p53 suppresses Ras-driven invasion. (A and B) NIH3T3 cells, iMEFs, and p53^−/− MEFs were infected with a control or Ha-RasV12–expressing retrovirus. (C and D) NIH3T3 cells were infected with a Ha-RasV12–expressing retrovirus together with a control or p53R175H-expressing retrovirus. (A and C) Inverted invasion assays were performed. Images of serial Z-sections (10-µm intervals). Bars, 100 µm. (B and D) Cells invaded 30 µm or more were quantified. Data represent the mean ± SD; n = 3. *, P < 0.05.