MOLECULAR BIOLOGY OF HEPATITIS B VIRUS DNA-CELL INTERACTION

Abstract

Liver-specificity of hepatitis B virus (HBV) replication has been attributed to the action of its second enhancer (EII). This thesis reports the characterization of EII and the subsequent isolation of a novel liver-specific DNA-binding protein which binds to, and activates EII. The cDNA clone of the protein designated here as E2BP, was isolated from a ?gtll expression library constructed from the hepatoma cell line HuH-6 which was screened with a binding site probe derived from EII. Sequence analysis of E2BP revealed 86.6% homology with a rat hnRNP-C c-terminal protein sequence while conformational studies suggest a "helix-loop-helix'' motif as a DNA-binding site. Cloned E2BP expressed in human fibroblasts by transient transfection displayed similar EII binding and activating characteristics as native E2BP in hepatocytes. This is the first report of the interaction of a hnRNP-binding protein with a viral enhancer element. The concept that tissue-specificity of HBV replication may be dependent on such nuclear proteins is indeed intriguing and would certainly help to better understand and give insight into the steps leading to HBV pathogenesis.