Transcriptional activation of thymidylate synthase by 17 beta-estradiol inMCF-7 human breast cancer cells

Thymidylate synthase (TS) catalyzes methylation of deoxyuridine phosphate t o give deoxythymidine phosphate, and 17 beta-estradiol (E-2) induces TS gen e expression in MCF-7 human breast cancer cells. Analysis of the TS gene pr omoter showed that E-2-responsiveness required the -229 to -140 promoter re gion containing a G-rich sequence and CACCC box. Subsequent mutational anal ysis of this region indicated that only the G-rich motif(-150 to -142) was required for E-2 action. Results of gel mobility shift and in. vitro DNA fo otprinting assays showed that both estrogen receptor or (ER alpha) and Sp1 proteins were required for hormone-induced trans-activation that involved E R alpha/Sp1 binding to the G-rich site in which only Sp1 protein bound DNA. Both proteins also interacted in Drosophila cells in functional assays, co nfirming the transcriptional activation of TS-involved ER alpha/Sp1, and th is adds to the increasing number of genes that are activated through this p athway in breast cancer cells.