S100A8/A9-RAGE pathway and chronic airway inflammation in smoke-induced lung carcinogenesis

Background Cigarette smoke-induced chronic airway inflammation increases the risk of lung cancer and plays a multifaceted role in lung cancer initiation and progression. The RAGE-ligand axis (HMGB1, S100A8/A9) contributes to cigarette smoke-induced persistent and progressive inflammation. The aim of the present study was to determine the inflammatory effect on the S100A8/A9-RAGE pathway in smoke-induced lung cancer carcinogenesis. Methods Human alveolar adenocarcinoma cells (A549) and normal bronchial epithelial cells (BEAS-2B) were co-cultured for 24 h with PBMCs and then were incubated in the presence or absence of 1.5% cigarette smoke extract (CSE) for 24 h. The cells were then transfected with siRNA targeting S100A8/9 or RAGE. Cell viability, colony-forming ability, migration, invasion, metastasis, and morphological changes were assessed. Female A/J mice were given benzo(a)pyrene (B(a)P; 100 mg/kg) in 0.1 mL of corn oil via oral gavage once a week for 3 weeks and administrated CSE (1.25 ul/g) intratracheally twice a week for 4 weeks. Tumor load was determined by averaging the total tumor volume in each group. Bronchoalveolar lavage (BAL) cells were differentiated and counted to analyze inflammatory cells present. Results Cell growth and colony formation were promoted by exposure to CSE and significantly inhibited by S100A8/9 and RAGE-siRNA transfection, especially in A549 cells compared to BEAS-2B cells. Cell migration, invasion, MMP-2/9 activity, and the mRNA and protein expression of TLR4, NF-κB, RAGE, S100A8/9, and HMBG1 were increased in CSE-exposed A549 cells. S100A8/9 and RAGE-siRNA transfection significantly attenuated those expressions. B(a)P induced an average tumor volume of 7.28 mm 3 per mouse, and CSE significantly increased the tumor volume (8.10 mm 3 ) compared to the B(a)P group. The total cell number and lymphocytes in BAL fluid tended to increase after CSE administration in the lung cancer mouse group. Moreover, CSE significantly induced the levels of S100A8/9, RAGE, p38, and ERK, and decreased JNK in serum and tumors compared to adjacent lung tissues ( p < 0.05). Conclusion Our study suggests that the S100A8/A9-RAGE signal pathway is the mainstream of the inflammation-immune response induced in cancer progression in CSE-related smoke-induced lung carcinogenesis in vitro and in vivo. Further studies are needed to identify the therapeutic targets of cigarette smoke-induced inflammation and immunosuppression in the tumor microenvironment.