Cytokine inhibition of the hepatitis B virus core promoter

Abstract

Hepatitis B virus (HBV) DNA contains consensus elements for transactivating 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 promoter may be regulated by cytokines produced in response to infection. To evaluate this hypothesis, the HBV core/pregenomic (C/P) promoter and associated cis-acting elements were placed upstream of a luciferase-encoding plasmid. This reporter construct was transfected into cytokine-sensitive hepatoma cells permissive for HBV replication, which were exposed to stimulated mononuclear cell-conditioned medium or human recombinant cytokines. Conditioned medium reduced luciferase expression by 80%. Tumor necrosis factor alpha (TNF-alpha), interferon gamma (IFN-gamma), and interferon alfa (IFN-alpha) each reduced luciferase activity by 40%. Combinations of TNF-alpha and interferons mimicked the extent of conditioned medium inhibition. Non-specific effects from diminished cellular viability or growth were not responsible for decreased luciferase activity. Retention of HBV DNA 330 basepairs upstream of the 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 cells stably transfected with HBV DNA. The inhibitory action of these cytokines implicates a noncytolytic mechanism by which antigen-nonspecific immune responses in part regulate HBV replication in infected hepatocytes. This function may be beneficial in accelerating viral clearance, but in alternative circumstances could contribute to viral persistence by attenuating immunogen recognition.