Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0017636 (glioblastoma)
 18,345 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cancer is generally characterized by loss of CG dinucleotides methylation resulting in a global hypomethylation and the consequent genomic instability. The major contribution to the general decreased methylation levels seems to be due to demethylation of heterochromatin repetitive DNA sequences. In human immunodeficiency, centromeric instability and facial anomalies syndrome, demethylation of pericentromeric satellite 2 DNA sequences has been correlated to functional mutations of the de novo DNA methyltransferase 3b (DNMT3b), but the mechanism responsible for the hypomethylated status in tumors is poorly known. Here, we report that human glioblastoma is affected by strong hypomethylation of satellite 2 pericentromeric sequences that involves the stem cell compartment. Concomitantly with the integrity of the DNMTs coding sequences, we report aberrations in DNA methyltrasferases expression showing upregulation of the DNA methyltransferase 1 (DNMT1) and downregulation of the de novo DNA methyltransferase 3a (DNMT3a). Moreover, we show that DNMT3a is the major de novo methyltransferase expressed in normal neural progenitor cells (NPCs) and its forced re-expression is sufficient to partially recover the methylation levels of satellite 2 repeats in glioblastoma cell lines. Thus, we speculate that DNMT3a decreased expression may be involved in the early post-natal inheritance of an epigenetically altered NPC population that could be responsible for glioblastoma development later in adult life.
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PMID:Loss of pericentromeric DNA methylation pattern in human glioblastoma is associated with altered DNA methyltransferases expression and involves the stem cell compartment. 1765 95

Brain tumor cells respond poorly to radiotherapy and chemotherapy due to inherently efficient anti-apoptotic and DNA repair mechanisms. This necessitates the development of new strategies for brain cancer therapy. Here, we report that the DNA-demethylating agent Zebularine preferentially sensitizes the killing of human glioblastomas deficient in DNA-dependent protein kinase (DNA-PK). In contrast to DNA-PK-proficient human glioblastoma cells (MO59K), cytotoxicity assay with increasing Zebularine concentrations up to 300 microM resulted in a specific elevation of cell killing in DNA-PK-deficient MO59J cells. Further, an elevated frequency of polyploid cells observed in MO59J cells after Zebularine treatment pointed out a deficiency in mitotic checkpoint control. Existence of mitotic checkpoint deficiency in MO59J cells was confirmed by the abnormal centrosome number observed in Zebularine-treated MO59J cells. Although depletion of DNA methyltransferase 1 by Zebularine occurred at similar levels in both cell lines, MO59J cells displayed increased extent of DNA demethylation detected both at the gene promoter-specific level and at the genome overall level. Consistent with increased sensitivity, deoxy-Zebularine adduct level in the genomic DNA was 3- to 6-fold higher in MO59J than in MO59K cells. Elevated micronuclei frequency observed after Zebularine treatment in MO59J cells indicates the impairment of DNA repair response in MO59J cells. Collectively, our study suggests that DNA-PK is the major determining factor for cellular response to Zebularine.
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PMID:DNA-dependent protein kinase (DNA-PK)-deficient human glioblastoma cells are preferentially sensitized by Zebularine. 1993 7

Failure of conventional therapies to alleviate glioblastoma (GBM) fosters search for novel therapeutic strategies. These include epigenetic modulators as histone deacetylase inhibitors (HDACi), which relax abnormally compact tumor cell chromatin organization, enabling cells to overcome blockage in differentiation. However, in clinical settings, HDACi efficacy is confined to subsets of hematologic malignancies. We reasoned that molecules targeting multiple epigenetic mechanisms may exhibit superior anti-cancer activities. We focused on the redox perylene-quinone Hypericin (HYP) and showed that HYP targets Hsp90 for polyubiquitination, degradation and inactivation. Hsp90 is implicated in mediating inheritable epigenetic modifications transferable to progeny. We therefore examined if HYP can induce epigenetic alterations in GBM cells and show here that HYP indeed, targets multiple mechanisms in human glioblastoma tumor cell lines via unique manners. These elicit major epigenetic signature changes in key developmentally regulated genes. HYP induces neuroglial tumor cell differentiation modulating the cytoarchitecture, neuroglial differentiation antigen expression and causes exit from cell proliferation cycles. Such activities characterize HDACi however HYP is not an HDAC inhibitor. Instead, HYP effectively down-regulates expression of Class-I HDACs, creating marked deficiencies in HDACs cellular contents, leading to histones H3 and H4 hyperacetylation. Expression of EZH2, the Polycomb repressor complex-2 catalytic subunit, which trimethylates histone H3K27 is also suppressed. The resulting histone hyperacetylation and diminished H3K27-trimethylation relax chromatin structure, activating gene transcription including differentiation-promoting genes. DNMT profiles are also modulated increasing global DNA methylation. HYP induces unique epigenetic down-regulations of HDACs, EZH2 and DNMTs, remodeling chromatin structure and culminating in tumor cell differentiation. These modulations generate clinically significant anti-GBM effects obtained in a clinical trial performed in patients with recurrent, progressive disease. Despite this advanced disease stage, patients responded to HYP, displaying stable disease and partial responses; patients on compassionate therapy survived for up to 34 months. Hypericin may constitute a novel anti-glioblastoma therapeutic paradigm.
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PMID:Unique anti-glioblastoma activities of hypericin are at the crossroad of biochemical and epigenetic events and culminate in tumor cell differentiation. 2406 60

Epigenetic regulation plays a critical role in glioblastoma (GBM) tumorigenesis. However, how microRNAs (miRNAs) and cytokines cooperate to regulate GBM tumor progression is still unclear. Here, we show that interleukin-6 (IL-6) inhibits miR142-3p expression and promotes GBM propagation by inducing DNA methyltransferase 1-mediated hypermethylation of the miR142-3p promoter. Interestingly, miR142-3p also suppresses IL-6 secretion by targeting the 3' UTR of IL-6. In addition, miR142-3p also targets the 3' UTR and suppresses the expression of high-mobility group AT-hook 2 (HMGA2), leading to inhibition of Sox2-related stemness. We further show that HMGA2 enhances Sox2 expression by directly binding to the Sox2 promoter. Clinically, GBM patients whose tumors present upregulated IL-6, HMGA2, and Sox2 protein expressions and hypermethylated miR142-3p promoter also demonstrate poor survival outcome. Orthotopic delivery of miR142-3p blocks IL-6/HMGA2/Sox2 expression and suppresses stem-like properties in GBM-xenotransplanted mice. Collectively, we discovered an IL-6/miR142-3p feedback-loop-dependent regulation of GBM malignancy that could be a potential therapeutic target.
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PMID:Epigenetic regulation of the miR142-3p/interleukin-6 circuit in glioblastoma. 2433 77

Aberrant expression of the microRNA-200 (miR-200) family has been linked to the occurrence and development of various types of malignant tumors, including hepatocellular carcinoma (HCC), colon cancer and breast cancer. However, little is known about the precise mechanism by which miR-200 expression is downregulated. The intricate relationship between DNA methylation and histone modifications has become a subject of increasing interest. The expression of miR-200 family members is modified by similar or complementary epigenetic mechanisms in MGC-803 and BGC-823 gastric cancer cells and U87 MG glioma cells. Chromatin immunoprecipitation assays revealed that DNA methyltransferase 1 (DNMT1) bound to miR-200b/a/429 promoter regions, indicating an interaction between DNMT1 and the miR-200b/a/429 promoter. Furthermore, Co-Immunoprecipitation (Co-IP) detection showed that DNMT1, together with the PcG protein Enhancer of Zeste homolog 2 (EZH2), a histone methyltransferase, contributed to the transcriptional repression of microRNA-200 family members. Knockdown of EZH2 not only impacted H3K27 trimethylation but also reduced DNMT1 presence on the miR-200b/a/429 promoter. EZH2 appeared to be essential for DNMT1 recruitment to the promoter region. Silencing EZH2 and DNMT1 using drugs or RNA interference dramatically reduced the levels of miR-200b/a/429 expression. Collectively, these results indicated that EZH2 and DNMT1-mediated epigenetic silencing contributed to the progression of gastric cancer and glioblastoma, and therefore represents a novel therapeutic target for malignant tumors.
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PMID:DNMT1 and EZH2 mediated methylation silences the microRNA-200b/a/429 gene and promotes tumor progression. 2559 91

Doxorubicin (DOX) is a key chemotherapeutic drug for cancer treatment. The antitumor mechanism of DOX is its action as a topoisomerase II poison by preventing DNA replication. Our study shows that DOX can be involved in epigenetic regulation of gene transcription through downregulation of DNA methyltransferase 1 (DNMT1) then reactivation of DNA methylation-silenced tumor suppressor genes in glioblastoma (GBM). Recent evidence demonstrated that microRNA (miR or miRNA) can mediate expression of genes through post-transcriptional regulation and modulate sensitivity to anticancer drugs. As one of the first miRNAs detected in the human genome, miR-21 has been validated to be overexpressed in GBM. Combination treatment of a chemotherapeutic and miRNA showed synergistically increased anticancer activities which has been proven to be an effective strategy for tumor therapy. In our study, co-treatment of DOX and miR-21 inhibitor (miR-21i) resulted in remarkably increased expression of tumor suppressor genes compared with DOX or the miR-21i treatment alone. Moreover, we demonstrate that combining DOX and miR-21i significantly reduced tumor cell proliferation, invasion and migration in vitro. Our study concludes that combining DOX and miR-21i is a new strategy for the therapy of GBM.
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PMID:Combination treatment with doxorubicin and microRNA-21 inhibitor synergistically augments anticancer activity through upregulation of tumor suppressing genes. 2562 75

Although methyltransferase has been recognized as a major element that governs the epigenetic regulation of the genome during temozolomide (TMZ) chemotherapy in glioblastoma multiforme (GBM) patients, its regulatory effect on glioblastoma chemoresistance has not been well defined. This study investigated whether DNA methyltransferase (DNMT) expression was associated with TMZ sensitivity in glioma cells and elucidated the underlying mechanism. DNMT expression was analyzed by western blotting. miR-20a promoter methylation was evaluated by methylation-specific PCR. Cell viability and apoptosis were assessed using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) and TdT-mediated dUTP-biotin nick end labeling assays, respectively. The results showed that compared with parental U251 cells, DNMT1 expression was downregulated, miR-20a promoter methylation was attenuated and miR-20a levels were elevated in TMZ-resistant U251 cells. Methyltransferase inhibition by 5-aza-2'-deoxycytidine treatment reduced TMZ sensitivity in U251 cells. In U251/TM cells, DNMT1 expression was negatively correlated with miR-20a expression and positively correlated with TMZ sensitivity and leucine-rich repeats and immunoglobulin-like domains 1 expression; these effects were reversed by changes in miR-20a expression. DNMT1 overexpression induced an increase in U251/TM cell apoptosis that was inhibited by the miR-20a mimic, whereas DNMT1 silencing attenuated U251/TM cell apoptosis in a manner that was abrogated by miR-20a inhibitor treatment. Tumor growth of the U251/TM xenograft was inhibited by pcDNA-DNMT1 pretreatment and boosted by DNMT1-small hairpin RNA pretreatment. In summary, DNMT1 mediated chemosensitivity by reducing methylation of the microRNA-20a promoter in glioma cells.
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PMID:DNMT1 mediates chemosensitivity by reducing methylation of miRNA-20a promoter in glioma cells. 2633 69

High-grade gliomas (HGG) are the most common brain tumors, with an average survival time of 14 months. A glioma-CpG island methylator phenotype (G-CIMP), associated with better clinical outcome, has been described in low and high-grade gliomas. Mutation of IDH1 is known to drive the G-CIMP status. In some cases, however, the hypermethylation phenotype is independent of IDH1 mutation, suggesting the involvement of other mechanisms. Here, we demonstrate that DNMT1 expression is higher in low-grade gliomas compared to glioblastomas and correlates with phosphorylated c-Jun. We show that phospho-c-Jun binds to the DNMT1 promoter and causes DNA hypermethylation. Phospho-c-Jun activation by Anisomycin treatment in primary glioblastoma-derived cells attenuates the aggressive features of mesenchymal glioblastomas and leads to promoter methylation and downregulation of key mesenchymal genes (CD44, MMP9 and CHI3L1). Our findings suggest that phospho-c-Jun activates an important regulatory mechanism to control DNMT1 expression and regulate global DNA methylation in Glioblastoma.
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PMID:c-Jun-N-terminal phosphorylation regulates DNMT1 expression and genome wide methylation in gliomas. 2803 97

Metabolic dysregulation promotes cancer growth through not only energy production, but also epigenetic reprogramming. Here, we report that a critical node in methyl donor metabolism, nicotinamide N-methyltransferase (NNMT), ranked among the most consistently overexpressed metabolism genes in glioblastoma relative to normal brain. NNMT was preferentially expressed by mesenchymal glioblastoma stem cells (GSCs). NNMT depletes S-adenosyl methionine (SAM), a methyl donor generated from methionine. GSCs contained lower levels of methionine, SAM, and nicotinamide, but they contained higher levels of oxidized nicotinamide adenine dinucleotide (NAD+) than differentiated tumor cells. In concordance with the poor prognosis associated with DNA hypomethylation in glioblastoma, depletion of methionine, a key upstream methyl group donor, shifted tumors toward a mesenchymal phenotype and accelerated tumor growth. Targeting NNMT expression reduced cellular proliferation, self-renewal, and in vivo tumor growth of mesenchymal GSCs. Supporting a mechanistic link between NNMT and DNA methylation, targeting NNMT reduced methyl donor availability, methionine levels, and unmethylated cytosine, with increased levels of DNA methyltransferases, DNMT1 and DNMT3A. Supporting the clinical significance of these findings, NNMT portended poor prognosis for glioblastoma patients. Collectively, our findings support NNMT as a GSC-specific therapeutic target in glioblastoma by disrupting oncogenic DNA hypomethylation.
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PMID:Nicotinamide metabolism regulates glioblastoma stem cell maintenance. 2851 64

Glioblastoma (GBM) remains one of the most lethal and difficult-to-treat cancers of the central nervous system. The poor prognosis in GBM patients is due in part to its resistance to available treatments, which calls for identifying novel molecular therapeutic targets. In this study, we identified a mediator of Notch signaling, HEY1, whose methylation status contributes to the pathogenesis of GBM. Datamining studies, immunohistochemistry and immunoblot analysis showed that HEY1 is highly expressed in GBM patient specimens. Since methylation status of HEY1 may control its expression, we conducted bisulphite sequencing on patient samples and found that the HEY1 promoter region was hypermethylated in normal brain when compared to GBM specimens. Treatment on 4910 and 5310 xenograft cell lines with sodium butyrate (NaB) significantly decreased HEY1 expression with a concomitant increase in DNMT1 expression, confirming that promoter methylation may regulate HEY1 expression in GBM. NaB treatment also induced apoptosis of GBM cells as measured by flow cytometric analysis. Further, silencing of HEY1 reduced invasion, migration and proliferation in 4910 and 5310 cells. Furthermore, immunoblot and q-PCR analysis showed the existence of a potential positive regulatory loop between HEY1 and p53. Additionally, transcription factor interaction array with HEY1 recombinant protein predicted a correlation with p53 and provided various bonafide targets of HEY1. Collectively, these studies suggest HEY1 may be an important predictive marker for GBM and potential target for future GBM therapy.
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PMID:Methylation regulates HEY1 expression in glioblastoma. 2857 40


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