Functional Analysis of Promoter Region from Eel Cytochrome P450 1A1 Gene in Transgenic Medaka

Transcription of the CYP1A1 genes in mammals and fish is stimulated by polyaromatic hydrocarbons. DNA sequencing analysis revealed that CYP1A1 gene in eel (Anguilla japonica) contains two kinds of putative cis-acting regulatory elements, XRE (xenobiotic-responsive element) and ERE (estrogen-responsive element). XRE is known as the enhancer that is responsible for the inducibility of the genes of CYP1A1 and some other drug-metabolizing enzymes. In the eel CYP1A1 gene, XRE motifs are distributed as follows: five times in the region from −2136 to −1125 bp, XRE(−6) to (−2); once in the proximal basal promoter region, XRE(−1); and once in the first intron, XRE(+1). The region between XRE(−2) and XRE(−1) contains three ERE motifs. To investigate the function of the cis-acting regulatory elements in the eel CYP1A1 gene, recombinant plasmids prepared with its 5′ upstream sequence and the structural gene for luciferase were microinjected into fertilized eggs of medaka at the one-cell stage. Hatched fry were treated with 3-methylcholanthrene, and the transcription efficiency was assayed using competitive polymerase chain reaction analysis. Deletion of the region containing the five XREs, XRE(−6) to XRE(−2), and the point mutation of XRE(−1) reduced the inducible expressions by 75% and 56%, respectively, showing apparent dependency of the drug induction on the XREs. Constitutive expression, however, was not significantly affected by deletion or disruption of the XREs. When the region between XRE(−2) and XRE(−1) containing no XREs but three ERE motifs was internally deleted, the inducible expression and the constitutive expression were reduced by 88% and 75%, respectively. Replacement of this region with a partial fragment of eel CYP1A1 complementary DNA, with slight alteration of the distance between the five XREs and XRE(−1), reduced the inducible expression and the constitutive expression by 91% and 60%, respectively. These results strongly suggest that not only XRE but also other regulatory elements, possibly ERE, play an important role in induced and constitutive expressions of the eel CYP1A1 gene.