Identification of estrogen receptor beta expression in Chinese hamster ovary (CHO) cells and comparison of estrogen-responsive gene transcription in cells adapted to serum-free media

Most cultured cell lines require addition of serum to the medium to maintain their proliferative capacity. For studies examining the cellular effects of estrogens serum is charcoal-stripped to remove steroids. Nonetheless, addition of the selective estrogen receptor modulator (SERM) 4-hydroxytamoxifen (4-OHT) inhibits the basal transcriptional activity of estrogen receptors alpha or beta (ERα or ERβ) in transfected cells. We tested the hypothesis that elimination of serum from the culture medium will block 4-OHT’s repression of basal activity. Chinese hamster ovary (CHO-K1) cells adapted to serum-free medium exhibited estrogen responsiveness that was identical with that of the cells grown in serum-containing media. 4-OHT-suppressed basal transcription of an estrogen response element (ERE)-reporter in ERα-transfected cells even in the absence of serum, indicating that the 4-OHT suppressive activity is not mediated by blocking ER interaction with serum estrogens. We speculate that 4-OHT-ER recruits co-repressors to suppress basal transcription. We discovered that CHO-K1 cells express ERα and ERβ mRNA. However only ERβ protein was expressed and use of ERβ-selective 2,3-bis(4-hydroxy-phenyl)propionitrile (DPN) and ERα-selective 4-propyl-1,3,5-tris(4-hydroxy-phenyl)pyrazole) (PPT) revealed that only ERβ was transcriptionally active. In conclusion, growing CHO-K1 in serum-free medium does not impact the estrogen responsiveness and this cell line expresses functional ERβ. [Copyright &y& Elsevier]