HER2 (ErbB2) has been reported to be overexpressed in 20-30% of breast cancer and confers poor survival because of high proliferation and metastasis rates. MicroRNAs are small noncoding RNAs that are responsible for the post-transcriptional regulation of target genes. We found miR-199b-5p inhibited HER2 expression by direct targeting its 3'-untranslated region (3'UTR) in breast cancer cells. In addition, miR-199b-5p inhibited HER2 downstream signaling by ERK1/2 and AKT pathways in breast cancer cells. Besides, transwell migration, wound healing, and clonogenicity were obviously inhibited by overexpression of miR-199b-5p in HER2-positive breast cancer cells. We also found that miR-199b-5p could enhance the suppression of trastuzumab on cell migration and clonogenicity. These results suggest that miR-199b-5p may have the potential to be a novel important alternative therapeutic target for HER2-positive breast cancer.
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