γ-Tocotrienol-induced Autophagy in Malignant Mammary Cancer Cells

Exp Biol Med (Maywood). 2014 Jan;239(1):33-44. doi: 10.1177/1535370213511022. Epub 2013 Nov 14.

Abstract

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.

Keywords: Protein kinase B (Akt); autophagy; breast cancer; mammalian target of rapamycin; γ-Tocotrienol.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis Regulatory Proteins / biosynthesis
  • Autophagy / drug effects*
  • Beclin-1
  • Breast Neoplasms / drug therapy
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • Caspase 3 / biosynthesis
  • Cell Line, Tumor
  • Chromans / pharmacology*
  • Female
  • Gene Expression Regulation, Neoplastic / drug effects
  • Humans
  • Lipoylation / drug effects
  • Mammary Neoplasms, Experimental / drug therapy
  • Mammary Neoplasms, Experimental / metabolism*
  • Mammary Neoplasms, Experimental / pathology
  • Membrane Proteins / biosynthesis
  • Mice
  • Mice, Inbred BALB C
  • Microtubule-Associated Proteins / biosynthesis
  • Poly (ADP-Ribose) Polymerase-1
  • Poly(ADP-ribose) Polymerases / biosynthesis
  • Time Factors
  • Vitamin E / analogs & derivatives*
  • Vitamin E / pharmacology
  • bcl-2-Associated X Protein / biosynthesis

Substances

  • Apoptosis Regulatory Proteins
  • BAX protein, human
  • BECN1 protein, human
  • Bax protein, mouse
  • Beclin-1
  • Becn1 protein, mouse
  • Chromans
  • MAP1LC3 protein, mouse
  • MAP1LC3B protein, human
  • Membrane Proteins
  • Microtubule-Associated Proteins
  • bcl-2-Associated X Protein
  • Vitamin E
  • plastochromanol 8
  • Parp1 protein, mouse
  • Poly (ADP-Ribose) Polymerase-1
  • Poly(ADP-ribose) Polymerases
  • CASP3 protein, human
  • Casp3 protein, mouse
  • Caspase 3