Nicotine-induced PD-L1 expression in lung squamous cell carcinoma is mediated by the α7-nAChR/STAT3 signaling pathway.

Background: Nicotine, the principal addictive component of tobacco smoke, promotes lung cancer cell proliferation via α7 nicotinic acetylcholine receptors (α7-nAChRs). Programmed death-ligand 1 (PD-L1) serves as a crucial predictive biomarker for immune checkpoint inhibitor (ICI) therapy in lung squamous cell carcinoma (LUSC). This study aimed to investigate the expression patterns of α7-nAChR and its encoding gene CHRNA7 in LUSC tissues, and to evaluate their associations with PD-L1 expression.

Methods: CHRNA7 expression, its correlation with clinicopathological features, and survival outcomes in LUSC were analyzed using The Cancer Genome Atlas (TCGA) database and Kaplan-Meier plotter. The expression levels of α7-nAChR and PD-L1 in LUSC tissues and cell lines were evaluated by immunohistochemistry and Western blot (WB). Following nicotine stimulation and small interfering RNA (siRNA) transfection, messenger RNA (mRNA) expression levels of CHRNA7, signal transducer and activator of transcription 3 (STAT3), and CD274 (PD-L1) were quantified using quantitative real-time polymerase chain reaction (qRT-PCR), while their protein levels were assessed by WB.

Results: CHRNA7 expression was significantly elevated in LUSC tissues and cell lines compared to adjacent normal tissues and bronchial epithelial cell lines (P<0.05), and correlated with smoking status. Higher CHRNA7 expression was associated with shorter overall survival. Nicotine stimulation (1.0 μM) significantly increased the mRNA expression levels of CHRNA7, STAT3, and CD274 in LUSC cell lines. Knockdown of siRNA-mediated CHRNA7 in LUSC cell lines decreased STAT3 phosphorylation (pSTAT3) and PD-L1 protein levels, while attenuating nicotine-induced PD-L1 upregulation. STAT3 silencing had no significant effect on α7-nAChR protein expression but downregulated PD-L1 protein levels and attenuated nicotine-induced PD-L1 upregulation.

Conclusions: α7-nAChR and its encoding gene CHRNA7 are upregulated in LUSC tissue and are associated with smoking status. Patients with high expression of CHRNA7 have a relatively worse prognosis. Nicotine may upregulate PD-L1 expression in LUSC through the α7-nAChR/STAT3 pathway.