Localization of estradiol-responsive region in the phenobarbital-responsive enhancer module of mouse Cyp2b-10 gene

The mouse Cyp2b-10 gene is inducible by treatment with estradiol as well as so-called phenobarbital (PB)-like inducers. To identify 5'-flanking elements responsible for induction by estradiol, we carried out reporter gene assays using a primary mouse hepatocyte culture system. Cyp2b-10 gene-driven luciferase activities were induced by estradiol as well as PB in this system. Deletion analysis demonstrated that the sequence contained within the region from -2331 bp to -2281 bp was responsible for the estradiol-induced luciferase activity. This region corresponds to the core element of PB-responsive enhancer module (PBREM). Several nucleotide mutations in the putative binding sites of the PBREM core element showed that the NR1 site was required for estradiol induction, and the same element was required for PB induction. These results indicate that estradiol induces Cyp2b-10 gene expression via PBREM.