IL-21/IL-21R inhibit tumor growth and invasion in non-small cell lung cancer cells via suppressing Wnt/β-catenin signaling and PD-L1 expression

Lung cancer is considered to be one of the world's deadliest diseases, with non-small cell lung cancer (NSCLC) accounting for 85% of all lung cancer cases. The present study aimed to investigate the role and underlying mechanisms of interleukin-21 (IL-21), and its receptor IL-21R, in NSCLC. Lung tissues and blood samples of NSCLC were used to measure IL-21, IL-21R and programmed death 1 ligand 1 (PD-L1) expression using ELISA, western blot and immunohistochemistry analyses. Following treatment with different doses of IL-21, the proliferation, invasion and migration of human NSCLC cell line A549 was evaluated using a cell counting kit-8, colony formation, Transwell and scratch wound healing assays, respectively. Additionally, IL-21R and PD-L1 expression in A549 cells was detected using western blot analysis and immunofluorescence. IL-21R silencing was subsequently used to investigate its effects in cell proliferation, invasion and migration. PD-L1, IL-1β and tumor necrosis factor α (TNF-α) expression were measured. Finally, Wnt/β-catenin signaling expression was evaluated using western blot analysis following treatment with IL-21. Cells were then treated with lithium chloride (LiCl), which is an agonist of Wnt/β-catenin signaling, and the levels of PD-L1, IL-1β and TNF-α were detected. The results revealed that IL-21 and IL-21R expression in the lung tissues and blood samples of patients with NSCLC were decreased, while PD-L1 expression was increased, compared with normal tissues or healthy controls. Treatment of A549 cells with IL-21 upregulated IL-21R expression, downregulated PD-L1 and inhibited cell growth and metastasis in a dose-dependent manner. Following IL-21R silencing, the effects of IL-21 treatment were reversed, suggesting that IL-21 acted on A549 cells through binding to IL-21R. In addition, the results demonstrated that IL-21 treatment reduced the expression levels of proteins associated with the Wnt/β-catenin signaling, whereas activation of Wnt/β-catenin signaling with the LiCl agonist upregulated PD-L1, IL-1β and TNF-α expression. In conclusion, the IL-21/IL-21R axis reduced the growth and invasion of NSCLC cells via inhibiting Wnt/β-catenin signaling and PD-L1 expression. The present results may provide a novel molecular target for NSCLC diagnosis and therapy.