Divergent homeobox gene hex regulates promoter of the Na(+)-dependent bile acid cotransporter.
The divergent homeobox gene Hex is expressed in both developing and mature liver. A putative Hex binding site was identified in the promoter region of the liver-specific Na(+)-bile acid cotransporter gene (ntcp), and we hypothesized that Hex regulates the ntcp promoter through this site. Successive 5'-deletions of the ntcp promoter in a luciferase reporter construct transfected into Hep G2 cells confirmed a Hex response element (HRE) within the ntcp promoter (nt -733/-714). Moreover, p-CMHex transactivated a heterologous promoter construct containing HRE multimers (p4xHRELUC), whereas a 5-bp mutation of the core HRE eliminated transactivation. A dominant negative form of Hex (p-Hex-DN) suppressed basal luciferase activity of p-4xHRELUC and inhibited activation of this construct by p-CMHex. Interestingly, p-CMHex transactivated the HRE in Hep G2 cells but not in fibroblast-derived COS cells, suggesting the possibility that Hex protein requires an additional liver cell-specific factor(s) for full activity. Electrophoretic mobility shift assays confirmed that liver and Hep G2 cells contain a specific nuclear protein that binds the native HRE. We have demonstrated that the liver-specific ntcp gene promoter is the first known target of Hex and is a useful tool for evaluating function of the Hex protein.
Denson
L A
LA
Department of Pediatrics, Yale University, New Haven, CT 06520-8064, USA.
Karpen
S J
SJ
Bogue
C W
CW
Jacobs
H C
HC
D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D005816:Genetic Complementation Test; D018197:Hepatoblastoma; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000166:cytology / Q000502:physiology*; D008113:Liver Neoplasms; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000502:physiology; D015345:Oligonucleotide Probes; D029363:Organic Anion Transporters, Sodium-Dependent; D011401:Promoter Regions, Genetic / Q000502:physiology*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D027981:Symporters; D014157:Transcription Factors; D014158:Transcription, Genetic / Q000502:physiology; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; C078492:HHEX protein, human; C513079:Hhex protein, rat; D018398:Homeodomain Proteins; D026901:Membrane Transport Proteins; D015345:Oligonucleotide Probes; D029363:Organic Anion Transporters, Sodium-Dependent; D011993:Recombinant Fusion Proteins; D027981:Symporters; D014157:Transcription Factors; C071908:sodium-bile acid cotransporter