Involvement of p21Waf1 in mediating inhibition of paclitaxel-induced apoptosis by epidermal growth factor in MDA-MB-468 human breast cancer cells.

Paclitaxel (Taxol) is currently one of the most widely used anti-cancer drugs for human breast cancer. In this study, we investigated how epidermal growth factor (EGF) modulated paclitaxel-induced apoptosis in MDA-MB-468 human breast adenocarcinoma cells. Pulse-exposure of the cells to paclitaxel resulted in cell death through apoptosis. When EGF was present during the post-paclitaxel culture period, this paclitaxel-induced apoptosis was inhibited in an EGF dose-dependent manner. The induction of apoptosis by paclitaxel was accompanied by an elevated level of p34cdc2 kinase activity, which was inhibited in the presence of EGF during the post-paclitaxel culture period. Exposure of MDA-MB-468 cells to EGF induced expression of the cyclin-dependent kinase inhibitor p21Waf1. Incubation of paclitaxel-treated MDA-MB-468 cell extracts with EGF-treated MDA-MB-468 cell extract, which exhibited elevation of p34cdc2 activity, inhibited the kinase activity. This inhibition was not observed with p21Waf1-immunodepleted EGF-treated cell extract. Transfection of the cells with p21Waf1 antisense oligonucleotide abolished the induction of p21Waf1 and also significantly reduced inhibition by EGF of paclitaxel-induced apoptosis. These studies demonstrate that p21Waf1 plays a key role in the inhibition of paclitaxel-induced apoptosis by EGF in MDA-MB-468 cells.