Cisplatin-resistant HeLa cells are resistant to apoptosis via p53-dependent and -independent pathways

Since HeLa cells possess very little functional p53 activity, they could be originally resistant to genotoxic stress-induced apoptosis. Therefore, it is likely that the drug-resistant cells derived from HeLa cells are more resistant to apoptosis. The aim of this study was to determine whether cisplatin-resistant cells derived from HeLa cells have an apoptosis-resistant phenotype. A cisplatin-resistant cell subline, HeLa/CDDP cells, showed a 19-fold resistance to cisplatin compared with the parent cells. The subline showed a collateral sensitivity to paclitaxel. An equitoxic dose (IC50) of cisplatin produced DNA fragmentation in HeLa cells but not in HeLa/CDDP cells. Transfection of wild-type p53 gene enhanced the cytotoxicity of cisplatin and cisplatin-induced apoptosis in HeLa cells but not in HeLa/CDDP cells, although it caused p53 overexpression in both cell lines. The expression of caspase 1 (interleukin-1beta-converting enzyme, ICE) mRNA and the overexpression of bax protein were observed only in HeLa cells. Paclitaxel-induced DNA fragmentation appeared less in HeLa/CDDP cells than in HeLa cells. p53 gene transfection did not affect the extent of DNA fragmentation in either cell line, suggesting that paclitaxel may induce p53-independent apoptosis. These findings suggest that HeLa/CDDP cells may have an acquired phenotype that is resistant to p53-dependent and -independent apoptosis.