Apoptosis after knockdown of Bak1 and the involvement of miR-125b in drug-resistant leukemic cells. (A) Western blotting images showing low Bak1 protein expression when NB4 cells were transfected with three different strands of si-RNA of Bak1. (B), (C) and (D) The NB4 cells were transfected with 100 nM si-RNA control, a strand of si-Bak1-3 or a mixture of these three strands of si-Bak. Forty-eight hours following transfection, camptothecin was added and cells were labeled with Annexin V/PI and analyzed by flow cytometry. Three independent experiments were performed and similar results were obtained. (E) miR-125b expression was up-regulated in drug-resistant cell lines compared to their drug-sensitive parental cells. *p < 0.05 compared with corresponding parents cells. (F) Transfection of HL60/DOX cells with miR-125b duplex increases their resistance to DOX treatment. The IC50 of HL60/DOX cells transfected with miR-125b duplex was higher (p < 0.05) compared with the IC50 for HL60/DOX cells transfected with miRNA duplex control and miR-195. Three independent experiments were performed.