Abstract: Background and purpose: Cigarette smoke-induced inflammatory response remarkably promotes lung tumor growth. This study aimed to elucidate the mechanism of Wnt/β-catenin signaling activation by cigarette smoke in lung cancer cells. Methods: To understand the effect of cigarette smoke on mice, a kind of metastatic lung cancer mouse model which was established by intravenous injection of Lewis lung carcinoma cells. By immunohistochemical analysis, we analyzed the expression of CD68 (macrophage marker), TNF-α and unphosphorylated β-catenin in mice and human lung cancer samples. To coculture human lung adenocarcinoma cell line A549 cells with macrophages, the “Transwell® Inserts” system was used in coculturing model. The expressions of unphosphorylated β-catenin, phosphorylated GSK-3β and Akt in A549 cells were detected by Western blot assay. Results: The immunohistochemical results showed positive staining for CD68, TNF-α and unphosphorylated β-catenin increased significantly in smoke-exposed mice compared to air exposure mice. In human lung cancer samples, CD68 and TNF-α expressions were significantly higher than in healthy lung tissue. The positive staining rates of unphosphorylated β-catenin in lung adenocarcinoma and squamous cell carcinoma were 68.9% and 62.2%, respectively. This positive rate had a relationship with smoking status and tumor stage, there was statistical significance (both P<0.05). It also showed the number of CD68+ cells had a significant increase in tumors positive for unphosphorylated β-catenin (P<0.01). Western blot results showed that the expression of unphosphorylated β-catenin in A549 cells had a significant concentration-dependent increase of CSE after coculturing with macrophages. The neutralizing antibody against TNF-α could significantly suppressed unphosphorylated β-catenin in A549 cells. TNF-α exposure resulted in phosphorylation of GSK-3β and Akt in A549 cells after 2 h and the expression of unphosphorylated β-catenin increased 4 h later. Conclusion: Cigarette smoke induces TNF-α release from macrophages in lung tumor tissue, which could activate the Wnt/β-catenin pathway of tumor cells through Akt/GSK-3β.

Key words: Macrophages, Lung cancer, Tumor necrosis factor alpha, Wnt/β-catenin pathway