circMELK promotes glioblastoma multiforme cell tumorigenesis through the miR-593/EphB2 axis

Abstract

A number of studies indicate that circular RNAs (circRNAs) play paramount roles in regulating the biological behavior of glioblastoma multiforme (GBM). In this study, we investigated the underlying mechanism of circMELK in GBM. Real-time PCRs were used to examine the expression of circMELK in glioma tissues and normal brain tissues (NBTs). Localization of circMELK in GBM cells was estimated by fluorescence in situ hybridization (FISH). Transwell migration and three-dimensional invasion assays were performed to examine glioma cell migration and invasion in vitro . Spheroid formation, clonogenicity, and cell viability assays were implemented to test the stemness of glioma stem cells (GSCs). The functions of circMELK in vivo were investigated in a xenograft nude-mouse model. We have proved that circMELK functions as a sponge for tumor suppressor microRNA-593 (miR-593) by RNA immunoprecipitation and circRNA precipitation assays, which targets the oncogenic gene Eph receptor B2 (EphB2). Dual-luciferase reporter assays were adopted to estimate the interactions between miR-593 and circMELK or EphB2. We demonstrated that circMELK was upregulated in GBM, acting as an oncogene and regulating GBM mesenchymal transition and GSC maintenance via sponging of miR-593. Furthermore, we found that EphB2 was involved in circMELK/miR-593 axis-induced GBM tumorigenesis. This function opens the opportunity for the development of a novel therapeutic target for the treatment of gliomas.

The Roles of EphB2 in Cancer

“…In glioblastoma multiforme (GBM), EphB2 overexpression correlated to poor overall survival in GBM patients. CircMELK could upregulate EphB2 expression by sponging miR-593, thereby promoting the proliferation, invasion, migration, and glioma stem cell (GSC) maintenance of GBM cells ( Zhou et al, 2021 ). Moreover, Qiu et al reported that EphB2 expression was upregulated in GBM cells under hypoxia and the stabilization of EPHB2 by hypoxia required the participation of hypoxia-inducible factor-2α (HIF-2α).…”

Research Progress of circRNAs in Glioblastoma

“…Mucin (MUC) acts as an inducer to activate various signaling pathways that also contribute to EMT ( Ponnusamy et al, 2013 ). We found that among the circRNAs involved in GBM, circ-MMP9( Wang et al, 2018b ), hsa_circ_0067934 ( Xin et al, 2019 ), hsa_circ_0001801 ( Chen et al, 2019 ), circ-PARP4 ( Zhou J. et al, 2021 ), circ-PITX1 ( Cao et al, 2021 ), hsa_circ_0006168 ( Wang T. et al, 2021 ), hsa_circ_0001588 ( Wang Q. et al, 2021 ) and circ-MELK ( Zhou F. et al, 2021 ) can regulate GBM invasion and metastasis by modulating the EMT process. Hsa_circ_0067934 ( Xin et al, 2019 ), circ-EPB41L5 ( Lv et al, 2020 ) and circ-ABCC3( Zhang and Xu, 2021 ) can participate in the invasion and metastasis of GBM by regulating the PI3K/Akt/mtor signaling pathway.…”

“…CircRNAs have vital roles in the invasion and metastasis of GBM. Hsa_circ_0008344 ( Zhou et al, 2018 ), circ-MMP9( Wang et al, 2018b ), hsa_circ_0029426 ( Zhang G. et al, 2019 ), hsa_circ_0074027 ( Qian et al, 2019 ), hsa_circ_0067934 ( Xin et al, 2019 ), circ-FOXO3 ( Zhang S. et al, 2019 ), hsa_circ_0001801 ( Chen et al, 2019 ), circ-EPB41L5 ( Lv et al, 2020 ), circ-ENTPD7 ( Zhu et al, 2020 ), hsa_circ_0043278 ( Wu et al, 2020 ), circ-PARP4 ( Zhou J. et al, 2021 ), circ-SMARCA5 ( Barbagallo et al, 2021 ), circ-PITX1 ( Cao et al, 2021 ), circ-ABCC3( Zhang and Xu, 2021 ), hsa_circ_0006168 ( Wang T. et al, 2021 ), hsa_circ_0001588 ( Wang Q. et al, 2021 ), circ-MELK ( Zhou F. et al, 2021 ), circ-FLN1 ( Sun et al, 2021 ), circ-LGMN( Chen B. et al, 2021 ), circ-NT5E ( Wang et al, 2018a ), hsa_circ_0001946 ( Li and Diao, 2019 ) and circ-MTO1 ( Zhang X. et al, 2019 ) are involved in the regulation of GBM invasion and metastasis ( Table 2 ).…”

“…It has been found that circRNAs also play an important role in GBM cell stemness ( Figure 3B ). Zhou et al, Found that circ-MELK expression was significantly increased in GBM tissues and that circ-MELK could regulate GBMEMT progression and glioma stem cells (GSCs) maintenance by binding to miR-593 to promote ephb2 expression ( Zhou F. et al, 2021 ). Gao et al, Demonstrated that circ-E-cadherin encodes a 14 amino acid peptide that binds to the CR2 structural domain of EGFR and activates EGFR-STAT3 signalling, thereby maintaining the tumorigenicity of glioma stem cells ( Gao et al, 2021 ).…”

Research Progress on Circular RNA in Glioma

“…Its overexpression can rescue the inhibition regulation of the oncogenic proteins SOX9 and ITGA5 by miR-145-5p and miR-330-5p in GSCs, respectively, resulting in increased proliferation, self-renewal and stemness of GSCs ( 67 ). Simliar to circPTN, circMELK and circPARP4 regulate GBM EMT and stemness of GSCs through upregulating oncogenic protein EphB2 and FUT4 by acting as sponges for miR-593 and miR-125a-5p, respectively ( 66 , 150 ).…”