[摘要] 目的：探讨外泌体(EXO)传输Let-7a 调控MYC基因在三阴性乳腺癌（TNBC）细胞恶性生物学行为中的作用及其机制。方法：TNBC细胞MDA-MB-231 培养完成后，qPCR实验检测TNBC组织和细胞中MYC与Let-7a mRNA的表达水平，WB实验检测MYC与Let-7a 蛋白的表达水平。携Let-7a 重组慢病毒和敲除MYC的Crisper/Cas-9 系统分别转染MDA-MB-231 细胞，MTT、Transwell、划痕愈合实验检测MDA-MB-231 细胞增殖、侵袭和迁移能力。荧光素酶活性实验验证MYC和Let-7a 的作用靶点。分别在野生型和过表达Let-7a 的MDA-MB-231 细胞中分离EXO，并以透射电镜和WB实验鉴定。qPCR、WB、MTT、Transwell等实验检测两种EXO分别和MDA-MB-231 细胞共孵育后Let-7a 通过EXO影响MDA-MB-231 细胞的生物学功能。结果：Let-7a 与MYC在TNBC组织和细胞系中表达呈负相关（P<0.05）；MYC促进MDA-MB-231 细胞的增殖、迁移与侵袭，Let-7a 可以抑制MDA-MB-231 细胞的增殖、迁移与侵袭（均P<0.01）。Let-7a 通过作用于MYC基因的3'UTR 使其沉默，从而减少MYC蛋白的表达（P＜0.05）。Let-7a 由EXO包裹运输至肿瘤细胞，进而抑制MDA-MB-231 细胞的增殖、迁移与侵袭能力（P<0.05）。结论：EXO介导的Let-7a通过作用于MYC基因3’UTR区使得MYC基因沉默，从而抑制MDA-MB-231 细胞的增殖、迁移与侵袭。

[Abstract] 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< .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.

国家中医药管理局基金资助项目(No. 20140814)