MicroRNAs (miRNAs) play a key role in tumor metastasis based on their capacity to regulate the expression of tumor-related genes. Over-expression of key genes such as c-MYC and CTNNB1 (encoding β-catenin) in Wnt/β-catenin-dependent and ROCK1 in Wnt/β-catenin-independent signaling pathways (Rho/Rho-associated kinase (ROCK) signaling pathway) has already been identified as the hallmarks of many tumors, and their role in breast cancer has also been investigated and confirmed. miR-340 characterization as an onco-suppressor miRNA has been previously reported. However, the mechanism by which it inhibits metastasis has not been completely elucidated. Quantitative real-time PCR (qPCR), Western blot, and luciferase assays were used to confirm the effect of miR-340 on the 3'-untranslated region (UTR) of the target genes. Lentiviral particles containing miR-340 were also used to evaluate the effect of miR-340 restoration on cell proliferation, migration, and invasion in vitro in the invasive MDA-MB-231 cell line. By applying bioinformatic approaches for the prediction of miRNAs targeting 3'-UTRs of CTNNB1, c-MYC, and ROCK1, we found out that miR-340 could dramatically down-regulate metastasis by targeting Wnt signaling in breast cancer cells. In the current study, analyzing miR-340 by reverse transcription quantitative PCR (RT-qPCR) in MDA-MB-231 showed that it was remarkably down-regulated in the metastatic breast cancer cell line. We found that restoration of miR-340 in the invasive breast cancer cell line, MDA-MB-231, suppresses the expression of the target genes' messenger RNA (mRNA) and protein and, as a result, inhibits tumor cell invasion and metastasis. Our findings highlight the ability of bioinformatic approaches to find miRNAs targeting specific genes. By bioinformatic analysis, we confirmed the important role of miR-340 as a pivotal regulator of breast cancer metastasis in targeting previously validated (ROCK1) and potentially novel genes, i.e., (CTNNB1 and c-MYC).
Keywords: Breast cancer; CTNNB1; Metastasis; MicroRNA-340; ROCK1; c-MYC.