REACTIVATION OF THE PREVIOUSLY SILENCED CYTOMEGALOVIRUS MAJOR IMMEDIATE-EARLY PROMOTER IN THE MOUSE-LIVER - INVOLVEMENT OF NF-KAPPA-B

The cytomegalovirus (CMV) major immediate-early promoter/enhancer is a ctive in many cell culture systems and is considered to be one of the strongest promoters in vitro. However, when this promoter was used in in vivo approaches to gene therapy, it was silenced within a few weeks in several organs including the liver. In this study, we demonstrated transcriptional inactivation of the CMV promoter in mouse liver. In c ontrast to the CMV promoter, a hybrid promoter consisting of a minimal CMV promoter and the enhancer II of hepatitis B virus was active for at least 11 weeks in mouse liver. While investigating the reason for t he shutdown of the CMV promoter, we did not find evidence for methylat ion of adenovirus DNA in the region of transgene insertion, but we cou ld show that the silenced CMV promoter was reactivated after lipopolys accharide treatment of mice or partial hepatectomy. Both stimuli are k nown to activate the transcription factor NF kappa B, which binds to f our sites in the CMV promoter/enhancer. We show that expression from t he CMV promoter in hepatocyte-derived cell lines in vitro depends on N F kappa B. In vivo experiments demonstrate that NF kappa B, which is n ot present in mouse hepatocytes in vivo, is activated after infection with recombinant adenoviruses and that the time course of NF kappa B a ctivation parallels that of CMV promoter-dependent expression. Moreove r, adenovirus infection of transgenic mice carrying a CMV promoter-dri ven lacZ gene leads to strong activation of the expression of this gen e in the liver. Thus, NF kappa B is involved in the activation of the CMV promoter in the liver.