@misc{oai:repo.qst.go.jp:00069044,
 author = {Iizuka, Daisuke and et.al and 飯塚 大輔},
 month = {Jul},
 note = {[Purpose]
Ionizing radiation is known to cause cell-cycle arrest at G2 phase in various tumor cells. Recently, treatment with drugs such as UCN-01 and caffeine induces cell killing in X-irradiated tumor cells through the abrogation of G2 checkpoint. In this study, we focus on Cdc2 and investigated the mechanism of enhancement of radiation-induced cell killing by the inhibition of Cdc2 kinase activity with cyclin dependent kinase (cdk) inhibitor purvalanol A.
\n[Materials and Methods]
Human gastric adenocarcinoma MKN45 (wild p53) and MKN28 (mutated p53) cells were exposed to X rays with or without purvalanol A. For measurements of apoptosis, apoptotic morphological changes of nuclei were assessed by fluorescence microscopy. Cell cycle distribution was observed by flow-cytometry. Observation of Cdc2 kinase activity was performed using Cdc2-associated histone H1 kinase assay. Expression of mRNA was assessed by semi-quantitative RT-PCR. Expression of proteins was assessed by Western blotting with corresponding antibodies.
\n[Results and Discussion]
Cotreatment of cells with X rays and purvalanol A induced the significant increase in the number of apoptosis in MKN45 and MKN28 cells. When cells were exposed to X rays alone, G2/M arrest occurred. Cotreatment of X rays with purvalanol A rendered the decrease in G2/M fraction and the increase in subG1 fraction. Treatment of cells with X rays increased the expression of proteins relating to the G2 checkpoint and Cdc2 kinase activity and resulted in the G2 arrest, and purvalanol A decreased the expression of the G2-related proteins and the Cdc2 kinase activity. On the expression of anti-apoptotic proteins, purvalanol A inhibited the radiation-induced upregulation of Bcl-2 and Bcl-XL. The expression of survivin and XIAP was slightly increased by X irradiation, but were also inhibited by purvalanol A. On the other hand, pro-apoptotic protein, Bax, was not increased by X irradiation but slightly decreased by purvalanol A. Total RNA synthesis was inhibited by purvalanol A and as a consequence, the expression of mRNA of survivin, Bcl-XL and Bcl-2 was inhibited. These results indicated that purvalanol A sensitized radiation-induced apoptosis through the abrogation of G2 checkpoint and the downregulation of anti-apoptotic proteins by the inhibition of RNA synthesis., 13th International Congress of Radiation Research},
 title = {Enhancement of radiation-induced cell killing by inhibiting G2 checkpoint with purvalanol A.},
 year = {2007}
}