Molecular Mechanisms of Dioxin Action

描述（由申请人提供）：本提案的长期目标是了解二恶英（2，3，7，8-四氯二苯并对二恶英; TCDD）暴露的生物反应的分子机制。四氯二苯并对二恶英是二恶英的原型，也是许多其他有机氯化化合物的模型，它产生许多显然不相关的生物效应，从人类的氯痤疮到实验室动物的发育畸形、肿瘤促进、胸腺萎缩、消瘦综合征和死亡。此外，四氯二苯并对二恶英是一种啮齿动物致癌物，强烈怀疑它也对人类致癌。TCDD生物效应的分子基础在很大程度上是未知的。二恶英是芳烃（Ah）受体（AHR）的配体，其作为与Ah受体核转运蛋白ARNT的二聚体，介导细胞色素P450单加氧酶家族中基因的转录激活。然而，尽管是TCDD对Ah受体激活的最佳特征效应之一，但CYP 1A 1、CYP 1A 2和CYP 1 B1基因的激活并不能充分解释TCDD效应的多样性。我们最近对人类肝癌细胞的全球表达谱分析表明，暴露于二恶英诱导或抑制了总共300多个基因，其中抑制更为频繁。AHR的反式激活潜力可以很容易地解释诱导作用，但基因阻遏是激活的AHR的一种新效应，在分子水平上尚未表征。这里提出的实验的目标是定义和表征的激活AHR和其他转录因子，共调节和染色质重塑因子负责二恶英对基因表达的影响之间的调节相互作用。本工作的主要目的是：（1）确定AHR的离散结构域在基因调控中的作用;（2）利用蛋白质组学分析来鉴定AHR在基因诱导和抑制中的共调控伙伴;（3）克隆AHR调控基因的启动子并表征它们对二恶英暴露的反应。这些实验的结果对于我们理解接触二恶英和其他有机氯化化合物的长期生物后果至关重要，并将有助于制定适当的理由来处理因接触这些环境因子不断增加而引起的健康问题。

DESCRIPTION (provided by applicant): The long-term objective of this proposal is to understand the molecular mechanisms underlying the biological responses to dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD) exposure. TCDD, the prototypic dioxin and a model for many other organochlorinated compounds, produces many apparently unrelated biological effects, ranging from chloracne in humans to developmental teratogenesis, tumor promotion, thymic atrophy, wasting syndrome and death in laboratory animals. In addition, TCDD, a rodent carcinogen, is strongly suspected of being carcinogenic also in humans. The molecular basis of the biological effects of TCDD is largely unknown. Dioxin is a ligand for the aromatic hydrocarbon (Ah) receptor (AHR), which, as a dimer with the Ah receptor nuclear translocator protein ARNT, mediates the transcriptional activation of genes in the CYP 1 family of cytochrome P450 monooxygenases. However, activation of the CYP1A1, CYP1A2 and CYP1 B1 genes, although one of the best characterized effects of Ah receptor activation by TCDD, does not adequately explain the diversity of TCDD effects. Our recent global expression profiling analyses of human hepatoma cells shows that exposure to dioxin induces or represses a total of more than 300 genes, with repression being the more frequent. Induction may readily be explained by the transactivating potential of the AHR, but gene repression is a novel effect of the activated AHR that is uncharacterized at the molecular level. The goal of the experiments proposed here is to define and characterize the regulatory interactions between the activated AHR and other transcription factors, co-regulators and chromatin remodeling factors responsible for the effects of dioxin on gene expression. The major objectives of this work are, (1) to define the role of discrete domains of the AHR in gene regulation; (2) to use proteomic analyses to identify AHR coregulatory partners in gene induction and repression; and (3) to clone the promoters of AHR regulated genes and characterize their response to dioxin exposure. Results from these experiments will be crucial for our understanding of the long-range biological consequences of exposure to dioxin and to other organochlorinated compounds and will help formulate an adequate rationale to deal with health problems arising from an ever-increasing exposure to these environmental agents.