Molecular Mechanisms of Dioxin Action

描述(由申请人提供)：这项建议的长期目标是了解接触二恶英(2，3，7，8-四氯二苯并-对二恶英；TCDD)的生物学反应的分子机制。TCDD是二恶英的原型，也是许多其他有机氯化合物的模型，它产生许多明显无关的生物效应，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，啮齿动物致癌物质TCDD被强烈怀疑在人类身上也是致癌的。TCDD的生物学效应的分子基础在很大程度上是未知的。二恶英是芳香烃受体的配体，作为芳香烃受体核转位蛋白ArnT的二聚体，介导细胞色素P450单加氧酶家族基因的转录激活。然而，尽管CYP1A1、CYP1A2和CYP1B1基因的激活是TCDD激活AH受体的最佳特征之一，但这并不能充分解释TCDD作用的多样性。我们最近对人肝癌细胞的全球表达谱分析表明，暴露于二恶英中总共诱导或抑制了300多个基因，其中抑制更为频繁。可以很容易地用AHR的反式激活潜力来解释诱导，但基因抑制是激活的AHR的一种新的效应，在分子水平上还没有描述。这些实验的目的是定义和描述激活的AHR与其他转录因子、共调节因子和染色质重塑因子之间的调控相互作用，这些转录因子和染色质重塑因子负责二恶英对基因表达的影响。这项工作的主要目的是：(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确定AHR在基因诱导和抑制中的协同调节伙伴；以及(3)克隆AHR调节基因的启动子，并研究它们对二恶英暴露的反应。这些实验的结果将对我们了解接触二恶英和其他有机氯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论基础，以处理因不断增加接触这些环境物质而产生的健康问题。

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.