Molecular Epidemiology of Human Cancer

我们研究的主要目标是确定当前，前和被动吸烟者中患肺癌风险最高的个体。吸烟仍然是一个主要的公共卫生问题，不仅在美国，而且是全世界的。肺癌风险的分子流行病学的两个主要方面是：第一，致癌物暴露的评估，包括影响的生物标志物;第二，遗传或获得的宿主癌症易感性因素。我们利用病例对照和病例系列策略来研究肺癌风险中基因-环境相互作用的假设。我们有一个多层次的策略来进行假设驱动的研究。 最近的分子流行病学研究已经确定了XPD基因的多态性与脑胶质瘤和头、颈、肺和皮肤癌的风险增加有关。然而，这些多态性变体在改变细胞过程如细胞周期检查点、DNA修复和细胞凋亡中的功能意义尚不确定。然后，我们对来自6个CEPH/犹他州家系和1个CEPH/法国家系的34种不同的淋巴母细胞样细胞系进行了密码子751和312多态性的基因分型，评估了它们在UV或IR暴露后的凋亡反应。细胞凋亡率，而在密码子312处具有纯合或杂合Asp的细胞系具有相似的细胞凋亡率，在密码子312处具有纯合Asn的细胞系显示对UV的响应增加2.5倍（p=0.005;学生t检验）。这是我们已知的第一个报告的功能多态性基因参与DNA损伤诱导的细胞凋亡。然而，在密码子751处存在赖氨酸或谷氨酰胺并不影响对UV的凋亡反应。含有312 Asp等位基因的细胞的凋亡反应减弱可以允许致癌物损伤细胞的存活和选择性克隆扩增，并且是不同组织部位癌症风险增加的机制解释。 体细胞p53突变在肺癌中很常见。主动吸烟与p53突变和非转录（DNA编码）链上G：C至T：A颠换的总频率呈正相关。p53基因内的突变热点，例如，密码子157，已被确定为烟草相关的肺癌，而这些相同的突变很少在其他癌症中发现。这些数据暗示特定的p53突变是吸烟的分子标记。由于关于戒烟者和非吸烟者p53突变频率和谱的数据有限，我们分析了来自密苏里州的非吸烟（n = 117）或戒烟（n=9）妇女的基于人群的病例对照研究中126例肺癌的p53和K-ras突变，并对暴露于环境烟草烟雾进行了定量评估。p53基因突变见于终生不吸烟者（19%）和既往吸烟者（67%;比值比，9.08; 95%置信区间，2.06-39.98）的肺癌。所有的缺失都发现于曾经吸烟或接触被动吸烟的非吸烟者的肿瘤中。G：C到A：T的转换（28个中的11个; 39%）是最常见的p53突变，并聚集在肿瘤中的终身非吸烟者无被动吸烟暴露。K-ras密码子12或13突变的发生率为11%（14/115），长期戒烟者和非吸烟者之间没有差异。这些和其他结果表明，p53突变发生在吸烟者和戒烟者比从不吸烟者更常见。这种比较为肺癌发生过程中烟草烟雾引起的遗传损伤提供了额外的证据。 p53突变在肺癌中很常见。在吸烟相关的肺癌中，热点密码子处G：C到T：A颠换的发生，例如，157、248、249和273，与烟草烟雾中致癌化学物质的存在有关，包括多环芳烃，如苯并（a）芘（BP）。在本研究中，我们使用了一种高灵敏度的突变试验，以确定p53突变负荷在非肿瘤的人肺，并研究p53密码子157，248，249和250的突变性苯并（a）芘二醇环氧化物（BPDE），BP在人支气管BEAS-2B细胞的活性代谢产物。我们测定了非肿瘤外周肺组织中p53密码子157、248、249和250的突变负荷，这些组织来自吸烟者中的肺癌病例或吸烟者和非吸烟者中的非癌症对照。与非癌症对照组相比，在癌症病例（n=14）的非肿瘤样品（57%）中发现密码子157处的GTCval至TTCphe颠换的频率高5-15倍（n=8; p<0.01）。这些肺癌病例的肿瘤组织（38%）含有p53突变，但与上述非肿瘤对中发现的突变不同。暴露于0.125、0.5和1.0 μ m BPDE剂量的BEAS-2B支气管上皮细胞在密码子157处显示G：C至T：A颠换，频率分别为3.5 x 10-7、4.4 x 10-7和8.9 x 10-7。在DMSO处理的对照中未发现密码子157处的突变。这些数据与以下假设一致：香烟烟雾中的化学致癌物（如BP）导致p53密码子157、248和249处的G：C至T：A颠换，并且肺癌吸烟者的非肿瘤肺组织在这些密码子处携带高p53突变负荷。

The primary goal of our studies is to identify individuals with the highest risk of lung cancer among current, ex-, and passive-smokers. Tobacco smoking continues to be a major public health problem, not only in the U.S., but also worldwide. The two major facets of the molecular epidemiology of lung cancer risk are first, the assessment of carcinogen exposure including biomarkers of effect, and second, the inherited or acquired host cancer susceptibility factors. We utilize both case-control and case-series strategies to investigate hypotheses of gene-environment interactions in lung cancer risk. We have a multi-tiered strategy for conducting our hypotheses-driven studies. Recent molecular epidemiological studies have identified polymorphisms in the XPD gene that are associated with increased risk of brain gliomas and head, neck, lung, and skin cancers. However, the functional significance of these polymorphic variants in altering cell processes such as cell cycle checkpoints, DNA repair, and apoptosis, is uncertain. We then genotyped 34 different lymphoblastoid cell lines from six CEPH/Utah pedigree families and a CEPH/French pedigree family for polymorphisms at codons 751 and 312, as assessed their apoptotic response after either UV or IR exposure. The apoptotic rates, whereas cell lines with homozygous or heterozygous Asp at codon 312 have similar apoptotic rates, cell lines with homozygous Asn at codon 312 showed a 2.5-fold increased response to UV (p=0.005; Student's t-test). This is the first report known to us of a functional polymorphism in a gene involved in DNA damage-induced apoptosis. The presence of Lys or Gln at codon 751, however, did not influence the apoptotic response to UV. The diminished apoptotic response of cells containing the 312 Asp allele could both allow the survival and selective clonal expansion of carcinogen-damaged cells, and be a mechanistic explanation for the increased risk of cancer at diverse tissue sites. Somatic p53 mutations are common in lung cancer. Active cigarette smoking is positively correlated with the total frequency of p53 mutations and G:C to T:A transversions on the nontranscribed (DNA coding) strand. Mutational hotspots within the p53 gene, e.g., codon 157, have been identified for tobacco-related lung cancer, whereas these same mutations are found rarely in other cancers. Such data implicate specific p53 mutations as molecular markers of smoking. Because limited data exist concerning the p53 mutation frequency and spectra in ex-smokers and nonsmokers, we have analyzed p53 and K-ras mutations in 126 lung cancers from a population-based case-control study of nonsmoking (n-117) or ex-smoking (n=9) women from Missouri with quantitative assessments of exposure to environmental tobacco smoke. Mutations in the p53 gene were found in lung cancers from lifetime nonsmokers (19%) and ex-smokers (67%; odds ratio, 9.08; 95% confidence interval, 2.06-39.98). All deletions were found in tumors from patients who were either ex-smokers or nonsmokers exposed to passive smoking. The G:C to A:T transitions (11 of 28; 39%) were the most frequent p53 mutations found and clustered in tumors from lifetime nonsmokers without passive smoke exposure. The incidence of K-ras codon 12 or 13 mutations was 11% (14 of 115 analyzed) with no difference between long-term ex-smokers and nonsmokers. These and other results indicate that p53 mutations occur more commonly in smokers and ex-smokers than in never-smokers. Such comparisons provide additional evidence of genetic damage caused by tobacco smoke during lung carcinogenesis. p53 mutations are common in lung cancer. In smoking-associated lung cancer, the occurrence of G:C to T:A transversions at hotspot codons, e.g., 157, 248, 249, and 273, has been linked to the presence of carcinogenic chemicals in tobacco smoke including polycyclic aromatic hydrocarbons such as benzo(a)pyrene (BP). In the present study, we have used a highly sensitive mutation assay to determine the p53 mutation load in nontumorous human lung and to study the mutability of p53 codons 157, 248, 249, and 250 to benzo(a)pyrene-diol-epoxide (BPDE), an active metabolite of BP in human bronchial BEAS-2B cells. We determined the p53 mutational load at codons 157, 248, 249, and 250 in nontumorous peripheral lung tissue either from lung cancer cases among smokers or noncancer controls among smokers and nonsmokers. A 5-15-fold higher frequency of GTCval to TTCphe transversions at codon 157 was found in nontumorous samples (57%) from cancer cases (n=14) when compared with noncancer controls (n=8; p<0.01). Tumor tissue from these lung cancer cases (38%) contained p53 mutations but were different from the above mutations found in the nontumorous pair. BEAS-2B bronchial epithelial cells exposed to doses of 0.125, 0.5, and 1.0 um BPDE, showed G:C to T:A transversions at codon 157 at a frequency of 3.5 x 10-7, 4.4 x 10-7, and 8.9 x 10-7, respectively. No mutations at codon 157 were found in the DMSO-treated controls. These data are consistent with the hypothesis that chemical carcinogens such as BP in cigarette smoke causes G:C to T:A transversions at p53 codons 157, 248, and 249, and that nontumorous lung tissues from smokers with lung cancer carry a high p53 mutational load at these codons.