GREB1a and GREB1b differentially regulate ERα target genes. (A) MCF7 cells were transduced with GFP, GREB1a or GREB1b adenovirus. Immunoblot depicting overexpression of GREB1a or GREB1b in comparison to control, GFP treated MCF7 cells. (B) MCF7 cells were transduced with GFP, GREB1a, or GREB1b adenovirus then starved of hormone for 72 h and treated with ethanol (−E2) or 10 nM estradiol (+E2) for 2 h. Real-time PCR was used to measure relative levels of known ERα target genes. Results are displayed as expression relative to RPL13a mean + s.e.; n = 3. (C) The indicated reporters were transfected with 3xFLAG-tagged GREB1a, GREB1b or empty vector (EV), and ERα, into HEK 293 cells and luciferase activity was measured after 48 h with either ethanol (−E2) or 10 nM estradiol (+E2). Results are displayed as firefly luciferase activity relative to Renilla luciferase activity + s.e.; n = 3. *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001.