Recently, novel mechanisms underlying the pro-tumorigenic effects of cancer-associated fibroblasts (CAFs) have been identified in several cancers, including breast cancer. CAFs can secrete exosomes that are loaded with proteins, lipids, and RNAs to affect tumor microenvironment. Herein, we identify CAF-derived exosomes that can transfer miR-181d-5p to enhance the aggressiveness of breast cancer. Cancerous tissues and matched paracancerous tissues were surgically resected from 122 patients with breast cancer. Chromatin immunoprecipitation (ChIP) and dual luciferase reporter assays were employed to identify interaction between homeobox A5 (HOXA5) and caudal-related homeobox 2 (CDX2), as well as between CDX2 and miR-181d-5p, respectively. Human breast cancer Michigan Cancer Foundation-7 (MCF-7) cells were cocultured with CAF-derived exosomes. 5-Ethynyl-2′-deoxyuridine (EdU) assay, TUNEL staining, Transwell invasion assays, and scratch tests were carried out to evaluate MCF-7 cell functions. Nude mice bearing xenografted MCF-7 cells were injected with CAF-derived exosomes, and the tumor formation was evaluated. HOXA5 expressed at a poor level in breast cancer tissues, and its overexpression retarded MCF-7 cell proliferation, invasion, migration, and epithelial-mesenchymal transition (EMT) and facilitated its apoptosis in vitro. miR-181d-5p targets CDX2, a transcription factor binding to HOXA5 promoter. Coculture of CAFs and MCF-7 cells showed that CAFs prolonged proliferation and antagonized apoptosis of MCF-7 cells via release of exosomes. Coculture of MCF-7 cells and exosomes derived from CAFs identified miR-181d-5p as a mediator of the exosomal effects on MCF-7 cells, in part, via downregulation of CDX2 and HOXA5. CAF-derived exosomes containing miR-181d-5p promoted the tumor growth of nude mice bearing xenografted MCF-7 cells. In conclusion, exosomal miR-181d-5p plays a key role in CAF-mediated effects on tumor environment in breast cancer, likely via CDX2 and HOXA5.

最近，在包括乳腺癌在内的多种癌症中发现了癌症相关成纤维细胞（CAF）促肿瘤作用的新机制。CAF 可以分泌负载蛋白质、脂质和 RNA 的外泌体来影响肿瘤微环境。在此，我们鉴定了 CAF 衍生的外泌体，可以转移 miR-181d-5p 以增强乳腺癌的侵袭性。通过手术切除 122 名乳腺癌患者的癌组织和匹配的癌旁组织。采用染色质免疫沉淀 (ChIP) 和双荧光素酶报告基因测定分别鉴定同源盒 A5 (HOXA5) 和尾部相关同源盒 2 (CDX2) 之间以及 CDX2 和 miR-181d-5p 之间的相互作用。人乳腺癌密歇根癌症基金会-7 (MCF-7) 细胞与 CAF 衍生的外泌体共培养。进行5-乙炔基-2'-脱氧尿苷（EdU）测定、TUNEL染色、Transwell侵袭测定和划痕试验来评估MCF-7细胞功能。向携带异种移植 MCF-7 细胞的裸鼠注射 CAF 衍生的外泌体，并评估肿瘤形成。HOXA5在乳腺癌组织中表达水平较低，其过表达可延缓MCF-7细胞的增殖、侵袭、迁移和上皮间质转化（EMT），并促进其体外凋亡。miR-181d-5p 靶向 CDX2，这是一种与 HOXA5 启动子结合的转录因子。CAF 和 MCF-7 细胞的共培养表明，CAF 通过释放外泌体来延长 MCF-7 细胞的增殖并拮抗细胞凋亡。MCF-7 细胞和源自 CAF 的外泌体的共培养确定 miR-181d-5p 是外泌体对 MCF-7 细胞影响的介质，部分是通过下调 CDX2 和 HOXA5 实现的。含有 miR-181d-5p 的 CAF 衍生外泌体促进携带异种移植 MCF-7 细胞的裸鼠的肿瘤生长。总之，外泌体 miR-181d-5p 可能通过 CDX2 和 HOXA5 在 CAF 介导的对乳腺癌肿瘤环境的影响中发挥关键作用。