Cigarette smoke induces demethylation of prometastatic oncogene synuclein-γ in lung cancer cells by downregulation of DNMT3B

Abstract

The prometastatic oncogene synuclein-c (SNCG) is not expressed in normal lung tissues, but it is highly expressed in lung tumors. Here, we show that cigarette smoke extract (CSE) has strong inducing effects on SNCG gene expression in A549 lung cancer cells through demethylation of SNCG CpG island. CSE treatment also augments the invasive capacity of A549 cells in an SNCG-dependent manner. To elucidate the mechanisms underlying the demethylating effects of CSE, we examined expression levels of DNA methyltransferases (DNMTs), 1, 3A and 3B in CSE-treated cells. We show that the mRNA expression of DNMT3B is specifically downregulated by CSE with a kinetics concurrent to SNCG reexpression. Utilizing siRNA to knockdown DNMT3B expression, we show that inhibition of DNMT3B directly increases SNCG mRNA expression. We further show that exogenous overexpression of DNMT3B in an SNCG-positive lung cancer cell line H292 suppresses SNCG mRNA and protein expression and induces de novo methylation of SNCG CpG island, whereas overexpression of DNMT1 or DNMT3A has no effects. Taken together, these new findings demonstrate that tobacco exposure induces the abnormal expression of SNCG in lung cancer cells through downregulation of DNMT3B. This work sheds light on the molecular understanding of demethylation of this oncogene during cancer progression.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone Induces Retinoic Acid Receptor β Hypermethylation through DNA Methyltransferase 1 Accumulation in Esophageal Squamous Epithelial Cells

“…But the detailed molecular mechanism is not yet fully understood. Liu et al (2007) showed that cigarette smoke extract (CSE) had a strong inducing effect on Synuclein-γ (SNCG) demethylation through the downregulation of DNMT3B in lung cancer cells. Zong et al (2009) treated ESCC cells with different concentrations of nicotine, and found cell migration and invasion could be enhanced, accompanied by increasing levels of COX2 protein and matrix metalloproteinase2 (MMP2) activity.…”

“…Tobacco contains more than 60 carcinogens (Hoffmann et al, 1990;Hecht et al, 2006) and tobacco exposure is known to induce genetic and epigenetic changes in esophageal squamous and lung cancer cells (Hecht et al, 1999;Soma et al, 2006;Liu et al, 2007;Lin et al, 2010;Huang et al, 2011). NNK is a key ingredient of tobacco smoke carcinogens.…”

Oxidative Stress and Chromatin Remodeling in Chronic Obstructive Pulmonary Disease and Smoking-Related Diseases

“…CS downregulates DNA methyltransferase 3B in alveolar A549 epithelial cells resulting in demethylation of the CpG island in the oncogene synucleingamma and leading to high expression of this prometastatic oncogene in A549 cells (78). Sood et al identified the promoter methylation from sputum samples of patients demonstrating wood smoke (biomass fuel burning) exposure associated with the COPD phenotype (decline in lung function, airflow obstruction, and chronic bronchitis), and smokers with aberrant p16 and GATA binding protein 4 methylation (136).…”

Prospects for Epigenetic Epidemiology

“…Cigarette smoking is associated with increased methylation at tumor suppressor genes in human case-control studies (116) and in mice (117) and with loss of methylation at oncogenes in human cancer cell lines (118). Disruption of DNMTs is implicated in the mechanism of induced change (118).…”