Inhibition of arachidonate 5-lipoxygenase triggers prostate cancer cell death through rapid activation of c-Jun N-terminal kinase

Previously, we reported that inhibition of arachidonate 5-lipoxygenase triggers massive apoptosis in both androgen-sensitive (LNCaP) and androgen-refractory (PC3) human prostate cancer cells within hours of treatment [Proc. Natl. Acad. Sci. USA 95 (1998) 13182-13187]. Apoptosis was prevented by exogenous 5(S)-HETE, a product of 5-lipoxygenase, indicating a role of this eicosanoid as an essential survival/anti-apoptotic factor for prostate cancer cells. However, nothing was clearly known about details of the underlying molecular mechanisms or events mediating the induction of fulminating apoptosis in these cells. This report documents the fact that inhibition of arachidonate 5-lipoxygenase induces rapid activation of c-Jun N-terminal kinase (JNK) in human prostate cancer cells which is prevented by the 5-lipoxygenase metabolite, 5(S)-HETE. Activation of JNK is unaffected by the cell-permeable tetra-peptide inhibitors of caspase 8 or caspase 3 (IETD-FMK and DEVD-FMK), though these inhibitors effectively blocked apoptosis triggering, suggesting that activation of JNK is independent or upstream of caspase activation. Both 5-lipoxygenase inhibition-induced activation of JNK and induction of apoptosis are prevented by curcumin, an inhibitor of JNK-signaling pathway. Apoptosis is also blocked by SP600125, a specific inhibitor of JNK activity, indicating that JNK activity is required for the induction of apoptosis in these cells. These findings suggest that the metabolites of arachidonate 5-lipoxygenase promote survival of prostate cancer cells involving down-regulation of stress-activated protein kinase.