Distinct Roles of Cholinergic Receptors in Small Cell Lung Cancer Cells

Background: Cholinergic receptors are expressed in small cell lung cancer (SCLC); however, the distinct functions of muscarinic cholinergic receptor 3 (mAChR3) and the nicotinic cholinergic receptor (nAChR) in SCLC have not yet been completely elucidated. Materials and Methods: RTPCR and Western blotting were used to investigate the expression of cholinergic receptors. Flow cytometry was used to detect the integrin expression. Cell proliferation, adhesion and migration assays were carried out in vitro to determine the roles of the cholinergic receptors in SBC3 human SCLC cells. Results: Both mAChR3 and nAChR were expressed in the SBC3 cells. Acetylcholine iodide (Ach) stimulated SBC3 cell proliferation, adhesion and migration toward fibronectin (Fit). The mAChR3 antagonist, 4-diphenylocetox-N-methylpiperidine methiodide (4-DAMP), or the nAChR antagonist, mecamylamine hydrochloride (Meca), inhibited SBC3 cell proliferation in the presence or the absence of exogenous Ach. 4-DAMP abrogated cell adhesion and migration toward Fit induced by Ach, while Meca had no effect. Interestingly, Ach did not alter Fn receptor (alpha v beta 1 or alpha 5 beta 1 integrin) expression, while anti-beta 1 integrin antibody or anti-alpha v and anti-alpha 5 integrin antibody completely abrogated cell adhesion to Fit induced by Ach. Conclusion: Both mAChR3 and nAChR are expressed in SCLC. SBC3 cell proliferation is regulated in vitro through both cholinergic receptors. In contrast, SBC3 cell migration and adhesion toward Fit are modulated only by mAChR. Moreover, the stimulatory effects of Ach on cell adhesion and migration through mAChR3 are presumably modulated by functional alteration of alpha v beta 1 and alpha 5 beta 1 integrin, but not by any variation in their expression. The mAChR3 antagonist may therefore be a beneficial therapeutic modality for SCLC patients, especially those with chronic obstructive pulmonary disease (COPD) as a comorbidity.