microRNA-612 suppresses the malignant development of non-small-cell lung cancer by directly targeting bromodomain-containing protein 4

Background: Aberrant expression of microRNAs (miRNAs) in non-small-cell lung cancer (NSCLC) has been reported. Dysregulation of miRNAs exerts tumor-suppressing or tumor-promoting actions on the pathology and biological behaviors of NSCLC. miR-612 is associated with many types of human cancer; however, the expression, potential roles, and regulatory mechanisms of miR-612 in NSCLC remain unclear. Material and methods: Here, the expression level of miR-612 in NSCLC tissue specimens and a panel of cell lines were evaluated by RT-qPCR. Cell-Counting Kit 8, flow cytometry, Transwell migration and invasion, and in vivo tumor growth assays were performed to determine the functional role of miR-612 in malignant phenotypes of NSCLC cells. The molecular mechanism underlying the tumor-suppressive roles of miR-612 in NSCLC was investigated. Results: miR-612 was expressed at low levels in NSCLC, and low miR-612 expression was significantly correlated with TNM stage and lymph node metastasis. NSCLC patients with low miR-612 expression had shorter overall survival rate than those with high levels. Exogenous miR-612 expression decreased proliferation, migration, and invasion, and promoted apoptosis of NSCLC cells in vitro. miR-612 upregulation hindered NSCLC tumor growth in vivo. Bromodomain-containing protein 4 (BRD4) was confirmed as a direct target gene of miR-612 in NSCLC cells. BRD4 was obviously overexpressed in human NSCLC tissues and inverse correlated with miR-612 expression. Inhibition of BRD4 expression simulated the tumor-suppressive functions of miR-612 overexpression in NSCLC cells. Reintroduction of miR-612 expression abrogated the miR-612-mediated suppressive effects on NSCLC cells. BRD4 upregulation inhibited activation of the PI3K/Akt pathway in NSCLC cells in vitro and in vivo. Conclusion: This study supports the first evidence that miR-612 exerts tumor-suppressive roles in the aggressive behaviors of NSCLC cells in vitro and in vivo through direct targeting BRD4 and deactivating the PI3K/Akt pathway. Thus, miR-612 might be a promising target for anticancer therapies in patients with NSCLC.