Phenobarbital-responsive nuclear translocation of the receptor CAR in induction of the CYP2B gene.
The constitutively active receptor (CAR) transactivates a distal enhancer called the phenobarbital (PB)-responsive enhancer module (PBREM) found in PB-inducible CYP2B genes. CAR dramatically increases its binding to PBREM in livers of PB-treated mice. We have investigated the cellular mechanism of PB-induced increase of CAR binding. Western blot analyses of mouse livers revealed an extensive nuclear accumulation of CAR following PB treatment. Nuclear contents of CAR perfectly correlate with an increase of CAR binding to PBREM. PB-elicited nuclear accumulation of CAR appears to be a general step regulating the induction of CYP2B genes, since treatments with other PB-type inducers result in the same nuclear accumulation of CAR. Both immunoprecipitation and immunohistochemistry studies show cytoplasmic localization of CAR in the livers of nontreated mice, indicating that CAR translocates into nuclei following PB treatment. Nuclear translocation of CAR also occurs in mouse primary hepatocytes but not in hepatocytes treated with the protein phosphatase inhibitor okadaic acid. Thus, the CAR-mediated transactivation of PBREM in vivo becomes PB responsive through an okadaic acid-sensitive nuclear translocation process.
Kawamoto
T
T
Pharmacogenetics Section, Laboratory of Reproductive and Developmental Toxicology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
Sueyoshi
T
T
Zelko
I
I
Moore
R
R
Washburn
K
K
Negishi
M
M
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001483:Base Sequence; D001693:Biological Transport, Active / Q000187:drug effects; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D000090702:Constitutive Androstane Receptor; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D000072467:Cytochrome P450 Family 2; D017931:DNA Primers / Q000235:genetics; D004742:Enhancer Elements, Genetic; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D019319:Okadaic Acid / Q000494:pharmacology; D010634:Phenobarbital / Q000494:pharmacology*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D013250:Steroid Hydroxylases; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors
D000090702:Constitutive Androstane Receptor; D017931:DNA Primers; D018160:Receptors, Cytoplasmic and Nuclear; D015534:Trans-Activators; D014157:Transcription Factors; D019319:Okadaic Acid; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C101679:Cyp2b10 protein, mouse; D000072467:Cytochrome P450 Family 2; D010634:Phenobarbital