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Sameer Agnihotri,
Amparo Wolf,
Diana M Munoz,
Christopher J Smith,
Aaron Gajadhar, Andres Restrepo,
Ian D Clarke,
Gregory N Fuller,
Santosh Kesari,
Peter B Dirks,
C Jane McGlade,
William L Stanford,
Kenneth Aldape,
Paul S Mischel,
Cynthia Hawkins,
Abhijit Guha
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ABSTRACT: Glioblastoma Multiforme (GBM), the most common and lethal primary human brain tumor, exhibits multiple molecular aberrations. We report that loss of the transcription factor GATA4, a negative regulator of normal astrocyte proliferation, is a driver in glioma formation and fulfills the hallmarks of a tumor suppressor gene (TSG). Although GATA4 was expressed in normal brain, loss of GATA4 was observed in 94/163 GBM operative samples and was a negative survival prognostic marker. GATA4 loss occurred through promoter hypermethylation or novel somatic mutations. Loss of GATA4 in normal human astrocytes promoted high-grade astrocytoma formation, in cooperation with other relevant genetic alterations such as activated Ras or loss of TP53. Loss of GATA4 with activated Ras in normal astrocytes promoted a progenitor-like phenotype, formation of neurospheres, and the ability to differentiate into astrocytes, neurons, and oligodendrocytes. Re-expression of GATA4 in human GBM cell lines, primary cultures, and brain tumor-initiating cells suppressed tumor growth in vitro and in vivo through direct activation of the cell cycle inhibitor P21(CIP1), independent of TP53. Re-expression of GATA4 also conferred sensitivity of GBM cells to temozolomide, a DNA alkylating agent currently used in GBM therapy. This sensitivity was independent of MGMT (O-6-methylguanine-DNA-methyltransferase), the DNA repair enzyme which is often implicated in temozolomide resistance. Instead, GATA4 reduced expression of APNG (alkylpurine-DNA-N-glycosylase), a DNA repair enzyme which is poorly characterized in GBM-mediated temozolomide resistance. Identification and validation of GATA4 as a TSG and its downstream targets in GBM may yield promising novel therapeutic strategies.
Journal of Experimental Medicine 04/2011; 208(4):689-702. · 13.85 Impact Factor
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ABSTRACT: Glial fibrillary acidic protein (GFAP) is an intermediate filament expressed in glial cells that stabilizes and maintains the cytoskeleton of normal astrocytes. In glial tumors, GFAP expression is frequently lost with increasing grade of malignancy, suggesting that GFAP is important for maintaining glial cell morphology or regulating astrocytoma cell growth. Most permanent human glioma cell lines are GFAP negative by immunocytochemistry. Given that the GFAP gene is not mutated in human glioma specimens or glioma cell lines, we considered epigenetic mechanisms, such as promoter methylation, as a cause of silencing of GFAP in these tumors. In this study, we treated known GFAP-negative glioma cell lines with 5-aza-2'-deoxycytidine to examine GFAP promoter hypermethylation. Additionally, we performed bisulfite sequencing on primary glioma samples and glioma cell lines and showed an inverse relationship between GFAP promoter methylation status and GFAP expression. Using a gene reporter assay with the GFAP promoter cloned upstream of a luciferase gene, we showed that methylation of the GFAP promoter downregulates the expression of the luciferase gene. Our results suggest that epigenetic silencing of the GFAP gene through DNA methylation of its promoter region may be one mechanism by which GFAP is downregulated in human gliomas and glioma cell lines.
Neuro-Oncology 11/2010; 13(1):42-50. · 5.72 Impact Factor
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James T Rutka,
Paul Kongkham,
Paul Northcott,
Carlos Carlotti,
Mustafa Guduk,
Hirokatsu Osawa,
Orlando Moreno,
Ho Jun Seol, Andres Restrepo,
Adrienne Weeks,
Shoichi Nagai,
Christian Smith
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ABSTRACT: Since the establishment of the AANS/CNS Section on Tumors in 1984, neurosurgeons have been actively involved in basic science research of human brain tumors that has moved the field forward considerably. Here, we chronicle the major advances that have been made with respect to our understanding of the concepts guiding the biology of human malignant brain tumors. Numerous technical advances in science, such as the development of gene transfer techniques, the polymerase chain reaction, the discovery of oncogenes and tumor suppressor genes, and the refinement of approaches to cancer cytogenetics have enabled researchers to identify many of the non-random genetic alterations associated with brain tumor growth, invasion, immunology, angiogenesis and apoptosis. These data led to some astounding progress, for example with the use of gene therapy, whereby in the 1990s several human clinical trials were conducted for patients with brain tumors. More recently, the human genome project has been completed providing a blueprint for the human species. What has followed are exciting new techniques in molecular biology such as transcriptional profiling, single nucleotide polymorphism (SNP)-arrays, array comparative genomic hybridization (array-CGH), microRNA profiling, and detection of epigenetic silencing of tumor suppressor genes. The cancer genome is now being sequenced at break neck speed using advanced DNA sequencing techniques. We are on the threshold of cataloguing the major genetic alterations observed in all human brain tumors. What will follow is modeling of these genetic alterations in systems that will allow for the development of novel pharmacotherapeutics and translational research therapies.
Journal of Neuro-Oncology 06/2009; 92(3):261-73. · 3.21 Impact Factor
