Epstein-Barr virus nuclear antigen 2 retards cell growth, induces p21WAF1 expression, and modulates p53 activity post-translationally

The Epstein-Barr virus (EBV) nuclear antigen 2 (EBNA2) has been shown to be required for promotion of cell-cycle progression in EBV-immortalized B-lymphocytes. However, other studies have indicated that EBNA2 alone, in the absence of other EBV genes, may retard cell growth. To resolve this discrepancy, we investigated the effect of EBNA2 on the growth of various cells, including EBV target nasopharyngeal carcinoma cells, NPC-TW01 and NPC-TW04. We found that EBNA2 could retard cell growth, in stable Vero, HEp-2, and U2OS cell clones expressing EBNA2, and in Vero, 293, NPC-TW01, and NPC-TW04 cells transiently transfected with EBNA2. While investigating the mechanism underlying the growth-retarding function of EBNA2, we found that EBNA2 induced p21WAF1 expression in these cells. This induction of p21WAF1 expression was mediated through p53. EBNA2 was found to stimulate p53 to bind to the p53-response element within the p21WAF1 promoter, possibly by promoting p53 phosphorylation. This enhancement of p53 sequence-specific DNA-binding activity may be the mechanism through which EBNA2 activates the expression of p53-regulated genes, including p21WAF1 and mdm-2. Together, these studies reveal a possible intrinsic function of EBNA2 in cell-growth regulation and elucidate a novel mechanism by which EBNA2 modulates transcription.