SIGNIFICANCE OF GENETIC VARIATION IN ESTROGEN METABOLISM

虽然人类中大多数癌症的病因尚不清楚，但人们认识到，大多数癌症既有遗传因素，也有环境因素。某些基因在体内通过“解毒”外源性和内源性化学物质发挥作用，而解毒这些化学物质能力的个体差异可能是癌症风险的重要因素。在这项研究中，我们建议研究这些“生物转化”酶的遗传差异是否可能导致子宫内膜癌的风险。子宫内膜癌的确切病因尚不清楚，尽管人们普遍认为内源性激素雌激素在其中起着重要作用。雌激素可能在两个方面增加子宫内膜癌的风险：1)由于其激素活性，它影响子宫内膜组织细胞分裂的速度，这可能增加受损DNA传递给子细胞的机会；2)最近的证据表明，雌激素可能在体内代谢为化学形式（儿茶酚雌激素），可能直接或间接损害子宫内膜组织中的DNA。人体中有许多酶既能产生也能消除儿茶酚类雌激素，其中一些酶在人体中的存在形式略有不同（它们表现出“基因多态性”）。在本研究中，我们拟确定：a)细胞色素P4501A1和细胞色素p4501b1的某些人类多态性变异是否比正常形式的酶更有效（或更少）产生儿茶酚雌激素，b)儿茶酚- o -甲基转移酶和特定形式的谷胱甘肽s -转移酶是否更有效（或更少）结合儿茶酚雌激素，c)这些酶是否以及在多大程度上在人类子宫内膜组织中表达，d)携带这些酶变体的人是否表现出子宫内膜组织中DNA损伤增加（或减少）。为了进行这些研究，每种酶的单独形式将在酵母中表达，使用正常形式和变异形式的cdna。然后将对表达的蛋白质进行评估，以确定它们代谢儿茶酚类雌激素的相对能力。研究人员将从100名因各种医学原因接受子宫切除术的患者身上获取人体子宫内膜组织，并对这些组织进行分析，以确定这些蛋白质的存在、活性和mRNA水平。这些组织还将通过两种技术来评估随着时间推移发生的DNA损伤程度：一种是测量氧化损伤DNA碱基的实际数量，另一种是通过测量其红外光谱多样性来测量DNA的整体结构。研究中的每种酶的遗传形式（基因型）也将在每个样品中确定。统计方法将用于确定来自某些“易感”基因型的子宫组织是否相对于不那么易感的基因型具有更高水平的DNA损伤。我们假设，有利于增加形成速率和/或降低儿茶酚类雌激素消除速率的基因型在子宫内膜组织中具有相对较高的氧化损伤DNA水平。测量这些酶在子宫内膜组织中的活性和相对表达水平的体外工作将提供重要的机制信息，为未来基于人群的研究提供依据，最终确定这些遗传多态性是单独的还是联合的是子宫内膜癌的重要危险因素。

Although the causes of most cancers in the human population are unknown, it is recognized that most cancers have both a genetic and an environmental component. Certain genes play a role in the body by "detoxifying" both exogenous and endogenous chemicals, and individual differences in the ability to detoxify such chemicals could be an important contributor of cancer risk. In this study, we propose to examine whether genetic differences in some of these "biotransformation" enzymes might contribute to risk of endometrial cancer. Exactly what causes endometrial cancer is uncertain, although it is widely recognized that the endogenous hormone, estrogen, plays an important role. Estrogen might increase endometrial cancer risk in two ways: 1) because of its hormonal activity, it affects the rate of cell division in endometrial tissue, which may increase the chances of damaged DNA being passed on to daughter cells, and 2) recent evidence indicates that estrogen may be metabolized in the body to chemical forms (catechol estrogens) that may directly or indirectly damage DNA in endometrial tissue. There are numerous enzymes in the body that both make and eliminate catechol estrogens, and several of these enzymes exist in slightly different forms in the human population (they exhibit "genetic polymorphism"). In this study, we propose to determine: a) if certain human polymorphic variants of cytochrome P4501A1 and cytochrome P450 1B1 produce catechol estrogens more (or less) efficiently than the normal forms of the enzymes, b) if polymorphic variants in catechol-O-methyltransferase and specific forms of glutathione S-transferases are more (or less) efficient at conjugating catechol estrogens, c) whether and to what extent these enzymes are expressed in human endometrial tissue, and d) whether people with variant forms of these enzymes exhibit increased (or decreased) DNA damage in endometrial tissue. To do these studies, individual forms of each of these enzymes will be expressed in yeast, using the cDNAs for the normal and variant forms. The expressed proteins will then be evaluated to determine their relative abilities to metabolize catechol estrogens. Human endometrial tissues will be obtained from 100 patients undergoing hysterectomies for various medical reasons, and the tissues will be analyzed for the presence of these proteins, their activities, and their mRNA levels. The tissues will also be evaluated for the extent of DNA damage that has occurred over time by two techniques: one measures the actual number of oxidatively damaged DNA bases, and the other measures the overall structure of the DNA by measuring its infrared spectral diversity. The genetic forms (genotypes) of each of the enzymes under study will also be determined in each sample. Statistical methods will be used to determine if uterine tissues from certain "susceptibility" genotypes have higher levels of DNA damage, relative to less susceptible genotypes. We hypothesize that genotypes that favor an increased rate of formation and/or decreased rate of elimination of catechol estrogens will have relatively greater levels of oxidatively damaged DNA in endometrial tissues. The in vitro work to measure the activities and relative levels of expression of these enzymes in endometrial tissues will provide important mechanistic information to justify future population-based studies to ultimately determine if these genetic polymorphisms individually or in combination are important risk factors for endometrial cancer.