The Role Of Usp9x In Triple-negative Breast Cancer Chemotherapy Resistance

AimBreast Cancer is one of the most common malignancies in women.As a special type of breast cancer,triple-negative breast cancer(TNBC)has strong invasiveness,easy to relapse and metastasis.Seeking the right target to improve the chemosensitivity of TNBC is the key to its research.The X-linked ubiquitin-specific protease 9(usp9x)is a gene encoding ubiquitin-specific proteases that is highly expressed in a variety of tumors,including triple-negative breast cancers.Usp9x plays an important role in the development and progression of tumor,which can regulate the transcription of target genes and control the growth,differentiation,and apoptosis of tumor cells.With the deepening of the study of usp9x,its role in tumor resistance is gradually proposed.The aim of this study was to investigate the role of usp9x in drug resistance in cisplatin in triple-negative breast cancer and its possible mechanism.Methods and methodIn this study,MDA-MB-231,MDA-MB-468 and Bcap-37 breast cancer cell lines were treated with cisplatin.The cell viability of the breast cancer cell line was detected by cell viability assay kit(CCK-8).Proliferation assay kit(EdU test)was used to detect the proliferation of breast cancer cell lines and the expression of usp9x protein was detected by Western blot;Usp9x inhibitor WP1130 was used to inhibit the activity of usp9x in breast cancer cell lines.The cell viability,proliferation and expression of usp9x protein in the three cells were studied after the combined treatment of cisplatin and WP1130;Aftre the expression of usp9x in breast cancer cell lines were interfered by usp9x SiRNA,the changes of cell viability of the three kinds of cell lines was studied after cisplatin treatment.The changes of cell viability of three kinds of cell lines after treated with SiRNA disturbance and then with WP1130 were also studied.To explore the mechanism of usp9x influence on breast cancer resistance,we also examined the expression of Mcl-1 protein as well as the expression of usp9x proteins in three cell lines,and analyzed the relationship between Mcl-1 change and usp9x expression in different treatments.Results:1.After cisplatin treatment,the cell viability and proliferation of three breast cancer cells decreased,and the sensitivity of breast cancer cell lines to cisplatin was negatively correlated with the usp9x expression.2.The sensitivity of ER-negative breast cancer cell lines to cisplatin decreased after the combined application of the usp9x inhibitor,and ER-positive cell lines were unaffected.3.The sensitivity of ER-negative breast cancer cell lines to cisplatin decreased after the knockdown of usp9x with siRNA,and ER-positive cell lines were unaffected.4.The sensitivity of three breast cancer cell lines to cisplatin no longer changes after treated with SiRNA disturbance and then with WP1130.5.The expression changes of usp9x in three cell strains were positively correlated with expression of anti-apoptotic protein Mcl-1.ConclusionsThe high expression of usp9x significantly reduces the sensitivity of breast cancer cells to cisplatin.Decreasing the activity of usp9x or inhibiting usp9x expression in breast cancer cell lines can significantly increase the sensitivity to cisplatin in ER-negative breast cancer cells,but not impact the response to cisplatin of ER-positive breast cancer cells.Usp9x may affects the sensitivity of ER-negative breast cancer cell lines to cisplatin by affecting the anti-apoptotic protein Mcl-1 pathway.