CISPLATIN-INDUCED AND PACLITAXEL-INDUCED APOPTOSIS OF OVARIAN-CARCINOMA CELLS AND THE RELATIONSHIP BETWEEN BAX AND BAK UP-REGULATION AND THE FUNCTIONAL STATUS OF P53

We investigated the roles of p53 and Bcl-2 homologues in the induction of apoptosis by cisplatin and paclitaxel in wild-type p53-expressing human ovarian carcinoma cells and cisplatin-resistant derivatives that have lost p53 function. Cisplatin induced apoptosis in parental A2780 but not in cisplatin-resistant A2780/cp70 cells, whereas paclitaxel i nduced apoptosis in both cell lines. Immunoprecipitation of p53 using antibodies specific for p53 conformation (pAb 1620 and pAb 240) showed that there were no relative changes in p53 conformation before and af ter cisplatin treatment in either cell line. A2780/cp70 cells have los t p53 function, yet they have wild-type p53 gene sequence. However, A2 780/cp70 cells constitutively express more p53 in a form detected by p Ab 240, an antibody that also detects mutant conformations of p53 that are transcriptionally inactive. There were no changes in levels of Bc l-2, Bcl-X-L, or 24-kDa Bar over 72 hr after exposure to cisplatin or paclitaxel, but each agent led to up-regulation of Bak and 21-kDa Bar in A2780 cells. Paclitaxel, but not cisplatin, increased Bak and 21-kD a Bar levels in A2780/cp70 cells. These data suggest that apoptosis in A2780 and A2780/cp70 is associated with an increased level of Bak and 21 kDa Bar after drug-induced damage and that functional p53 may be r equired for this effect after cisplatin but not after paclitaxel.