Down-Regulation of Estrogen Receptor Alpha-Mediated Transcription by p27

Abstract

Estrogen receptor α (ERα) is a DNA binding transcription factor which regulates reproductive function and transcription of its target genes. A member of cip/kip family of cyclin-dependent kinase inhibitors, p27 is responsible for cell cycle arrest at G1 stage. To investigate the effect of p27 on ER-mediated transcription, we generated p27 knock-out MCF-7 breast cancer cells (MCF-7 hp27shRNA) via retroviral delivery of p27 shRNA. Knock-down of p27 in MCF-7 cells resulted in up-regulation of ER-mediated transcription by estradiol as compared to control MCF-7 cells (MCF-7 mp27shRNA). Accordingly, transient transfection studies revealed that overexpression of p27 in 293T cells reduced ER-mediated transcription. It appears that the effect of p27 on ER transcriptional activity is independent from cell cycle arrest by p27 since cell cycle arrest induced by serum starvation did not significantly affect ER-mediated transcription. The effect of p27 on transcription was appeared to be ER-specific since overexpression of p27 did not significantly affect activities of other transcription reporters, TOPFLASH-luc, FHRE-Luc and NFκB-Luc.