a, siRNA-mediated DBC1 knockdown inhibits p53 proapoptotic target gene expression. Western blot of U2OS whole-cell extracts treated with siRNA as shown. b, DBC1 siRNA effects on p53-dependent PUMA and BAX expression require SIRT1. Western blot of siRNA-treated U2OS cell extracts. p53 acetylation levels are shown after p53 immunoprecipitation. c, d, DBC1 siRNA inhibits p53-mediated apoptosis after DNA damage. U2OS cells were treated with siRNA as indicated and treated with Etoposide (30 h) before assaying apoptosis by TUNEL staining (c, Supplementary Fig. 11) or Annexin V staining (d, Supplementary Fig. 12). Error bars represent s.d., n = 3 (c, d).