GREB1 and breast cancer: Treatment with ICI.182.780 or GREB1 knockdown increased PAI-1 mRNA expression in MCF7 breast cancer cells (Supplementary Fig. 5i, j) and GREB1 formed a complex with Smad2/3 in MCF7 cells (Supplementary Fig. 5k), suggesting that GREB1 functions as a negative regulator of TGFβ signaling not only in HB but also breast cancer cells.