The Role Of EIF-5A2 In Estrogen Receptor Negative Breast Cancer Doxorubicin Resistance

Introduction:Breast cancer is the most common malignant tumor in women and accounts for about 25%percent of all cancer diagnoses.In China,the incidence of breast cancer has been higher and higher in recent years.The breast cancer has even been the most common killer in women malignant tumor in some modern cities in China.Available treatments include radiotherapy,surgery,monoclonal antibody therapy,endocrine therapy,and especially chemotherapy.Chemotheropy is the most commom system therapy method,which effect is restricted by the status of neither ER nor HER2.Despite significant improvements in the diagnosis and treatment of breast cancer over the past several decades,it remains the second highest cause of cancer-related deaths in women.Resistance to chemotherapy is the primary cause of breast cancer treatment failure.Eukaryotic initiation factor 5A2(eIF-5A2)was a novel oncogene.Overexpression of eIF-5A2 has also been observed in some solid tumors and has been defined as an adverse prognostic marker.We found eIF5A2 must be a chemoresistance gene in breast cancer in our former studies.Epithelial-mesenchymal transition(EMT)is an essential basic process in many procedures,such as embryonic development and wound healing.Increasing evidencies demonstrate that EMT has been recoganized as a critical procedure regulating the chemoresistance properties of breast cancer.And by some studies,eIF-5A2 has been proved as an oncogene regulating EMT.To sum up,as a novel oncogene,although few studies reveal the relationship between eIF-5A2 and breast cancer,we believed it as an important role in breast cancer chemoresistance.The objective of this study is to reveal the role of eIF-5A2 in breast cancer chemoresistance,and to explore the regulating mechanism and the possibility of being a therapy target.Part ? The Relationship Between eIF-5A2 and Breast Cancer ChemoresistanceBackground:The eIF-5A2 is overexpressed in many cancers.The eIF-5A2 overexpression correlates significantly with tumor metastasis and is an adverse prognostic marker.However,eIF-5A2 overexpression in breast cancer and its effect on chemotherapy is unknown.Objective:To observe the expression of eIF-5A2 in different breast cancer cells and discover the relationship between it and breast cancer cell chemoresistance.Method:We measured eIF-5A2 expression and doxorubicin sensitivity in different human breast cancer cell lines(Bcap-1937,HCC1937,and MCF-7).To investigate a role for eIF-5A2 in chemoresistance,cells were treated with eIF5A2-siRNA,exposed to various concentrations of doxorubicin,and toxicity was assayed by CCK-8.Results:The eIF5A2 expression levels varied among breast cancer cells,especially higher in estrogen receptor negative breast cancer cells.Higher expression levels correlated with decreased doxorubicin sensitivity.Silencing of eIF5A2 improved doxorubicin toxicity in all three breast cancer cell lines significantly.Conclusions:This study shows that eIF-5A2 expression differs in different breast cancer cells,and is significant higher in estrogen receptor negative breast cancer cells.It plays an important role in doxorubicin chemoresistance in breast cancer cells.Part ? The Mechanism of Chemoresistance Induced by eIF5A2 in Estrogen Receptor Negative Breast CancerBackground:Increasing evidencies demonstrate that EMT has been recoganized a critical procedure regulating the chemoresistance properties of breast cancer.And by some studies,eIF5A2 has been proved as an oncogene regulating EMT.We had proved eIF-5A2(expression much higher in estrogen receptor negative breast cancer cells)as a chemoresistance gene in formor study.Objective:To reveal the mechanism of chemoresistance in breast cancer regulated by eIF-5A2,whether it is by regulating EMT or not.Methods:We use doxorubicin to induce different human breast cancer cell lines(Bcap-1937,HCC1937,and MCF-7)to EMT.GC7(Nl-Guanyl-1,7-Diaminoheptane,eIF5A2 activation inhibitor)was used to inhibit the function of eIF-5A2 and eIF5A2-siRNA was used to interference the expression of eIF-5A2.The EMT procedures were compared between control group and experimental groups mentioned above.Results:Both GC7 and eIF5A2-siRNA could reverse the EMT of estrogen receptor negative breast cancer cells by targeting on eIF-5A2 in.But neither of them show obviously function on reversing the EMT of estrogen receptor positive breast cancer cells.Conclusion:eIF-5A2 may enhance the chemoresistance of estrogen receptor negative breast cancer cells to doxorubicin by regulating EMT.Part III GC7 Sensitizes Estrogen Receptor Negative Breast Cancer Cells to Doxorubicin by Preventing EMT through Inhibition of eIF5A2 ActivationBackground:Multiple studies showed GC7(Nl-Guanyl-1,7-Diaminoheptane,eIF-5A2 activation inhibitor)could sensitize some tumors to chemotherapy.We found eIF-5A2 could enhance the chemoresistance of estrogen receptor negative breast cancer cells to doxorubicin by regulating EMT in formor study.GC7 can inhibit eIF-5A2 activation.Objective:To observe that whether GC7 can regulate the efficacy of doxorubicin in breast cancer cells and to explore the regulating mechanism.Methods:The present study used cell viability assays,EdU incorporation assays,western blot,and immunofluorescence to explore whether Nl-guanyl-1,7-diaminoheptane(GC7),which inhibits eIF5A2 activation,exerts synergistic cytotoxicity with doxorubicin in breast cancer.Results:We found that GC7 enhanced doxorubicin cytotoxicity in ER-negative HCC1937 cells but had little effect in ER-positive MCF-7 and Bcap-37 cells.Administration of GC7 reversed the doxorubicin-induced EMT in estrogen receptor negative breast cancer cells.Knockdown of eIF-5A2 by siRNA inhibited the doxorubicin-induced EMT in estrogen receptor negative HCC1937 cells.Conclusion:These data demonstrated that GC7 combination therapy may enhance the therapeutic efficacy of doxorubicin in estrogen negative breast cancer cells by preventing EMT through inhibition of eIF-5A2 activation.Total ConclusioneIF5A2 expression differs in different breast cancer cells and plays an important role in doxorubicin chemoresistance in breast cancer cells.eIF5A2 may enhance the chemoresistance of estrogen receptor negative breast cancer cells to doxorubicin by regulating EMT.GC7 combination therapy may enhance the therapeutic efficacy of doxorubicin in estrogen negative breast cancer cells by preventing EMT through inhibition of eIF5A2 activation.These findings help us on further understanding the estrogen negative breast cancer chemoresistance mechanism regulated by eIF5A2 and showing us a new potential therapy target on reversing breast cancer chemoresistance.