title: Aspirin inhibits serine phosphorylation of insulin receptor substrate 1 in tumor necrosis factor-treated cells through targeting multiple serine kinases.
abstract: The hypoglycemic effects of high dose salicylates in the treatment of diabetes were documented before the advent of insulin. However, the molecular mechanisms by which salicylates exert these anti-diabetic effects are not well understood. In this study, we analyzed the effects of aspirin (acetylsalicylic acid) on serine phosphorylation of insulin receptor substrate 1 (IRS-1) in cells treated with tumor necrosis factor (TNF)-alpha. Phosphorylation of IRS-1 at Ser307, Ser267, and Ser612 was monitored by immunoblotting with phospho-specific IRS-1 antibodies. In 3T3-L1 and Hep G2 cells, phosphorylation of IRS-1 at Ser307 in response to TNF-alpha treatment correlated with phosphorylation of JNK, c-Jun, and degradation of IkappaBalpha. Moreover, phosphorylation of IRS-1 at Ser307 in embryo fibroblasts derived from either JNK or IKK knockout mice was reduced when compared with that in the wild-type controls. Taken together, these data suggest that serine phosphorylation of IRS-1 in response to TNF-alpha is mediated, in part, by JNK and IKK. Interestingly, aspirin treatment inhibited the phosphorylation of IRS-1 at Ser307 as well as the phosphorylation of JNK, c-Jun, and degradation of IkappaBalpha. Furthermore, other serine kinases including Akt, extracellular regulated kinase, mammalian target of rapamycin, and PKCzeta were also activated by TNF-alpha (as assessed by phospho-specific antibodies). Phosphorylation of IRS-1 at Ser267 and Ser612 correlated with the activation of these kinases. Phosphorylation of Akt and the mammalian target of rapamycin (but not extracellular regulated kinase or PKCzeta) in response to TNF-alpha was inhibited by aspirin treatment. Finally, aspirin rescued insulin-induced glucose uptake in 3T3-L1 adipocytes pretreated with TNF-alpha. We conclude that aspirin may enhance insulin sensitivity by protecting IRS proteins from serine phosphorylation catalyzed by multiple kinases.
authors.affiliation: Pennington Biomedical Research Center, Louisiana State University, Baton Rouge 70808, USA.
authors.forename: Zhanguo
authors.initials: Z
authors.lastname: Gao
authors.forename: Aamir
authors.initials: A
authors.lastname: Zuberi
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Quon
authors.forename: Zigang
authors.initials: Z
authors.lastname: Dong
authors.forename: Jianping
authors.initials: J
authors.lastname: Ye
mesh_terms: D016475:3T3 Cells; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D001241:Aspirin / Q000494:pharmacology*; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance; D051379:Mice; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012694:Serine; D015398:Signal Transduction / Q000187:drug effects*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010750:Phosphoproteins; D014409:Tumor Necrosis Factor-alpha; D012694:Serine; D017346:Protein Serine-Threonine Kinases; D001241:Aspirin