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.