Functional interaction of nuclear factors EF-C, HNF-4, and RXR alpha with hepatitis B virus enhancer I.
Hepatitis B virus (HBV) enhancer I contains cis-acting elements that are both sufficient and essential for liver-specific enhancer function. The EF-C binding site was previously shown to be a key element in enhancer I. EF-C binding activity is evident in hepatic and nonhepatic cells. Although the EF-C binding site is required for efficient HBV enhancer I function, the EF-C site does not possess intrinsic enhancer activity when assayed in the absence of flanking elements. We have defined a novel region in HBV enhancer I, termed the GB element, that is adjacent to and functions in conjunction with the EF-C binding site. The GB element and EF-C site confer interdependent liver-specific enhancer activity in the absence of flanking HBV enhancer sequences. The nucleotide sequence of the GB element is similar to sequences of the DNA binding sites for members of the steroid receptor superfamily. Among these proteins, we demonstrate that HNF-4, RXR (retinoid X receptor), and COUP-TF bind to the GB element in vitro. HNF-4 transactivates a promoter linked to a multimerized GB/EF-C domain via the GB element in vivo in a manner that is dependent on the integrity of the adjacent EF-C binding site. RXR alpha also transactivates promoter expression via the GB element in vivo in response to retinoic acid but in a largely EF-C-independent manner. Finally, we show that COUP-TF antagonizes the activity of the GB element in human liver cells.
Department of Microbiology, State University of New York, Stony Brook 11794.
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Garcia
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Ostapchuk
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Hearing
D001483:Base Sequence; D001665:Binding Sites; D051838:COUP Transcription Factor I; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D015967:Gene Expression Regulation, Viral; D006515:Hepatitis B virus / Q000235:genetics*; D051557:Hepatocyte Nuclear Factor 4; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D010750:Phosphoproteins; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D016415:Sequence Alignment; D017384:Sequence Deletion; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation
D051838:COUP Transcription Factor I; D004268:DNA-Binding Proteins; D051557:Hepatocyte Nuclear Factor 4; D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; D010750:Phosphoproteins; D011956:Receptors, Cell Surface; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors