Expression of cyclooxygenase 2 (COX-2) in human glioma and in vitro inhibition by a specific COX-2 inhibitor, NS-398

The up-regulation of cyclooxygenase 2 (COX-2) expression is a frequent occurrence in a variety of different tumors. In this study, COX-2 protein expression was investigated in 50 glioma and 3 normal brain specimens by immunohistochemistry. Expression of COX-2 protein was observed in all normal brain and glioma specimens by immunohistochemistry, regardless of histological grade. The immunoreactive score was significantly higher in high-grade glioma than low-grade glioma and normal brain specimens. For a subset of these tumors (nine gliomas and three normal brain), Western blot analysis was also performed. COX-2 protein was detected in all specimens by Western blot analysis. The effect of the specific COX-2 inhibitor NS-398 on monolayer cell cultures and three-dimensional glioma spheroids was investigated using U-87MG and U-251MG human glioblastoma cell lines. The proliferation rate was assessed in monolayer cultures. In addition, a growth assay, a migration assay, an apoptosis assay, and a tumor invasion assay were performed in a three-dimensional spheroid culture system. NS-398 was able to reduce the proliferation of monolayer cell cultures, as well as the growth of spheroids and tumor cell migration, in a dose-dependent manner. There was also a moderate increase in the number of apoptotic cells in the treated spheroids. NS-398 did not have an inhibitory effect on tumor invasion in the coculture spheroid system. Our study provides evidence that COX-2 is up-regulated in the majority of high-grade gliomas and that a potential role of COX-2 inhibitors as an adjuvant therapy for brain tumors may exist.     

Thromboxane synthase regulates the migratory phenotype of human glioma cells

The capacity of glial tumor cells to migrate and diffusely infiltrate normal brain compromises surgical eradication of the disease. Identification of genes associated with invasion may offer novel strategies for anti-invasive therapies. The gene for TXsyn, an enzyme of the arachidonic acid pathway, has been identified by differential mRNA display as being overexpressed in a glioma cell line selected for migration. In this study TXsyn mRNA expression was found in a large panel of glioma cell lines but not in a strain of human astrocytes. Immunohistochemistry demonstrated TXsyn in the parenchyma of glial tumors and in reactive astrocytes, whereas it could not be detected in quiescent astrocytes and oligodendroglia of normal brain. Glioma cell lines showed a wide range of thromboxane B2 formation, the relative expression of which correlated with migration rates of these cells. Migration was effectively blocked by specific inhibitors of TXsyn, such as furegrelate and dazmegrel. Other TXsyn inhibitors and cyclooxygenase inhibitors were less effective. Treatment with specific inhibitors also resulted in a decrease of intercellular adhesion in glioma cells. These data indicate that TXsyn plays a crucial role in the signal transduction of migration in glial tumors and may offer a novel strategy for anti-invasive therapies.     

Osteopontin regulates human glioma cell invasiveness and tumor growth in mice

Human malignant glioma cells are characterized by local invasion. In the present study, we investigated the role of osteopontin (OPN) in the invasiveness of human glioma cells isolated from grade IV tumors. We found that the expression levels of OPN in these cell lines paralleled matrix metalloproteinase-2 (MMP-2) expression and cell invasiveness potential. When U87MG glioma cells (with a high-OPN expression level) were stably transformed with specific small hairpin RNA to knock down OPN expression, MMP-2 secretion, cell invasiveness, and tumor growth in implanted brains were dramatically reduced. Conversely, forced expression of OPN in GBM-SKH glioma cells (which expressed OPN at a low level) increased MMP-2 secretion, enhanced cell invasiveness, and increased tumor growth in a rodent xenograft model. Expression of OPN was associated with increased expression of vimentin and decreased expression of glial fibrillary acidic protein. Treatment of glioma cells with 5-aza-2′-deoxycytidine (5-aza-dC) suppressed OPN expression in a concentration-dependent manner. Suppression of OPN expression by 5-aza-dC was associated with reductions in MMP-2 secretion, vimentin expression, cell invasion, intravasation, and tumor growth. These data suggest that OPN may play important roles in regulating cell invasion in glioma cells and that 5-aza-dC may serve as a therapeutic agent for human gliomas.     

Phagocytic capacity of normal and malignant rat glial cells in culture

The phagocytic capacity of 4 continuous rat glioma cell lines (BT2C, BT4Cn, BT5c, and 9L) and normal BD IX fetal rat glial cells in culture has been studied. This was done by flow cytometric measurements of single cells from monolayer cultures having ingested fluorescent bacteria, zymosan particles, red blood cells, or fragments of normal glial cells. In addition, phagocytosis was studied in a three-dimensional culture system. The BT4Cn, BT5C, and 9L cell lines were tumorigenic and invasive both in vivo and in organ culture in vitro. In contrast, BT2C has shown variable tumorigenicity and does not seem to be invasive. The phagocytic capacity of the cell lines was compared to their destructive properties during invasion. Depending on the particle type, 30-40% of the normal glial cells were phagocytic. The fractions of phagocytic glioma cells were dependent on the particle type and the prey load. Of the invasive cell lines, BT5C showed high phagocytic activity both in monolayer and three-dimensional cultures. Two of the invasive cell lines (BT5C and 9L) had about the same fraction of phagocytic cells as normal glial cells. These 2 cell lines showed highly destructive growth during invasion. In contrast, the third invasive cell line (BT4Cn) had almost no phagocytic cells. The BT4Cn cells showed single-cell invasion with little destruction of target tissue. The noninvasive cell line (BT2C) showed low phagocytic activity, and almost no destruction was observed in the border zone between tumor cells and normal tissue. Phagocytosis seems to be an inherent property of both normal and malignant glial cells, although the fraction of phagocytic cells varies from one cell line to another. In organ culture high phagocytic capacity of invasive glioma cells seems to be related to destructive activity on the normal brain tissue during invasion.     

ELMO1 and Dock180, a bipartite Rac1 guanine nucleotide exchange factor, promote human glioma cell invasion

A distinct feature of malignant gliomas is the intrinsic ability of single tumor cells to disperse throughout the brain, contributing to the failure of existing therapies to alter the progression and recurrence of these deadly brain tumors. Regrettably, the mechanisms underlying the inherent invasiveness of glioma cells are poorly understood. Here, we report for the first time that engulfment and cell motility 1 (ELMO1) and dedicator of cytokinesis 1 (Dock180), a bipartite Rac1 guanine nucleotide exchange factor (GEF), are evidently linked to the invasive phenotype of glioma cells. Immunohistochemical analysis of primary human glioma specimens showed high expression levels of ELMO1 and Dock180 in actively invading tumor cells in the invasive areas, but not in the central regions of these tumors. Elevated expression of ELMO1 and Dock180 was also found in various human glioma cell lines compared with normal human astrocytes. Inhibition of endogenous ELMO1 and Dock180 expression significantly impeded glioma cell invasion in vitro and in brain tissue slices with a concomitant reduction in Rac1 activation. Conversely, exogenous expression of ELMO1 and Dock180 in glioma cells with low level endogenous expression increased their migratory and invasive capacity in vitro and in brain tissue. These data suggest that the bipartite GEF, ELMO1 and Dock180, play an important role in promoting cancer cell invasion and could be potential therapeutic targets for the treatment of diffuse malignant gliomas.     

Triptolide inhibits proliferation and invasion of malignant glioma cells

Malignant glioma is the most devastating and aggressive tumor in brain, characterized by rapid proliferation and diffuse invasion. Chemotherapy and radiotherapy are the pivotal strategies after surgery; however, high drug resistance of malignant glioma and the blood-brain barrier usually render chemotherapy drugs ineffective. Here, we find that triptolide, a small molecule with high lipid solubility, is capable of inhibiting proliferation and invasion of malignant glioma cells effectively. In both investigated malignant glioma cell lines, triptolide repressed cell proliferation via inducing cell cycle arrest in G0/G1 phase, associated with downregulation of G0/G1 cell cycle regulators cyclin D1, CDK4, and CDK6 followed by reduced phosphorylation of retinoblastoma protein (Rb). In addition, triptolide induced morphological change of C6 cells through downregulation of protein expression of MAP-2 and inhibition of activities of GTPases Cdc42 and Rac1/2/3, thus significantly suppressing migratory and invasive capacity. Moreover, in an in vivo tumor model, triptolide delayed growth of malignant glioma xenografts. These findings suggest an important inhibitory action of triptolide on proliferation and invasion of malignant glioma, and encourage triptolide as a candidate for glioma therapy.     

Expression of matrix metalloproteinases in human glioma cell lines in the presence of IL-10

Matrix metalloproteinases have been implicated to play a vital role in glioma invasion as they degrade extracellular matrix to facilitate the subsequent migration of tumor cells into the surrounding brain tissue. The cytokine Interleukin-10 (IL-10) was detected recently in glial tumors in vivo. Expression of specific IL-10 mRNA as well as blood serum levels of IL-10 in glioma patients increased with malignancy suggesting a functional role of IL-10 in glioma progression. Moreover, glioma cell migration in vitro was enhanced in the presence of IL-10. We therefore investigated the expression of the matrix metalloproteinases (MMPs) stromelysin-1 (MMP-3), 72-kDa collagenase (MMP-2), 92-kDa collagenase (MMP-9), matrilysin (MMP-7) and the human macrophage metalloelastase (MMP-12). In addition, a possible relation between exposure of glioma cells to IL-10 and invasiveness of these cells due to MMP expression was analyzed. Experiments with Matrigel coated Boyden chambers revealed a pronounced dose dependent effect of IL-10 on glioma invasiveness. The synthetic MMP-inhibitor Marimastat markedly reduced cell invasion in the Boyden chambers confirming the significance of MMPs in the process of invasion. Subsequently, the expression level of MMPs and the serine protease uPA was investigated in 7 glioma cell lines (U373, GaMG, U251, GHE, SNB19, U138 and D54) by RT-PCR. In all but one cell line no enhancement of MMP expression by IL-10 was detected. Matrilysin in U373 cells was the only protease found to be upregulated in the presence of IL-10 dependent on cell density. The present data suggest that IL-10 related effects on the invasive properties of the cell lines are not directly mediated by an upregulation of matrix metalloproteinase expression.     

Silencing Pre-B-cell leukemia homeobox 3 decreases the proliferation of human glioma cells in vitro and in vivo

Among primary brain tumors, gliomas are the most common and most aggressive, with a poor prognosis and limited treatment options. Thus, it is essential to determine the mechanisms involved in glioma development to develop effective therapies for glioma patients. Pre-B-cell leukemia homeobox 3 (PBX3), a critical member of the PBX family, is frequently overexpressed in multiple human malignancies. However, the expression patterns and biological functions, as well as the involved molecular functions of PBX3 in human gliomas remain largely unknown. In this study, we demonstrate that PBX3 expression is increased in both human glioma tissues and cell lines compared with their normal counterparts. These results suggested that PBX3 might be involved in glioma progression. Thus, the role of PBX3 in glioma cell proliferation was investigated using genetic knockdown and overexpression methods. The results showed that PBX3 knockdown inhibited glioma cell proliferation and induced apoptosis, while PBX3 overexpression significantly promoted glioma cell proliferation. Mechanistically, we found that PBX3 promoted cell proliferation by modulating cell cycle progression. A xenograft LN229 model was used to confirm that PBX3 depletion decreased tumor growth in vivo. In summary, our findings reveal that PBX3 may be a potential therapeutic target in gliomas.     

Elevated JNK activation contributes to the pathogenesis of human brain tumors

The ERK pathway is typically associated with activation of the EGF receptor and has been shown to play a major role in promoting several tumor phenotypes. An analogous signaling module, the JNK pathway, has not been shown to be consistently activated by the EGF receptor but is instead more uniformly stimulated by cellular stresses and cytokines. The function of the JNK pathway in primary tumors is unclear as it has been implicated in both promoting apoptosis and cell growth in vitro, which may be a reflection of the cell lines chosen. Primary human brain tumors frequently show overexpression of the EGF receptor. To clarify the role of JNK in tumorigenesis, we have investigated the role of JNK in a large panel of primary human brain tumors and tumor derived cell lines. Here we present evidence that JNK has a major role in promoting tumorigenesis both in vivo and in vitro. Western blot analysis demonstrated that 86% (18 of 21) of primary brain tumors showed evidence of JNK activation but only 38% (8 of 21) showed evidence of ERK activation. Kinase assays revealed that 77% of brain tumor cell lines activated JNK in response to EGF (7 of 13) or had high levels of basal activity (3 of 13), whereas none of six normal cell lines analysed, including astrocytes, had these properties. Of several growth factors examined, EGF produced the highest level of JNK induction in tumor cell lines and the duration of activation was greater than that seen for ERK. Expression of a dominant-negative (dn) form of JNK potently inhibited EGF mediated anchorage independent growth and protection from cell death in two glial tumor cell lines. These findings demonstrate that enhanced JNK activation is frequently found in primary brain tumors and that this activation contributes to phenotypes related to transformation.     

LncRNA WEE2-AS1 knockdown inhibits the proliferation,migration and invasion of glioma cells via regulating miR-29b-2- 5p/TPM3 axis

Glioma is a general malignant tumor with a dismal prognosis. Long noncoding RNAs (lncRNAs) have been implicated in the initiation and processes of tumors. An investigation of the GEPIA database revealed that long noncoding RNA WEE2 antisense RNA 1 (WEE2-AS1) is upregulated in glioma tissues compared to normal brain tissues, and validation with quantitative real-time polymerase chain reaction (qRT–PCR) revealed that WEE2-AS1 expression was consistent with the database prediction. Fluorescence in situ hybridization (FISH) assays revealed that WEE2-AS1 was localized primarily in the cytoplasm. Clone formation experiment and EDU assay were used to detect cell proliferation ability, and Transwell assay was used to detect cell migration and invasion ability, Western-blot assay and immunofluorescence were used to determine TPM3 protein level. Functional experiments revealed that the downregulation of WEE2-AS1 impeded cell proliferation, migration, and invasion in glioma cell lines. Furthermore, downregulation of WEE2-AS1 suppressed tumor growth in vivo. Bioinformatics predictions and integrated experiments indicated that WEE2-AS1 promoted tropomyosin 3 (TPM3) expression by sponging miR-29b-2-5p. A dual-luciferase reporter assay was conducted to uncover the binding of WEE2-AS1 and miR-29b-2-5p and that of miR-29b-2-5p and TPM3. Additionally, a series of rescue assays showed that WEE2-AS1 promotes proliferation, migration, and invasion by targeting miR-29b-2-5p to regulate TPM3 expression. Ultimately, the results of this study indicate that WEE2-AS1 plays an oncogenic role in glioma and may promote further investigations of the diagnostic and prognostic value of WEE2-AS1 in glioma.     

敲低DCLK1抑制神经胶质瘤细胞增殖、 迁移与侵袭CSCD

目的探讨双肾上腺皮质激素样激酶 1(DCLK1)对胶质瘤细胞增殖、迁移与侵袭的影响及其机制。方法 RT-qPCR、免疫组织化学染色和Western blot检测胶质瘤组织和细胞(U87和A172)中DCLK1 mRNA和蛋白的表达情况;sh-DCLK1和阴性对照(sh-Con)转染U87和A172细胞;MTT和Transwell法分析敲低DCLK1对神经胶质瘤细胞增殖、迁移和侵袭能力的影响;蛋白印迹法检测敲低DCLK1对神经胶质瘤细胞中TGF-β/Smads信号通路相关蛋白TGF-β1、p-Smad2、p-Smad7表达的影响;将已转染sh-DCLK1或sh-Con的U87细胞注射到BALB/c裸鼠颈部皮下,定期测量瘤体体积,收集瘤体并称重。结果胶质瘤组织和细胞中DCLK1 mRNA和蛋白表达较癌旁正常组织和正常神经胶质细胞均显著升高(P<0.001)。与sh-Con组比,sh-DCLK1组的胶质瘤细胞增殖、迁移和侵袭能力及细胞中TGF-β1、p-Smad2和p-Smad7表达显著降低(P<0.01;P<0.001);sh-DCLK1组裸鼠体内的瘤体体积和瘤体质量明显降低(P<0.001)。结论敲低DCLK1能抑制胶质瘤细胞增殖、迁移和侵袭,其机制可能与抑制TGF-β/Smads信号活性有关。     

Fibulin-3 promotes glioma growth and resistance through a novel paracrine regulation of Notch signaling

Malignant gliomas are highly invasive and chemoresistant brain tumors with extremely poor prognosis. Targeting of the soluble factors that trigger invasion and resistance, therefore, could have a significant impact against the infiltrative glioma cells that are a major source of recurrence. Fibulin-3 is a matrix protein that is absent in normal brain but upregulated in gliomas and promotes tumor invasion by unknown mechanisms. Here, we show that fibulin-3 is a novel soluble activator of Notch signaling that antagonizes DLL3, an autocrine inhibitor or Notch, and promotes tumor cell survival and invasion in a Notch-dependent manner. Using a strategy for inducible knockdown, we found that controlled downregulation of fibulin-3 reduced Notch signaling and led to increased apoptosis, reduced self-renewal of glioblastoma-initiating cells, and impaired growth and dispersion of intracranial tumors. In addition, fibulin-3 expression correlated with expression levels of Notch-dependent genes and was a marker of Notch activation in patient-derived glioma samples. These findings underscore a major role for the tumor extracellular matrix in regulating glioma invasion and resistance to apoptosis via activation of the key Notch pathway. More importantly, this work describes a noncanonical, soluble activator of Notch in a cancer model and shows how Notch signaling can be reduced by targeting tumor-specific accessible molecules in the tumor microenvironment.     

Heme oxygenase-1 expression in human gliomas and its correlation with poor prognosis in patients with astrocytoma

In human glioma tumors, heme oxygenase-1 (HO-1) has been shown to be upregulated both when compared with normal brain tissues and also during oligodendroglioma progression. The cell types that express HO-1 have been shown to be mainly macrophages/microglia and T cells. However, many other reports also demonstrated that cell lines derived from glioma tumors and astrocytes express HO-1 after the occurrence of a wide variety of cell injuries and stressors. In addition, the significance of HO-1 upregulation in glioma had not, so far, been addressed. We therefore aimed at investigating the expression and significance of HO-1 in human glial tumors. For this purpose, we performed a wide screening of HO-1 expression in gliomas by using tissue microarrays containing astrocytomas, oligodendrogliomas, mixed tumors, and normal brain tissues. We subsequently correlated protein expression with patient clinicopathological data. We found differences in HO-1 positivity rates between non-malignant brain (22 %) and gliomas (54 %, p?=?0.01). HO-1 was expressed by tumor cells and showed cytoplasmic localization, although 19 % of tumor samples also depicted nuclear staining. Importantly, a significant decrease in the overall survival time of grade II and III astrocytoma patients with HO-1 expression was observed. This result was validated at the mRNA level in a cohort of 105 samples. However, no association of HO-1 nuclear localization with patient survival was detected. In vitro experiments aimed at investigating the role of HO-1 in glioma progression showed that HO-1 modulates glioma cell proliferation, but has no effects on cellular migration. In conclusion, our results corroborate the higher frequency of HO-1 protein expression in gliomas than in normal brain, demonstrate that HO-1 is expressed by glial malignant cells, and show an association of HO-1 expression with patients’ shorter survival time.     

Silencing of WNK2 is associated with upregulation of MMP2 and JNK in gliomas

Matrix metalloproteinases (MMPs) are proteolytic enzymes that degrade extracellular matrix (ECM), thus assisting invasion. Upregulation of MMPs, frequently reported in gliomas, is associated with aggressive behavior. WNK2 is a tumor suppressor gene expressed in normal brain, and silenced by promoter methylation in gliomas. Patients without WNK2 exhibited poor prognosis, and its downregulation was associated with increased glioma cell invasion.Here we showed that MMP2 expression and activity are increased in glioma cell lines that do not express WNK2. Also, WNK2 inhibited JNK, a process associated with decreasing levels of MMP2. Thus, WNK2 promoter methylation and silencing in gliomas is associated with increased JNK activation and MMP2 expression and activity, thus explaining in part tumor cell invasion potential.     

Imaging of brain and brain tumor specimens by time-resolved multiphoton excitation microscopy ex vivo

Multiphoton excitation fluorescent microscopy is a laser-based technology that allows subcellular resolution of native tissues in situ. We have recently applied this technology to the structural and photochemical imaging of cultured glioma cells and experimental gliomas ex vivo. We demonstrated that high microanatomical definition of the tumor, invasion zone, and normal adjacent brain can be obtained down to single-cell resolution in unprocessed tissue blocks. In this study, we used multiphoton excitation and four-dimensional microscopy to generate fluorescence lifetime maps of the murine brain anatomy, experimental glioma tissue, and biopsy specimens of human glial tumors. In murine brain, cellular and noncellular elements of the normal anatomy were identified. Distinct excitation profiles and lifetimes of endogenous fluorophores were identified for specific brain regions. Intracranial grafts of human glioma cell lines in mouse brain were used to study the excitation profiles and fluorescence lifetimes of tumor cells and adjacent host brain. These studies demonstrated that normal brain and tumor could be distinguished on the basis of fluorescence intensity and fluorescence lifetime profiles. Human brain specimens and brain tumor biopsies were also analyzed by multiphoton microscopy, which demonstrated distinct excitation and lifetime profiles in glioma specimens and tumor-adjacent brain. This study demonstrates that multiphoton excitation of autofluorescence can distinguish tumor tissue and normal brain based on the intensity and lifetime of fluorescence. Further technical developments in this technology may provide a means for in situ tissue analysis, which might be used to detect residual tumor at the resection edge.