miR-515-5p inhibits the proliferation, migration and invasion of human breast cancer cells by targeting CBX4

microRNA (miR)-515-5p has been previously suggested to function as a tumor suppressor in various types of human cancer. Therefore, the role of miR-515-5p in breast cancer (BC) was explored in the present study. A series of assays were performed to study the function of miR-515-p in BC cells, including Cell Counting Kit-8, TUNEL, flow cytometric and colony formation to detect cell viability and apoptosis, wound healing and Transwell assays to measure cell motility. In addition, reverse transcription quantitative PCR and western blot analysis were used to assess miR-515-5p, CBX4, Cox-2, MMP2, MMP9, CDK2, p21 and Cyclin D1 respectively. Bioinformatics and dual-luciferase reporter assays were used to analyze the target genes of miR-515-5p, which confirmed the direct binding between miR-515-5p and polycomb chromobox 4 (CBX4). It was found that the expression of miR-515-5p is lower in BC cells compared with that in normal breast cells (MCF10A). Overexpression of miR-515-5p using the miR-515 mimic was found to reduce cell viability, facilitate cell apoptosis, inhibit cell proliferation and arrest cell cycle progressio at G(1) phase. In addition, miR-515-5p overexpression could inhibit cell migration and invasion, whilst decreasing the expression levels of prostaglandin-endoperoxide synthase 2, MMP2 and MMP9 proteins. In addition, miR-515-5p overexpression could reduce the expression levels of CBX4 in MCF7 and ZR-75-30 cells. By contrast, overexpression of CBX4 reversed the effects of the miR-515-5p mimic transfection on cell proliferation, migration and invasion in MCF7 and ZR-75-30 cells. In combination, these results suggest that miR-515-5p inhibits BC cell proliferation, migration and invasion by directly targeting CBX4.