Bisphenol AF as an activator of human estrogen receptor β1 (ERβ1) in breast cancer cell lines.

Abstract

Bisphenol AF (BPAF) is now recognized as one of the replacements for bisphenol A (BPA). Although considerable experimental evidence suggests that BPA is an endocrine-disrupting chemical, the toxicological profile of BPAF has been investigated in less detail than that of BPA, even at the in vitro level. BPAF has been established as an activator of estrogen receptor α (ERα) in many cell lines; however, controversy surrounds its effects on the other isoform, ERβ (i.e., whether it functions as a stimulator). Five human ERβ isoforms have been cloned and characterized. Of these, we focused on the interactions between BPAF and the two isoforms, ERβ1 and ERβ2. We demonstrated that i) BPAF functioned as a stimulator of ERβ1 (and ERα), which is transiently expressed in the two types of human breast cancer cells (MDA-MB-231 and SK-BR-3 cells) (EC50 values for ERβ: 6.87 nM and 2.58 nM, respectively, and EC50 values for ERα: 24.7 nM and 181 nM, respectively), ii) the stimulation of ERβ1 by BPAF (1-25 nM) was abrogated by PHTPP (an ERβ selective antagonist), and iii) the expression of ERβ1 and ERβ2 was not modulated by BPAF at nanomolar concentrations up to 25 nM. These results indicate that BPAF activates not only human ERα, but also the ERβ1 isoform in breast cancer cells, and exhibits higher activation potency for ERβ1.