Irradiated Glioblastoma Cells Research Articles

Gelsolin knockdown confers radiosensitivity to glioblastoma cells.

Radiotherapy (RT) is a cornerstone of the glioblastoma (GBM) treatment. However, the resistance of tumour cells to radiation results in early recurrence. The mechanisms underlying GBM radioresistance remain unclear. Screening for differentially expressed genes (DEGs) related to radiation might be a potential solution to this problem. RT-associated DEGs were screened based on the RNA sequencing of 15 paired primary and recurrent GBMs. The mRNA and protein expression of candidate genes were validated in RNA sequencing of The Chinese Genome Atlas (CGGA) dataset and 18 cases of GBM samples. The relationship between the candidate gene and radiation was confirmed in irradiated GBM cells. The association of candidate gene with clinical characteristics and survival was investigated in the CGGA and TCGA dataset. Biological function and pathway analysis were explored by gene ontology analysis. The association of the candidate gene with radiosensitivity was verified using cell counting Kit-8, comet, and colony formation assays invitro and subcutaneous tumour xenograft experiments invivo. Gelsolin (GSN) was selected for further study. GSN expression was significant elevated in recurrent GBM and up-regulated in irradiated GBM cell lines. High expression of GSN was enriched in malignant phenotype of glioma. Moreover, high expression of GSN was associated with poor prognosis. Further investigation demonstrated that GSN-knockdown (GSN-KD) combined with RT significantly inhibited cell proliferation and enhanced radiosensitivity invivo and invitro. Mechanistically, GSN-KD could lead to more serious DNA damage and promotes apoptosis after RT. Radiation induced up-regulated of GSN. GSN-KD could enhance the radiosensitivity of GBM.

BCL6 is a context-dependent mediator of the glioblastoma response to irradiation therapy

Glioblastoma is a rapidly fatal brain cancer that does not respond to therapy. Previous research showed that the transcriptional repressor protein BCL6 is upregulated by chemo and radiotherapy in glioblastoma, and inhibition of BCL6 enhances the effectiveness of these therapies. Therefore, BCL6 is a promising target to improve the efficacy of current glioblastoma treatment. BCL6 acts as a transcriptional repressor in germinal centre B cells and as an oncogene in lymphoma and other cancers. However, in glioblastoma, BCL6 induced by therapy may not be able to repress transcription. Using a BCL6 inhibitor, the whole proteome response to irradiation was compared with and without BCL6 activity. Acute high dose irradiation caused BCL6 to switch from repressing the DNA damage response to promoting stress response signalling. Rapid immunoprecipitation mass spectrometry of endogenous proteins (RIME) enabled comparison of BCL6 partner proteins between untreated and irradiated glioblastoma cells. BCL6 was associated with transcriptional coregulators in untreated glioblastoma including the known partner NCOR2. However, this association was lost in response to acute irradiation, where BCL6 unexpectedly associated with synaptic and plasma membrane proteins. These results reveal the activity of BCL6 under therapy-induced stress is context-dependent, and potentially altered by the intensity of that stress.

Microglia and glioblastoma heterocellular interplay sustains tumour growth and proliferation as an off-target effect of radiotherapy.

Glioblastoma (GBM), a WHO grade IV glioma, is a malignant primary brain tumour for which combination of surgery, chemotherapy and radiotherapy is the first-line approach despite adverse effects. Tumour microenvironment (TME) is characterized by an interplay of cells and soluble factors holding a critical role in neoplastic development. Significant pathophysiological changes have been found in GBM TME, such as glia activation and oxidative stress. Microglia play a crucial role in favouring GBM growth, representing target cells of immune escape mechanisms. Our study aims at analysing radiation-induced effects in modulating intercellular communication and identifying the basis of protective mechanisms in radiation-naïve GBM cells. Tumour cells were treated with conditioned media (CM) derived from 0, 2 or 15 Gy irradiated GBM cells or 0, 2 or 15 Gy irradiated human microglia. We demonstrated that irradiated microglia promote an increase of GBM cell lines proliferation through paracrine signalling. On the contrary, irradiated GBM-derived CM affect viability, triggering cell death mechanisms. In addition, we investigated whether these processes involve mitochondrial mass, fitness and oxidative phosphorylation and how GBM cells respond at these induced alterations. Our study suggests that off-target radiotherapy modulates microglia to support GBM proliferation and induce metabolic modifications.

EXPLORING THE EFFECT OF EXOSOMES AND RADIATION ON GLIOBLASTOMA CANCER CELLS

Abstract Glioblastoma is the most common and aggressive type of brain cancer, with higher incidences in aging adults over 75 and little to no long-term survival or cure. The median survival time under the current standard of care, surgical resection and chemoradiation, is 15-18 months. Glioblastoma tumors consist of multiple cell types, including mature brain cells in cell cycle arrest and cancer stem cells (CSCs) that replenish cancer cell populations. However, the cancerous non-stem cells are induced into a cell fate called glioma-initiating cells in response to radiation, where they begin to express stem-like phenotypes. Glioma-initiating cells proliferate at an aggressive rate and are the reason for cancer recurrence, making them a necessary target for new and more effective therapeutics. This research is studying the effect of exposure to exosomes, extracellular vesicles that carry proteins and RNA, on the stem-like phenotype expression of irradiated non-stem cells. Irradiated glioblastoma cells were exposed to varying concentrations of exosomes isolated from glioblastoma CSCs in vitro. The results showed a decrease in ZsGreen expression, a marker for stem-like phenotypes, as exosome concentration increased. Exposure of glioblastoma cancer cells to exosomes post-irradiation decreased the rate of transition to glioma-initiating cells. This suggests that CSC exosomes may signal that stem cells are present, decreasing the need for the formation of glioma-initiating cells. Further research is necessary to better understand the role of exosomes in glioblastoma tumors, however, this result may suggest exosomes as a potential way to delay or reduce the aggressive nature of glioblastoma cancer recurrence.

Radiation therapy promotes unsaturated fatty acids to maintain survival of glioblastoma

Radiation therapy (RT) is essential for the management of glioblastoma (GBM). However, GBM frequently relapses within the irradiated margins, thus suggesting that RT might stimulate mechanisms of resistance that limits its efficacy. GBM is recognized for its metabolic plasticity, but whether RT-induced resistance relies on metabolic adaptation remains unclear.Here, we show in vitro and in vivo that irradiated GBM tumors switch their metabolic program to accumulate lipids, especially unsaturated fatty acids. This resulted in an increased formation of lipid droplets to prevent endoplasmic reticulum (ER) stress. The reduction of lipid accumulation with genetic suppression and pharmacological inhibition of the fatty acid synthase (FASN), one of the main lipogenic enzymes, leads to mitochondrial dysfunction and increased apoptosis of irradiated GBM cells. Combination of FASN inhibition with focal RT improved the median survival of GBM-bearing mice. Supporting the translational value of these findings, retrospective analysis of the GLASS consortium dataset of matched GBM patients revealed an enrichment in lipid metabolism signature in recurrent GBM compared to primary.Overall, these results demonstrate that RT drives GBM resistance by generating a lipogenic environment permissive to GBM survival. Targeting lipid metabolism might be required to develop more effective anti-GBM strategies.

Expression of TMEM59L associated with radiosensitive in glioblastoma.

Radiotherapy is one of the cornerstone of the glioblastoma treatment paradigm. However, the resistance of tumor cells to radiation results in poor survival. The mechanism of radioresistance has not been fully elucidated. This study aimed to screen the differential expressed genes related with radiosensitivity. The differentially expressed genes were screened based on RNA sequencing in 15 pairs of primary and recurrent glioblastoma that have undergone radiotherapy. Candidate genes were validated in 226 primary and 134 recurrent glioblastoma (GBM) obtained from the Chinese Glioma Genome Atlas (CGGA) database. RNA and protein expression were verified by Quantitative Real-time PCR (qPCR) and western blot in irradiated GBM cell lines. The candidate gene was investigated to explore the relationship between mRNA levels and clinical characteristics in the CGGA and The Cancer Genome Atlas dataset. Kaplan-Meier survival analysis and Cox regression analysis were used for survival analysis. Gene ontology and KEGG pathway analysis were used for bioinformatics analysis. Four genes (TMEM59L, Gelsolin, ZBTB7A and ATX) were screened. TMEM59L expression was significantly elevated in recurrent glioblastoma and lower in normal brain tissue. We selected TMEM59L as the target gene for further study. The increasing of TMEM59L expression induced by radiation was confirmed by mRNA and western blot in irradiated GBM cell. Further investigation revealed that high expression of TMEM59L was enriched in IDH mutant and MGMT methylated gliomas and associated with a better prognosis. Gene ontology and KEGG pathway analysis revealed that TMEM59L was closely related to the DNA damage repair and oxidative stress respond process. We speculated that the high expression of TMEM59L might enhance radiotherapy sensitivity by increasing ROS-induced DNA damage and inhibiting DNA damage repair process.

M2 isoform of pyruvate kinase rewires glucose metabolism during radiation therapy to promote an antioxidant response and glioblastoma radioresistance.

Resistance to existing therapies is a significant challenge in improving outcomes for glioblastoma (GBM) patients. Metabolic plasticity has emerged as an important contributor to therapy resistance, including radiation therapy (RT). Here, we investigated how GBM cells reprogram their glucose metabolism in response to RT to promote radiation resistance. Effects of radiation on glucose metabolism of human GBM specimens were examined in vitro and in vivo with the use of metabolic and enzymatic assays, targeted metabolomics, and FDG-PET. Radiosensitization potential of interfering with M2 isoform of pyruvate kinase (PKM2) activity was tested via gliomasphere formation assays and in vivo human GBM models. Here, we show that RT induces increased glucose utilization by GBM cells, and this is accompanied with translocation of GLUT3 transporters to the cell membrane. Irradiated GBM cells route glucose carbons through the pentose phosphate pathway (PPP) to harness the antioxidant power of the PPP and support survival after radiation. This response is regulated in part by the PKM2. Activators of PKM2 can antagonize the radiation-induced rewiring of glucose metabolism and radiosensitize GBM cells in vitro and in vivo. These findings open the possibility that interventions designed to target cancer-specific regulators of metabolic plasticity, such as PKM2, rather than specific metabolic pathways, have the potential to improve the radiotherapeutic outcomes in GBM patients.

Downregulation of the Rho GTPase pathway abrogates resistance to ionizing radiation in wild-type p53 glioblastoma by suppressing DNA repair mechanisms

Glioblastoma (GBM), the most common aggressive brain tumor, is characterized by rapid cellular infiltration and is routinely treated with ionizing radiation (IR), but therapeutic resistance inevitably recurs. The actin cytoskeleton of glioblastoma cells provides their high invasiveness, but it remains unclear whether Rho GTPases modulate DNA damage repair and therapeutic sensitivity. Here, we irradiated glioblastoma cells with different p53 status and explored the effects of Rho pathway inhibition to elucidate how actin cytoskeleton disruption affects the DNA damage response and repair pathways. p53-wild-type and p53-mutant cells were subjected to Rho GTPase pathway modulation by treatment with C3 toxin; knockdown of mDia-1, PFN1 and MYPT1; or treatment with F-actin polymerization inhibitors. Rho inhibition increased the sensitivity of glioma cells to IR by increasing the number of DNA double-strand breaks and delaying DNA repair by nonhomologous end-joining in p53-wild-type cells. p53 knockdown reversed this phenotype by reducing p21 expression and Rho signaling activity, whereas reactivation of p53 in p53-mutant cells by treatment with PRIMA-1 reversed these effects. The interdependence between p53 and Rho is based on nuclear p53 translocation facilitated by G-actin and enhanced by IR. Isolated IR-resistant p53-wild-type cells showed an altered morphology and increased stress fiber formation: inhibition of Rho or actin polymerization decreased cell viability in a p53-dependent manner and reversed the resistance phenotype. p53 silencing reversed the Rho inhibition-induced sensitization of IR-resistant cells. Rho inhibition also impaired the repair of IR-damaged DNA in 3D spheroid models. Rho GTPase activity and actin cytoskeleton dynamics are sensitive targets for the reversal of acquired resistance in GBM tumors with wild-type p53.

TMET-10. FATTY ACID METABOLISM REGULATES IMMUNE REACTIVITY OF IRRADIATED GLIOBLASTOMA

Abstract Radiation therapy (RT) is the standard-of-care for glioblastoma (GBM) and is the only treatment for inoperable brain tumors. In multiple cancer, RT stimulates anti-tumor immunity by at least activating cancer cell-intrinsic type I interferon (IFN-I) responses. However, GBM inevitably recur, suggesting that RT promotes immune evasion mechanisms. Altered fatty acid (FA) metabolism is an emerging mechanism that can account for treatment resistance and immune escape of GBM. Therefore, we hypothesize that RT induces a metabolic shift toward the production of FAs to foster immunosuppression of GBM. Supporting this hypothesis, our data show that RT upregulates the expression of the fatty acid synthase (FASN) and the activity of the fatty acid desaturase 2 (FADS2) to generate FAs in murine GBM models, GL261 and CT2A. To determine whether FA metabolism was preventing RT-induced IFN-I, we impaired FA synthesis by inhibiting either FASN or FADS2 using genetic (CRISPR-Cas9) or pharmacological inhibitors (FASNi or FADS2i). As expected, protein quantification (ELISA) as well as gene expression (RT-qPCR) revealed that irradiated GBM cells released greater levels of IFN-beta 24hrs post RT; an effect that was more pronounced when FASN or FADS2 were blocked. Reinforcing the role of FA metabolism in regulating immune activation, in situ immunofluorescence of irradiated intracranial GL261 tumors showed that mice treated with FASNi improved the recruitment of CD8+ T cells into GBM. Along similar lines, flow cytometry of digested GL261 tumors revealed an increase infiltration of CD11c+ CD103+ dendritic cells as well as activated CD86+ CD11b+ cells when FAs synthesis was blocked with FADS2i. Altogether, our data suggest that RT-induced FA synthesis represents a mechanism of resistance by preventing IFN-I and promoting immunological evasion of GBM. Targeting FA metabolism is a promising strategy to promote anti-tumor immunity and sensitize irradiated GBM to immunotherapies.

Radiated glioblastoma cell-derived exosomal circ_0012381 induce M2 polarization of microglia to promote the growth of glioblastoma by CCL2/CCR2 axis

BackgroundRadiotherapy is the primary therapeutic option for glioblastoma. Some studies proved that radiotherapy increased the release of exosomes from cells. The mechanism by which these exosomes modify the phenotype of microglia in the tumor microenvironment to further determine the fate of irradiated glioblastoma cells remains to be elucidated.MethodsWe erected the co-culture system of glioblastoma cells and microglia. After radiation, we analyzing the immunophenotype of microglia and the proliferation of radiated glioblastoma cells. By whole transcriptome sequencing, we analyzed of circRNAs in exosomes from glioblastoma cells and microglia. We used some methods, which included RT-PCR, dual-luciferase reporter, et al., to identify how circ_0012381 from radiated glioblastoma cell-derived exosomes regulated the immunophenotype of microglia to further affect the proliferation of radiated glioblastoma cells.ResultsRadiated glioblastoma cell-derived exosomes markedly induced M2 microglia polarization. These M2-polarized microglia promoted the proliferation of irradiated glioblastoma cells. Circ_0012381 expression was increased in the irradiated glioblastoma cells, and circ_0012381 entered the microglia via exosomes. Circ_0012381 induced M2 microglia polarization by sponging with miR-340-5p to increase ARG1 expression. M2-polarized microglia suppressed phagocytosis and promoted the growth of the irradiated glioblastoma cells by CCL2/CCR2 axis. Compared with the effects of radiotherapy alone, the inhibition of exosomes significantly inhibited the growth of irradiated glioblastoma cells in a zebrafish model.ConclusionsOur data suggested that the inhibition of exosome secretion might represent a potential therapeutic strategy to increase the efficacy of radiotherapy in patients with glioblastoma.

Exosomal B7–H4 from irradiated glioblastoma cells contributes to increase FoxP3 expression of differentiating Th1 cells and promotes tumor growth

BackgroundGlioblastoma (GBM) is the most common and aggressive form of primary brain tumor. Although numerous postoperative therapeutic strategies have already been developed, including radiotherapy, tumors inevitably recur after several years of treatment. The coinhibitory molecule B7–H4 negatively regulates T cell immune responses and promotes immune escape. Exosomes mediate intercellular communication and initiate immune evasion in the tumor microenvironment (TME). ObjectiveThis study aimed to determine whether B7–H4 is upregulated by radiation and loaded into exosomes, thus contributing to immunosuppression and enhancing tumor growth. MethodsIodixanol density-gradient centrifugation and flow cytometry were used to verify exosomal B7–H4. Naïve T cells were differentiated into Th1 cells, with or without exosomes. T cell-secreted cytokines and markers of T cell subsets were measured. Mechanistically, the roles of B7–H4, and ALIX in GBM were analyzed using databases and tissue samples. Co‐immunoprecipitation, and pull-down assays were used to tested the direct interactions between ATM and ALIX or STAT3. In vitro ATM kinase assays, western blotting, and site-directed mutation were used to assess ATM-mediated STAT3 phosphorylation. Finally, the contribution of exosomal B7–H4 to immunosuppression and tumor growth was investigated in vivo. ResultsExosomes from irradiated GBM cells decreased the anti-tumor immune response of T cell in vitro and in vivo via delivered B7–H4. Mechanistically, irradiation promoted exosome biogenesis by increasing the ATM-ALIX interaction. Furthermore, the ATM-phosphorylated STAT3 was found to directly binds to the B7–H4 promoter to increase its expression. Finally, the radiation-induced increase in exosomal B7–H4 induced FoxP3 expression during Th1 cell differentiation via the activated STAT1 pathway. In vivo, exosomal B7–H4 decreased the radiation sensitivity of GBM cells, and reduced the survival of GBM mice model. ConclusionThis study showed that radiation-enhanced exosomal B7–H4 promoted immunosuppression and tumor growth, hence defining a direct link between irradiation and anti-tumor immune responses. Our results suggest that co-administration of radiotherapy with anti-B7-H4 therapy could improve local tumor control and identify exosomal B7–H4 as a potential tumor biomarker.

Extracellular vesicles originating from glioblastoma cells increase metalloproteinase release by astrocytes: the role of CD147 (EMMPRIN) and ionizing radiation

BackgroundGlioblastoma multiforme is an aggressive primary brain tumor that is characterized by local invasive growth and resistance to therapy. The role of the microenvironment in glioblastoma invasiveness remains unclear. While carcinomas release CD147, a protein that signals for increased matrix metalloproteinase (MMP) release by fibroblasts, glioblastoma does not have a significant fibroblast component. We hypothesized that astrocytes release MMPs in response to CD147 contained in glioblastoma-derived extracellular vesicles (EVs) and that ionizing radiation, part of the standard treatment for glioblastoma, enhances this release.MethodsAstrocytes were incubated with EVs released by irradiated or non-irradiated human glioblastoma cells wild-type, knockdown, or knockout for CD147. Levels of CD147 in glioblastoma EVs and MMPs secreted by astrocytes were quantified. Levels of proteins in the mitogen activated protein kinase (MAPK) pathway, which can be regulated by CD147, were measured in astrocytes incubated with EVs from glioblastoma cells wild-type or knockdown for CD147. Immunofluorescence was performed on the glioblastoma cells to identify changes in CD147 localization in response to irradiation, and to confirm uptake of the EVs by astrocytes.ResultsImmunoblotting and mass spectrometry analyses showed that CD147 levels in EVs were transiently increased when the EVs were from glioblastoma cells that were irradiated with γ rays. Specifically, the highly-glycosylated 45 kDa form of CD147 was preferentially present in the EVs relative to the cells themselves. Immunofluorescence demonstrated that astrocytes incorporate glioblastoma EVs and subsequently increase their secretion of active MMP9. The increase was greater if the EVs were from irradiated glioblastoma cells. Testing MAPK pathway activation, which also regulates MMP expression, showed that JNK signaling, but not ERK1/2 or p38, was increased in astrocytes incubated with EVs from irradiated compared to non-irradiated glioblastoma cells. Knockout of CD147 in glioblastoma cells blocked the increased JNK signaling and the rise in secreted active MMP9 levels.ConclusionsThe results support a tumor microenvironment-mediated role of CD147 in glioblastoma invasiveness, and reveal a prominent role for ionizing radiation in enhancing the effect. They provide an improved understanding of glioblastoma intercellular signaling in the context of radiotherapy, and identify pathways that can be targeted to reduce tumor invasiveness.1D3uFmTqHFEH8Tq79aQmnJVideo abstractGraphical abstract

The use of metformin to enhance radiation effects on M1 macrophage subtype polarization in bone marrow-derived macrophage in glioblastoma tumor environment.

e13513 Background: Given the clinical relevance of tumor-associated macrophage (TAM) with its pro-tumor role and as a cell type compromising a large portion in glioblastoma (GBM), reversing the imbalance of TAM polarization in the tumor environment has emerged as a promising novel field for GBM treatment. Radiation therapy (RT) is the standard treatment for GBM patients after surgery, which has been shown to transiently induce M1 polarization of macrophage (M1Ø). Recent studies suggested that metformin could also promote M1Ø in tumor microenvironment. We thus postulate that metformin may enhance and sustain the M1-inducing effect of radiation in GBM. Methods: We first examined the polarization effect of metformin (0.1mM, 1mM and 2mM) on mouse bone marrow-derived macrophage (BMDM) cultured in GBM tumor environment, including media conditioned by GBM cells in monolayer culture or tumor spheres as well as in trans-well co-culturing system. We irradiated GBM cells with different doses (2 Gy, 8 Gy, and 20 Gy) after the treatment of Metformin at various time points; then we used conditioned media to treat BMDM either cultured alone or co-cultured with GBM cells in trans-well system for 24 or 48 hours. A separate set of experiment was conducted by first irradiating GBM cells and then co-culturing them with BMDM at 24 or 48 hours after radiation with metformin added at the start of co-culture. Percentage of various subtypes of BMDM was calculated after flow cytometry. Results: High concentrations of metformin (1mM and 2mM) significantly increased M1Ø and inhibited M2Ø in all culture conditions. Co-culture with irradiated GBM cells or treatment with medium conditioned by irradiated GBM cells could temporally induce M1Ø polarization in BMDM, with the effects being RT dose-dependent. Metformin at high concentrations further promoted M1Ø and suppressed M2Ø polarization in those conditions mimicking tumor microenvironment. This enhancing effect was sustained for at least 48 hours. Conclusions: Metformin at mili-molar concentrations significantly enhances the effects of radiation on M1Ø polarization in BMDM in vitro.

Identification of radiation responsive genes and transcriptome profiling via complete RNA sequencing in a stable radioresistant U87 glioblastoma model.

The absence of major progress in the treatment of glioblastoma (GBM) is partly attributable to our poor understanding of both GBM tumor biology and the acquirement of treatment resistance in recurrent GBMs. Recurrent GBMs are characterized by their resistance to radiation. In this study, we used an established stable U87 radioresistant GBM model and total RNA sequencing to shed light on global mRNA expression changes following irradiation. We identified many genes, the expressions of which were altered in our radioresistant GBM model, that have never before been reported to be associated with the development of radioresistant GBM and should be concertedly further investigated to understand their roles in radioresistance. These genes were enriched in various biological processes such as inflammatory response, cell migration, positive regulation of epithelial to mesenchymal transition, angiogenesis, apoptosis, positive regulation of T-cell migration, positive regulation of macrophage chemotaxis, T-cell antigen processing and presentation, and microglial cell activation involved in immune response genes. These findings furnish crucial information for elucidating the molecular mechanisms associated with radioresistance in GBM. Therapeutically, with the global alterations of multiple biological pathways observed in irradiated GBM cells, an effective GBM therapy may require a cocktail carrying multiple agents targeting multiple implicated pathways in order to have a chance at making a substantial impact on improving the overall GBM survival.

RNF138-mediated ubiquitination of rpS3 is required for resistance of glioblastoma cells to radiation-induced apoptosis

An interaction between ribosomal protein S3 (rpS3) and nuclear factor kappa B or macrophage migration inhibitory factor in non-small-cell lung cancer is responsible for radioresistance. However, the role of rpS3 in glioblastoma (GBM) has not been investigated to date. Here we found that in irradiated GBM cells, rpS3 translocated into the nucleus and was subsequently ubiquitinated by ring finger protein 138 (RNF138). Ubiquitin-dependent degradation of rpS3 consequently led to radioresistance in GBM cells. To elucidate the apoptotic role of rpS3, we analyzed the interactome of rpS3 in ΔRNF138 GBM cells. Nuclear rpS3 interacted with DNA damage inducible transcript 3 (DDIT3), leading to DDIT3-induced apoptosis in irradiated ΔRNF138 GBM cells. These results were confirmed using in vivo orthotopic xenograft models and GBM patient tissues. This study aims to clarify the role of RNF138 in GBM cells and demonstrate that rpS3 may be a promising substrate of RNF138 for the induction of GBM radioresistance, indicating RNF138 as a potential target for GBM therapy.

Irradiation of Glioblastoma Cells Increases CD147 Levels in their Extracellular Vesicles: Contribution to Increased MMP9 Activity in the Tumor Microenvironment

Glioblastoma is a locally invasive primary cancer of the central nervous system. Current treatment modalities are unable to adequately limit this invasiveness, leading to a 95% recurrence rate. Moreover, although radiotherapy has produced the largest improvement in survival for these patients, it is also associated with increased tumor invasiveness, perhaps contributing to the high recurrence rate. This study found that CD147, a protein which is commonly overexpressed in glioblastoma, may contribute to this invasion, in particular the increased invasion after radiation exposure. Interestingly, CD147 works to promote invasion in cancer cells via intercellular communication: tumors secrete CD147 in extracellular vesicles (EVs) to induce neighboring cells to produce matrix metalloproteinases (MMPs), which can degrade the extracellular matrix. We irradiated T98G human glioblastoma cells with 8Gy of 137Cs γ-rays, and collected EVs from the medium at 24h using serial ultracentrifugation. The EVs were characterized by cryo-electron microscopy, NanoSight, and immunoblots. They were either collected for biochemical analyses or added at a 3x concentration to SVG human astrocytes maintained in culture for 24 h. One-way ANOVA with p<0.05 was considered significant, and the Holm test was used to control for multiple comparisons. Mass spectrometry analysis had CD147 in the top 1% of increased proteins in EVs from irradiated glioblastoma cells (IR-EVs) relative to EVs from control, non-irradiated glioblastoma cells (C-EVs). This increase was validated by immunoblot. Notably, EVs were enriched in the active (highly glycosylated) form of the protein. In contrast, CD147 protein levels in the glioblastoma cells were not increased, and PCR demonstrated the mRNA levels had not changed – suggesting irradiated cells mobilize existing CD147 into EVs. We then examined the effects of glioblastoma cells on the microenvironment, reporting fold change in astrocytes receiving glioblastoma cell EVs relative to those receiving no EVs. All results have an n=6 with p<0.01. Astrocytes receiving C-EVs or IR-EVs had 3-fold higher MMP2 activity as determined by zymography. The activity of MMP9 secreted by astrocytes increased 10-fold in response to receiving C-EVs, but increased 14-fold in response to IR-EVs – a significant difference. Knockdown of CD147 by shRNA in the glioblastoma cells rendered its levels in the EVs undetectable by immunoblot. The C-EVs from these CD147-knockdown glioblastoma cells could still produce a 3-fold increase in MMP2 and an 8-fold increase in MMP9 activity, but IR-EVs could no longer produce an increase in MMP9 activity, i.e. MMP9 activity was reduced from 14-fold to 7-fold of the control astrocytes’. Glioblastoma cells can increase CD147 levels in their EVs in response to irradiation, contributing to increased MMP9 activity, but not necessarily MMP2 activity, through intercellular communication with astrocytes.

PO-0998: The Robo1-receptor is involved in the migration of irradiated glioblastoma cells

PO-0998: The Robo1-receptor is involved in the migration of irradiated glioblastoma cells

Abstract 3323: Radiation-induced ER stress contributes to survival in glioblastoma cell lines

Abstract Glioblastoma is the most common primary malignant brain tumor in adults in the United States. While the standard of care for afflicted patients has evolved to include surgery, ionizing radiation (IR) and temozolomide chemotherapy, the prognoses of these patients remain dismal. With the median survival of glioblastoma patients remaining in the range of 12-15 months, there is an unmet need for approaches that can overcome the inherent therapeutic resistance of these tumors. In recent years, several studies have demonstrated that IR can activate pro-survival signaling that may facilitate adaptation to therapy and the development of radio-resistance. The endoplasmic reticulum stress response (ERSR) is a conserved program known to be deregulated in cancer and can mediate pro-survival signaling in the context of therapy. The ATF6, IRE1 and PERK pathways of the ERSR are known to be important mediators in the initiation of this signaling. In this research, we show for the first time that IR, a key component in glioblastoma therapy, can induce genes downstream of ATF6, IRE1 and PERK in glioblastoma cell lines. Furthermore, we identify the ATF6 and PERK-eIF2a-ATF4 pathways as important contributors to the radiation-response in glioblastoma. Our study began with the observation of protein and mRNA induction of targets associated with the ERSR in irradiated glioblastoma cell lines. In addition to ATF6 target genes, we observed robust induction of PERK target genes 48h after 6 Gy IR. This induction of PERK target genes was accompanied with increased phosphorylation of eIF2a in a time and dose-dependent manner. To evaluate the requirement of PERK for radiation-induced eIF2a phosphorylation, we used a specific inhibitor of PERK - GSK2606414, and found that PERK inhibition was sufficient to prevent radiation-induced eIF2a phosphorylation. We also analyzed expression of several genes downstream of PERK after treatment with GSK2606414, and found that PERK inhibition lead to 70-80% reduction in radiation-induction of downstream genes. Since ATF4 is downstream of PERK-eIF2a, we examined ATF4 expression in irradiated glioblastoma and found that it was also induced by radiation. Using RNA-interference, we found that knockdown of ATF4 reduced proliferation and clonogenic survival by 50%, and resulted in 38% increase in PARP cleavage in irradiated glioblastoma. We observed similar trends when we knocked down ATF6, suggesting that multiple aspects of the ERSR can contribute to the radiation response in glioblastoma. These results indicate that IR-induced activation of ER-stress signaling through PERK and ATF6 contributes to adaptive survival mechanisms in glioblastoma. Further characterization of the mechanism by which ATF6 and ATF4 mediate cell survival after irradiation may reveal novel targets for the enhancement of radiotherapy for glioblastoma. Citation Format: David Dadey, Vaishali Kapoor, Arpine Khudanyan, Dinesh Thotala, Dennis Hallahan. Radiation-induced ER stress contributes to survival in glioblastoma cell lines. [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 3323. doi:10.1158/1538-7445.AM2015-3323

Radiation-induced glioblastoma signaling cascade regulates viability, apoptosis and differentiation of neural stem cells (NSC).

Ionizing radiation alone or in combination with chemotherapy is the main treatment modality for brain tumors including glioblastoma. Adult neurons and astrocytes demonstrate substantial radioresistance; in contrast, human neural stem cells (NSC) are highly sensitive to radiation via induction of apoptosis. Irradiation of tumor cells has the potential risk of affecting the viability and function of NSC. In this study, we have evaluated the effects of irradiated glioblastoma cells on viability, proliferation and differentiation potential of non-irradiated (bystander) NSC through radiation-induced signaling cascades. Using media transfer experiments, we demonstrated significant effects of the U87MG glioblastoma secretome after gamma-irradiation on apoptosis in non-irradiated NSC. Addition of anti-TRAIL antibody to the transferred media partially suppressed apoptosis in NSC. Furthermore, we observed a dramatic increase in the production and secretion of IL8, TGFβ1 and IL6 by irradiated glioblastoma cells, which could promote glioblastoma cell survival and modify the effects of death factors in bystander NSC. While differentiation of NSC into neurons and astrocytes occurred efficiently with the corresponding differentiation media, pretreatment of NSC for 8h with medium from irradiated glioblastoma cells selectively suppressed the differentiation of NSC into neurons, but not into astrocytes. Exogenous IL8 and TGFβ1 increased NSC/NPC survival, but also suppressed neuronal differentiation. On the other hand, IL6 was known to positively affect survival and differentiation of astrocyte progenitors. We established a U87MG neurosphere culture that was substantially enriched by SOX2(+) and CD133(+) glioma stem-like cells (GSC). Gamma-irradiation up-regulated apoptotic death in GSC via the FasL/Fas pathway. Media transfer experiments from irradiated GSC to non-targeted NSC again demonstrated induction of apoptosis and suppression of neuronal differentiation of NSC. In summary, intercellular communication between glioblastoma cells and bystander NSC/NPC could be involved in the amplification of cancer pathology in the brain.

Inhibition of the PERK Arm of the Endoplasmic Reticulum Stress Response Attenuates VEGF Production in Irradiated Glioblastoma Cell Lines

Inhibition of the PERK Arm of the Endoplasmic Reticulum Stress Response Attenuates VEGF Production in Irradiated Glioblastoma Cell Lines