EPSTEIN-BARR-VIRUS CONTRIBUTES TO THE MALIGNANT PHENOTYPE AND TO APOPTOSIS RESISTANCE IN BURKITTS-LYMPHOMA CELL-LINE AKATA

In the present study, we established an in vitro system representing t he Burkitt's lymphoma (BL)-type Epstein-Barr virus (EBV) infection whi ch is characterized by expression of EBV-determined nuclear antigen 1 (EBNA-1) and absence of EBNA-2 and latent membrane protein 1 (LMP1) ex pression, EBV-negative cell clones isolated from the EBV-positive BL l ine Akata were infected with an EBV recombinant carrying a selectable marker, and the following selection culture easily yielded EBV-infecte d clones, EBV-reinfected clones showed BL-type EBV expression and rest ored the capacity for growth on soft agar and tumorigenicity in SCID m ice that were originally retained in parental EBV-positive Akata cells and lost in EBV-negative subclones. Moreover, it was found that EBV-p ositive cells were more resistant to apoptosis than were EBV-negative cells, EBV-infected cells expressed the bcl-2 protein, through which c ells might become resistant to apoptosis, at a higher level than did u ninfected cells. This is the first report that BL-type EBV infection c onfers apoptosis resistance even in the absence of expression of LMP1 and BHRF1, both of which are known to have an antiapoptotic function. Surprisingly, transfection of the EBNA-1 gene into EBV-negative Akata clones could not restore malignant phenotypes and apoptosis resistance , thus suggesting that EBNA-1 alone was not sufficient for conferring them. Our results suggest that the persistence of EBV in BL cells is r equired for the cells to be more malignant and apoptosis resistant, wh ich underlines the oncogenic role of EBV in BL genesis.