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, (ERα, and transactivation was also observed with a mutant ERα 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 ERα- bound this sequence. Transcriptional activation of DNA polymerase α by E2 is associated with ERα/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 ERα/Sp1 protein interactions that do not require direct binding of the hormone receptor to DNA.
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