Biochem Biophys Res Commun. 1998 Jun 18;247(2):383-6.  

Silencing of CYP1A1 expression in rabbits by DNA methylation.

Takahashi Y, Suzuki C, Kamataki T.

Faculty of Pharmaceutical Sciences, Hokkaido University, N12W6, Kita-ku,
Hokkaido, Sapporo, 060-0812, Japan.

Unlike most experimental animals, treatment of adult rabbits with
3-methylcholanthrene (MC) does not induce the expression of the CYP1A1 gene. In
this study, we show that DNA methylation plays one of the key roles in the
suppression of CYP1A1 gene expression. S1 nuclease protection assay showed that
the induction of CYP1A1 mRNA by MC occurred in rabbit kidney RK13 cells but not
in rabbit lung R9ab cells, while aryl hydrocarbon receptor (AhR) and AhR nuclear
translocator (Arnt) mRNAs were expressed in both cells at similar levels.
Interestingly, the treatment of R9ab cells with a DNA demethylating agent,
5-aza-2'-deoxycitidine, resulted in the induction of the expression of the
CYP1A1 gene by MC. The results indicate that DNA methylation is one of the
factors involved in the loss of the MC-induced expression of the CYP1A1 gene.
Thus, it seemed that the binding of the AhR/Arnt complex to the
xenobiotic-responsive element (XRE) was inhibited by the hypermethylation of CpG
dinucleotides within an XRE core sequence (5'-CGTG-3'). To explore this
possibility, we compared the methylation status of XRE in R9ab cells with that
in RK13 cells. A bisulfite sequence analysis using genomic DNAs from R9ab cells
showed that the CpG site within XRE was highly methylated on both coding and
non-coding strands. In contrast to this result, the hypomethylation of XRE was
seen in RK13 cells. To examine whether or not the binding of the AhR/Arnt
heterodimer to XRE is affected by the methylation status of XRE, a gel shift
assay using a methylated XRE as a probe was carried out. As expected, the
AhR/Arnt complex could not bind to the methylated XRE. From these results, we
conclude that the cell type-specific transcription of the rabbit CYP1A1 gene is
caused by DNA methylation. Copyright 1998 Academic Press.

PMID: 9642136 [PubMed - indexed for MEDLINE]