MiR-218 inhibits malignant phenotypes of glioma by targeting TNC/AKT/AP-1/TGFβ1 feedback signaling loop

Abstract Background: Gliomas are the most common and malignant tumors in the brain of humans, and the prognosis of glioma patient is very poor. MicroRNAs (miRNAs) play critical roles in different types of cancer by regulating gene expression at the posttranscriptional levels. Although miR-218 has been reported to be downregulated in gliomas, its role in gliomas still remains largely unknown. Methods: MiR-218 expression in gliomas and normal brain tissues (control subjects) were analyzed using TCGA dataset. The biological roles of miR-218 in glioma cells were determined by a series of in vitro and in vivo studies. The dual-luciferase reporter system was performed to identify potential targets of miR-218. The regulatory effect of miR-218 on TNC/AKT/AP-1/TGFβ1 pathway was evaluated by dual-luciferase reporter system and western blot.Results: We demonstrated miR-218 was significantly downregulated in gliomas compared to control subjects, and exerted a potent tumor suppressor in glioma cells by inhibiting cell proliferation, colony formation, migration, invasion and tumorigenic potential in nude mice, as well as inducing cell cycle arrest and apoptosis.Mechanistically, miR-218 inhibited malignant phenotypes of glioma cells by binding to the 3’ UTR of its target TNC and subsequently repressing its expression. As a result, it could reduce AKT phosphorylation and subsequently inhibit transcriptional activity of AP-1 by reducing JNK phosphorylation, downregulating the expression of TGFβ1, while TGFβ1 is able to, in turn, activate the TNC/AKT/AP-1 signaling axis.Conclusions: Our data uncover a previously unknown tumor suppressor role of miR-218 in glioma by blocking the TNC/AKT/AP-1/TGFβ1 positive feedback loop.