ERαK206A super-stimulates in cells that contain endogenous ERs. Both Ishikawa (A) and MCF-7 cells (B) were transfected with Coll73-Luc and treated with ligands as indicated in Fig. 1B. The insets show the effect of treatment with endogenous receptor only. The main graphs show ligand effect in the presence of the indicated transfected ERα (5 μg).