Effects of miRNA-21 knock down on the apoptosis of A549 cells induced by gamma radiation. A, Expression of miRNA-21 decreased in miRNA-21 RNAi cells. B, Detection of apoptosis induced by various dose of irradiation through annexin V-FITC/PI staining and results were ploted as mean ± s.d. from triplicate experiments. p<0.01 vs parental and scrambled RNAi groups. Percentage of apoptosis in miRNA-21 knock-down group were significantly higher than that of control groups in both 4 and 8 Gy dose. C, Down-regulation of miRNA-21 led to increased activation of Caspase 3, as evident from increased levels of Cleaved-PARP.