| Background:Breast cancer is one of malignant tumors in women, and also the most common and the second-leading cause of cancer death in American. In our country, the incidence of breast cancer in city accounted for second in female malignant tumors, sometimes the first in some super cities.The incidence and mortality of breast cancer showed a clear upward trend, which has a serious impact on women’s physical and mental health and even be life-threatening. The traditional treatment of breast cancer includes surgery, chemotherapy and radiotherapy. In the affirmation of chemotherapy effect, we have to admit that the phenomenon of chemotherapy resistance of tumor cells is a significant cause of the failure of the treatment of breast cancer at the same time. Breast cancer is a process of multifactor and the accumulation of mutation and the disease etiology is not yet clear. In recent years, the study of the excessive expression or abnormal activation of metastasis related protein in the process of breast cancer occurrence, development has always been the hot spot of the research in this field.STAT3 is an important member of the STATs(signal transducer and activator of transcription) family.Once it is activated,STAT3 translocate into the nucleus from cytoplasm, binding with DNA and thus mediates a variety of signal transduction to the nucleus produced by growth factors and cytokines.Under normal physiological conditions, the activity of STAT3 is under strict regulation, however, the constitutive activation of STAT3 is continuously found in a wide variety of tumor cells.STAT3 regulates the transcription of a variety of target genes such as survivin,VEGF,Bcl-x L, Cycline D1, c-myc and at the same time involved in the survival, proliferation, angiogenesis, invasion and metastasis, and the immune escape of tumor cells.There is no doubt that STAT3 is closely related in tumor development. STAT3 plays a central role in the abnormal proliferation and malignant transformation of tumor cells and indirectly induced drug resistance to chemotherapy. Studies found that therapeutic effect of chemotherapy drugs to cancer cells which have high expression of STAT3 is usually low, thus inhibiting the pathway may reverse the drug resistance. The high expression of STAT3 can cause cell drug resistance, and blocking the signal pathway could reverse drug resistance has been verified in different cancer cell lines and tissue samples of in vitro experiments. Nevertheless, whether abnormal expression of STAT3 in drug resistant breast cancer cells could be found and its role in breast cancer cells resistance has not been reported.In the study, small interfering RNA is transfected into breast cancer MCF-7/TR cells via RNA interference technology to decrease the gene expression of STAT3 and then the influence of STAT3 on the sensitivity of breast cancer cells to chemotherapy drugs is observed. Objective:To detect the different expression of STAT3 in drug resistant breast cancer cell lines MCF-7/ TR and sensitive breast cancer cell line MCF-7 and to explore whether RNA interferance targeted STAT3 could effectively reverse drug resistance in drug resistant breast cancer cell lines MCF-7/ TR. Materials and Methods:1. The levels of the expression of STAT3 m RNA and protein in MCF-7/ TR and MCF-7 cells were detected by real-time PCR and Westem blott respectively.2. RT-PCR and Westem blotting were used to validate whether the STAT3 gene expression was silenced after STAT3-si RNA is transfected into MCF-7/ TR cell.3. The effect of STAT3-si RNA on cell growth and the resistance to paclitaxel was evaluated using MTT assays.4. The SPSS 17.0 was applied to analyze the results of experiment. All of the measurement data were expressed as mean±standard deviation(x±s), The Group-t test was used in two groups. The level of expression among different tissues were tested by One-way analysis of variance. P < 0.05 showed statistically significant difference. Results:1. The STAT3 m RNA and protein expression levels are excessively expressed in paclitaxel sensitive and resistant breast cancer cell lines. At the same time, STAT3 m RNA and protein expression levels in paclitaxel resistant breast cancer cell are higher remarkably compared with paclitaxel sensitive paclitaxel sensitive. The difference was significant(P<0.05).2. The expression of STAT3 m RNA and protein in breast cancer cell line MCF-7/TR after transfected with small interfering RNA targeting STAT3 gene were detected by RT-PCR and Western blot respectively. Compared with the controlled group, STAT3 m RNA and protein level in STAT3-si RNA group were significantly reduced(P<0.05), the change of STAT3 m RNA and protein level in Scramble-si RNA group is not obvious(P>0.05).3. Results from MTT suggested that, the growth of MCF-7/TR after transfected with STAT3-si RNA was remarkedly inhibited. Compared with the blank control group and negative control group, the IC50 of the experimental group was significantly deceased. The drug sensitivity of paclitaxel resistant breast cancer cells was improved after STAT3 pathway was blocked by STAT3-si RNA. Conclusions:1. STAT3 is highly expressed in MCF-7 and MCF-7/TR cells and it is also overexpressed in MCF-7/TR cell line compared with parental cell line MCF-7.2. Targeting STAT3 by RNA interference effectively reverse the resistance of MCF-7/TR cells to paclitaxel.3. STAT3 could serve as a potential gene target for therapy and prevention of breast cancer. |
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