Increased phosphorylation of nuclear phosphoproteins in human lung-cancer cells resistant to cis-diamminedichloroplatinum (II).
A novel non-phorbol-ester-like tumor promoter, okadaic acid (OA) has been shown to be an inhibitor of protein phosphatase I and IIA and, thus, to cause an "apparent activation" of protein kinase C (PKC). We previously showed that cis-diamminedichloroplatinum(II) (CDDP)-resistant cells, PC-9/CDDP, were cross-resistant to OA and that the cross-resistance was not due to the increased efflux of OA. We hypothesized that the phosphorylation status of some cellular proteins might be important in CDDP-resistance. No significant difference in PKC activity or total protein phosphatase activity measured in vitro was seen between PC-9 and PC-9/CDDP cells, nor in their sensitivity to inhibition by OA, nor in the amount of phosphorylation of whole cells or TCA-insoluble material. By SDS-PAGE after incubation of intact cells with 32P, we detected a marked increase, compared to PC-9 cells, in phosphorylation of the nuclear proteins of MW 32 and 20 kDa in CDDP-resistant PC-9/CDDP cells with no apparent difference in protein content. When phosphorylation of nuclear proteins observed in PC-9/CDDP cells was analyzed by 2-dimensional SDS-PAGE, the 32-kDa protein had a PI of about 4.5. The 32-kDa and 20-kDa bands were increased in a dose-dependent manner by CDDP treatment. On the other hand, no increase in phosphorylation of these proteins was observed in parental PC-9 cells. These results demonstrate a marked difference in the phosphorylation status of specific nuclear proteins between parental and CDDP-resistant cell lines, which may be related to CDDP-resistance.
Nishio
K
K
Pharmacology Division, National Cancer Center Research Institute, Tokyo, Japan.
Sugimoto
Y
Y
Kasahara
K
K
Fujiwara
Y
Y
Nishiwaki
S
S
Fujiki
H
H
Ohata
M
M
Saijo
N
N
D000230:Adenocarcinoma / Q000188:drug therapy* / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002945:Cisplatin / Q000494:pharmacology*; D004351:Drug Resistance; D015180:Electrophoresis, Gel, Two-Dimensional; D004988:Ethers, Cyclic / Q000494:pharmacology; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D008970:Molecular Weight; D009687:Nuclear Proteins / Q000378:metabolism*; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors; D014407:Tumor Cells, Cultured
D004988:Ethers, Cyclic; D009687:Nuclear Proteins; D010750:Phosphoproteins; D019319:Okadaic Acid; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; D013755:Tetradecanoylphorbol Acetate; D002945:Cisplatin