Neel Brian A, Brady Matthew J, Sargis Robert M
Committee on Molecular Pathogenesis and Molecular Medicine, The University of Chicago, Chicago, IL 60637, USA.
Mol Endocrinol. 2013 Mar;27(3):394-406. doi: 10.1210/me.2012-1270. Epub 2013 Jan 22.
Glucocorticoid signaling plays a critical role in regulating energy metabolism. Emerging data implicate environmental endocrine-disrupting chemicals as contributors to the obesity and diabetes epidemics. Previous studies have shown that the phenylsulfamide fungicide tolylfluanid (TF) augments glucocorticoid receptor (GR)-dependent luciferase expression in 3T3-L1 preadipocytes while modulating insulin action in primary murine and human adipocytes. Studies were performed to interrogate glucocorticoid signaling in primary adipocytes exposed to TF. TF mimicked the gene transcription profile of the murine glucocorticoid corticosterone (Cort). Cellular fractionation assays demonstrated that TF treatment promoted the activating serine phosphorylation of GR, augmenting its cytoplasmic-to-nuclear translocation as well as its enrichment at glucocorticoid response elements on the glucocorticoid-induced leucine zipper gene promoter. After acute treatment, Cort or TF promoted insulin receptor substrate-1 (IRS-1) gene and protein expression. Either treatment also enriched GR binding at an identified glucocorticoid response element in the IRS-1 gene. TF or Cort each increased insulin-stimulated lipogenesis, an effect resulting from increased lipogenic gene expression and enhanced insulin-stimulated dephosphorylation of acetyl-coenzyme A carboxylase. The augmentation of insulin-stimulated lipogenesis was mediated through a specific enhancement of Akt phosphorylation at T308. These findings support modulation of IRS-1 levels as a mechanism for glucocorticoid-mediated changes in insulin action in primary adipocytes. Albeit with less affinity than Cort, in silico analysis suggests that TF can interact with the ligand binding pocket of GR. Collectively, these studies identify TF as a structurally unique environmental glucocorticoid. Glucocorticoid signaling may thus represent a novel pathway by which environmental toxicants promote the development of metabolic diseases.
糖皮质激素信号传导在调节能量代谢中起关键作用。新出现的数据表明，环境内分泌干扰化学物质是肥胖和糖尿病流行的促成因素。先前的研究表明，苯基磺胺类杀菌剂甲苯氟磺胺（TF）可增强3T3-L1前脂肪细胞中糖皮质激素受体（GR）依赖性荧光素酶的表达，同时调节原代小鼠和人类脂肪细胞中的胰岛素作用。本研究旨在探讨暴露于TF的原代脂肪细胞中的糖皮质激素信号传导。TF模拟了小鼠糖皮质激素皮质酮（Cort）的基因转录谱。细胞分级分离试验表明，TF处理促进了GR的激活丝氨酸磷酸化，增强了其从细胞质到细胞核的转运以及在糖皮质激素诱导的亮氨酸拉链基因启动子上糖皮质激素反应元件处的富集。急性处理后，Cort或TF促进胰岛素受体底物-1（IRS-1）基因和蛋白表达。两种处理还使GR在IRS-1基因中一个已确定的糖皮质激素反应元件处的结合增加。TF或Cort各自增加了胰岛素刺激的脂肪生成，这一效应是由脂肪生成基因表达增加和胰岛素刺激的乙酰辅酶A羧化酶去磷酸化增强所致。胰岛素刺激的脂肪生成增加是通过T308处Akt磷酸化的特异性增强介导的。这些发现支持将IRS-1水平的调节作为糖皮质激素介导的原代脂肪细胞胰岛素作用变化的一种机制。尽管与Cort的亲和力较低，但计算机模拟分析表明TF可与GR的配体结合口袋相互作用。总的来说，这些研究将TF鉴定为一种结构独特的环境糖皮质激素。因此，糖皮质激素信号传导可能代表了一种新的途径，通过该途径环境毒物促进代谢疾病的发展。
