miR-542-3p/PIK3R1 axis is involved in hsa_circ_0087104-mediated inhibition of esophageal squamous cell carcinoma metastasis.

Esophageal squamous cell carcinoma (ESCC), the most predominant subtype of esophageal cancer, is notorious for its high lymph node metastatic potential and poor prognosis. Growing evidence has demonstrated crucial function of circRNAs in human malignancies. However, the knowledge of circRNAs in lymph node metastasis of ESCC is still inadequate. In this study, a series of bioinformatic analyses and experimental validation were performed. By performing differential expression analysis and selection for GEO dataset GSE150476, a total of 8 circRNAs associated with lymph node metastasis of ESCC were identified. Expression analysis confirmed their low expression in ESCC tissues (relative to normal tissues) or metastatic sites (relative to primary sites). By combination of binding miRNAs from CSCD and starBase databases, six potential miRNAs (miR-532-5p, miR-2681-5p, miR-670-5p, miR-1252-5p, miR-382-3p and miR-542-3p) were predicted and a circRNA-miRNA regulatory network was constructed. Next, 695 target genes were predicted to bind to the 6 miRNAs. After conducting protein-protein interaction (PPI) network analysis, hub gene identification and expression analysis, a hub gene PIK3R1 was identified as the most potential downstream target gene of hsa_circ_0087104/miR-542-3p in ESCC. Hsa_circ_0087104 and PIK3R1 were decreased while miR-542-3p was increased in ESCC cells compared with normal esophageal epithelial cell line. Luciferase reporter and MS2-RIP assays confirmed the direct bind of miR-542-3p to hsa_circ_0087104 or PIK3R1. Hsa_circ_0087104 increased PIK3R1 expression but ectopic expression of miR-542-3p reversed hsa_circ_0087104-mediated PIK3R1 overexpression in ESCC. Overexpression of hsa_circ_0087104 suppressed