Objective: To investigate the role and mechanism of miR-155 in invasion and metastasis of lung adenocarcinoma A549 cells.

Methods: Real-time PCR and fluorescence in situ hybridization were used to detect the miR-155 expression in patients' lung adenocarcinoma and adjacent tissue and lymph nodes. Scratch test and Transwell migration assay were used to assess the effect of miR-155 on the A549 cell migration and invasion capability. Bioinformatics software was used to predict the target genes of miR-155, and using luciferase to assay the target gene. Western blot and real-time PCR were performed to confirm the role of miR-155 expression in the regulation of target gene PTEN.

Results: The real-time quantitative PCR showed that the miR-155 expression levels in adjacent normal tissue, lung adenocarcinoma and metastatic lymph nodes were 4.1±0.5, 9.6±3.1 and 7.8±2.2, respectively. The in situ hybridization showed that the expression rates of miR-155 in the adjacent normal tissue, lung adenocarcinoma and metastatic lymph nodes were (23.2±15.3)%, (75.4±20.2)% and (60.4±25.1)%, respectively. The Scratch assay showed that the wound healing rates in the miR-155 mimics group, miR-155 mimics NC group, miR-155 inhibitor group and miR-155 inhibitor NC group at 24 h were (43.2±2.2)%, (21.3±4.2)%, (24.3±5.3)%, and (35.2±5.1)%, and that at 48 h were (75.2±4.5)%, (52.6±5.2)%, (39.4±4.2)%, and (51.5±4.3)%, respectively. Dual luciferase reporter gene assay showed that the value of the luciferase in the miR-155 mimics group co-transfected with PTEN 3'UTR-containing wild-type and mutant plasmids were 4.7±0.5 and 7.3±0.7, and the miR-155 mimics luciferase values of the control group co-transfected with PTEN 3'UTR-containing wild-type and mutant plasmids were 7.8±0.9 and 7.5±0.8, respectively. The real-time quantitative fluorescence PCR showed that the relative expression of PTEN protein in the miR-155 mimics group, miR-155 mimics control group, miR-155 mimics inhibitor group, and miR-155 inhibitor control group were 0.5±0.3, 1.0±0.1, 2.2±0.2 and 1.2±0.1, respectively. The Western blot assay detected that the relative expression of PTEN protein levels in the miR-155 mimics group, miR-155 mimics control group, miR-155 inhibitor group and miR-155 inhibitor control group were 0.4±0.1, 1.0±0.3, 2.8±0.2 and 1.4±0.1, respectively. The differences in PTEN mRNA and protein expressions of the four groups were statistically significant (P<0.05 for all).

Conclusions: miR-155 may promote the invasion and metastasis of lung adenocarcinoma through reducing the target PTEN gene expression.