The repressed nuclear receptor CAR responds to phenobarbital in activating the human CYP2B6 gene.
The endogenous CYP2B6 gene becomes phenobarbital (PB) inducible in androstenol-treated HepG2 cells either transiently or stably transfected with a nuclear receptor CAR expression vector. The PB induction mediated by CAR is regulated by a conserved 51-base pair element called PB-responsive enhancer module (PBREM) that has now been located between -1733 and -1683 bp in the gene's 5'-flanking region. An in vitro translated CAR acting as a retinoid X receptor alpha heterodimer binds directly to the two nuclear receptor sites NR1 and NR2 within PBREM. In a stably transfected HepG2 cell line, both PBREM and NR1 are activated by PB and PB-type compounds such as chlorinated pesticides, polychlorinated biphenyls and chlorpromazine. In addition to PBREM, CAR also transactivates the steroid/rifampicin-response element of the human CYP3A4 gene in HepG2 cells. Thus, activation of the repressed nuclear receptor CAR appears to be a versatile mediator that regulates PB induction of the CYP2B and other genes.
Pharmacogenetics Section, Laboratory of Reproductive and Developmental Toxicology, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
T
T
Sueyoshi
T
T
Kawamoto
I
I
Zelko
P
P
Honkakoski
M
M
Negishi
D001189:Aryl Hydrocarbon Hydroxylases; D001483:Base Sequence; D000090702:Constitutive Androstane Receptor; D065702:Cytochrome P-450 CYP2B6; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D006801:Humans; D008969:Molecular Sequence Data; D010089:Oxidoreductases, N-Demethylating / Q000235:genetics* / Q000378:metabolism; D010634:Phenobarbital / Q000494:pharmacology*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors; D014162:Transfection; D014407:Tumor Cells, Cultured
D000090702:Constitutive Androstane Receptor; D018691:Excitatory Amino Acid Antagonists; D018160:Receptors, Cytoplasmic and Nuclear; D015534:Trans-Activators; D014157:Transcription Factors; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; D065702:Cytochrome P-450 CYP2B6; D010089:Oxidoreductases, N-Demethylating; D010634:Phenobarbital