Estrogens up-regulate expression of the estrogen receptor alpha (ER) gene in most mammalian tissues studied. Using the ovariectomized ewe as a model, we determined that estradiol (E(2)) acted post-transcriptionally to increase endometrial ER mRNA concentrations by enhancing the stability of the message. The purpose of this study was to determine whether a similar E(2) effect occurs in Ishikawa cells, a well-differentiated human endometrial adenocarcinoma cell line. The presence and function of ER protein in Ishikawa cells was demonstrated by transactivation of a transfected plasmid (ERE(2)tkCAT) in response to 10(-)(9) M E(2), resulting in a 550% increase in reporter gene RNA. Ishikawa cells also responded to E(2) by up-regulating their ER mRNA concentration an average of 100% between 7 and 24 h of treatment. The effect of E(2) on ER mRNA stability was measured after blocking transcription with actinomycin D to find that the half-life increased from 6 to 10 h in control and E(2)-treated cells respectively. These results are consistent with cell-free studies which showed significant enhancement of the half-life of radiolabeled ER 3' untranslated region (3'UTR) RNA in extracts from E(2)-treated cells versus those from control cells. Thus, Ishikawa cells provide a relevant model system for the study of E(2)-regulated endometrial gene expression.

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