Abstract A16: Reversibly expressed and differentially methylated genes in airways of current and former smokers
Authors: Stewart Greg L. , Vucic Emily A. , Chari Raj , Wilson Ian M. , Lonergan Kim M. , Lam Steven , Lam Wan L. 
Published: January 2011

Background: Smoking-related disease, including chronic obstructive pulmonary disease (COPD) and lung cancer, account for the third greatest cause of mortality and the number one cause of cancer-related death worldwide. Former smokers (FS) remain at an elevated risk for both diseases and are the fastest growing population of newly diagnosed lung cancer patients, emphasizing the need for greater understanding of molecular mechanisms associated with smoking and smoking cessation. Cigarette smoke induces DNA damage in airway and lung tissues at the genomic and epigenomic levels, where it is associated with changes to gene expression. Studies on current (CS), FS, and never smokers have identified reversible and irreversible changes in gene expression that occur upon smoking cessation. Since methylation is a reversible gene regulatory mark that is also aberrantly affected by cigarette smoke, we hypothesize that the reversible nature of genes differentially expressed in bronchial epithelial cells in the airways of CS and FS, may be due to changes in DNA methylation.

Methods: Bronchial epithelial cells were obtained from brushings of small airways (&lt; 2mm diameter) during bronchoscopy from 12 current smokers (CS) and 6 former smokers (FS). Methylation profiles were generated for 27,579 probes corresponding to 14,575 genes, using the Illumina Infinium Human Methylation27 platform. Methylation results were aligned to the set of reversibly expressed genes described in previous studies. Genes that become either hypermethylated and underexpressed or hypomethylated and overexpressed upon smoking cessation were selected for further study.

Results: Methylation and expression analysis identified 9 genes overexpressed and hypomethylated in CS relative to FS, notably GPX2 and GSTA2 both involved in pathways previously shown to be upregulated in CS. These pathways include aryl hydrocarbon receptor signaling; a central metabolic pathway activated in response to halogenated and polycyclic aromatic hydrocarbons, and the NRF2 mediated oxidative stress response pathway, involved in the detoxification of reactive oxygen and intermediates. Additionally, 3 genes were found to be underexpressed and hypermethylated in CS relative to FS, notably SYF2 and CXCL6, involved in cell cycle regulation and inflammatory disease (including COPD) respectively.

Conclusion: Our data reveal a panel of genes whose change in gene expression upon smoking cessation may be regulated by DNA methylation, corresponding to well known genes involved in smoking metabolism and oxidative stress response. The identification of differentially methylated and expressed genes between CS and FS may provide insight into the mechanism of smoking related disease. As methylation is a reversible DNA modification, this knowledge may lead to the application of preventative epigenetic therapeutics for the growing population of FS and the immense health burden and mortality associated with cigarette smoke.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):A16.