Involvement of c-Jun N-terminal Kinase in G₂/M Arrest and Caspase-Mediated Apoptosis Induced by Sulforaphane in DU145 Prostate Cancer Cells

Abstract

Sulforaphane (SFN) is a major isothiocyanate compound in cruciferous vegetables such as broccoli, cauliflower, and Brussels sprouts. Preclinical animal models have recently shown that SFN and other isothiocyanates may be useful for prostrate cancer (PCa) chemoprevention. In this study we used a DU145 human PCa cell culture model to investigate the role of protein kinase signaling pathway(s) in SFN-induced cell cycle arrest and apoptosis and whether another chemopreventive agent selenium enhances the apoptosis potency of SFN. The results showed that SFN exposure for 24 h or longer significantly decreased the number of viable DU145 cells in a dose-dependent manner with an IC50 of asymptotically equal to 10 microM. The decreased cell number was associated with G2/M phase arrest and apoptotic cell death, with the latter being evidenced by caspase-mediated cleavage of poly(ADP-ribose) polymerase and increased release of histone-associated DNA fragments. A peptide inhibitor of caspase-8 completely blocked SFN-induced apoptosis and that for caspase-9 exerted a major protection; however, neither inhibitor attenuated SFN-induced G2/M arrest. Regarding potential mediators, SFN treatment induced a transient rise of reactive oxygen species (ROS) peaking within (1/2) h and the activation of JNK within 1 h but did not have any detectable effect on the phosphorylation of p38MAPK or ERK1/2 from 6 h to 24 h. Pretreatment of cells with N-acetylcysteine to enrich intracellular glutathione blocked SFN-induced ROS and apoptotic cell death. Inhibiting the JNK activity with a pharmacologic inhibitor SP600125 abolished the induction of G2/M arrest and apoptosis by SFN, whereas chemical inhibitors for p38MAPK and MEK1/2 did not have any modulating effect on SFN-induced apoptosis. Taken together, the data indicate that SFN decreased viable DU145 cell number in large part through the generation of ROS and JNK-mediated signaling to G2/M arrest and caspase-dependent apoptosis. Selenium in the form of inorganic sodium selenite salt or methylseleninic acid did not enhance SFN-induced apoptosis in this cell culture model.

Induction of p21 protein protects against sulforaphane-induced mitotic arrest in LNCaP human prostate cancer cell line

“…On the other hand, the SFN-mediated G 2 -M phase cell cycle arrest is rapid and evident as early as 4 h posttreatment. The G 2 -M phase cell cycle arrest by SFN treatment at concentrations within the range used in the present study has also been observed in other cellular systems including HT29 human colon cancer cell line (15), F3II mouse sarcomatoid mammary carcinoma cell line (17), PC-3 and DU145 human prostate cancer cells (19,20), and human benign prostate hyperplasia epithelial cell line BPH-1 (23). In contrast, previous studies by Chiao et al (46) have documented a G 1 phase cell cycle arrest in LNCaP cells following a 24-h exposure to 3 and 9 Amol/L SFN.…”

“…Previous studies have revealed that SFN treatment causes G 2 -M phase cell cycle arrest in different cells including p53-deficient PC-3 cells (15,19,20,23). We also found that the SFN-induced G 2 -M phase cell cycle arrest in PC-3 cells is caused by checkpoint kinase 2 (Chk2) -mediated phosphorylation of Cdc25C leading to its sequestration in the cytosol (19).…”

Plitidepsin Has a Dual Effect Inhibiting Cell Cycle and Inducing Apoptosis via Rac1/c-Jun NH2-Terminal Kinase Activation in Human Melanoma Cells

“…In addition, the involvement of JNK in the regulation of cell cycle progression has also been noted in previous reports; JNK mediates G 2 /M arrest induced by sulforaphane (Cho et al, 2005) and diallyl trisulfide (Antosiewicz et al, 2006) in human prostate cancer cells, and by thiazolidin compounds in human non-small-cell lung and colon cancer cells (Teraishi et al, 2005). It is interesting to note that glial cell line-derived neurotropic factor induces G 2 /M cell cycle delay via the Rac1/JNK pathway (Fukuda et al, 2005).…”

Marine Sponge Cribrochalina vasculum Compounds Activate Intrinsic Apoptotic Signaling and Inhibit Growth Factor Signaling Cascades in Non–Small Cell Lung Carcinoma

“…It has been shown that Akt regulates cell cycle by controlling of cyclins and CDK inhibitors (49)(50)(51)(52). In addition, JNK is involved in cell-cycle progression and mediates G 2 -M phase cell-cycle arrest in different tumor cells (53)(54)(55)(56)(57)(58). As both, decreased phosphorylation of Akt and increased phosphorylation of JNK are evident after treatment with 1, these signaling cascades may be responsible for the observed G 2 -M arrest upon treatment.…”