α-TEA cooperates with MEK or mTOR inhibitors to induce apoptosis via targeting IRS/PI3K pathways.
BACKGROUND
α-Tocopherol ether-linked acetic acid (α-TEA) is a promising agent for cancer prevention/therapy based on its antitumour actions in a variety of cancers.


METHODS
Human breast cancer cells, MCF-7 and HCC-1954, were used to study the effect of α-TEA using Annexin V/PI staining, western blot analyses, and siRNA knockdown techniques.


RESULTS
α-Tocopherol ether-linked acetic acid suppressed constitutively active basal levels of pAKT, pERK, pmTOR, and their downstream targets, as well as induced both cell types to undergo apoptosis. Phosphoinositide 3-kinase (PI3K) inhibitor wortmannin suppressed pAKT, pERK, pmTOR, and their downstream targets, indicating PI3K to be a common upstream mediator. In addition, α-TEA induced increased levels of pIRS-1 (Ser-307), a phosphorylation site correlated with insulin receptor substrate-1 (IRS-1) inactivation, and decreased levels of total IRS-1. Small interfering RNA (siRNA) knockdown of JNK blocked the impact of α-TEA on pIRS-1 and total IRS-1 and impeded its ability to downregulate the phosphorylated status of AKT, ERK, and mTOR. Combinations of α-TEA+MEK or mTOR inhibitor acted cooperatively to induce apoptosis and reduce basal levels of pERK and pmTOR. Importantly, inhibition of MEK and mTOR resulted in increased levels of pAKT and IRS-1, and α-TEA blocked them.


CONCLUSIONS
Downregulation of IRS-1/PI3K pathways via JNK are critical for α-TEA and α-TEA+MEK or mTOR inhibitor-induced apoptosis in human MCF-7 and HCC-1954 breast cancer cells.
School of Biological Sciences/C0900, University of Texas, 1 University Station, Austin, TX 78712, USA.
R
R
Tiwary
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Yu
B G
BG
Sanders
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Kline
D019870:1-Phosphatidylinositol 4-Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000730:Androstadienes / Q000494:pharmacology; D000873:Anthracenes / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D002070:Butadienes / Q000494:pharmacology; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D048670:MAP Kinase Kinase 4 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014407:Tumor Cells, Cultured; D000077191:Wortmannin; D024502:alpha-Tocopherol / Q000494:pharmacology*
D000730:Androstadienes; D000873:Anthracenes; D000975:Antioxidants; D002070:Butadienes; D004791:Enzyme Inhibitors; D007166:Immunosuppressive Agents; D055504:Insulin Receptor Substrate Proteins; D009570:Nitriles; D034741:RNA, Small Interfering; C113580:U 0126; C432165:pyrazolanthrone; C546842:MTOR protein, human; D019870:1-Phosphatidylinositol 4-Kinase; D058570:TOR Serine-Threonine Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D024502:alpha-Tocopherol; D020123:Sirolimus; D000077191:Wortmannin