Jarmalaite Sonata, Kannio Annamaria, Anttila Sisko, Lazutka Juozas R, Husgafvel-Pursiainen Kirsti
Department of Industrial Hygiene and Toxicology, Finnish Institute of Occupational Health, Helsinki, Finland.
Int J Cancer. 2003 Oct 10;106(6):913-8. doi: 10.1002/ijc.11322.
Hypermethylation of cytosines in CpG-rich islands of the promoter regions of regulatory genes has been discovered as a common mechanism of gene silencing during carcinogenesis. We analysed 64 primary lung carcinomas for promoter methylation of the tumour suppressor genes (TSGs) p16 (p16(INK4a)/CDKN2A) and p14 (p14(ARF)) by methylation-specific PCR, in order to evaluate aberrant methylation as a potential biomarker for epigenetic alterations in tobacco-related lung cancer. Methylation of p16 was observed in 34% (22/64) of the lung tumours examined. In particular, p16 methylation occurred in nonsmall cell lung cancer (NSCLC) only, with 41 % (22/54) of the tumours being positive. The highest frequency was found in large cell carcinoma (5/7, 71%), followed by adenocarcinoma (9/25, 36%) and squamous cell carcinoma (7/21, 33%). Methylation of the p14 gene was less frequent in lung cancer (4/52, 8%). When association with tobacco smoking was analysed, 42% (21/50) of NSCLC from ever smokers exhibited p16 methylation. Interestingly, the analysis revealed a significantly higher risk of p16 methylation in former smokers as compared to current smokers [odds ratio (OR) 5.1; 95% confidence interval (CI) 1.3-22]. The difference was retained after adjustment for age (OR 3.7; 95% CI 0.9-17). The promoter methylation results were then combined with data on genetic alterations determined previously in the same set of tumours. This data similarly showed that p16 methylation in parallel with p53 gene mutation or p14 methylation occurred more frequently in former smokers than in current smokers (44% vs. 14%; P = 0.035). Taken together, our data suggest that analysis of promoter methylation in TSGs may provide a valuable biomarker for identification of groups with an elevated risk of cancer, such as smokers and ex-smokers.
在致癌过程中，调控基因启动子区域富含CpG岛的胞嘧啶发生高甲基化已被发现是基因沉默的常见机制。我们通过甲基化特异性PCR分析了64例原发性肺癌中肿瘤抑制基因（TSGs）p16（p16(INK4a)/CDKN2A）和p14（p14(ARF)）的启动子甲基化情况，以评估异常甲基化作为烟草相关肺癌表观遗传改变潜在生物标志物的可能性。在所检测的肺肿瘤中，34%（22/64）观察到p16甲基化。具体而言，p16甲基化仅发生在非小细胞肺癌（NSCLC）中，41%（22/54）的肿瘤呈阳性。在大细胞癌中发现的频率最高（5/7，71%），其次是腺癌（9/25，36%）和鳞状细胞癌（7/21，33%）。p14基因甲基化在肺癌中出现的频率较低（4/52，8%）。当分析与吸烟的相关性时，曾经吸烟者的NSCLC中有42%（21/50）表现出p16甲基化。有趣的是，分析显示，与当前吸烟者相比，既往吸烟者中p16甲基化的风险显著更高[优势比（OR）5.1；95%置信区间（CI）1.3 - 22]。在调整年龄后，差异仍然存在（OR 3.7；95% CI 0.9 - 17）。然后将启动子甲基化结果与先前在同一组肿瘤中确定的基因改变数据相结合。这些数据同样表明，与p53基因突变或p14甲基化同时发生的p16甲基化在既往吸烟者中比在当前吸烟者中更频繁出现（44%对14%；P = 0.035）。综上所述，我们的数据表明，分析TSGs中的启动子甲基化可能为识别癌症风险升高的人群（如吸烟者和既往吸烟者）提供有价值的生物标志物。
