After that, purified exosomes had been found in adhesion, invasion assays, and tumor peritoneal dissemination tests. its focus on genes SMAD7 HJC0152 had been verified by Luciferase reporter assays. The MMT of PMCs was dependant on invasion assays, adhesion assays, immunofluorescent assay, and traditional western blot. On the other hand, mouse style of tumor peritoneal dissemination model was performed to research the function of exosomal miR-21-5p in peritoneal metastasis in vivo. We discovered that PMCs could internalize GC-derived exosomal led and miR-21-5p to increased degrees of miR-21-5p in PMCs. Through numerous kinds of in vitro and in vivo assays, we verified that exosomal miR-21-5p could induce MMT of PMCs and promote tumor peritoneal metastasis. Furthermore, our study uncovered that this procedure was marketed by exosomal miR-21-5p through activating TGF-/Smad pathway via concentrating on SMAD7. Entirely, our data claim that exosomal miR-21-5p induces MMT of PMCs and promote cancers peritoneal dissemination by concentrating on SMAD7. The exosomal miR-21-5p may be a novel therapeutic target for GC peritoneal metastasis. Introduction Gastric cancers (GC) is among the most common malignancies worldwide, with an increase of than 50% HJC0152 of situations taking place in Eastern Asia1. In china, GC is among the most second leading cause of cancer deaths2. According to the national survey, the number of new GC cases in China in 2015 was 679,000, with 498,000 deaths. Although surgery, radiotherapy, chemotherapy and biological treatment have been adopted so far, the 5-12 months survival rate of GC is still poor, partially on account of up to 50% of GC patients have unspecific gastrointestinal symptoms, and alarm symptoms are usually present at advanced stage in most cases3. Peritoneal metastases are common in advanced GC patients which usually leads to poor prognosis4. So far, there are still no effective treatments for peritoneal metastases due to little understandings around the underlying mechanisms. A monolayer of peritoneal mesothelial HJC0152 cells (PMCs) that lines the peritoneal cavity has been reported to be able to undergo mesothelial-to-mesenchymal transition (MMT), an important morphological switch in peritoneal metastases5. Emerging evidence shows that MMT of PMCs was observed in peritoneal dissemination and promoted early malignancy metastasis6C9. Many studies have exhibited that, through MMT, PMCs obtain enhanced invasive capacity and attach to malignancy cells, and also acquire the capacity to synthesize inflammatory and angiogenic factors, such as fibroblast growth factor, vascular endothelial growth factor and growth factor, which have a growth promotion effect in malignancy cells10C12. However, the molecular mechanisms that cause MMT of PMCs have yet to be fully explained. Exosomes were first described as 5-nucleotidase activity microvesicles by Trams et al. in 198113 which are now recognized by a few characteristics, such as, 30C150?nm in diameter, round or cup-shaped morphology, lipid composition and double lipid layer14. Exosomes contain proteins, lipids, miRNA, mRNA, and DNA, and enable the target cells to change gene expression15. Specifically, GC-derived exosomes have been proved to induce MMT of PMCs via MAPK/ERK pathway16. Furthermore, Tokuhisa M investigated exosomal miRNA profiles in peritoneal fluid and found that miR-21-5p experienced a high expression in serosal invasion GC. Their findings suggest that miR-21-5p may serve as biomarkers of peritoneal metastasis after GC resection17. Therefore we hypothesized that GC-derived exosomal miR-21-5p induces PMCs MMT, which leads to peritoneal metastasis. In this study, our experimental results indicated that GC-derived exosomal miR-21-5p can convert PMCs into MMT via targeting SMAD7, leading to the increased invasion of PMCs and attachment to tumor cells. Finally, it promoted GC peritoneal metastasis. In addition, our results suggested that TGF/Smad pathway might be involved in this pathological process. Results Characterization of GC cells-derived exosomes and internalization Exosomes from supernatant of four GC cell lines (MGC803, MKN45, HGC27, and SGC7901) and normal human gastric epithelial cell collection GES-1 were isolated and evaluated by TEM and western blot. As shown in Fig.?1a, TEM showed that exosomes had the typical round or cup-shaped morphology, measuring about 100?nm in diameter. Furthermore, western blot profile showed the presence of known exosome markers, including proteins CD63 and TSG10118, in both exosomes and cells fractions. The protein calnexin was used as the unfavorable control which was confirmed absent in exosomes but present in cells19 (Fig.?(Fig. 1 1b). Open in a separate window Fig. 1 Characterization of GC cells-derived exosomes and internalization.a Exosomes purified from culture supernatant of the four GC cells and GES-1 cells were detected by TEM (Level LRP2 bar, 200?nm). b Exosomes marker proteins CD63 and TSG101 were recognized by western blot. Calnexin was used as an internal research. c Exosomes purified from culture supernatant of the four GC cells and GES-1 cells.