Mitochondrial complex III inhibitors specifically up-regulate p53 and stimulate p53-dependent apoptosis. (A and B) Western analysis of p53 levels in RKO (A) and HeLa (B) cells exposed for 16 h and 18 h, respectively, to the indicated inhibitors: 2 μM myxothiazol (MXT), 1 μM stigmatellin (STG), 2 μM piericidin (PRC), 2 μM rotenone (RTN), 2 μM antimycin A (ANT), 100 μM TTFA (TTFA), 5 mM KCN (KCN), or without drugs (C). (C) Luciferase assay for p53-dependent transcription in HeLa cells exposed for 20 h to the indicated inhibitors, as described in A and B. (D) Western analysis of caspase-3 processing in HCT116 cells exposed to 2 μM myxothiazol (MXT) or MXT + 100 μM ZVAD-FMK. (E) Western analysis of caspase 7 processing in HCT116 wt and p53 -/- cells exposed to 2 μM myxothiazol (MXT) or MXT + 100 μM ZVAD-FMK.