| 1. |
- Bolin, Sara, 1988-, et al.
(författare)
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Dormant SOX9-positive cells behind MYC-driven medulloblastoma recurrence
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Tidskriftsartikel (refereegranskat)abstract
- Tumor recurrence is a slow biological process involving therapy resistance, immune escape, and metastasis and is the leading cause of death in medulloblastoma, the most frequent malignant pediatric brain tumor. By studying paired primary-recurrent patient samples and patient-derived xenografts we identified a significant accumulation of SOX9-positive cells in relapses and metastases. They exist as rare, quiescent cells in Group 3 and Group 4 patients that constitute two-thirds of medulloblastoma. To follow relapse at the single-cell level we developed an inducible dual Tet model of MYC-driven MB, where MYC can be directed from treatment-sensitive bulk cells to resistant, dormant SOX9-positive cells by doxycycline. SOX9 promoted immune es-cape, DNA repair suppression and was essential for recurrence. Tumor cell dormancy was non-hierarchical, migratory, and depended on MYC suppression by SOX9 to promote relapse. By using computational modeling and treatment we further showed how doxorubicin and MGMT inhibitors are specifically targeting relapsing cells.
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| 2. |
- Hellwig, Malte, et al.
(författare)
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TCF4 (E2-2) harbors tumor suppressive functions in SHH medulloblastoma
- 2019
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Ingår i: Acta Neuropathologica. - : Springer Science and Business Media LLC. - 0001-6322 .- 1432-0533. ; 137:4, s. 657-673
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Tidskriftsartikel (refereegranskat)abstract
- The TCF4 gene encodes for the basic helix–loop–helix transcription factor 4 (TCF4), which plays an important role in the development of the central nervous system (CNS). Haploinsufficiency of TCF4 was found to cause Pitt-Hopkins syndrome (PTHS), a severe neurodevelopmental disorder. Recently, the screening of a large cohort of medulloblastoma (MB), a highly aggressive embryonal brain tumor, revealed almost 20% of adult patients with MB of the Sonic hedgehog (SHH) subtype carrying somatic TCF4 mutations. Interestingly, many of these mutations have previously been detected as germline mutations in patients with PTHS. We show here that overexpression of wild-type TCF4 in vitro significantly suppresses cell proliferation in MB cells, whereas mutant TCF4 proteins do not to the same extent. Furthermore, RNA sequencing revealed significant upregulation of multiple well-known tumor suppressors upon expression of wild-type TCF4. In vivo, a prenatal knockout of Tcf4 in mice caused a significant increase in apoptosis accompanied by a decreased proliferation and failed migration of cerebellar granule neuron precursor cells (CGNP), which are thought to be the cells of origin for SHH MB. In contrast, postnatal in vitro and in vivo knockouts of Tcf4 with and without an additional constitutive activation of the SHH pathway led to significantly increased proliferation of CGNP or MB cells. Finally, publicly available data from human MB show that relatively low expression levels of TCF4 significantly correlate with a worse clinical outcome. These results not only point to time-specific roles of Tcf4 during cerebellar development but also suggest a functional linkage between TCF4 mutations and the formation of SHH MB, proposing that TCF4 acts as a tumor suppressor during postnatal stages of cerebellar development.
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| 3. |
- Keck, Michaela Kristina, et al.
(författare)
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Amplification of the PLAG-family genes—PLAGL1 and PLAGL2—is a key feature of the novel tumor type CNS embryonal tumor with PLAGL amplification
- 2023
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Ingår i: Acta Neuropathologica. - : Springer Science and Business Media LLC. - 0001-6322 .- 1432-0533. ; 145:1, s. 49-69
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Tidskriftsartikel (refereegranskat)abstract
- Pediatric central nervous system (CNS) tumors represent the most common cause of cancer-related death in children aged 0–14 years. They differ from their adult counterparts, showing extensive clinical and molecular heterogeneity as well as a challenging histopathological spectrum that often impairs accurate diagnosis. Here, we use DNA methylation-based CNS tumor classification in combination with copy number, RNA-seq, and ChIP-seq analysis to characterize a newly identified CNS tumor type. In addition, we report histology, patient characteristics, and survival data in this tumor type. We describe a biologically distinct pediatric CNS tumor type (n = 31 cases) that is characterized by focal high-level amplification and resultant overexpression of either PLAGL1 or PLAGL2, and an absence of recurrent genetic alterations characteristic of other pediatric CNS tumor types. Both genes act as transcription factors for a regulatory subset of imprinted genes (IGs), components of the Wnt/β-Catenin pathway, and the potential drug targets RET and CYP2W1, which are also specifically overexpressed in this tumor type. A derived PLAGL-specific gene expression signature indicates dysregulation of imprinting control and differentiation/development. These tumors occurred throughout the neuroaxis including the cerebral hemispheres, cerebellum, and brainstem, and were predominantly composed of primitive embryonal-like cells lacking robust expression of markers of glial or neuronal differentiation (e.g., GFAP, OLIG2, and synaptophysin). Tumors with PLAGL1 amplification were typically diagnosed during adolescence (median age 10.5 years), whereas those with PLAGL2 amplification were diagnosed during early childhood (median age 2 years). The 10-year overall survival was 66% for PLAGL1-amplified tumors, 25% for PLAGL2-amplified tumors, 18% for male patients, and 82% for female patients. In summary, we describe a new type of biologically distinct CNS tumor characterized by PLAGL1/2 amplification that occurs predominantly in infants and toddlers (PLAGL2) or adolescents (PLAGL1) which we consider best classified as a CNS embryonal tumor and which is associated with intermediate survival. The cell of origin and optimal treatment strategies remain to be defined.
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| 4. |
- Savov, Vasil, 1986-
(författare)
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The Role of SOX9 in Medulloblastoma
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Overall survival is about 70% and in cases where current treatment fails, the disease recurs and most often is fatal. At the molecular level, MB can be divided into four defined subgroups: WNT, SHH, Group 3 and Group 4. Amplification of MYC family genes is common in MB and correlates with poor prognosis and tumor relapse.In this thesis we showed how MYCN initiates brain tumors when transduced in neural stem cells (NSCs). Prior to transduction, NSCs were isolated from different brain regions and at various time points. While overexpression of wild-type MYCN did not generate any tumors, orthotopic transplantation of MYCNT58A-expressing forebrain, brain stem and cerebellar NSCs induced diffuse malignant glioma, PNET-like tumors and MB, respectively. Interestingly, MYCNT58A-expressing cerebellar NSCs induced SHH-dependent MB from embryonic cells but SHH-independent MB from postnatal cells. We further showed that cerebellar NSCs transduced with both MYCNT58A and transcription factor SOX9 developed tumors faster and promoted distant migration into the forebrain.The function and regulation of SOX9 in MB cells is poorly understood. We identified SOX9 protein as target of FBW7 ubiquitin ligase and demonstrated the effects of SOX9 on MB cells migration, metastasis and drug resistance. We further blocked PI3K pathway to destabilize SOX9 which sensitized cells to cytostatic treatment.We used a (TetOFF) transgenic mouse model of MYCN-induced MB (GTML) and crossed it with a (TetON) transgene which allowed us to specifically target rare SOX9-positive cells in the tumor. In this system, MB develops spontaneously and SOX9-negative tumor cells can be killed off by doxycycline. The few remaining SOX9-positive cancer cells were able to promote distant MB recurrences. Such a pattern of relapse was recently shown for Group 3 and 4 human MB where about 90% of the recurrences were distant.In summary, this thesis demonstrates that MYCN can generate various types of brain tumors depending on the timing and location of its expression. It further defines the existence of a rare population of SOX9-expressing MB cells that are involved in causing distant MB recurrences. Finally, it describes how SOX9 is stabilized in MB cells and increases MB migration and therapy resistance.
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