Holger Weishaupt

Utilizing the Dog Genome in the Search for Novel Candidate Genes Involved in Glioma Development-Genome Wide Association Mapping followed by Targeted Massive Parallel Sequencing Identifies a Strongly Associated Locus.

Gliomas are the most common form of malignant primary brain tumors in humans and second most common in dogs, occurring with similar frequencies in both species. Dogs are valuable spontaneous models of human complex diseases including cancers and may provide insight into disease susceptibility and oncogenesis. Several brachycephalic breeds such as Boxer, Bulldog and Boston Terrier have an elevated risk of developing glioma, but others, including Pug and Pekingese, are not at higher risk. To identify glioma-associated genetic susceptibility factors, an across-breed genome-wide association study (GWAS) was performed on 39 dog glioma cases and 141 controls from 25 dog breeds, identifying a genome-wide significant locus on canine chromosome (CFA) 26 (p = 2.8 x 10−8). Targeted re-sequencing of the 3.4 Mb candidate region was performed, followed by genotyping of the 56 SNVs that best fit the association pattern between the re-sequenced cases and controls. We identified three candidate genes that were highly associated with glioma susceptibility: CAMKK2, P2RX7 and DENR. CAMKK2 showed reduced expression in both canine and human brain tumors, and a non-synonymous variant in P2RX7, previously demonstrated to have a 50% decrease in receptor function, was also associated with disease. Thus, one or more of these genes appear to affect glioma susceptibility.

Deregulated proliferation and differentiation in brain tumors

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.

Oncoprotein stabilization in brain tumors

Proteins involved in promoting cell proliferation and viability need to be timely expressed and carefully controlled for the proper development of the brain but also efficiently degraded in order to prevent cells from becoming brain cancer cells. A major pathway for targeted protein degradation in cells is the ubiquitin–proteasome system (UPS). Oncoproteins that drive tumor development and tumor maintenance are often deregulated and stabilized in malignant cells. This can occur when oncoproteins escape degradation by the UPS because of mutations in either the oncoprotein itself or in the UPS components responsible for recognition and ubiquitylation of the oncoprotein. As the pathogenic accumulation of an oncoprotein can lead to effectively sustained cell growth, viability and tumor progression, it is an indisputable target for cancer treatment. The most common types of malignant brain tumors in children and adults are medulloblastoma and glioma, respectively. Here, we review different ways of how deregulated proteolysis of oncoproteins involved in major signaling cancer pathways contributes to medulloblastoma and glioma development. We also describe means of targeting relevant oncoproteins in brain tumors with treatments affecting their stability or therapeutic strategies directed against the UPS itself.

FBW7 suppression leads to SOX9 stabilization and increased malignancy in medulloblastoma

SOX9 is a master transcription factor that regulates development and stem cell programs. However, its potential oncogenic activity and regulatory mechanisms that control SOX9 protein stability are poorly understood. Here, we show that SOX9 is a substrate of FBW7, a tumor suppressor, and a SCF (SKP1/CUL1/F‐box)‐type ubiquitin ligase. FBW7 recognizes a conserved degron surrounding threonine 236 (T236) in SOX9 that is phosphorylated by GSK3 kinase and consequently degraded by SCFFBW7α. Failure to degrade SOX9 promotes migration, metastasis, and treatment resistance in medulloblastoma, one of the most common childhood brain tumors. FBW7 is either mutated or downregulated in medulloblastoma, and in cases where FBW7 mRNA levels are low, SOX9 protein is significantly elevated and this phenotype is associated with metastasis at diagnosis and poor patient outcome. Transcriptional profiling of medulloblastoma cells expressing a degradation‐resistant SOX9 mutant reveals activation of pro‐metastatic genes and genes linked to cisplatin resistance. Finally, we show that pharmacological inhibition of PI3K/AKT/mTOR pathway activity destabilizes SOX9 in a GSK3/FBW7‐dependent manner, rendering medulloblastoma cells sensitive to cytostatic treatment.

Context-Dependent Development of Lymphoid Stroma from Adult CD34+ Adventitial Progenitors

Despite the key role of primary and secondary lymphoid organ stroma in immunity, our understanding of the heterogeneity and ontogeny of these cells remains limited. Here, we identify a functionally distinct subset of BP3(-)PDPN(+)PDGFRβ(+)/α(+)CD34(+) stromal adventitial cells in both lymph nodes (LNs) and thymus that is located within the vascular niche surrounding PDPN(-)PDGFRβ(+)/α(-)Esam-1(+)ITGA7(+) pericytes. CD34(+) adventitial cells developed in late embryonic thymus and in postnatal LNs and in the thymus originated, along with pericytes, from a common anlage-seeding progenitor population. Using lymphoid organ re-aggregate grafts, we demonstrate that adult CD34(+) adventitial cells are capable of differentiating into multiple lymphoid stroma-like subsets including pericyte-, FRC-, MRC-, and FDC-like cells, the development of which was lymphoid environment-dependent. These findings extend the current understanding of lymphoid mesenchymal cell heterogeneity and highlight a role of the CD34(+) adventitia as a potential ubiquitous source of lymphoid stromal precursors in postnatal tissues.

Modeling and Targeting MYC Genes in Childhood Brain Tumors

Brain tumors are the second most common group of childhood cancers, accounting for about 20%–25% of all pediatric tumors. Deregulated expression of the MYC family of transcription factors, particularly c-MYC and MYCN genes, has been found in many of these neoplasms, and their expression levels are often correlated with poor prognosis. Elevated c-MYC/MYCN initiates and drives tumorigenesis in many in vivo model systems of pediatric brain tumors. Therefore, inhibition of their oncogenic function is an attractive therapeutic target. In this review, we explore the roles of MYC oncoproteins and their molecular targets during the formation, maintenance, and recurrence of childhood brain tumors. We also briefly summarize recent progress in the development of therapeutic approaches for pharmacological inhibition of MYC activity in these tumors.

Mouse models of pediatric supratentorial high-grade glioma reveal how cell of origin influences tumor development and phenotype

High-grade glioma (HGG) is a group of primary malignant brain tumors with dismal prognosis. Whereas adult HGG has been studied extensively, childhood HGG, a relatively rare disease, is less well-characterized. Here, we present two novel platelet-derived growth factor (PDGF)-driven mouse models of pediatric supratentorial HGG. Tumors developed from two different cells of origin reminiscent of neural stem cells (NSC) or oligodendrocyte precursor cells (OPC). Cross-species transcriptomics showed that both models are closely related to human pediatric HGG as compared with adult HGG. Furthermore, an NSC-like cell-of-origin enhanced tumor incidence, malignancy, and the ability of mouse glioma cells (GC) to be cultured under stem cell conditions as compared with an OPC-like cell. Functional analyses of cultured GC from these tumors showed that cells of NSC-like origin were more tumorigenic, had a higher rate of self-renewal and proliferation, and were more sensitive to a panel of cancer drugs compared with GC of a more differentiated origin. These two mouse models relevant to human pediatric supratentorial HGG propose an important role of the cell-of-origin for clinicopathologic features of this disease. Cancer Res; 77(3); 802-12. ©2016 AACR.

Serglycin as a potential biomarker for glioma: association of serglycin expression, extent of mast cell recruitment and glioblastoma progression

Serglycin is an intracellular proteoglycan with a unique ability to adopt highly divergent structures by glycosylation with variable types of glycosaminoglycans (GAGs) when expressed by different cell types. Serglycin is overexpressed in aggressive cancers suggesting its protumorigenic role. In this study, we explored the expression of serglycin in human glioma and its correlation with survival and immune cell infiltration. We demonstrate that serglycin is expressed in glioma and that increased expression predicts poor survival of patients. Analysis of serglycin expression in a large cohort of low- and high-grade human glioma samples reveals that its expression is grade dependent and is positively correlated with mast cell (MC) infiltration. Moreover, serglycin expression in patient-derived glioma cells is significantly increased upon MC co-culture. This is also accompanied by increased expression of CXCL12, CXCL10, as well as markers of cancer progression, including CD44, ZEB1 and vimentin. In conclusion, these findings indicate the importance of infiltrating MCs in glioma by modulating signaling cascades involving serglycin, CD44 and ZEB1. The present investigation reveals serglycin as a potential prognostic marker for glioma and demonstrates an association with the extent of MC recruitment and glioma progression, uncovering potential future therapeutic opportunities for patients.

Combined BET-bromodomain and CDK2 inhibition in MYC-driven medulloblastoma

Medulloblastoma (MB) is the most common malignant brain tumor in children. MYC genes are frequently amplified and correlate with poor prognosis in MB. BET bromodomains recognize acetylated lysine residues and often promote and maintain MYC transcription. Certain cyclin-dependent kinases (CDKs) are further known to support MYC stabilization in tumor cells. In this report, MB cells were suppressed by combined targeting of MYC expression and MYC stabilization using BET bromodomain inhibition and CDK2 inhibition, respectively. Such combination treatment worked synergistically and caused cell cycle arrest as well as massive apoptosis. Immediate transcriptional changes from this combined MYC blockade were found using RNA-Seq profiling and showed remarkable similarities to changes in MYC target gene expression when MYCN was turned off with doxycycline in our MYCN-inducible animal model for Group 3 MB. In addition, the combination treatment significantly prolonged survival as compared to single-agent therapy in orthotopically transplanted human Group 3 MB with MYC amplifications. Our data suggest that dual inhibition of CDK2 and BET bromodomains can be a novel treatment approach for suppressing MYC-driven cancer.

Mast Cell Infiltration in Human Brain Metastases Modulates the Microenvironment and Contributes to the Metastatic Potential

Metastatic brain tumors continue to be a clinical problem, despite new therapeutic advances in cancer treatment. Brain metastases (BMs) are among the most common mass lesions in the brain that are resistant to chemotherapies, have a very poor prognosis, and currently lack any efficient diagnostic tests. Predictions estimate that about 40% of lung and breast cancer patients will develop BM. Despite this, very little is known about the immunological and genetic aberrations that drive tumorigenesis in BM. In this study, we demonstrate the infiltration of mast cells (MCs) in a large cohort of human BM samples with different tissues of origin for primary cancer. We applied patient-derived BM cell models to the study of BM cell–MC interactions. BM cells when cocultured with MCs demonstrate enhanced growth and self-renewal capacity. Gene set enrichment analyses indicate increased expression of signal transduction and transmembrane proteins related genes in the cocultured BM cells. MCs exert their effect by release of mediators such as IL-8, IL-10, matrix metalloprotease 2, and vascular endothelial growth factor, thereby permitting metastasis. In conclusion, we provide evidence for a role of MCs in BM. Our findings indicate MCs’ capability of modulating gene expression in BM cells and suggest that MCs can serve as a new target for drug development against metastases in the brain.