title: Transcription factor AP-2beta: a negative regulator of IRS-1 gene expression.
abstract: Down-regulation of insulin receptor substrate-1 (IRS-1) expression could modify the ability of IRS-1 to fulfill its functions. It has been proposed that the phosphorylation of IRS-1 on serine residues could promote its degradation. However, few studies have investigated the transcriptional regulation of IRS-1 in the pathogenesis of insulin resistance. Genotyping for genome-wide single nucleotide polymorphisms revealed that the transcription factor activating enhancer-binding protein-2beta (AP-2beta) is a novel candidate gene for conferring susceptibility to obesity and type 2 diabetes. AP-2beta is expressed in adipose tissue and its expression is increased during the maturation of adipocytes. Overexpression of AP-2beta leads to adipocyte hypertrophy, directly inhibits adiponectin expression, and enhanced the expression of inflammatory adipokines such as IL-6 and MCP-1. In this study, we found that overexpression of AP-2beta in 3T3-L1 adipocytes impaired the promoter activity of IRS-1, and subsequently decreased mRNA and protein expression. Electrophoretic mobility shift assays showed that AP-2beta bound specifically to the IRS-1 promoter region. Furthermore, site-directed mutagenesis of the AP-2 binding site located at -362 to -351, relative to the transcription start site, markedly decreased AP-2-induced suppression of IRS-1 promoter activity, whereas other putative AP-2 binding sites did not. Our results clearly showed that AP-2beta directly decreased IRS-1 expression by binding to its promoter. Based on these findings, we speculate that the AP-2beta transcriptional factor is a unique regulator of IRS-1 and a candidate gene for insulin resistance.
authors.affiliation: Laboratory of Medical Genetics, Department of Biology, Harbin Medical University, Harbin 150086, China.
authors.forename: Xiangning
authors.initials: X
authors.lastname: Meng
authors.forename: Motoyuki
authors.initials: M
authors.lastname: Kondo
authors.forename: Katsutaro
authors.initials: K
authors.lastname: Morino
authors.forename: Tomoya
authors.initials: T
authors.lastname: Fuke
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Obata
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yoshizaki
authors.forename: Satoshi
authors.initials: S
authors.lastname: Ugi
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Nishio
authors.forename: Shiro
authors.initials: S
authors.lastname: Maeda
authors.forename: Eiichi
authors.initials: E
authors.lastname: Araki
authors.forename: Atsunori
authors.initials: A
authors.lastname: Kashiwagi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Maegawa
mesh_terms: D041721:3T3-L1 Cells; D000818:Animals; D024202:Electrophoretic Mobility Shift Assay; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D055504:Insulin Receptor Substrate Proteins / Q000235:genetics*; D007333:Insulin Resistance / Q000235:genetics; D051379:Mice; D008815:Mice, Inbred Strains; D009154:Mutation; D009690:Nucleic Acid Conformation; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis / Q000737:chemistry; D020218:Response Elements; D050656:Transcription Factor AP-2 / Q000235:genetics / Q000378:metabolism*
chemical_list: D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D012333:RNA, Messenger; D050656:Transcription Factor AP-2