Epstein-Barr virus nuclear antigen 1 does not induce lymphoma in transgenic FVB mice

Abstract

The lymphoma-inducing potential of Ig heavy-chain enhancer-and promoter-regulated Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) was evaluated in three transgenic FVB mouse lineages. EBNA1 was expressed at a higher level in transgenic B220(؉) splenocytes than in EBV-infected lymphoblastoid cell lines. EBNA1 was also expressed in B220(؊) transgenic splenocytes and thymocytes. Before killing and assessments at 18 -26 months, EBNA1-transgenic mice did not differ from control mice in mortality. At 18 -26 months EBNA1-transgenic mice did not differ from littermate control in ultimate body weight, in spleen size or weight, in lymph node, kidney, liver, or spleen histology, in splenocyte fractions positive for cluster of differentiation (CD)3 , CD4, CD8, CD62L, B220, CD5, IgM, IgD, MHC class II, CD11b, or CD25, or in serum IgM, IgG, or total Ig levels. Lymphomas were not found in spleens or other organs of 18-to 26-month-old EBNA1-transgenic (n ‫؍‬ 86) or control (n ‫؍‬ 45) FVB mice. EBNA1-transgenic lineages had a higher pulmonary adenoma prevalence than did littermate controls (39% versus 7%). However, the adenoma prevalence was not higher in EBNA1-transgenic mice than has been described for FVB mice, and EBNA1 was not expressed in normal pulmonary epithelia or adenomas.cancer ͉ herpesvirus ͉ latent ͉ persistence I n initial lymphocyte infection, Epstein-Barr Virus (EBV) causes B lymphocyte proliferation through a latency III program of expression of six nuclear proteins (EBNAs), two different integral membrane proteins, two small RNAs, and Bam A-initiated transcripts (1, 2). Although, in vitro, latency III-infected lymphocytes are able to grow endlessly as lymphoblastoid cell lines (LCLs), EBV proteins expressed in latency III-infected cells, in vivo, engender T cell responses that limit infected cell survival. EBV mostly persists long term in nonproliferating, latency I-or II-infected B cells that express EBNA1 or EBNA1 and latent infection membrane proteins, respectively (2-4). Latency I or latency II are also characteristic of Burkitt's lymphoma, Hodgkin's disease, and nasopharyngeal carcinoma (2). EBNA1 is expressed in almost all latent EBV infections and associated malignant diseases.EBNA1 enables efficient EBV episome replication, transcription, and maintenance in latently infected dividing cells (5-21). EBNA1 amino acids 379-641 include a dimerization and DNAbinding domain, which binds cognate 30-bp inverted repeat DNA sequences. EBV origin of plasmid replication (oriP) consists of 20 tandem cognate 30-bp repeats and four others 1 kbp away in a dyad symmetry (22). OriP has intrinsic origin activity. EBNA1 enhances oriP-dependent episome replication, transcription, and maintenance (7,8). EBNA1 amino acids 1-378 are necessary for chromosome association, transcriptional enhancement, and episome persistence, although not for initial DNA replication (21,(23)(24)(25). Within amino acids 1-378 is an irregular glycine͞alanine repeat, which inhibits EBNA1 processing through the proteasome͞TAP pathway (26,27).Becau...

Expression of Epstein-Barr nuclear antigen 1 in gastric carcinoma cells is associated with enhanced tumorigenicity and reduced cisplatin sensitivity

“…In previous reports, the oncogenic potential of EBNA1 was also identified in other cellular systems including the induction of lymphomagenesis in transgenic mice (35,57) and the enhancement of malignant progression of NPC cells in vivo (36) at low-level expression only detected by immunoprecipitated Western blotting. However, EBNA1 failed to induce lymphomas in transgenic FVB mice at an expression level similar to that of latent EBV infection in human B lymphocytes (38). These discrepant findings might have resulted from different expression levels of EBNA1.…”

“…These findings suggest that EBNA-1 is the EBV-encoded protein consistently expressed in all EBV-associated malignancies, which has biological effects and as such would seem to play a critical role in viral persistence and EBV-mediated cellular transformation (37). In contrast, it was also shown that EBNA1 is unable to induce lymphomas in transgenic FVB mice (38) and may act as a transforming suppressor of the HER2/neu oncogene by its N-terminal domain (39). Furthermore, it is able to sensitize HER2/neu-overexpressing ovarian cancer cells to topoisomerase II-targeted and paclitaxel drugs (40).…”

Epstein-Barr Virus Nuclear Antigen 1 Does Not Cause Lymphoma in C57BL/6J Mice

“…In C57BL/6 mice, EBNA1 expression in lymphocytes under an immunoglobulin (Ig) heavy-chain enhancer (E) and a polyomavirus promoter resulted in one lineage with very low EBNA1 expression and uniform death from malignant lymphoma at 6 to 9 months of age and another lineage with higher EBNA1 expression, no premature death, and increased lymphoma histology in 19-to 24-month-old mice (44,47). In another study, EBNA1 transgene expression in three FVB lineages under E and promoter at levels higher than LCLs did not change survival, weight, serum IgG, IgM, total Ig, spleen size, lymphocyte numbers, lymphocyte types, lymphoid organ size, and spleen histology (23). A lymphoma and a histiocytic sarcoma were found in 111 autopsied EBNA1 transgenic mice versus none in 63 littermate control mice (23).…”

“…Nevertheless, EBNA1 associates with chromosomes, ubiquitinspecific protease 7, importin, EBP2, and p32TAP and could affect cell growth, survival, or gene expression through these associations (13,17,46). Indeed, EBNA1 expression in non-EBV-infected Burkitt tumor lymphoblasts has been associated with changes in cell growth or gene expression in some experiments (14,25,26,48), but not in others (22,23). Previous assays of transgene EBNA1 effects on lymphoma prevalence in inbred mice have been inconclusive.…”

“…In another study, EBNA1 transgene expression in three FVB lineages under E and promoter at levels higher than LCLs did not change survival, weight, serum IgG, IgM, total Ig, spleen size, lymphocyte numbers, lymphocyte types, lymphoid organ size, and spleen histology (23). A lymphoma and a histiocytic sarcoma were found in 111 autopsied EBNA1 transgenic mice versus none in 63 littermate control mice (23). However, FVB mice have a much lower propensity for lymphoma than C57BL/6J mice and may be less sensitive to an EBNA1 effect on lymphoma incidence (3,4,30).…”