Tocotrienols induce apoptosis in breast cancer cell lines via an endoplasmic reticulum stress-dependent increase in extrinsic death receptor signaling.
Tocotrienols are naturally occurring forms of vitamin E based on their structural similarity. This study focused on investigating anticancer effects of tocotrienols and the mechanisms of apoptosis induction by tocotrienols in vivo and in vitro. Dietary delivery of γ-tocotrienol (γ-T3) suppressed tumor growth in a syngeneic implantation mouse mammary cancer model by inhibiting cell proliferation and inducing apoptosis. In cell culture studies, γ-T3 inhibited colony formation of a mouse mammary cancer cell line and human breast cancer cell lines. The anti-proliferative effects of tocotrienols were highly correlated with an increase in apoptosis based on Annexin V assessment. Treatment of human MDA-MB-231 and MCF-7 cells with γ-T3 induced cleavages of PARP as well as caspase-8, -9, and -3. Additional analyses showed that γ-T3 activated c-Jun NH(2)-terminal kinase (JNK) and p38 MAPK, and upregulated death receptor 5 (DR5) and C/EBP homologous protein (CHOP), an endoplasmic reticulum (ER) stress marker. Silencing either JNK or p38 MAPK reduced the increase in DR5 and CHOP and partially blocked γ-T3-induced apoptosis. Both DR5 and CHOP upregulation were required for γ-T3-induced apoptosis, and DR5 was transcriptionally regulated by CHOP after γ-T3 treatment. Moreover, γ-T3 increased the level of other ER-stress markers. Taken together, these results suggest that upregulation of DR5 by γ-T3 treatment is dependent on JNK and p38 MAPK activation which is mediated by ER-stress.
Institute of Cellular and Molecular Biology/A5000, The University of Texas at Austin, Austin, TX 78712, USA.
Sook Kyung
SK
Park
Bob G
BG
Sanders
Kimberly
K
Kline
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D005260:Female; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D034622:RNA Interference; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D013312:Stress, Physiological / Q000187:drug effects*; D013997:Time Factors; D024508:Tocotrienols / Q000494:pharmacology*; D051742:Transcription Factor CHOP / Q000378:metabolism; D047368:Tumor Burden / Q000187:drug effects; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D000970:Antineoplastic Agents; C497249:DDIT3 protein, human; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; C505639:TNFRSF10B protein, human; D024508:Tocotrienols; D051742:Transcription Factor CHOP; D011065:Poly(ADP-ribose) Polymerases; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020169:Caspases