miR-720 inhibits tumor invasion and migration in breast cancer by targeting TWIST1

Breast cancer is the leading cause of cancer death among females, with tumor metastasis being primarily responsible for breast cancer-associated mortality. Current literatures have shown that microRNAs (miRNAs) are implicated in tumor metastasis. In this study, we found that the expression of miR-720 was significantly downregulated in primary breast cancer, with greater downregulation in metastatic tumors. Statistical analysis of 105 cases of primary human breast cancer demonstrated that decreased expression of miR-720 was correlated with lymph node metastasis. Furthermore, reexpression of miR-720 in breast cancer cells remarkably inhibited cell invasiveness and migration both in vitro and in vivo. Mechanistically, downregulation of TWIST1, a promoter of metastasis that was identified as a direct functional target of miR-720, was attributed to the inhibition of metastasis. Consistent with the reduced TWIST1 levels in breast cancer, reexpression of miR-720 upregulated epithelial markers (E-cadherin and -catenin) and downregulated mesenchymal markers (N-cadherin, fibronectin, vimentin and matrix metalloproteinase-2). Expression of miR-720 was inversely associated with TWIST1 in human breast cancer tissues. Knockdown of TWIST1 expression by small interfering RNA exhibited similar effects to reintroduction of miR-720, whereas overexpression of TWIST1 (without the 3-untranslated region) abrogated miR-720-mediated metastasis inhibition. Collectively, our data indicate that miR-720 is frequently decreased in breast cancer and manifests antimetastatic activity by downregulating TWIST1, presenting a novel mechanism of miRNA-mediated regulation of tumor metastasis.