Transcriptional activation of deoxyribonucleic acid polymerase α gene expression in MCF-7 cells by 17β-estradiol

Treatment of MCF-7 human breast cancer cells with 17β-estradiol (E₂) results in increased DNA synthesis and cell proliferation and enhanced enzyme activities associated with purine/pyrimidine biosynthesis. The mechanism of enhanced DNA polymerase α activity was investigated by analysis of the promoter region of this gene. E₂ induced luciferase (reporter gene) activity in MCF-7 cells transfected with pDNAP1, pDNAP2, and pDNAP3 containing -1515 to +45, -248 to +45 and -116 to +45 inserts from the DNA polymerase α gene promoter, whereas no induction was observed with pDNAP4 (-65 to +45 insert). The induction response was dependent on cotransfection with estrogen receptor α, (ER_α, and transactivation was also observed with a mutant ER_α that did not express the DNA-binding domain. Subsequent functional, DNA binding, and DNA footprinting studies showed that a GC-rich region at -106 to -100 was required for E₂-mediated transactivation, and Sp1 protein, but not ER_α- bound this sequence. Transcriptional activation of DNA polymerase α by E₂ is associated with ER_α/Sp1 action at a proximal GC-rich promoter sequence, and this gene is among a growing list of E₂-responsive genes that are induced via ER_α/Sp1 protein interactions that do not require direct binding of the hormone receptor to DNA.