Cis-diamminedichloroplatinum(II) inhibits p34cdc2 protein kinase in human lung-cancer cells.
cis-Diamminedichloroplatinum(II) (CDDP) induced G2-phase arrest in PC-9 human cancer cells. To elucidate how CDDP acts on cell-cycle regulation, we analyzed the effect of CDDP on cell-cycle regulators such as p34cdc2 protein kinase. p34cdc2 protein kinase activity was maximum in G2 phase and decreased after G2/M transition in synchronized PC-9 human lung cancer cells. Evidence for a phosphorylated p34cdc2 protein kinase complexed with cyclin B was obtained from cells in G2 phase and the p34cdc2 protein kinase appeared to be dephosphorylated at M phase. After exposure to CDDP in G1 phase, PC-9 cells were arrested in G2 phase. The activation of p34cdc2 protein kinase was inhibited by CDDP. Cyclin A and wee-I kinase were not affected by the exposure to CDDP. Cyclin B was degraded in M phase in PC-9 cells. Exposure to CDDP did not affect the degradation of cyclin B. Our data suggest that the effect of CDDP on cell-cycle phase might be regulated by the dephosphorylation of p34cdc2 protein kinase. To determine whether the p34cdc2 protein kinase is a primary target for CDDP, we examined the direct effect of CDDP on tyrosine dephosphorylation of p34cdc2 protein kinase in cellular extracts. Cell lysates from synchronized PC-9 in G2 phase were immunoprecipitated with p13-Sepharose beads. In vitro dephosphorylation of phosphotyrosine of p34cdc2 protein kinase was observed after exposure to okadaic acid in a concentration-dependent manner. The dephosphorylation of p34cdc2 protein kinase by okadaic acid was inhibited by CDDP. We hypothesize that inhibition of p34cdc2 dephorphorylation by CDDP is important for its growth-inhibiting properties.
Nishio
K
K
Pharmacology Division, National Cancer Center Research Institute, Tokyo, Japan.
Fujiwara
Y
Y
Miyahara
Y
Y
Takeda
Y
Y
Ohira
T
T
Kubota
N
N
Ohta
S
S
Funayama
Y
Y
Ogasawara
H
H
Ohata
M
M
D016203:CDC2 Protein Kinase / Q000378:metabolism*; D018797:Cell Cycle Proteins; D016213:Cyclins / Q000378:metabolism; D016195:G2 Phase / Q000187:drug effects*; D006801:Humans; D015151:Immunoblotting; D008175:Lung Neoplasms / Q000201:enzymology*; D008938:Mitosis / Q000187:drug effects*; D009687:Nuclear Proteins; D009944:Organoplatinum Compounds / Q000494:pharmacology*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases; D014407:Tumor Cells, Cultured
D018797:Cell Cycle Proteins; D016213:Cyclins; D009687:Nuclear Proteins; D009944:Organoplatinum Compounds; C055423:didimethylsulfoxide dichloroplatinum(II); D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; C499349:WEE1 protein, human; D016203:CDC2 Protein Kinase