Catechol-o-Methyltansferase and Breast Cancer

儿茶酚邻甲基转移酶与乳腺癌

• 批准号: 6779433
• 负责人: JAMES Donald YAGER
• 金额: $ 27.18万
• 依托单位: JOHNS HOPKINS UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-04-20 至 2008-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6779433
• 关键词: DNA damage; antiantibody; breast neoplasms; catechol methyltransferase; cell transformation; clinical research; conformation; enzyme activity; estrogens; gene targeting; genetically modified animals; genotype; high performance liquid chromatography; human tissue; laboratory mouse; lactation; mammary gland; methylation; neoplastic growth; nucleic acid purification; polymerase chain reaction; pregnancy; restriction fragment length polymorphism; western blottings

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.

描述(申请人提供)：乳腺癌的风险因素，包括长月经史、绝经后肥胖、使用激素替代疗法、未生育、首次怀孕年龄较晚、血清或尿液雌激素水平高，以及实验证据表明，它与长时间或改变的雌激素暴露有关。雌二醇(E_2)被氧化生物转化为邻苯二酚类雌激素(CES)。CES被氧化成对苯二酚，与DNA中的腺嘌呤和鸟嘌呤形成诱变加合物，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水平在乳腺组织中为10到20 pmoles/g，越来越多的证据支持CE在乳腺癌中的作用。CES主要由邻苯二酚-O-甲基转移酶(COMT)催化的O-甲基化失活。COMT是多态的，25%的高加索美国人是低活性COMT(COMTLL)的纯合子，COMTLL也是不耐热的。在一项遗传流行病学研究中，我们发现COMTLL基因型显著增加了体重指数较高的绝经后妇女患乳腺癌的风险。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产物失活的一种酶的多态性与乳腺癌风险的增加有关。随后，又进行了7项流行病学研究，结果喜忧参半，表明需要更多地了解CES和COMT在预防其潜在不良影响方面的作用机制。在本项目期内，我们观察到以下情况：1)COMT对CES引起的MCF-7细胞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动力学差异；3)COMTL酶活性在人体组织胞浆中的表型是由于较少的酶蛋白所致；4)COMTL的热稳定性研究表明，其不稳定性可能是由于其与细胞蛋白质存在的结合发生变化；以及5)某些叶酸途径微量营养素介导了COMT基因与乳腺癌风险之间的关联。本项目的目标仍然是“对COMT活性降低会导致DNA损伤增加从而导致细胞转化增加和乳腺癌这一假说进行严格的实验研究。下一个项目期的具体目标是：1)利用COMT基因敲除小鼠来确定COMT在小鼠乳腺发育和肿瘤发生中的作用；2)确认COMT基因和活性与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。