Date Published: April 22, 2019
Publisher: Public Library of Science
Author(s): Senem Noyan, Hakan Gurdal, Bala Gur Dedeoglu, Aamir Ahmad.
miRNAs may play effective roles in breast cancer so modulating their expression levels could have therapeutic benefits. Recent studies have found the combination of miRNA-based therapeutics with conventional drugs as promising. This study aimed to find drug-responsive miRNAs, and explore their anticancer activities in HER2+ breast cancer cells and regulatory role in the trastuzumab response. qRT-PCR-array analysis was performed with effective concentrations of tamoxifen and trastuzumab treated BT-474, SK-BR-3 and MCF-7 cells. Motility and invasion analyses were performed with wound healing and xCELLigence impedance-based assays respectively. Viability of cells following mimic transfection and drug treatment was assessed by WST-1 assay. Western blot analysis was used to assess miR-770-5p regulation of proteins and their phosphorylated forms. The clinical relevance of miR-770-5p was examined by TCGA data analysis. The qRT-PCR-array results indicated that miR-770-5p was responsive in a drug and cell line independent manner. Overexpression of miR-770-5p inhibited the motility and cell invasion through regulation of AKT and ERK proteins. Additionally, miR-770-5p potentiated the effectiveness of trastuzumab. Thus, regulating the expression level of miR-770-5p in combination with trastuzumab treatment may simultaneously inhibit the downstream elements of PI3K and MAPK signalling, thereby blocking the proliferation, motility and invasion capacities of HER2+ breast cancer cells.
Breast cancer is the most common malignancy in women, constituting approximately 30% of all cancer types . Breast cancer is a heterogeneous disease with complex clinical behavior and responses to therapeutic intervention [2,3]. It is classified based on gene expression profiling, including HER2 positive (HER2+), luminal A or B, basal-like and presence of hormone receptors . Approximately 70% of human breast cancers are estrogen receptor alpha positive (ER+), so anti-estrogen therapy is an effective treatment . Tamoxifen citrate (TAM), which competes with the estrogen that binds to the estrogen receptor (ER), was the first selective estrogen receptor modulator (SERM) to be developed . Tamoxifen has been used clinically for over 30 years as a partial agonist of ER to reduce the risk of recurrence and contralateral neoplasia in breast cancer treatment. However, the development of resistance to this drug is inevitable because of molecular crosstalk mechanisms in the tumor cells [7,8]. Additionally, HER2+ tumors, which constitute 25% of breast cancers, are also known to show resistance to tamoxifen and standard chemotherapeutic approaches [8–10]. Trastuzumab (Herceptin) is a FDA-approved recombinant humanized monoclonal antibody developed against the extracellular domain of the HER2 protein, which is currently used as a therapy for HER2-overexpressing breast cancer patients [11–14]. Elucidation of the molecular mechanism of trastuzumab treatment is therefore important as it may contribute to determining the resistance mechanisms of tumor cells to this drug.
Ethical approval: This article does not contain any studies with human participants or animals performed by any of the authors.
In this study, we identified a common miRNA response in cells expressing ER and HER2 to two different drugs, tamoxifen and trastuzumab. According to the qRT-PCR-array results, miR-770-5p was significantly responsive, independent of cell and drug type, with consistent overexpression. miR-770-5p has been linked to various cancers, such as gastric cardia adenocarcinoma , ovarian cancer , non-small cell lung cancer  and hepatocellular carcinoma . It has also been shown to be downregulated in breast cancer. A recent study reported that miR-770-5p is downregulated in chemo-resistant triple negative breast cancer (TNBC) tissues while its ectopic expression antagonized resistance and metastases by targeting STMN1 . One of the deregulated miRNAs may be a potential biomarker to predict clinical outcomes in TNBCs recieving neoadjuvant chemotherapy . However, the role of miR-770-5p in ER+ and HER2+ breast cancer cells, and its response to tamoxifen and trastuzumab treatment has not previously been determined. Furthermore, our TCGA data analysis, which indicates its significant downregulation in breast tumors compared to normal breast tissues, supports its possible clinical importance and led us to conduct further functional analysis.