RESUMO
@#Objective: To investigate the role of exosome (EXO) transporting Let-7a to regulate MYC gene in the malignant biological behaviors of triple negative breast cancer (TNBC) cell, and to explore the underlying mechanism. Methods: After the completion of cell culture, the gene and protein expressions of MYC and Let-7a in TNBC MDA-MB-231cells were detected by qPCR and WB, respectively. Recombinant lenti-virus vector carrying Let-7a and Crisper/Cas-9 system with MYC knockdown were transfected into MDA-MB-231 cells; MTT assay, Transwell assay and Scratch healing assay were performed to examine the proliferation, invasion and migration of MDA-MB-231 cells. Luciferase activity assay was performed to validate the binding between MYC and Let-7a. EXO was isolated and identified by transmission electron microscopy and WB assay in wild-type and Let-7a over-expressed MDA-MB-231 cells, respectively. After co-incubation of two types of EXO and MDA-MB-231 cells, the effects of Let-7a on biological behaviors of MDAMB-231 cells via EXO were detected by qPCR, WB, MTT and Transwell etc. Results: Let-7a was negatively correlated with MYC in breast cancer tissues and cell lines (all P<0.05); MYC promoted while Let-7a inhibited the proliferation, migration and invasion of breast cancer cells (all P<0.01); Let-7a silenced MYC by acting on 3'UTR of MYC gene, thereby reducing the expression of MYC protein (P<0.05); Let-7a was enveloped by EXO and transported to cancer cells, there by inhibiting the proliferation, migration and invasion of MDA-MB-231 cells. Conclusion: EXO some mediated Let-7a silences MYC gene by acting on its 3'UTR region, thus inhibiting the proliferation, migration and invasion of MDA-MB-231 cells.