Radiation down-regulates miR-99b which targets mTOR in pancreatic cancer cells. (A) miR-101, miR-144, miR-100, miR-451, miR-199a and miR-99b were tested by real-time PCR before and after radiotherapy (5 Gy), **, P < 0.01 vs. control. (B) miR-99b precursor or miR-99b inhibitor was transfected into PANC-1 cells, followed by radiation at 5 Gy, and mTOR expression was analyzed by Western blot using an mTOR antibody. Western blot bands of mTOR were further quantified by the ImageJ software for calculating the expression of mTOR before and after miR-99b precursor/inhibitor transfection, **, P < 0.01 vs. control with IR. (C) PANC-1 cells were treated with radiotherapy (5 Gy) before and after miR99b precursor/inhibitor transfection for 48 h. Cell viability (%) was analyzed by SRB assay. Error bars represent as mean ± SD, **, P < 0.01 vs. control with IR or miR-99b inhibitor with IR. (D) PANC-1 cells were untreated or treated with radiation (1.5 Gy × 3) before and after miR-99b precursor/inhibitor transfection for 10 days and cell viability was analyzed by colony formation assay. The experiment was repeated three times and the number of colonies was represented as mean ± SD. **, P < 0.01 vs. control with IR or miR-99b inhibitor with IR.