γ-Tocotrienol-induced autophagy in malignant mammary cancer cells.
γ-Tocotrienol, a member of the vitamin E family of compounds, displays potent antiproliferative and cytotoxic effects in a variety of cancer cell types at treatment doses that have little or no effect on normal cell viability or growth. Autophagy is a tightly regulated lysosomal self-digested process that can either promote cell survival or programmed cell death, but the role of autophagy in mediating γ-tocotrienol-induced cytotoxicity in breast cancer is not presently completely understood. Mouse (+SA) and human (MCF-7 and MDA-MD-231) mammary tumor cells lines were exposed to 0-40 µmol/L γ-tocotrienol for a 24 h treatment period. γ-Tocotrienol treatment caused a relatively large increase in the accumulation of monodansylcadaverine (MDC)-labeled vacuoles, a marker of autophagosome formation, in all tumor cell lines. Results also showed that γ-tocotrienol treatment induced an increased conversion of microtubule-associated protein, 1A/1B-light chain 3, from its cytosolic form (LC3B-I) to its lipidated form (LC3B-II), increased Beclin-1 levels, and increased acridine orange staining as determined by flow cytometry analysis, providing further evidence of γ-tocotrienol-induced autophagy in these mammary cancer cell lines. In contrast, similar treatment with γ-tocotrienol was not found to increase autophagy marker expression in immortalized mouse (CL-S1) and human (MCF-10 A) normal mammary epithelial cell lines. Treatment with γ-tocotrienol also caused a reduction in PI3K/Akt/mTOR signaling and a corresponding increase in the Bax/Bcl-2 ratio, cleaved caspase-3, and cleaved poly (ADP-ribose) polymerase (PARP) levels in these cancer cell lines, suggesting that γ-tocotrienol-induced autophagy may be involved in the initiation of apoptosis. In summary, these findings demonstrate that the cytotoxic effects of γ-tocotrienol are associated with the induction of autophagy in a mouse and human mammary cancer cells.
College of Pharmacy, University of Louisiana at Monroe, LA 71209, USA.
Roshan V
RV
Tiwari
Parash
P
Parajuli
Paul W
PW
Sylvester
D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis; D001343:Autophagy / Q000187:drug effects*; D000071186:Beclin-1; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D053148:Caspase 3 / Q000096:biosynthesis; D045744:Cell Line, Tumor; D002839:Chromans / Q000494:pharmacology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D054878:Lipoylation / Q000187:drug effects; D008325:Mammary Neoplasms, Experimental / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D008565:Membrane Proteins / Q000096:biosynthesis; D051379:Mice; D008807:Mice, Inbred BALB C; D008869:Microtubule-Associated Proteins / Q000096:biosynthesis; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000096:biosynthesis; D013997:Time Factors; D014810:Vitamin E / Q000031:analogs & derivatives* / Q000494:pharmacology; D051028:bcl-2-Associated X Protein / Q000096:biosynthesis
D051017:Apoptosis Regulatory Proteins; C494826:BAX protein, human; C491997:BECN1 protein, human; C494827:Bax protein, mouse; D000071186:Beclin-1; C115010:Becn1 protein, mouse; D002839:Chromans; C502070:MAP1LC3B protein, human; C480860:Map1lc3b protein, mouse; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D051028:bcl-2-Associated X Protein; D014810:Vitamin E; C013649:plastochromanol 8; C499321:Parp1 protein, mouse; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3
Protein kinase B (Akt); autophagy; breast cancer; mammalian target of rapamycin; γ-Tocotrienol