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。 TCDD 是典型的二恶英，也是许多其他有机氯化化合物的模型，它会产生许多明显不相关的生物效应，从人类的氯痤疮到发育性畸胎、肿瘤促进、胸腺萎缩、消耗综合症和实验动物的死亡。此外，TCDD这种啮齿动物致癌物也被强烈怀疑对人类也具有致癌性。 TCDD 生物效应的分子基础在很大程度上尚不清楚。二恶英是芳香烃 (Ah) 受体 (AHR) 的配体，作为与 Ah 受体核转位蛋白 ARNT 的二聚体，介导细胞色素 P450 单加氧酶 CYP1 家族基因的转录激活。然而，CYP1A1、CYP1A2 和 CYP1 B1 基因的激活虽然是 TCDD 激活 Ah 受体的最佳特征效应之一，但并不能充分解释 TCDD 效应的多样性。我们最近对人类肝癌细胞进行的全局表达谱分析表明，接触二恶英会诱导或抑制总共 300 多个基因，其中抑制更为频繁。诱导可以很容易地用 AHR 的反式激活潜力来解释，但基因抑制是激活的 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的是定义和表征激活的 AHR 与其他转录因子、协同调节因子和染色质重塑因子之间的调节相互作用，这些因子负责二恶英对基因表达的影响。这项工作的主要目标是，（1）定义 AHR 离散域在基因调控中的作用； (2) 使用蛋白质组学分析来识别基因诱导和抑制中的 AHR 共调节伙伴； (3) 克隆 AHR 调节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了解接触二恶英和其他有机氯化化合物的长期生物学后果至关重要，并将有助于制定适当的理由来处理因不断增加的接触这些环境因素而产生的健康问题。

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.