Toyooka Shinichi, Tokumo Masaki, Shigematsu Hisayuki, Matsuo Keitaro, Asano Hiroaki, Tomii Kunitoshi, Ichihara Shuji, Suzuki Makoto, Aoe Motoi, Date Hiroshi, Gazdar Adi F, Shimizu Nobuyoshi
Department of Cancer and Thoracic Surgery, Graduate School of Medicine and Dentistry, Okayama University, 2-5-1 Shikata-cho, Okayama 700-8558, Japan.
Cancer Res. 2006 Feb 1;66(3):1371-5. doi: 10.1158/0008-5472.CAN-05-2625.
Genetic and epigenetic alterations are considered to play important roles in lung cancer. Recent studies showed that EGFR and K-RAS mutations exhibited a mutually exclusive pattern in adenocarcinoma of the lung, suggesting the presence of two independent oncogenic pathways. However, it is unknown how epigenetic alterations were involved in lung carcinogenesis mediated by EGFR or K-RAS mutation. In this study, we examined the relationship between genetic and epigenetic alterations in 164 cases of lung adenocarcinoma. Somatic mutations were determined by direct sequence of EGFR exons 18 to 21 and K-RAS codons 12 and 13. Methylation status of p16(INK4a), RASSF1A, APC, RARbeta, and CDH13, frequently methylated in lung cancer, was determined by methylation-specific PCR and the degree of methylation was defined as the methylation index. Multivariate analysis adjusted for age, sex, and smoking dose showed that the probability of having EGFR mutation was significantly lower among those with p16(INK4a) and CDH13 methylation than in those without [p16(INK4a): odds ratio (OR), 0.07; 95% confidence interval (95% CI), 0.02-0.33; CDH13: OR, 0.34; 95% CI, 0.15-0.77] and the methylation index was significantly lower in EGFR mutant cases than in wild type (OR, 0.70; 95% CI, 0.52-0.95). By contrast, K-RAS mutation was significantly higher in p16(INK4a) methylated cases than in unmethylated cases (OR, 4.93; 95% CI, 1.54-15.7) and the methylation index was higher in K-RAS mutant cases than in wild type with marginal significance (OR, 1.46; 95% CI, 0.95-2.25). Our results indicate the differences in the evolvement of epigenetic alterations between the EGFR- and K-RAS-mediated tumorigenesis and suggest the specific interaction of genetic and epigenetic changes in tumorigenesis of lung cancer.
遗传和表观遗传改变被认为在肺癌中起重要作用。最近的研究表明，EGFR和K-RAS突变在肺腺癌中呈现相互排斥的模式，提示存在两条独立的致癌途径。然而，尚不清楚表观遗传改变如何参与由EGFR或K-RAS突变介导的肺癌发生过程。在本研究中，我们检测了164例肺腺癌中遗传和表观遗传改变之间的关系。通过对EGFR外显子18至21以及K-RAS密码子12和13进行直接测序来确定体细胞突变。通过甲基化特异性PCR确定肺癌中经常发生甲基化的p16(INK4a)、RASSF1A、APC、RARβ和CDH13的甲基化状态，并将甲基化程度定义为甲基化指数。对年龄、性别和吸烟量进行校正的多因素分析显示，p16(INK4a)和CDH13甲基化者中发生EGFR突变的概率显著低于未甲基化者[p16(INK4a)：比值比(OR)，0.07；95%置信区间(95%CI)，0.02 - 0.33；CDH13：OR，0.34；95%CI, 0.15 - 0.77]；EGFR突变病例的甲基化指数显著低于野生型(OR，0.70；95%CI，0.52 - 0.95)。相比之下, p16(INK4a)甲基化病例中K-RAS突变显著高于未甲基化病例(OR，4.93；95%CI，1.54 - 15.7)，K-RAS突变病例的甲基化指数高于野生型，具有边缘显著性(OR，1.46；95%CI，0.95 - 2.25)。我们的结果表明，EGFR和K-RAS介导的肿瘤发生过程中表观遗传改变的演变存在差异，并提示肺癌发生过程中遗传和表观遗传变化存在特定的相互作用。
