Checkpoints, DNA repair & human carcinogenesis

该项目涉及细胞周期检查点和DNA修复基因在保护人类细胞免受超级基金致癌物诱发的突变和染色体异常方面的作用。“基因组的守护者”和肿瘤抑制基因p53现在已知在致癌物质受损的细胞中协调一系列复杂的检查点和DNA修复反应。激活P53功能的信号之一来自ATM激酶基因产物。ATM还向P53独立的细胞周期检查点发送信号。缺乏P53或ATM基因功能的细胞表现出遗传不稳定和恶性转化的易感性增加。这些细胞为防止人类致癌的DNA损伤反应系统提供了一个窗口。在许多超级基金废弃场中发现的一种人类致癌物质是氯乙烯(VC)。虽然不直接与DNA反应，但在吸收和代谢活化形成环氧氯乙烷(CEO)后，在DNA碱基上产生诱变的乙烯加合物。在工作场所接触VC的人中，有一小部分人在血淋巴细胞中表达了高频率的HPRT突变，而大多数接触VC的人没有。我们将通过评估CeO对敏感和耐药人群的淋巴母细胞系的遗传毒性，来测试这种高突变频率是否与DNA修复缺陷有关。超级基金废物场所的致癌物，如苯和苯并[a]芘，可以在细胞内代谢，分别产生活性亲电体，如苯二环氧化物，以及活性氧物种(ROS)。亲电体和ROS都可以攻击DNA产生的突变和染色体异常。该项目将确定P53和ATM是否能保护细胞免受CEO、ROS和二环氧化物的遗传毒性。乳腺癌风险的增加与参与DNA修复的基因突变有关，这些基因包括P53和ATM。这个项目将使用一种外周和淋巴细胞DNA修复能力的功能性测试，以测量辐射诱导的染色单体断裂的重新连接。这项试验将用于一项病例对照研究，以检验乳腺癌的发生与DNA修复缺陷有关的假设。在我们的病例对照研究中确定的敏感细胞将作为永生化的线，以确定超敏反应是否延伸到超级基金致癌物诱导的ROS。

This project concerns the roles of cell cycle checkpoint and DNA repair genes in protecting human cells from mutations and chromosomal aberrations induced by Superfund carcinogens. The "guardian of the genome" and tumor suppressor gene, p53, is now known to coordinate a complex set of checkpoint and DNA repair responses in carcinogen- damaged cells. Sone of the signals to activated p53 function come from the ATM kinase gene product. ATM also signals to p53-independent cell cycle checkpoints. Cells lacking p53 or ATM gene function display genetic instability and increased susceptibility to malignant transformation. Such cells provide a window to the systems of response to DNA damage that protect against human carcinogenesis. One human carcinogen found in many Superfund waste-sites is vinyl chloride (VC). Although not directly reactive with DNA, after absorption and metabolic activation to form chloroethylene oxide (CEO), mutagenic etheno adducts are produced on DNA bases. A subfraction of people exposed to VC in the workplace expressed high frequencies of hprt mutations in blood lymphocytes, while the majority of VC-exposed people did not. We will test whether this elevated mutation frequency is associated with a DNA repair defect by assessing CEO-induced genotoxicity in lymphoblastoid lines derived from sensitive and resistant people. Superfund waste-site carcinogens such as benzene and benzo[a]pyrene can be metabolized within cells to produce reactive electrophiles such as benzene- diolepoxide, respectively, as well as reactive oxygen species (ROS). The electrophiles and ROS both may attack DNA producing mutations and chromosomal aberrations. This project will determine whether p53 and ATM protect against genotoxicity by CEO, ROS, and diolepoxides. Enhanced risk of development of breast cancer has been linked to mutations in genes that participate in DNA repair including p53 and ATM. This project will employ a functional assay for DNA repair capacity in peripheral and lymphocytes that measures rejoining of radiation-induced chromatid breaks. This assay will be used in a case- control study to test the hypothesis that development of breast cancer is associated with a defect in DNA repair. Sensitive cells identified in our case control study will be available as immortalized lines to determine whether hypersensitivity extends to ROS induced by Superfund carcinogens.