Background: Cancer-associated fibroblasts (CAFs) have been intensively studied in recent studies with aims of finding more concrete evidence on their mechanism of involvement in tumor progression, which is currently unknown. CAFs can secrete exosomes which are loaded with proteins, lipids and RNAs, all of which affect tumor microenvironment. The present study identified microRNA-93-5p (miR-93-5p) as a novel exosomal cargo responsible for the pro-tumorigenic effects of CAFs on colorectal cancer (CRC). Methods: CAFs and normal fibroblasts (NFs) were isolated from cancerous tissues and matched with paracancerous tissues that had been surgically resected from CRC patients. The interaction among miR-93-5p, forkhead box A1 (FOXA1) and TGFB3 was identified through ChIP and dual luciferase reporter assays. The proliferation and apoptosis of SW480 cells co-cultured with CAFs-derived exosomes under irradiation were evaluated by CCK-8, colony formation, and flow cytometric assays. Tumorigenesis of SW480 cells in nude mice was assessed under the irradiation. Results: FOXA1 was found to be associated with reduced radioresistance in CRC cells and was verified as a target of miR-93-5p. CAFs-derived exosomes contained higher miR-93-5p than those from NFs, which augmented SW480 cell proliferation and rescued them from radiation-induced apoptosis. miR-93-5p was identified as a mediator of the exosomal effects of CAFs on SW480 cells, possibly through downregulating FOXA1 and upregulating TGFB3. FOXA1 could bind to the promoter of TGFB3, thereby inhibiting nuclear accumulation of TGFB3. Also, CAFs-derived exosomes containing miR-93-5p increased the tumor growth of SW480 cells in irradiated nude mice. Conclusion: The present study identifies miR-93-5p as a specific exosomal cargo that rescues CRC cells against radiation-induced apoptosis.
Radiotherapeutic resistance is a major obstacle for the effective treatment of colorectal cancer (CRC). MicroRNAs (miRNAs) play a critical role in chemoresistance and radioresistance. Here, we aimed to investigate whether miR-590-3p participates in the radioresistance of CRC. High expression of miR-590-3p and low expression of CLCA4 were found in both CRC tissues and cell lines. CLCA4 was indicated to be a target gene of miR-590-3p. CAF-derived exosomes were extracted and co-cultured with CRC cells, which were then exposed to radiation. CRC cells were transfected with plasmids and injected into nude mice to detect the
in vivo
effect of CAF-derived exosomes. Treatment with CAF-derived exosomes decreased the sensitivity of CRC cells to radiation. CAF-derived exosomes overexpressing miR-590-3p increased cell survival and the ratio of p-PI3K/PI3K and p-AKT/AKT while lowering the expressions of cleaved-PARP, cleaved-caspase 3, and γH2AX in cells. Furthermore,
in vivo
experimental results confirmed that CAF-derived exosomal miR-590-3p stimulated tumor growth in mice following radiotherapy. Our results demonstrate that miR-590-3p delivery via exosomes derived from CAFs enhances radioresistance in CRC through the positive regulation of the CLCA4-dependent PI3K/Akt signaling pathway.
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