Nitric oxide down-regulates Epstein-Barr virus reactivation in epithelial cell lines

Nitric oxide (NO), a mediator of biological functions, has an antimicrobial activity against a variety of pathogens including viruses. In this study, we found that a constitutive, low level of inducible NO synthase (iNOS) mRN A was expressed in the EBV-infected gastric tissue-derived GT38 and GT39 ce ll lines, by analysis with the reverse transcription-polymerase chain react ion (RT-PCR) and Southern blotting. Treatment of these cells with a specifi c NOS inhibitor, N-G-monomethyl-L arginine (L-NMMA), induced the immediate- early, EBV transactivator gene BZLF1 protein ZEBRA, suggesting a significan t increase in EBV reactivation by L-NMMA. Northern blotting demonstrated th at BZLF1 and BRLF1 transcripts were also induced by 12-O-tetradecanoylphorb ol-13 acetate (TPA). Meanwhile, constitutive expression of iNOS mRNA was in hibited by TPA. L-NMMA also enhanced TPA-induced expression of the BZLF1 ge ne. On the other hand, a NO donor, S-nitroso-N-acetylpenicillamine (SNAP), which releases NO in an aqueous solution, inhibited the TPA-induced BZLF1 g ene expression in a dose-dependent manner at both mRNA and protein levels. These results demonstrated that NO is a regulatory factor in maintaining vi rus latency via inhibiting EBV reactivation in the infected epithelial cell s, (C) 1999 Academic Press.