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、初孕年龄晚、血清或尿液雌激素水平高，以及实验证据，表明其与长期或改变的雌激素暴露有关。雌二醇（E2）被氧化生物转化为儿茶酚雌激素（CEs）。ce被氧化成醌，与DNA中的腺嘌呤和鸟嘌呤形成致突变加合物，并参与氧化还原循环过程，导致DNA氧化损伤。乳腺组织中的CE水平为10 - 20 pmol /g，越来越多的证据支持CE在乳腺癌中的作用。ce主要通过由儿茶酚- o -甲基转移酶（COMT）催化的o -甲基化灭活。COMT是多态的，25%的美国白人是低活性COMT （COMTLL）的纯合子，COMTLL也是耐热的。在一项遗传流行病学研究中，我们发现COMTLL基因型显著增加了绝经后体重指数高的妇女患乳腺癌的风险。这一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，又有其他7项流行病学研究得出了不同的结果，表明有必要进一步了解ce和COMT的作用机制，以防止其潜在的不良影响。在目前的项目期间，我们做了以下观察：1)COMT对MCF-7细胞中ce引起的DNA氧化损伤具有高度的保护作用；2) COMTL和COMTH活性酶之间没有内在的动力学差异；3)人组织细胞质中COMTL酶活性表型是由于酶蛋白较少所致；4)对COMTL的耐热性研究表明，它的不稳定性可能是由于它与细胞蛋白的关联发生了改变；5)某些叶酸途径微量营养素介导COMT基因型与乳腺癌风险之间的关系。该项目的目标仍然是“对COMT活性降低导致DNA损伤增加，从而增加细胞转化和乳腺癌的假设进行严格的实验调查”。下一个项目期的具体目标是：1)利用敲除COMT的小鼠确定COMT在小鼠乳腺发育和肿瘤发生中的作用；2)确认人乳腺组织提取物中COMT基因型、活性和降低的COMT蛋白水平之间的关系；3)明确导致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.