Up-regulation of c-Jun-NH2-kinase pathway contributes to the induction of mitochondria-mediated apoptosis by α-tocopheryl succinate in human prostate cancer cells

Previously, α-tocopheryl succinate ( α -TOS) has been reported to induce caspase-mediated apoptosis in PC-3 human prostate cancer cells. Caspase-9 was among several initiator caspases activated by α -TOS, suggesting a potential contribution of the intrinsic apoptotic pathway in mediating the response to α -TOS. Gene expression microarray was carried out as a screen to identify novel signaling molecules modulated by α -TOS, with a special focus on those known to play a role in mitochondria-mediated apoptosis. We discovered that Ask1, GADD45 β , and Sek1, three key components of the stress-activated mitogen-activated protein kinase pathway, are novel targets of α -TOS. Western blot analysis showed increased levels of phospho-Sek1 and phospho-c- Jun -NH 2 -kinase (JNK) in addition to total Ask1, GADD45 β , and Sek1. α -TOS also altered JNK-specific phosphorylation of Bcl-2 and Bim in a manner consistent with enhanced mitochondrial translocation of Bax and Bim. Because the expression level of most Bcl-2 family members remained unchanged, the posttranslational modification of Bcl-2 and Bim by JNK is likely to be a driving force in α -TOS activation of the intrinsic apoptotic pathway. Based on our findings, we propose a working model to capture the salient features of the apoptotic signaling circuitry of α -TOS.