A DNA-binding factor specific for xenobiotic responsive elements of P-450c gene exists as a cryptic form in cytoplasm: its possible translocation to nucleus.
Transcription of the drug-metabolizing cytochrome P-450c gene is induced by 3-methylcholanthrene or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Previously, we defined two xenobiotic responsive elements (XREs) of approximately equal to 15 base pairs, both of which activate transcription in cis in response to these xenobiotics. Using a gel mobility shift assay, we have identified a factor that specifically binds to the XREs. This factor appears in nuclei of mouse hepatoma cell line Hepa-1 only when the cells are treated with the xenobiotics, while the factor is undetectable in the nuclei of a 3-methylcholanthrene-treated mutant of Hepa-1 with defective function of a xenobiotic receptor. In addition, the nuclear factor bound to the XRE in the gel was found to be associated with [3H]TCDD when the cells were treated with it, suggesting that the xenobiotic receptor is at least a component of the DNA-binding factor. The cytoplasmic fraction from nontreated Hepa-1 cells also contains the factor as a cryptic form and prominently reveals its DNA-binding activity by incubation with 3-methylcholanthrene in vitro. These results not only suggest the involvement of the XRE-binding factor in transcriptional activation via XREs but also provide evidence that the binding of ligands to the preexisting factor in a cryptic form induces its XRE-binding activity, which is probably followed by its translocation from cytoplasm to nucleus.
Fujisawa-Sehara
A
A
Department of Biochemistry, Cancer Institute, Japanese Foundation for Cancer Research, Tokyo.
Yamane
M
M
Fujii-Kuriyama
Y
Y
D001483:Base Sequence; D001665:Binding Sites; D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D003593:Cytoplasm / Q000378:metabolism*; D004247:DNA / Q000032:analysis / Q000378:metabolism*; D008748:Methylcholanthrene / Q000494:pharmacology; D000072317:Polychlorinated Dibenzodioxins / Q000378:metabolism; D011955:Receptors, Drug / Q000378:metabolism*; D014158:Transcription, Genetic
D000072317:Polychlorinated Dibenzodioxins; D011955:Receptors, Drug; D008748:Methylcholanthrene; D004247:DNA; D003577:Cytochrome P-450 Enzyme System