Differentiation Of Glioma Cells Research Articles

Glioblastoma stem cells deliver ABCB4 transcribed by ATF3 via exosomes conferring glioblastoma resistance to temozolomide

Glioblastoma stem cells (GSCs) play a key role in glioblastoma (GBM) resistance to temozolomide (TMZ) chemotherapy. With the increase in research on the tumour microenvironment, exosomes secreted by GSCs have become a new focus in GBM research. However, the molecular mechanism by which GSCs affect drug resistance in GBM cells via exosomes remains unclear. Using bioinformatics analysis, we identified the specific expression of ABCB4 in GSCs. Subsequently, we established GSC cell lines and used ultracentrifugation to extract secreted exosomes. We conducted in vitro and in vivo investigations to validate the promoting effect of ABCB4 and ABCB4-containing exosomes on TMZ resistance. Finally, to identify the transcription factors regulating the transcription of ABCB4, we performed luciferase assays and chromatin immunoprecipitation-quantitative PCR. Our results indicated that ABCB4 is highly expressed in GSCs. Moreover, high expression of ABCB4 promoted the resistance of GSCs to TMZ. Our study found that GSCs can also transmit their highly expressed ABCB4 to differentiated glioma cells (DGCs) through exosomes, leading to high expression of ABCB4 in these cells and promoting their resistance to TMZ. Mechanistic studies have shown that the overexpression of ABCB4 in GSCs is mediated by the transcription factor ATF3. In conclusion, our results indicate that GSCs can confer resistance to TMZ in GBM by transmitting ABCB4, which is transcribed by ATF3, through exosomes. This mechanism may lead to drug resistance and recurrence of GBM. These findings contribute to a deeper understanding of the mechanisms underlying drug resistance in GBM and provide novel insights into its treatment.

The PTPRZ1-MET/STAT3/ISG20 axis in glioma stem-like cells modulates tumor-associated macrophage polarization

Recent studies have revealed that PTPRZ1-MET (ZM) fusion plays a pivotal role in the progression of glioma to glioblastoma multiforme (GBM), thus serving as a biomarker to distinguish between primary GBM and secondary GBM (sGBM). However, the mechanisms through which ZM fusion influences this progression remain to be elucidated. GBMs with ZM showed poorer prognoses and greater infiltration of tumor-associated macrophages (TAMs) than those without ZM. Glioma stem-like cells (GSCs) and TAMs play complex roles in glioma recurrence, glioma progression and therapy resistance. In this study, we analyzed RNA-seq data from sGBM patients' glioma tissues with or without ZM fusion, and found that stemness and macrophage markers were more highly expressed in sGBM patients harboring ZM than in those without ZM fusion. ZM enhanced the self-renewal and proliferation of GSCs, thereby accelerating glioma progression. In addition, ZM-positive GSCs facilitated the infiltration of TAMs and drove their polarization toward an immunosuppressive phenotype, which was primarily accomplished through the extracellular secretion of ISG20. Our research identified the MET–STAT3–ISG20 axis within GSCs, thus demonstrating the critical role of ZM in GBM initiation and progression. Our study demonstrated that, in contrast to ZM-positive differentiated glioma cells, ZM-positive GSCs upregulated ISG20 expression through the MET–STAT3–ISG20 axis. The extracellular secretion of ISG20 recruited and induced M2-like polarization in macrophages, thereby promoting tumor progression. Our results reveal a novel mechanism involved in ZM-positive GBM pathogenesis and identify potential therapeutic targets.

Reactivating PTEN to impair glioma stem cells by inhibiting cytosolic iron-sulfur assembly.

Glioblastoma, the most lethal primary brain tumor, harbors glioma stem cells (GSCs) that not only initiate and maintain malignant phenotypes but also enhance therapeutic resistance. Although frequently mutated in glioblastomas, the function and regulation of PTEN in PTEN-intact GSCs are unknown. Here, we found that PTEN directly interacted with MMS19 and competitively disrupted MMS19-based cytosolic iron-sulfur (Fe-S) cluster assembly (CIA) machinery in differentiated glioma cells. PTEN was specifically succinated at cysteine (C) 211 in GSCs compared with matched differentiated glioma cells. Isotope tracing coupled with mass spectrometry analysis confirmed that fumarate, generated by adenylosuccinate lyase (ADSL) in the de novo purine synthesis pathway that is highly activated in GSCs, promoted PTEN C211 succination. This modification abrogated the interaction between PTEN and MMS19, reactivating the CIA machinery pathway in GSCs. Functionally, inhibiting PTEN C211 succination by reexpressing a PTEN C211S mutant, depleting ADSL by shRNAs, or consuming fumarate by the US Food and Drug Administration-approved prescription drug N-acetylcysteine (NAC) impaired GSC maintenance. Reexpressing PTEN C211S or treating with NAC sensitized GSC-derived brain tumors to temozolomide and irradiation, the standard-of-care treatments for patients with glioblastoma, by slowing CIA machinery-mediated DNA damage repair. These findings reveal an immediately practicable strategy to target GSCs to treat glioblastoma by combination therapy with repurposed NAC.

IDH1 mutation inhibits differentiation of astrocytes and glioma cells with low oxoglutarate dehydrogenase expression by disturbing α-ketoglutarate-related metabolism and epigenetic modification

Abstract Isocitrate dehydrogenase (IDH) mutations frequently occur in lower-grade gliomas and secondary glioblastomas. Mutant IDHs exhibit a gain-of-function activity, leading to the production of D-2-hydroxyglutarate (D-2HG) by reducing α-ketoglutarate (α-KG), a central player in metabolism and epigenetic modifications. However, the role of α-KG homeostasis in IDH-mutated gliomagenesis remains elusive. In this study, we found that low expression of oxoglutarate dehydrogenase (OGDH) was a common feature in IDH-mutated gliomas, as well as in astrocytes. This low expression of OGDH resulted in the accumulation of α-KG and promoted astrocyte maturation. However, IDH1 mutation significantly reduced α-KG levels and increased glutaminolysis and DNA/histone methylation in astrocytes. These metabolic and epigenetic alterations inhibited astrocyte maturation and led to cortical dysplasia in mice. Moreover, our results also indicated that reduced OGDH expression can promote the differentiation of glioma cells, while IDH1 mutations impeded the differentiation of glioma cells with low OGDH by reducing the accumulation of α-KG and increasing glutaminolysis. Finally, we found that l-glutamine increased α-KG levels and augmented the differentiation-promoting effects of AGI5198, an IDH1-mutant inhibitor, in IDH1-mutant glioma cells. Collectively, this study reveals that low OGDH expression is a crucial metabolic characteristic of IDH-mutant gliomas, providing a potential strategy for the treatment of IDH-mutant gliomas by targeting α-KG homeostasis.

LncRNA INHEG promotes glioma stem cell maintenance and tumorigenicity through regulating rRNA 2’-O-methylation

Glioblastoma (GBM) ranks among the most lethal of human cancers, containing glioma stem cells (GSCs) that display therapeutic resistance. Here, we report that the lncRNA INHEG is highly expressed in GSCs compared to differentiated glioma cells (DGCs) and promotes GSC self-renewal and tumorigenicity through control of rRNA 2’-O-methylation. INHEG induces the interaction between SUMO2 E3 ligase TAF15 and NOP58, a core component of snoRNP that guides rRNA methylation, to regulate NOP58 sumoylation and accelerate the C/D box snoRNP assembly. INHEG activation enhances rRNA 2’-O-methylation, thereby increasing the expression of oncogenic proteins including EGFR, IGF1R, CDK6 and PDGFRB in glioma cells. Taken together, this study identifies a lncRNA that connects snoRNP-guided rRNA 2’-O-methylation to upregulated protein translation in GSCs, supporting an axis for potential therapeutic targeting of gliomas.

SYST-24 PROPOFOL EXERTS ANTI-TUMOR EFFECTS IN GLIOMA AND THE TUMOR MICROENVIRONMENT VIA NON-CODING RNAS AND SECRETED EXOSOMES

Abstract BACKGROUND Glioblastoma (GBM), is the most common primary brain tumor. GBM contains a small subpopulation of glioma stem cells (GSCs) that are implicated in tumor recurrence and treatment resistance and therefore represent important therapeutic targets. Recent clinical studies suggest propofol impacts subsequent tumor response to treatments and patient prognosis. The effects of propofol on patient derived GSCs alone and in combination with radiation and temozolomide, (TMZ) have not been reported. Objectives: The molecular mechanisms underlying propofol’s anti-tumor effects on GSCs and its effect on cellular communication with microglia was studied. Using GSC spheroids, differentiated glioma and tumor cells on a microfluid chip, effects of propofol alone and together with radiation and TMZ on the self-renewal and stemness of GSCs, their mesenchymal transit and the proliferation and apoptosis of differentiated glioma cells was analyzed. Using transwell plates, the effects of propofol on the cross-talk of GSCs with human microglia cells was examined. RESULTS Propofol exerted a dose-dependent inhibitory effect on the self-renewal, expression of mesenchymal markers and migration of GSCs and sensitized them to both temozolomide (TMZ) and radiation. At higher concentrations propofol induced a large degree of cell death as demonstrated using microfluid chip. Propofol increased the expression of the lncRNA BDNF-AS, which acts as a tumor suppressor in GBM and silencing of this lncRNA partially abrogated propofol’s anti-tumor effects. Propofol also inhibited the pro-tumorigenic GSC-microglia cross talk via extracellular vesicles (EVs) and delivery of BDNF-AS. CONCLUSIONS Propofol exerted anti-tumor effects on GSCs and differentiated glioma cells by inhibiting cell renewal, proliferation, and mesenchymal transition and by inducing cell death at higher concentration. Propofol also sensitized GSCs to radiation and TMZ. Propofol, which is widely used in GBM surgeries, should be further explored as a potential repurposed drug during resection and an effective adjunct to radiation and TMZ.

Glioblastoma Stem Cell Targeting Peptide Isolated Through Phage Display Binds Cadherin 2.

Glioblastoma stem cells (GSCs) have unique properties of self-renewal and tumor initiation that make them potential therapeutic targets. Development of effective therapeutic strategies against GSCs requires both specificity of targeting and intracranial penetration through the blood-brain barrier. We have previously demonstrated the use of in vitro and in vivo phage display biopanning strategies to isolate glioblastoma targeting peptides. Here we selected a 7-amino acid peptide, AWEFYFP, which was independently isolated in both the in vitro and in vivo screens and demonstrated that it was able to target GSCs over differentiated glioma cells and non-neoplastic brain cells. When conjugated to Cyanine 5.5 and intravenously injected into mice with intracranially xenografted glioblastoma, the peptide localized to the site of the tumor, demonstrating intracranial tumor targeting specificity. Immunoprecipitation of the peptide with GSC proteins revealed Cadherin 2 as the glioblastoma cell surface receptor targeted by the peptides. Peptide targeting of Cadherin 2 on GSCs was confirmed through ELISA and in vitro binding analysis. Interrogation of glioblastoma databases demonstrated that Cadherin 2 expression correlated with tumor grade and survival. These results confirm that phage display can be used to isolate unique tumor-targeting peptides specific for glioblastoma. Furthermore, analysis of these cell specific peptides can lead to the discovery of cell specific receptor targets that may serve as the focus of future theragnostic tumor-homing modalities for the development of precision strategies for the treatment and diagnosis of glioblastomas.

Expression, Significance, and Correlation of Histone Deacetylase 1/RE-1 Silencing Transcription Factor and Neuronal Markers in Glioma.

Inducing the differentiation of glioma cells into neuron-like cells may be an effective strategy to combat glioma. The histone deacetylase 1/RE-1 silencing transcription factor (HDAC1/REST) complex regulates the expression of multiple neuronal genes. In this study, we analyzed the presence and significance of this regulatory effect in glioma based on bioinformatics methods. The Human Protein Atlas database was used to obtain immunohistochemical staining images. The Gene Expression Profiling Interactive Analysis and Chinese Glioma Genome Atlas databases were used to analyze the expression of HDAC1/REST and neuronal markers in glioma, their effects on survival, and the association between HDAC1/REST and the expression of neuronal markers and stem cell markers. The differentially expressed genes between the high and low HDAC1/REST groups were explored. The Database for Annotation, Visualization and Integrated Discovery database was used for gene ontology and kyoto encyclopedia of genes and genomes pathway enrichment analysis. The results showed that the expression of HDAC1 and REST increased with the grade of glioma, while the expression of neuronal markers decreased with the grade of glioma. High expression of HDAC1/REST and low expression of neuronal markers were associated with poor prognosis. HDAC1/REST expression was negatively correlated with the expression of neuronal markers, and positively correlated with the expression of neural stem cell markers. The genes up-regulated in the high HDAC1/REST group were mainly related to extracellular matrix and inflammation, and the down-regulated genes were mainly related to synapsis. This study suggested that HDAC1/REST may be involved in maintaining the malignant phenotype of glioma cells and the stem cell status of glioma stem cells by inhibiting the expression of neuronal markers, which promote the progression of glioma.

Ablation efficacy of 5-aminolevulinic acid-mediated photodynamic therapy on human glioma stem cells.

Cancer cells with stem cell-like features are generally more resistant to chemotherapy and radiotherapy than differentiated tumor cells. Thus, these cells tend to increase the propensity for tumor recurrence and metastasis. This study investigated the efficacy of 5-aminolevulinic acid-mediated photodynamic therapy (ALA-PDT) in destructing glioma stem cells (GSCs), including the mesenchymal subtype (MES-GSCs) demonstrated to have the lowest radio- and chemosensitivity. Five high-grade glioma (HGG) GSC lines and derived differentiated glioma cell (DGC) lines were examined for protoporphyrin-IX (PpIX) expression using fluorescence-activated cell sorting (FACS) and then assessed for ALA-PDT sensitivity using cell viability assays. MES-GSCs surviving ALA-PDT were then isolated and evaluated for stem cell and mesenchymal marker expression levels (CD44, ALDH1A3, KLF4, nestin) by qRT-PCR. The ability of these surviving cells to form tumors was then examined using colony forming and by xenograft tumor assays in athymic mice. Finally, the relationship between PpIX expression level (high versus low) and ALA-PDT sensitivity was examined by FACS and colony forming assays. ALA-PDT was effective against all GSC lines including MES-GSCs. MES-GSC lines exhibited higher PpIX expression than derived DGCs. Surviving MES-GSCs demonstrated lower stem cell marker expression and tumor forming potential than naive MES-GSCs. Higher PpIX production capacity by MES-GSCs was associated with greater colony forming ability, and ALA-PDT was more effective against MES-GSCs with greater PpIX accumulation. ALA-PDT may be clinically effective against HGG by targeting GSCs, including MES-GSCs.

Purinergic approach to effective glioma treatment with temozolomide reveals enhanced anti-cancer effects mediated by P2X7 receptor

The purinergic signaling pathway is the oldest evolutionary transmitter system that regulates a wide array of physiological and pathophysiological processes in central nervous system. However, the question of how the purinergic compounds interact with administrated drugs is rarely addressed. We aimed to clarify the interplay between purinergic signaling and chemotherapeutic drug temozolomide (TMZ) in human glioma cell line.We applied an initial retinoic acid-induced differentiation of A172 glioma cells and tested the P2X7 receptor expression in undifferentiated and differentiated gliomas. We compared the P2X7 receptor agonists/antagonists influence and their co-action with TMZ in both cell types through assessment of cell proliferation, viability and migrative properties. Molecular docking allowed to indicate the potential binding site for TMZ in the structure of hP2X7 receptor. Differentiated cells turned out to be more susceptible to ATP and TMZ alone but also to the concerted action of TMZ and ATP. Enhanced effects triggered by ATP and TMZ treatment include the decreased by 70% viability, and reduced migration ability of differentiated A172 glioma cells. Noteworthy, these results can be achieved already at low non-toxic ATP concentration and at reduced to 125 μM effective concentration of TMZ.Therefore, ATP molecules must be present and maintained at appropriate concentration in glioma cells microenvironment to achieve their co-action with TMZ and enhanced anti-cancer activity. All that, in turn, could shorten the therapy, increase its efficacy and limit the side effects for the patient. Our purinergic approach creates a promising perspective for developing novel combined oncological therapies.

Predicting Glioma Cell Differentiation-inducing Drugs Using a Drug Repositioning Strategy.

Currently, there are no effective differentiation-inducing agents for gliomas. Drug repositioning is a time-saving, low-risk, and low-cost drug development strategy. In this study, drugs that could induce the differentiation of glioma cells were searched by using a drug repositioning strategy. Data mining was used to screen for differentially expressed genes (DEGs). The STRING 11.0 database was used for enrichment analysis. The Connectivity Map database was used for drug screening. The ChEMBL and STITCH databases were used to search for drug targets. The SwissDock database was used for molecular docking. A total of 45 DEGs were identified. The biological processes in which the DEGs were enriched mainly involved nervous system development and the regulation of biological processes. The enriched molecular functions mainly involved transcription-related molecular binding. The enriched cellular components mainly involved membrane-bound organelles and cellular protrusions. The enriched local network clusters mainly involved autophagy, the retinoic acid signalling pathway, and DNA methylation. The drug screening results showed that the drug with the highest score was acenocoumarol. A total of 12 acenocoumarol targets were obtained, among which histone deacetylase 1 (HDAC1) was the target with the highest degree value; the lowest ΔG value for acenocoumarol docked with HDAC1 was -7.52 kcal/mol, which was between those of the HDAC1 inhibitors romidepsin and vorinostat. Acenocoumarol may be a potential differentiation-inducing agent for glioma cells.

STEM-06. NUCLEAR STRUCTURE MAINTAINS GLIOBLASTOMA STEM CELLS

Abstract Glioblastoma stem cells (GSCs) contribute to therapeutic resistance, promote tumor angiogenesis, and evade anti-tumor immune responses. We and others have shown that GSCs display differential regulation of their epigenetic landscapes and metabolic profiles and contribute to the striking cellular heterogeneity and complex tumor microenvironments. Here, we find that GSCs undergo dramatic changes in chromatin organization and nuclear morphology upon differentiation. Leveraging unbiased RNA sequencing and protein profiling screens comparing GSCs and differentiated glioma cells, we identified nuclear membrane molecular regulation that defines nuclear size and lipid regulation. Genetic or pharmacologic targeting of nuclear envelope function reduced cancer stem cell proliferation, self-renewal, and in vivo tumor growth. Collectively, we define a novel role of the nuclear envelope in maintaining chromatin state and cancer stem cell self-renewing, informing the development of novel potential therapeutic paradigms for glioblastoma.

Role of Lysine-specific Demethylase 1 and Its Small Molecule Inhibitors in Glioblastoma Multiforme Therapy

Glioblastoma multiforme (GBM) is among the most critical and aggressive carcinomas of CNS, characterised by poor prognosis, low survival rate and difficult clinical correlations. Current treatment opportunities have proved to be insufficient due to high chemoresistance and relapse of the disease with enhanced malignancy. Molecular diagnostics and epigenetic profiling of GBM have discovered several signaling pathways and cellular mediators, which play key roles in triggering GBM phenotypic manifestations via somatic and genetic aberrations and recruitment of GBM stem-like cells (GSCs). Lysine specific demethylase 1 (LSD1), a flavin-containing oxidoreductase encoded by the KDM1A gene and containing the unique CoREST component, is an important histone-modifying enzyme belonging to the histone demethylase (KDM) subfamily and is responsible for master regulation of several signaling pathways in glioma cells. Pharmacological inhibition of LSD1, either individually or in a dual-targeted approach, is a logical strategy for the management of GBM. The current review discusses the role of LSD1 in various epigenetic modulations in differentiated glioma cells and GSCs. The 2D and 3D structural similarities/dissimilarities between LSD1 and MAOs have been analysed and presented along with a detailed discussion on different chemical classes of small molecule LSD1 inhibitors (both standalone and hybrid pharmacophores) that have shown promise in GBM chemotherapy.

Abstract 6383: Paracrine signaling between differentiated tumor cell-secreted fibromodulin and the stroma promotes tumor growth by enhancing angiogenesis

Abstract Cancer stem-like cells (CSCs) and the differentiated bulk cells mainly contribute to cellular heterogeneity within a tumor. The dichotomous division pattern of the CSCs sitting atop the tumor hierarchy allow them to self-renew, and differentiate to initiate and repopulate aggressive tumors. These CSC-differentiation-derived bulk tumor cells reprogram to stem-like states, accounting for high plasticity within a tumor; a phenomenon governed by the distinct epigenetic profiles of the two cell populations. Reciprocal signaling between the tumor and its complex microenvironment is a vital driver of plasticity and heterogeneity in cancer. The indispensable role of CSCs in cellular cross-talk in the tumor niche as critical drivers of tumorigenesis is well-studied. However, the massive outnumbering of the CSCs by the differentiated cells raises several vital questions regarding the role of the latter in tumor growth; whether they contribute to the complex signaling within the tumor microenvironment (TME) to drive tumor growth remains unexplored. In this study, we aimed to mechanistically delineate the distinct roles of the cancer stem-like and differentiated cells by investigating their interactions with other stromal cells in the TME.In our model system, Glioblastoma (GBM), a highly aggressive brain cancer, we adopted a quantitative, label-free, high-throughput proteomics-based approach to identify the differentially abundant secreted proteins between the glioma stem-like cell (GSC) and differentiated glioma cell (DGC). This analysis showed a significantly higher abundance of the Fibromodulin (FMOD), a collagen-binding proteoglycan, in the conditioned medium of the DGCs compared with that of the GSCs. Our investigation revealed that an activated TGF-β signaling leads to p-SMAD2 occupancy on the FMOD promoter region, leading to increased FMOD secretion by the DGCs. DGCs silenced for FMOD fail to cooperate with co-implanted GSCs to promote tumor growth in a subcutaneous mouse model. We also observed that FMOD downregulation neither affects GSC growth and differentiation nor DGC growth and reprogramming in vitro. Moreover, DGC-secreted FMOD activates integrin-dependent Notch signaling in endothelial cells, promoting angiogenesis. FMOD-silencing also inhibits the capability of the transdifferentiated endothelial cells (derived from the DGCs) to form angiogenic networks. Conditional silencing of FMOD in the de novo formed DGCs in an orthotopic intracranial C57BL/6 mouse model inhibited the growth of GSC-initiated tumors due to poorly developed vasculature, thereby increasing mouse survival. The same observation was recapitulated using patient-derived GSCs in an immunocompromised intracranial mouse model, thereby highlighting the human relevance of our findings. Collectively, our findings demonstrate how paracrine signaling between DGC-secreted FMOD and the stromal cells promotes tumor growth by enhancing angiogenesis, thereby highlighting a previously less studied supportive role of DGCs in tumor growth, albeit the GSCs retaining the tumor-initiating capacity. Thus our study identifies DGC-specific FMOD as a potential therapeutic target and emphasizes that targeting both cancer stem cells and differentiated cancer bulk cells is vital to achieving a durable response in GBM. Citation Format: Shreoshi Sengupta, Kumaravel Somasundaram, Dinorah Friedmann Morvinski, Philippe Marin, Prasasvi Reddy, Arani Mukherjee, Prerna Magod, Mainak Mondal, Serge Urbach. Paracrine signaling between differentiated tumor cell-secreted fibromodulin and the stroma promotes tumor growth by enhancing angiogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6383.

Integrative analysis of cell adhesion molecules in glioblastoma identified prostaglandin F2 receptor inhibitor (PTGFRN) as an essential gene

BackgroundGlioblastoma (GBM) is the most common primary malignant brain tumor in adults exhibiting infiltration into surrounding tissues, recurrence, and resistance to therapy. GBM infiltration is accomplished by many deregulated factors such as cell adhesion molecules (CAMs), which are membrane proteins that participate in cell-cell and cell-ECM interactions to regulate survival, proliferation, migration, and stemness.MethodsA comprehensive bioinformatics analysis of CAMs (n = 518) in multiple available datasets revealed genetic and epigenetic alterations among CAMs in GBM. Univariate Cox regression analysis using TCGA dataset identified 127 CAMs to be significantly correlated with survival. The poor prognostic indicator PTGFRN was chosen to study its role in glioma. Silencing of PTGFRN in glioma cell lines was achieved by the stable expression of short hairpin RNA (shRNA) against the PTGFRN gene. PTGFRN was silenced and performed cell growth, migration, invasion, cell cycle, and apoptosis assays. Neurosphere and limiting dilution assays were also performed after silencing of PTGFRN in GSCs.ResultsAmong the differentially regulated CAMs (n = 181, 34.9%), major proportion of them were found to be regulated by miRNAs (n = 95, 49.7%) followed by DNA methylation (n = 32, 16.7%), and gene copy number variation (n = 12, 6.2%). We found that PTGFRN to be upregulated in GBM tumor samples and cell lines with a significant poor prognostic correlation with patient survival. Silencing PTGFRN diminished cell growth, colony formation, anchorage-independent growth, migration, and invasion and led to cell cycle arrest and induction of apoptosis. At the mechanistic level, silencing of PTGFRN reduced pro-proliferative and promigratory signaling pathways such as ERK, AKT, and mTOR. PTGFRN upregulation was found to be due to the loss of its promoter methylation and downregulation of miR-137 in GBM. PTGFRN was also found to be higher in glioma stem-like cells (GSCs) than the matched differentiated glioma cells (DGCs) and is required for GSC growth and survival. Silencing of PTGFRN in GSCs reduced transcript levels of reprogramming factors (Olig2, Pou3f2, Sall2, and Sox2).ConclusionIn this study, we provide a comprehensive overview of the differential regulation of CAMs and the probable causes for their deregulation in GBM. We also establish an oncogenic role of PTGFRN and its regulation by miR-137 in GBM, thus signifying it as a potential therapeutic target.

Differentiated glioma cell-derived fibromodulin activates integrin-dependent Notch signaling in endothelial cells to promote tumor angiogenesis and growth.

Cancer stem cells (CSCs) alone can initiate and maintain tumors, but the function of non-cancer stem cells (non-CSCs) that form the tumor bulk remains poorly understood. Proteomic analysis showed a higher abundance of the extracellular matrix small leucine-rich proteoglycan fibromodulin (FMOD) in the conditioned medium of differentiated glioma cells (DGCs), the equivalent of glioma non-CSCs, compared to that of glioma stem-like cells (GSCs). DGCs silenced for FMOD fail to cooperate with co-implanted GSCs to promote tumor growth. FMOD downregulation neither affects GSC growth and differentiation nor DGC growth and reprogramming in vitro. DGC-secreted FMOD promotes angiogenesis by activating integrin-dependent Notch signaling in endothelial cells. Furthermore, conditional silencing of FMOD in newly generated DGCs in vivo inhibits the growth of GSC-initiated tumors due to poorly developed vasculature and increases mouse survival. Collectively, these findings demonstrate that DGC-secreted FMOD promotes glioma tumor angiogenesis and growth through paracrine signaling in endothelial cells and identifies a DGC-produced protein as a potential therapeutic target in glioma.

Spatial Heterogeneity of Invading Glioblastoma Cells Regulated by Paracrine Factors.

Glioblastoma (GBM) is the most common and lethal type of malignant primary brain tumor in adults. GBM displays heterogeneous tumor cell population comprising glioma-initiating cells (GICs) with stem cell-like characteristics and differentiated glioma cells. During GBM cell invasion into normal brain tissues, which is the hallmark characteristic of GBM, GICs at the invasion front retain stemness, while cells at the tumor core display cellular differentiation. However, the mechanism of cellular differentiation underlying the formation of spatial cellular heterogeneity in GBM remains unknown. In the present study, we first observed spatially heterogeneous GBM cell populations emerged from an isogenic clonal population of GICs during invasion into a 3D collagen hydrogel in a microfluidic device. Specifically, GICs at the invasion front maintained stemness, while trailing cells displayed astrocytic differentiation. The spatial cellular heterogeneity resulted from the difference in cell density between GICs at the invasion front and trailing cells. Trailing GICs at high cell density exhibited astrocytic differentiation through local accumulation of paracrine factors they secreted, while cells at the invasion front of low cell density retained stemness due to the lack of paracrine factors. In addition, we demonstrated that interstitial flow suppressed astrocytic differentiation of trailing GICs by the clearance of paracrine factors. Our findings suggest that intercellular crosstalk between tumor cells is an essential factor in developing the spatial cellular heterogeneity of GBM cells with various differentiation statuses. It also provides insights into the development of novel therapeutic strategies targeting GBM cells with stem cell characteristics at the invasion front. Impact Statement We elucidated the mechanism of cellular differentiation underlying the spatial cellular heterogeneity of glioblastoma composed of glioma-initiating cells (GICs) and differentiated glioma cells during invasion in a microfluidic device. Trailing cells at high cell density exhibited astrocytic differentiation through local accumulation of paracrine factors they produced, while cells at the invasion front of low cell density were shown to retain stemness due to the lack of paracrine factors. Our findings provide valuable knowledge for the development of effective therapeutic strategies targeting GICs at the invasion front.

Endoplasmic Reticulum Stress Contributed to Dipyridamole-Induced Impaired Autophagic Flux and Glioma Apoptosis.

Elevation of intracellular cAMP levels has been implicated in glioma cell proliferation inhibition, differentiation, and apoptosis. Inhibition of phosphodiesterase is a way to elevate intracellular cAMP levels. The present study aimed to investigate the anti-glioma potential of dipyridamole, an inhibitor of phosphodiesterase. Upon treatment with dipyridamole, human U87 glioma cells decreased cell viability, clonogenic colonization, migration, and invasion, along with Noxa upregulation, Endoplasmic Reticulum (ER) stress, impaired autophagic flux, Yes-associated Protein 1 (YAP1) phosphorylation, and YAP1 reduction. Pharmacological and genetic studies revealed the ability of dipyridamole to initiate Noxa-guided apoptosis through ER stress. Additionally, the current study further identified the biochemical role of YAP1 in communicating with ER stress and autophagy under situations of dipyridamole treatment. YAP1 promoted autophagy and protected glioma cells from dipyridamole-induced apoptotic cell death. Dipyridamole impaired autophagic flux and rendered glioma cells more vulnerable to apoptotic cell death through ER stress-inhibitable YAP1/autophagy axis. The overall cellular changes caused by dipyridamole appeared to ensure a successful completion of apoptosis. Dipyridamole also duplicated the biochemical changes and apoptosis in glioma T98G cells. Since dipyridamole has additional biochemical and pharmacological properties, further research centered on the anti-glioma mechanisms of dipyridamole is still needed.

Organophosphates modulate tissue transglutaminase activity in differentiated C6 neural cells.

The organophosphate compounds chlorpyrifos (O, O-diethyl O-[3,5,6-trichloro-2-pyridinyl] phosphorothioate, CPF) and phenyl saligenin phosphate (PSP) have been widely implicated in developmental neurotoxicity and neurodegeneration. However, the underlying mechanism remains unclear. Transglutaminase (TG)2 is a calcium ion (Ca2+)-dependent enzyme with an important role in neuronal cell outgrowth and differentiation and in neurotoxin activity and is modulated by organophosphates. We studied TG2 activity modulation by CPO and PSP during differentiation in C6 glioma cells. We studied the effects of CPO or PSP treatment with or without the TG2 inhibitor Z-DON and identified potential TG2 protein substrates via mass spectrometry. PSP and CPO did not affect cell viability but affected TG2 activity in differentiating cells. Our results indicate that the organophosphate-induced amine incorporation activity of TG2 may have a direct effect on neuronal outgrowth, differentiation, and cell survival by modifying several essential microtubule proteins, including tubulin. Inhibiting TG2 reduced neurite length but not cell survival. TG2 inhibitors can protect against organophosphate-induced neuropathy and could be used for developing novel therapeutic strategies for treating brain cancer and neurodegenerative disorders.

HIF1α/HIF2α induces glioma cell dedifferentiation into cancer stem cells through Sox2 under hypoxic conditions.

Objective: Our previous study showed that glioma stem-like cells could be induced to undergo dedifferentiation under hypoxic conditions, but the mechanism requires further study. HIF1α and HIF2α are the main molecules involved in the response to hypoxia, and Sox2, as a retroelement, plays an important role in the formation of induced pluripotent stem cells, especially in hypoxic microenvironments. Therefore, we performed a series of experiments to verify whether HIF1α, HIF2α and Sox2 regulated glioma cell dedifferentiation under hypoxic conditions.Materials and methods: Sphere formation by single glioma cells was observed, and CD133 and CD15 expression was compared between the normoxic and hypoxic groups. HIF1α, HIF2α, and Sox2 expression was detected using the CGGA database, and the correlation among HIF1α, HIF2α and Sox2 levels was analyzed. We knocked out HIF1α, HIF2α and Sox2 in glioma cells and cultured them under hypoxic conditions to detect CD133 and CD15 expression. The above cells were implanted into mouse brains to analyze tumor volume and survival time.Results: New spheres were formed from single glioma cells in 1% O2, but no spheres were formed in 21% O2. The cells cultured in 1% O2 highly expressed CD133 and CD15 and had a lower apoptosis rate. The CGGA database showed HIF1α and HIF2α expression in glioma. Knocking out HIF1α or HIF2α led to a decrease in CD133 and CD15 expression and inhibited sphere formation under hypoxic conditions. Moreover, tumor volume and weight decreased after HIF1α or HIF2α knockout with the same temozolomide treatment. Sox2 was also highly expressed in glioma, and there was a positive correlation between the HIF1α/HIF2α and Sox2 expression levels. Sox2 was expressed at lower levels after HIF1α or HIF2α was knocked out. Then, Sox2 was knocked out, and we found that CD133 and CD15 expression was decreased. Moreover, a lower sphere formation rate, higher apoptosis rate, lower tumor formation rate and longer survival time after temozolomide treatment were detected in the Sox2 knockout cells.Conclusion: In a hypoxic microenvironment, the HIF1α/HIF2α-Sox2 network induced the formation of glioma stem cells through the dedifferentiation of differentiated glioma cells, thus promoting glioma cell chemoresistance. This study demonstrates that both HIF1α and HIF2α, as genes upstream of Sox2, regulate the malignant progression of glioma through dedifferentiation.