Differential Expression of nicotinic acetylcholine receptor subunit genes in non-small cell lung cancers from smokers and non-smokers

Abstract

Background Nicotine and its derivatives, by binding to nicotinic acetylcholine receptors (nAChRs) on bronchial epithelial cells, can regulate cellular proliferation and apoptosis via the Akt pathway. Delineation of nAChR subtypes in non-small cell lung cancers (NSCLCs) may reveal molecular targets for tumor prevention or therapy. Materials and Methods Expression of nAChR α1, α3, α4, α5, α6, α7, α9, α10, β2, β3 and β4 subunit genes in 66 resected primary NSCLCs, 7 histologically normal lung tissues, 13 NSCLC cell lines and 6 human bronchial epithelial cell lines (HBECs) were analyzed by quantitative reverse transcription-polymerase chain reaction (q RT-PCR). Five non-malignant HBECs were exposed to nicotine in vitro to study the variation of nAChR subunit gene expression. Results nAChR α4 and β4 subunit gene expression showed significant differences (relatively low expression of α4 [p < 0.001] and relatively high expression of β4 [p = 0.029] in NSCLCs) between NSCLCs and normal lung. nAChR α5 (p = 0.022), α7 (p = 0.023), α9 (p = 0.001) and β2 (p = 0.037) subunit gene expressions demonstrated significantly higher expression in NSCLC cells compared to HBECs. NSCLCs from non-smokers showed significantly higher expression of nAChR α6 (p < 0.001) and β3 (p = 0.007) subunit genes than those from smokers, adjusted for gender. nAChR α1, α5 and α7 showed significant rise in expression levels at 72hrs of nicotine exposure which returned to baseline levels of expression after nicotine removal for another 72 hrs in HBECs. Conclusions Different nAChR subunit gene expression patterns were found in NSCLCs and normal lung, and between NSCLCs from smokers and non-smokers. Nicotine exposure in HBECs resulted in reversible differences in nAChR subunit gene expression. These results further implicate nicotine in bronchial carcinogenesis and suggest targeting nAChRs for prevention and therapy in lung cancer. (Supported by the Lung Cancer SPORE Grant P50CA70907 & the Hong Kong Special Administrative Region RGC grant 7468/04M.)