MicroRNA-155-5p promotes cell proliferation and invasion in lung squamous cell carcinoma through negative regulation of fibroblast growth factor 9 expression

BACKGROUND: Non-small cell lung cancer (NSCLC) ranks first for mortality among all malignancies. Squamous cell carcinoma (SCC) is one of the main types of NSCLC. Previous studies have found that fibroblast growth factor 9 (FGF9) is closely related to lung SCC via different molecular regulatory mechanisms. This study aimed to explore the relationship between microRNA-155-5p (miR-155-5p) and FGF9 gene expression and their effects on the proliferation and invasion of lung SCC through experiments, in order to provide theoretical basis for overcoming this disease. METHODS: Fluorescence quantitative polymerase chain reaction was employed for the detection miR-155-5p and FGF9 expression in lung SCC tissues (n=40) and the corresponding adjacent normal tissues. The expression of FGF9 in the cancerous and adjacent tissues was detected by western blot. Transwell assay used to verify the effect of miR-155-5p on FGF-induced invasion and migration. Finally, subcutaneous tumor formation experiments in nude mice were used to verify how miR-155-5p and FGF9 affect the proliferative ability of lung SCC cells. RESULTS: The results of fluorescence quantitative PCR revealed that miR-155-5p and FGF9 were expressed at high and low levels, respectively, in lung SCC tissue samples relative to normal adjacent tissue samples. Western blot analysis of 6 lung SCC tissue samples revealed a significantly reduced level of FGF9. Correlation analysis uncovered that miR-155-5p and FGF9 share a significant negative correlation in lung SCC. At the messenger RNA and protein levels miR-155-5p could negatively regulate the expression of FGF9. Bioinformatics and dual luciferase reporter assay results confirmed FGF9 to be a downstream regulatory gene targeted by miR-155-5p. Our in vitro and in vivo results demonstrated that FGF9 overexpression exerted a significant inhibitory effect on miR-155-5p’s ability to promote lung cancer cell growth, invasion, and proliferation. CONCLUSIONS: Our results show that miR-155-5p, as an oncogene, negative regulates FGF9 expression to promote SCC occurrence and development in the lungs.