BZLF1 controlled by family repeat domain induces lytic cytotoxicity in Epstein-Barr virus-positive tumor cells

Background: BZLF1, an EBV (Epstein-Barr virus) immediate early gene, is required for EBV lytic replication that causes the death of host cells. EBNA1, the product of EBV latent gene, binds to the family repeats (FR) of the origin of replication (Orip) regulating EBV replication. Materials and Methods: A vector pFR-Z (BZLF1 controlled by FR domain of EBV) was constructed and transfected into EBV-positive 5-8F and-negative HNE3 nasopharyngeal carcinoma cells and BZLF1-induced cytotoxicity was tested. Results: EBNA1 expression was detected in 5-8F but not HNE3 cells and, in agreement, pFR controlled luciferase expression was activated in 5-8F cells but inhibited in HNE3 cells. Gardella gel assay demonstrated that pFR-Z effectively induced EBV lytic replication in 5-8F but not HNE3 cells. The lytic cytotoxicity was confirmed by a diminished cell survival and the induction of lytic proteins EA-D and gp125. The cytotoxicity was also strikingly enhanced by addition of GCV (gancyclovir) that kill cells with lytic form EBV Conclusion: pFR-Z is a specific gene therapy vehicle for EBV-positive carcinomas.