MiR-634 Decreases The Radioresistance Of Human Breast Cancer Cells By Targeting STAT3

Breast cancer is one of the most common malignancies in women and the second common cause of death from cancer in women,which seriously affects women’s physical and mental health.At present,the treatment of breast cancer mainly includes surgery,radiotherapy,chemotherapy,targeted drug therapy and endocrine therapy.Radiotherapy can reduce the 10 year recurrence risk of breast cancer by 50%,and reduce the risk of breast cancer death by 17%.Nevertheless,in patients receiving radiotherapy,local breast cancer patients with 8%-15%still fail.Nevertheless,in patients receiving radiotherapy,local breast cancer patients with 8%-15%still fail.Therefore,it is an important clinical problem to find the inherent or acquired resistance to radiotherapy that leads to treatment failure.MicroRNA(miRNA)is a class of non-coding small RNA,widely found in animals and plants primarily involved in gene post-transcriptional level regulation.Several studies have shown that multiple miRNAs play a key role in the occurrence,development,metastasis and invasion of breast cancer.It has also been reported that some miRNAs can promote radiation resistance or increase sensitivity in the radiation treatment of breast cancer.As a member of miRNAs,studies have shown that miR-634 can regulate the proliferation,migration and drug sensitivity of other malignant tumors.However,little is known about the role of miR-634 in the radiation resistance of human breast cancer cells.In this study,we have studied the effect of miR-634 on the sensitivity of breast cancer cells to radiotherapy and the molecular regulation mechanism,providing new ideas for radiotherapy of breast cancer.ObjectiveTo preliminarily study the expression of miR-634 in human breast cancer cells with radiation resistance,further explore the effect of miR-634 on the radiosensitivity of human breast cancer cells and its molecular regulation mechanism.Methods1.After constructing radiation-resistant human breast cancer cells,MCF-7 and MCF-7/R and MDA-MB231 and MDA-MB231/R cells were irradiated with X ray.Cells were irradiated by radiation dose of(0,1,2,4,6,8 Gy),the survival rates of cells were tested by MTT assay,and the expression of miR-634 in MCF-7 and MCF-7/R and MDA-MB231 and MDA-MB231/R cells was determined by qRT-PCR.2.MCF-7/R and MDA-MB-231/R cells were transfected with miR-634 mimics,Control mimics,miR-634 inhibitor and NC inhibitor by using cell transfection,and then irradiated by 0,1,2,4,6,8 Gy.Survival of cells in each group was determined by MTT experiments.3.MCF-7/R and MDA-MB-231/R transfected with miR-634 mimics/Control mimic or miR-634 inhibitor/NC inhibitor were exposed in 4 Gy for 24 h,and cell apoptosis was examined by FCM.The expression of Cleaved caspase-3 and Cleaved PARP was examined by western blot.4.The TargetScan was performed to predict that miR-634 combined with STAT3,and the dual-luciferase reporter experiment was carried out to prove this combination.The rescue experiment was further performed to verify that miR-634 decreased the radio-resistance of human breast cancer cell by targeting STAT3.Results1.The survival capacity of MCF-7,MDA-MB-231,MCF-7/R and MDA-MB-231/R cells was reduced.But MCF-7 and MDA-MB-231 cells were found to be decreased significantly in comparison with MCF-7/R and MDA-MB-231/R.The expression level of miR-634 was decreased significantly in MCF-7/R and MDA-MB-231/R in comparison with MCF-7 and MDA-MB-231.2.The MTT results showed that the group of miR-634 overexpression significantly reduced the survival of radiation-resistant cells as compared with the control simulations in both MCF-7/R and MDA-MB-231/R cells.3.In MCF-7/R and MDA-MB-231/R cells,cell apoptosis was significantly increased in the miR-634 mimics group than in the control group,while cell apoptosis in the miR-634 inhibitor group was significantly lower than in the NC inhibitor group.The results of western blot showed that Cleaved caspase-3 and Cleaved PARP expression were significantly higher in the miR-634 mimics group in both MCF-7/R and MDA-MB-231/R cells than the control groups,while significantly lower in miR-634 inhibitor cells.4.The luciferase activity of cells transfected with STAT3 WT plasmid was significantly decreased by miR-634 mimics(P<0.01),while no difference in cells transfected with STAT3 MUT plasmid.These indicated that miR-634 was able to bind STAT3 transcript STAT3 was efficiently pulled down in miR-634 mimics group(P<0.01),and instead,expression of STAT3 was increased in miR-634 inhibitor group(P<0.01).5.MTT assay showed that survival rate in "miR-634 mimics+ Vector" group,the survival rate was significantly decreased in compared with "Control mimics+Vector" and"miR-634 mimics+STAT3" groups.Apoptotic rate of HEK-MCF-7/R cell was decreased blatantly in "miR-634 mimics+Vector" group compared with other two "miR-634 mimics+STAT3”and "miR-634 mimics+Vector" groups(P<0.01).The expression of STAT3 was significantly up-regulated in "miR-634 mimics+STAT3”group,but its expression was down-regulated in "miR-634 mimics+Vector" group.In addition,the expression levels of cleaved caspase-3 and cleaved PARP were found to be significantly increased in"miR-634 mimics+Vector" group(P<0.01),but decreased obviously in "miR-634 mimics+STAT3" group(P<0.01).Conclusion:miR-634 was able to regulate STAT3 and enhance the sensitivity of breast cancer cells to radiation;these results might shed new light on radiation therapy for breast cancer.