Gastric cancer (GC) is one of the most prevalent gastrointestinal malignancies. Long noncoding RNA (lncRNA) DANCR is a newly identified oncogenic lncRNA. However, the functional role and underlying molecular mechanisms of DANCR involved in GC progress remain unclear. In the present study, we investigated the biological function and underlying mechanisms of DANCR in GC cell migration and invasion. The results showed that knockdown of DANCR inhibited migration and invasion of GC cells, whereas overexpression of DANCR showed the opposite effect. Further investigation demonstrated that lncRNA-LET was a bona fide target gene of DANCR. In addition, high DANCR and low lncRNA-LET were significantly correlated with lymph node metastasis and late clinical stage. DANCR associated with EZH2 and HDAC3 to epigenetically silence lncRNA-LET and then regulated GC migration and invasion. Taken together, these findings indicate an important role for DANCR–lncRNA-LET axis in GC cell migration and invasion, and reveal a novel epigenetic mechanism for lncRNA-LET silencing.

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of cells, which have been revealed to inhibit T-cell responses in tumor-bearing mice. In addition, a number of immune suppressive mechanisms have linked MDSCs and the development of human cancer. However, the role of MDSCs in human gastric cancer tissue remains to be elucidated as specific markers are lacking. Therefore, the aim of the present study was to investigate the frequency and immune suppressive function of MDSCs denoted in the present study as cluster of differentiation 14 (CD14)+human leukocyte antigen (HLA)-DR-/low in gastric cancer patients. In the present study, MDSCs were directly isolated and characterized from the tumor and adjacent normal tissue of gastric cancer patients. Functional analysis of the CD14+HLA-DR-/low MDSCs co-cultured with allogeneic CD4+ T cells were performed and compared with controls. In addition, the interferon-γ (IFN-γ) and interleukin (IL)-2 production was compared in order to investigate the capacity of vasoactive intestinal peptide (VIP) to induce CD14+HLA-DR(-/low) MDSC-mediated CD4+ T-cell dysfunction and whether IL-10 secretion is involved in this mechanism. As a result, the quantity of CD14+HLA-DR(-/low) cells in tumor tissue from gastric cancer patients was significantly higher than that in the adjacent normal tissue. In addition, CD14+HLA-DR-/low MDSCs isolated from tumor tissue were observed to inhibit the CD4+ T-cells' immune responses in comparison with those from the adjacent normal tissue. Furthermore, VIP was able to induce the differentiation of CD14+ mononuclear cells isolated from healthy donor peripheral blood mononuclear cells into activated MDSC cells. Of note, the immunosuppressive effect of VIP-induced CD14+HLA-DR(-/low) MDSCs on CD4+ T cells was mediated by IL-10 secretion, which was demonstrated in the subsequent decrease of IFN-γ and IL-2 production. In conclusion, CD14+HLA-DR(-/low) cells were significantly increased in gastric cancer tissue and were shown to have a critical role in CD4+T-cell immunosuppression. In addition, VIP as a novel cytokine may induce the differentiation of CD14+ mononuclear cells towards CD14+HLA-DR(-/low) MDSCs. An improved understanding of phenotypic heterogeneity and the mechanism of generation of MDSCs in gastric cancer patients is important in the design of effective immunotherapeutic strategies.