Estrogen-Estrogen Receptor alpha (ERα) belongs to one of the most important signaling pathways controlling breast tissue development and progression of breast cancer. ERRF was recently identified as a candidate breast cancer associated protein and showed positive association with ERα status in clinical samples and cell lines. To further explore the relationship between ERRF and ERα, we studied whether ERRF plays any roles in estrogen-ERα pathway. Knockdown of ERRF in ER positive breast cancer cells T-47D and BT-474 reduced the level of p-AKT, p-MAPK, and phosphorylation of ERα at Ser 118 and Ser 167, and the transcriptional activity of ERα was inhibited as well. Further mechanism study proved ERRF to be an interacting partner of ERα. In total, these data revealed that ERRF is essential for the activity of E2-ERα pathway VSports手机版. .