripheral leukocytes or T cells of RA patients might lead to the failure of the immune system to eliminate the EBV-infected synovial lining cells in joints of RA patients. Our findings have suggested that decreased expression of the SAP gene might be involved in the onset or progress of RA.

Spontaneous establishment of an Epstein-Barr virus-infected fibroblast line from the synovial tissue of a rheumatoid arthritis patient

An Epstein-Barr virus (EBV)-infected fibroblast line, designated DSEK, was spontaneously established from synovial tissue of a patient with rheumatoid arthritis (RA). DSEK cells expressed EBV nuclear antigens EBNA-1 and EBNA-2 and latent membrane protein LMP-1. Cell surface markers of DSEK cells were similar to those of EBV-negative fibroblast clones derived from synoviocytes and were negative for lymphocyte and macrophage markers. DSEK cells expressed CD44, CD58, and HLA-DR antigens and spontaneously produced interleukin-10 basic fibroblast growth factor and transforming growth factor beta1. These results indicate that rheumatoid synoviocytes can be a target for EBV infection and suggest that EBV may play a role in the pathogenesis of RA.

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

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

Identification of a short amino acid sequence essential for efficient nuclear targeting of the Epstein-Barr virus nuclear antigen 3A

The Epstein-Barr virus nuclear antigen 3A is expressed in the nuclei of cells latently infected by the Epstein-Barr virus. We have previously shown that a fragment of 265 amino acids was essential for the proper subcellular localization of the Epstein-Barr virus nuclear antigen 3A. As described in this paper, we have used deletion analysis to identify a decapeptide, RDRRRNPASR, which is essential for nuclear localization of this protein. Furthermore, this decapeptide is a functional nuclear localization signal as demonstrated by its ability to target expression of beta-galactosidase in the nuclei of transfected cells.

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

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

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

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

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.

cDNA cloning and transient expression of the Epstein-Barr virus-determined nuclear antigen EBNA3B in human cells and identification of novel transcripts from its coding region

Recombinant plasmids containing sequences from the BamHI-E rightward reading frames 2a and 2b (BERF2a and 2b) of the Epstein-Barr virus (EBV) genome were isolated from a library of cDNA clones which had been previously made from the EBV B95-8 lymphoblastoid cell line (M. Bodescot, O. Brison, and M. Perricaudet, Nucleic Acids Res. 14:7103-7114, 1986). The characterization of these clones in combination with RNase mapping experiments led to the identification of one leftward and several rightward transcripts traversing the EBV-determined nuclear antigen EBNA3B coding region. One cDNA (T7) contains a continuous open reading frame generated by the splicing together of BERF2a and BERF2b. The T7 clone was used to reconstruct a complete fused BERF2a/2b open reading frame in an adenovirus-based expression vector. Western immunoblotting and immunofluorescence experiments using human 293 cells showed that the recombinant plasmid is capable of expressing a protein with a size, immunological characteristics, and a subcellular localization indistinguishable from those of native B95-8 EBNA3B.

Transcription of the Epstein-Barr virus genome during latency in growth-transformed lymphocytes

Nuclear run-on assays revealed extensive transcription of the Epstein-Barr virus genome during latent infection in in vitro-infected human fetal lymphoblastoid cells (IB-4). The EBER genes were the most heavily transcribed viral genes in these cells. Their transcription was partially inhibited in the presence of 1 microgram of alpha-amanitin per ml and fully inhibited at 100 micrograms/ml, consistent with RNA polymerase III transcription. All other transcription was inhibited at 1 microgram of alpha-amanitin per ml, consistent with RNA polymerase II sensitivity to alpha-amanitin. Other than EBER transcription, almost no transcription occurred from the U1 region. Specifically, no transcription was detected from the U1 latent promoter. RNA polymerase II transcription was highest in IR1, extending rightward through U2 and IR2 into the U3 domain and gradually decreased, but was measurable throughout the rest of the genome. This is consistent with EBNA gene transcription initiation within IR1. The higher level of transcription of the IR1 and U2 domains, which encode EBNA-LP and EBNA-2, as opposed to the domains which encode EBNA-3A, EBNA-3B, or EBNA-3C or EBNA-1, correlated with a higher level of EBNA-LP/EBNA-2 mRNA. Transcription extended through U4 into U5, even though no known latent-gene mRNAs are expressed from U4 downstream of the EBNA-1 open reading frame. This may result from inefficient termination of EBNA gene transcription. Leftward transcription from the latent membrane protein promoter was lower than EBNA transcription, although the latent membrane protein mRNA was the most abundant of the latent-gene mRNAs, indicating that this mRNA is more efficiently processed or has a longer half-life. Although transcription was detected from the DL strong early promoters and to a lesser extent from other early promoters, early mRNAs were less abundant than EBNA mRNAs or undetectable, suggesting that there may be posttranscriptional as well as transcriptional control over early mRNA expression in these latently infected cells.

Size and stability of the Epstein-Barr virus major internal repeat (IR-1) in Burkitt's lymphoma and lymphoblastoid cell lines

We have used field inversion gel electrophoresis to survey EBV strains for the size of the major internal repeat, IR-1, and estimate the number of 3.1-kb repeat units present. The B95-8 strain of EBV was estimated to contain 8.6 repeats. The repeat number varies considerably among naturally occurring isolates around a mean of six repeats. Some cell lines harbored multiple viral genomes with differing numbers of repeats and our results suggest that the repeat number in IR-1 is more likely to change during lytic replication than during latency. The Jijoye strain had 6.6 repeats and the Jijoye deletion mutant clone P3HR-1 retained 5.9 repeats setting the size of the P3HR-1 deletion at 6.8 kb. Thus, the nonimmortalizing mutant has retained all of the W1 and W2 exons of the immortalizing parent and has lost only the 3' unique exons of EBNA4 and all of EBNA2.

Epstein-Barr virus gene expression in malignant lymphomas induced by experimental virus infection of cottontop tamarins

Inoculation of cottontop tamarins with a large dose of Epstein-Barr virus (EBV) leads to the induction of multiple EBV genome-positive lymphomas. These tumors have been characterized as oligoclonal or monoclonal large-cell malignant lymphomas that closely resemble the EBV genome-positive B-cell lymphomas that arise in human allograft recipients. The expression of latent and lytic EBV-encoded proteins was investigated in these virus-induced tamarin lymphomas and in derived cell lines. The tamarin tumors were found to express EBV nuclear antigen 1 (EBNA 1), EBNA 2, EBNA leader protein, and the latent membrane protein (LMP) as determined both by immunohistochemical staining and by immunoblotting. However, within the limits of the immunoblotting assays, no expression of the EBNA 3a protein family could be detected. Assays for lytic-cycle proteins by using both polyclonal human sera and monoclonal antibodies against viral capsid antigen, early antigen, and membrane antigen (gp340/220) showed minimal, if any, expression of these antigens in the lymphoma biopsies. In contrast, the cell lines derived from these lymphomas, even in early passage, expressed abundant levels of the lytic-cycle antigens and also expressed the EBNA 3a protein as well as EBNA 1, EBNA 2, EBNA leader protein, and LMP. This finding suggests that the virus-lymphoma cell interaction, in particular the switch to lytic cycle, is subject to some form of host control in vivo. The expression of EBNA 2 and LMP in these tamarin lymphomas strengthens their resemblance to posttransplant lymphomas in humans, since these human tumors are also EBNA 2 and LMP positive (L. S. Young, C. Alfieri, K. Hennessy, H. Evans, C. O'Hara, K. Anderson, A. Rickinson, E. Kieff, and J. I. Cohen, submitted for publication). Since both proteins are known to be important effector molecules of virus-induced B-cell growth transformation in vitro, their expression in these lymphomas constitutes the best evidence for a direct oncogenic role for EBV in vivo.

Distinction between Epstein-Barr virus type A (EBNA 2A) and type B (EBNA 2B) isolates extends to the EBNA 3 family of nuclear proteins

The Epstein-Barr virus (EBV) nuclear antigens EBNA 3a, 3b, and 3c have recently been mapped to adjacent reading frames in the BamHI L and E fragments of the B95.8 EBV genome. We studied by immunoblotting the expression of the family of EBNA 3 proteins in a panel of 20 EBV-transformed lymphoblastoid cell lines (LCLs) carrying either type A (EBNA 2A-encoding) or type B (EBNA 2B-encoding) virus isolates. Certain human sera from donors naturally infected with type A isolates detected the EBNA 3a, 3b, and 3c proteins in all type A virus-transformed LCLs (with a single exception in which EBNA 3b was not detected) but detected only EBNA 3a in LCLs carrying type B isolates. These results were confirmed with human and murine antibodies with specific reactivity against sequences of the type A EBNA 3a, 3b, or 3c expressed in bacterial fusion proteins. Conversely, selected human sera from donors naturally infected with type B strains of EBV identified the EBNA 3a encoded by both types of isolates plus two novel EBNAs present only in type B, and not in type A, virus-transformed LCLs; these novel proteins appear to be the type B homologs of EBNA 3b and 3c. The distinction between type A and type B EBV isolates therefore extends beyond the EBNA 2 gene to the EBNA 3 family of proteins. This has important implications with respect to the evolutionary origin of these two EBV types and also places in a new light recent studies which identified differences between type A and type B transformants in terms of growth phenotype (A. B. Rickinson, L. S. Young, and M. Rowe, J. Virol. 61:1310-1317, 1987) and of detection by EBV-specific cytotoxic T cells (D. J. Moss, I. S. Misko, S. R. Burrows, K. Burman, R. McCarthy, and T. B. Sculley, Nature [London] 331:719-721, 1988).