Involvement of FOS-mediated miR-181b/miR-21 signalling in the progression of malignant gliomas

Recently, a group of microRNAs (miRNAs) were shown to be dysregulated in gliomas, and involved in glioma development. However, the effect of miRNA–miRNA functional networks on gliomas is poorly understood. In this study, we identified that FBJ murine osteosarcoma viral oncogene homolog (FOS)-mediated miR-181b/miR-21 signalling was critical for glioma progression. Using microarrays and quantitative RT-PCR (qRT-PCR), we found increased FOS in high grade gliomas. FOS depletion (via FOS-shRNA), inhibited invasion and promoted apoptosis in glioma cells. Using microarrays, combined with Pearson correlation analysis, we found FOS positively correlated with miR-21 expression. Reduction of FOS inhibited miR-21 expression by binding to the miR-21 promoter using luciferase reporter assays. Introduction of miR-21 abrogated FOS knockdown-induced cell invasion and apoptosis. Moreover, bioinformatics and luciferase reporter assays showed that miR-181b modulated FOS expression by directly targeting the binding site within the 3′UTR. Expression of FOS with a FOS cDNA lacking 3′UTR overrided miR-181b-induced miR-21 expression and cell function. Finally, immunohistochemistry (IHC) and in situ hybridisation (ISH) analysis revealed a significant correlation in miR-181b, FOS and miR-21 expression in nude mouse tumour xenograft and human glioma tissues. To our knowledge, it is the first time to demonstrate that miR-181b/FOS/miR-21 signalling plays a critical role in the progression of gliomas, providing important clues for understanding the key roles of transcription factor mediated miRNA–miRNA functional network in the regulation of gliomas.