Abstract 401: Array analysis of cigarette smoke condensate (CSC) on gene promoter methylation in human lung cells

Abstract

Abstract Lung cancer is the most common malignancy affecting both genders and remains the main cause of cancer-related deaths worldwide. Epidemiological studies indicate that cigarette smoking has a strong association, since approximately 80-90% of lung cancers are attributable to cigarette smoking. In lung cancer, epigenetic alterations such as promoter DNA methylation that leads to gene silencing are common events. A positive correlation between tobacco smoking and promoter hypermethylation in human lung cancer tissue has been demonstrated for many genes. However, the underlying mechanisms in tobacco-induced cancer and by which tobacco smoke disrupts a cell's capacity to maintain the normal epigenetic code during the malignant transformation are yet to be fully established. In the present study, the degree of promoter methylation across a defined panel of genes, reported to be altered in a variety of lung cancers, was evaluated in control and cigarette smoke condensate (CSC) exposed human lung cells using the Methyl-Profiler DNA Methylation PCR System technology. PSAE cells, a primary cell line, were exposed to 0.3 µg/ml or 1.0 µg/ml CSC for 72 hours and chronically for 14 days and 30 days. NL-20 cells, an immortalized cell line, were exposed chronically for 30 days at doses of 10 µg/ml and 100 µg/ml CSC. Promoters of several genes, hsa-let-7a-3, CHD1, CXCL12, PAX5, RASSF2, and TCF21, were identified as being highly methylated (>90%) after CSC exposure. Level of methylation tended to increase with dose and duration of exposure. The ability of the dietary agent genistein to modulate CSC-induced promoter methylation was also explored. Promoter methylation was assessed in the genes panel. Under the conditions employed, the percentage methylation of TCF21, which was >98% at exposures of 10 µg/ml or 100 µg/ml CSC, was reduced to 28% and 42%, respectively, in the presence of genistein. Using the array techniques, several tumor suppressors in human lung cells were identified whose promoter methylation can be increased upon exposure to CSC, providing further evidence of their potential involvement in tobacco smoke-induced lung carcinogenesis and may provide potential biomarkers of harm in tobacco smoke exposure. Results from the study also demonstrated the potential of dietary agents to exert chemopreventive activity in human tissue against tobacco smoke related diseases through modulation of DNA methylation. Additional studies are needed to confirm these findings, to screen other genes, and to further characterize the role and their impact of epigenetic changes in tumor suppressor genes in tobacco smoke-induced harm. Citation Format: Lascelles E. Lyn-Cook, Beverly Word, George Hammons. Array analysis of cigarette smoke condensate (CSC) on gene promoter methylation in human lung cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 401. doi:10.1158/1538-7445.AM2014-401