Purvalanol A enhances cell killing by inhibiting up-regulation of CDC2 kinase activity in tumor cells irradiated with high doses of X rays.
To clarify the relationship between CDC2 kinase activity and radiation-induced apoptosis, we examined whether the cyclin-dependent kinase (CDK) inhibitor purvalanol A enhanced radiation-induced apoptosis in gastric tumor cells. MKN45 cells exposed to 20 Gy of X rays increased the CDC2 kinase activity and the expression of regulatory proteins (phospho-CDC2 and cyclin B1) of the G2/M phase, followed by activation of the G2/M checkpoint, whereas the treatment of X-irradiated MKN45 cells with 20 microM purvalanol A suppressed the increase in the CDC2 kinase activity and expression of the G2/M-phase regulatory proteins and reduced the fraction of the cells in the G2/M phase in the cell cycle. Furthermore, this treatment resulted in not only a significant increase in radiation-induced apoptosis but also the loss of clonogenicity in both MKN45 (p53-wild) and MKN28 (p53-mutated) cells. The expression of anti-apoptosis proteins, inhibitor of apoptosis protein (IAP) family members (survivin and XIAP) and BCL2 family members (Bcl-X(L) and Bcl-2), in purvalanol A-treated cells with and without X rays was significantly lower than for cells exposed to X rays alone. These results suggest that the inhibition of radiation-induced CDC2 kinase activity by purvalanol A induces apoptosis through the enhancement of active fragments of caspase 3.
Iizuka
Daisuke
D
Laboratory of Radiation Biology, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, 060-0818, Japan.
Inanami
Osamu
O
Kashiwakura
Ikuo
I
Kuwabara
Mikinori
M
D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects*; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects; D002460:Cell Line; D016195:G2 Phase / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D009369:Neoplasms / Q000201:enzymology* / Q000473:pathology; D011687:Purines / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects* / Q000528:radiation effects*; D014965:X-Rays
C471843:6-((3-chloro)anilino)-2-(isopropyl-2-hydroxyethylamino)-9-isopropylpurine; D018797:Cell Cycle Proteins; D011687:Purines; D016203:CDC2 Protein Kinase