An Aberrant Transcription Factor Network Essential for Wnt Signaling and Stem Cell Maintenance in Glioblastoma
ABSTRACT Glioblastoma (GBM) is thought to be driven by a subpopulation of cancer stem cells (CSCs) that self-renew and recapitulate tumor heterogeneity yet remain poorly understood. Here, we present a comparative analysis of chromatin state in GBM CSCs that reveals widespread activation of genes normally held in check by Polycomb repressors. These activated targets include a large set of developmental transcription factors (TFs) whose coordinated activation is unique to the CSCs. We demonstrate that a critical factor in the set, ASCL1, activates Wnt signaling by repressing the negative regulator DKK1. We show that ASCL1 is essential for the maintenance and in vivo tumorigenicity of GBM CSCs. Genome-wide binding profiles for ASCL1 and the Wnt effector LEF-1 provide mechanistic insight and suggest widespread interactions between the TF module and the signaling pathway. Our findings demonstrate regulatory connections among ASCL1, Wnt signaling, and collaborating TFs that are essential for the maintenance and tumorigenicity of GBM CSCs.
SourceAvailable from: Alexandre Raposo[Show abstract] [Hide abstract]
ABSTRACT: The proneural transcription factor Ascl1 coordinates gene expression in both proliferating and differentiating progenitors along the neuronal lineage. Here, we used a cellular model of neurogenesis to investigate how Ascl1 interacts with the chromatin landscape to regulate gene expression when promoting neuronal differentiation. We find that Ascl1 binding occurs mostly at distal enhancers and is associated with activation of gene transcription. Surprisingly, the accessibility of Ascl1 to its binding sites in neural stem/progenitor cells remains largely unchanged throughout their differentiation, as Ascl1 targets regions of both readily accessible and closed chromatin in proliferating cells. Moreover, binding of Ascl1 often precedes an increase in chromatin accessibility and the appearance of new regions of open chromatin, associated with de novo gene expression during differentiation. Our results reveal a function of Ascl1 in promoting chromatin accessibility during neurogenesis, linking the chromatin landscape at Ascl1 target regions with the temporal progression of its transcriptional program. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.Cell Reports 03/2015; 10(9):1-13. DOI:10.1016/j.celrep.2015.02.025 · 7.21 Impact Factor
Article: Genetics and epigenetics of gliomas[Show abstract] [Hide abstract]
ABSTRACT: Gliomas are the most common primary intrinsic brain tumours. Their classification is based on phenotypic resemblance to normal glial cells (astrocytomas, oligodendrogliomas, mixed oligoastrocytomas) and pathological grading. Whereas this system is clinically relevant and has been the basis for our understanding of gliomas, systematic use of next-generation sequencing has transformed our knowledge of their pathogenesis and has uncovered genetic changes in an unanticipated number of genes and regulatory elements. In the past few years, in-depth analysis of low-grade astrocytomas and glioblastomas in both paediatric and adult populations has clarified our molecular understanding of these diseases, with distinct molecular events occurring in different age groups. In oligodendrogliomas, recent studies have highlighted mutations in candidate tumour suppressor genes located on 1p/19q, chromosome arms frequently deleted in this tumour. In this review, we discuss recent discoveries in the genetics of adult and paediatric gliomas, and highlight how some of the founding genetic mutations reshape the cancer epigenome. These studies provide an in-depth view of the molecular routes leading to brain tumour development and will be key for refining classification systems and improving clinical care.Swiss medical weekly: official journal of the Swiss Society of Infectious Diseases, the Swiss Society of Internal Medicine, the Swiss Society of Pneumology 10/2014; 144:w14018. DOI:10.4414/smw.2014.14018 · 1.88 Impact Factor
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ABSTRACT: Neurogenesis, the generation of new neurons, is deregulated in neural stem cell (NSC)- and progenitor-derived murine models of malignant medulloblastoma and glioma, the most common brain tumors of children and adults, respectively. Molecular characterization of human malignant brain tumors, and in particular brain tumor stem cells (BTSCs), has identified neurodevelopmental transcription factors, microRNAs, and epigenetic factors known to inhibit neuronal and glial differentiation. We are starting to understand how these factors are regulated by the major oncogenic drivers in malignant brain tumors. In this review, we will focus on the molecular switches that block normal neuronal differentiation and induce brain tumor formation. Genetic or pharmacological manipulation of these switches in BTSCs has been shown to restore the ability of tumor cells to differentiate. We will discuss potential brain tumor therapies that will promote differentiation in order to reduce treatment resistance, suppress tumor growth, and prevent recurrence in patients.Cell and Tissue Research 11/2014; 359(1). DOI:10.1007/s00441-014-2046-y · 3.33 Impact Factor