Impaired death-associated protein kinase-mediated survival signals in 5-fluorouracil-resistant human endometrial adenocarcinoma cells

A recent study showed that both 5-fluorouracil (5FU)-stimulated apoptosis and Fas-mediated apoptosis in human endometrial adenocarcinoma cells are enhanced by targeted knockdown of endogenous death-associated protein kinase (DAPK) with DAPK small-interfering RNAs. Therefore, we investigated the DAPK survival signals in three 5FU-resistant subclones. DAPK knockdown did not enhance 5FU-stimulated or Fas-mediated apoptosis in any of the three 5FU-resistant subclones, but the subclones acquired resistance to VP16-stimulated cell death that was DAPK-independent. Semi-quantitative flow cytometric analyses showed that there was no differential expression in nine cell surface antigens, including Fas, and six intracellular molecules, including DAPK, that may regulate cell death or survival between the parent cells and 5FU-resistant cells. DAPK mRNA and protein were expressed in the 5FU-resistant subclones at similar levels to the parent cells. These results indicate that acquisition of 5FU-resistance may be accompanied by impairment of common apoptotic signals regulating both DAPK-dependent and DAPK-independent pathways.