Identification of an estrogen-mediated deoxyribonucleic acid-binding independent transactivation pathway on the epidermal growth factor receptor genepromoter

To investigate the estrogenic effects on the transcriptional regulation of the epidermal growth factor (EGF) receptor (EGFR) gene, we assayed its prom oter ability to direct transcription of the luciferase reporter gene after transfection into HeLa cells. Our studies demonstrated a dose-dependent act ivation of the EGFR gene transcription by ligand-bound estrogen receptor al pha (ER alpha). This action was retained by the 36-bp core promoter fragmen t and did not require the receptor DNA binding domain, as demonstrated by a nalyzing the role of ER alpha deletion mutants on EGFR gene promoter-derive d constructs. The 36-bp promoter fragment does not contain an estrogen resp onse element but an imperfect thyroid hormone response element; half-site t hat overlaps the Spl binding site. ER alpha does not bind this imperfect th yroid hormone response element half-site but is able to enhance binding of Spl to its site, in gel mobility shift assays, suggesting that the mechanis m by which the receptor stimulated the transcription involved protein-prote in interactions that replaced DNA binding. To explain this action, we propo se a model in which induction of the EGFR gene expression by estrogens in H eLa cells is dependent upon the formation of a transcriptionally active ER alpha-Sp1 complex that binds to the GO-rich (Spl) region of the minimal pro moter.