title: Arg972 insulin receptor substrate-1 enhances tumor necrosis factor-α-induced apoptosis in osteoblasts.
abstract: The presence of Arg972 insulin receptor substrate-1 (IRS-1) is associated with impaired insulin/IRS-1 signaling to activate phosphatidylinositol-3 kinase (PI3K). Tumor necrosis factor-α (TNF-α), an inflammatory cytokine with a central role in the pathogenesis of rheumatoid arthritis (RA), induces apoptosis in osteoblasts, which are the principal cell type responsible for bone loss in RA. In our previous study, an association between Arg972 IRS-1 and a high risk and severity of RA was identified. In the present study, the effects of Arg972 IRS-1 and IRS-1 on TNF-α-induced apoptosis in human osteoblasts were examined. Normal and RA osteoblasts were stably transfected with Arg972 IRS-1 and IRS-1. In addition, cells were stably transduced with IRS-1-shRNA to knock down IRS1. Following stimulation with 10 nM insulin for 30 min, the stable overexpression of Arg972 IRS-1 and knock down of IRS-1 significantly decreased IRS-1-associated PI3K activity and Akt activation/phosphorylation at serine 473 (ser473) and enhanced TNF-α-induced apoptosis in normal and in RA osteoblasts. By contrast, the stable overexpression of IRS-1 significantly increased the levels of IRS-1-associated PI3K activity and Akt phosphorylation (ser473) and inhibited TNF-α-induced apoptosis, which was eliminated by pretreatment with 50 µn BJM120, a selective PI3K inhibitor, for 30 min. In conclusion, the present study provided the first evidence, to the best of our knowledge, that insulin stimulation of Arg972 IRS-1 and IRS-1 enhanced and inhibited TNF-α-induced apoptosis, respectively in normal and RA osteoblasts by a PI3K‑dependent mechanism. These findings suggest that insulin/IRS-1 signaling is important in the pathogenesis of RA.
authors.affiliation: Department of Rheumatology and Immunology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China.
authors.forename: Yunhui
authors.initials: Y
authors.lastname: You
authors.affiliation: Department of Rheumatology and Immunology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China.
authors.forename: Shiqing
authors.initials: S
authors.lastname: Liu
authors.affiliation: Department of Rheumatology and Immunology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China.
authors.forename: Lijuan
authors.initials: L
authors.lastname: Peng
authors.affiliation: Department of Rheumatology and Immunology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China.
authors.forename: Mei
authors.initials: M
authors.lastname: Long
authors.affiliation: Department of Rheumatology and Immunology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China.
authors.forename: Hongxiang
authors.initials: H
authors.lastname: Deng
authors.affiliation: Department of Rheumatology and Immunology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China.
authors.forename: Hongjun
authors.initials: H
authors.lastname: Zhao
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D001120:Arginine / Q000378:metabolism; D001172:Arthritis, Rheumatoid / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D006801:Humans; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D007333:Insulin Resistance / Q000235:genetics; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D020641:Polymorphism, Single Nucleotide; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D001120:Arginine; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha; C526292:IRS1 protein, human