EPSTEIN-BARR-VIRUS EFFICIENTLY IMMORTALIZES HUMAN B-CELLS WITHOUT NEUTRALIZING THE FUNCTION OF P53

Epstein-Barr virus (EBV) efficiently converts resting human B cells in to actively cycling, immortal, lymphoblastoid cell lines (LCLs). Here we show that LCLs expressing the full complement of latent viral genes are very sensitive to DNA-damaging agents such as cisplatin. The resp onse includes a rapid accumulation of the tumour suppressor protein p5 3 and induction of the cellular genes mdm2 and WAF1/p21. Although the levels of Bc12 protein and Bar mRNA appear unaltered by the activation of p53, within 24 h the majority of cells undergo apoptosis. Over-exp ression of wild-type p53 in an LCL also resulted in apoptosis; this wa s preceded by the dephosphorylation of the retinoblastoma gene product , pRb. Primary resting B cells showed no response to cisplatin and eve n after drug treatment, p53 remained undetectable. However, after infe ction with EBV, p53 gene expression was induced to a similar level to that found in mitogen-activated B cells. When the physiologically acti vated primary B cells were exposed to cisplatin, although p53 accumula ted as in LCLs, the outcome was growth-arrest rather than gross cell d eath. We conclude that, in contrast to the transformation of fibroblas ts by adenovirus, SV40 or HPV, when B cells become activated and immor talized by EBV they are sensitized to the p53-mediated damage response . When the resulting LCLs are treated with genotoxic agents such as ci splatin, they are unable to arrest like normal cells because they are driven to proliferate by EBV and consequently undergo apoptosis.