Replication of the wild type and a natural hepatitis B virus nucleocapsid promoter variant is differentially regulated by nuclear hormone receptors in cell culture

A natural hepatitis B virus (HBV) variant associated with seroconversion fr om HBeAg to anti-HBe antibody contains two nucleotide substitutions (A1764T and G1766A) in the proximal nuclear hormone receptor binding site in the n ucleocapsid promoter. These nucleotide substitutions prevent the binding of the retinoid X receptor alpha (RXR alpha)-peroxisome proliferator-activate d receptor alpha (PPAR alpha) heterodimer without greatly altering the effi ciency of binding of hepatocyte nuclear factor 4 (HNF4) to this recognition sequence. In addition, these nucleotide substitutions create a new binding site for HNF1 Analysis of HBV transcription and replication in nonhepatoma cells indicates that RXR alpha -PPAR alpha heterodimers support higher lev els of pregenomic RNA transcription from the wild-type than from the varian t nucleocapsid promoter, producing higher levels of wildtype than of varian t replication intermediates. In contrast, HNF4 supports higher levels of pr egenomic RNA transcription from the variant than from the wild-type nucleoc apsid promoter, producing higher levels of variant than of wild-type replic ation intermediates. HNF1 can support variant virus replication at a low le vel but is unable to support replication of the wild-type HBV genome. These observations indicate that the replication of wild-type and variant viruse s can be differentially regulated by the liver-specific transcription facto rs that bind to the proximal nuclear hormone receptor binding site of the n ucleocapsid promoter. Differential regulation of viral replication may be i mportant in the selection of specific viral variants as a result of an anti viral immune response.