Multiplicity of abnormal promoter methylation in lung adenocarcinomas from smokers and never smokers

Abstract

The prevalence of methylation of the p16, DAPK and RASSF1A genes was investigated in lung adenocarcinoma from smokers, former uranium miners and never smokers. The association between a common genetic alteration in adenocarcinoma, mutation of the K-ras gene and methylation of these genes, as well as survival was examined. Adenocarcinomas from 157 smokers, 46 never smokers and 34 former uranium miners were evaluated for methylation of the p16, DAPK and RASSF1A genes using the methylation-specific PCR assay. Comparisons were also made to prevalences of methylation of the MGMT gene and mutation of the K-ras gene previously examined in these tumors. The prevalence of methylation for all genes was similar between adenocarcinomas from smokers and never smokers, although the prevalence for methylation of the p16 gene tended to be higher in smokers compared to never smokers. A significantly higher prevalence for p16 methylation was seen in central vs. peripheral lung tumors. At least 1 gene was methylated in 35% of stage I tumors, whereas 2 and >3 genes were methylated in 40% and 16% of tumors, respectively. Methylation of all genes was independent of K-ras mutation, whereas methylation of the DAPK and RASSF1A genes was positively associated. Environmental tobacco smoke, the strongest lung cancer risk factor among never smokers, induces adenocarcinoma in part through inactivation of the p16, DAPK and RASSF1A genes. Adenocarcinomas may develop through 2 distinct processes: multiple gene inactivations through promoter hypermethylation and activation of the K-ras gene.

CpG Site–Specific Hypermethylation of p16INK4α in Peripheral Blood Lymphocytes of PAH-Exposed Workers

“…INK4a methylation were also observed in smokers (20) and in human lung cancer associated with chromate exposure (21). Consistent with the results from patients with lung cancers, the frequency of p16…”

“…When analyzing the difference at each CpG site between 2 groups using a Mann-Whitney U test, we found that 22 sites located at No. 1,2,8,9,11,12,17,18,[20][21][22][23][24], and 26-34 were significantly higher in PAH-exposed workers (Fig. 2B), indicating that these 22 CpG sites might be the regulatory "hot CpG sites" participating in gene transcriptional suppression.…”

Gene Promoter Hypermethylation in Mouse Lung Tumors

“…The etiology for lung cancer in the never-smoker may be due to in part to exposure to environmental tobacco smoke and other environmental and occupational carcinogens (e.g., radon). Although these exposures cannot account for spontaneous tumors in the mouse lung, it is interesting that these tumors develop in part through inactivation of genes, such as ER-a, DAPK, RAR-h, and H-cadherin, which are also silenced in adenocarcinomas from the never-smoker (9,20,30,31).…”

“…A nested, two-stage approach was used (30) to increase the efficiency for gene amplification, thereby allowing the determination of methylation state in samples whose DNA has been degraded through formalin fixation and/or long-term storage in paraffin. Stage 1 primers amplify both methylated and unmethylated alleles of the genes being analyzed.…”

Genome-scale meta-analysis of DNA methylation during progression of lung adenocarcinoma

“…One of the hallmarks of cancer is aberrant DNA methylation; however, its precise role in carcinogenesis and clinical prognosis remains unclear (Baylin and Jones, 2011). Although multiple studies have attempted to assess the methylated gene profiles in lung cancer (Shiraishi et al, 2002;Divine et al, 2005;Feng et al, 2008;Tsou et al, 2008;Anglim et al, 2008;Buckingham et al, 2010), they have either included a limited number of samples or genes assayed or have focused on a mix of lung cancer histologies and different stage tumors, limiting the ability to identify dynamic changes in DNA methylation during carcinogenesis.…”