miR-504 suppresses mesenchymal phenotype of glioblastoma by directly targeting the FZD7-mediated Wnt–β-catenin pathway

BACKGROUND: MicroRNAs (miRNAs) play crucial roles in tumor initiation and development. Previously, we indicated that miR-504 is downregulated and suppresses tumor proliferation in glioblastoma (GBM). However, the regulation and relevant mechanism of miR-504 in GBM mesenchymal (ME) transition remain unclear. METHODS: Transcriptome and clinical data were obtained from The Cancer Genome Atlas (TCGA) database. The potential functions of miR-504 were predicted using gene ontology analysis. GBM cell migration and invasion were examined using wound healing and Transwell assays. Epithelial–mesenchymal transition (EMT) progression in GBM cell lines was detected with immunofluorescence and western blotting. The stemness activity of glioma stem-like cells (GSCs) was assessed by sphere formation assay and tumor xenograft model. miR-504 binding to the FZD7 (frizzled class receptor 7) 3′ untranslated region (3′UTR) was validated using dual luciferase reporter assay. TOP/FOP Flash assays were conducted to determine the effects of miR-504 on Wnt/β-catenin signaling. RESULTS: Analysis of TCGA transcriptomic data showed that low miR-504 expression correlated with ME subtype transition and poor survival in patients with GBM. Functional experiments showed that miR-504 overexpression suppressed malignant behaviors of GBM cells, such as migration, invasion, EMT, and stemness activity. Furthermore, miR-504 was a negative regulator of the Wnt–β-catenin pathway by directly repressing FZD7 expression, and FZD7 overexpression reversed the EMT inhibition caused by miR-504. Moreover, the low miR-504/FZD7 expression ratio was a ME subtype marker and could serve as a significant prognostic indicator and predict the clinical outcome of chemotherapy and radiotherapy for patients with GBM in TCGA dataset. CONCLUSIONS: Our results suggest that miR-504 suppresses the aggressive biological processes associated with the ME phenotype of GBM and could be a potential candidate for therapeutic applications in these malignant brain tumors. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13046-019-1370-1) contains supplementary material, which is available to authorized users.