miR-1275 Targets MDK/AKT Signaling to Inhibit Breast Cancer Chemoresistance by Lessening the Properties of Cancer Stem Cells

Background: Chemoresistance is a major obstacle in the neoadjuvant chemotherapy (NCT) of locally advanced breast cancer (LABC). Identification of miRNAs as prognostic biomarkers may help overcome chemoresistance of breast cancer (BC). The aim of this study was to evaluate the expression level of miR-1275 in plasma samples and the biological functions in the chemoresistance of BC. Methods: The expression levels of miR-1275 in plasma samples and cells were measured by RT-qPCR. The associations between the expression levels of miR-1275 and clinicopathological features were studied. CRISPR/Cas9-mediated gene editing was used to construct miR-1275 knock-out cells. CCK-8, colony formation assays, epirubicin accumulation assay and xenograft tumor models were used to detect the sensitivity of breast cancer cells to epirubicin in vitro and in vivo. Mammosphere formation assay, flow cytometry analysis and western blot analyses were used to evaluate the effects of miR-1275 on cancer stem cells (CSCs) characteristics in BC cells. Dual-luciferase reporter, RNA pulldown, ELISA and IHC were used to verify the relationship between the expression of miR-1275 and Midkine (MDK). Results: We found that miR-1275 was significantly downregulated in plasma from patients resistant to chemotherapy with LABC and in chemoresistant breast cancer cell lines, while patients with low levels of miR-1275 show poor overall survival. Mir-1275 knock-out promoted chemoresistance in breast cancer cells by increasing the properties of cancer stem cells in vitro and in vivo. Mechanistically, we identified that Midkine was determined to be direct downstream protein of miR-1275 which initiated PI3K/Akt signaling in breast cancer cells. Conclusions: We demonstrated that the high expression level of miR-1275 in plasma predicted better response to NCT. The reduction of miR-1275 promoted BC cells chemoresistance by increasing CSC properties via targeting MDK/AKT axis. The potential of miR-1275 as a new prognostic biomarker and therapeutic target of breast cancer patients was identified.