Abstract
BackgroundAngiogenesis plays a critical role in the progression of glioma. Previous studies have indicated that RNA-binding proteins (RBPs) interact with RNAs and participate in the regulation of the malignant behaviors of tumors. As a type of endogenous non-coding RNAs, circular RNAs (circRNAs) are abnormally expressed in various cancers and are involved in diverse tumorigeneses including angiogenesis.MethodsThe expression levels of FUS, circ_002136, miR-138-5p, SOX13, and SPON2 were determined using quantitative real-time PCR (qRT-PCR) and western blot. Transient cell transfection was performed using the Lipofectamine 3000 reagent. The RNA-binding protein immunoprecipitation (RNA-IP) and the RNA pull-down assays were used to detect the interaction between FUS and circ_002136. The dual-luciferase reporter assay system was performed to detect the binding sites of circ_002136 and miR-138-5p, miR-138-5p and SOX13. The chromatin immunoprecipitation (ChIP) assays were used to examine the interactions between transcription factor SOX13 and its target proteins .ResultsWe demonstrated that down-regulation of FUS or circ_002136 dramatically inhibited the viability, migration and tube formation of U87 glioma-exposed endothelial cells (GECs). MiR-138-5p was down-regulated in GECs and circ_002136 functionally targeted miR-138-5p in an RNA-induced silencing complex (RISC). Inhibition of circ_002136, combined with the restoration of miR-138-5p, robustly reduced the angiogenesis of GECs. As a target gene of miR-138-5p, SOX13 was overexpressed in GECs and was proved to be involved in circ_002136 and miR-138-5p-mediated angiogenesis in gliomas. In addition, we found that SOX13 was directly associated with and activated the SPON2 promoter, thereby up-regulating the expression of SPON2 at the transcriptional level. Knockdown of SPON2 suppressed the angiogenesis in GECs. More important, SOX13 activated the FUS promoter and increased its expression, forming a feedback loop.ConclusionOur data suggests that the feedback loop of FUS/circ_002136/miR-138-5p/SOX13 played a crucial role in the regulation of angiogenesis in glioma. This also provides a potential target and an alternative strategy for combined glioma therapy.
Highlights
Angiogenesis plays a critical role in the progression of glioma
The shRNA of Fused in sarcoma (FUS) was transfected into Glioma-exposed endothelial cells (GEC) to silence FUS, and the transfection efficiency was evaluated by western blot (Additional file 1: Figure S1A)
This study demonstrated for the first time that FUS, circ_002136, SOX13 and SPON2 were highly expressed, while miR-138-5p was under-expressed in GECs
Summary
Angiogenesis plays a critical role in the progression of glioma. Previous studies have indicated that RNA-binding proteins (RBPs) interact with RNAs and participate in the regulation of the malignant behaviors of tumors. Malignant glioma is the most common primary tumor in the human central nervous system. Despite many advances in surgical techniques, chemotherapeutics and radiation therapy, the prognosis of patients with malignant gliomas remains obstinately poor. Glioma progression depends on tumor blood vessel growth. Glioma cells secrete vascular endothelial growth factor and other pro-angiogenic factors to promote the growth of vascular endothelial cells. Glial vascular endothelial cells secrete a variety of factors that promote tumor growth. The interactions of these secreted factors can promote glioma growth [1]. Anti-angiogenesis therapeutics are considered as important treatments for malignant glioma, and an in-depth study of angiogenesis in glioma is in need
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