To further investigate the tumor microenvironmental signals responsible for ectopic Zeb1 expression in breast cancer, we performed small-interfering RNA (siRNA) library screening using a human Zeb1 promoter construct and found that interference of the Notch1 receptor resulted in marked downregulation of Zeb1 transcription in MDA-MB-231 cells (Fig. 3a and Supplementary Table 1). Here, ZEB1 is linked to breast cancer.