title: Impact of mitochondrial reactive oxygen species and apoptosis signal-regulating kinase 1 on insulin signaling.
abstract: Tumor necrosis factor (TNF)-alpha inhibits insulin action; however, the precise mechanisms are unknown. It was reported that TNF-alpha could increase mitochondrial reactive oxygen species (ROS) production, and apoptosis signal-regulating kinase 1 (ASK1) was reported to be required for TNF-alpha-induced apoptosis. Here, we examined roles of mitochondrial ROS and ASK1 in TNF-alpha-induced impaired insulin signaling in cultured human hepatoma (Huh7) cells. Using reduced MitoTracker Red probe, we confirmed that TNF-alpha increased mitochondrial ROS production, which was suppressed by overexpression of either uncoupling protein-1 (UCP)-1 or manganese superoxide dismutase (MnSOD). TNF-alpha 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-alpha, 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-alpha-induced events. In addition, TNF-alpha activated c-jun NH(2)-terminal kinases (JNKs), and this observation was partially inhibited by overexpression of UCP-1, MnSOD, or dominant-negative ASK1. These results suggest that TNF-alpha increases mitochondrial ROS and activates ASK1 in Huh7 cells and that these TNF-alpha-induced phenomena contribute, at least in part, to impaired insulin signaling.
authors.affiliation: Department of Metabolic Medicine, Faculty of Medical and Pharmaceutical Sciences, Kumamoto University, 1-1-1 Honjo, Kumamoto 860-8556, Japan.
authors.forename: Koujiro
authors.initials: K
authors.lastname: Imoto
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kukidome
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nishikawa
authors.forename: Takako
authors.initials: T
authors.lastname: Matsuhisa
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Sonoda
authors.forename: Kazuo
authors.initials: K
authors.lastname: Fujisawa
authors.forename: Miyuki
authors.initials: M
authors.lastname: Yano
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Motoshima
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Taguchi
authors.forename: Kaku
authors.initials: K
authors.lastname: Tsuruzoe
authors.forename: Takeshi
authors.initials: T
authors.lastname: Matsumura
authors.forename: Hidenori
authors.initials: H
authors.lastname: Ichijo
authors.forename: Eiichi
authors.initials: E
authors.lastname: Araki
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular; D002352:Carrier Proteins / Q000494:pharmacology; D045744:Cell Line, Tumor; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D007473:Ion Channels; D008113:Liver Neoplasms; D048848:MAP Kinase Kinase Kinase 5 / Q000378:metabolism*; D008565:Membrane Proteins / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D024101:Mitochondrial Proteins; D051381:Rats; D017382:Reactive Oxygen Species; D015398:Signal Transduction / Q000502:physiology*; D013482:Superoxide Dismutase / Q000235:genetics / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D014475:Uncoupling Agents / Q000494:pharmacology; D000071256:Uncoupling Protein 1
chemical_list: D002352:Carrier Proteins; D007328:Insulin; D007473:Ion Channels; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D017382:Reactive Oxygen Species; D014409:Tumor Necrosis Factor-alpha; C000604371:UCP1 protein, human; C000604373:Ucp1 protein, rat; D014475:Uncoupling Agents; D000071256:Uncoupling Protein 1; D013482:Superoxide Dismutase; D048848:MAP Kinase Kinase Kinase 5