Despite the high frequency of
prostate cancer, therapeutic options for advanced disease are limited to
chemotherapy, radiation or hormonal
therapy and eventually fail in all patients. Therefore, alternative approaches need to be developed. We previously reported that
FTY720, a metabolite from Isaria sinclarii, is a unique
antitumor agent for an
androgen-independent
prostate cancer cell line and requires
caspase-3 activation in apoptosis. In our study, we have evaluated the effect of
FTY720 on a family of
mitogen-activated protein kinases (MAPKs),
focal adhesion kinase (FAK), mitochondrial transmembrane potential,
caspase-9 and
caspase-8 and analyzed the expression of some cell-cycle regulator
proteins in DU145 cells in order to understand the various antitumor effects of
FTY720. Apoptosis was quantified by
phosphatidylserine exposure. Activation of MAPKs, cleavage of
caspase-9 and
caspase-8, status of
cyclin-dependent kinases (CDKs) and Cip1/p21, a
cyclin-dependent kinase inhibitor, were evaluated by Western blot analysis, in addition to FAK and phospho-FAK immunoprecipitation and cell-cycle analysis by FACScan. We found that in DU145 cells, 40 microM
FTY720 caused activation of
p38 MAPK and the upstream
kinase MKK3/MKK6 but not SAPK/JNK. Mitochondrial transmembrane potential, FAK and ERK1/2 were reduced while
caspase-9 and
caspase-8 were cleaved. The p38-specific inhibitor had no effect on apoptosis induced by
FTY720, whereas
z-VAD.FMK, a broad-spectrum
caspase inhibitor, did not inhibit the
p38 MAPK activation. An amount of 20 microM
FTY720 resulted in G(1) arrest and a decrease of CDK2 as well as CDK4, whereas it induced Cip1/p21.
FTY720 may exert
anticarcinogenic effects against
prostate cancer cells possibly involving modulation of mitogenic signaling, cell-cycle regulators, induction of G(1) arrest and apoptotic death in DU145 cells.