Cigarette smoking is the main causative factor for Chronic Obstructive Pulmonary Disease (COPD) and lung cancer and the pathogenesis of these diseases is believed to be linked because individuals with COPD have a 2-4-fold higher risk of developing lung cancer. Epigenetic silencing of genes through promoter methylation of cytosines and histone modifications is now recognized as a major and causal event affecting expression of hundreds of genes during initiation and clonal development of lung cancer. Our initial nested, case-control study of incident cancer within a cohort of smokers with COPD showed that the concomitant methylation of three or more genes of a six gene panel was associated with a 6.5-fold increased risk for lung cancer. Extension of these studies in cancer-free smokers from the Lovelace Smokers Cohort (LSC) showed that a high methylation index (two or more genes methylated) and methylation of the p16 and GATA4 genes was associated with lower lung function. Studies also identified double-strand break repair capacity and specific genes within this pathway as determinants for gene methylation in sputum and that the proline variant at codon 72 of p53 is protective from mucous cell hyperplasia and decline of pulmonary function in the LSC. Based on these studies we hypothesize that the development of COPD mediated through tissue damage and remodeling will drive the epigenetic silencing of specific genes that in turn contribute to the development of lung cancer. The detection of these genes in sputum from smokers with COPD may provide new biomarkers for COPD development and progression, and early cancer detection.
Aim 1 will identify and validate signatures for methylation as a function of COPD status by comparing the methylome in adenocarcinoma from patients with and without COPD and assess the association by genotype of p53 codon 72.
Aim 2 will use primary human bronchial epithelial cells (BECs) from non smokers with the p53 codon 72 arginine versus proline genotype exposed chronically to cigarette smoke to identify genes and affected pathways with a focus on genes regulating tissue remodeling and apoptosis, and polycomb repressive complex 2 (PRC2) genes.
Aim 3 will analyze the prevalence for methylation of selected genes from Aims 1 and 2 in a nested, cross-sectional study of 200 subjects with COPD and 400 controls from the LSC and the prevalence for methylation will be validated in Pittsburgh Lung Screening Study (PLuSS) Cohort.
Aim 4 will determine whether methylation biomarkers found to be associated with COPD show increase in prevalence over time and predict for decline in pulmonary function. Methylation prevalence and methylation index among participants showing significant or no decline in pulmonary function over 3-4 years will be compared. Future studies will assess the genes validated under Aims 3 and 4 in sputum from subjects from a large nested lung cancer case-control study for their contribution to a developing genetic and epigenetic risk profile for early incident COPD and cancer detection. Together, the integrated results from these studies will provide novel insights into mechanisms that connect COPD to the development of lung cancer.
Identifying biomarkers for early detection of COPD and lung cancer is crucial for effective management of these deadly diseases. The proposed studies will provide new biomarkers for COPD development and progression and early lung cancer detection using sputum DNA from at risk patients. A non-invasive means of diagnosing patients with COPD and lung cancer will allow early detection and improve the management and treatment of these chronic and deadly diseases.
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