Search

Gliomas account for approximately 80% of primary malignant tumors in the central nervous system. Despite aggressive therapy, the prognosis of patients remains extremely poor. Glioma stem cells (GSCs) which considered as the potential target of therapy for their crucial role in therapeutic resistance and tumor recurrence, are believed to be key factors for the disappointing outcome. Here, we took advantage of GSCs as the cell model to perform high-throughput drug screening and the old antibiotic, clofoctol, was identified as the most effective compound, showing reduction of colony-formation and induction of apoptosis of GSCs. Moreover, growth of tumors was inhibited obviously in vivo after clofoctol treatment especially in primary patient-derived xenografts (PDXs) and transgenic xenografts. The anticancer mechanisms demonstrated by analyzing related downstream genes and discovering the targeted binding protein revealed that clofoctol exhibited the inhibition of GSCs by upregulation of Kruppel-like factor 13 (KLF13), a tumor suppressor gene, through clofoctol's targeted binding protein, Upstream of N-ras (UNR). Collectively, these data demonstrated that induction of KLF13 expression suppressed growth of gliomas and provided a potential therapy for gliomas targeting GSCs. Importantly, our results also identified the RNA-binding protein UNR as a drug target.

Internal ribosomal entry site (IRES)-mediated translation initiation is constitutively activated during stress conditions such as tumorigenesis and hypoxia. The RNA editing enzyme ADAR1 plays an important role in physiology and pathology. Initially, we found that the ADAR1 p150 or p110 transcript levels were decreased in glioma cells compared with normal astrocyte cells. In contrast, protein levels of ADAR1 p110 were significantly upregulated in glioma tissues and cells. This expression pattern indicated translationally controlled regulation. We identified an 885-nt sequence that was located between AUG1 and AUG2 within the ADAR1 mRNA that exhibited IRES-like activity. Furthermore, we confirmed that the translational mode of ADAR1 p110 was mediated by PTBP1 in glioma cells. The protein levels of PTBP1 and ADAR1 were cooperatively expressed in glioma tissues and cells. Knocking down ADAR1 p110 significantly decreased cell proliferation in three types of glioma cells (T98G, U87MG and A172). The removal of a minimal IRES-like sequence in a p150-overexpression construct could effectively abolish p110 induction and resulted in the slight suppression of cell proliferation compared with ADAR1-p150 overexpression in siPTBP1-treated T98G cells. In summary, our study revealed a mechanism whereby ADAR1 p110 can be activated by PTBP1 through an IRES-like element in glioma cells, and ADAR1 is essential for the maintenance of gliomagenesis.

Although the roles of circadian Clock genes and microRNAs in tumorigenesis have been profoundly studied, mechanisms of cross-talk between them in regulation of gliomagenesis are poorly understood. Here we show that the expression level of CLOCK is significantly increased in high-grade human glioma tissues and glioblastoma cell lines. In contrast miR-124 is attenuated in similar samples. Further studies show that Clock is a direct target of miR-124, and either restoration of miR-124 or silencing of CLOCK can reduce the activation of NF-κB. In conclusion, we suggest that as a target of glioma suppressor miR-124, CLOCK positively regulates glioma proliferation and migration by reinforcing NF-κB activity., (Copyright © 2013. Published by Elsevier B.V.)

It has been reported that ubiquitin-conjugating enzyme 9 (Ubc9), the unique enzyme2 in the sumoylation pathway, is up-regulated in many cancers. However, the expression and regulation of UBC9 in glioma remains unknown. In this study, we found that Ubc9 was up-regulated in glioma tissues and cell lines compared to a normal control. UBC9 knockdown by small interfering RNA (siRNA) affected cell proliferation and apoptosis in T98G cells. Further experiments revealed that microRNA (miR)-214 directly targeted the 3' untranslated region (UTR) of UBC9 and that there was an inverse relationship between the expression levels of miR-214 and UBC9 protein in glioma tissues and cells. miR-214 overexpression suppressed the endogenous UBC9 protein and affected T98G cell proliferation. These findings suggest that miR-214 reduction facilitates UBC9 expression and is involved in the regulation of glioma cell proliferation.

MicroRNAs are approximately 21nt single-stranded RNAs and function as regulators of gene expression. Previous studies have shown that microRNAs play crucial roles in tumorigenesis by targeting the mRNAs of oncogenes or tumor suppressors. Here we show that brain-enriched miR-128 is down-regulated in glioma tissues and cell lines when compared to normal brain tissues. Overexpression of miR-128 in glioma cells inhibited cell proliferation. A bioinformatics search revealed a conserved target site within the 3'untranslated region (UTR) of E2F3a, a transcription factor that regulates cell cycle progression. The protein levels of E2F3a in gliomas and normal brain tissues were negatively correlated to the expression levels of miR-128 in these tissues. Overexpression of miR-128 suppressed a luciferase-reporter containing the E2F3a-3'UTR and reduced the level of E2F3a protein in T98G cells. Moreover, knocking down of E2F3a had similar effect as overexpression of miR-128, and overexpression of E2F3a can partly rescue the proliferation inhibition caused by miR-128. Taken together, our study demonstrates that miR-128 can inhibit proliferation of glioma cells through one of its targets, E2F3a.

RNA-binding proteins (RBPs) play important roles in many cancer types. However, RBPs have not been thoroughly and systematically studied in gliomas. Global analysis of the functional impact of RBPs will provide a better understanding of gliomagenesis and new insights into glioma therapy. In this study, we integrated a list of the human RBPs from six sources—Gerstberger, SONAR, Gene Ontology project, Poly(A) binding protein, CARIC, and XRNAX—which covered 4127 proteins with RNA-binding activity. The RNA sequencing data were downloaded from The Cancer Genome Atlas (TCGA) (n = 699) and Chinese Glioma Genome Atlas (CGGA) (n = 325 + 693). We examined the differentially expressed genes (DEGs) using the R package DESeq2, and constructed a weighted gene co-expression network analysis (WGCNA) of RBPs. Furthermore, survival analysis was also performed based on the univariate and multivariate Cox proportional hazards regression models. In the WGCNA analysis, we identified a key module involved in the overall survival (OS) of glioblastomas. Survival analysis revealed eight RBPs (PTRF, FNDC3B, SLC25A43, ZC3H12A, LRRFIP1, HSP90B1, HSPA5, and BNC2) are significantly associated with the survival of glioblastoma patients. Another 693 patients within the CGGA database were used to validate the findings. Additionally, 3564 RBPs were classified into canonical and non-canonical RBPs depending on the domains that they contain, and non-canonical RBPs account for the majority (72.95%). The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that some non-canonical RBPs may have functions in glioma. Finally, we found that the knockdown of non-canonical RBPs, PTRF, or FNDC3B can alone significantly inhibit the proliferation of LN229 and U251 cells. Simultaneously, RNA Immunoprecipitation (RIP) analysis indicated that PTRF may regulate cell growth and death- related pathways to maintain tumor cell growth. In conclusion, our findings presented an integrated view to assess the potential death risks of glioblastoma at a molecular level, based on the expression of RBPs. More importantly, we identified non-canonical RNA-binding proteins PTRF and FNDC3B, showing them to be potential prognostic biomarkers for glioblastoma. [ABSTRACT FROM AUTHOR]