A novel induction mechanism of the rat CYP1A2 gene mediated by Ah receptor-Arnt heterodimer.
We have identified an enhancer responsible for induction by 3-methylcholanthrene in the upstream region of the CYP1A2 gene. The enhancer does not contain the invariant core sequence of XREs that are binding sites for the Ah receptor (AhR) and Arnt heterodimer. The enhancer did not show any inducible expression in Hepa-1-derived cell lines, C4 and C12, deficient of Arnt and AhR, respectively. On the other hand, bacterially expressed AhR-Arnt heterodimer could not bind to the enhancer. Mutational analysis of the enhancer revealed that a repeated sequence separated by six nucleotides is important for expression. A factor binding specifically to the enhancer was found by using gel shift assays. Bacterially expressed AhR-Arnt heterodimer interacted with the factor. A dominant negative mutant of the AhR to XRE activated the enhancer. Collectively, these results demonstrate that a novel induction mechanism is present in which the AhR-Arnt heterodimer functions as a coactivator.
Sogawa
Kazuhiro
K
Department of Biomolecular Science, Graduate School of Life Sciences, Tohoku University, Aoba-ku, Sendai 980-8578, Japan. sogawa@mail.tains.tohoku.ac.jp
Numayama-Tsuruta
Keiko
K
Takahashi
Tomohiro
T
Matsushita
Natsuki
N
Miura
Chisa
C
Nikawa
Jun-ichi
J
Gotoh
Osamu
O
Kikuchi
Yasuo
Y
Fujii-Kuriyama
Yoshiaki
Y
D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D001483:Base Sequence; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D015500:Chloramphenicol O-Acetyltransferase / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2 / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D004742:Enhancer Elements, Genetic / Q000235:genetics; D004790:Enzyme Induction; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008748:Methylcholanthrene / Q000494:pharmacology; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D011485:Protein Binding; D051381:Rats; D018336:Receptors, Aryl Hydrocarbon / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection
C497396:ARNT protein, human; C497398:ARNT protein, rat; D004268:DNA-Binding Proteins; D009838:Oligodeoxyribonucleotides; D018336:Receptors, Aryl Hydrocarbon; D011994:Recombinant Proteins; D014157:Transcription Factors; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D008748:Methylcholanthrene; D019388:Cytochrome P-450 CYP1A2; D015500:Chloramphenicol O-Acetyltransferase