BMI1 and breast cancer: Quantitative real-time PCR data showed that among the 25 stemness-related transcription factors, four (SOX2, POU3F2, OCT-4, and OLIG1) and five (SOX2, SALL2, OCT-4, POU3F2, and Bmi-1) transcription factors were significantly downregulated in YB-1 knockout melanoma stem cells and breast cancer stem cells, respectively (Fig. 5a).