HepG2 cells were transfected with control siRNA or p53 siRNA along with MnSOD promoter (−555 to+24)-driven luciferase reporter vectors. After 24 h of co-transfection, cells were split into separate dishes and grown for another 24 h. A, cells were collected for luciferase activity as a measure of MnSOD gene transcription. B, total RNA was isolated from control siRNA- or p53 siRNA-transfected HepG2 cells. RT-PCR was carried out using primers for each specific gene as described under “Experimental Procedures.” C, HepG2 cells were transfected with p53 expression vector (pcDNA3.1/p53, 4µg) or empty-vector (pcDNA3.1, equivalent amount), and total RNA was purified. The mRNA level of Bax gene under p53 overexpression conditions was determined by RT-PCR. A transcriptional off-target, the β-actin mRNA, was examined as an internal control. Statistical analyses were performed in three independent experiments **, p < 0.01 compared with the control.