Catechol-o-Methyltansferase and Breast Cancer

描述（由申请人提供）：乳腺癌的危险因素，包括月经史长、绝经后肥胖、使用激素替代疗法、未生育、初次妊娠年龄晚、血清或尿雌激素水平高，以及实验证据表明，乳腺癌与长期或改变的雌激素暴露有关。雌激素（E2）通过氧化作用生物转化为儿茶酚雌激素（CEs）。 CEs被氧化成醌类，醌类与DNA中的腺嘌呤和鸟嘌呤形成诱变加合物，并参与导致氧化性DNA损伤的氧化还原循环过程。 乳腺组织中的CE水平为10至20 pmole/g，越来越多的证据支持CE在乳腺癌中的作用。 CE主要通过儿茶酚-O-甲基转移酶（COMT）催化的O-甲基化失活。 COMT是多态性的，25%的美国白人是低活性COMT（COMTLL）的纯合子，这也是不耐热的。在一项遗传流行病学研究中，我们发现COMTLL基因型使绝经后体重指数高的妇女患乳腺癌的风险显著增加。 这项假设驱动的流行病学研究首次表明，参与活性雌激素代谢物失活的酶的多态性与乳腺癌风险增加有关。 随后，有7个其他流行病学研究的混合结果表明，需要增加对CE和COMT的作用机制的了解，以保护其免受潜在的不良反应。 在本项目期间，我们观察到：1）COMT对MCF-7细胞中CE引起的氧化DNA损伤具有高度保护作用; 2）COMTL和COMTH活性酶之间没有内在动力学差异; 3）人组织胞质溶胶中COMTL酶活性表型是由于较少的酶蛋白; 4）COMTL的热不稳定性研究表明，它的不稳定性可能是由于它与细胞蛋白质的关系改变;和5）某些叶酸途径微量营养素介导COMT基因型和乳腺癌风险之间的关联。 该项目的目标仍然是“对COMT活性降低导致DNA损伤增加，从而导致细胞转化增加和乳腺癌的假设进行严格的实验研究。 下一个项目期的具体目标是：1）使用COMT基因敲除小鼠确定COMT在小鼠乳腺发育和肿瘤发生中的作用; 2）确认COMT基因型、活性和人乳腺组织提取物中COMT蛋白水平降低之间的关系; 3）确定导致COMTL活性酶蛋白水平降低的机制。

DESCRIPTION (provided by applicant): Risk factors for breast cancer, including a long menstrual history, obesity after menopause, use of hormone replacement therapy, nulliparity, late age at first pregnancy, and high serum or urinary estrogen levels, and experimental evidence, suggest that it is associated with prolonged or altered estrogen exposure. Estradiol (E2) is oxidatively biotransformed to catechol estrogens (CEs). CEs are oxidized to quinones which form mutagenic adducts with adenine and guanine in DNA and participate in redox cycling processes that lead to oxidative DNA damage. Breast tissue CE levels in breast tissue are 10 to 20 pmoles/g, and mounting evidence supports a role for CE in breast cancer. CEs are primarily inactivated by O-methylation catalyzed by catechol-O-methyltransferase (COMT). COMT is polymorphic and 25% of Caucasian Americans are homozygous for low activity COMT (COMTLL), which is also thermolabile. In a genetic epidemiology study, we found that COMTLL genotype confers a significantly increased risk for breast cancer in postmenopausal women with a high body mass index. This hypothesis driven epidemiology study was the fist to suggest that polymorphism in an enzyme involved in the inactivation of a reactive estrogen metabolite is associated with an increased risk for breast cancer. Subsequently, there have been 7 other epidemiology studies with mixed results demonstrating the need for increased understanding of the mechanisms of effects of CEs and of COMT in protection from their potential adverse effects. During the current project period we made the following observations: 1) COMT is highly protective against oxidative DNA damage caused by CEs in MCF-7 cells; 2) there are no intrinsic kinetic differences between the COMTL and COMTH activity enzymes; 3) the COMTL enzyme activity phenotype in human tissue cytosol is due to less enzyme protein; 4) thermolability studies on COMTL suggests that its instability may be due to its altered association with a cellular protein present; and 5) certain folate pathway micronutrients mediate the association between COMT genotype and breast cancer risk. The goal of this project remains "to conduct a rigorous experimental investigation of the hypothesis that decreased COMT activity results in increased DNA damage that contributes to increased cell transformation and breast cancer. The specific aims for the next project period are to: 1) determine the role of COMT in mouse mammary gland development and tumorigenesis using a COMT knockout mouse; 2) Confirm the relationship among COMT genotype, activity, and reduced COMT protein levels in extracts of human breast tissue; 3) define the mechanisms causing reduced levels of COMTL activity enzyme protein.