Differential interactions of bisphenol A and 17β-estradiol with estrogen receptor α (ERα) and ERβ

Bisphenol A (BPA), a monomer of plastic used in consumer products, is abundant in the environment and enters the body by ingestion or adsorption. We developed a cell based transcription assay system using a reporter gene under the transcriptional control of estrogen receptor alpha (ER alpha) as well as ER beta and performed chloramphenicol acetyltransferase (CAT) assay on HeLa cells transfected with either human ER alpha cDNA or ER beta cDNA to characterize the estrogenic effect of BPA. Estrogenic activity of BPA was detectable at a concentration of 10(-9) M and the activity increased in a dose dependent manner between. concentrations of 10(-9) M and 10(-6) M of BPA for both ER alpha and ER beta. The estrogenic activity of 17 beta-estradiol at a concentration of 10(-8) M was almost compatible with that of BPA at the concentration of 10(-6) M of BPA for ER alpha as well as ER beta. CAT activity was significantly decreased when cells expressing ER alpha were incubated with 10(-6) M of BPA and 10(-8) M of 17 beta-estradiol while the activity was essentially the same for ER beta in the same condition, indicating that BPA exhibits only agonistic action for ER beta whereas it has dual actions as an agonist and antagonist of estrogen for ER alpha. These results indicates that BPA exerts its effects in ER subtype specific way, thus suggesting that the mode of action of endocrine disrupters are more complex than thought.