This study examined the effect of Notch-1 signaling on malignant behaviors of breast cancer cells by regulating breast cancer stem cells （BCSCs）. BCSCs were enriched by using serum-free me- dium and knocked out of Notch-1 by using a lentiviral vector. Real-time polymerase chain reaction （RT-PCR） and Western blotting were used to detect the Notch-1 expression levels in breast cancer cell lines and BCSCs, and fl0w cytometry to detect the proportion of BCSCs in BCSC spheres. The BCSC self-renewal, migration, invasion, and tumorigenicity were examined by the tumor microsphere-forming assay and transwell assay and after xenotransplantation. The results showed that the Notch-1 silencing reduced the number of BCSC spheres, the proportion of BCSCs, and the number of cells penetrating through the transwell membrane. It also decreased the size of tumors that were implanted in the nude mice. These results suggest that Notch-1 signaling is intimately linked to the behaviors of BCSCs. Blocking Notch-1 signaling can inhibit the malignant behaviors of BCSCs, which may provide a prom- ising therapeutical approach for breast cancer.
