Transcription factors ASCL1 and OLIG2 drive glioblastoma initiation and co-regulate tumor cell types and migration
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ABSTRACT: Glioblastomas (GBMs) are highly aggressive, infiltrative, and heterogeneous brain tumors driven by complex genetic alterations. The basic-helix-loop-helix (bHLH) transcription factors ASCL1 and OLIG2 are dynamically co-expressed in GBMs; however, their combinatorial roles in regulating the plasticity and heterogeneity of GBM cells are unclear. Here, we show that induction of somatic mutations in subventricular zone (SVZ) progenitor cells leads to the dysregulation of ASCL1 and OLIG2, which then function redundantly and are required for brain tumor formation in a mouse model of GBM. Subsequently, the binding of ASCL1 and OLIG2 to each other’s loci and to downstream target genes then determines the cell types and degree of migration of tumor cells. Single-cell RNA sequencing (scRNA-seq) reveals that a high level of ASCL1 is key in specifying highly migratory neural stem cell (NSC)/astrocyte-like tumor cell types, which are marked by upregulation of ribosomal protein, oxidative phosphorylation, cancer metastasis, and therapeutic resistance genes.
Project description:Glioblastomas (GBMs) are highly aggressive, infiltrative, and heterogeneous brain tumors driven by complex genetic alterations. The basic-helix-loop-helix (bHLH) transcription factors ASCL1 and OLIG2 are dynamically co-expressed in GBMs; however, their combinatorial roles in regulating the plasticity and heterogeneity of GBM cells are unclear. Here, we show that induction of somatic mutations in subventricular zone (SVZ) progenitor cells leads to the dysregulation of ASCL1 and OLIG2, which then function redundantly and are required for brain tumor formation in a mouse model of GBM. Subsequently, the binding of ASCL1 and OLIG2 to each other’s loci and to downstream target genes then determines the cell types and degree of migration of tumor cells. Single-cell RNA sequencing (scRNA-seq) reveals that a high level of ASCL1 is key in specifying highly migratory neural stem cell (NSC)/astrocyte-like tumor cell types, which are marked by upregulation of ribosomal protein, oxidative phosphorylation, cancer metastasis, and therapeutic resistance genes.
Project description:The basic helix-loop-helix proteins Olig1 and Olig2 are expressed in high grade, aggressive human glioblastoma multiformes (GBMs). Here we investigated genetic mechanisms regulating Olig1/2 function during gliomagenesis. Although Olig2 function is necessary for early-aggressive tumor formation in a genetically relevant model of classic GBMs with intact p53 function, late-onset gliomas do eventually form. Using an unbiased approach, we identified Id4, encoding a negative HLH protein, as a gene target potently repressed by Olig2 in glioma progenitors. Although Id4 is thought to antagonize proneural genes involved in differentiation, we report a paradoxical role for Id4 in glioma. Genetic deletion of Id4 converts Olig2-/- gliomas to the early-aggressive form, and conversely, overexpression of Id4 inhibits intact Olig2 and prevents even late-onset tumors. Olig1 overexpression is sufficient for gliomagenesis in an Id4-dependent manner. Together, these findings indicate that gliomagenic factors Olig1 and Olig2 are opposed by Id4 function, which acts as tumor suppressor in p53-intact gliomas.
Project description:We identified a subgroup of patient-derived glioblastoma (GBM) cells that express high levels of the neurogenic transcription factor, ASCL1, which predicts response to pharmacological inhibition of the Notch signaling pathway. Treatment of ASCL1hi GBM cells with a Notch signaling inhibitor induced a change in cell fate from neoplastic to neuronal. Importantly, acquisition of the neuronal fate was accompanied by a reduction in tumorigenic potential. Loss of ASCL1 in GBM cells rendered cells no longer responsive to Notch signaling inhibition and we determined ASCL1 is required for the competency of GBM cells to undergo neuronal differentiation. Enforced ASCL1 expression directed GBM cells towards a neuronal cell fate reminiscent of terminal differentiation. RNA-seq analysis of GBM cells treated with the Notch signaling inhibitor reveals neuronal target gene activation is associated with increased stoichiometric levels of ASCL1, suggesting threshold levels of ASCL1 in GBM cells governs neuronal differentiation. We demonstrate that neoplastic cells which retain expression of key neurogenic programs can have their fates redirected towards terminal differentiation. Directed fate specification to neuronal cell types by exploiting latent neurogenic programs may be a strategy to treat a subset of GBM patients. Our findings therefore highlight the potential of differentiation therapy for a subset of molecularly defined GBMs.
Project description:Definition of genome wide binding profile of Olig2, Ascl1, Tcf3, Max, NFI, Sox2, Sox9 and Sox21 in mouse neural stem cells. Three sets of processed data files, together with a README file (README_E-MTAB-2228.docx) describing the source and content of each file, are provided as additional files to this ArrayExpress submission and can be found in https://www.ebi.ac.uk/arrayexpress/files/E-MTAB-2228 .
Project description:In this study, we explored the transcriptomic consequences of strong activation of the Notch pathway in embryonic human neural stem cells and in gliomas. For this we used a forced expression of the Notch intracellular domain (NICD). Glioblastoma multiforms (GBMs) are highly vascularized brain tumors containing a subpopulation of multipotent cancer stem cells. These cells closely interact with endothelial cells in neurovascular niches. In this study we have uncovered a close link between the Notch1 pathway and the tumoral vascularization process of GBM stem cells. We observed that although the Notch1 receptor was activated, the typical target proteins (HES5, HEY1, HEY2) were not or barely expressed in two explored GBM stem cell cultures. Notch1 signalling activation by expression of the intracellular form (NICD) in these cells was found to reduce their growth rate and migration which was accompanied by the sharp reduction of neural stem cell transcription factor expression (ASCL1, OLIG2, SOX2) while HEY1/2, KLF9, SNAI2 transcription factors were upregulated. Expression of OLIG2 and growth were restored after termination of Notch1 stimulation. Remarkably, NICD expression induced the expression of pericyte cell markers (NG2, PDGFRb and a-smooth muscle actin (aSMA)) in GBM stem cells. This was paralleled with the induction of several angiogenesis-related factors most notably cytokines (HB-EGF, IL8, PLGF), metalloprotease (MMP9) and adhesion proteins (VCAM-1, ICAM-1, ITGA9). In xenotransplantation experiments, contrasting with the infiltrative and poorly-vascularized tumors obtained with control GBM stem cells, Notch1 stimulation resulted in poorly-disseminating but highly-vascularized grafts containing large vessels with lumen. Notch1-stimulated GBM cells expressed pericyte cell markers and closely associated with endothelial cells. These results reveal an important role for the Notch1 pathway in regulating GBM stem cell plasticity and angiogenic properties. Embryonic human neural progenitors obtained from Lonza, the U87 glioma cell line, and glioma cancer stem cells (Gb4 and Gb7) characterized in Guichet et al. (Glia, 2013, 61(2), 225-39) were infected with lentiviruses expressing YFP or YFP-IRES-NICD (activated form of Notch receptor). After 48h, RNA were extracted for Affymetrix microarray analysis.
Project description:Several basic helix-loop-helix (bHLH) transcription factors are upregulated in Sonic Hedgehog subgroup of medulloblastoma (SHH MB). Olig2, a neural bHLH transcription factor known to regulate differentiation of neural cell populations, is broadly expressed in mouse models of SHH MB. ChIP-Seq of Olig2 revealed its binding to a large number of sites near genes known to promote SHH MB tumorigenesis, suggesting a potential role for Olig2 in regulating transcriptional programme of MB.
Project description:Neuroblastoma is an embryonic malignancy originating from early nerve cells. Neuroblastoma retains plasticity, interconverting between the mesenchymal (MES) and adrenergic (ADRN) states, which are controlled by different sets of transcription factors forming the core regulatory circuit (CRC). However, their functional roles and cooperative mechanisms in neuroblastoma pathogenesis are poorly understood. Here, we demonstrate that overexpression of ASCL1 in MES neuroblastoma cells opens closed chromatin at the promoters of key ADRN genes, accompanied by epigenetic activation and establishment of enhancer-promoter interactions, thereby initiating subtype switching. ASCL1 inhibits the TGFb-SMAD2/3 pathway but activates the BMP-SMAD1-ID3/4 pathway, serving as negative feedback to balance the function of ASCL1-TCF12 dimers. ASCL1 and other ADRN CRC members potentiate each other’s activity, increasing the expression of the original targets and inducing a new set of genes, thereby promoting conversion to ADRN neuroblastoma. Thus, via its pioneer factor function, ASCL1 serves as a master regulator that characterizes ADRN neuroblastoma.
Project description:Small cell lung carcinoma (SCLC) and large cell neuroendocrine carcinoma (LCNEC) are high-grade pulmonary neuroendocrine tumors. The neural basic helix-loop-helix (bHLH) transcription factors ASCL1 and NEUROD1 have been shown to play crucial roles in promoting the malignant behavior and survival of human SCLC cell lines. In this study, we find ASCL1 and NEUROD1 identify distinct neuroendocrine tumors, bind distinct genomic loci, and regulate mostly distinct genes. ASCL1 and NEUROD1 are often bound in super-enhancers that are associated with highly expressed genes in their respective SCLC cell lines suggesting different cell lineage of origin for these tumors. ASCL1 targets oncogenic genes such as MYCL1, RET, and NFIB, while NEUROD1 targets the oncogenic gene MYC. Although ASCL1 and NEUROD1 regulate different genes, many of these gene targets commonly contribute to neuroendocrine and cell migration function. ASCL1 in particular also regulates genes in the NOTCH pathway and genes important in cell-cycle dynamics. Finally, we demonstrate ASCL1 but not NEUROD1 is required for SCLC and LCNEC tumor formation in current in vivo genetic mouse models of pulmonary neuroendocrine tumors ChIP-seq analysis performed on three ASCL1high and two NEUROD1high human SCLC cell lines to identify ASCL1 and/or NEUROD1 binding sites in these two types of cells. Also, we performed ChIP-seq for Ascl1 binding sites in mouse neuroendocrine lung tumors obtained from Trp53;Rb1;Rbl2 triple knockout model mice treated with Adeno-CMVCRE intratracheally.
Project description:Small cell lung carcinoma (SCLC) and large cell neuroendocrine carcinoma (LCNEC) are high-grade pulmonary neuroendocrine tumors. The neural basic helix-loop-helix (bHLH) transcription factors ASCL1 and NEUROD1 have been shown to play crucial roles in promoting the malignant behavior and survival of human SCLC cell lines. In this study, we find ASCL1 and NEUROD1 identify distinct neuroendocrine tumors, bind distinct genomic loci, and regulate mostly distinct genes. ASCL1 and NEUROD1 are often bound in super-enhancers that are associated with highly expressed genes in their respective SCLC cell lines suggesting different cell lineage of origin for these tumors. ASCL1 targets oncogenic genes such as MYCL1, RET, and NFIB, while NEUROD1 targets the oncogenic gene MYC. Although ASCL1 and NEUROD1 regulate different genes, many of these gene targets commonly contribute to neuroendocrine and cell migration function. ASCL1 in particular also regulates genes in the NOTCH pathway and genes important in cell-cycle dynamics. Finally, we demonstrate ASCL1 but not NEUROD1 is required for SCLC and LCNEC tumor formation in current in vivo genetic mouse models of pulmonary neuroendocrine tumors RNA-seq analysis performed on two ASCL1high and two NEUROD1high human SCLC cell lines to identify gene expression patterns in these cells. Also, we performed RNA-seq in mouse neuroendocrine lung tumors obtained from Trp53;Rb1;Rbl2 triple knockout model mice treated with Adeno-CMVCRE intratracheally.
Project description:Previous lineage analyses have shown that retinal progenitor cells (RPCs) are multipotent throughout development, and expression profiling studies have shown a great deal of molecular heterogeneity among RPCs. To determine if the molecular heterogeneity predicts that an RPC will produce particular types of progeny, clonal lineage analysis was used to investigate the progeny of a subset of RPCs, those that express the basic helix-loop-helix (bHLH) transcription factor, Olig2. In contrast to the large and complex set of clones generated by viral marking of random embryonic RPCs, the embryonic Olig2+ RPCs underwent terminal divisions, producing small clones with primarily two of the five cell types being made by the pool of RPCs at that time. The embryonically produced cell types made by Olig2+ RPCs were cone photoreceptors and horizontal cell (HC) interneurons. Moreover, the embryonic Olig2+ RPC did not make the later Olig2+ RPC. The later, postnatal Olig2+ RPCs also made terminal divisions, which were biased towards production of rod photoreceptors and amacrine cell (AC) interneurons. These data indicate that the multipotent progenitor pool is made up of distinctive types of RPCs, which have biases towards producing subsets of retinal neurons in a terminal division, with the types of neurons produced varying over time. This strategy is similar to that of the developing Drosophila melanogaster ventral nerve cord, with the Olig2+ cells behaving as ganglion mother cells. Single retinal cells were isolated in tubes containing lysis buffer, their mRNAs were reverse transcribed, and the resulting cDNAs were PCR amplified for 35 cycles. Labeled cDNA samples were hybridized to Affymetrix 430 2.0 microarrays and the data was normalized using MAS5.0 software. These cells were examined for the expression of Olig2 or other bHLH factors.