A factor binding to the xenobiotic responsive element (XRE) of P-4501A1 gene consists of at least two helix-loop-helix proteins, Ah receptor and Arnt.
Xenobiotic responsive element (XRE) is an inducible enhancer element that drives inducible expression of P-4501A1 gene in response to xenobiotic inducers. The XRE-binding factor appears in the nuclei of Hepa-1 cells treated with 3-methylcholanthrene (3-MC). Association of the Ah receptor and Arnt (Ah receptor nuclear translocator) in an XRE-binding complex was examined by anti-Ah receptor and Arnt antibodies. Both antibodies inhibited the sequence-specific XRE-binding activity of nuclear extracts from 3-MC-treated Hepa-1 cells and of the cytosolic fraction which was prepared from the nontreated cells and treated in vitro with 3-MC. These results indicate that Ah receptor and Arnt proteins are components of the XRE-binding factor and suggest that Arnt as well as the Ah receptor are localized in the cytosol of nontreated cells. The Ah receptor present in C4 cells, a mutant of Hepa-1 cells defective in the Arnt function, showed an inducer-dependent association with Arnt synthesized in an in vitro translation system. Co-transfection of the expression plasmids of the Ah receptor and Arnt exhibited synergistically more activated transcription from a reporter gene pMC6.3k consisting of the P-4501A1 gene promoter and enhancer than transfection with either of the two plasmids alone. These findings indicate that the Ah receptor and Arnt proteins form a complex that activates transcription in an inducer-dependent manner.
Matsushita
N
N
Department of Chemistry, Faculty of Science, Tohoku University, Sendai, Japan.
Sogawa
K
K
Ema
M
M
Yoshida
A
A
Fujii-Kuriyama
Y
Y
D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D001483:Base Sequence; D001665:Binding Sites; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D018257:Helix-Loop-Helix Motifs; D051379:Mice; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D011506:Proteins / Q000032:analysis*; D018336:Receptors, Aryl Hydrocarbon / Q000032:analysis*; D014157:Transcription Factors; D014407:Tumor Cells, Cultured; D015262:Xenobiotics / Q000494:pharmacology*
C497397:Arnt protein, mouse; D004268:DNA-Binding Proteins; D009838:Oligodeoxyribonucleotides; D011506:Proteins; D018336:Receptors, Aryl Hydrocarbon; D014157:Transcription Factors; D015262:Xenobiotics; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D003577:Cytochrome P-450 Enzyme System