Time-dependent Dox-regulated expression of p53 protein. In the removing group, medium was removed 24 h after p53-13 cells were cultured in 1 μg/ml Dox (Dox+), and then the cells were cultured continually in the absence of Dox (Dox-). In the adding group, cells were cultured in the absence of Dox for 24 h, and then the cells were incubated with 1 μg/ml of Dox. The expression of p53 protein was analyzed by Western blotting. Lane1: Dox+; Lanes 2, 3, 4: Dox- 1 h; 3 h; and 6 h; Lane 5: Dox-; Lanes 6, 7, 8: Dox+ 3 h; 6 h; and 12 h. β-actin was served as an internal control.