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Genomic Space of MGMT in Human Glioma Revisited: Novel Motifs, Regulatory RNAs, NRF1, 2, and CTCF Involvement in Gene Expression. Int J Mol Sci 2021; 22:ijms22052492. [PMID: 33801310 PMCID: PMC7958331 DOI: 10.3390/ijms22052492] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 02/18/2021] [Accepted: 02/25/2021] [Indexed: 01/08/2023] Open
Abstract
Background: The molecular regulation of increased MGMT expression in human brain tumors, the associated regulatory elements, and linkages of these to its epigenetic silencing are not understood. Because the heightened expression or non-expression of MGMT plays a pivotal role in glioma therapeutics, we applied bioinformatics and experimental tools to identify the regulatory elements in the MGMT and neighboring EBF3 gene loci. Results: Extensive genome database analyses showed that the MGMT genomic space was rich in and harbored many undescribed RNA regulatory sequences and recognition motifs. We extended the MGMT’s exon-1 promoter to 2019 bp to include five overlapping alternate promoters. Consensus sequences in the revised promoter for (a) the transcriptional factors CTCF, NRF1/NRF2, GAF, (b) the genetic switch MYC/MAX/MAD, and (c) two well-defined p53 response elements in MGMT intron-1, were identified. A putative protein-coding or non-coding RNA sequence was located in the extended 3′ UTR of the MGMT transcript. Eleven non-coding RNA loci coding for miRNAs, antisense RNA, and lncRNAs were identified in the MGMT-EBF3 region and six of these showed validated potential for curtailing the expression of both MGMT and EBF3 genes. ChIP analysis verified the binding site in MGMT promoter for CTCF which regulates the genomic methylation and chromatin looping. CTCF depletion by a pool of specific siRNA and shRNAs led to a significant attenuation of MGMT expression in human GBM cell lines. Computational analysis of the ChIP sequence data in ENCODE showed the presence of NRF1 in the MGMT promoter and this occurred only in MGMT-proficient cell lines. Further, an enforced NRF2 expression markedly augmented the MGMT mRNA and protein levels in glioma cells. Conclusions: We provide the first evidence for several new regulatory components in the MGMT gene locus which predict complex transcriptional and posttranscriptional controls with potential for new therapeutic avenues.
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De Sousa SMC, Toubia J, Hardy TSE, Feng J, Wang P, Schreiber AW, Geoghegan J, Hall R, Rawlings L, Buckland M, Luxford C, Novos T, Clifton-Bligh RJ, Poplawski NK, Scott HS, Torpy DJ. Aberrant Splicing of SDHC in Families With Unexplained Succinate Dehydrogenase-Deficient Paragangliomas. J Endocr Soc 2020; 4:bvaa071. [PMID: 33195952 PMCID: PMC7646550 DOI: 10.1210/jendso/bvaa071] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Indexed: 12/12/2022] Open
Abstract
Context Germline mutations in the succinate dehydrogenase genes (SDHA/B/C/D, SDHAF2-collectively, "SDHx") have been implicated in paraganglioma (PGL), renal cell carcinoma (RCC), gastrointestinal stromal tumor (GIST), and pituitary adenoma (PA). Negative SDHB tumor staining is indicative of SDH-deficient tumors, usually reflecting an underlying germline SDHx mutation. However, approximately 20% of individuals with SDH-deficient tumors lack an identifiable germline SDHx mutation. Methods We performed whole-exome sequencing (WES) of germline and tumor DNA followed by Sanger sequencing validation, transcriptome analysis, metabolomic studies, and haplotype analysis in 2 Italian-Australian families with SDH-deficient PGLs and various neoplasms, including RCC, GIST, and PA. Results Germline WES revealed a novel SDHC intronic variant, which had been missed during previous routine testing, in 4 affected siblings of the index family. Transcriptome analysis demonstrated aberrant SDHC splicing, with the retained intronic segment introducing a premature stop codon. WES of available tumors in this family showed chromosome 1 deletion with loss of wild-type SDHC in a PGL and a somatic gain-of-function KIT mutation in a GIST. The SDHC intronic variant identified was subsequently detected in the second family, with haplotype analysis indicating a founder effect. Conclusions This is the deepest intronic variant to be reported among the SDHx genes. Intronic variants beyond the limits of standard gene sequencing analysis should be considered in patients with SDH-deficient tumors but negative genetic test results.
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Affiliation(s)
- Sunita M C De Sousa
- Endocrine and Metabolic Unit, Royal Adelaide Hospital, Adelaide, Australia.,Department of Genetics and Molecular Pathology, Centre for Cancer Biology, an SA Pathology and University of South Australia alliance, Adelaide, Australia.,Adult Genetics Unit, Royal Adelaide Hospital, Adelaide, Australia.,School of Medicine, University of Adelaide, Adelaide, Australia
| | - John Toubia
- ACRF Cancer Genomics Facility, Centre for Cancer Biology, SA Pathology, Adelaide, Australia
| | | | - Jinghua Feng
- ACRF Cancer Genomics Facility, Centre for Cancer Biology, SA Pathology, Adelaide, Australia.,School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, Australia
| | - Paul Wang
- ACRF Cancer Genomics Facility, Centre for Cancer Biology, SA Pathology, Adelaide, Australia
| | - Andreas W Schreiber
- ACRF Cancer Genomics Facility, Centre for Cancer Biology, SA Pathology, Adelaide, Australia.,School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, Australia.,School of Biological Sciences, University of Adelaide, Adelaide, Australia
| | - Joel Geoghegan
- ACRF Cancer Genomics Facility, Centre for Cancer Biology, SA Pathology, Adelaide, Australia
| | - Rachel Hall
- SA Pathology, Flinders Medical Centre, Bedford Park, Australia
| | | | - Michael Buckland
- Department of Neuropathology, Royal Prince Alfred Hospital, Camperdown, Australia.,School of Medical Sciences, University of Sydney, Sydney, Australia
| | - Catherine Luxford
- Cancer Genetics, Kolling Institute of Medical Research, Royal North Shore Hospital, Sydney, Australia
| | - Talia Novos
- Cancer Genetics, Kolling Institute of Medical Research, Royal North Shore Hospital, Sydney, Australia
| | - Roderick J Clifton-Bligh
- Cancer Genetics, Kolling Institute of Medical Research, Royal North Shore Hospital, Sydney, Australia
| | - Nicola K Poplawski
- Adult Genetics Unit, Royal Adelaide Hospital, Adelaide, Australia.,School of Medicine, University of Adelaide, Adelaide, Australia
| | - Hamish S Scott
- Department of Genetics and Molecular Pathology, Centre for Cancer Biology, an SA Pathology and University of South Australia alliance, Adelaide, Australia.,School of Medicine, University of Adelaide, Adelaide, Australia.,ACRF Cancer Genomics Facility, Centre for Cancer Biology, SA Pathology, Adelaide, Australia.,School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, Australia.,School of Biological Sciences, University of Adelaide, Adelaide, Australia
| | - David J Torpy
- Endocrine and Metabolic Unit, Royal Adelaide Hospital, Adelaide, Australia.,School of Medicine, University of Adelaide, Adelaide, Australia
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Beyond Brooding on Oncometabolic Havoc in IDH-Mutant Gliomas and AML: Current and Future Therapeutic Strategies. Cancers (Basel) 2018; 10:cancers10020049. [PMID: 29439493 PMCID: PMC5836081 DOI: 10.3390/cancers10020049] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2017] [Revised: 02/03/2018] [Accepted: 02/06/2018] [Indexed: 12/21/2022] Open
Abstract
Isocitrate dehydrogenases 1 and 2 (IDH1,2), the key Krebs cycle enzymes that generate NADPH reducing equivalents, undergo heterozygous mutations in >70% of low- to mid-grade gliomas and ~20% of acute myeloid leukemias (AMLs) and gain an unusual new activity of reducing the α-ketoglutarate (α-KG) to D-2 hydroxyglutarate (D-2HG) in a NADPH-consuming reaction. The oncometabolite D-2HG, which accumulates >35 mM, is widely accepted to drive a progressive oncogenesis besides exacerbating the already increased oxidative stress in these cancers. More importantly, D-2HG competes with α-KG and inhibits a large number of α-KG-dependent dioxygenases such as TET (Ten-eleven translocation), JmjC domain-containing KDMs (histone lysine demethylases), and the ALKBH DNA repair proteins that ultimately lead to hypermethylation of the CpG islands in the genome. The resulting CpG Island Methylator Phenotype (CIMP) accounts for major gene expression changes including the silencing of the MGMT (O6-methylguanine DNA methyltransferase) repair protein in gliomas. Glioma patients with IDH1 mutations also show better therapeutic responses and longer survival, the reasons for which are yet unclear. There has been a great surge in drug discovery for curtailing the mutant IDH activities, and arresting tumor proliferation; however, given the unique and chronic metabolic effects of D-2HG, the promise of these compounds for glioma treatment is uncertain. This comprehensive review discusses the biology, current drug design and opportunities for improved therapies through exploitable synthetic lethality pathways, and an intriguing oncometabolite-inspired strategy for primary glioblastoma.
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Abstract
Epigenetic alterations are associated with all aspects of cancer, from tumor initiation to cancer progression and metastasis. It is now well understood that both losses and gains of DNA methylation as well as altered chromatin organization contribute significantly to cancer-associated phenotypes. More recently, new sequencing technologies have allowed the identification of driver mutations in epigenetic regulators, providing a mechanistic link between the cancer epigenome and genetic alterations. Oncogenic activating mutations are now known to occur in a number of epigenetic modifiers (i.e. IDH1/2, EZH2, DNMT3A), pinpointing epigenetic pathways that are involved in tumorigenesis. Similarly, investigations into the role of inactivating mutations in chromatin modifiers (i.e. KDM6A, CREBBP/EP300, SMARCB1) implicate many of these genes as tumor suppressors. Intriguingly, a number of neoplasms are defined by a plethora of mutations in epigenetic regulators, including renal, bladder, and adenoid cystic carcinomas. Particularly striking is the discovery of frequent histone H3.3 mutations in pediatric glioma, a particularly aggressive neoplasm that has long remained poorly understood. Cancer epigenetics is a relatively new, promising frontier with much potential for improving cancer outcomes. Already, therapies such as 5-azacytidine and decitabine have proven that targeting epigenetic alterations in cancer can lead to tangible benefits. Understanding how genetic alterations give rise to the cancer epigenome will offer new possibilities for developing better prognostic and therapeutic strategies.
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Dai Z, Jin Y. Promoter methylation of the DLC‑1 gene and its inhibitory effect on human colon cancer. Oncol Rep 2013; 30:1511-7. [PMID: 23783552 DOI: 10.3892/or.2013.2551] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2013] [Accepted: 06/07/2013] [Indexed: 11/05/2022] Open
Abstract
Deleted in liver cancer‑1 (DLC‑1), a candidate tumor suppressor gene which is inactive in liver carcinogenesis, is located at 8p21.3, where deletions are frequently found in several types of human cancer. Promoter hypermethylation is an epigenetic mechanism leading to silencing of the gene expression, which may be the primary cause for the absence of DLC‑1. We investigated the expression of the DLC‑1 gene and the methylation of the DLC‑1 gene in colon cancer cell lines (Caco‑2, LoVo and HT‑29). The data showed that reduced or undetectable levels of DLC‑1 mRNA were found in HT‑29 by reverse transcription-polymerase chain reaction (RT‑PCR). By contrast, the DLC‑1 gene was significantly expressed in Caco‑2 and LoVo cells. These findings were in agreement with the data obtained from western blot analysis. To further determine whether aberrant methylation is a contributing factor to transcriptional inactivation of DLC‑1 in HT‑29, the methylation of promoter was examined using methylation‑specific PCR and sodium bisulfite genomic sequencing in LoVo and HT‑29 cells, which suggests that promoter hypermethylation accounts for silencing of the DLC‑1 gene in HT‑29 cells. Since DLC‑1 is a candidate tumor suppressor gene, we sought to determine whether DLC‑1 expression is associated with cell proliferation in colon cancer cell lines. RNA interference techniques were adopted to inhibit DLC‑1 expression in the LoVo cell line and resulted in inhibition of cell growth and reduced colony formation. Collectively, our observations suggest that hypermethylation is responsible for abrogating the function of the DLC‑1 gene in colon cancer and indicate a role of DLC‑1 in colon carcinogenesis.
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Affiliation(s)
- Zhensheng Dai
- Department of Hematology‑Oncology, Shanghai Pudong Hospital Affiliated to Fudan University, Shanghai 201399, P.R. China
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