Purpose: Taxol (Paclitaxel) is a new generation of chemotherapeutic drug proven to be effective in the treatment of many cancers. In this study, to further demonstrate the differential effect of the tumor suppressor gene, p53, on the Taxol-induced apoptosis in osteogenic sarcoma cell lines, we used p53-defected SaOS2 cells and wild type p53-expressed U2OS cells.
Materials and methods: The cell viability was measured by the XTT assay. To examine whether the differential expressions of p53, in U2OS and SaOS2 cells, were associated with Taxol-induced apoptosis, DNA fragmentation assays were performed on both cytosolic and genomic DNA. Since the cleavage of poly (ADP-ribose) polymerase (PARP) is primarily responsible for apoptosis, the cleavage of PARP, and the expression of cyclin B1, polo-like kinase, Bax, Bcl-xL, Bcl-2 in U2OS and SaOS2 cells were compared by Western blot analyses.
Results: The cell viability of the p53-defected SaOS2 cells was markedly decreased with Taxol treatment. Whereas, the cell viabilities due to 6-mercaptopurine and adriamycin were no different between the U2OS and SaOS2 cells. Treatment with Taxol induced a ladder- like pattern of DNA fragments, which is a biochemical hallmark of apoptosis, consisting of multiples of approximately 180-200 base pairs, in a dose-dependent manner in the SaOS2 cells, but insignificantly with the U2OS cells. When the cells were treated with Taxol, the 89 kDa cleavage product of PARP clearly appeared as a function of time in the SaOS2 cells, but not in the U2OS cells. The Taxol-induced apoptosis in p53 defected-osteogenic sarcoma cells was associated with the PARP cleavage as a result of the increased activity of caspase 3, and the high expressions of cyclin B1 and PLK. Bax, as a proapoptotic factor, was increased in the SaOS2cells, but the Bcl-xL and Bcl-2 were decreased when the cells were exposed to 10miceoM Taxol.
Conclusion: From these results, it was concluded that p53-defected SaOS2 cells are much more sensitive to Taxol-induced apoptosis than p53-expressed U2OS cells.
Keywords: Apoptosis; Osteogenic sarcoma; Poly (ADP-ribose) polymerase; Taxol; p53.