Dominant-negative derivative of EBNA1 represses EBNA1-mediated transforming gene expression during the acute phase of Epstein-Barr virus infection independent of rapid loss of viral genome.

The oncogenic human herpes virus, the Epstein-Barr virus (EBV), expresses EBNA1 in almost all forms of viral latency. EBNA1 plays a major role in the maintenance of the viral genome and in the transactivation of viral transforming genes, including EBNA2 and latent membrane protein (LMP-1). However, it is unknown whether inhibition of EBNA1 from the onset of EBV infection disrupts the establishment of EBV's latency and transactivation of the viral oncogenes. To address this, we measured EBV infection kinetics in the B cell lines BALL-1 and BJAB, which stably express a dominant-negative EBNA1 (dnE1) fused to green fluorescent protein (GFP). The EBV genome was surprisingly unstable 1 week postinfection: the average loss rate of EBV DNA from GFP- and GFP-dnE1-expressing cells was 53.4% and 41.0% per cell generation, respectively, which was substantially higher than that of an 'established' oriP replicon (2-4%). GFP-dnE1 did not accelerate loss of the EBV genome, suggesting that EBNA1-dependent licensing of the EBV genome occurs infrequently during the acute phase of EBV infection. In the subacute phase, establishment of EBV latency was completely blocked in GFP-dnE1-expressing cells. In contrast, C /W promoter-driven transcription was strongly restricted in GFP-dnE1-expressing cells at 2 days post-infection. These data suggest that inhibition of EBNA1 from the onset of EBV infection is effective in blocking the positive feedback loop in the transactivation of viral transforming genes, and in eradicating the EBV genome during the subacute phase. Our results suggest that gene transduction of GFP-dnE1 could be a promising therapeutic and prophylactic approach toward EBV-associated malignancies. (Cancer Sci 2010; 101: 876-881)