Overlapping and distinct functions between ERa and ERß homodimers and corresponding transcriptomes in the same cellular context

The two estrogen receptors, ERa and ERß function as ligand-inducible transcription factors. Most in vitro studies have reported that ERa drives breast cancer growth whereas ERß, if expressed, suppresses growth. To dissect function and gene expression profile regulated by ERa or ERß, respectively, we generated a novel cell model expressing only ERß, by applying CRISPR-cas9 to delete ERa in MCF7 cells with stable Tet-Off-inducible ERß expression. This model with ERß expression only, exhibited regulation of known estrogen responsive genes in a ligand-dependent manner. By cell proliferation assay, we found that either ER was required for proliferation, and that while E2 increased proliferation of ERa (only) MCF7, it reduced proliferation of ERß (only) MCF7 cells. RNA-Seq analysis revealed 768 and 984 specific target genes regulated by ERa and ERß in response to E2, respectively. Furthermore, functional enrichment analysis showed that the two ER isoforms regulated cell proliferation in opposite direction. In conclusion, within the same cellular context the two ERs regulated cell proliferation in opposite manner by regulating distinct sets of target genes in response to E2. The novel developed cell model provides a novel and valuable resource to further complement the mechanistic understanding of the two different ER isoforms. Overall design: mRNA profiles of MCF7 tetoff cell model upon E2/vehicle treatment