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

Treatment of MCF-7 human breast cancer cells with 17 beta -estradiol (E-2) results in increased DNA synthesis and cell proliferation and enhanced enzy me activities associated with purine/pyrimidine biosynthesis. The mechanism of enhanced DNA polymerase alpha activity was investigated by analysis of the promoter region of this gene. E-2 induced luciferase (reporter gene) ac tivity in MCF-7 cells transfected with pDNAP1, pDNAP2, and pDNAP3 containin g -1515 to +45, -248 to +45 and -116 to +45 inserts from the DNA polymerase alpha gene promoter, whereas no induction was observed with pDNAP4 (-65 to +45 insert). The induction response was dependent on cotransfection with e strogen receptor alpha (ERalpha), and transactivation was also observed wit h a mutant ERalpha 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 E-2-mediated transactivation, and Sp1 protein, but not ERalpha, bound this sequence. Transcriptional activati on of DNA polymerase alpha by E-2 is associated with Er-alpha/Sp1 action at a proximal GC-rich promoter sequence, and this gene is among a growing lis t of E-2-responsive genes that are induced via ERalpha/Sp1 protein interact ions that do not require direct binding of the hormone receptor to DNA.