Although many miRNAs are reported to be involved in tumor formation and progression,the effect of miR-219a-5p on breast cancer metastasis is not well-known.The aim of this study is to investigate the effect of miR-219a-5p on the migratory ability and epithelial-mesenchymal transition (EMT) of breast cancer cells.First,miR-219a-5p was found to be highly expressed in Iow-invasive breast cancer MCF-7 cells,but lowly expressed in high-invasive breast cancer MDA-MB-231 cells.Wound scratch assay and transwell assay showed that miR-219a-5p inhibited the migratory ability of MDA-MB-231 cells.miR-219a-5p also suppressed the cellular EMT,confirmed by suppressing the expression of mesenchymal markers vimentin and N-cadherin and increasing the expression of epithelial marker E-cadherin.Using the epithelial-mesenchymal-epithelial model in MCF-7 cells,we confirmed that the level of miR-219a-5p was highly expressed in epithelial-type cells and lowly expressed in mesenchymal-type cells.Importantly,we identified myocardin-related transcription factor A (MRTF-A) as a novel potential target gene of miR-219a-5p.Overexpression of miR-219a-5p in MDA-MB-231 cells could inhibit the expression of MRTF-A as revealed by real-time PCR and west blot analysis.miR-219a-5p inhibited the transcription of MRTF-A by targeting the 3’UTR of MRTF-A,which was confirmed by wild-type or mutant MRTF-A 3’UTR luciferase reporter system.Furthermore,knockdown of MRTF-A using siRNA for MRTF-A could depress breast cell migration.In conclusion,our present study revealed the tumor suppressive role of miR-219a-5p in regulating breast cancer migration by targeting MRTF-A,suggesting that miR-219a-5p might be a therapeutic target in breast cancer through regulating EMT.