Long Noncoding RNA DCST1-AS1 Promotes Cell Proliferation and Metastasis in Triple-negative Breast Cancer by Forming a Positive Regulatory Loop with miR-873-5p and MYC

Background: DC-STAMP domain containing 1-antisense 1 (DCST1-AS1) is a long noncoding RNA (lncRNA) that is up-regulated in triple-negative breast cancer (TNBC) tissues. Here, we attempt to investigate the oncogenic property of DCST1-AS1. Methods: LncRNA microarrays were used to detect differentially expressed lncRNA in cancerous tissues. Fluorescence in situ hybridization assay was used to detect the distribution of DCST1-AS1 in BT-549 and MDA-MB-231 cells. Lentiviral systems, inhibitors, siRNA and overexpression plasmids were used for gain- and loss-of-function experiments. Colony formation assay, wound healing assay, CCK8 assay, transwell assay, and flow cytometry assay were used to study the function of DCST1-AS1. Luciferase assay was used to verify the binding of MYC to the promoter region and the binding of miR-873-5p to DCST1-AS1. RNA immunoprecipitation assay was used to verify that argonaute 2 binds to both miR-873-5p and DCST1-AS1. Western blotting was used to measure changes in protein expression. Results: Consistent with the microarray results, we found that DCST1-AS1 was up-regulated in both TNBC tissue samples and cell lines. DCST1-AS1 was positively correlated with distant metastasis and histopathological grades. DCST1-AS1 is distributed in both nucleus and cytoplasm. Knockdown of DCST1-AS1 inhibits TNBC cell proliferation and metastasis, while overexpression of DCST1-AS1 promotes TNBC cell proliferation and metastasis. We confirmed that DCST1-AS1 expression in TNBC cells is regulated by MYC. Furthermore, we found that DCST1-AS1 is negatively correlated with miR-873-5p in TNBC tissues and is a direct target gene of miR-873-5p. Argonaute 2 is involved in the binding of DCST1-AS1 and miR-873-5p and promotes the degradation of DCST1-AS1. The interaction of DCST1-AS1 with miR-873-5p ultimately up-regulated the expression of insulin-like growth factor 2 mRNA binding protein 1 (IGF2BP1), MYC, CD44 and lymphoid enhancer binding factor 1 (LEF1). Conclusions: DCST1-AS1 is activated by MYC and is degraded by binding to miR-873-5p, thereby upregulating the expression of miR-873-5p downstream proteins IGF2BP1, MYC, LEF1 and CD44. MYC, DCST1-AS1 and miR-873-5p form a positive regulatory loop to promote TNBC cell proliferation and metastasis.