mTOR play a critical role in pancreatic cancer radioresistance. (A) Parental PANC-1 (PANC-1-P) and radiation resistant PANC-1 cells (PANC-1-RR) were treated with increasing doses of radiation and cultured for 10 days, cell growth was analyzed by colony formation assay and the data were statistically analyzed. The experiment was repeated three times and the number of colonies was presented as mean ± SD. *, P < 0.05 vs. control and **, P < 0.01 vs. control and PANC-1-RR cells. (B) Expression and/or phosphorylation of mTOR, Akt, 4EBP1, Bcl-2, Bcl-XL and Mcl-1 in PANC-1-P and PANC-1-RR cells were analyzed by Western blot. (C) mTOR shRNA and control were transfected into PANC-1 cells and mTOR expression was analyzed by Western blot. (D) Cells were transfected and then treated with increasing doses of radiation for 48 h, cell viability was analyzed by SRB assay. Error bars represent ± S.D. *, P < 0.05 vs. vector-only control and **, P < 0.01 vs. vector-only control.