Promoter hypermethylation of the O6-methylguanine-DNA methyltransferase gene: more common in lung adenocarcinomas from never-smokers than smokers and associated with tumor progression.

Adenocarcinoma (AC) is the most common type of lung cancer diagnosed in the United States, comprising up to 40% of tumors in smokers and 50-80% of tumors in never-smokers. Exposures to cigarette smoke, direct or second-hand, and radiation in the form of radon progeny are the major risk factors for lung AC in both smokers and never-smokers. The goal of the current study was to determine the prevalence for O(6)-methylguanine-DNA methyltransferase (MGMT) promoter methylation in a large sample of central or peripheral ACs from smokers (n = 157), former uranium miners (n = 34), and never-smokers (n = 46). The mutation rate at codon 12 of the K-ras gene was determined to assess whether activation of this oncogene was associated with MGMT methylation. The overall prevalence for MGMT methylation was 51%. Significantly more tumors from never-smokers than smokers exhibited MGMT methylation (66 versus 47%, respectively). In contrast, exposure to radon through uranium mining did not affect the prevalence for methylation. The frequency of MGMT methylation was increased significantly in association with tumor stage. K-ras mutations were detected in 24% of all ACs and 22, 24, and 28% of tumors from never-smokers, smokers, and miners, respectively. Alterations in both the K-ras and MGMT genes were seen in only 11% of ACs. Kaplan-Meier survival estimates did not reveal any difference between patient survival with or without MGMT methylation. In contrast, survival was significantly reduced over the initial 60 months after diagnosis for patients with a transition mutation in the K-ras gene compared with those with a transversion mutation. This investigation demonstrates that MGMT promoter hypermethylation is a common event in the progression of early stage AC of the lung. We have shown that the incidence of MGMT methylation was significantly higher in never-smokers than smokers and have detected a higher frequency of mutations within the K-ras gene than previously reported in never-smokers. This study also suggests that K-ras activation is independent of MGMT methylation.

Aberrant promoter methylation in bronchial epithelium and sputum from current and former smokers.

Recent studies from our laboratory suggest that gene-specific methylation changes in sputum could be good intermediate markers for the early detection of lung cancer and defining the efficacy of chemopreventive interventions. The purpose of our study was to determine the prevalence for aberrant promoter methylation of the p16, O(6)-methylguanine-DNA methyltransferase (MGMT), death-associated protein (DAP) kinase, and Ras effector homologue (RASSFIA) genes in nonmalignant bronchial epithelial cells from current and former smokers in a hospital-based, case control study of lung cancer. The relationship between loss of heterozygosity, at 9p and p16 methylation in bronchial epithelium and the prevalence for methylation of these four genes in sputum from cancer-free, current and former smokers were also determined. Aberrant promoter methylation of p16 was seen in at least one bronchial epithelial site from 44% of cases and controls. Methylation of the DAP kinase gene was seen in only 1 site from 5 cases and 4 controls, whereas methylation of the RASSFIA was not detected in the bronchial epithelium. Promoter methylation for p16 and DAP kinase was seen as frequently in bronchial epithelium from current smokers as from former smokers. No promoter methylation of these genes was detected in bronchial epithelium from never-smokers. Methylation of the p16 gene was detected in sputum from 23 of 66 controls. DAP kinase gene promoter methylation was also seen in sputum from 16 controls, and 8 of these subjects were positive for p16 methylation. Methylation of the MGMT gene was seen in sputum from 9 controls, whereas RASSFIA promoter methylation was only seen in 2 controls. The correlation between p16 status in the bronchial epithelium obtained from lung lobes that did not contain the primary tumor and the tumor itself was examined. Seventeen of 18 tumors (94%) showed an absolute concordance, being either methylated in the tumor and at least 1 bronchial epithelial site, or unmethylated in both tumor and bronchial epithelium. These results indicate that aberrant promoter hypermethylation of the p16 gene, and to a lesser extent, DAP kinase, occurs frequently in the bronchial epithelium of lung cancer cases and cancer-free controls and persists after smoking cessation. The strong association seen between p16 methylation in the bronchial epithelium and corresponding primary tumor substantiates that inactivation of this gene, although not transforming by itself, is likely permissive for the acquisition of additional genetic and epigenetic changes leading to lung cancer.

Subchronic inhalation of soluble manganese induces expression of hypoxia-associated angiogenic genes in adult mouse lungs.

Although the lung constitutes the major exposure route for airborne manganese (Mn), little is known about the potential pulmonary effects and the underlying molecular mechanisms. Transition metals can mimic a hypoxia-like response, activating the hypoxia inducible factor-1 (HIF-1) transcription factor family. Through binding to the hypoxia-response element (HRE), these factors regulate expression of many genes, including vascular endothelial growth factor (VEGF). Increases in VEGF, an important biomarker of angiogenesis, have been linked to respiratory diseases, including pulmonary hypertension. The objective of this study was to evaluate pulmonary hypoxia-associated angiogenic gene expression in response to exposure of soluble Mn(II) and to assess the genes' role as intermediaries of potential pulmonary Mn toxicity. In vitro, 0.25 mM Mn(II) altered morphology and slowed the growth of human pulmonary epithelial cell lines. Acute doses between 0.05 and 1 mM stimulated VEGF promoter activity up to 3.7-fold in transient transfection assays. Deletion of the HRE within the promoter had no effect on Mn(II)-induced VEGF expression but decreased cobalt [Co(II)]-induced activity 2-fold, suggesting that HIF-1 may not be involved in Mn(II)-induced VEGF gene transcription. Nose-only inhalation to 2 mg Mn(II)/m(3) for 5 days at 6 h/day produced no significant pulmonary inflammation but induced a 2-fold increase in pulmonary VEGF mRNA levels in adult mice and significantly altered expression of genes associated with murine angiogenesis. These findings suggest that even short-term exposures to soluble, occupationally relevant Mn(II) concentrations may alter pulmonary gene expression in pathways that ultimately could affect the lungs' susceptibility to respiratory disease.

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

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.