ATF3 and breast cancer: Bioinformatics prediction revealed that the promoter region of pri-miR-216a contains binding sites for ATF3 (Supplementary Fig. 13), which has been revealed to be a master regulator of the response to DOX in breast cancer.27,28 Consistent with previous reports, ATF3 expression was significantly increased in DOX-treated 4T1 cells, and an siRNA construct targeting ATF3 successfully knocked down ATF3 (Fig. 5b).