Aberrant DNA methylation links cancer susceptibility locus 15q25.1 to apoptotic regulation and lung cancer

Abstract

Nicotinic acetylcholine receptor (nAChR) genes form a highly conserved gene cluster at the lung cancer susceptibility locus 15q25.1. In this study, we show that the CHRNα3 gene encoding the nAChRα3 subunit is a frequent target of aberrant DNA hypermethylation and silencing in lung cancer, whereas the adjacent CHRNβ4 and CHRNα5 genes exhibit moderate and no methylation, respectively. Treatment of cancer cells exhibiting CHRNα3 hypermethylation with DNA methylation inhibitors caused demethylation of the CHRNα3 promoter and gene reactivation. Restoring CHRNα3 levels through ectopic expression induced apoptotic cell death. Small hairpin RNA-mediated depletion of nAChRalpha;3 in CHRNalpha;3-expressing lung cancer cells elicited a dramatic Ca2+ influx response in the presence of nicotine, followed by activation of the Akt survival pathway. CHRNalpha;3-depleted cells were resistant to apoptosis-inducing agents, underscoring the importance of epigenetic silencing of the CHRNalpha;3 gene in human cancer. In defining a mechanism of epigenetic control of nAChR expression in nonneuronal tissues, our findings offer a functional link between susceptibility locus 15q25.1 and lung cancer, and suggest nAChRs to be theranostic targets for cancer detection and chemoprevention. ©2010 American Association for Cancer Research.