miR-181 suppresses metastasis via MMP-14

deaths. Much effort has been made to identify key molecules controlling metastasis. However, due to the complicated wiring of the cancer signaling networks, key players initiating cancer metastasis have not been defined. This situation has thwarted target-based drug discovery aimed at preventing cancer metastasis. Regardless of which molecules initiate tumor, cancer cells must be equipped with proteases for invasive behavior [1]. A key cell surface-anchored protease, membrane type 1-matrix metalloproteinase (MMP-14), plays a critical role in digesting basement membrane and extracellular matrices (ECMs) and in inducing cancer cell migration, thereby promoting cancer invasion and metastasis [2]. MMP-14 is highly expressed in most human cancers and correlates with breast cancer mortality [3]. However, the regulatory mechanism of upregulated MMP-14 expression in cancer is poorly understood. We, for the first time, demonstrated that MMP-14 is directly inhibited by miR-181a-5p through targeting the 3' untranslated region (UTR) resulting in decreased cell migration, invasion, and angiogenesis [4]. This relation introduces the possibility of miR-181a-5p as a biomarker for prognosis, or as a target to prevent cancer metastasis. MicroRNAs (miRNA or miR) are a relatively new element in gene regulation that have been shown to regulate several aspects of metastasis. They are short noncoding RNAs which are transcribed as approximately 70 nucleotide precursors, and are processed to a 22 nucleotide mature form. It is the mature form that enacts genetic regulation, primarily through post transcriptional repression. Although some studies suggest miRNAs enhance expression by binding to the promoter region, most exert their effect by binding the 3' UTR of transcribed mRNA, thereby signaling degradation or preventing protein translation. This regulatory element has been shown to play an important role in the transformation to malignancy [5]. Using two miRNA target prediction algorithms, TargetScan and miRanda, a putative miR-181a-5p binding site within the 3'-UTR of MMP-14 was identified. Overexpression of miR-181a-5p reduced ectopically expressed 3'UTR containing-MMP-14 mRNA and protein; however, it had no effect on MMP-14 lacking the 3' UTR. In order to decrease endogenous Editorial miR-181a-5p levels, a sponge construct with four repeats containing miR-181 binding sites was generated. When stably integrated, the sponge decreased highly expressed endogenous miR-181a-5p in MCF-7 cells, resulting in increased expression of hypoxia-induced endogenous MMP-14. These effects of overexpression and knockdown both suggest miR-181a-5p has a negative regulation of MMP-14 expression. To determine whether miR-181a-5p targets the MMP-14 3'-UTR directly, a luciferase reporter gene construct was generated by fusing the 3'-UTR …