BMI1 and breast cancer: The results of quantitative real-time PCR and Western blot showed that the expression of stemness genes (Nanog, ALDH1, and ABCG2) was significantly downregulated in YB-1 knockout melanoma or breast cancer stem cells when the other 4 (SOX2, POU3F2, OCT-4, and OLIG1) or 5 (SOX2, SALL2, OCT-4, POU3F2, and Bmi-1) transcription factors, respectively, were overexpressed (Fig. 5d).