Insulin receptor substrate-1 prevents autophagy-dependent cell death caused by oxidative stress in mouse NIH/3T3 cells.
BACKGROUND
Insulin receptor substrate (IRS)-1 is associated with tumorigenesis; its levels are elevated in several human cancers. IRS-1 protein binds to several oncogene proteins. Oxidative stress and reactive oxygen species (ROS) are involved in the initiation and progression of cancers. Cancer cells produce greater levels of ROS than normal cells do because of increased metabolic stresses. However, excessive production of ROS kills cancer cells. Autophagy usually serves as a survival mechanism in response to stress conditions, but excessive induction of autophagy results in cell death. In addition to inducing necrosis and apoptosis, ROS induces autophagic cell death. ROS inactivates IRS-1 mediated signaling and reduces intracellular IRS-1 concentrations. Thus, there is a complex relationship between IRS-1, ROS, autophagy, and cancer. It is not fully understood how cancer cells grow rapidly and survive in the presence of high ROS levels.


RESULTS
In this study, we established mouse NIH/3T3 cells that overexpressed IRS-1, so mimicking cancers with increased IRS-1 expression levels; we found that the IRS-1 overexpressing cells grow more rapidly than control cells do. Treatment of cells with glucose oxidase (GO) provided a continuous source of ROS; low dosages of GO promoted cell growth, while high doses induced cell death. Evidence for GO induced autophagy includes increased levels of isoform B-II microtubule-associated protein 1 light chain 3 (LC3), aggregation of green fluorescence protein-tagged LC3, and increased numbers of autophagic vacuoles in cells. Overexpression of IRS-1 resulted in inhibition of basal autophagy, and reduced oxidative stress-induced autophagy and cell death. ROS decreased the mammalian target of rapamycin (mTOR)/p70 ribosomal protein S6 kinase signaling, while overexpression of IRS-1 attenuated this inhibition. Knockdown of autophagy-related gene 5 inhibited basal autophagy and diminished oxidative stress-induced autophagy and cell death.


CONCLUSIONS
Our results suggest that overexpression of IRS-1 promotes cells growth, inhibits basal autophagy, reduces oxidative stress-induced autophagy, and diminishes oxidative stress-mediated autophagy-dependent cell death. ROS-mediated autophagy may occur via inhibition of IRS-1/phosphatidylinositol 3-kinase/mTOR signaling. Our data afford a plausible explanation for IRS-1 involvement in tumor initiation and progression.
Institute of Clinical Medicine, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
Shih-Hung
SH
Chan
Ushio
U
Kikkawa
Hidenori
H
Matsuzaki
Jyh-Hong
JH
Chen
Wen-Chang
WC
Chang
D000818:Animals; D001343:Autophagy / Q000235:genetics* / Q000502:physiology; D016923:Cell Death / Q000235:genetics* / Q000502:physiology; D002471:Cell Transformation, Neoplastic / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D055504:Insulin Receptor Substrate Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D041681:NIH 3T3 Cells; D009369:Neoplasms / Q000378:metabolism / Q000628:therapy; D018384:Oxidative Stress / Q000235:genetics / Q000502:physiology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction
D055504:Insulin Receptor Substrate Proteins; D017382:Reactive Oxygen Species