IRF1 and cancer: To further examine the role of ID4 in cancer stemness, we knocked down ID4 in MDA-MB-468 breast tumor cells using SMARTpool siRNAs (Figure 4E), and tested the expression of a panel of stemness genes including Twist1, Twist2 [27], Snail, Slug [24], BMP2 [28], IRF1 [29], SOX4 [30], Foxk1 [31] and Notch3 [27].