The Role And Mechanism Of SIRT7 In Breast Cancer

Objective To make sure the role of SIRT7 in regulation of breast cancer cell proliferation,migration and invasion and then to verify the molecular mechanism of the functional changes.Methods SIRT7-overexpressing MCF-7 cells were constructed by using lentivirus system.MDA-MB-231 cells were transfected with siRNA against SIRT7.Western blot analysis and qRT-PCR were used to detect the efficiency of transfection.Capacity of proliferation in breast cancer cell lines was detected by xCELLligence system and colony formation assay after overexpression or knockdown of SIRT7.The effect of SIRT7 on cell cycle and apoptosis of breast cancer cells was analyzed by flow cytometry.The changes of capacity of migration and invasion in breast cancer cell lines were detected by real-time xCELLigence system and transwell assays after overexpression or knockdown of SIRT7.The change of cell cycle and EMT related proteins in MCF-7 and MDA-MB-231 after overexpression or knockdown of SIRT7 was detected by Western blot analysis.Then we explored the underlying molecular mechanism of SIRT7 in regulating cell proliferation,migration and invasion in breast cancer.The expression levels of SIRT7 in human breast cancer tissues were deteced by immunohistochemical analysis compared to adjacent non-cancerous breast tissues.The relationships between SIRT7 and clinicopathological characteristics,overall survival were analyzed by statistical methods.Results The overexpression and interference efficiency were detected by Western blot analysis and qRT-PCR.SIRT7 overexpression promoted proliferation in stablely transfected MCF-7 cell lines,whereas SIRT7 knockdown inhibited proliferation in transiently transfected MDA-MB-231 cells by xCELLigence monitoring system.The colony formation assay showed that SIRT7 upregulation significantly increased the number of MCF-7 colonies compared with the controls,while SIRT7 downregulation reduced the number of MDA-MB-231 colonies compared with the controls.The frequency of apoptotic cells in MCF-7-hSIRT7 group was much less than that in the control group and the frequency of apoptotic cells in MDA-MB-231-siSIRT7 group was much higher than that in the controls.The percentage of the MCF-7-hSIRT7 cells in G0-G1 phase was less than the control group.Western blot analysis showed that SIRT7 overexpression was associated with increased cyclin D1 and C-myc levels.After incubation for 8h,the percentage of cells that migrated in the MCF-7-hSIRT7 cell groups was dramatically higher than in the control cells.In addition,increased SIRT7 expression led to a significant increase in the invasion activity of MCF-7 cells on matrigel.Conversely,the migration and invasion capacity were reduced after knockdown of SIRT7 in MDA-MB-231 cells.SIRT7 overexpression promoted migration in stablely transfected MCF-7 cell lines,whereas SIRT7 knockdown inhibited migration in transiently transfected MDA-MB-231 cells by xCELLigence RTCA instrument.SIRT7 overexpression resulted in upregulation of N-cadherin,Vimentin and Snail,downregulation of E-cadherin.SIRT7 was highly expressed in 68.8%(110/160)of breast cancer tissues,while in only 30%(15/50)of adjacent non-cancerous breast tissues.There were no any significant associations between SIRT7 and tumor size,lymph node metastasis,TNM stage,ER,PR,HER2 status or index of Ki-67.However,the higher expression level of SIRT7 was significantly related to older patients(P=0.017)and higher histological grade(P=0.010).The expression level of SIRT7 was significantly correlated with overall survival,as patients with higher SIRT7 had worse survival(134.5 months vs.116.3 months,P=0.002).Conclusions 1.SIRT7 promoted the proliferation of breast cancer cells,inhibited apoptosis,and shortened the G0-G1 phase in the cell cycle.2.SIRT7 promoted breast cancer cell migration and invasion,and it could be achieved by EMT signaling pathway.3.The levels of SIRT7 protein were higher in breast cancer tissue samples than adjacent non-cancerous breast tissue specimens using immunohistochemical staining.The higher expression level of SIRT7 was significantly correlated with older patients and higher histological grade.The expression level of SIRT7 was significantly correlated with overall survival,as patients with higher SIRT7 had worse survival.