Estrogen receptor-mediated transcriptional activation by 17β-estradiol and its analogs

We investigated the effects of natural and synthetic estrogens on estrogen receptor-mediated signal transduction and transcription. To assess estrogen receptor-dependent gene expression, we constructed a reporter plasmid that can express the luciferase gene under the control of the estrogen-responsive element. A transcriptional assay was performed by transfection of the reporter plasmid into estrogen-responsive MCF-7 cells. Transcription was completely dependent on the natural estrogen, 17β- estradiol (E₂), in a dose-dependent manner. Retinoic acids and other steroid hormones had no effect on gene expression. The effect of synthetic estrogens on estrogen receptor-mediated signal transduction was also examined using the specific reporter assay system. A synthetic estrogen, diethylstilbestrol, exhibited higher activity than E₂ at lower concentrations. In addition, transcriptional activities of the (+)- and (-)-enantiomers of indenestrol A, a metabolite of diethylstilbestrol, could be distinguished using the reporter assay system.