miR-638 mediated regulation of BRCA1affects DNA repair and sensitivity to UV and cisplatin in triple-negative breast cancer

Xiaohui Tan, Jin Peng, Yebo Fu, Shejuan An, Katayoon Rezaei, Sana Tabbara, Christine B Teal, Yan-gao Man, Rachel F Brem, Sidney W Fu

IntroductionTriple negative breast cancer (TNBC) represents 15-20% of all types of breast cancer; however, it accounts for a large number of metastatic cases and deaths, and there is still no effective treatment. The deregulation of microRNAs (miRNAs) in breast cancer has been widely reported. We previously identified that miR-638 was one of the most deregulated miRNAs in breast cancer progression. Bioinformatics analysis revealed that miR-638 directly targets BRCA1. The aim of this study was to investigate the role of miR-638 in breast cancer prognosis and treatment.MethodsFormalin-fixed, paraffin-embedded (FFPE) breast cancer samples were microdissected into normal epithelial cells and invasive ductal carcinoma (IDC), and total RNA was isolated. Several breast cancer cell lines were used for the functional analysis. miR-638 target genes were identified by TARGETSCAN-VERT 6.2 and miRanda. The expression of miR-638 and its target genes were analyzed by real-time qRT-PCR and Western blotting. Dual luciferase reporter assay was employed to confirm the specificity of miR-638 target genes. The biological function of miR-638 was analyzed by MTT chemosensitivity, matrigel invasion and host cell reactivation assays.ResultsThe expression of miR-638 was decreased in IDC tissue samples compared to their adjacent normal controls. The decreased miR-638 expression was more prevalent in non-TNBC compared with TNBC cases. miR-638 expression was significantly down-regulated in breast cancer cell lines compared to the immortalized MCF-10A epithelial cells. BRCA1 is one of the direct targets of miR-638, which was subsequently confirmed by dual luciferase reporter assay. Forced expression of miR-638 resulted in a significantly reduced proliferation rate as well as decreased invasive ability in TNBC cells. Furthermore, miR-638 overexpression increased sensitivity to DNA damaging agents, ultraviolet (UV) and cisplatin but not to 5-fluorouracil (5-FU) and epirubicin exposure in TNBC cells. Host cell reactivation assays showed that miR-638 reduces DNA repair capability in post-UV/cisplatin exposed TNBC cells. The reduced proliferation, invasive ability, and DNA repair capabilities are associated with down-regulated BRCA1.ConclusionsOur findings suggest that miR-638 plays an important role in TNBC progression via BRCA1 deregulation. Therefore, miR-638 might serve as a potential prognostic indicator and therapeutic target for breast cancer.