CircTTBK2 Contributes to the Progression of Glioma Through Regulating miR-145-5p/CPEB4 Axis

Background: Currently, circular RNAs (circRNAs) have been demonstrated to play vital roles in malignant tumors, including glioma. Nevertheless, the functions of circTTBK2 in glioma are largely unclear. Materials and Methods: Quantitative real-time polymerase chain reaction (qRT-PCR) was applied for the expression levels of circTTBK2, TTBK2 mRNA, miR-145-5p and cytoplasmic polyadenylation element binding protein 4 (CPEB4) mRNA. Actinomycin D and RNase R digestion assays were utilized for the characteristics of circTTBK2. 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT) assay, flow cytometry analysis and transwell assay were conducted for cell proliferation, apoptosis and metastasis, respectively. The glycolysis level was estimated with specific kits. Western blot assay was adopted for the protein levels of hexokinase2 (HK2) and CPEB4. The targeting relationship between miR-145-5p and circTTBK2 or CPEB4 was verified by Dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. Murine xenograft assay was used for the role of circTTBK2 in tumorigenesis in vivo. Results: CircTTBK2 was upregulated in glioma tissues and cells, and its level was associated with poor survival of glioma patients. CircTTBK2 knockdown suppressed glioma cell proliferation, migration, invasion and glycolysis and accelerated apoptosis in vitro and hampered tumor growth in vivo. CircTTBK2 functioned as a sponge of miR-145-5p, and miR-145-5p inhibition restored the effects of circTTBK2 knockdown on the malignant behaviors of glioma cells. Moreover, CPEB4 was the direct target gene of miR-145-5p, and miR-145-5p inhibition facilitated glioma cell progression by targeting CPEB4. Conclusion: CircTTBK2 functioned as a tumor promoter in glioma by modulating miR-145-5p/CPEB4 axis, which might offer a new sight for glioma therapy.