Tumor cell sensitivity to IR correlates with BTG1 levels. (A) Western blot showing the up-regulation of BTG1 protein in 786-O cells after transfection with the BTG1 expression vector pcDNA3.0-BTG1 as compared to the control pcDNA3.0 vector and untransfected (blank) cells after 24, 48 and 72 h. GAPDH is used as loading control. Fold changes of protein levels represent the average of three separate blots. (B) The trypan blue exclusion assay was used to assess cell viability in 7860-O cells without transfection or after transfection with pcDNA3.0 vector or pcDNA3.0-BTG1 vector at 48 h after X-ray exposure. (C) The changes of caspase-3 activity of the three group of 786-O cells was analyzed by caspase-3 activity assay kit at 24 h after X-rays. (D) Survival fractions of cells transfected with the control pcDNA3.0 vector and pcDNA3.0-BTG1 vector in response to 0, 5 Gy of X-rays were measured by colony formation assay. (E) Photographs of colonies formed by 786-O cells after various treatments. The data (means ± SE) are representative for at least five independent experiments.