Laboratory of Medical Genetics, Department of Biology, Harbin Medical University, Harbin 150086, China.
Biochem Biophys Res Commun. 2010 Feb 19;392(4):526-32. doi: 10.1016/j.bbrc.2010.01.056. Epub 2010 Jan 25.
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.
胰岛素受体底物-1（IRS-1）表达的下调可能会改变 IRS-1 发挥其功能的能力。有人提出，丝氨酸残基上 IRS-1 的磷酸化可能会促进其降解。然而，很少有研究调查 IRS-1 在胰岛素抵抗发病机制中的转录调节。全基因组单核苷酸多态性的基因分型表明，激活增强子结合蛋白-2β（AP-2β）转录因子是肥胖和 2 型糖尿病易感性的新候选基因。AP-2β在脂肪组织中表达，其表达在脂肪细胞成熟过程中增加。AP-2β 的过表达导致脂肪细胞肥大，直接抑制脂联素的表达，并增强促炎脂肪因子如 IL-6 和 MCP-1 的表达。在这项研究中，我们发现 3T3-L1 脂肪细胞中 AP-2β 的过表达会损害 IRS-1 的启动子活性，随后降低 mRNA 和蛋白表达。电泳迁移率变动分析表明，AP-2β特异性结合 IRS-1 启动子区域。此外，相对于转录起始位点，位于-362 到-351 的 AP-2 结合位点的定点突变显著降低了 AP-2 诱导的 IRS-1 启动子活性抑制，而其他假定的 AP-2 结合位点则没有。我们的结果清楚地表明，AP-2β 通过结合其启动子直接降低 IRS-1 的表达。基于这些发现，我们推测 AP-2β 转录因子是 IRS-1 的独特调节剂和胰岛素抵抗的候选基因。
