Mesenchymal differentiation mediated by NF-κB promotes radiation resistance in glioblastoma

Despite extensive study, few therapeutic targets have been identified for glioblastoma (GBM). Here we show that patient-derived glioma sphere cultures (GSCs) that resemble either the proneural (PN) or mesenchymal (MES) transcriptomal subtypes differ significantly in their biological characteristics. Moreover, we found that a subset of the PN GSCs undergoes differentiation to a MES state in a TNF-α/NF-κB-dependent manner with an associated enrichment of CD44 subpopulations and radioresistant phenotypes. We present data to suggest that the tumor microenvironment cell types such as macrophages/microglia may play an integral role in this process. We further show that the MES signature, CD44 expression, and NF-κB activation correlate with poor radiation response and shorter survival in patients with GBM.

Spt4 selectively regulates the expression of C9orf72 sense and antisense mutant transcripts

An expanded hexanucleotide repeat in C9orf72 causes amyotrophic lateral sclerosis and frontotemporal dementia (c9FTD/ALS). Therapeutics are being developed to target RNAs containing the expanded repeat sequence (GGGGCC); however, this approach is complicated by the presence of antisense strand transcription of expanded GGCCCC repeats. We found that targeting the transcription elongation factor Spt4 selectively decreased production of both sense and antisense expanded transcripts, as well as their translated dipeptide repeat (DPR) products, and also mitigated degeneration in animal models. Knockdown of SUPT4H1, the human Spt4 ortholog, similarly decreased production of sense and antisense RNA foci, as well as DPR proteins, in patient cells. Therapeutic targeting of a single factor to eliminate c9FTD/ALS pathological features offers advantages over approaches that require targeting sense and antisense repeats separately.

Neuronal ROS-induced glial lipid droplet formation is altered by loss of Alzheimer's disease-associated genes

A growing list of Alzheimer's disease (AD) genetic risk factors is being identified, but the contribution of each variant to disease mechanism remains largely unknown. We have previously shown that elevated levels of reactive oxygen species (ROS) induces lipid synthesis in neurons leading to the sequestration of peroxidated lipids in glial lipid droplets (LD), delaying neurotoxicity. This neuron-to-glia lipid transport is APOD/E-dependent. To identify proteins that modulate these neuroprotective effects, we tested the role of AD risk genes in ROS-induced LD formation and demonstrate that several genes impact neuroprotective LD formation, including homologs of human ABCA1, ABCA7, VLDLR, VPS26, VPS35, AP2A, PICALM, and CD2AP Our data also show that ROS enhances Aβ42 phenotypes in flies and mice. Finally, a peptide agonist of ABCA1 restores glial LD formation in a humanized APOE4 fly model, highlighting a potentially therapeutic avenue to prevent ROS-induced neurotoxicity. This study places many AD genetic risk factors in a ROS-induced neuron-to-glia lipid transfer pathway with a critical role in protecting against neurotoxicity.

Toxic expanded GGGGCC repeat transcription is mediated by the PAF1 complex in C9orf72-associated FTD

An expanded GGGGCC hexanucleotide of more than 30 repeats (termed (G4C2)30+) within C9orf72 is the most prominent mutation in familial frontotemporal degeneration (FTD) and amyotrophic lateral sclerosis (ALS) (termed C9+). Through an unbiased large-scale screen of (G4C2)49-expressing Drosophila we identify the CDC73/PAF1 complex (PAF1C), a transcriptional regulator of RNA polymerase II, as a suppressor of G4C2-associated toxicity when knocked-down. Depletion of PAF1C reduces RNA and GR dipeptide production from (G4C2)30+ transgenes. Notably, in Drosophila, the PAF1C components Paf1 and Leo1 appear to be selective for the transcription of long, toxic repeat expansions, but not shorter, nontoxic expansions. In yeast, PAF1C components regulate the expression of both sense and antisense repeats. PAF1C is upregulated following (G4C2)30+ expression in flies and mice. In humans, PAF1 is also upregulated in C9+-derived cells, and its heterodimer partner, LEO1, binds C9+ repeat chromatin. In C9+ FTD, PAF1 and LEO1 are upregulated and their expression positively correlates with the expression of repeat-containing C9orf72 transcripts. These data indicate that PAF1C activity is an important factor for transcription of the long, toxic repeat in C9+ FTD.

eIF4B and eIF4H mediate GR production from expanded G4C2 in a Drosophila model for C9orf72-associated ALS

The discovery of an expanded (GGGGCC)n repeat (termed G4C2) within the first intron of C9orf72 in familial ALS/FTD has led to a number of studies showing that the aberrant expression of G4C2 RNA can produce toxic dipeptides through repeat-associated non-AUG (RAN-) translation. To reveal canonical translation factors that impact this process, an unbiased loss-of-function screen was performed in a G4C2 fly model that maintained the upstream intronic sequence of the human gene and contained a GFP tag in the GR reading frame. 11 of 48 translation factors were identified that impact production of the GR-GFP protein. Further investigations into two of these, eIF4B and eIF4H, revealed that downregulation of these factors reduced toxicity caused by the expression of expanded G4C2 and reduced production of toxic GR dipeptides from G4C2 transcripts. In patient-derived cells and in post-mortem tissue from ALS/FTD patients, eIF4H was found to be downregulated in cases harboring the G4C2 mutation compared to patients lacking the mutation and healthy individuals. Overall, these data define eIF4B and eIF4H as disease modifiers whose activity is important for RAN-translation of the GR peptide from G4C2-transcripts.

TNPO2 variants associate with human developmental delays, neurologic deficits, and dysmorphic features and alter TNPO2 activity in Drosophila

Transportin-2 (TNPO2) mediates multiple pathways including non-classical nucleocytoplasmic shuttling of >60 cargoes, such as developmental and neuronal proteins. We identified 15 individuals carrying de novo coding variants in TNPO2 who presented with global developmental delay (GDD), dysmorphic features, ophthalmologic abnormalities, and neurological features. To assess the nature of these variants, functional studies were performed in Drosophila. We found that fly dTnpo (orthologous to TNPO2) is expressed in a subset of neurons. dTnpo is critical for neuronal maintenance and function as downregulating dTnpo in mature neurons using RNAi disrupts neuronal activity and survival. Altering the activity and expression of dTnpo using mutant alleles or RNAi causes developmental defects, including eye and wing deformities and lethality. These effects are dosage dependent as more severe phenotypes are associated with stronger dTnpo loss. Interestingly, similar phenotypes are observed with dTnpo upregulation and ectopic expression of TNPO2, showing that loss and gain of Transportin activity causes developmental defects. Further, proband-associated variants can cause more or less severe developmental abnormalities compared to wild-type TNPO2 when ectopically expressed. The impact of the variants tested seems to correlate with their position within the protein. Specifically, those that fall within the RAN binding domain cause more severe toxicity and those in the acidic loop are less toxic. Variants within the cargo binding domain show tissue-dependent effects. In summary, dTnpo is an essential gene in flies during development and in neurons. Further, proband-associated de novo variants within TNPO2 disrupt the function of the encoded protein. Hence, TNPO2 variants are causative for neurodevelopmental abnormalities.

Dipeptide repeat proteins activate a heat shock response found in C9ORF72-ALS/FTLD patients

A hexanucleotide (GGGGCC) repeat expansion in C9ORF72 is the most common genetic contributor to amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Reduced expression of the C9ORF72 gene product has been proposed as a potential contributor to disease pathogenesis. Additionally, repetitive RNAs and dipeptide repeat proteins (DPRs), such as poly-GR, can be produced by this hexanucleotide expansion that disrupt a number of cellular processes, potentially contributing to neural degeneration. To better discern which of these mechanisms leads to disease-associated changes in patient brains, we analyzed gene expression data generated from the cortex and cerebellum. We found that transcripts encoding heat shock proteins (HSPs) regulated by the HSF1 transcription factor were significantly induced in C9ORF72-ALS/FTLD patients relative to both sporadic ALS/FTLD cases and controls. Treatment of human neurons with chemically synthesized DPRs was sufficient to activate a similar transcriptional response. Expression of GGGGCC repeats and also poly-GR in the brains of Drosophila lead to the upregulation of HSF1 and the same highly-conserved HSPs. Additionally, HSF1 was a modifier of poly-GR toxicity in Drosophila. Our results suggest that the expression of DPRs are associated with upregulation of HSF1 and activation of a heat shock response in C9ORF72-ALS/FTLD.

Drosophila Ref1/ALYREF regulates transcription and toxicity associated with ALS/FTD disease etiologies

RNA-binding proteins (RBPs) are associated with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), but the underlying disease mechanisms remain unclear. In an unbiased screen in Drosophila for RBPs that genetically interact with TDP-43, we found that downregulation of the mRNA export factor Ref1 (fly orthologue to human ALYREF) mitigated TDP-43 induced toxicity. Further, Ref1 depletion also reduced toxicity caused by expression of the C9orf72 GGGGCC repeat expansion. Ref1 knockdown lowered the mRNA levels for these related disease genes and reduced the encoded proteins with no effect on a wild-type Tau disease transgene or a control transgene. Interestingly, expression of TDP-43 or the GGGGCC repeat expansion increased endogenous Ref1 mRNA levels in the fly brain. Further, the human orthologue ALYREF was upregulated by immunohistochemistry in ALS motor neurons, with the strongest upregulation occurring in ALS cases harboring the GGGGCC expansion in C9orf72. These data support ALYREF as a contributor to ALS/FTD and highlight its downregulation as a potential therapeutic target that may affect co-existing disease etiologies.

A gene expression signature predicts recurrence-free survival in meningioma

BACKGROUND

Meningioma is the most common primary brain tumor and has a variable risk of local recurrence. While World Health Organization (WHO) grade generally correlates with recurrence, there is substantial within-grade variation of recurrence risk. Current risk stratification does not accurately predict which patients are likely to benefit from adjuvant radiation therapy (RT). We hypothesized that tumors at risk for recurrence have unique gene expression profiles (GEP) that could better select patients for adjuvant RT.

METHODS

We developed a recurrence predictor by machine learning modeling using a training/validation approach.

RESULTS

Three publicly available AffymetrixU133 gene expression datasets (GSE9438, GSE16581, GSE43290) combining 127 primary, non-treated meningiomas of all grades served as the training set. Unsupervised variable selection was used to identify an 18-gene GEP model (18-GEP) that separated recurrences. This model was validated on 62 primary, non-treated cases with similar grade and clinical variable distribution as the training set. When applied to the validation set, 18-GEP separated recurrences with a misclassification error rate of 0.25 (log-rank p=0.0003). 18-GEP was predictive for tumor recurrence [p=0.0008, HR=4.61, 95%CI=1.89-11.23)] and was predictive after adjustment for WHO grade, mitotic index, sex, tumor location, and Simpson grade [p=0.0311, HR=9.28, 95%CI=(1.22-70.29)]. The expression signature included genes encoding proteins involved in normal embryonic development, cell proliferation, tumor growth and invasion (FGF9, SEMA3C, EDNRA), angiogenesis (angiopoietin-2), cell cycle regulation (CDKN1A), membrane signaling (tetraspanin-7, caveolin-2), WNT-pathway inhibitors (DKK3), complement system (C1QA) and neurotransmitter regulation (SLC1A3, Secretogranin-II).

CONCLUSIONS

18-GEP accurately stratifies patients with meningioma by recurrence risk having the potential to guide the use of adjuvant RT.

Autolysosomal exocytosis of lipids protect neurons from ferroptosis

During oxidative stress neurons release lipids that are internalized by glia. Defects in this coordinated process play an important role in several neurodegenerative diseases. Yet, the mechanisms of lipid release and its consequences on neuronal health are unclear. Here, we demonstrate that lipid-protein particle release by autolysosome exocytosis protects neurons from ferroptosis, a form of cell death driven by lipid peroxidation. We show that during oxidative stress, peroxidated lipids and iron are released from neurons by autolysosomal exocytosis which requires the exocytic machinery VAMP7 and syntaxin 4. We observe membrane-bound lipid-protein particles by TEM and demonstrate that these particles are released from neurons using cryoEM. Failure to release these lipid-protein particles causes lipid hydroperoxide and iron accumulation and sensitizes neurons to ferroptosis. Our results reveal how neurons protect themselves from peroxidated lipids. Given the number of brain pathologies that involve ferroptosis, defects in this pathway likely play a key role in the pathophysiology of neurodegenerative disease.

Recent insights into the role of glia and oxidative stress in Alzheimer's disease gained from Drosophila

Here, we discuss findings made using Drosophila on Alzheimer's disease (AD) risk and progression. Recent studies have investigated the mechanisms underlying glia-mediated neuroprotection in AD. First, we discuss a novel mechanism of glial lipid droplet formation that occurs in response to elevated reactive oxygen species in neurons. The data suggest that disruptions to this process contribute to AD risk. We further discuss novel mechanistic insights into glia-mediated Aβ42-clearance made using the fly. Finally, we highlight work that provides evidence that the aberrant accumulation of reactive oxygen species in AD may not just be a consequence of disease but contribute to disease progression as well. Cumulatively, the discussed studies highlight recent, relevant discoveries in AD made using Drosophila.

New Roles for Canonical Transcription Factors in Repeat Expansion Diseases

The presence of microsatellite repeat expansions within genes is associated with >30 neurological diseases. Of interest, (GGGGCC)_>30-repeats within C9orf72 are associated with amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD). These expansions can be 100s to 1000s of units long. Thus, it is perplexing how RNA-polymerase II (RNAPII) can successfully transcribe them. Recent investigations focusing on GGGGCC-transcription have identified specific, canonical complexes that may promote RNAPII-transcription at these GC-rich microsatellites: the DSIF complex and PAF1C. These complexes may be important for resolving the unique secondary structures formed by GGGGCC-DNA during transcription. Importantly, this process can produce potentially toxic repeat-containing RNA that can encode potentially toxic peptides, impacting neuron function and health. Understanding how transcription of these repeats occurs has implications for therapeutics in multiple diseases.

A fly model for the CCUG-repeat expansion of myotonic dystrophy type 2 reveals a novel interaction with MBNL1

Expanded non-coding RNA repeats of CUG and CCUG are the underlying genetic causes for myotonic dystrophy type 1 (DM1) and type 2 (DM2), respectively. A gain-of-function of these pathogenic repeat expansions is mediated at least in part by their abnormal interactions with RNA-binding proteins such as MBNL1 and resultant loss of activity of these proteins. To study pathogenic mechanisms of CCUG-repeat expansions in an animal model, we created a fly model of DM2 that expresses pure, uninterrupted CCUG-repeat expansions ranging from 16 to 720 repeats in length. We show that this fly model for DM2 recapitulates key features of human DM2 including RNA repeat-induced toxicity, ribonuclear foci formation and changes in alternative splicing. Interestingly, expression of two isoforms of MBNL1, MBNL135 and MBNL140, leads to cleavage and concurrent upregulation of the levels of the RNA-repeat transcripts, with MBNL140 having more significant effects than MBNL135. This property is shared with a fly CUG-repeat expansion model. Our results suggest a novel mechanism for interaction between the pathogenic RNA repeat expansions of myotonic dystrophy and MBNL1.

Repeat-associated non-AUG (RAN) translation mechanisms are running into focus for GGGGCC-repeat associated ALS/FTD

Many human diseases are associated with the expansion of repeat sequences within the genes. It has become clear that expressed disease transcripts bearing such long repeats can undergo translation, even in the absence of a canonical AUG start codon. Termed "RAN translation" for repeat associated non-AUG translation, this process is becoming increasingly prominent as a contributor to these disorders. Here we discuss mechanisms and variables that impact translation of the repeat sequences associated with the C9orf72 gene. Expansions of a G4C2 repeat within intron 1 of this gene are associated with the motor neuron disease ALS and dementia FTD, which comprise a clinical and pathological spectrum. RAN translation of G4C2 repeat expansions has been studied in cells in culture (ex vivo) and in the fly in vivo. Cellular states that lead to RAN translation, like stress, may be critical contributors to disease progression. Greater elucidation of the mechanisms that impact this process and the factors contributing will lead to greater understanding of the repeat expansion diseases, to the potential development of novel approaches to therapeutics, and to a greater understanding of how these players impact biological processes in the absence of disease.

PDPN marks a subset of aggressive and radiation-resistant glioblastoma cells

Treatment-resistant glioma stem cells are thought to propagate and drive growth of malignant gliomas, but their markers and our ability to target them specifically are not well understood. We demonstrate that podoplanin (PDPN) expression is an independent prognostic marker in gliomas across multiple independent patient cohorts comprising both high- and low-grade gliomas. Knockdown of PDPN radiosensitized glioma cell lines and glioma-stem-like cells (GSCs). Clonogenic assays and xenograft experiments revealed that PDPN expression was associated with radiotherapy resistance and tumor aggressiveness. We further demonstrate that knockdown of PDPN in GSCs in vivo is sufficient to improve overall survival in an intracranial xenograft mouse model. PDPN therefore identifies a subset of aggressive, treatment-resistant glioma cells responsible for radiation resistance and may serve as a novel therapeutic target.

Abstract 3313: A proliferating population of glioma stem-like cells as characterized by expression of the cell surface glycoprotein CD58

Glioblastomas (GBMs) are among the most common and most lethal primary brain tumors, characterized by a high cellular proliferation and invasion into brain parenchyma. Glioma stem-like cells (GSCs) have been proposed as being responsible for tumor initiation and recurrence following conventional therapy with chemoradiation. Attempts to identify a single cell surface marker which specifically identifies GSCs within human tumors have had limited success. In an effort to refine GSC identification through the use of a panel of cell surface markers, we identified the glycoprotein CD58 as a marker which more selectively identifies GSCs when added to established markers, such as CD133, podoplanin (pdpn), or CD15. To characterize the frequency of CD58 expression in neurosphere forming primary culture cell lines and freshly obtained surgical specimens, cells were subjected to flow cytometry using an anti-CD58 monoclonal antibody. In vitro analysis of self-renewal, a principle feature of GSCs, was performed with the neurosphere assay. Treatment resistance was compared by radiating single cell suspensions with 2 Gy ionizing radiation prior to neurosphere formation. Cell cycle was measured by flow cytometry and S-phase by incorporation of EdU. Survival analysis was performed on archival tumor specimens following immunohistochemistry with an anti-CD58 monoclonal antibody. Using a panel of 14 GSC primary cultures, CD58 expression was found in all lines, with a median expression of 85.4% of cells, ranging from 8.7% to 100%. CD58 expression was found in 67% of fresh GBM specimens, with expression ranging from 5% to 89% of tumor cells (median 9.4). Culturing of cells beyond 5 passages led to further enrichment for CD58 expressing cells. Neurosphere assays demonstrated an increase in self-renewal in cells expressing CD58 compared to pdpn/CD133/CD15 alone. To investigate whether this difference was a result of increased proliferation of CD58 cells, we performed cell cycle analysis and found a significantly higher percentage of CD58 expressing cells in S-phase (mean of 23.2% vs. 7.9% for CD58 expressing vs. non-expressing, respectively). Immunofluorescence of archival specimens with MIB1/Ki-67 revealed preferential staining in CD58 expression cells. In cell mixing experiments, we observed that CD58 expressing cells rapidly outgrew CD58 non-expressing, highlighting the differences in proliferative capacity. Analysis of patients based on CD58 expression in their tumors revealed that patients with CD58 expression tumors had a poorer survival compared to patients with low or non-expressing tumors (median survival 64 vs 43 weeks, 2yr survival 3% vs 25%, p=0.0192, logrank). In summary, CD58 expression identifies a highly proliferative subpopulation of GSCs, improves upon established markers of these cells, and is an independent predictor of survival based on expression in patient tumors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3313. doi:10.1158/1538-7445.AM2011-3313

Abstract 2467: Podoplanin expressing cancer stem cells show increased resistance to DNA damage induced by ionizing radiation

The majority of patients with malignant gliomas, the most common and most lethal brain tumor, develop disease recurrence despite aggressive, multi-modality therapies. This treatment resistance has been attributed to a small population of tumor-initiating glioma cancer stem cells (GSCs). We recently described a new marker of GSCs, the transmembrane glycoprotein podoplanin (pdpn), based on analysis of gene expression profiling data and have found it to be more accurately identify the stem cell population than other described markers. Pdpn expression correlates with poor patient survival and decreased response to radiotherapy. Pdpn expressing cells form neurospheres at high rates in vitro, are more resistant to ionizing radiation, and initiate tumors in vivo. Silencing of pdpn leads to increased radiosensitivity. To identify the mechanism of radiation resistance in pdpn-expressing GSCs, we screened for putative binding partners and identified target of myb-like-1 (tom1l1), a known regulator of Src-pathway activation. We hypothesized that modulation of pdpn and/or tom1l1 expression would lead to alternations in the response of GSCs to radiation via src signaling. Mechanisms of radiation resistance in GSCs are poorly understood to date and the role of src family kinases in modulating radiosensitivity has not previously been reported in gliomas. Pdpn binding of tom1l1 was confirmed by co-immunoprecipation and src activation monitored by immunoblot. Pdpn and tom1l1 expression was downregulated by RNA interference and dsDNA damage and repair assayed by neutral comet assay and by scoring of γH2AX foci. Silencing of pdpn in primary culture, neurophere forming GSC-like cells resulted in increased DNA damage following 2 and 6 Gy ionizing radiation. We similarly examined effects of decreased tom1l1 to determine if the effects on DNA repair mediating by pdpn were acting via the src pathway. In summary, our data suggest that pdpn expression correlates with increased dsDNA repair following ionizing radiation and presents a possible mechanism by which GSCs resist treatment and regrow the tumor.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2467. doi:10.1158/1538-7445.AM2011-2467

Alzheimer's disease protective allele of Clusterin modulates neuronal excitability through lipid-droplet-mediated neuron-glia communication

Genome-wide association studies (GWAS) of Alzheimer's disease (AD) have identified a plethora of risk loci. However, the disease variants/genes and the underlying mechanisms remain largely unknown. For a strong AD-associated locus near Clusterin (CLU), we tied an AD protective allele to a role of neuronal CLU in promoting neuron excitability through lipid-mediated neuron-glia communication. We identified a putative causal SNP of CLU that impacts neuron-specific chromatin accessibility to transcription-factor(s), with the AD protective allele upregulating neuronal CLU and promoting neuron excitability. Transcriptomic analysis and functional studies in induced pluripotent stem cell (iPSC)-derived neurons co-cultured with mouse astrocytes show that neuronal CLU facilitates neuron-to-glia lipid transfer and astrocytic lipid droplet formation coupled with reactive oxygen species (ROS) accumulation. These changes cause astrocytes to uptake less glutamate thereby altering neuron excitability. Our study provides insights into how CLU confers resilience to AD through neuron-glia interactions.

Abstract 4305: Refinement of the glioma cancer stem cell marker profile

Infiltrating gliomas are the most frequently occurring adult brain tumor and, among high-grade forms, typically result in poor patient survival. These tumors tend to be refractory to most treatments, including aggressive surgical resection and chemoradiation. This treatment resistance is hypothesized to be the result of a small population of cells within the tumor which are responsible for tumor initiation, called glioma cancer stem cells (GCSCs). As is true in other stem cell systems, such as hematopoiesis, multiple cell-surface protein markers are needed to accurately define the true stem cell population. We and others have previously identified the glycoprotein podoplanin (pdpn) as a marker of GCSC, which improves upon the established marker, CD133. To refine the GCSC marker profile beyond these two proteins, we examined a number of candidate markers in combination with pdpn that have been proposed as stem cell markers in gliomas or other tumors or tissues. Candidate markers were analyzed by flow cytometry using primary glioma cell lines maintained as neurosphere cultures and fresh tumor specimens. Markers identifying a unique cell population either alone or in combination with pdpn were further analyzed by in vitro neurosphere formation assay and clonogenic survival assay following 2 Gy ionizing radiation. Candidates showing enrichment for stem cells based on these assays were examine for in vivo tumor initiation using flow sorted subpopulations of cells with and without the expression of the candidate protein. As expression of putative stem cell markers will likely predict for poor patient survival, candidate markers were also examined in human tumors by immunohistochemsitry. Among the most promosing candidates were CD97, CXCR4, CD58 and CD44. Flow cytometry revealed CD97 expression in 75%, CD58 in 80%, CXCR4 in 100%, and CD44 in 100% of tumors examined to date. Examination of primary neurosphere cultures, found CD97 in 80%, CXCR4 in 83%, CD58 in 100%, and CD44 in 100% of lines examined. Both CD44+ and CD58+ cells exhibited increased neurophere formation rates and in vivo tumor initiation. These stem-like characteristics were enhanced in those subpopulations also expressing pdpn. RNAs collected from these subpopulations were used for expression profiling to determine if these subpopulation express a unique gene expression. Results thus far indicate that pdpn expression is needed for the stem-like phenotype and that this is enhanced in populations co-expressing CD44, CD15, and/or CD58. Further refinement of this profile will aide in the isolation of the “true” GCSC and allow for improved therapeutic targeting of these resistant cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4305.

Abstract 5157: Functional and regulatory role of src kinase in podoplanin expressing glioma cancer stem cells

The majority of patients with malignant gliomas, the most common and most lethal brain tumor, develop disease recurrence despite aggressive, multi-modality therapies. This treatment resistance has been attributed to a small population of tumor-initiating glioma cancer stem cells (GSCs). We recently described a new marker of GSCs, podoplanin (pdpn), based on analyses of gene expression profiling data and have found it to more accurately identify the stem cell population than other described markers, such as CD133, and to play a functional role stem cell phenotype. Pdpn expressing cells formed neurospheres at high rates in vitro, were more resistant to ionizing radiation, and initiated tumors in vivo. Pdpn belongs to a mesenchymal gene signature that is characteritic of poor patients survival from malignant gliomas. To identify the mechasism of pdpn within GSCs, we evaluated putuative binding partners to this transmembrane glycoprotein. One such partner, target of myb-like-1 (tom1l1) has been shown to regulate the Src oncogene pathway. The cytoplasmic tyrosine kinases of the Src family (SFK) play important roles in signal transduction induced by growth factors leading to DNA synthesis, cytoskeletal rearrangement, and receptor endocytosis. We therefore hypothesized that pdpn's role GSCs is due to its interaction with the Src pathway. Our aim for this study was to analyze downstream signaling events of Src in association with pdpn and its functional significance in glioma stem cell maintanence, invasion, and chemoradiation resistance. Using primary GSC and established glioma cell lines engineered to either overexpress or silence PDPN, we screened for SFK protein activation (phosphorylation) by immunblot. Changes in Src activation were correlated to in vitro invasion assays, in vivo tumor initiation, and radiation resistance. Preliminary data confirms binding of tom1l1 to pdpn and regulation of SFK activation. Engineered clones with shRNA targeting pdpn and/or tom1l1 were examined by expression profiling for downstream transcriptional changes. In summary, our data suggest a role of SFKs in the regulation of stemness by pdpn. These data integrate well with ongoing trials using Src-kinase inhibitors which may directly target the pdpn-expressing, GSC population in tumors and perhaps overcome the treatment resistance of these critical cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5157.

Abstract 4795: A novel gene fusion in glioblastoma and a radiation response methylation signature identified by genomic characterization of glioma sphere-forming cells

Purpose: High fidelity models of the lethal primary brain tumor glioblastoma (GBM) are essential to develop new therapies. Glioma sphere-forming cells (GSCs) are derived from surgical specimens and are thought to play important roles in tumor maintenance and treatment resistance. We performed genomic characterization of the largest reported panel of GSCs. We hypothesized that GSCs would recapitulate the genomic alterations of their GBMs of origin while identifying novel changes identifiable only in a pure tumor cell population.

Methods: All GSCs were obtained at the time of surgical resection and all analyses were conducted at early passage. We performed exome and transcriptome sequencing, DNA methylation profiling (Illumina Infinium 450K Bead Arrays) and DNA copy number determination (Affymetrix OncoScan). Radiation (RT) sensitivity was determined by clonogenic survival and in vivo survival by orthotopic xenograft.

Results: We analyzed 43 GSCs, 40 of which had tissue available from their tumors of origin. Somatically mutated genes previously described in GBM, such as TP53, EGFR, PTEN, NF1, PIK3CA and RB1, were found at similar mutation frequencies. Likewise, DNA copy number variations were similar to their matched tumor and those reported by the TCGA, with novel or more pronounced alterations, such as MYC application and QKI deletion, identified in the GSCs. GSCs were classified into TCGA GBM subtypes by expression signatures, identifying a subset of GSCs with a subtype differing from their matched tumors that correlated to decreased stromal enrichment. GSCs exhibited upregulation of self-renewal pathways, such as MYC, WNT, and NOTCH, and of stem-cell factors, such as MSI1, NESTIN, OLIG2, and SOX2, consistent with the stem-like phenotype attributed to GSCs. Transcript analyses identified the previously reported FGFR3-TACC3 and EGFR-SEPT14 gene fusions as well as a novel KIF1B-KMT2A (MLL) fusion, which was found to have been retained in the matching recurrent GBM as well as the GSC derived from the recurrence. A signature derived by the differential methylation pattern of RT sensitive vs. resistant GSCs was applied to the subset of TCGA cases that received upfront RT. Survival by methylation class in this subset was significantly different (median survival 84 vs. 61 weeks; HR 1.64 adjusting for patient age, p-value<0.008), suggesting this signature is predictive of clinical RT response.

Conclusions: Based on genomic analyses, GSCs are robust models of GBM which can be used for therapeutic development. We have identified a novel gene fusion involving MLL with a predicted driving role suggesting a new mode of gliomagenesis. A methylation signature predictive of RT response may have potential for personalizing RT treatment of GBM patients and provides insights into RT sensitivity phenotypes.

Citation Format: Qianghu Wang, Ravesanker Ezhilarasan, Lindsey D. Goodman, Joy Gumin, Siyuan Zheng, Kosuke Yoshihara, Peng Sun, Jie Yang, Tim Heffernan, Giulio Draetta, Kenneth D. Aldape, Frederick F. Lang, Roel G.W. Verhaak, Erik P. Sulman. A novel gene fusion in glioblastoma and a radiation response methylation signature identified by genomic characterization of glioma sphere-forming cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4795. doi:10.1158/1538-7445.AM2015-4795

Abstract 5147: Trancriptional activation of the glioma stem cell marker podoplanin by the homeobox transcription factor prox1

The homeobox transcription factor Prox1 is related to the Drosophila prospero gene, which mediates cell fate decisions of neuroblasts. Prox1 is a regulator of lymphangiogenesis but it is also expressed in the developing central nervous system. Homeobox proteins are known to play essential role in the determination of cell fate and the development of the body plan. It has been shown in Drosophila that prospero-mediated transcriptional repression of stem cell genes and activation of differentiation genes prevents tumorigenic growth, suggesting that prospero is in fact a tumor suppressor. Due to its homology to prospero, we speculated that prox1 may play a role in glioma tumorigensis. We previously identified the transmembrane glycoprotein podoplanin (pdpn) as a prognostic marker in infiltrating gliomas, the most common and lethal of adult brain tumors, by analyses of gene expression profiling data. Subsequent functional studies revealed that pdpn identified a subpopulation of cells from primary neurophere cultures and fresh tumors that have characteristics of glioma cancer stem cells (GSCs), such as radiation resistance and tumor initiation, and that the protein played a functional role in maintaining the stem cell phenotype. Like prox1, pdpn is expressed both during lymphangiogenesis and neural development and mice null for either protein have a similar phenotype, including lymphedema and the lack of terminal alveoli formation in the lung. While other transcription factors have been implicated in cancer stem cells, such as Bmi-1, prox1 has note previously been implicated to have a role in this tumor-initiating, treatment resistant cell population. We therefore hypothesized that prox1 transcriptionally regulates PDPN expression in GSCs. To test this, we examined gene expression profiling data from a large glioma dataset for correlations between PDPN and PROX1 expression. No correlation was seen between expression of the two genes; however, PROX1 expression was predictive of patient survival independent of tumor grade (p=.0333). Next, we screened primary neurosphere cell lines for levels of prox1 and pdpn by immunoblot. Co-expression with pdpn was observed in all cell lines expressing prox1. To examine the role of prox1 in PDPN expression, we compared the levels of PDPN in cells for whom prox1 expression had been silenced. In preliminary results, real-time PCR for PDPN showed significant decreases in expression in the presence of PROX1-targeting siRNA. Ongoing promotor and functional analyses will validate the role of prox1 in the transcriptional activation of PDPN. Comparison of the expression profiles of isogenic clones differing only in their expression of PROX1 identifies additional transcriptional targets. In summary, we have identified prox1 as a candidate transcription factor in the regulation of the glioma stem cell phenotype.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5147.

Does glial lipid dysregulation alter sleep in Alzheimer's and Parkinson's disease?

In this opinion article, we discuss potential connections between sleep disturbances observed in Alzheimer's disease (AD) and Parkinson's disease (PD) and the dysregulation of lipids in the brain. Research using Drosophila has highlighted the role of glial-mediated lipid metabolism in sleep and diurnal rhythms. Relevant to AD, the formation of lipid droplets in glia, which occurs in response to elevated neuronal reactive oxygen species (ROS), is required for sleep. In disease models, this process is disrupted, arguing a connection to sleep dysregulation. Relevant to PD, the degradation of neuronally synthesized glucosylceramides by glia requires glucocerebrosidase (GBA, a PD-associated risk factor) and this regulates sleep. Loss of GBA in glia causes an accumulation of glucosylceramides and neurodegeneration. Overall, research primarily using Drosophila has highlighted how dysregulation of glial lipid metabolism may underlie sleep disturbances in neurodegenerative diseases.