Identification of the tumor-suppressive function of circular RNA ITCH in glioma cells through sponging miR-214 and promoting linear ITCH expression

Circular RNAs (circRNAs) is a class of endogenous noncoding RNAs that, unlike linear RNAs, form covalently closed continuous loops and have recently shown huge capabilities as gene regulators in mammals. However, little is known about their roles in cancer initiation and progression, such as glioma. In this study, we determined the expression level of circRNA ITCH (cir-ITCH) in glioma specimens and further investigated its functional role in glioma cells. By performing Taq-man based RT-qPCR, we identified that cir-ITCH was downregulated in glioma tissues and cell lines. Receiver operating curve analysis suggested cir-ITCH showed a relatively high diagnostic accuracy. Kaplan-Meier assay revealed that decreased cir-ITCH level was associated with poor survival of glioma patients. The functional relevance of cir-ITCH was further examined by biological assays. Cir-ITCH significantly promoted the capacities of cell proliferation, migration and invasion of glioma cells. The linear isomer of cir-ITCH, ITCH gene was then identified as the down stream target. Subsequently, RNA immunoprecipitation clearly showed that cir-ITCH sponged miR-214, which further promoted the ITCH expression. Finally, the gain and loss functional assays indicate that cir-ITCH plays an anti-oncogenic role through sponging miR-214 and regulating ITCH-Wnt/β-catenin pathway. These results suggest that cir-ITCH is a tumor-suppressor gene in glioma and may serve as a promising prognostic biomarker for glioma patients. Therefore, restoration of cir-ITCH expression could be a future direction to develop a novel treatment strategy.