Quantitative analysis of DNA methylation profiles in lung cancer identifies aberrant DNA methylation of specific genes and its association with gender and cancer risk factors

摘要

The global rise in lung cancer burden, together with its poor survival and resistance to classical chemotherapy underscores the need for identification of critical molecular events involved in lung carcinogenesis. Here, we have applied quantitative profiling of DNA methylation states in a panel of five cancer-associated genes (CDH1, CDKN2A, GSTP1, MTHFR and RASSF1A) to a large case-control study of lung cancer. Our analyses revealed a high frequency of aberrant hypermethylation of MTHFR, RASSF1A and CDKN2A in lung tumours as compared to control blood samples, whereas no significant increase in methylation levels of GSTP1 and CDH1 was observed, consistent with the notion that aberrant DNA methylation occurs in a tumour-specific and gene-specific manner. Importantly, we found that tobacco smoking, sex, and alcohol intake had a strong influence on the methylation levels of distinct genes (RASSF1A and MTHFR), whereas folate intake, age and histological subtype had no significant influence on methylation states. We observed a strong association between MTHFR hypermethylation in lung cancer and tobacco smoking, whereas methylation levels of CDH1, CDKN2A, GSTP1 and RASSF1A were not associated with smoking, indicating that tobacco smoke targets specific genes for hypermethylation. We also found that methylation levels in RASSF1A, but not the other genes under study, were influenced by sex, with males showing higher levels of methylation. Together, this study identifies aberrant DNA methylation patterns in lung cancer and thus exemplifies the mechanism by which environmental factors may interact with key genes involved in tumour suppression and contribute to lung cancer.