Abstract
Dysregulated microRNAs play important pathological roles in carcinogenesis that are yet to be fully elucidated. This study was performed to investigate the biological functions of microRNA-320a (miR-320a) in breast cancer and the underlying mechanisms. Function analyses for cell proliferation, cell cycle, and cell invasion/migration, were conducted after miR-320a silencing and overexpression. The specific target genes of miR-320a were predicted by TargetScan algorithm and then determined by dual luciferase reporter assay and rescue experiment. The relationship between miR-320a and its target genes was explored in human breast cancer tissues. We found that miR-320a overexpression could inhibit breast cancer invasion and migration abilities in vitro, while miR-320a silencing could enhance that. In addition, miR-320a could suppress activity of 3'-untranslated region luciferase of metadherin (MTDH), a potent oncogene. The rescue experiment revealed that MTDH was a functional target of miR-320a. Moreover, we found that MTDH was negatively correlated with miR-320a expression, and it was related to clinical outcomes of breast cancer. Further xenograft experiment also showed that miR-320a could inhibit breast cancer metastasis in vivo. Our findings clearly demonstrate that miR-320a suppresses breast cancer metastasis by directly inhibiting MTDH expression. The present study provides a new insight into anti-oncogenic roles of miR-320a and suggests that miR-320a/MTDH pathway is a putative therapeutic target in breast cancer.