Transactivation of cellular promoters by an integrated hepatitis B virus DNA

A new Hepatitis B virus(HBV) DNA integrant clone DA2-6, isolated from a human hepatocellular carcinoma(HCC) genomic library, was tested for its ability to transactivate expression of other genes. DA2-6 consists of 3.7 kb flanking cellular sequences and an integrated 2.8 kb HBV DNA which covers the region of preS, S, and the 3' truncated X. Using a chloramphenicol acetyltransferase (CAT) assay, a number of cellular and viral promoters were transactivated by DA2-6, and the spectrum of transactivational effect was the same as that by the wild type X gene of the virus. Deletion mutant analyses indicated that the transactivation function of DA2-6 is expressed by the region that encodes a truncated X-cell fusion product.