Expression of the α7 nicotinic acetylcholine receptor in human lung cells -: art. no. 29

Background: We and others have shown that one of the mechanisms of growth regulation of small cell lung cancer cell lines and cultured pulmonary neuroendocrine cells is by the binding of agonists to the alpha 7 neuronal nicotinic acetylcholine receptor. In addition, we have shown that the nicotine-derived carcinogenic nitrosamine, 4( methylnitrosamino)-1-(3-pyridyl)-1-butanone(NNK), is a high affinity agonist for the alpha 7 nicotinic acetylcholine receptor. In the present study, our goal was to determine the extent of alpha 7 mRNA and protein expression in the human lung. Methods: Experiments were done using reverse transcription polymerase chain reaction ( RTPCR), a nuclease protection assay and western blotting using membrane proteins. Results: We detected mRNA for the neuronal nicotinic acetylcholine receptor alpha 7 receptor in seven small cell lung cancer (SCLC) cell lines, in two pulmonary adenocarcinoma cell lines, in cultured normal human small airway epithelial cells (SAEC), one carcinoid cell line, three squamous cell lines and tissue samples from nine patients with various types of lung cancer. A nuclease protection assay showed prominent levels of alpha 7 in the NCI-H82 SCLC cell line while alpha 7 was not detected in SAEC, suggesting that alpha 7 mRNA levels may be higher in SCLC compared to normal cells. Using a specific antibody to the alpha 7 nicotinic receptor, protein expression of alpha 7 was determined. All SCLC cell lines except NCI-H187 expressed protein for the alpha 7 receptor. In the non-SCLC cells and normal cells that express the alpha 7 nAChR mRNA, only in SAEC, A549 and NCI-H226 was expression of the alpha 7 nicotinic receptor protein shown. When NCI-H69 SCLC cell line was exposed to 100 pm NNK, protein expression of the alpha 7 receptor was increased at 60 and 150 min. Conclusion: Expression of mRNA for the neuronal nicotinic acetylcholine receptor alpha 7 seems to be ubiquitously expressed in all human lung cancer cell lines tested ( except for NCI-H441) as well as normal lung cells. The alpha 7 nicotinic receptor protein is expressed in fewer cell lines, and the tobacco carcinogen NNK increases alpha 7 nicotinic receptor protein levels.