TTBK2 circular RNA promotes glioma malignancy by regulating miR-217/HNF1β/Derlin-1 pathway

Abstract

BackgroundCircular RNAs are a subgroup of non-coding RNAs and generated by a mammalian genome. Herein, the expression and function of circular RNA circ-TTBK2 were investigated in human glioma cells.MethodsFluorescence in situ hybridization and quantitative real-time PCR were conducted to profile the cell distribution and expression of circ-TTBK2 and microRNA-217 (miR-217) in glioma tissues and cells. Immunohistochemical and western blot were used to determine the expression of HNF1β and Derlin-1 in glioma tissues and cells. Stable knockdown of circ-TTBK2 or overexpression of miR-217 glioma cell lines (U87 and U251) were established to explore the function of circ-TTBK2 and miR-217 in glioma cells. Further, luciferase reports and RNA immunoprecipitation were used to investigate the correlation between circ-TTBK2 and miR-217. Cell Counting Kit-8, transwell assays, and flow cytometry were used to investigate circ-TTBK2 and miR-217 function including cell proliferation, migration and invasion, and apoptosis, respectively. ChIP assays were used to ascertain the correlations between HNF1β and Derlin-1.ResultsWe found that circ-TTBK2 was upregulated in glioma tissues and cell lines, while linear TTBK2 was not dysregulated in glioma tissues and cells. Enhanced expression of circ-TTBK2 promoted cell proliferation, migration, and invasion, while inhibited apoptosis. MiR-217 was downregulated in glioma tissues and cell lines. We also found that circ-TTBK2, but not linear TTBK2, acted as miR-217 sponge in a sequence-specific manner. In addition, upregulated circ-TTBK2 decreased miR-217 expression and there was a reciprocal negative feedback between them in an Argonaute2-dependent manner. Moreover, reintroduction of miR-217 significantly reversed circ-TTBK2-mediated promotion of glioma progression. HNF1β was a direct target of miR-217, and played oncogenic role in glioma cells. Remarkably, circ-TTBK2 knockdown combined with miR-217 overexpression led to tumor regression in vivo.ConclusionsThese results demonstrated a novel role circ-TTBK2 in the glioma progression.Electronic supplementary materialThe online version of this article (doi:10.1186/s13045-017-0422-2) contains supplementary material, which is available to authorized users.

Circular RNA Expression Profiles Alter Significantly in Mouse Brain After Transient Focal Ischemia

“…14,15 The miR-223 is known to cause cardiac hypertrophy and the heart-related circRNA HRCR is thought to protect the heart by sponging miR-223. 49 The circRNA TTBK2 was shown to promote malignancy of gliomas by modulating miR-217 that controls hepatocyte nuclear factor 1β/Derlin-1 pathway, 50 and circRNA ITCH is known to suppress lung cancer by sponging miR-7 and miR-214 thereby suppressing the activation of Wnt/β-catenin 51 . In the present study, the circRNAs altered after stroke were identified to contain binding sites for many miRNAs indicating their potential to modulate miRNA-mediated translation and thus ischemic pathophysiology.…”

The circRNA–microRNA code: emerging implications for cancer diagnosis and treatment

“…Zheng et al . () found that circ‐TTBK2, but not linear TTBK2, is upregulated in human malignant glioma. circ‐TTBK2 gains oncogene features by binding with miR‐217, which is usually downregulated in glioma tissues and cell lines.…”

“…circ‐TTBK2 increases HNF1β expression in cancer, acting as miR‐217 sponge, and as a result, miR‐217 cannot negatively regulate HNF1β by targeting its 3′‐UTR. HNF1β is known to activate the transcription of oncogene Derlin‐1 binding its promoter region (Zheng et al ., ).…”

The role of micro-RNA in the regulation of signal pathways in gliomas

“…Например, РНК circ-TTBK2 гиперрегулирована в тканях глиомы и клеточных линиях, в то время как линейная TTBK2 не изменяет своего уровня [136]. Circ-TTBK2 действует как губка для miR-217, уровень которой был снижен при глиоме, и мишенью которой является онкогенный белок HNF1b (HNF1 homeobox beta).…”

“…Circ-TTBK2 действует как губка для miR-217, уровень которой был снижен при глиоме, и мишенью которой является онкогенный белок HNF1b (HNF1 homeobox beta). Нокдаун circ-TTBK2 совместно с гиперэкспрессией miR-217 приводили к регрессии опухоли in vivo [136]. Совсем недавно был разработан компьютерный алгоритм-pipeline "UROBORUS" для детекции circRNA, исходя из данных RNA-seq [137].…”