MicroRNA library screening identifies growth-suppressive microRNAs that regulate genes involved in cell cycle progression and apoptosis

Micro(mi)RNAs play important and varied roles in tumorigenesis; however, the full repertoire of miRNAs that affect cancer cell growth is not known. In this study, an miRNA library was screened to identify those that affect the growth of A549 tumor cells. Among 300 miRNAs, miR-28-5p, -323-5p, -510-5p, -552-3p, and -608 were the most effective in inhibiting cell growth. More specifically, overexpressing miR-28-5p, -323-5p, and -510-5p induced G1 arrest, as determined by flow cytometry, whereas that of miR-608 induced cell death in a caspase-dependent manner. Moreover, several genes involved in apoptosis and cell cycle progression were downregulated upon overexpression of each of the five miRNAs, with the functional targets of miR-552-3p and miR-608 confirmed by microarray, quantitative real-time PCR, and luciferase reporter assay. In miR-608-transfected cells, B cell lymphoma 2-like 1 (BCL2L1), D-type cyclin 1 (CCND1), CCND3, cytochrome b5 reductase 3 (CYB5R3), phosphoinositide 3-kinase regulatory subunit 2 (PIK3R2), specificity protein 1 (SP1), and phosphorylated Akt were all downregulated, while Bcl-2-interacting killer (BIK) was upregulated. Moreover, miR-608 was determined to have a suppressive function on tumor growth in an NCI-H460 xenograft model. These findings provide insights into the roles of five miRNAs in growth inhibition and their potential function as cancer therapeutics.