In Vitro Nicotine Exposure Induces microRNA-124 and Suppresses STAT3 Expression through the Alpha-7 Subtype of Nicotinic Acetylcholine Receptors in the SW-480 Cell Line

Nicotine is an alkaloid compound commonly found in tobacco smoke. This compound, as an agonist of nicotinic acetylcholine receptors (nAChRs), binds to these receptors and induces many downstream intracellular signaling pathways. Numerous studies have shown that nicotine leads to changes in the expression of microRNAs (miRs). Among these miRs, miR-124 is an essential post-transcriptional regulator of several cancer-related and inflammatory genes expression. The present study aimed to investigate the nicotine‑induced effects on miR-124 expression in colon cancer cell lines. First, the SW-480 colon carcinoma cell line was inoculated in 6-well plates to determine the effects of treatments with low and high concentrations of nicotine (1 and 10 μM) on the expression level of miR-124 and α7-subtype of nAChR (α7nAChR) and STAT-3 by quantitative real-time PCR. Next, the electroporation method was used to transfer specific siRNA targeting α7nAChR expression after identification of the optimum dose (60 nM) and time (48 h) of α7nAchR-siRNA. Following that, the changes in the expression of miR-124, α7nAChR, and STAT-3 were measured after transfection of the α7nAchR-siRNA in combination with nicotine treatment. The findings showed that nicotine increases the expression of both miR-124 and α7nAChR and decreases the STAT-3 mRNA expression. Transfection with α7nAChR-siRNA prevents the observed effects of nicotine which indicates that these effects of nicotine are α7nAChR dependent. Nicotine alters miR-124 expression in the SW-480 cell line and exerts its effects through the α7nAChR/miR-124/STAT-3 axis. Studying the exact molecular mechanism of nicotine signaling can be useful both in diagnosing and treatment of nicotine-related diseases and finding novel potential therapeutic benefits.