Impact of proximal promoter polymorphisms on AHR gene expression in human lung

描述(申请人提供)：自发现以来，芳香烃受体(AhR)一直被认为是由烟雾中的多环芳烃和其他不完全燃烧引起的致癌物质引发的致癌过程的一个组成部分。AhR调节一组编码第一相细胞色素P450单加氧酶、第二相结合酶和第三相代谢物转运蛋白的基因的表达，这些基因代谢和处置多环芳烃致癌物，同时也导致有限水平的反应性、诱变性中间产物。尽管AhR在人类肺的致癌过程中起着关键作用，但控制AhR表达的潜在分子机制还不是很清楚。最近，我们发现了人类AHR基因的四个新的重复多态变异，其中包括两个以前未见报道的重复序列内的单核苷酸多态，并建立了一种新的分析方法。这些新的多态发生在近端启动子的关键控制区，该区域包含多个特异性蛋白质转录因子的结合位点。我们的中心假设是，这些新发现的AHR基因多态性影响AhR表达的转录调控，进而导致致癌物生物活化酶的表达和诱导性改变，以及II和III期失活途径。我们应用的具体目的是：1)确定AHR基因这些新的多态在肺癌患者正常组织中的等位基因频率；2)确定这些新的多态在AhR表达的转录调控中的作用。我们将在体外进行肺肿瘤细胞系中转录因子结合和AHR启动子活性的检测，并确定这些多态杂合子个体正常肺组织中AhR mRNA的等位基因表达。这些研究将确定AHR基因启动子上新的多态对AhR表达的重要性，并最终可能导致对肺癌遗传易感性的更清楚的理解。

DESCRIPTION (provided by applicant): Since its discovery, the aryl hydrocarbon receptor (AhR) has been recognized as an integral component of the carcinogenic process initiated by smoke-born polycyclic aromatic hydrocarbons and other carcinogens that result from incomplete combustion. The AhR regulates the expression of a group of genes encoding phase I cytochrome P450 monooxygenases, phase II conjugating enzymes, and phase III metabolite transporters that metabolize and dispose of PAH carcinogens, while also causing a limited level of reactive, mutagenic intermediates. Despite the pivotal importance of the AhR in the carcinogenic process in human lung, the underlying molecular mechanisms controlling AhR expression are not well established. Recently, we identified four novel variants of a repeat polymorphism, including two previously unreported single-nucleotide polymorphisms within the repeat, of the human AHR gene and have established a new method for analyzing them. These novel polymorphisms occur in a critical control region of the proximal promoter that contains multiple binding sites for specificity protein transcription factors. Our central hypothesis is tha these newly characterized AHR gene polymorphisms affect the transcriptional regulation of AhR expression, which in turn leads to altered expression and inducibility of the carcinogen-bioactivating enzymes as well as phase II and III pathways of deactivation. The specific aims of our application are: 1) to determine the allelic frequencies of these novel polymorphisms of the AHR gene in normal tissue from lung cancer patients, and 2) to determine the roles of these novel polymorphisms in the transcriptional regulation of AhR expression. We will perform in vitro assays of transcription factor binding and AHR promoter activities in a lung tumor cell line and determine allelic expression of AhR mRNA in normal lung tissue from individuals heterozygous for these polymorphisms. These studies will determine the importance of novel polymorphisms in the AHR gene promoter on AhR expression and may ultimately lead to a clearer understanding of the genetic susceptibility to lung cancer.