ESR1 and breast cancer: Interestingly, RNF208 expression was markedly induced by E2 treatment, similar to other ERα-responsive genes, such as FOXOM1 and GREB1 (Fig. 2b), and siRNA-induced ESR1 knockdown attenuated the E2-induced expression level of RNF208 in T47D cells (Fig. 2c), indicating that RNF208 expression may depend on ERα expression in luminal breast cancer cells.