Involvement of de novo ceramide synthesis in gamma-tocopherol and gamma-tocotrienol-induced apoptosis in human breast cancer cells

Scope This study further examines mechanisms involved in the pro-apoptotic action of gamma-tocopherol (?T) and gamma-tocotrienol (?T3) in human breast cancer cell lines. Methods and results ?T upregulates phospho-JNK (pJNK), CCAAT/enhancer-binding protein homologous protein (CHOP), and death receptor-5 (DR5) protein expression as detected by Western blot assays. siRNA knockdown of JNK, CHOP, or DR5 shows that ?T-induced apoptosis is JNK/CHOP/DR5 signaling dependent, which is similar to ?T3-mediated apoptotic signaling. Furthermore, both ?T and ?T3 induce increased levels of cellular ceramides and dihydroceramides as determined by LC-MS/MS analyses. Inhibition of de novo ceramide synthesis using chemical inhibitors blocked the ability of ?T and ?T3 to induce apoptosis as detected by Annexin V-FITC/PI assay and to activate JNK/CHOP/DR5 pro-apoptotic signaling thereby demonstrating the involvement of de novo ceramide synthesis in ?T- and ?T3-induced apoptosis. Conclusion Taken together, data show that both ?T and ?T3 induce apoptosis via de novo ceramide synthesis dependent activation of JNK/CHOP/DR5 pro-apoptotic signaling.