Role of specificity protein transcription factors in estrogeninduced gene expression in MCF-7 breast cancer cells

Deletion analysis of several 17 beta-estradiol (E-2)-responsive genes have identified GC-rich sites that are associated with hormone-induced transactivation in MCF-7 breast cancer cells. However, the role of individual specificity proteins (Sps) in mediating hormone-induced gene expression has not been unequivocally determined. In transient transfection studies using E-2-responsive GC-rich promoters from the E(2)F1, carbamoylphosphate synthetase/aspartate transcarbamylase/dihydroorotase (CAD), and retinoic acid receptor alpha (RAR alpha) genes, RNA interference using small inhibitory RNAs for Sp1 (iSp1), Sp3 (iSp3), and Sp4 (iSp4) decreased both basal and E-2-induced transactivation. The contributions of individual Sp proteins to basal and E-2-induced activity were promoter dependent. iSp1, iSp3, and iSp4 also significantly inhibited hormonal induction of E(2)F1, CAD, and RAR alpha m RNA levels; however, the enhanced inhibitory effects of the latter two small inhibitory RNAs suggest that Sp3 and Sp4 play a major role in estrogen receptor alpha/Sp-mediated gene expression in MCF-7 cells.