Identification of regulatory sites in the human PXR (NR1I2) promoter region.
The human pregnane X receptor (hPXR, NR1I2) is a member of the nuclear receptor superfamily and a key regulator of genes encoding several major cytochrome P450 enzymes and transporters. However, the transcriptional regulation of hPXR itself remains unclear. We recently reported significant diversity in the 5' region of human hepatic PXR transcripts and identified the major transcription initiation site. Here, we investigate the transcriptional regulatory sites in the hPXR 5'-flanking region. Luciferase reporter constructs containing various lengths of 5'-flanking region, up to 10.5 kb upstream of the major transcription initiation site, were assessed for promoter activity in HepG2 cells. We mapped the minimal essential region for promoter activity to a 160 bp region upstream of the transcription initiation site, an area that also showed nuclear protein binding. Constructs with mutations introduced into these protein-binding sites demonstrated reduced promoter activity concomitant with reduced DNA-protein binding activity. hPXR promoter activity was observed in HepG2 cells but not in HeLa cells. Likewise, nuclear protein binding to promoter elements was also observed in HepG2 but not HeLa cells. The present study provides basic information on the transcriptional regulation of hPXR and may help elucidate the regulatory mechanisms of hPXR target genes.
Kurose
Kouichi
K
Project Team for Pharmacogenetics, National Institute of Health Sciences, Tokyo, Japan. kurose@nihs.go.jp
Ikeda
Shinobu
S
Koyano
Satoru
S
Tohkin
Masahiro
M
Hasegawa
Ryuichi
R
Sawada
Jun-ichi
J
D024506:5' Flanking Region / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D000077297:Pregnane X Receptor; D011401:Promoter Regions, Genetic; D051381:Rats; D011987:Receptors, Steroid / Q000235:genetics*; D050436:Regulatory Elements, Transcriptional / Q000235:genetics*
D004268:DNA-Binding Proteins; C000625852:NR1I2 protein, human; C000625853:Nr1i2 protein, mouse; C000625854:Nr1i2 protein, rat; D009687:Nuclear Proteins; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid