(A) MDA231, MCF-7, and BT474 cells were transfected with indicated miRNA mimics or a 1:1:1 mixture of miR-9–5p, miR-203a-3p, and miR-195–5p mimics, or with a negative control mimic. A total of 25 pmol miRNA mimics were used to transfect 2×105 cells seeded on 6-well plates one day prior to transfection. After 48 h, cells were collected for sphere formation assay. (B) ALDEFLUOR assay of MDA231 cells transfected with indicated miRNA mimics for 72 h. (C) RT-qPCR-determined RNA levels of indicated genes in various BC cells at 48 h following transfection with indicated miRNA mimics. (D) Western blots showing the expression levels of indicated proteins in BC cells at 48 h following transfection of indicated miRNA mimics. *P<0.05, **P<0.01, ***P<0.001. Numbers below Western images indicate quantification after normalization to GAPDH with the first lane set as 1.