Abstract
Cancer results from an imbalance between cell cycle progression and apoptosis. Therefore, most anticancer drugs exert their antiproliferative and cytotoxic activity via cell cycle arrest and induction of apoptosis, a controlled form of cell death that is dysregulated in cancer. Many polyadenylation__trans__-acting factors, including polyadenylate polymerase (PAP), are increasingly found to be involved in cell cycle, apoptosis and cancer prognosis. The objective of the present study was to identify PAP modulations in the response of two epithelial cancer cell lines (HeLa and MCF-7) to apoptosis induction by the anticancer drugs etoposide and cordycepin. Cells were assessed for PAP activity and isoforms by the highly sensitive PAP activity assay and Western blotting, respectively. Induction of apoptosis was determined by endonucleosomal DNA cleavage, 4โฒ6-diamidino-2-phenylindol (DAPI) staining and caspase-6 activity assay, whereas cytotoxicity and cell cycle status were assessed by trypan blue staining, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry. Our results indicate that PAP changes very early in response to either etoposide or cordycepin treatment, even prior to the hallmarks of apoptosis (chromatin condensation and cleavage), in both cell lines tested, but in a different mode. Our results suggest, for the first time, that in the epithelial cancer cell lines used, PAP modulations follow cell cycle progression rather than the course of apoptosis.