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Submitted on June 6, 2003
Accepted on November 21, 2003
1 Department of Obstetrics and Gynecology, Osaka University Medical School, 2-2, Yamadaoka, Suita, Osaka 565-0871, Japan.
* To whom correspondence should be addressed. E-mail: masa{at}gyne.med.osaka-u.ac.jp.
Although tamoxifen (TAM), which is widely used in the treatment of breast cancer, also has a beneficial effect on cisplatin-refractory ovarian cancer, the biological mechanism of this effect has remained obscure. TAM, besides its action as an anti-estrogen, also inhibits cell proliferation of estrogen receptor (ER)-negative cells by an unknown mechanism. Therefore, we examined the roles of the mitogen-activated protein kinase family in the antiproliferative effect of TAM on cisplatin-resistant Caov-3, which expresses ER and cisplatin-sensitive A2780, which does not express ER. The number of viable cells was reduced by TAM dose-dependently. TAM induced the activation of ERK, JNK, and p38 with different time courses. PD98059 canceled the reduction of the number of viable cells by 1 µM TAM and inhibited the TAM-induced cell-cycle arrest at the G1 phase and dephosphorylation of the retinoblastoma protein. Either expression of dominant-negative JNK or pretreatment with SB203580 canceled the reduction of the number of viable cells by 5 µM TAM and inhibited the apoptotic nuclear changes and the cleavage of poly (ADP-ribose) polymerase induced by TAM. These results provide evidence that whereas the ERK cascade is involved in the induction of cell-cycle arrest at the G1 phase by lower concentrations of TAM, the JNK or p38 cascade is involved in the induction of apoptosis by higher concentrations of TAM in both types of cells.
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