SIGNIFICANCE OF GENETIC VARIATION IN ESTROGEN METABOLISM

虽然人类中大多数癌症的原因尚不清楚，但人们认识到，大多数癌症都有遗传和环境因素。 某些基因通过“解毒”外源性和内源性化学物质在体内发挥作用，解毒这些化学物质的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，我们建议检查这些“生物转化”酶的遗传差异是否可能导致子宫内膜癌的风险。 虽然人们普遍认为内源性激素雌激素在子宫内膜癌中起着重要的作用，但确切的原因尚不确定。 雌激素可能会以两种方式增加子宫内膜癌的风险：1）由于其激素活性，它会影响子宫内膜组织中细胞分裂的速率，这可能会增加受损DNA传递给子细胞的机会，以及2）最近的证据表明雌激素可能会在体内代谢为化学形式（儿茶酚雌激素），可能会直接或间接损害子宫内膜组织中的DNA。 人体内有许多酶可以制造和消除儿茶酚雌激素，其中几种酶在人类中以略微不同的形式存在（它们表现出“遗传多态性”）。 在本研究中，我们建议确定：a）如果细胞色素P450 1A 1和细胞色素P450 1B 1的某些人多态性变体比酶的正常形式更有效（或更不有效）地产生儿茶酚雌激素，B）如果儿茶酚-O-甲基转移酶和谷胱甘肽S-转移酶的特定形式的多态性变体在缀合儿茶酚雌激素方面更有效（或更不有效），c）这些酶是否以及在何种程度上在人类子宫内膜组织中表达，以及d）具有这些酶的变体形式的人是否在子宫内膜组织中表现出增加（或减少）的DNA损伤。 为了进行这些研究，这些酶中的每一种的单独形式将在酵母中表达，使用正常和变体形式的cDNA。 然后评价表达的蛋白质以确定它们代谢儿茶酚雌激素的相对能力。 将从100名因各种医学原因接受子宫内膜切除术的患者中获得人子宫内膜组织，并分析组织中这些蛋白质的存在、其活性及其mRNA水平。 还将通过两种技术评估组织随时间推移发生的DNA损伤程度：一种是测量氧化损伤的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。 还将在每个样品中确定所研究的每种酶的遗传形式（基因型）。将使用统计学方法来确定来自某些“易感性”基因型的子宫组织相对于不太易感的基因型是否具有更高水平的DNA损伤。 我们假设，有利于儿茶酚雌激素形成率增加和/或消除率降低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。 在体外工作，以衡量这些酶在子宫内膜组织中的活动和相对水平的表达将提供重要的机制信息，以证明未来的人口为基础的研究，最终确定这些基因多态性单独或组合是否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.