Epstein-Barr Virus (EBV) is a human herpes virus associated with several malignancies including endemic Burkitt's lymphoma (eBL), nasopharyngeal carcinoma (NPC) and polyclonal B-cell lympho-proliferations in immunosuppressed individuals. Epstein-Barr virus nuclear antigen 1 (EBNA 1) plays a key role in the life cycle of the virus and is consistently expressed in all these tumour types. However, no oncogenic activities of EBNA 1 have been identified in cell cultures. Nevertheless, EBNA 1 is a viral oncogene when expressed in vivo in transgenic mice which succumb to monoclonal B cell lymphoma (Wilson and Levine, 1992, Wilson et al., 1996). The experiments described in this thesis were designed to explore how EBNA 1 may act as an oncogene in vivo. EBNA 1 was found to be redundant in terms of tumour latency with Bcl2 in transgenic crossbreeding experiments. Therefore, the ability of EBNA 1 to inhibit cell death or differentiation was examined by cell culture techniques. Moreover, cell surface markers examined by FACS. Flow cytometric analysis of spleen and bone marrow (BM) cells from EmuEBNA 1 transgenic mice revealed that the percentage of slg+ (and possibly CD23+) cells was statistically significantly higher when compared to the wild type control littermates. EmuEBNA 1 spleen and bone marrow (BM) cell survival cultures showed no survival advantage over the wt cultures. However, a proliferation/survival assay revealed that EmuEBNA 1 transgenic positive BM cells have statistically significant higher proliferation/survival rate than the wt BM cells. These results may indicate that EBNA 1 drives cells to differentiate and supports their survival/proliferation leading to increased sig. Since EBNA 1 is a DNA-binding protein acting as a transcriptional transactivator the expression levels of cellular genes involved in cell death and differentiation were examined in transgenic mice at pre- and post-tumour stages. The antiapoptotic gene BclxL was found up-regulated and the pro-apoptotic gene Bad was found downregulated. This strongly supports the earlier phenotypic observation that EBNA 1 may act in a similar fashion or through Bcl2 family genes. Moreover, RagJ and Rag2 genes were also found to be up-regulated in EmuEBNA 1 transgenic mouse spleens and this could lead to increased recombination, genome instability and possibly tumour development. Further studies, using a macroarray for differential gene expression, suggest that several immediate early response genes such as Jun and Fos family members and Egrl may be affected by EBNA 1. If EBNA 1 does up-regulate these genes this action could lead to increased differentiation and/or proliferation of EBNA 1 positive B cells. Thus, there are several lines of evidence suggesting that EBNA 1 supports B cell survival/proliferation and differentiation through de-regulation of genes responsible for the development of B cells. This may be the mechanism by which EBNA 1 causes tumourigenesis
