Radiation-induced Epstein–Barr virus reactivation in gastric cancer cells with latent EBV infection

Abstract

Epstein–Barr virus, a ubiquitous human herpes virus with oncogenic activity, can be found in 6%–16% of gastric carcinomas worldwide. In Epstein–Barr virus–associated gastric carcinoma, only a few latent genes of the virus are expressed. Ionizing irradiation was shown to induce lytic Epstein–Barr virus infection in lymphoblastoid cell lines with latent Epstein–Barr virus infection. In this study, we examined the effect of ionizing radiation on the Epstein–Barr virus reactivation in a gastric epithelial cancer cell line (SNU-719, an Epstein–Barr virus–associated gastric carcinoma cell line). Irradiation with X-ray (dose = 5 and 10 Gy; dose rate = 0.5398 Gy/min) killed approximately 25% and 50% of cultured SNU-719 cells, respectively, in 48 h. Ionizing radiation increased the messenger RNA expression of immediate early Epstein–Barr virus lytic genes (BZLF1 and BRLF1), determined by real-time reverse transcription polymerase chain reaction, in a dose-dependent manner at 48 h and, to a slightly lesser extent, at 72 h after irradiation. Similar findings were observed for other Epstein–Barr virus lytic genes (BMRF1, BLLF1, and BcLF1). After radiation, the expression of transforming growth factor beta 1 messenger RNA increased and reached a peak in 12–24 h, and the high-level expression of the Epstein–Barr virus immediate early genes can convert latent Epstein–Barr virus infection into the lytic form and result in the release of infectious Epstein–Barr virus. To conclude, Ionizing radiation activates lytic Epstein–Barr virus gene expression in the SNU-719 cell line mainly through nuclear factor kappaB activation. We made a brief review of literature to explore underlying mechanism involved in transforming growth factor beta–induced Epstein–Barr virus reactivation. A possible involvement of nuclear factor kappaB was hypothesized.