Factors for Epigenetic Silencing of Lung Cancer Genes

描述(申请人提供)：肺癌是美国男性和女性癌症相关死亡的主要原因。慢性吸烟者患肺癌的易感性可能与关键基因的胚系多态有关，关键基因涉及烟草致癌物造成的DNA损伤的生物激活、解毒和修复，以及随后在关键调控基因中获得的体细胞遗传和表观遗传变化。表观遗传学通过启动子高甲基化介导的基因沉默是一种常见的事件，对癌症的发生和发展至关重要。尚未对无癌症的男性和女性吸烟者进行基于人群的研究，以评估临床危险因素、生殖系和躯体变化之间的相互关系，以确定它们对肺癌发展的贡献。为了支持这一方法，我们已经证明，在临床诊断前3年，100%的鳞状细胞肺癌(SCCs)的痰DNA中可以检测到pl6和/或O6-甲基鸟嘌呤-DNA甲基转移酶(MGMT)启动子的异常甲基化。将这些发现扩展到嵌套的病例对照研究显示，所检查的四种甲基化标记中的任何一种的存在与发生肺癌的风险增加6.3倍相关。此外，我们进行了一项初步研究，以确定肺癌易感基因的胚系突变是否与非癌症高危受试者痰中p16和MGMT甲基化等位基因的存在有关。编码NAD(P)H-苯醌氧化还原酶和谷胱甘肽-S-转移酶P1基因的风险等位基因与p16或mgmt基因甲基化显著相关。这些发现将扩展到将代谢易感因素与遗传生物标记物和临床风险因素相结合，以更好地了解肺癌的病因。将通过一项横断面和纵向研究实现四个具体目标，研究对象包括1500名受试者，现有的两个吸烟者队列中的每一个750人，退伍军人队列中的2250人，以及女性队列中的1500人。第一个将确定参与烟草致癌物激活和解毒、氧化应激、DNA修复和CpG位点从头甲基化的基因的风险等位基因是否与痰中基因特异性启动子高甲基化有关。第二个目标将确定饮食和/或已确定的临床风险因素COPD和吸烟史是否与在痰中脱落细胞中检测到的DNA甲基化有关。第三个目标将确定包括吸烟在内的临床风险因素对甲基化模式的影响是否随着基因的不同而不同。最后，我们将描述研究开始时和18个月随访时的基因特异性启动子超甲基化模式。

DESCRIPTION (provided by applicant): Lung cancer is the leading cause of cancer-related death for men and women in the U.S. The susceptibility of the chronic smoker for developing lung cancer is likely linked to germ-line polymorphisms in critical genes involved in the bioactivation, detoxification, and repair of DNA damage stemming from tobacco carcinogens and the subsequent acquisition of somatic genetic and epigenetic changes in critical regulatory genes. Epigenetically mediated gene silencing through promoter hypermethylation is a common event that is critical for initiation and progression of cancer. Population-based studies of cancer-free male and female smokers have not been conducted to evaluate the interrelationships between clinical risk factors, germ-line, and somatic changes for their contribution to lung cancer development. In support of this approach, we have demonstrated that aberrant methylation of the pl6 and/or O6-methylguanine-DNA methyltransferase (MGMT) promoters can be detected in DNA from sputum in 100% of squamous cell lung carcinomas (SCCs) up to 3 years before clinical diagnosis. The extension of these findings to a nested, case-control study revealed that the presence of any one of four methylation markers examined was associated with a 6.3 fold increase in risk for incident lung cancer. In addition, we conducted a pilot study to determine whether germ-line mutations in lung cancer susceptibility genes are associated with the presence of methylated alleles of p 16 and MGMT in sputum from cancer-free, high-risk subjects. Risk alleles for the genes encoding the NAD(P)H quinone oxidoreductase and glutathione-S-transferase P1 genes were significantly associated with methylation of the pl6 or MGMT genes. These findings will be extended to integrate metabolic susceptibility factors with genetic biomarkers and clinical risk factors to better understand the etiology of lung cancer. Four specific aims will be accomplished through a cross-sectional and longitudinal study using 1500 subjects, 750 from each of the two existing cohorts of current and former smokers, a 2,250-person cohort of veterans, and a 1,500-person female cohort. The first will determine whether the risk alleles for genes involved in tobacco carcinogen activation and detoxification, oxidative stress, DNA repair, and de novo methylation of CpG sites are associated with gene-specific promoter hypermethylation in sputum. The second aim will determine whether diet and/or the established clinical risk factors COPD and smoking history are associated with DNA methylation detected in exfoliated cells within sputum. The third aim will determine whether the effect of clinical risk factors that include smoking on methylation patterns vary as a function of genotype. Finally we will describe the gene-specific promoter hypermethylation patterns at study entry and at 18-month follow-up.