Impact of Mitochondrial Reactive Oxygen Species and Apoptosis Signal–Regulating Kinase 1 on Insulin Signaling

  1. Koujiro Imoto1,
  2. Daisuke Kukidome1,
  3. Takeshi Nishikawa1,
  4. Takako Matsuhisa1,
  5. Kazuhiro Sonoda1,
  6. Kazuo Fujisawa1,
  7. Miyuki Yano1,
  8. Hiroyuki Motoshima1,
  9. Tetsuya Taguchi1,
  10. Kaku Tsuruzoe1,
  11. Takeshi Matsumura1,
  12. Hidenori Ichijo2 and
  13. Eiichi Araki1
  1. 1Department of Metabolic Medicine, Faculty of Medical and Pharmaceutical Sciences, Kumamoto University, Kumamoto, Japan
  2. 2Laboratory of Cell Signaling and Core Research for Evolutional Science and Technology, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo, Japan
  1. Address correspondence and reprint requests to Takeshi Nishikawa, Department of Metabolic Medicine, Faculty of Medical and Pharmaceutical Sciences, Kumamoto University, 1-1-1 Honjo, Kumamoto 860-8556, Japan. E-mail: takeshi{at}kaiju.medic.kumamoto-u.ac.jp

Abstract

Tumor necrosis factor (TNF)-α inhibits insulin action; however, the precise mechanisms are unknown. It was reported that TNF-α could increase mitochondrial reactive oxygen species (ROS) production, and apoptosis signal–regulating kinase 1 (ASK1) was reported to be required for TNF-α–induced apoptosis. Here, we examined roles of mitochondrial ROS and ASK1 in TNF-α–induced impaired insulin signaling in cultured human hepatoma (Huh7) cells. Using reduced MitoTracker Red probe, we confirmed that TNF-α increased mitochondrial ROS production, which was suppressed by overexpression of either uncoupling protein-1 (UCP)-1 or manganese superoxide dismutase (MnSOD). TNF-α significantly activated ASK1, increased serine phosphorylation of insulin receptor substrate (IRS)-1, and decreased insulin-stimulated tyrosine phosphorylation of IRS-1 and serine phosphorylation of Akt, and all of these effects were inhibited by overexpression of either UCP-1 or MnSOD. Similar to TNF-α, overexpression of wild-type ASK1 increased serine phosphorylation of IRS-1 and decreased insulin-stimulated tyrosine phosphorylation of IRS-1, whereas overexpression of dominant-negative ASK1 ameliorated these TNF-α–induced events. In addition, TNF-α activated c-jun NH2-terminal kinases (JNKs), and this observation was partially inhibited by overexpression of UCP-1, MnSOD, or dominant-negative ASK1. These results suggest that TNF-α increases mitochondrial ROS and activates ASK1 in Huh7 cells and that these TNF-α–induced phenomena contribute, at least in part, to impaired insulin signaling.

Footnotes

  • K.I. and D.K. contributed equally to this work.

    The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

    • Accepted February 6, 2006.
    • Received September 8, 2005.
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