Peritoneal metastasis is a primary metastatic route for gastric cancers, and the mechanisms underlying this process are still unclear. Peritoneal mesothelial cells (PMCs) undergo mesothelial-to-mesenchymal transition (MMT) to provide a favorable environment for metastatic cancer cells. In this study, we investigated how the exosomal miR-21-5p induces MMT and promotes peritoneal metastasis. Gastric cancer (GC)-derived exosomes were identified by transmission electron microscopy and western blot analysis, then the uptake of exosomes was confirmed by PKH-67 staining. The expression of miR-21-5p and SMAD7 were measured by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot, and the interactions between miR-21-5p and its target genes SMAD7 were confirmed by Luciferase reporter assays. The MMT of PMCs was determined by invasion assays, adhesion assays, immunofluorescent assay, and western blot. Meanwhile, mouse model of tumor peritoneal dissemination model was performed to investigate the role of exosomal miR-21-5p in peritoneal metastasis in vivo. We found that PMCs could internalize GC-derived exosomal miR-21-5p and led to increased levels of miR-21-5p in PMCs. Through various types of in vitro and in vivo assays, we confirmed that exosomal miR-21-5p was able to induce MMT of PMCs and promote tumor peritoneal metastasis. Moreover, our study revealed that this process was promoted by exosomal miR-21-5p through activating TGF-β/Smad pathway via targeting SMAD7. Altogether, our data suggest that exosomal miR-21-5p induces MMT of PMCs and promote cancer peritoneal dissemination by targeting SMAD7. The exosomal miR-21-5p may be a novel therapeutic target for GC peritoneal metastasis.

Cisplatin (CDDP) resistance is a major clinical problem associated with poor prognosis in gastric cancer (GC) patients. In this study, we performed integrated analysis of TCGA data from microRNAs (miRNAs) expression matrix of GC patients who received CDDP-based chemotherapy with GEO dataset which contains differential miRNAs expression profiles in CDDP-resistant and -sensitive cell lines. We identified miR-148a-3p downregulation as a key step involved in CDDP resistance. Using a cohort consisting 105 GC patients who received CDDP-based therapy, we found that miR-148a-3p downregulation was associated with a decrease in patients’ disease-free survival (DFS, P=0.0077). A series of experiment data demonstrated that: 1) miR-148a-3p was downregulated in CDDP-resistant GC cell lines; 2) miR-148a-3p reconstitution sensitized CDDP-resistant cells to CDDP treatment through promoting mitochondrial fission and decreasing AKAP1 expression level; 3) AKAP1 played a novel role in CDDP resistance by inhibiting P53-mediated DRP1 dephosphorylation; 4) miR-148a-3p reconstitution in CDDP-resistant cells inhibits the cyto-protective autophagy by suppressing RAB12 expression and mTOR1 activation. Taken together, our study demonstrates that miR-148a-3p could be a promising prognostic marker or therapeutic candidate for overcoming CDDP resistance in GC.

BackgroundMicroRNAs are endogenously expressed, small non-coding RNAs that modulate gene expression by targeting specific mRNAs, resulting in translational repression or mRNA degradation. Although miR-584-5p has been reported to play a vital role in various malignancies, its role and the molecular mechanisms underlying the effects of miR-584-5p in gastric cancer (GC) remain to be clarified. In this study, we investigated the role of miR-584-5p in GC.MethodsThe expression of miR-584-5p and its specific target gene were determined in human GC specimens and cell lines by microRNA real-time polymerase chain reaction (RT-PCR), quantitative RT-PCR (qRT-PCR) and Western blot. The effects of miR-584-5p depletion or ectopic expression on GC proliferation were evaluated in vitro using CCK-8 proliferation assays, 5-ethynyl-2'-deoxyuridine (EdU) incorporation, colony formation assays and cell-cycle assays and the in vivo effects were investigated using a mouse tumorigenicity model. Cell apoptosis was evaluated by in vitro flow cytometric analysis, cell viability assays and in vivo TUNEL assays. Luciferase reporter assays were employed to identify interactions between miR-584-5p and its specific target gene.ResultsA series of in vitro and in vivo gain- and loss-of-function assays revealed that miR-584-5p inhibited GC cell proliferation, while apoptosis was induced. Luciferase reporter assays and Western blot analysis revealed WWP1 to be a direct target of miR-584-5p. The effects of miR-584-5p-mimic were rescued by WWP1 overexpression. In contrast, the effects of the miR-584-5p-inhibitor were impaired by WWP1-shRNA. Furthermore, miR-584-5p expression levels correlated negatively with WWP1 protein expression in GC tissues and GC cell lines. A series of investigations indicated that miR-584-5p promoted senescence and activated the TGFβ signaling pathway by downregulation of WWP1.ConclusionTaken together, these results suggest that downregulation of miR-584-5p contributes to tumor progression by downregulation of WWP1, thus, highlighting the potential of miR-584-5p as a therapeutic target for human GC.