Transcriptional activation of transforming growth factor alpha by estradiol: requirement for both a GC-rich site and an estrogen response element half-site

Estradiol (E2) induces transforming growth factor (TGF) gene expression in MCF-7 cells and previous studies have identified a 53 bp (252 to 200) sequence containing two imperfect estrogen responsive elements (EREs) that contrib- ute to E2 responsiveness. Deletion analysis of the TGF gene promoter in this study identified a second upstream region of the promoter (623 to 549) that is also E2 responsive. This sequence contains three GC-rich sites and an imperfect ERE half-site, and the specific cis-elements and trans- acting factors were determined by promoter analysis in transient transfection experiments, gel mobility shift assays and in vitro DNA footprinting. The results are consistent with an estrogen receptor (ER)/Sp1 complex interacting with an Sp1(N)30 ERE half-site (½) motif in which both ER and Sp1 bind promoter DNA. The ER/Sp1-DNA complex is formed using nuclear extracts from MCF-7 cells but not with recombinant human ER or Sp1 proteins, suggesting that other nuclear factor(s) are required for complex stabilization. The E2- responsive Sp1(N) x ERE½ motif identified in the TGF gene promoter has also been characterized in the cathepsin D and heat shock protein 27 gene promoters; however, in the latter two promoters the numbers of intervening nucleotides are 23 and 10 respectively.