MicroRNA-4651 targets bromodomain-containing protein 4 to inhibit non-small cell lung cancer cell growth

Abstract

Background: Bromodomain-containing protein 4 (BRD4) overexpression in non-small cell lung cancer (NSCLC) is important for cancer cell progression. The aim of the present study is to silence BRD4 through expression of its targeted microRNAs in NSCLC cells. Methods: Expression of BRD4 and its targeting miRNA, microRNA-4651 (miR-4651), was tested by qPCR and Western blotting assays. Genetic strategies were utilized to exogenously alter miR-4651 expression. NSCLC cell growth, proliferation and migration were tested. Results: miR-4651 selectively targets and negatively regulates BRD4 in A549 and primary human NSCLC cells. The Ago-2 immunoprecipitation experiments further confirmed that miR-4651 directly binds to BRD4 mRNA. Significantly, in A549 cells and primary NSCLC cells ectopic overexpression of miR-4651 downregulated BRD4’s 3-UTR activity and its expression, both were however elevated with miR-4651 inhibition. Functional studies demonstrated that NSCLC cell growth, proliferation and migration were significantly inhibited with miR-4651 overexpression, but enhanced with miR-4651 inhibition. BRD4 re-expression, by an 3’-UTR mutant BRD4, reversed miR-4651 overexpression-induced inhibitions on A549 cells. Additionally, miR-4651 overexpression or inhibition failed to affect the functions of BRD4-KO A549 cells. In vivo, miR-4651-overexpressed A549 xenografts grew significantly slower than control A549 xenografts in severe combined immunodeficient mice. At last we show that miR-4651 is downregulated in human NSCLC tissues, correlating with BRD4 elevation. Conclusions: miR-4651 targets BRD4 to inhibit NSCLC cell growth in vitro and in vivo.