Study On The Regulatory Mechanisms Of Bcl-2 And Autophagy In Breast Cancer Cells

Breast cancer is a malignant tumor that grows out of control in the breast epithelium.It is the most common cancer in women.Triple Negative Breast Cancer(TNBC)is a subtype of breast cancer that have been tested negative for estrogen receptors(ER),progesterone receptors(PR)and human epidermal growth factor receptor 2(HER2).There isn't any targeted drug for TNBC yet.In our preliminary study,we found that the expression level of Bcl-2 in TNBC cell HCC-1937 was significantly lower than that in non-TNBC cell MCF-7.Low expression of Bcl-2 relates to poor therapeutic effects of breast cancer.Phosphorylated Bcl-2 is involved in autophagy regulation,and autophagy is closely associated with cancers.Therefore,this study mainly focuses on the correlation between Bcl-2 expression level and autophagy level,whether Bcl-2 regulates breast cancer cell proliferation and drug sensibility to chloroquine through regulating autophagy,thus providing theoretical basis for the diagnosis and treatment for breast cancer,especially TNBC that have low Bcl-2 expressions.We found that,in non-TNBC cell MCF-7 and TNBC cell MDA-MB-231,which have high Bcl-2 expressions,the autophagy levels were high;while in TNBC cell HCC-1937,which has significantly lower Bcl-2 expressions,the autophagy levels were significantly lower than the other two cells.It preliminarily indicates that the expression level of Bcl-2 is positively correlated with autophagy level.Chloroquine(CQ)is an autophagy inhibitor and a common drug for breast cancers.32 ?M CQ inhibited the autophagy levels and cell proliferations of non-TNBC cell MCF-7 and TNBC cell MDA-MB-231 which have high expressions of Bcl-2 and high autophagy levels;while 32 ?M CQ cannot inhibit the autophagy levels or cell proliferations of TNBC cell HCC-1937 which has lower expressions of Bcl-2 and lower autophagy levels.It indicates that autophagy is related to cell proliferation,CQ may inhibit cell proliferations through inhibiting autophagy,while HCC-1937 was not sensitive to CQ.To verify the effect of Bcl-2 on cell autophagy and CQ sensitivity,we used small interfering RNA to knock down Bcl-2 in MCF-7 cells,and transient transfection to overexpress Bcl-2 in HCC-1937 cells.We found that in MCF-siBcl2 cells,the autophagy levels were downregulated,cell proliferations were inhibited,and there were no response to CQ.In HCC-1937-Bcl2 cells,the autophagy levels were upregulated,cell proliferations were promoted,and CQ inhibited cell proliferations.It indicates that enhancing the expressions of Bcl-2 to a certain extent could acivate autophagy,therefore enhancing the drug sensitivity to CQ and inhibiting cell proliferations eventually.Finally,to detect the relationship between autophagy and cell proliferation,without changing Bcl-2 expressions,we further used serum starvation method and anisomycin to induce the autophagy of MCF-7,MDA-MB-231 and HCC-1937.We found that,P-Bcl-2 expressions of those cells were upregulated,while there wasn't significant change of Bcl-2,autophagy levels were upregulated,cell proliferations were inhibited.It indicates that,phospholated Bcl-2 may play a key role in the regulation of autophagy and cell proliferation.Together,in this study,the relationships among Bcl-2 expression level,autophagy level,cell proliferation and the drug sensitivity to CQ in three breast cancer cells were explored,the differences between TNBC cells and non-TNBC cell were discussed.These results may help further understand the specificities of TNBC,expecially TNBC which has low expression of Bcl-2,and provide a new strategy for breast cancer treatment from the perspective of autophagy and phosphorylated Bcl-2.