Molecular Epidemiology of Human Cancer

我们研究的主要目标是确定当前吸烟者、前吸烟者和被动吸烟者中肺癌风险最高的个体。吸烟仍然是一个主要的公共健康问题，不仅在美国，而且在全世界。肺癌风险分子流行病学的两个主要方面是：一是致癌物暴露的评估，包括生物标志物的影响；二是遗传或获得性宿主癌症易感因素。我们采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发现，XPD基因的多态性与脑胶质瘤、头颈部、肺癌和皮肤癌的风险增加有关。然而，这些多态变异在改变细胞过程（如细胞周期检查点、DNA修复、细胞凋亡）中的功能意义尚不确定。然后，我们对来自6个CEPH/犹他家系和一个CEPH/法国家系的34个不同的淋巴母细胞系进行基因分型，检测密码子751和312的多态性，以评估它们在紫外线或红外照射后的凋亡反应。而密码子312纯合或杂合的Asp细胞株的凋亡率相似，而密码子312纯合的Asn细胞株对紫外线的反应增加了2.5倍（p=0.005；学生t检验）。这是我们所知的第一个涉及DNA损伤诱导的细胞凋亡的基因功能多态性的报告。然而，密码子751上的Lys或Gln的存在并不影响细胞对紫外线的凋亡反应。含有312 Asp等位基因的细胞的凋亡反应减弱，可能既允许致癌物质损伤细胞的存活和选择性克隆扩增，也可能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。吸烟与p53突变的总频率和非转录链（DNA编码链）上G:C到T:A的转换呈正相关。p53基因内的突变热点，如密码子157，已被确定为烟草相关肺癌，而这些相同的突变在其他癌症中很少发现。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中p53突变频率和谱的数据有限，我们分析了来自密苏里州不吸烟（n-117）或戒烟（n=9）妇女的126例肺癌中的p53和K-ras突变，并对环境烟草烟雾暴露进行了定量评估。在终生不吸烟者（19%）和戒烟者（67%）的肺癌患者中发现p53基因突变；优势比为9.08；95%可信区间为2.06-39.98。所有的基因缺失都发生在曾经吸烟或不吸烟的被动吸烟患者的肿瘤中。G:C到A:T的转变（28个中的11个，39%）是最常见的p53突变，聚集在没有被动吸烟的终身不吸烟者的肿瘤中。K-ras密码子12或13突变的发生率为11%（分析115例中的14例），长期戒烟者和不吸烟者之间没有差异。这些和其他结果表明，p53突变在吸烟者和戒烟者中比在从不吸烟者中更常见。这种比较提供了在肺癌发生过程中烟草烟雾造成遗传损伤的额外证据。

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, 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, whereas 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 of 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.