Activation of muscarinic acetylcholine receptors inhibits cell cycle progression of small cell lung carcinoma

We previously reported that activation of muscarinic acetylcholine receptors (mAChR) of M₃ subtype causes hydrolysis of phosphoinositides and inhibits voltage-gated Ca²⁺ channel activity in small cell lung carcinoma (SCLC) cells. We now report that mAChR activation causes exponentially growing SCLC cells to arrest in S and G₂/M phases of the cell cycle, concomitant with a decrease in DNA synthesis. Cell cycle progression and DNA synthesis resume when mAChR are down-regulated. In serum-starved SCLC cells, mAChR activation inhibits DNA synthesis induced by serum, bombesin, insulin, or insulin-like growth factor-I. The finding that DNA synthesis is inhibited even when mAChR are activated after exposure of cells to growth factors indicates that decreased signal transduction by growth factor receptors is not the mechanism of mAChR-mediated growth inhibition. Our data suggest that mAChR activation disrupts a common event that is induced by different growth factors and is fundamental for cell cycle progression.