DNA SEQUENCE DIVERSITY IN THE HUMAN PREGNANE X RECEPTOR

妊娠素X受体（PXR）的发现使人们对细胞色素P4503A和其他药物解毒酶上调的基本机制有了更深入的了解。我们假设，CYP3A4基因中PXR或其同源结合元件（PXRE）的序列变异（包括单核苷酸多态性，snp）是人类CYP3A基础表达和诱导表达变异的核心。为了严格研究PXR snp对CYP3A调控的重要性，需要一种安全、可靠、方便的检测方法来确定个体的PXR基因型。为了实现这一目标，我们已经克隆、绘制并测序了PXR。我们的总体目标是：(1)确定PXR（或CYP3A4 PXRE）的序列变异，并确定其功能重要性；(2) PXR snp与CYP3A表型变异的相关性；(3)确定PXR序列变化的总体频率和模式；(4)在细胞和生化分析中确定PXR snp的功能重要性以及导致无功能PXR的分子机制。我们的药物基因组学方法利用了我们独特的资源——来自CYP3A表型人类组织的基因组dna和来自大量CYP3A底物和诱导剂临床试验的人类研究群体。此外，利用CYP3A诱导表型的人肝细胞培养物，我们将前瞻性地确定诱导药物反应的异常值。我们研究的目标是同时使用这些确定的患者群体作为基因型-表型关系的来源和SNP发现资源。我们的假设驱动方法将立即阐明PXR或PXRE SNP对PXR功能和CYP3A药物反应的功能影响，并将作为一个重要的基因型-表型/SNP药物基因组学模型，并为CYP3A代谢药物高度可变的药代动力学机制提供进一步的见解。

The discovery of the Pregnane X receptor (PXR) has led to a greater understanding of the fundamental mechanisms underlying upregulation of cytochrome P4503A and potentially other drug detoxification enzymes. We hypothesize that sequence variations (including single nucleotide polymorphisms, SNPs) in PXR or its cognate binding element (PXRE) in the CYP3A4 gene are central to human variation in both basal and inducible CYP3A expression. To critically study the importance of PXR SNPs to regulation of CYP3A a safe, reliable, and convenient assay will be needed to determine an individual s PXR genotype. Towards this goal we have cloned, mapped and are sequencing PXR. Our overall objectives are: (1) to identify sequence variations in PXR (or in the CYP3A4 PXRE) and determine their functional importance; (2) to correlate PXR SNPs to phenotypic variations in CYP3A; (3) to determine the overall frequency and pattern of sequence variations in PXR; and (4) to determine the functional importance of PXR SNPs and the molecular mechanisms leading to non- functional PXR in cellular and biochemical assays. Our pharmacogenomic approach takes advantage of our unique resources - genomic DNAs from CYP3A phenotyped human tissues and human study populations from numerous clinical trials with CYP3A substrates and inducers. Additionally, using cultures of human hepatocytes phenotyped for CYP3A induction we will prospectively identify the outliers in inductive drug response. The goal of our study is to use these defined patient populations simultaneously as a source of genotype-phenotype relationships and as a SNP discovery resource. Our hypothesis driven approach will immediately elucidate the functional consequences of PXR or PXRE SNPs to not only PXR function but CYP3A drug response as well and will serve as an important gentotype-phenotype/SNP pharmacogenomics model and provide further insights into mechanisms responsible for the highly variable pharmacokinetics of CYP3A metabolized drugs.