The hepatitis B virus core promoter is strongly activated by the liver nuclear receptor fetoprotein transcription factor or by ectopically expressed steroidogenic factor 1

Orphan nuclear receptor fetoprotein transcription factor (FTF) was previous ly identified as a specific regulator of the a,alpha(1)-fetoprotein gene du ring early liver development and in response to hormonal signals (L. Galarn eau, J.-F. Pare, D.Allard, D. Hamel, L. Levesque, J. D. Tugwood, S. Green, and L. Belanger, Mol. Cell. Biol. 16:3853-3865, 1996), Here we report a fun ctional analysis of FTF interactions with the hepatitis B virus (HBV) nucle ocapsid promoter. DNA-protein-binding assays shaw that the REV core promote r contains two high-affinity FTF-binding sites and a third, lower-affinity site shared with other receptors. Transfections in HepG2, Hep3B, and PLC/PR F/5 hepatoma cells using chloramphenicol acetyltransferase reporter genes,w ith the nucleocapsid promoter linked or not linked to enhancer I indicate t hat FTF is a potent activator of the HBV core promoter, more efficient than HNF4 alpha, HNF3 alpha, HNF3 beta, or C/EBP alpha. Steroidogenic factor 1, a close FTF homolog which binds to the same DNA motif and is expressed ect opically in HepG2 cells, seems to be an even stronger inducer than FTF. Poi nt mutations of the FTF-binding sites indicate direct FTF activatory effect s on the core promoter and the use of both high-affinity sites for producti ve interaction between the core promoter and enhancer I. Coexpression assay s further indicate that FTF and HNF4 alpha are the most efficient partners for coactivation of the pregenomic core promoter, which mag. largely accoun t for the hepatic tropism and the early amplification of HBV infection. Car boxy terminus-truncated FTF behaves as a dominant negative mutant to compet e all three FTF sites and strongly deactivate core promoter interactions wi th enhancer I; this suggests possible new ways to interfere with HBV infect ion.