Cancer-derived exosomes are considered a major driver of cancer-induced pre-metastatic niche formation at foreign sites, but the mechanisms remain unclear. Here, we show that miR-25-3p, a metastasis-promoting miRNA of colorectal cancer (CRC), can be transferred from CRC cells to endothelial cells via exosomes. Exosomal miR-25-3p regulates the expression of VEGFR2, ZO-1, occludin and Claudin5 in endothelial cells by targeting KLF2 and KLF4, consequently promotes vascular permeability and angiogenesis. In addition, exosomal miR-25-3p from CRC cells dramatically induces vascular leakiness and enhances CRC metastasis in liver and lung of mice. Moreover, the expression level of miR-25-3p from circulating exosomes is significantly higher in CRC patients with metastasis than those without metastasis. Our work suggests that exosomal miR-25-3p is involved in pre-metastatic niche formation and may be used as a blood-based biomarker for CRC metastasis.

Background Cancer associated fibroblasts (CAFs) are key stroma cells that play dominant roles in tumor progression. However, the CAFs-derived molecular determinants that regulate colorectal cancer (CRC) metastasis and chemoresistance have not been fully characterized. Methods CAFs and NFs were obtained from fresh CRC and adjacent normal tissues. Exosomes were isolated from conditioned medium and serum of CRC patients using ultracentrifugation method and ExoQuick Exosome Precipitation Solution kit, and characterized by transmission electronic microscopy, nanosight and western blot. MicroRNA microarray was employed to identify differentially expressed miRNAs in exosomes secreted by CAFs or NFs. The internalization of exosomes, transfer of miR-92a-3p was observed by immunofluorescence. Boyden chamber migration and invasion, cell counting kit-8, flow cytometry, plate colony formation, sphere formation assays, tail vein injection and primary colon cancer liver metastasis assays were employed to explore the effect of NFs, CAFs and exosomes secreted by them on epithelial-mesenchymal transition, stemness, metastasis and chemotherapy resistance of CRC. Luciferase report assay, real-time qPCR, western blot, immunofluorescence, and immunohistochemistry staining were employed to explore the regulation of CRC metastasis and chemotherapy resistance by miR-92a-3p, FBXW7 and MOAP1. Results CAFs promote the stemness, epithelial-mesenchymal transition (EMT), metastasis and chemotherapy resistance of CRC cells. Importantly, CAFs exert their roles by directly transferring exosomes to CRC cells, leading to a significant increase of miR-92a-3p level in CRC cells. Mechanically, increased expression of miR-92a-3p activates Wnt/β-catenin pathway and inhibits mitochondrial apoptosis by directly inhibiting FBXW7 and MOAP1, contributing to cell stemness, EMT, metastasis and 5-FU/L-OHP resistance in CRC. Clinically, miR-92a-3p expression is significantly increased in CRC tissues and negatively correlated with the levels of FBXW7 and MOAP1 in CRC specimens, and high expression of exosomal miR-92a-3p in serum was highly linked with metastasis and chemotherapy resistance in CRC patients. Conclusions CAFs secreted exosomes promote metastasis and chemotherapy resistance of CRC. Inhibiting exosomal miR-92a-3p provides an alternative modality for the prediction and treatment of metastasis and chemotherapy resistance in CRC. Electronic supplementary material The online version of this article (10.1186/s12943-019-1019-x) contains supplementary material, which is available to authorized users.

Circular RNAs (circRNAs), a large class of RNAs, have recently shown huge capabilities as gene regulators in mammals. Some of them bind with microRNAs (miRNAs) and act as natural miRNA sponges to inhibit related miRNAs’ activities. Here we showed that hsa_circ_001569 acted as a positive regulator in cell proliferation and invasion of colorectal cancer (CRC). Moreover, hsa_circ_001569 was identified as a sponge of miR-145 and up-regulated miR-145 functional targets E2F5, BAG4 and FMNL2. In CRC tissues, circ_001569 negatively correlated with miR-145, and miR-145 correlated negatively with E2F5, BAG4 and FMNL2 expressions. Our study reveals a novel regulatory mechanism of circ_001569 in cell proliferation and invasion in CRC, provides a comprehensive landscape of circ_001569 that will facilitate further biomarker discoveries in the progression of CRC.