Convergence of TCDD Gene Activation with Other Pathways

描述（由申请人提供）：本提案的长期目标是 剖析环境污染物的分子机制， 主要是2，3，7，8，四氯二苯并对二恶英（TCDD），作为肿瘤 发起人。TCDD的许多不良生物效应被认为是 在其活化芳烃受体（AHR）后， AHR与其DNA结合伴侣，芳烃受体核 AHR/ARNT异源二聚体的基因激活。这里我们 这表明存在一个额外的机制; TCDD诱导核 AHR的定位及其与破坏ARNT的ARNT的异源二聚化 从它在其他信号通路中的作用，即，关于Myc/Max 异二聚体。Myc/Max是一种被充分描述的细胞增殖调节因子， 细胞凋亡和分化，其部分通过基因上调起作用， 例如p53。我们发现10个ARNT协同增强Myc 上调p53启动子，2）ARNT对Myc 反式激活通过ARNT的HLH结构域发生，3）TCDD降低mRNA p53水平和Myo上调p53启动子的能力。这些 结果，以及其他人，形成了我们假设ARNT作用的基础， 与Myc/Max异源二聚体协同上调表达 p53的水平。此外，我们假设，添加TCDD和 ARNT与AHR的异源二聚化，使ARNT失去这种作用，降低了ARNT与AHR之间的相互作用。 Myc调节p53表达水平的能力降低， Myc诱导细胞凋亡和分化的能力。为了验证这个想法， 我们将确定ARNT的表达水平是否显著改变， 影响Myc上调p53（Aim 1）的能力，并增强细胞凋亡 并在存在或不存在TCDD的情况下诱导分化（Aim 2）（Aim 3）。 然后，我们将确定ARNT是否存在于DNA结合复合物中， p53启动子（Aim 4），并鉴定与ARNT相互作用的蛋白质， 引起其对Myc反式激活的协同作用（Aim 5）。

DESCRIPTION (provided by applicant): The long-term goals of this proposal are to dissect the molecular mechanism(s) by which environmental contaminants, primarily 2, 3, 7, 8, tetrachlorodibenzo-p-dioxin (TCDD), act as tumor promoters. Many of the adverse biological effects of TCDD are thought to occur following its activation of the aryl hydrocarbon receptor (AHR), dimerization of the AHR with its DNA binding partner, the aryl hydrocarbon receptor nuclear translocator (ARNT) and gene activation by the AHR/ARNT heterodimer. Here, we suggest the existence of an additional mechanism; that TCDD induces nuclear localization of the AHR and its heterodimerization with ARNT that disrupts ARNT from its role in other signaling pathways, i.e., that of the Myc/Max heterodimer. Myc/Max is a well-described regulator of cell proliferation, apoptosis, and differentiation that acts, in part, by upregulation of genes such as p53. We found that 10 ARNT synergistically enhances the ability of Myc to upregulate the p53 promoter, 2) the synergistic actions of ARNT on Myc transactivation occurs via the HLH domain of ARNT, 3) TCDD decreases the mRNA levels of p53 and the ability of Myo to upregulated the p53 promoter. These results, and that of others, form the basis of our hypothesis that ARNT acts synergistically with the Myc/Max heterodimer to upregulate the expression levels of p53. Further, we hypothesize that the addition of TCDD and heterodimerization of ARNT with AHR, removes ARNT form this role, decreases the ability of Myc to regulate the expression levels of p53 and hence, decreases the ability of Myc to induce apoptosis and differentiation. To test this idea, we will determine whether altered expression levels of ARNT significantly impact the ability of Myc to upregulate p53 (Aim 1), and potentiate apoptosis and induce differentiation (Aim 2) in the presence or absence of TCDD (Aim 3). We will then determine whether ARNT is present within DNA binding complexes at the p53 promoter (Aim 4) and identify the protein(s) that interact with ARNT to elicit its synergistic effect on Myc transactivation (Aim 5).