Regulation of transcription from the hepatitis B virus large surface antigen promoter by hepatocyte nuclear factor 3

The influence of hepatocyte nuclear factor 3 (HNF3) on the level of transcriptional activity from the four hepatitis B virus promoters was investigated by transient-transfection analysis in the dedifferentiated hepatoma cell line, HepG2.1. It was found that the large surface antigen promoter and, to a much lesser extent, the nucleocapsid promoter were transactivated in the presence of HNF3. DNase I footprinting analysis demonstrated that purified recombinant HNF3 alpha protects one region of the large surface antigen promoter. Gel retardation analysis showed that a double-stranded oligonucleotide containing this HNF3-binding site formed a specific complex with DNA-binding proteins in the differentiated hepatoma cell lines, Huh7 and HepG2. The complex formed with Huh7 cell extract comigrated with exogenously expressed HNF3 beta in HeLa S3 extracts and was specifically inhibited from forming by the addition of HNF3 beta antiserum. The promoter element which appears to mediate the HNF3 transactivation was functionally mapped by mutational analysis to a region between nucleotides -65 and -54 relative to the transcriptional start site. This regulatory sequence is within the region protected from DNase I digestion by HNF3 alpha and contains 10 of 12 nucleotides homologous to the HNF3-binding-site consensus sequence. A synthetic promoter construct containing this HNF3-binding site was able to mediate transactivation by HNF3 beta. These and previous results suggest that the hepatitis B virus large surface antigen promoter is regulated by at least two liver-enriched transcription factors, HNF1 and HNF3, which together may contribute to the differentiated liver cell type specificity of this promoter.