Role of Wnt5a in the proliferation of human glioblastoma cells

Wnt5a operates as either a tumor suppressor or a tumor stimulator, according to tumor type. The functions of Wnt5a in human glioblastoma (GBM) have yet to be determined. We initially evaluated the expression of Wnt5a in human glioma. The results of immunohistochemical analyses have revealed that Wnt5a expression was higher in human GBM than in normal brain tissue and low-grade astrocytoma. In order to assess the role of Wnt5a on proliferation in human glioblastoma cells, we employed U87MG and GBM-05, a newly established GBM cell line. GBM-05 was established from a patient diagnosed with GBM. GBM-05 cells were shown to express Nestin, but did not express GFAP and Map2ab. GBM-05 cells formed infiltrating brain tumors after being intracerebrally transplanted into nude mice, and xenotransplanted GBM-05 cells were observed to differentiate into neuronal and astrocyte lineages. Wnt5a expression in the xenotransplanted tumors was higher than that detected in the surrounding brain tissues. The overexpression of Wnt5a increased the proliferation of GBM-05 and U87MG in vitro. By way of contrast, the downregulation of Wnt5a expression as the result of RNA interference reduced proliferation from GBM-05 and U87MG cells in vitro, and reduced tumorigenicity in vivo. Our data indicate that Wnt5a signaling is an important regulator in the proliferation of human glioma cells.     

CC chemokine receptor-2A is frequently overexpressed in glioblastoma

Macrophages and monocytes migrate in response to chemotactic cytokines such as monocyte chemoattractant protein 1 (MCP-1/CCL2) in a variety of tissues including the central nervous system. Overexpression of MCP-1 has been reported in glioblastoma (GBM), which correlates to prominent macrophage infiltration characterized by this tumor type, but whether MCP-1 receptor is also expressed by the neoplastic cells remains unclear. Expression of MCP-1 and its receptor, CC chemokine receptor 2 (CCR2), were examined in GBM using cDNA microarrays and validated in two independent microarray datasets. We investigated the expression of the CCR2A isoform in human glioma cell lines and GBM, and found overexpression of CCR2A in most GBM specimens examined when compared to normal brain tissues. CCR2A is mainly localized in the cytoplasm of neoplastic cells, and pronounced neuronal cytoplasmic CCR2A immunoreactivity in tumor-infiltrating area was associated with prior chemo/radiation therapy. Glioma cells ectopically overexpressing CCR2A demonstrated increased migration compared to vector-transfected cells in vitro. Inhibition of MCP-1 synthesis suppressed migration of CCR2A-overexpressed glioma cells. Our data suggest that CCR2A might be associated with the pathobiology of GBM such as host response to treatment and tumor cell migration.     

MicroRNA-34a targets notch1 and inhibits cell proliferation in glioblastoma multiforme

Aberrant expression of microRNAs (miRNAs) has been implicated in cancer initiation and progression. In this study, we found that microRNA-34a (miR-34a) is significantly downregulated in glioblastoma multiforme (GBM) specimens compared with normal brain tissues. Growth curve and colony formation assays revealed that miR-34a suppresses proliferation of U373MG and SHG44 glioblastoma cells. Overexpression of miR-34a could induce apoptosis of glioblastoma cells. Also, we identified notch1 as a direct target gene of miR-34a. Knockdown of notch1 showed similar cellular functions as overexpression of miR-34a both in vitro and in vivo. Collectively, our findings show that miR-34a is downregulated in GBM cells and inhibits GBM growth by targeting notch1.     

Glioblastoma-secreted factors induce IGFBP7 and angiogenesis by modulating Smad-2-dependent TGF-beta signaling

Insulin-like growth factor-binding protein 7 (IGFBP7) is a selective biomarker of glioblastoma (GBM) vessels, strongly expressed in tumor endothelial cells and vascular basement membrane. IGFBP7 gene regulation and its potential role in tumor angiogenesis remain unclear. Mechanisms of IGFBP7 induction and its angiogenic capacity were examined in human brain endothelial cells (HBECs) exposed to tumor-like conditions. HBEC treated with GBM cell (U87MG)-conditioned media (-CM) exhibited fourfold upregulation of IGFBP7 mRNA and protein compared to control cells. IGFBP7 gene regulation in HBEC was methylation independent. U87MG-CM analysed by enzyme-linked immunosorbent assay contained approximately 5 pM transforming growth factor (TGF)-beta1, a concentration sufficient to stimulate IGFBP7 in HBEC to similar levels as U87MG-CM. Both pan-TGF-beta-neutralizing antibody (1D11) and the TGF-beta1 receptor (activin receptor-like kinase 5, ALK5) antagonist, SB431542, blocked U87MG-CM-induced IGFBP7 expression in HBEC, indicating that TGF-beta1 is an important tumor-secreted effector capable of IGFBP7 induction in endothelial cells. HBEC exposed to either U87MG-CM or IGFBP7 protein exhibited increased capillary-like tube (CLT) formation in Matrigel. Both TGF-beta1- and U87MG-CM-induced Smad-2 phosphorylation and U87MG-CM-induced CLT formation in HBEC were inhibited by the ALK5 antagonist, SB431542. These data suggest that proangiogenic IGFBP7 may be induced in brain endothelial cells by TGF-betas secreted by GBM, most likely through TGF-beta1/ALK5/Smad-2 pathway.     

Genetic alterations of the NRP/B gene are associated with human brain tumors

Nearly all brain tumors develop following the progressive accumulation of genetic alterations of oncogenes and tumor suppressor genes (such as p53 and retinoblastoma protein). Furthermore, aberrations in the nuclear matrix often contribute to genomic instabilities and the development of cancer. We have previously shown that nuclear-restricted protein/brain (NRP/B), a member of the BTB/Kelch repeat family, is a nuclear matrix protein normally expressed in neurons but not in astrocytes, and that it is an early and specific marker of neurons during the development of the central nervous system. Here, we show aberrant expression of NRP/B in human brain tissues. NRP/B is expressed in the cytoplasm of human brain tumor cells (glioblastoma, GBM) arising from astrocytes. NRP/B mutations (13 mutations in the Kelch domains, two in the intervening sequence (IVS) domain and two in the BTB domain) were detected in brain tumor cell lines (A-172, CCF-STTG1, SK-N-SH and U87-MG) and in primary human malignant GBM tissues (eight samples). More importantly, we found that NRP/B mutants, but not wild-type (wt) NRP/B, increased the activation of ERK and consequently promoted cell proliferation, attenuated caspase activation and suppressed the cellular apoptosis induced by the stressful stimulus cisplatin (10 microM). These events were observed to occur via a p53-mediated pathway. In addition, while wt NRP/B was associated with actin, mutations in the Kelch domains of NRP/B led to its reduced binding affinity to actin. Thus, alterations and gene mutations within the NRP/B gene may contribute to brain tumorigenesis by promoting cell proliferation, suppressing apoptosis and by affecting nuclear cytoskeleton dynamics.     

Aberrant methylation and silencing of the SPINT2 gene in high‐grade gliomas

Hepatocyte growth factor activator inhibitor type 2 (HAI‐2), encoded by the SPINT2 gene, is a membrane‐anchored protein that inhibits proteases involved in the activation of hepatocyte growth factor (HGF), a ligand of MET receptor. Epigenetic silencing of the SPINT2 gene has been reported in a human glioblastoma cell line (U87) and glioblastoma‐derived cancer stem cells. However, the incidence of SPINT2 methylation in tumor tissues obtained from glioma patients is unknown. In this study, we analyzed the methylation status of the SPINT2 gene of eight human glioblastoma cell lines and surgically resected glioma tissues of different grades (II, III, and IV) by bisulfite sequence analysis and methylation‐specific PCR. Most glioblastoma lines (7/8) showed methylation of the SPINT2 gene with a significantly reduced level of SPINT2mRNA compared to cultured astrocytes and normal brain tissues. However, all glioblastoma lines expressed mRNA for HGF activator (HGFAC), a target protease of HAI‐2/SPINT2. Forced expression of SPINT2 reduced MET phosphorylation of U87 glioblastoma cells both in vitro and in intracranial xenografts in nude mice. Methylation‐specific PCR analysis of the resected glioma tissues indicated notable methylation of the SPINT2 gene in 33.3% (2/6), 71.4% (10/14), and 74.3% (26/35) of grade II, III, and IV gliomas, respectively. Analysis of RNA sequencing data in a public database indicated an increased HGFAC/SPINT2 expression ratio in high‐grade compared to low‐grade gliomas (P = .01). In summary, aberrant methylation of the SPINT2 gene is frequently observed in high‐grade gliomas and might confer MET signaling in the glioma cells.     

The phosphorylation of ephrin‐B2 ligand promotes glioma cell migration and invasion

To reveal molecular drivers of glioma invasion, two distinct glioblastoma (GBM) cell phenotypes (invading cells and tumor core cells) were collected from 19 GBM specimens using laser capture microdissection. Isolated RNA underwent whole human genome expression profiling to identify differentially expressed genes. Pathway enrichment analysis highlighted the bidirectional receptor/ligand tyrosine kinase system, EphB/ephrin‐B, as the most tightly linked system to the invading cell phenotype. Clinical relevance of ephrin‐B genes was confirmed in a clinically annotated expression data set of 195 brain biopsy specimens. Levels of ephrin‐B1 and ‐B2 mRNA were significantly higher in GBM (n = 82) than in normal brain (n = 24). Kaplan–Meier analysis demonstrated ephrin‐B2, but not ephrin‐B1, expression levels were significantly associated with short term survival in malignant astrocytomas (n = 97, p = 0.016). In human brain tumor specimens, the production and phosphorylation of ephrin‐B2 were high in GBM. Immunohistochemistry demonstrated ephrin‐B2 localization primarily in GBM cells but not in normal brain. A highly invasive glioma cell line, U87, expressed high levels of ephrin‐B2 compared with relatively less invasive cell lines. Treatment with EphB2/Fc chimera further enhanced migration and invasion of U87 cells, whereas treatment with an ephrin‐B2 blocking antibody significantly slowed migration and invasion. Forced expression of ephrin‐B2 in the U251 cell line stimulated migration and invasion in vitro and ex vivo, concomitant with tyrosine phosphorylation of ephrin‐B2. These results demonstrate that high expression of ephrin‐B2 is a strong predictor of short‐term survival and that ephrin‐B2 plays a critical role in glioma invasion rendering this signaling pathway as a potential therapeutic target.     

人脑胶质瘤细胞株中RIZ1基因启动子甲基化状态的研究

检测4种人脑成胶质细胞瘤细胞株中成视网膜细胞瘤蛋白结合锌指结构基因1（retinoblastoma protein-interacting zinc finger gene1,RIZ1）基因启动子区的甲基化状态,进一步认识RIZ1在胶质瘤发病机制中的作用。方法：应用甲基化特异性PCR法（methylation specific PCR,MSP）检测4种人脑成胶质细胞瘤细胞株U87、U251、A172和T98中RIZ1基因启动子区的甲基化水平,其中U87细胞发生甲基化,被选为后续实验对象。RT-PCR检测U87细胞经5-Aza-CdR处理前后RIZ1 mRNA表达量的变化,MTT检测5-Aza-CdR对U87细胞生长增殖的影响。结果：4种人脑成胶质细胞瘤细胞株中U87和U251细胞中检测到RIZ1基因启动子区域发生甲基化;U87细胞经5-Aza-CdR处理后其RIZ1 mRNA的表达量上调;MTT法检测显示5-Aza-CdR能抑制U87的生长增殖,且与5-Aza-CdR的浓度和作用时间呈负相关。结论：RIZ1基因启动子高甲基化是人脑成胶质细胞瘤细胞株中RIZ1基因表达下调的重要机制。     

CrkI adapter protein modulates cell migration and invasion in glioblastoma

The human crk gene is translated into crkI and crkII by alternative splicing. crkII mRNA was detected both in normal brain and glioblastoma tissues, whereas crkI mRNA levels were quite low in normal brain and up-regulated in glioblastoma tissues. Expression of CrkI but not CrkII in glioblastoma U87MG cells induced transformation that stimulated cell migration and invasion concomitant with tyrosine phosphorylation of p130 Crk-associated substrate. N-cadherin-mediated signal transduction, which was essential for invasion by U87MG cells, was no longer required for CrkI-transformed cells. These results suggest that CrkI contributes to malignancy of glioblastoma by inducing phosphorylation of p130 Crk-associated substrate.     

Fas-induced expression of chemokines in human glioma cells: involvement of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase

Fas transduces not only apoptotic signals through various pathways but also angiogenic and proinflammatory responses in vivo. Human glioma cells express Fas although sensitivity to Fas-mediated cell death is variable, suggesting that Fas may have functions other than apoptosis in these cells. In this study, we addressed alternative functions of Fas expressed on human gliomas by Fas ligation in three human glioma cell lines, CRT-MG, U373-MG, and U87-MG, and the in vivo expression of Fas and chemokines in human glioblastoma multiforme (GBM). Herein, we demonstrate that: (a) stimulation with agonistic anti-Fas monoclonal antibody CH-11 and human recombinant soluble Fas ligand induces expression of the CC chemokine MCP-1 and the CXC chemokine interleukin-8 by human glioma cell lines at the mRNA and protein levels in a dose- and time-dependent manner; (b) selective pharmacological inhibitors of MEK1 (U0126 and PD98059) and p38 mitogen-activated protein kinase (MAPK) (SB202190) suppress Fas-mediated chemokine expression in a dose-dependent manner; (c) Fas ligation on human glioma cells leads to activation of both extracellular signal-regulated kinases ERK1/ERK2 and p38 MAPK; and (d) GBM samples express higher levels of Fas compared with normal control brain, which correlates with increased interleukin 8 expression. These findings indicate that Fas ligation on human glioma cells leads to the selective induction of chemokine expression, which involves the ERK1/ERK2 and p38 MAPK signaling pathways. Therefore, the Fas-Fas ligand system in human brain tumors may be involved not only in apoptotic processes but also in the provocation of angiogenic and proinflammatory responses.     

OTX015 (MK‐8628), a novel BET inhibitor,displays in vitro and in vivo antitumor effects alone and in combination with conventional therapies in glioblastoma models

Bromodomain and extraterminal (BET) bromodomain (BRD) proteins are epigenetic readers that bind to acetylated lysine residues on chromatin, acting as co‐activators or co‐repressors of gene expression. BRD2 and BRD4, members of the BET family, are significantly increased in glioblastoma multiforme (GBM), the most common primary adult brain cancer. OTX015 (MK‐8628), a novel BRD2/3/4 inhibitor, is under evaluation in dose‐finding studies in solid tumors, including GBM. We investigated the pharmacologic characteristics of OTX015 as a single agent and combined with targeted therapy or conventional chemotherapies in glioblastoma cell lines. OTX015 displayed higher antiproliferative effects compared to its analog JQ1, with GI₅₀ values of approximately 0.2 µM. In addition, C‐MYC and CDKN1A mRNA levels increased transiently after 4 h‐exposure to OTX015, while BRD2, SESN3, HEXIM‐1, HIST2H2BE, and HIST1H2BK were rapidly upregulated and sustained after 24 h. Studies in three additional GBM cell lines supported the antiproliferative effects of OTX015. In U87MG cells, OTX015 showed synergistic to additive activity when administered concomitant to or before SN38, temozolomide or everolimus. Single agent oral OTX015 significantly increased survival in mice bearing orthotopic or heterotopic U87MG xenografts. OTX015 combined simultaneously with temozolomide improved mice survival over either single agent. The passage of OTX015 across the blood–brain barrier was demonstrated with OTX015 tumor levels 7 to 15‐fold higher than in normal tissues, along with preferential binding of OTX015 to tumor tissue. The significant antitumor effects seen with OTX015 in GBM xenograft models highlight its therapeutic potential in GBM patients, alone or combined with conventional chemotherapies.     

EGFR gene overexpression retained in an invasive xenograft model by solid orthotopic transplantation of human glioblastoma multiforme into nude mice

Orthotopic xenograft animal model from human glioblastoma multiforme (GBM) cell lines often do not recapitulate an extremely important aspect of invasive growth and epidermal growth factor receptor (EGFR) gene overexpression of human GBM. We developed an orthotopic xenograft model by solid transplantation of human GBM into the brain of nude mouse. The orthotopic xenografts sharing the same histopathological features with their original human GBMs were highly invasive and retained the overexpression of EGFR gene. The murine orthotopic GBM models constitute a valuable in vivo system for preclinical studies to test novel therapies for human GBM.     

Comprehensive analysis of microRNA expression profile in malignant glioma tissues

Malignant gliomas represent the most devastating group of brain tumors in adults, among which glioblastoma multiforme (GBM) exhibits the highest malignancy rate. Despite combined modality treatment, GBM recurs and is invariably fatal. A further insight into the molecular background of gliomagenesis is required to improve patient outcomes. The primary aim of this study was to gain broad information on the miRNA expression pattern in malignant gliomas, mainly GBM. We investigated the global miRNA profile of malignant glioma tissues with miRNA microarrays, deep sequencing and meta‐analysis. We selected miRNAs that were most frequently deregulated in glioblastoma tissues, as well as in peritumoral areas, in comparison with normal human brain. We identified candidate miRNAs associated with the progression from glioma grade III to glioma grade IV. The meta‐analysis of miRNA profiling studies in GBM tissues summarizes the past and recent advances in the investigation of the miRNA signature in GBM versus noncancerous human brain and provides a comprehensive overview. We propose a list of 35 miRNAs whose expression is most frequently deregulated in GBM patients and of 30 miRNA candidates recognized as novel GBM biomarkers.     

Inhibition of Proliferation by Knockdown of Transmembrane (TMEM) 168 in Glioblastoma Cells via Suppression of Wnt/β-Catenin Pathway

Human glioblastoma multiforme (GBM) accounts for the majority of human brain gliomas. Several TMEM proteins, such as TMEM 45A, TMEM 97, and TMEM 140, are implicated in human brain gliomas. However, the roles of TMEM168 in human GBM remain poorly understood. Herein we found that mRNA levels of TMEM168 were overexpressed in GBM patients (n=85) when compared with healthy people (n=10), which was also supported by data from The Cancer Genome Atlas (TCGA). Kaplan–Meier analysis of Gene Expression Omnibus dataset GSE16011 suggested that enhanced TMEM168 expression was associated with shorter survival time. To investigate whether and how TMEM168 functioned in the tumorigenesis of human GBM cells, two human GBM cell lines (U87 and U373) were used for study. Lithium chloride (LiCl), an activator for Wnt/β-catenin pathway, was used for the treatment. Our data suggested that siRNA-TMEM168 (siTMEM168) prevented viability of U87 and U373 cells, induced cell cycle arrest (G₀/G₁ phase) and promoted apoptosis, and the mechanisms involved in blocking Wnt/β-catenin pathway, as evidenced by reducing expression of β-catenin, C-myc, cyclin D1, and survivin. Furthermore, the inhibited effect of siTMEM168 on human GBM cell growth was significantly alleviated with additional LiCl treatment, substantiating the involvement of the Wnt/β-catenin pathway in this process. In summary, our data demonstrated that TMEM168 may represent a therapeutic target for the treatment of human GBM.     

Inhibition of Necl-5 (CD155/PVR) reduces glioblastoma dispersal and decreases MMP-2 expression and activity

Patients afflicted with glioblastoma (GBM) have poor survival due to dispersive invasion throughout the brain. Necl-5, a cell surface receptor for vitronectin, is expressed in GBM but not normal brain. In several GBM cell lines Necl-5 promotes migration and invasion but the mechanism is poorly understood. In this study, we show that knockdown of Necl-5 by RNAi results in markedly decreased invasion of A172 GBM cells in a 3-dimensional matrix. There is a concomitant decrease in the expression and activity of matrix metalloproteinase-2 (MMP-2), a known factor in GBM invasion and disease severity. Knockdown of Necl-5 diminishes basal activation of Akt, an established mediator of MMP-2 expression in gliomas. Knockdown of Necl-5 also limits the maximal Akt activation in response to vitronectin, which requires the activity of Integrin-linked kinase (ILK). During migration, Necl-5, Akt and ILK co-localize at focal contacts at the leading edge of the plasma membrane, suggesting that these molecules may act to integrate Akt signaling at the leading edge to induce MMP-2 expression. By virtue of its restricted expression in GBM and its role in invasion, Necl-5 may be an attractive target for limiting MMP-2 production in glioblastoma, and therefore limiting dispersal.     

Oncogenic effects of miR-10b in glioblastoma stem cells

MicroRNAs and cancer stem cells have emerged as critical players in glioblastoma, one of the deadliest human cancers. In this study, we investigated the expression and function of microRNA-10b in glioblastoma cells and stem cells. An analysis of The Cancer Genome Atlas data revealed a correlation between high miR-10b levels and poor prognosis in glioblastoma patients. We measured the levels of miR-10b and found that it is upregulated in human glioblastoma tissues, glioblastoma cell and stem cell lines as compared to normal human tissues or astrocytes. Inhibition of miR-10b with a specific antagomir inhibited the proliferation of glioblastoma established and stem cell lines. Inhibition of miR-10b strongly reduced cell invasion and migration in glioblastoma cell and stem cell lines while overexpression of miR-10b induced cell migration and invasion. We also investigated several predicted targets of miR-10b but could not verify any of them experimentally. Additionally, miR-10b inhibition significantly decreased the in vivo growth of stem cell-derived orthotopic GBM xenografts. Altogether, our findings confirm the oncogenic effects of miR-10b in GBM cells and show for the first time a role of this microRNA in GBM stem cells. Targeting miR-10b might therefore inhibit glioblastoma stem cells, which are thought to be at the origin of glioblastoma and to contribute its recurrence and resistance to therapy.