Rapamycin suppresses ROS-dependent apoptosis caused by selenomethionine in A549 lung carcinoma cells.
OBJECTIVE
Although selenium compounds possess chemotherapeutic features by inducing apoptosis in cancer cells with trivial side effects on normal cells, the mechanisms underlying its anti-cancer activity are insufficiently understood at the present. In this study, we investigated the effects of rapamycin on apoptosis induced by seleno-L-methionine (SeMet) or selenite in A549 cells.


METHODS
The effects of Se compounds, SeMet and selenite, on cell proliferation, apoptosis and its signaling pathway were investigated in established human adenocarcinoma cell line (A549). Cancer cells were treated with each Se during different periods. Cell apoptosis and signaling molecules were analyzed by flow cytometry (TUNEL method) or immunoblotting, respectively.


RESULTS
SeMet induces reactive oxygen species generation associated with the induction of apoptosis, because pretreatment of cells with N-acetyl-L-cysteine completely blocked SeMet-induced apoptosis. We also found that rapamycin completely suppressed the apoptosis of cells treated by SeMet, but not selenite. SeMet-induced apoptosis is significantly downregulated in combination with PI3 K family inhibitors (LY294002, wortmannin, PI-103, and 3-methyladenine). In addition, ROS generation was included in downstream signaling events associated with the phosphorylation of mTOR, because pretreatment of cells with rapamycin inhibited ROS generation.


CONCLUSIONS
These results suggest that SeMet-induced apoptosis is affected by the Akt/mTOR/ROS pathway in A549 cells. Akt serves an anti-survival function in the system of SeMet-treated lung cancer cells, but autophagic signaling remained unsolved.
Suzuki
Maiko
M
Department of Microbiology and Immunology, Tohoku University Graduate School of Dentistry, 4-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan.
Endo
Manabu
M
Shinohara
Fumiaki
F
Echigo
Seishi
S
Rikiishi
Hidemi
H
D000230:Adenocarcinoma; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D006801:Humans; D008175:Lung Neoplasms; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012645:Selenomethionine / Q000494:pharmacology*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology*; D018038:Sodium Selenite / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
D000970:Antineoplastic Agents; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017382:Reactive Oxygen Species; D012645:Selenomethionine; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D018038:Sodium Selenite; D020123:Sirolimus