Nicotine downregulates miR-375-3p via neurotrophic tyrosine receptor kinase 2 to enhance the malignant behaviors of laryngopharyngeal squamous epithelial cells

Nicotine exposure from smoking constitutes a significant global public health concern. Furthermore, smoking represents a pivotal risk factor for head and neck squamous cell carcinoma (HNSCC). However, the influence of nicotine on HNSCC remains relatively underexplored. Our aim was to unravel the molecular mechanisms that underlie the effect of nicotine on the metastatic cascade of HNSCC. In this study, we discovered a significant association between smoking and HNSCC metastasis and prognosis. Nicotine significantly enhanced HNSCC cell proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) in vitro. Analysis of TCGAHNSCC and FDEENT-HNSCC cohorts revealed reduced miR-375-3p levels in HNSCC tumor tissues, particularly among current smokers. Additionally, miR-375-3p level was strongly correlated with both lymph node metastasis and tumor stage. By downregulating miR-375-3p, nicotine promotes HNSCC cell metastasis in vitro and hematogenous metastatic capacity in vivo. Utilizing transcriptomic sequencing, molecular docking, dualluciferase reporter assay, and fluorescence in situ hybridization (FISH), we demonstrated that miR-375-3p specifically binds to 3 ' untranslated region (3'UTR) of NTRK2 mRNA. Thus, this study uncovers a novel nicotineinduced mechanism involving miR-375-3p-mediated NTRK2 targeting, which promotes HNSCC metastasis. These findings have implications for improving the prognosis of patients with HNSCC, especially in smokers.