Abstract: Objective: To observe the expression of forkhead box protein 3(FOXP3) in human lung adenocarcinoma tissue and the effects of FOXP3 on the cell proliferation and the chemosensitivity to cisplatin in the lung adenocarcinoma cells,and to elucidate the relevant mechanism of the resistance of lung adenocarcinoma cells to cisplatin. Methods: A total of 50 paraffin-embedded samples of cancer tissue of the patients with lung adenocarcinoma and 10 normal lung tissue samples were selected. The expressions of FOXP3 and Ki-67 in the lung adenocarcinoma and normal lung tissues were detected by immunohistochemistry,the difference in the positive expression rates of FOXP3 between lung adenocarcinoma and normal lung tissues was analyzed,and the correlation between the expressions of FOXP3 and Ki-67 was analyzed by Pearson correlation analysis.The human lung adenocarcinoma A549 cells at the logarithmic phase were transfected with siRNAs,and the A549 cells were divided into Mock group (transfected with liposome),Control-siRNA group (transfected with Control-siRNA) and FOXP3-siRNA group (transfected with FOXP3-siRNA).RT-qPCR and Western blotting methods were used to detect the expression levels of FOXP3 mRNA and protein in the A549 cells in various groups,and CCK-8 method was used to detect the proliferation activities of cells in various groups and the inhibitory rates of proliferation of the A549 cells in various groups after treated with 0,0.63,1.25,and 2.50 mg·L^-1 cisplatin;RT-qPCR and Western blotting methods were used to detect the expression levels of FOXP3 mRNA and protein in the A549 cells after treated with cisplatin. Results: The positive expression rates of FOXP3 in lung adenocarcinoma tissue and normal lung tissue were 62.0% and 13.3%,and the difference was statistically significant(P<0.05);the expression of FOXP3 in lung adenocarcinoma tissue was positively correlated with the expression of Ki-67 in lung adenocarcinoma tissue (r=0.370,P<0.01). The expression levels of FOXP3 mRNA and protein in the A549 cells in FOXP3-siRNA group were significantly decreased compared with Mock group and Control-siRNA group (P<0.01);the proliferation activities of A549 cells in FOXP3-siRNA group were significantly decreased compared with Mock group and Control-siRNA group after treated with cisplatin for 48 and 72 h (P<0.05);the inhibitory rates of proliferation of A549 cells in FOXP3-siRNA group were significantly higher than those in Mock group and Control-siRNA group after treatment with 1.25,2.50 and 5.00 mg·L^-1 cisplatin (P<0.05).The expression levels of FOXP3 mRNA and protein in the A549 cells in 1.25 and 2.50 mg·L^-1 cisplatin groups were both higher than those in 0 mg·L^-1 cisplatin group (P<0.05). Conclusion: Silencing FOXP3 can inhibit the levels proliferation and increase the chemosensitivity to cisplatin of the lung adenocarcinoma cells.

Key words: lung adenocarcinoma, forkhead box protein 3, Ki-67, cisplatin, chemosensitivity