circRNA derived from CLSPN (circCLSPN) is an oncogene in human glioblastoma multiforme by regulating cell growth, migration and invasion via ceRNA pathway

The Glioblastoma CircularRNAome

Glioblastoma remains one of the most aggressive cancers of the brain, warranting new methods for early diagnosis and more efficient treatment options. Circular RNAs (circRNAs) are rather new entities with increased stability compared to their linear counterparts that interact with proteins and act as microRNA sponges, among other functions. Herein, we provide a critical overview of the recently described glioblastoma-related circRNAs in the literature, focusing on their roles on glioblastoma cancer cell proliferation, survival, migration, invasion and metastasis, metabolic reprogramming, and therapeutic resistance. The main roles of circRNAs in regulating cancer processes are due to their regulatory roles in essential oncogenic pathways, including MAPK, PI3K/AKT/mTOR, and Wnt, which are influenced by various circRNAs. The present work pictures the wide implication of circRNAs in glioblastoma, thus highlighting their potential as future biomarkers and therapeutic targets/agents.

Exosomal circ-AHCY promotes glioblastoma cell growth via Wnt/β-catenin signaling pathway

BACKGROUND

Glioblastoma (GBM) is the most aggressive brain tumor. Reportedly, circular RNAs (circRNAs) participate in regulation of the development and progression of diverse cancers, including GBM.

METHODS

Dysregulated circRNAs in GBM tissues were screened out from GEO database. The expression of candidate circRNAs in GBM cells was measured by qRT-PCR. Loss-of function assays, including colony formation assay, EdU assay, TUNEL assay, and flow cytometry analysis were conducted to determine the effects of circ-AHCY knockdown on GBM cell proliferation and apoptosis. Animal study was further used to prove the inhibitory effect of circ-AHCY silencing on GMB cell growth. Mechanistic experiments like luciferase reporter, RNA pull-down and RNA-binding protein immunoprecipitation (RIP) assays were performed to unveil the downstream molecular mechanism of circ-AHCY. Nanosight Nanoparticle Tracking Analysis (NTA) and PKH67 staining were applied to identify the existence of exosomes.

RESULTS

Circ-AHCY was confirmed to be highly expressed in GBM cells. Circ-AHCY silencing suppressed GBM cell proliferation both in vitro and in vivo. Mechanistically, circ-AHCY activates Wnt/β-catenin signaling pathway by sequestering miR-1294 to up-regulate MYC which activated CTNNB1 transcription. It was also found that circ-AHCY recruited EIF4A3 to stabilize TCF4 mRNA. Enhanced levels of TCF4 and β-catenin contributed to the stability of TCF4/β-catenin complex. In turn, TCF4/β-catenin complex strengthened the transcriptional activity of circ-AHCY. Exosomal circ-AHCY derived from GBM cells induced abnormal proliferation of normal human astrocytes (NHAs).

CONCLUSION

Exosomal circ-AHCY forms a positive feedback loop with Wnt/β-catenin signaling pathway to promote GBM cell growth.

Identification and comprehensive analysis of circRNA-miRNA-mRNA regulatory networks in osteoarthritis

Osteoarthritis (OA) is a common orthopedic degenerative disease, leading to high disability in activities of daily living. There remains an urgent need to identify the underlying mechanisms and identify new therapeutic targets in OA diagnosis and treatment. Circular RNAs (circRNAs) play a role in the development of multiple diseases. Many studies have reported that circRNAs regulate microRNAs (miRNAs) through an endogenous competitive mechanism. However, it remains unclear if an interplay between circRNAs, miRNAs, and target genes plays a deeper regulatory role in OA. Four datasets were downloaded from the GEO database, and differentially expressed circRNAs (DECs), differentially expressed miRNAs (DEMs), and differentially expressed genes (DEGs) were identified. Functional annotation and pathway enrichment analysis of DEGs and DECs were carried out to determine the main associated mechanism in OA. A protein-protein network (PPI) was constructed to analyze the function of, and to screen out, hub DEGs in OA. Based on the artificial intelligence prediction of protein crystal structures of two hub DEGs, TOP2A and PLK1, digitoxin and oxytetracycline were found to have the strongest affinity, respectively, with molecular docking. Subsequently, overlapping DEMs and miRNAs targeted by DECs obtained target DEMs (DETMs). Intersection of DEGs and genes targeted by DEMs obtained target DEGs (DETGs). Thus, a circRNA-miRNA-mRNA regulatory network was constructed from 16 circRNAs, 32 miRNAs, and 97 mRNAs. Three hub DECs have the largest number of regulated miRNAs and were verified through in vitro experiments. In addition, the expression level of 16 DECs was validated by RT-PCR. In conclusion, we constructed a circRNA-miRNA-mRNA regulatory network in OA and three new hub DECs, hsa_circ_0027914, hsa_circ_0101125, and hsa_circ_0102564, were identified as novel biomarkers for OA.

Circ_0060055 Promotes the Growth, Invasion, and Radioresistance of Glioblastoma by Targeting MiR-197-3p/API5 Axis

Circular RNA (circRNA) has been shown to be involved in the regulation of human disease progression. Our study aims to reveal the role of circ_0060055 in the progression of glioblastoma (GBM) and its potential molecular mechanism. The expression of circ_0060055, microRNA (miR)-197-3p, and apoptosis inhibitor 5 (API5) was determined by quantitative real-time PCR. GBM cell proliferation, apoptosis, and invasion were assessed using cell counting kit 8 assay, colony formation assay, EdU assay, flow cytometry, and transwell assay. Besides, the radiosensitivity of cells also was assessed using colony formation assay. The interaction between miR-197-3p and circ_0060055 or API5 was analyzed by dual-luciferase reporter assay and RNA pull-down assay. Animal experiments were conducted to measure the effect of circ_0060055 on GBM tumor growth and radiosensitivity in vivo. Circ_0060055 was overexpressed in GBM tumor tissues and cells, and its silencing suppressed GBM cell proliferation and invasion, while promoted apoptosis and radiosensitivity. In terms of mechanism, circ_0060055 could interact with miR-197-3p, and miR-197-3p could target API5. API5 expression also could be positively regulated by circ_0060055. Function experiments suggested that miR-197-3p inhibitor abolished the effect of circ_0060055 knockdown on GBM cell growth, invasion, and radiosensitivity. MiR-197-3p repressed GBM cell progression and improved radiosensitivity, and this effect was eliminated by API5 upregulation. In vivo experiments confirmed that circ_0060055 knockdown reduced GBM tumor growth and enhanced the radiosensitivity of tumors. This study revealed that circ_0060055 contributed to GBM progression and radioresistance through miR-197-3p/API5 pathway, providing a potential target for GBM treatment.