Xin Liu

Purpose: Gastric cancer is a leading cause of cancer-related mortality worldwide, with metastasis being the primary cause of death. Exosomes secreted by tumor cells are key mediators of intercellular communication and can prepare distant sites for metastasis by altering the local microenvironment. We hypothesized that exosomes released by gastric cancer cells deliver cargo that regulates specific proteins in recipient gastric cancer cells, thereby enhancing tumor progression and metastatic potential. Methods: Human gastric cancer cell lines were treated with exosomes isolated from the conditioned medium of other gastric cancer cells. Differential proteomic analysis was performed to identify proteins significantly altered by exosome treatment. ITGA2 expression was validated in exosome-treated cells and in clinical gastric cancer tissues versus adjacent normal tissues using RT-qPCR and western blotting. The functional role of ITGA2 was assessed by siRNA-mediated knockdown, followed by MTT proliferation assays and fluorometric transwell assays for migration and invasion. A second proteomic analysis was conducted on ITGA2-knockdown versus control cells to identify downstream targets and affected pathways. Results: Exosome treatment significantly upregulated ITGA2 expression in recipient gastric cancer cells. ITGA2 was also markedly overexpressed in human gastric cancer tissues compared with adjacent normal mucosa. Knockdown of ITGA2 significantly suppressed cell proliferation, migration, and invasion. Proteomic profiling of ITGA2-knockdown cells revealed numerous differentially expressed proteins enriched in pathways related to cell adhesion, motility, extracellular matrix organization, and intercellular signaling. Conclusion: Exosomes derived from gastric cancer cells induce ITGA2 overexpression in recipient tumor cells, where ITGA2 functions as an oncogene that promotes proliferation, migration, and invasion. The downstream targets of ITGA2 implicate multiple pro-tumorigenic signaling networks, suggesting that the exosomes–ITGA2 axis may represent a novel therapeutic target in gastric cancer progression and metastasis.

Introduction: MiRNAs play important roles in development of various cancers including gastric cancer. Exosomes are extracellular vesicles for translocating molecules. This study aimed to investigate the tumor suppressive roles of miR-379-5p in gastric cancer and to investigate the roles of exosomes in transporting miR-379-5p from intracellular to extracellular. Methods: Fifty-three pairs of gastric cancer and non-tumor tissue samples were collected. Five cell lines were applied. Functional assays including cell proliferation, cell migration and invasion, and cell adhesion assay were performed. Targets of miR-379-5p were screened and validated by Western blot. Expressions of endogenous miR-379-5p in gastric cancer cells and exosomal miR-379-5p in cell culture medium were evaluated by RT-qPCR. Medium of culturing AGS or BCG23 was applied for culturing MKN45 and HEK293T. Results: The results indicated that miR-379-5p was significantly downregulated in gastric cancer tissue samples and cell lines. Enforced expression of miR-379-5p inhibited gastric cancer cell proliferation, migration, and invasion, while miR-379-5p mimic enhanced cell adhesion to extracellular matrix. IGF1R was a potential target of miR-379-5p in gastric cancer. Expression of miR-379-5p was dramatically higher in exosomes in cell culture medium than its endogenous expression. Exosomes from cell culture medium of AGS or BCG23 could regulate endogenous expression of miR-379-5p in HEK293T cells. Conclusions: MiR-379-5p was significantly downregulated and it functioned as a tumor suppressor in gastric cancer. MiR-379-5p was highly expressed in exosomes of culture medium than its endogenous expression. MiR-379-5p could be translocated from cells into cell culture medium and entered certain cell types via exosomes.

MicroRNAs play significant roles in cancer initiation and progression. Exosomes are important extracellular vesicles for transporting molecules to distant sites. This study aims to investigate the functional roles of miR-4103p in primary gastric cancer, as well as the roles of exosomes in regulating expression of miR-410-3p. In this study, forty-seven pairs of human gastric cancer tissue samples were collected. Endogenous expression of miR-410-3p in tissue samples and cell lines, and expression of exosomal miR-410-3p in cell culture medium were evaluated by RT-qPCR. Functional assays including cell proliferation assay by MTT, cell migration and invasion assay by transwell, and cell adhesion assay were performed. Targets of miR-410-3p were screened. Cell culture medium of culturing cell lines established from stomach (AGS and BCG23) was applied for culturing cell lines established from other sites (MKN45 and HEK293T). It was found that miR-410-3p was significantly downregulated in gastric cancer. Overexpression of miR-410-3p inhibited gastric cancer cell proliferation, migration, and invasion. MiR-410-3p mimic enhanced cell adhesion. HMGB1 was a target of miR-410-3p in primary gastric cancer. Expression of exosomal miR410-3p in cell culture medium was dramatically higher than its endogenous expression. Exosomes from cell culture medium of AGS or BCG23 regulated endogenous expression of miR-410-3p in MKN45. In conclusion, miR-410-3p functioned as a tumor suppressor in primary gastric cancer. MiR-410-3p was higher expressed in exosomes of cell culture medium than its endogenous expression in cells. Endogenous expression of miR-410-3p in a distant site could be regulated by exosomes from the original site.

Exosomes secreted by living cancer cells can regulate metastasis. Exosomal miRNAs can reflect pathological conditions of the original cancer cells. Therefore, we aim to identify exosomal miRNAs as circulating biomarkers for haematogenous metastasis of gastric cancer. Pre‐treatment serum samples of eighty‐nine patients with stage II/III gastric cancer were collected. Thirty‐four of them developed haematogenous metastasis after surgery and the other fifty‐five did not. Extraction of exosomes was validated by western blot, transmission electron microscopy and nanoparticle tracking analysis. MiRNA qPCR array was performed in three matched pairs of samples. Internal control was selected from PCR array and validated in the remaining samples. Expressions of exosomal miRNAs were evaluated in the remaining samples by RT‐qPCR, as well as in gastric cancer tissue samples and cell culture medium. Expression levels of exosomal miRNAs were analysed with clinical characteristics. The results indicated thirteen up‐regulated and six down‐regulated miRNAs were found after normalization. MiR‐379‐5p and miR‐410‐3p were significantly up‐regulated in metastatic patients (P < .01). Higher expression of exosomal miR‐379‐5p or miR‐410‐3p showed shorter progression‐free survival of the patients (P < .05). It was also found that miR‐379‐5p and miR‐410‐3p were down‐regulated in gastric cancer tissue samples, while they were significantly up‐regulated in gastric cancer cell culture medium compared with cancer cells. In conclusion, exosomal miRNAs are promising circulating biomarkers for prediction of development of haematogenous metastasis after surgery for stage II/III gastric cancer.

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gastrointestinal tract. However, the development of molecular markers, especially circulating biomarkers, remains largely undone for the prognosis of GIST. We discussed the clinical-pathological characteristics of GIST and identified potential biomarkers for guidance of therapy and prognosis of GIST. Around 90% of GISTs contain mutations in KIT or PDGFRA and the remaining 10% of GISTs are wild-type. Recent studies have indicated that various DNAs and miRNAs could serve as potential biomarkers for prognosis of GIST, including KIT, PDGFRA, other DNAs (such as BRAF, SDH, SETD2 and ROR2), and microRNAs (miRNAs). The pressing need and challenges in the development of circulating prognostic biomarkers for GIST are also discussed. Although challenges remain, DNAs and miRNAs are promising circulating biomarkers for surveillance and prognosis of GIST. Advances in clarification of aberrant molecular alterations may open new avenues for exploration of reliable and robust biomarkers to improve the management of GIST.

It was reported that circulating microRNAs could be applied as non-invasive biomarkers for cancer monitoring. The purpose of this study was to identify plasma miRNA that may serve as a novel biomarker for gastric cancer and to evaluate its clinical application. MicroRNA profiles were generated from plasma samples of 5 patients with gastric cancer (GC) versus 5 healthy controls (HC). MicroRNA-940 (miR-940) was one of the most downregulated miRNAs with fold change of 0.164. It was revealed that the expression of miR-940 was downregulated in both the initial set (N = 30, P < 0.0001) and the validation set (N = 80, P < 0.0001) of plasma samples of patients with gastric cancer. The sensitivity was obviously higher than the current biomarkers CEA and CA19-9 (81.25 % vs. 22.54 % and 15.71 %). MiR-940 was also significantly downregulated in gastric cancer tissue samples (N = 34, P = 0.0015), as well as in cancer cell lines (N = 7). Importantly, miR-940 was significantly highly expressed in stomach tissue samples than in other types of tissue samples including the liver, breast, thyroid, and lung. Moreover, there was a trend of lower expression of miR-940 from early to advanced stage of gastric cancer. Target prediction suggested that miR-940 regulated cell signaling including NF-κB and Wnt/β-catenin, as well as pathways of cell communication and adhesion. These pathways play critical roles in gastric cancer initiation and progression. It is the first report that miR-940 may mainly express in the stomach. Downregulation of plasma miR-940 may serve as a novel biomarker for detection of gastric cancer.