CYTOKINE INHIBITION OF THE HEPATITIS-B VIRUS CORE PROMOTER

Hepatitis B virus (HBV) DNA contains consensus elements for transactiv ating proteins whose binding activity in other systems is regulated by inflammatory cytokines, Because HBV replicates within an environment of provoked inflammation, we speculated that the HBV core/pregenomic p romoter may be regulated by cytokines produced in response to infectio n, To evaluate this hypothesis, the HBV core/pregenomic (C/P) promoter and associated cis-acting elements were placed upstream of a lucifera se-encoding plasmid, This reporter construct was transfected into cyto kine-sensitive hepatoma cells permissive for HBV replication, which we re exposed to stimulated mononuclear cell-conditioned medium or human recombinant cytokines. Conditioned medium reduced luciferase expressio n by 80%, Tumor necrosis factor alpha (TNF-alpha), interferon gamma (I FN-gamma), and interferon alfa (IFN-alpha) each reduced luciferase act ivity by 40%, Combinations of TNF-alpha and interferons mimicked the e xtent of conditioned medium inhibition, Nonspecific effects from dimin ished cellular viability or growth were not responsible for decreased luciferase activity, Retention of HBV DNA 330 basepairs upstream of th e C/P transcription start site was required to maintain the TNF-alpha effect, A 60% reduction in HBV replicative forms within intracellular core particles was demonstrated with TNF-alpha treatment of Hep G2 cel ls stably transfected with HBV DNA. The inhibitory action of these cyt okines implicates a noncytolytic mechanism by which antigen-nonspecifi c immune responses in part regulate HBV replication in infected hepato cytes. This function may be beneficial in accelerating viral clearance but in alternative circumstances could contribute to viral persistenc e by attenuating immunogen recognition.