Herein, we performed microRNA microarray containing 3100 probes to analyze differential miRNA expression profiles in U251 and U251R cell lines. As shown in Figure 2A, 23 miRNAs are up-regulated and 16 miRNAs are down-regulated in U251R cells. Figure see more 2 Differential miRNA expression profiles

in U251 and U251R cell lines. (A) MiRNA expression signature was analyzed by miRNA microarray. (B-G) Selected miRNAs were confirmed by real-time PCR. The microarray results were then validated by real-time PCR. Consistent with microarray data, miR-182 and miR-224 were up-regulated in U251R cells; Let-7b, miR-125b, miR-107 and miR-203 were significantly suppressed in U251R cells (Figure 2B-G). Re-sensitization of the resistant cells by transfection of Let-7b To investigate whether down-regulation of these miRNAs in U251R cells involved in cisplatin resistance, miRNA mimics were transfected into U251R cells, and then

their IC50 to cisplatin was determined. Interestingly, compared with negative control transfection, transfection of Let-7b greatly sensitized U251R cells to cisplatin, with IC50 this website decreased from 4.38±0.56 μg/mL to 1.62±0.03 μg/mL, which is similar to that of U251 parental cells (1.44±0.11 μg/mL) (Figure 3A). Notably, transfection of neither miR-125b mimics nor miR-107 mimics has significant effect on the sensitivity of U251R cells to cisplatin. MiR-203 mimics lead to moderate inhibition of cisplatin sensitivity. The dose response curves of U251R cells transfected with Let-7b mimics or Scramble to cisplatin were shown in Figure 3B. These results suggested that Let-7b plays a critical role in cisplatin resistance, and transfection of Let-7b re-sensitized the U251R cells to cisplatin. Figure 3 Transfection of Let- 7b re- sensitization of the resistant cells. (A) U251R cells were transfected with mimics of miR-107, miR-125b, miR-203, Let-7b or scramble

(SCR). Then their IC50 to cisplatin Celecoxib was determined. U251 parental cells were used as control. (B) U251R cells were transfected with Let-7b mimics or scramble (SCR), and then the dose–response curves were plotted. Transfection of Let-7b increased Selleckchem AMN-107 cisplatin-induced G1 arrest and apoptosis in U251R cells To further confirm the role of Let-7b in cisplatin resistance, cell cycle distribution was analyzed by flow cytometry. Compared with negative control, transfection of Let-7b mimics into U251R cells significantly increased cisplatin-induced G1 arrest (Figure 4A-C). Figure 4 Let- 7b increased cisplatin induced G0/ G1 arrest. U251R cells were transfected with scramble (SCR) (A) or Let-7b mimics (B) and then treated with cisplatin; cell cycle was detected by flow cytometry. The percentage of cells in different cell cycle phases was calculated (C). Data is presented from three independent experiments, and the symbol * indicates statistical difference (p < 0.05). The cisplatin-induced apoptosis was examined by Annexin V/PI staining (Figure 5A-C).