Hartman Helen B, Hu Xiao, Tyler Keala X, Dalal Chiraj K, Lazar Mitchell A
Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine and Genetics and The Penn Diabetes Center, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
J Biol Chem. 2002 May 31;277(22):19754-61. doi: 10.1074/jbc.M201451200. Epub 2002 Mar 18.
Resistin, also known as Adipocyte Secreted Factor (ADSF) and Found in Inflammatory Zone 3 (FIZZ3), is a mouse protein with potential roles in insulin resistance and adipocyte differentiation. The resistin gene is expressed almost exclusively in adipocytes. Here we show that a proximal 264-base pair fragment of the mouse resistin promoter is sufficient for expression in adipocytes. Ectopic expression of the adipogenic transcription factor CCAAT/enhancer-binding protein (C/EBPalpha) was sufficient for expression in non-adipogenic cells. C/EBPalpha binds specifically to a site that is essential for expression of the resistin promoter. Chromatin immunoprecipitation studies of the endogenous gene demonstrated adipocyte-specific association of C/EBPalpha with the proximal resistin promoter in adipocytes but not preadipocytes. C/EBPalpha binding was associated with the recruitment of coactivators p300 and CREB-binding protein and a dramatic increase in histone acetylation in the vicinity of the resistin promoter. The antidiabetic thiazolidinedione (TZD) drug rosiglitazone reduced resistin expression with an ED(50) similar to its K(d) for binding to peroxisome proliferator activated receptor gamma (PPARgamma). Other TZD- and non-TZD PPARgamma ligands also down-regulated resistin expression. However, no functional PPARgamma binding site was found within 6.2 kb of the transcriptional start site, suggesting that if PPARgamma is involved, it is either acting at a long distance from the start site, in an intron, or indirectly. Nevertheless, rosiglitazone treatment selectively decreased histone acetylation at the resistin promoter without a change in occupation by C/EBPalpha, CREB-binding protein, or p300. Thus, adipocyte specificity of resistin gene expression is because of C/EBPalpha binding, leading to the recruitment of transcriptional coactivators and histone acetylation that is characteristic of an active chromatin environment. TZD reduces resistin gene expression at least in part by reducing histone acetylation associated with the binding of C/EBPalpha in mature adipocytes.
抵抗素，也被称为脂肪细胞分泌因子（ADSF）和炎症区域3发现蛋白（FIZZ3），是一种在胰岛素抵抗和脂肪细胞分化中具有潜在作用的小鼠蛋白。抵抗素基因几乎只在脂肪细胞中表达。在此我们表明，小鼠抵抗素启动子近端的一段264个碱基对的片段足以在脂肪细胞中表达。脂肪生成转录因子CCAAT/增强子结合蛋白（C/EBPα）的异位表达足以在非脂肪生成细胞中表达。C/EBPα特异性结合到一个对于抵抗素启动子表达至关重要的位点。对内源基因的染色质免疫沉淀研究表明，在脂肪细胞而非前脂肪细胞中，C/EBPα与近端抵抗素启动子存在脂肪细胞特异性结合。C/EBPα的结合与共激活因子p300和CREB结合蛋白的募集以及抵抗素启动子附近组蛋白乙酰化的显著增加相关。抗糖尿病噻唑烷二酮（TZD）药物罗格列酮降低抵抗素表达，其半数有效剂量（ED50）与其与过氧化物酶体增殖物激活受体γ（PPARγ）结合的解离常数（Kd）相似。其他TZD和非TZD的PPARγ配体也下调抵抗素表达。然而，在转录起始位点6.2 kb范围内未发现功能性PPARγ结合位点，这表明如果PPARγ参与其中，它要么在远离起始位点的远距离处起作用，要么在内含子中起作用，要么是间接作用。尽管如此，罗格列酮处理选择性降低了抵抗素启动子处的组蛋白乙酰化，而C/EBPα、CREB结合蛋白或p300的占据情况没有改变。因此，抵抗素基因表达的脂肪细胞特异性是由于C/EBPα的结合，导致转录共激活因子的募集和组蛋白乙酰化，这是活跃染色质环境的特征。TZD至少部分通过减少成熟脂肪细胞中与C/EBPα结合相关的组蛋白乙酰化来降低抵抗素基因表达。
