Involvement of de novo ceramide synthesis in gamma-tocopherol and gamma-tocotrienol-induced apoptosis in human breast cancer cells.
METHODS
This study further examines mechanisms involved in the pro-apoptotic action of gamma-tocopherol (γT) and gamma-tocotrienol (γT3) in human breast cancer cell lines.


RESULTS
γT 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 γT-induced apoptosis is JNK/CHOP/DR5 signaling dependent, which is similar to γT3-mediated apoptotic signaling. Furthermore, both γT and γT3 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 γT and γT3 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 γT- and γT3-induced apoptosis.


CONCLUSIONS
Taken together, data show that both γT and γT3 induce apoptosis via de novo ceramide synthesis dependent activation of JNK/CHOP/DR5 pro-apoptotic signaling.
Department of Nutritional Sciences, University of Texas at Austin, Austin, TX 78712, USA.
Archana
A
Gopalan
Weiping
W
Yu
Qing
Q
Jiang
Yumi
Y
Jang
Bob G
BG
Sanders
Kimberly
K
Kline
D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000473:pathology; D045744:Cell Line, Tumor; D002518:Ceramides / Q000096:biosynthesis*; D002839:Chromans / Q000494:pharmacology*; D002853:Chromatography, Liquid; D005260:Female; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D061986:MCF-7 Cells; D034741:RNA, Small Interfering / Q000235:genetics / Q000302:isolation & purification; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D053719:Tandem Mass Spectrometry; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation; D014810:Vitamin E / Q000031:analogs & derivatives* / Q000494:pharmacology; D024504:gamma-Tocopherol / Q000494:pharmacology*
D002518:Ceramides; D002839:Chromans; C497249:DDIT3 protein, human; D034741:RNA, Small Interfering; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; C505639:TNFRSF10B protein, human; D014810:Vitamin E; D051742:Transcription Factor CHOP; C013649:plastochromanol 8; D024504:gamma-Tocopherol; D048031:JNK Mitogen-Activated Protein Kinases