Abstract: Objective The aim of this study was to investigate the effect of breast cancer cell-derived exosomes on the biological behavior of breast cancer MCF-7 cells. Methods Exosomes in human breast cancer MCF-7 cell culture medium were extracted and purified by ultracentrifugation,the morphology and size of exosomes were observed by transmission electron microscopy,and the marker protein of exosomes was identified by Western blot experiments.MCF-7 cells co-cultured with exosomes for 48 h were used as the experimental group,and untreated MCF-7 cells were used as the control group.The effects of breast cancer-derived exosomes on MCF-7 cell proliferation,clonal formation,migration,invasion,apoptosis,and epithelial-mesenchymal transition(EMT) were investigated by MTT,clonal formation,cell scratch experiment,cell invasion experiment,flow cytometry experiment and Western blot experiment. Results The shape of exosomes under transmission electron microscopy is a typical cup-tray or concave hemispherical structure,with a diameter of 40-110 nm;The results of Western blot showed that the exosomes′ signature proteins CD9 and CD81 were clearly expressed.The results of MTT and clonal formation experiments showed that the cell proliferation and clonal formation ability of the experimental group were significantly enhanced compared with the control group(P＜0.05);The results of the scratch experiment and invasion experiment showed that compared with the control group,the cell migration and invasion ability of the experimental group was significantly enhanced(P＜0.001);Flow cytometry analysis showed that the percentage of apoptotic cells in exosome-stimulated breast cancer cells was significantly lower than that in the control group(P＜0.05);Western blot results showed that breast cancer-derived exosomes increase the expression of N-cadherin and Vimentin,decrease E-cadherin expression,and promote the EMT process in breast cancer(P＜0.05). Conclusion Exosomes derived from breast cancer cells can enhance the cell proliferation,clonal formation,migration and invasion ability of tumor cells,promote the EMT process of breast cancer,and inhibit apoptosis of tumor cells.It shows that tumor-derived exosomes can be used as mediators for cell-to-cell signal transduction and play an important role in promoting information transmission of tumor growth and metastasis.

Key words: Breast cancer, Exosomes, Proliferation, Invasion, Epithelial-mesenchymal transition