Glioblastomas (GBMs) are highly vascular and lethal brain tumors that display cellular hierarchies containing self-renewing tumorigenic glioma stem cells (GSCs). Because GSCs often reside in ...perivascular niches and may undergo mesenchymal differentiation, we interrogated GSC potential to generate vascular pericytes. Here, we show that GSCs give rise to pericytes to support vessel function and tumor growth. In vivo cell lineage tracing with constitutive and lineage-specific fluorescent reporters demonstrated that GSCs generate the majority of vascular pericytes. Selective elimination of GSC-derived pericytes disrupts the neovasculature and potently inhibits tumor growth. Analysis of human GBM specimens showed that most pericytes are derived from neoplastic cells. GSCs are recruited toward endothelial cells via the SDF-1/CXCR4 axis and are induced to become pericytes predominantly by transforming growth factor β. Thus, GSCs contribute to vascular pericytes that may actively remodel perivascular niches. Therapeutic targeting of GSC-derived pericytes may effectively block tumor progression and improve antiangiogenic therapy.
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► Glioblastoma stem cells (GSCs) generate vascular pericytes to maintain tumor vessels ► Targeting GSC-derived pericytes disrupts vessel function and inhibits tumor growth ► GSCs are recruited to the perivascular niche via SDF-1-CXCR4 signaling ► Transforming growth factor β predominantly promotes GSCs to assume a pericyte lineage
In vivo lineage tracing shows that glioblastoma stem cells (GSCs) give rise to vascular pericytes—cells that support vessel function and hence promote tumor growth—and that targeting of GSC-derived pericytes inhibits the growth of these highly vascular and lethal brain tumors.
Diffuse intrinsic pontine glioma (DIPG) is a highly aggressive pediatric brainstem tumor genetically distinguished from adult GBM by the high prevalence of the K27M mutation in the histone H3 variant ...H3.3 (
). This mutation reprograms the H3K27me3 epigenetic landscape of DIPG by inhibiting the H3K27-specific histone methyltransferase EZH2. This globally reduces H3K27me2/3, critical repressive marks responsible for cell fate decisions, and also causes focal gain of H3K27me3 throughout the epigenome. To date, the tumor-driving effects of H3.3K27M remain largely unknown. Here, it is demonstrated that H3.3K27M cooperates with PDGF-B
enhancing gliomagenesis and reducing survival of p53 wild-type (WT) and knockout murine models of DIPG. H3.3K27M expression drives increased proliferation of tumor-derived murine neurospheres, suggesting that cell-cycle deregulation contributes to increased malignancy in mutant tumors. RNA sequencing on tumor tissue from H3.3K27M-expressing mice indicated global upregulation of PRC2 target genes, and a subset of newly repressed genes enriched in regulators of development and cell proliferation. Strikingly, H3.3K27M induced targeted repression of the p16/ink4a (
) locus, a critical regulator of the G
-G
to S-phase transition. Increased levels of H3K27me3 were observed at the p16 promoter; however, pharmacologic reduction of methylation at this promoter did not rescue p16 expression. Although DNA methylation is also present at this promoter, it is not K27M dependent. Intriguingly, inhibition of DNA methylation restores p16 levels and is cytotoxic against murine tumor cells. Importantly, these data reveal that H3.3K27M-mediated p16 repression is an important mechanism underlying the proliferation of H3.3K27M tumor cells, as
knockout eliminates the survival difference between H3.3K27M and H3.3WT tumor-bearing mice.
This study shows that H3.3K27M mutation and PDGF signaling act in concert to accelerate gliomagenesis in a genetic mouse model and identifies repression of p16 tumor suppressor as a target of H3.3K27M, highlighting the G
-S cell-cycle transition as a promising therapeutic avenue.
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Malignant gliomas are aggressive brain tumors with limited therapeutic options, and improvements in treatment require a deeper molecular understanding of this disease. As in other cancers, recent ...studies have identified highly tumorigenic subpopulations within malignant gliomas, known generally as cancer stem cells. Here, we demonstrate that glioma stem cells (GSCs) produce nitric oxide via elevated nitric oxide synthase-2 (NOS2) expression. GSCs depend on NOS2 activity for growth and tumorigenicity, distinguishing them from non-GSCs and normal neural progenitors. Gene expression profiling identified many
NOS2-regulated genes, including the cell-cycle inhibitor cell division autoantigen-1 (
CDA1). Further, high
NOS2 expression correlates with decreased survival in human glioma patients, and NOS2 inhibition slows glioma growth in a murine intracranial model. These data provide insight into how GSCs are mechanistically distinct from their less tumorigenic counterparts and suggest that NOS2 inhibition may be an efficacious approach to treating this devastating disease.
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► Glioma stem cell proliferation is supported by nitric oxide synthase-2 (NOS2) ► Nonstem glioma cells and normal neural stem cells are not dependent on NOS2 ► NOS2 affects glioma stem cell gene expression, including cell-cycle inhibitor CDA1 ► Pharmacological inhibition of NOS2 attenuates glioma growth in vivo
Tumour-associated macrophages (TAMs) are enriched in glioblastoma multiformes (GBMs) that contain glioma stem cells (GSCs) at the apex of their cellular hierarchy. The correlation between TAM density ...and glioma grade suggests a supportive role for TAMs in tumour progression. Here we interrogated the molecular link between GSCs and TAM recruitment in GBMs and demonstrated that GSCs secrete periostin (POSTN) to recruit TAMs. TAM density correlates with POSTN levels in human GBMs. Silencing POSTN in GSCs markedly reduced TAM density, inhibited tumour growth, and increased survival of mice bearing GSC-derived xenografts. We found that TAMs in GBMs are not brain-resident microglia, but mainly monocyte-derived macrophages from peripheral blood. Disrupting POSTN specifically attenuated the tumour-supportive M2 type of TAMs in xenografts. POSTN recruits TAMs through the integrin αvβ₃ as blocking this signalling by an RGD peptide inhibited TAM recruitment. Our findings highlight the possibility of improving GBM treatment by targeting POSTN-mediated TAM recruitment.
Malignant gliomas rank among the most lethal cancers. Gliomas display a striking cellular heterogeneity with a hierarchy of differentiation states. Recent studies support the existence of cancer stem ...cells in gliomas that are functionally defined by their capacity for extensive self-renewal and formation of secondary tumors that phenocopy the original tumors. As the c-Myc oncoprotein has recognized roles in normal stem cell biology, we hypothesized that c-Myc may contribute to cancer stem cell biology as these cells share characteristics with normal stem cells.
Based on previous methods that we and others have employed, tumor cell populations were enriched or depleted for cancer stem cells using the stem cell marker CD133 (Prominin-1). We characterized c-Myc expression in matched tumor cell populations using real time PCR, immunoblotting, immunofluorescence and flow cytometry. Here we report that c-Myc is highly expressed in glioma cancer stem cells relative to non-stem glioma cells. To interrogate the significance of c-Myc expression in glioma cancer stem cells, we targeted its expression using lentivirally transduced short hairpin RNA (shRNA). Knockdown of c-Myc in glioma cancer stem cells reduced proliferation with concomitant cell cycle arrest in the G(0)/G(1) phase and increased apoptosis. Non-stem glioma cells displayed limited dependence on c-Myc expression for survival and proliferation. Further, glioma cancer stem cells with decreased c-Myc levels failed to form neurospheres in vitro or tumors when xenotransplanted into the brains of immunocompromised mice.
These findings support a central role of c-Myc in regulating proliferation and survival of glioma cancer stem cells. Targeting core stem cell pathways may offer improved therapeutic approaches for advanced cancers.
Glioblastomas are highly lethal cancers that contain cellular hierarchies with self-renewing cancer stem cells that can propagate tumors in secondary transplant assays. The potential significance of ...cancer stem cells in cancer biology has been demonstrated by studies showing contributions to therapeutic resistance, angiogenesis, and tumor dispersal. We recently reported that physiologic oxygen levels differentially induce hypoxia inducible factor-2α (HIF2α) levels in cancer stem cells. HIF1α functioned in proliferation and survival of all cancer cells but also was activated in normal neural progenitors suggesting a potentially restricted therapeutic index while HIF2α was essential in only in cancer stem cells and was not expressed by normal neural progenitors demonstrating HIF2α is a cancer stem cell specific target. We now extend these studies to examine the role of hypoxia in regulating tumor cell plasticity. We find that hypoxia promotes the self-renewal capability of the stem and non-stem population as well as promoting a more stem-like phenotype in the non-stem population with increased neurosphere formation as well as upregulation of important stem cell factors, such as OCT4, NANOG, and c-MYC. The importance of HIF2α was further supported as forced expression of non-degradable HIF2α induced a cancer stem cell marker and augmented the tumorigenic potential of the non-stem population. This novel finding may indicate a specific role of HIF2α in promoting glioma tumorigenesis. The unexpected plasticity of the non-stem glioma population and the stem-like phenotype emphasizes the importance of developing therapeutic strategies targeting the microenvironmental influence on the tumor in addition to cancer stem cells.
A replication-defective poliovirus was injected directly into recurrent glioblastoma tumors, and dexamethasone and bevacizumab were used to control edema. A total of 20% of the treated patients have ...survived beyond 3 years.
Glioblastomas display cellular hierarchies containing tumor-propagating glioblastoma stem cells (GSCs). STAT3 is a critical signaling node in GSC maintenance but molecular mechanisms underlying STAT3 ...activation in GSCs are poorly defined. Here we demonstrate that the bone marrow X-linked (BMX) nonreceptor tyrosine kinase activates STAT3 signaling to maintain self-renewal and tumorigenic potential of GSCs. BMX is differentially expressed in GSCs relative to nonstem cancer cells and neural progenitors. BMX knockdown potently inhibited STAT3 activation, expression of GSC transcription factors, and growth of GSC-derived intracranial tumors. Constitutively active STAT3 rescued the effects of BMX downregulation, supporting that BMX signals through STAT3 in GSCs. These data demonstrate that BMX represents a GSC therapeutic target and reinforces the importance of STAT3 signaling in stem-like cancer phenotypes.
► BMX is preferentially expressed in glioblastoma stem cells ► BMX activates STAT3 signaling specifically in glioblastoma stem cells ► BMX controls the expression of key glioblastoma stem cell transcription factors ► Targeting BMX disrupts tumorigenic potential of glioblastoma stem cells
Glioblastomas are lethal cancers characterized by florid angiogenesis promoted in part by glioma stem cells (GSCs). Because hypoxia regulates angiogenesis, we examined hypoxic responses in GSCs. We ...now demonstrate that hypoxia-inducible factor HIF2α and multiple HIF-regulated genes are preferentially expressed in GSCs in comparison to non-stem tumor cells and normal neural progenitors. In tumor specimens, HIF2α colocalizes with cancer stem cell markers. Targeting HIFs in GSCs inhibits self-renewal, proliferation, and survival in vitro, and attenuates tumor initiation potential of GSCs in vivo. Analysis of a molecular database reveals that
HIF2A expression correlates with poor glioma patient survival. Our results demonstrate that GSCs differentially respond to hypoxia with distinct HIF induction patterns, and HIF2α might represent a promising target for antiglioblastoma therapies.
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