STAT3 Is Requried For MiR-17-5p-mediated Sensitization To Chemotherapy-induced Apoptosis In Breast Cancer Cells

Objective:These results demonstrate a novel pathway via which miR-17-5p inhibits STAT3 expression to promote apoptosis in breast cancer cells.Methods:1.miR-17-5p was used to transfect the breast cancer cells subject to paclitaxel treatment,and then TUNEL assay was used to determine the cell apoptosis.Western blot analysis was carried out to investigate the protein expression in MCF-7 cells treated by paclitaxel.2.The MCF-7 cells transfected using miR-17-5p were treated using 15μM Tamoxifen.Western blot analysis and ELISA were carried out to determine the expression of pro-apoptosis cells.SRB was used to evaluate the cellular survival.3.Brest cancer cells transfected using 15μM miR-17-5p were treated using paclitaxel for48 hrs and 72 hrs,respectively.Then the sensitivity of miR-17-5p to the paclitaxle in breast cancer cells.4.Annexin V staining and TUNEL assay were used to apoptosis of MCF-7 cells transfected with miR-17-5p in presence of STAT3 overexpression and knock-out,in order to determine the sensitivity of cells to paclitaxel.Western blot analysis was performed to investigate the expression of antioncogene in STAT3 overexpressing MCF-7 cells.5.Software was used to identify the potential targets of miR-17-5p in the 3’-UTR of STAT3.Besides,reporter vector was established for wild type 3’-UTR and mutation sites.Luciferase assay was used to determine the activity.Results:1.TUNEL technique demonstrated that miR-17-5p increased the sensitivity of MCF-7 to paclitaxel-induced DNA damage.Western Blot demonstrated that miR-17-5p makes breast cancer cells more sensitive to apoptosis induced by emergency signaling pathways.2.Western Blot has demonstrated that Tamoxifen enhances miR-17-5p-induced apoptosis in MCF-7 cells.ELISA showed that miR-17-5p up-regulated the expression of pro-apoptotic genes.TUNEL technique demonstrated that miR-17-5p promotes the sensitivity of MCF-7 cells to Tamoxifen apoptosis after treatment with 15μM Tamoxifen.3.SRB analysis demonstrated that miR-17-5p overexpression could reduce cell viability after Tamoxifen intervention.The survival rate of MCF-7 and MDA-MB-231 cells decreased after treated with different concentrations of paclitaxel for 48 hours.After 72 hours of paclitaxel treatment,the overexpression of miR-17-5p could decrease the half-inhibitory concentration of paclitaxel,MiR-17-5p reduces the resistance of breast cancer cells to paclitaxel.4.TUNEL demonstrated that miR-17-5p enhances the sensitivity of STAT3 overexpressing MCF-7 cell lines to paclitaxel treatment.Western blot analysis showed that miR-17-5p overexpression increased the expression of tumor suppressor gene in STAT3 overexpressing MCF-7 cell line.5.Detection of miR-17-5p by Luciferase can effectively reduce the activity of STAT3WT-UTR luciferase plasmid,indicating that miR-17-5p can directly target STAT3 to inhibit its expression.Conclutions:1.MiR-17-5p sensitized breast cancer cells to stress signal-induced apoptosis.2.MiR-17-5p sensitized MCF-7 cells to tamoxifen.3.MiR-17-5p attenuated Taxol resistance in MCF-7 cells.4.STAT3 is required for miR-17-5p-induced sensitization of breast tumor cells to Taxolinduced apoptosis.5.STAT3 and p STAT3 expression are elevated,while miR-17-5p expression is decreased,in breast cancer tissue.