15337828

pubmed:Citation

8

Tocotrienols, a subclass in the vitamin E family of compounds, have been shown to induce apoptosis by activating caspase-8 and caspase-3 in neoplastic mammary epithelial cells. Since caspase-8 activation is associated with death receptor apoptotic signaling, studies were conducted to determine the exact death receptor/ligand involved in tocotrienol-induced apoptosis. Highly malignant +SA mouse mammary epithelial cells were grown in culture and maintained in serum-free media. Treatment with 20 microM gamma-tocotrienol decreased+SA cell viability by inducing apoptosis, as determined by positive terminal dUTP nick end labeling (TUNEL) immunocytochemical staining. Western blot analysis showed that gamma-tocotrienol treatment increased the levels of cleaved (active) caspase-8 and caspase-3. Combined treatment with caspase inhibitors completely blocked tocotrienol-induced apoptosis. Additional studies showed that treatment with 100 ng/ml tumor necrosis factor-alpha (TNF-alpha), 100 ng/ml FasL, 100 ng/ml TNF-related apoptosis-inducing ligand (TRAIL), or 1 microg/ml apoptosis-inducing Fas antibody failed to induce death in +SA cells, indicating that this mammary tumor cell line is resistant to death receptor-induced apoptosis. Furthermore, treatment with 20 microM gamma-tocotrienol had no effect on total, membrane, or cytosolic levels of Fas, Fas ligand (FasL), or Fas-associated via death domain (FADD) and did not induce translocation of Fas, FasL, or FADD from the cytosolic to the membrane fraction, providing additional evidence that tocotrienol-induced caspase-8 activation is not associated with death receptor apoptotic signaling. Other studies showed that treatment with 20 microM gamma-tocotrienol induced a large decrease in the relative intracellular levels of phospho-phosphatidylinositol 3-kinase (PI3K)-dependent kinase 1 (phospho-PDK-1 active), phospho-Akt (active), and phospho-glycogen synthase kinase3, as well as decreasing intracellular levels of FLICE-inhibitory protein (FLIP), an antiapoptotic protein that inhibits caspase-8 activation, in these cells. Since stimulation of the PI3K/PDK/Akt mitogenic pathway is associated with increased FLIP expression, enhanced cellular proliferation, and survival, these results indicate that tocotrienol-induced caspase-8 activation and apoptosis in malignant +SA mammary epithelial cells is associated with a suppression in PI3K/PDK-1/Akt mitogenic signaling and subsequent reduction in intracellular FLIP levels.

eng

IM

MEDLINE

1535-3702

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NLM

745-55

pubmed-meshheading:15337828-Adenocarcinoma, pubmed-meshheading:15337828-Animals, pubmed-meshheading:15337828-Antioxidants, pubmed-meshheading:15337828-Apoptosis, pubmed-meshheading:15337828-Apoptosis Regulatory Proteins, pubmed-meshheading:15337828-Caspase 8, pubmed-meshheading:15337828-Caspases, pubmed-meshheading:15337828-Cell Death, pubmed-meshheading:15337828-Cell Line, Tumor, pubmed-meshheading:15337828-Cell Survival, pubmed-meshheading:15337828-Enzyme Activation, pubmed-meshheading:15337828-Epithelial Cells, pubmed-meshheading:15337828-Female, pubmed-meshheading:15337828-Mammary Neoplasms, Animal, pubmed-meshheading:15337828-Membrane Glycoproteins, pubmed-meshheading:15337828-Mice, pubmed-meshheading:15337828-Mice, Inbred BALB C, pubmed-meshheading:15337828-Protein-Serine-Threonine Kinases, pubmed-meshheading:15337828-Proto-Oncogene Proteins, pubmed-meshheading:15337828-Proto-Oncogene Proteins c-akt, pubmed-meshheading:15337828-Receptors, Tumor Necrosis Factor, pubmed-meshheading:15337828-Signal Transduction, pubmed-meshheading:15337828-TNF-Related Apoptosis-Inducing Ligand, pubmed-meshheading:15337828-Tocotrienols, pubmed-meshheading:15337828-Tumor Necrosis Factor-alpha

Tocotrienol-induced caspase-8 activation is unrelated to death receptor apoptotic signaling in neoplastic mammary epithelial cells.

Journal Article, Research Support, U.S. Gov't, P.H.S.