ESR1 and breast cancer: Consistent with this last observation, ERα could be localized to a tRNALeu and 5S rRNA genes by ChIP-qPCR, and transcription from these genes was decreased upon knockdown of either ERα or BRF1. Treatment of the MCF7 breast cancer cell line with the ER antagonist tamoxifen decreased (1) BRF1 mRNA and protein levels, (2) transcription from the tRNALeu and 5S rRNA genes, and (3) colony formation induced by ethanol.