It is not completely understood how certain epithelial cells harboring mutant p53 have better response to chemotherapy. We investigate the mechanism of cisplatin-induced apoptosis in two resistant cell lines (parental TCCSUP and R273L mutant p53 transfectant) and two sensitive cell lines (V143A and N247I mutant p53 transfectants). Activation of caspase 9 was demonstrated by Western blotting, and specific inhibitor for caspase 9 could inhibit apoptosis. Inhibitors for caspases 1, 2, 6, and 8 had no effect on apoptosis. Transcriptional repression of Bcl-2 occurred during apoptosis and could be reversed by the treatment of histone deacetylase inhibitor trichostatin A (TSA). The expression of Noxa, p53 inducible ribonucleotide reductase subunit 2 (p53R2), and p53 inducible death domain (PIDD) gene were not elevated with treatment of cisplatin (CDDP). Surface trafficking of Fas or Fas-L was not observed. Ser15 of wild-type p53 and mutant p53 was phosphorylated in response to cisplatin. Acetylation of wild-type p53 increased, while acetylation of mutant p53 decreased during cisplatin treatment. Both transcriptional inhibitor actinomycin D and translational inhibitor cycloheximide did not inhibit apoptosis. These results indicated that phosphorylated and hypoacetylated mutant p53 could enhance cisplatin-induced apoptosis through activation of caspase 9 independent of transcriptional activation and translation.

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