TGF-alpha differentially regulates GFAP, vimentin, and nestin gene expression in U-373 MG glioblastoma cells: correlation with cell shape and motility

Astrocytes Decreased the Sensitivity of Glioblastoma Cells to Temozolomide and Bay 11-7082

Glioblastoma multiforme (GBM) is the most common malignant type of astrocytic tumors. GBM patients have a poor prognosis with a median survival of approximately 15 months despite the "Stupp" Regimen and high tumor recurrence due to the tumor resistance to chemotherapy. In this study, we co-cultured GBM cells with human astrocytes in three-dimensional (3D) poly(ethylene glycol) dimethyl acrylate (PEGDA) microwells to mimic the tumor microenvironment. We treated 3D co- and mono-cultured cells with Temozolomide (TMZ) and the nuclear factor-κB (NF-κB) inhibitor Bay 11-7082 and investigated the combined effect of the drugs. We assessed the expressions of glial fibrillary acidic protein (GFAP) and vimentin that play a role in the tumor malignancy and activation of the astrocytes as well as Notch-1 and survivin that play a role in GBM malignancy after the drug treatment to understand how astrocytes induced GBM drug response. Our results showed that in the co-culture, astrocytes increased GBM survival and resistance after combined drug treatment compared to mono-cultures. These data restated the importance of 3D cell culture to mimic the tumor microenvironment for drug screening.

Knockdown of TXNDC9 induces apoptosis and autophagy in glioma and mediates cell differentiation by p53 activation

Glioma is the most common malignant brain tumor. Because of its high degree of malignancy, the effect of surgical treatment, radiotherapy, chemotherapy, or immunotherapy is not ideal. TXNDC9 belongs to thioredoxin domain-containing proteins, which is involved in tumor progression. However, no research associated with TXNDC9 has been reported in glioma. In this study, we found that TXNDC9 was upregulated in glioma. Knockdown of TXNDC9 would prevent proliferation and metastasis, induce the apoptosis rate of glioma cells, and promote the expression Cleaved-caspase3, Cleaved-caspase8, Cleaved-caspase9. Meanwhile, knockdown of TXNDC9 induced autophagy by increasing the level of LC3 and Beclin-1. Cell morphology and expression analysis of GFAP, Vimentin, verified that TXNDC9 could regulate glioma cell differentiation. During this program, the expression of p53 changes dramatically. The apoptosis, autophagy, and cell differentiation program were blocked by p53 inhibitor treatment. In conclusion, the silencing of TXNDC9 induces apoptosis and autophagy in glioma and promotes cell differentiation by controlling p53 and may function as a new mechanism in glioma.

Epithelial cell migration requires the interaction between the vimentin and keratin intermediate filaments

Epithelial migration plays a central role in development, wound repair and tumor metastasis, but the role of intermediate filament in this important event is unknown. We showed recently that vimentin coexists in the same cell with keratin-KRT14 at the leading edge of the migrating epidermal cells, and knockdown of vimentin impaired colony growth. Here we demonstrate that vimentin co-localizes and co-immunoprecipitates with keratin-KRT14, and mutations in the -YRKLLEGEE- sequence of vimentin significantly reduced migration of the keratinocytes. Our data demonstrates that keratinocyte migration requires the interaction between vimentin and keratins at the -YRKLLEGEE- sequence at the helical 2B domain of vimentin. These findings have broad implications for understanding the roles of vimentin intermediate filaments in normal and neoplastic epithelial cells.

Expression of pituitary tumor-transforming 2 in human glioblastoma cell lines and its role in glioblastoma tumorigenesis

The present study aimed to investigate the association between the expression of pituitary tumor-transforming 2 (PTTG2), and cell proliferation, invasion and apoptosis in glioblastoma. The U251 human glioblastoma cell line was transfected with the pcDNA-PTTG2 and small interfering (si)RNA-PTTG2 plasmids using Lipofectamine 2000. The expression of PTTG2 in U251 glioblastoma cells was determined using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis. The association between PTTG2 expression, and cell proliferation, invasion and apoptosis in vitro were investigated using an MTT assay, Matrigel Transwell assay and flow cytometry combined with Annexin V/propidium iodide staining, respectively. RT-qPCR and western blot analysis demonstrated that PTTG2 mRNA and protein expression were significantly overexpressed and significantly suppressed following transfection with pcDNA-PTTG2 and short interfering RNA (siRNA)-PTTG2 plasmids, respectively (P<0.05). In addition, the cell proliferation rate and invasive cell number in cells with overexpressed PTTG2 were significantly higher compared with cells in the untreated group, and the invasive cell number in the siRNA-PTTG2 group was significantly lower than the untreated group (P<0.05). Flow cytometry analysis demonstrated that, compared with the untreated group, the quantity of apoptotic cells in PTTG2 overexpression group was significantly reduced, and the quantity of apoptotic cells in the siRNA-PTTG2 group was increased. Similar results were obtained with regards to the expression level of caspase-3. The results of the present study indicate that PTTG2 overexpression promotes cell proliferation and invasion during glioblastoma progression. In addition, the results suggest that PTTG2 overexpression inhibits cell apoptosis in glioblastoma by affecting caspase-3-dependent signaling pathways. It can therefore be suggested that PTTG2 may serve as a novel therapeutic target for treating glioblastoma.

Roles and potential clinical applications of intermediate filament proteins in brain tumors

Intermediate filament (IF) proteins are cytoplasmic and nuclear cytoskeletal proteins. Of the ~70 IF proteins, nearly 12 are found in the nervous system, where their expression is largely cell-type specific. Astrocytes express glial fibrillary acidic protein (GFAP), whereas different neuron types contain neurofilament proteins, α-internexin, or peripherin. These proteins are often downregulated in brain cancer. In addition, brain cancer cells may also contain vimentin, nestin, and synemin, which are the IF proteins found in neural progenitor cells. In different brain tumor types, the expression of nestin, vimentin, and α-internexin appears to correlate with the clinical outcome. Experimental investigations have also demonstrated that IF proteins have distinct roles in specific brain tumor cell behaviors: nestin, for instance, is important for the proliferation of glioma cells, whereas synemin also affect their mobility. The mechanisms responsible for these effects involve the interaction of IF proteins with specific signaling pathways. Synemin, for instance, positively regulates glioma cell proliferation by antagonizing protein phosphatase 2A. Further evidence for the potential of IF proteins as therapeutic targets derives from animal models showing the influence of IF proteins on tumor growth. Nestin downregulation, for instance, dramatically reduced intracerebral glioma growth. Selective targeted therapies of IFs to date primarily include gene therapy approaches using nestin or GFAP gene promoters to drive transgene expression into glioma cells. Although attempts to identify small molecules specifically antagonizing IF proteins have been unsuccessful to date, it is anticipated that the identification of such compounds will be instrumental in expanding therapeutic approaches for brain tumors.

Cells with intense EGFR staining and a high nuclear to cytoplasmic ratio are specific for infiltrative glioma: a useful marker in neuropathological practice

BACKGROUND

The differential diagnosis between infiltrative glioma (IG) and benign or curable glial lesions, such as gliosis, pilocytic astrocytoma, dysembryoplastic neuroepithelial tumor, ganglioglioma, or demyelinating disease, may be challenging for the pathologist because specific markers are lacking. Recently, we described a strong EGFR immunolabelling pattern in cells with a high nuclear to cytoplasmic ratio that enables the discrimination of low-grade IG from gliosis. The aim of this study was to extend our observation to high-grade glioma to assess whether EGFR expression pattern is of value in the discrimination of all IG from noninfiltrative glial lesions (NIG), including gliosis, benign tumors, and demyelinating disease.

METHODS

One hundred one IG and 58 NIG were compared for immunohistochemical expression of EGFR with use of an antibody that recognizes an epitope in the extracellular domain of both EGFRwt and EGFRvIII. Highly EGFR-positive cells with a high nuclear to cytoplasmic ratio were isolated and further characterized.

RESULTS

Cells with intense EGFR staining and a high nuclear to cytoplasmic ratio were significantly associated with the diagnosis of IG (P < .0001). The sensitivity and specificity of this staining pattern for the diagnosis of IG were 95% and 100%, respectively. EGFR expression was independent of IDH1 mutations and EGFR amplification. Finally, we showed that these particular cells displayed the phenotype and properties of glial progenitors and coexpressed CXCR4, a marker of invasiveness.

CONCLUSIONS

We demonstrate that cells with intense EGFR staining and a high nuclear to cytoplasmic ratio are specific criteria for the diagnosis of IG, irrespective of grade, histological subtype, and progression pathway, and their identification represents a tool to discriminate IG from benign or curable glial lesions.

Antiproliferative effects of PACAP and VIP in serum-starved glioma cells

Emerging evidence have suggested that calorie restriction (CR) is a reliable method to decrease cancer development since it produces changes in tumor microenvironment that interfere with cell proliferation, tissue invasion, and formation of metastases. Studies on the role of pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) in cancer cells indicate that their influence on cell growth is either cell type specific or dependent on culture conditions. Evidence showing the effect of PACAP and VIP in glioma cells grown under conditions mimicking CR are currently unavailable. Therefore, we explored the effects of both PACAP and VIP in C6 glioma cells either grown in a normal growth medium or exposed to serum starvation, to resemble an acute condition of CR. Cell viability, expression of proteins related to cell proliferation (cyclin D1), apoptosis (Bcl2, p53, and cleaved caspase-3), and cell malignancy (GFAP and nestin) were assessed by MTT assay, immunoblot, and immunolocalization, respectively. Results demonstrated that CR significantly decreased cell proliferation, reduced levels of cyclin D1 and Bcl2, and increased the expression of p53 and cleaved caspase-3. Surprisingly, all of these CR-driven effects were further exacerbated by PACAP or VIP treatment. We also found that PACAP or VIP prevented GFAP decrease caused by CR and further reduced the expression of nestin, a prognostic marker of malignancy. In conclusion, these data demonstrate that PACAP and VIP possess antiproliferative properties against glioma cells that depend on the specific culture settings, further supporting the idea that CR might offer new avenues to improve peptide-oriented glioma cancer treatment.

Tanshinones: sources, pharmacokinetics and anti-cancer activities

Tanshinones are a class of abietane diterpene compound isolated from Salvia miltiorrhiza (Danshen or Tanshen in Chinese), a well-known herb in Traditional Chinese Medicine (TCM). Since they were first identified in the 1930s, more than 40 lipophilic tanshinones and structurally related compounds have been isolated from Danshen. In recent decades, numerous studies have been conducted to investigate the isolation, identification, synthesis and pharmacology of tanshinones. In addition to the well-studied cardiovascular activities, tanshinones have been investigated more recently for their anti-cancer activities in vitro and in vivo. In this review, we update the herbal and alternative sources of tanshinones, and the pharmacokinetics of selected tanshinones. We discuss anti-cancer properties and identify critical issues for future research. Whereas previous studies have suggested anti-cancer potential of tanshinones affecting multiple cellular processes and molecular targets in cell culture models, data from in vivo potency assessment experiments in preclinical models vary greatly due to lack of uniformity of solvent vehicles and routes of administration. Chemical modifications and novel formulations had been made to address the poor oral bioavailability of tanshinones. So far, human clinical trials have been far from ideal in their design and execution for the purpose of supporting an anti-cancer indication of tanshinones.

Low Concentration Microenvironments Enhance the Migration of Neonatal Cells of Glial Lineage

Glial tumors have demonstrated abilities to sustain growth via recruitment of glial progenitor cells (GPCs), which is believed to be driven by chemotactic cues. Previous studies have illustrated that mouse GPCs of different genetic backgrounds are able to replicate the dispersion pattern seen in the human disease. How GPCs with genetic backgrounds transformed by tumor paracrine signaling respond to extracellular cues via migration is largely unexplored, and remains a limiting factor in utilizing GPCs as therapeutic targets. In this study, we utilized a microfluidic device to examine the chemotaxis of three genetically-altered mouse GPC populations towards tumor conditioned media, as well as towards three growth factors known to initiate the chemotaxis of cells excised from glial tumors: Hepatocyte Growth Factor (HGF), Platelet-Derived Growth Factor-BB (PDGF-BB), and Transforming Growth Factor-α (TGF-α). Our results illustrate that GPC types studied exhibited chemoattraction and chemorepulsion by different concentrations of the same ligand, as well as enhanced migration in the presence of ultra-low ligand concentrations within environments of high concentration gradient. These findings contribute towards our understanding of the causative and supportive roles that GPCs play in tumor growth and reoccurrence, and also point to GPCs as potential therapeutic targets for glioma treatment.

Biosynthesis, total syntheses, and antitumor activity of tanshinones and their analogs as potential therapeutic agents

Tanshinones are a series of abietane diterpenes, isolated exclusively from Salvia miltiorrhiza and related species. More than 40 tanshinones and their analogs have been isolated since the 1930s. Their biosynthetic pathway correlates with the MEP/DOXP pathway, and many key enzymes, such as mCPS, are responsible for establishing their molecular scaffolds and stereospecificity. Because of their unique structural characteristics and promising biological activities, total syntheses of various tanshinones have attracted the interest of many synthetic chemists, including R. H. Thomson, H. Kakisawa, R. L. Danheiser, Y. Inouye and J. K. Snyder. Tanshinones and their analogs exhibit interesting and broad antitumor activity in various cell and animal models. Most recently, the tanshinone analog neo-tanshinlactone has shown potent and selective activity against breast cancer. This review will discuss the biosynthesis, total syntheses, and antitumor activities of tanshinones,especially neo-tanshinlactone and its analogs.

Nodal promotes growth and invasion in human gliomas

Uncontrolled growth and diffused invasion are major causes of mortality in patients with malignant gliomas. Nodal has been shown to have a central role in the tumorigenic signaling pathways of malignant melanoma. In this study, we show that grade IV human glioma cell lines expressed different levels of Nodal, paralleled to the potential for cell invasiveness. Treatment of glioma cell lines with recombinant Nodal (rNodal) increased matrix metalloproteinase 2 (MMP-2) secretion and cell invasiveness. The ectopic expression of Nodal in GBM glioma cells that expressed Nodal at low level resulted in increased MMP-2 secretion, enhanced cell invasiveness, raised cell proliferation rates in vitro, increased tumor growth in vivo, and was associated with poor survival in a mice xenograft model. In contrast, the knockdown of Nodal expression in U87MG glioma cells with high Nodal expression level had reduced MMP-2 secretion, less cell invasiveness, lower tumor growth in vivo and longer lifespan in mice with U87MG/shNodal cell xenografts. In addition, Nodal knockdown promoted the reversion of malignant glioma cells toward a differentiated astrocytic phenotype. Furthermore, our data support the notion that Nodal may regulate glioma progression through the induction of the leukemia inhibitory factor (LIF) and Cripto-1 through activated Smad.

Automated brain tumor biopsy prediction using single-labeling cDNA microarrays-based gene expression profiling

AIMS

Gene signatures obtained from microarray experiments may be of use to improve the prediction of brain tumor diagnosis. Nevertheless, automated and objective prediction with accuracy comparable to or better than the gold standard should be convincingly demonstrated for possible clinician uptake of the new methodology. Herewith, we demonstrate that primary brain tumor types can be discriminated using microarray data in an automated and objective way.

METHODS

Postsurgical biopsies from 35 patients [17 glioblastoma multiforme (Gbm) and 18 meningothelial meningioma (Mm)] were stored in liquid nitrogen, total RNA was extracted, and cDNA was labeled with Cy3 fluorochrome and hybridized onto a cDNA-based microarray containing 11,500 cDNA clones representing 9300 loci. Scanned data were preprocessed, normalized, and used for predictor development. The predictive functions were fitted to a subset of samples and their performance evaluated with an independent subset. Expression results were validated by means of real time-polymerase chain reaction.

RESULTS

Some gene expression-based predictors achieved 100% accuracy both in training resampling validation and independent testing. One of them, composed of GFAP, PTPRZ1, GPM6B and PRELP, produced a 100% prediction accuracy for both training and independent test datasets. Furthermore, the gene signatures obtained, increased cell detoxification, motility and intracellular transport in Gbm, and increased cell adhesion and cytochrome-family genes in Mm, agree well with the expected biologic and pathologic characteristics of the studied tumors.

CONCLUSIONS

The ability of gene signatures to automate prediction of brain tumors through a fully objective approach has been demonstrated. A comparison of gene expression profiles between Gbm and Mm may provide additional clues about patterns associated with each tumor type.

Human cytomegalovirus infection downregulates the expression of glial fibrillary acidic protein in human glioblastoma U373MG cells: identification of viral genes and protein domains involved

Human cytomegalovirus (HCMV) has tropism for glial cells, among many other cell types. It was reported previously that the stable expression of HCMV immediate-early protein 1 (IE1) could dramatically reduce the RNA level of glial fibrillary acidic protein (GFAP), an astroglial cell-specific intermediate filament protein, which is progressively lost with an increase in glioma malignancy. To understand this phenomenon in the context of virus infection, a human glioblastoma cell line, U373MG, was infected with HCMV (strain AD169 or Towne). The RNA level of GFAP was reduced by more than 10-fold at an m.o.i. of 3 at 48 h post-infection, whilst virus treated with neutralizing antibody C23 or with UV light had a much-reduced effect. Treatment of infected cells with ganciclovir did not prevent HCMV-mediated downregulation of GFAP. Although the expression of GFAP RNA is downregulated in IE1-expressing cells, a mutant HCMV strain lacking IE1 still suppressed GFAP, indicating that other IE proteins may be involved. IE2 is also proposed to be involved in GFAP downregulation, as an adenoviral vector expressing IE2 could also reduce the RNA level of GFAP. Data from the mutational analysis indicated that HCMV infection might affect the expression of this structural protein significantly, primarily through the C-terminal acidic region of the IE1 protein.

Capsaicin induces apoptosis and terminal differentiation in human glioma A172 cells

Capsaicin (8-methyl-N-vanillyl-6-nonenamide), the major pungent ingredient of red pepper, has been reported to possess anti-carcinogenic and anti-mutagenic activities. In this study, the effects of capsaicin on human glioblastoma A172 cells were investigated. Treatment of A172 cells with capsaicin inhibited cell growth and induced apoptosis through down-regulation of Bcl-2 and activation of caspase-3. Interestingly, synergistic induction of morphological alternation was observed when A172 cells were treated with capsaicin. A double immunostaining analysis indicated that capsaicin stimulated terminal differentiation predominantly to astrocyte-like cells. Moreover, capsaicin increased the transcription levels of glial fibrillary acidic protein (GFAP) and neuronal microtubule-associated protein 2ab (MAP2ab). These results demonstrated that capsaicin inhibits A172 cell growth through apoptosis and terminal differentiation. Consequently, this research may provide further support for capsaicin-based anti-tumor therapies and consideration should be given to developing capsaicin for use in chemotherapy for malignant human glioblastoma.

Assessment of the astrogliotic responses of three human astrocytoma cell lines to ethanol, trimethyltin chloride and acrylamide

The astrogliotic responses of the CCF-STTG1, U251-MG, and U373-MG human astrocytoma lines were determined after exposure to ethanol, trimethyltin chloride (TMTC), and acrylamide over 4, 16, and 24h. Basal glial fibrillary acidic protein (GFAP) expression in the U-251MG and U373-MG cells was 10-fold greater than the CCF-STGG1 line. Ethanol treatment over 24h, but not at 4 and 16h, resulted in significant increases in GFAP in all three glioma lines at sub-cytotoxic levels; the GFAP responses in the CCF-STTG1 line were the most sensitive, as concentrations of 0.1 and 1mM led to increases in GFAP expression compared with control of 56.8+/-15.7 and 58.9+/-11.5%, respectively (P<0.05). Treatment with TMTC (1 microM) over 4h showed elevated GFAP expression in the U251-MG cell line to 28.0+/-15.7% above control levels (P<0.01), but not in the other U373-MG or CCF-STTG1 cells. At 4h, MTT turnover was markedly increased compared with control, particularly in the U373-MG line at concentrations as low as 1 microM (17.1+/-2.3%; P<0.01). TMTC exposure over 16 and 24h resulted in reduction in GFAP expression in all three lines at concentrations; at 24h incubation, the reduction was >50% (P<0.01). There were no changes in GFAP expression or MTT turnover in response to acrylamide except at the highest concentration ranges of 10-100 mM. This study underlines the significance of period of exposure, as well as toxin concentration in astrocytoma cellular response to toxic pressure.

Identification and characterization of GFAPkappa, a novel glial fibrillary acidic protein isoform

Glial fibrillary acidic protein (GFAP) is the principal component of the intermediary filaments in mature astrocytes of the central nervous system (CNS). The protein consists of three domains: the head, the coiled-coil, and the tail. Here, we describe the isolation of an evolutionary conserved novel GFAP isoform, GFAPkappa, produced by alternative splicing and polyadenylation of the 3'-region of the human GFAP pre-mRNA. As a consequence, the resulting human GFAPkappa protein harbors a nonconserved C-terminal tail sequence distinct from the tails of GFAPalpha, the predominant GFAP isoform, and GFAPepsilon, an isoform which also results from alternative splicing. The head and coiled-coil rod domains are identical between the three GFAP isoforms. Interestingly, GFAPkappa is incapable of forming homomeric filaments, and increasing GFAPkappa expression levels causes a collapse of intermediate filaments formed by GFAPalpha. In searching for a biological relevance of GFAPkappa, we noticed that mRNA expression levels of GFAPalpha, GFAPepsilon, and GFAPkappa are gradually increased during development of the embryonic pig brain. However, whereas the GFAPalpha/GFAPepsilon ratio is constant, the GFAPkappa/GFAPepsilon ratio decreases during brain development. Furthermore, in glioblastoma tumors, an increased GFAPkappa/GFAPepsilon ratio is detected. Our results suggest that the relative expression level of the GFAPkappa isoform could modulate the properties of GFAP intermediate filaments and perhaps thereby influencing the motility of GFAP positive astrocytes and progenitor cells within the CNS.

Interindividual differences in anticancer drug cytotoxicity in primary human glioblastoma cells

Glioblastoma multiforme is a malignant astrocytic tumor characterized by rapid growth, extensive invasiveness and high vascularity. Despite advances in surgical techniques and in the development of new protocols in radio- and chemotherapy, the prognosis for patients suffering from this malignancy remains poor. Since the clinical response to chemotherapy varies greatly owing to different interindividual gene expression profiles, it would be of considerable interest to develop an in vitro model able to evaluate anticancer drug toxicity and the effectiveness of therapeutic strategies on cells obtained from individual patients. In the protocol for obtaining primary cultures of glioblastoma cells described in this report, a confluent monolayer of cells can be obtained within 1 or 2 weeks. A complementary immunocytochemical assay using glial fibrillary acidic protein (GFAP) to reliably mark glial cells confirms the glial origin of the cultured cells. A cytotoxicity test based on mitochondrial activity is then used to evaluate in vitro drug efficacy. Cell dedifferentiation as evidenced by loss of GFAP expression after a few passages requires determination of drug toxicity before the fourth passage. Data show a wide range of response to temozolomide (1000 microM) after 72 h with 24-81% cell death depending on patients. Results presented confirm the heterogeneity of response to anticancer drugs between the patients and methods described allow to carry out cytotoxicity studies in order to determine the individualized most effective treatment.

Growth inhibition and induction of apoptosis and differentiation of tanshinone IIA in human glioma cells

Tanshinone IIA is a derivative of phenanthrene-quinone isolated from Danshen, a widely used Chinese herbal medicine. It has antioxidant properties, cytotoxic activities against multiple human cancer cells, inducing apoptosis and differentiation of some human cancer cells. The purpose of this study is to confirm its anticancer activity on human glioma cells, and to elucidate mechanism of its activity. Human glioma cells were tested in vitro for cytotoxicity, colony formation inhibition, BrdU incorporation after treatment with tanshinone IIA. Its effect of apoptosis induction was detected through EB/AO staining, cell cycle analysis and the expressions of ADPRTL1 and CYP1A1 genes, the differentiation induction effect was investigated through morphology, mRNA and protein expressions of GFAP and nestin genes by RT-PCR and immunocytochemistry. Tanshinone IIA demonstrated a dose- and time-dependent inhibitory effect on cell growth, IC(50) was 100 ng/ml, and it significantly inhibited colony formation and BrdU incorporation of human glioma cells. After treatment with 25-100 ng/ml of tanshinone IIA, the apoptotic cells increased significantly (P < 0.01), the cells in G(0)/G(1) phase increased (P < 0.01), and decreased in S phase, ADPRTL1 and CYP1A1 mRNA expression increased 1-2 folds. The cells treated with 100 ng/ml tanshinone IIA demonstrated astrocytes or neuron-like morphology, GFAP mRNA and protein expressions increased, nestin mRNA and protein expressions decreased significantly. The findings in this study suggested that tanshinone IIA exhibited strong effects on growth inhibition and induction of apoptosis and differentiation in human glioma cells. It might serve as a novel promising differentiation-inducing and/or therapeutic agent for human gliomas, and need to be investigated further.

Epidermal growth factor receptor overexpression results in increased tumor cell motility in vivo coordinately with enhanced intravasation and metastasis

Although overexpression of the epidermal growth factor receptor (EGFR; ErbB1) has been correlated with poor prognosis in breast and other cancers, clinical trials of ErbB1 inhibitors have shown limited efficacy in inhibiting tumor proliferation. To evaluate other possible roles of ErbB1 in tumor malignancy besides proliferation, we have developed a series of tools for analysis of intravasation. Overexpression of ErbB1 in MTLn3 mammary adenocarcinoma cells results in increased intravasation and lung metastasis from tumors formed by injection of cells in the mammary fat pad. However, increased ErbB1 expression has no effect on primary tumor growth and lung seeding efficiency of cells injected i.v. Chemotactic responses to low concentrations of EGF in vitro and cell motility in vivo in the primary tumor measured using intravital imaging are significantly increased by ErbB1 overexpression. The increased cell motility is restricted to ErbB1-overexpressing cells in tumors containing mixtures of cells expressing different ErbB1 levels, arguing for a cell-autonomous effect of increased ErbB1 expression rather than alteration of the tumor microenvironment. In summary, we propose that ErbB1 overexpression makes more significant contributions to intravasation than growth in some tumors and present a novel model for studying ErbB1 contributions to tumor metastasis via chemotaxis and intravasation.

Nestin expression in the cell lines derived from glioblastoma multiforme

Background

Nestin is a protein belonging to class VI of intermediate filaments that is produced in stem/progenitor cells in the mammalian CNS during development and is consecutively replaced by other intermediate filament proteins (neurofilaments, GFAP). Down-regulated nestin may be re-expressed in the adult organism under certain pathological conditions (brain injury, ischemia, inflammation, neoplastic transformation). Our work focused on a detailed study of the nestin cytoskeleton in cell lines derived from glioblastoma multiforme, because re-expression of nestin together with down-regulation of GFAP has been previously reported in this type of brain tumor.

Methods

Two cell lines were derived from the tumor tissue of patients treated for glioblastoma multiforme. Nestin and other cytoskeletal proteins were visualized using imunocytochemical methods: indirect immunofluorescence and immunogold-labelling.

Results

Using epifluorescence and confocal microscopy, we described the morphology of nestin-positive intermediate filaments in glioblastoma cells of both primary cultures and the derived cell lines, as well as the reorganization of nestin during mitosis. Our most important result came through transmission electron microscopy and provided clear evidence that nestin is present in the cell nucleus.

Conclusion

Detailed information concerning the pattern of the nestin cytoskeleton in glioblastoma cell lines and especially the demonstration of nestin in the nucleus represent an important background for further studies of nestin re-expression in relationship to tumor malignancy and invasive potential.

Development of an in vitro blood–brain barrier model—cytotoxicity of mercury and aluminum

In this study, in vitro blood-brain barrier (BBB) models composed of two different cell types were compared. The aim of our study was to find an alternative human cell line that could be used in BBB models. Inorganic and organic mercury and aluminum were studied as model chemicals in the testing of the system. BBB models were composed of endothelial RBE4 cell line or retinal pigment epithelial (RPE) cell line ARPE-19 and neuronal SH-SY5Y cells as target cells. Glial U-373 MG cells were included in part of the tests to induce the formation of a tighter barrier. Millicell CM filter inserts were coated with rat-tail collagen, and RBE4 or ARPE-19 cells were placed on the filters at the density of 3.5-4 x 10(5) cells/filter. During culture, the state of confluency was microscopically observed and confirmed by the measurement of electrical resistance caused by the developing cell layer. The target cells, SH-SY5Y neuroblastoma cells, were plated on the bottom of cell culture wells at the density of 100000 cells/cm(2). In part of the studies, glial U-373 MG cells were placed on the under side of the membrane filter. When confluent filters with ARPE-19 or RBE4 cells were placed on top of the SH-SY5Y cells, different concentrations of mercuric chloride, methyl mercury chloride, and aluminum chloride were added into the filter cups along with a fluorescent tracer. Exposure time was 24 h, after which the cytotoxicity in the SH-SY5Y cell layer, as well as in the ARPE-19 or RBE4 cell layer, was evaluated by the luminescent measurement of total ATP. The leakage of the fluorescent tracer was also monitored. The results showed that both barrier cell types were induced by glial cells. Inorganic and organic mercury caused a leakage of the dye and cytotoxicity in SH-SY5Y cells. Especially, methyl mercury chloride could exert an effect on target cells before any profound cytotoxicity in barrier cells could be seen. Aluminum did not cause any leakage in the barrier cell layer, and even the highest concentration (1 mM) of aluminum did not cause any cytotoxicity in the SH-SY5Y cells. In conclusion, BBB models composed of RBE4 and ARPE-19 cells were able to distinguish between different toxicities, and ARPE-19 cells are thus promising candidates for studies of drug penetration through the blood-brain barrier.

Activation of erbB-1 signaling in tanycytes of the median eminence stimulates transforming growth factor beta1 release via prostaglandin E2 production and induces cell plasticity

The activation of transforming growth factor alpha (TGFalpha)-erbB-1 and neuregulin-erbB-4 signaling pathways in hypothalamic astrocytes has been shown to play a key role in the process by which the neuroendocrine brain controls luteinizing hormone-releasing hormone (LHRH) secretion. Earlier studies suggested that tanycytes, an ependymoglial cell type of the median eminence, regulate LHRH release during the estrous cycle by undergoing plastic changes that alternatively allow or prevent direct access of the LHRH nerve terminals to the portal vasculature. Neither the molecules responsible for these plastic changes nor the underlying controlling mechanisms have been identified. Here we show that cultured tanycytes express erbB-1 and erbB-2, two of the four members of the erbB receptor family, and respond to TGFalpha with receptor phosphorylation, release of prostaglandin E2 (PGE2), and a PGE2-dependent increase in the release of TGFbeta1, a growth factor previously implicated in the glial control of LHRH secretion. Blockade of either erbB-1 receptor signal transduction or prostaglandin synthesis prevented the stimulatory effect of TGFalpha on both PGE2 and TGFbeta1 release. Time-lapse studies revealed that TGFalpha and TGFbeta1 have dramatically opposite effects on tanycyte plasticity. Whereas TGFalpha promotes tanycytic outgrowth, TGFbeta1 elicits retraction of tanycytic processes. Blockade of metalloproteinase activity abolished the effect of TGFbeta1, suggesting that TGFbeta1 induces tanycytic retraction by facilitating dissolution of the extracellular matrix. Prolonged (>12 hr) exposure of tanycytes to TGFalpha resulted in focal tanycytic retraction, an effect that was abolished by immunoneutralization of TGFbeta1 action, indicating that the retraction was attributable to TGFalpha-induced TGFbeta1 formation. These in vitro results identify tanycytes as targets of TGFalpha action and demonstrate that activation of erbB-1-mediated signaling in these cells results in plastic changes that, involving PGE2 and TGFbeta1 as downstream effectors, mimic the morphological plasticity displayed by tanycytes during the hours encompassing the preovulatory surge of LHRH.

Glial expression of estrogen and androgen receptors after rat brain injury

Estrogens and androgens can protect neurons from death caused by injury to the central nervous system. Astrocytes and microglia are major players in events triggered by neural lesions. To determine whether glia are direct targets of estrogens or androgens after neural insults, steroid receptor expression in glial cells was assessed in two different lesion models. An excitotoxic injury to the hippocampus or a stab wound to the parietal cortex and hippocampus was performed in male rats, and the resultant expression of steroid receptors in glial cells was assessed using double-label immunohistochemistry. Both lesions induced the expression of estrogen receptors (ERs) and androgen receptors (ARs) in glial cells. ERalpha was expressed in astrocytes immunoreactive (ERalpha-ir) for glial fibrillary acidic protein or vimentin. AR immunoreactivity colocalized with microglial markers, such as Griffonia simplicifolia lectin-1 or OX-6. The time course of ER and AR expression in glia was studied in the stab wound model. ERalpha-ir astrocytes and AR-ir microglia were observed 3 days after lesion. The number of ERalpha-ir and AR-ir glial cells reached a maximum 7 days after lesion and returned to low levels by 28 days postinjury. The studies of ERbeta expression in glia were inconclusive; different results were obtained with different antibodies. In sum, these results suggest that reactive astrocytes and reactive microglia are a direct target for estrogens and androgens, respectively.

The hyaluronan receptor RHAMM/IHABP in astrocytoma cells: expression of a tumor-specific variant and association with microtubules

Hyaluronan binding to its cellular receptors CD44 and ICAM-1 appears to enhance the malignant behavior of tumors, including astrocytomas. RHAMM/IHABP, another hyaluronan receptor, has been identified in breast carcinoma cells, but its presence in astrocytomas is yet undetermined. Herein, we report that a monoclonal antibody against plectin (a cytoskeletal protein linker) recognizes on Western blots of U-373 MG glioblastoma cells, a 300-kDa band corresponding to plectin and two bands of 86 and 70 kDa. cDNA cloning and Northern blotting reveals that these two bands represent isoforms of RHAMM/IHABP. Sequence comparisons suggest that the plectin monoclonal antibody recognizes RHAMM/IHABP because this protein and plectin share short peptide sequences of similar primary and secondary structure. Western blotting demonstrates that most human astrocytoma tissues and cell lines express the 86- and 70-kDa isoforms of RHAMM/IHABP. Interestingly, the 70-kDa variant is undetectable in normal brain tissues and in primary cultures of astrocytes suggesting that its expression is tumor-specific. Transfection experiments with epitope-tagged RHAMM/IHABP cDNA established that RHAMM/IHABP associates with microtubules in astrocytoma cells, while in normal astrocytes it either co-localizes with microtubules or has a diffuse cytoplasmic distribution. This suggests that RHAMM/IHABP has the capacity to bind to microtubules in normal and transformed astrocytes, and that neoplasia may favor this association.

Expression of glial fibrillary acidic protein and glutamine synthetase by Müller cells after optic nerve damage and intravitreal application of brain-derived neurotrophic factor

Müller glia play an important role in maintaining retinal homeostasis, and brain-derived neurotrophic factor (BDNF) has proven to be an effective retinal ganglion cell (RGC) neuroprotectant following optic nerve injury. The goal of these studies was to investigate the relation between optic nerve injury and Müller cell activation, and to determine the extent to which BDNF affects the injury response of Müller cells. Using immunocytochemistry and Western blot analysis, temporal changes in the expression of glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS) were examined in rats after optic nerve crush alone, or in conjunction with an intravitreal injection of BDNF (5 microg). GFAP protein levels were normal at 1 day post-crush, but increased approximately 9-fold by day 3 and remained elevated over the 2-week period studied. Müller cell GS expression remained stable after optic nerve crush, but the protein showed a transient shift in its cellular distribution; during the initial 24-h period post-crush the GS protein appeared to translocate from the cell body to the inner and outer glial processes, and particularly to the basal endfeet located in the ganglion cell layer. BDNF alone, or in combination with optic nerve crush, did not have a significant effect on the expression of either GFAP or GS compared with the normal retina, or after optic nerve crush alone, respectively. The data indicate that although BDNF is a potent neuroprotectant in the vertebrate retina, it does not appear to have a significant influence on Müller cell expression of either GS or GFAP in response to optic nerve injury.

TGF-alpha induces a stationary, radial-glia like phenotype in cultured astrocytes

Transgenic mice studies have suggested that transforming growth factor-alpha (TGF-alpha) influences the postnatal differentiation of astrocytes. To understand the role of TGF-alpha during astrocytic differentiation, it is important to determine how this factor affects astrocytes in the absence of other influences. We have thus examined in vitro under serum-free medium conditions the effect of TGF-alpha on the properties of astrocytes derived from the cerebral cortex of newborn rats. When TGF-alpha is added to serum-free medium, most astrocytes lose their polygonal shape and extend two long processes running in opposite directions. This bipolar morphology strikingly resembles that of radial glial cells. Intriguingly, serum inhibits this morphological transformation. TGF-alpha also triggers an increase in glial fibrillary acidic protein (GFAP) expression and a decrease in nestin expression. Another major effect of TGF-alpha is to practically abolish the motility of astrocytes. TGF-alpha, however, does not appear to influence the proliferation and apoptosis of astrocytes. These results suggest that polygonal astrocytes are derived primarily from radial glial cells, and that in vivo TGF-alpha may be instrumental in determining the shape and migratory potential of radial glial cells.

Identification of cadherin-11 down-regulation as a common response of astrocytoma cells to transforming growth factor-alpha

Transforming growth factor-alpha (TGF-alpha) and its receptor are frequently co-expressed in high-grade astrocytomas, suggesting a role for TGF-alpha autocrine/paracrine loops in the malignant progression of astrocytomas. To identify genes that may be critical in mediating TGF-alpha impact on the malignant progression of astrocytomas, we have used cDNA arrays to investigate TGF-alpha effects on the gene expression profile of U-373 MG glioblastoma cells. We found that in these cells approximately 50% of the TGF-alpha regulated genes code for cell motility/invasion-related proteins. TGF-alpha action on the expression of four of these proteins, alpha-catenin, IQGAP1, RhoA, and cadherin-11, was further investigated by immunoblotting in four astrocytoma cell lines and in normal astrocytes. The results demonstrate that the effects of TGF-alpha on IQGAP1, alpha-catenin, and RhoA expression are cell-line dependent. On the other hand, under TGF-alpha treatment, cadherin-11 expression is consistently decreased in all astrocytoma cell lines tested but is increased in normal astrocytes. In addition, we found that cadherin-11 is consistently down-regulated in astrocytomas versus normal brain tissues. Altogether, these results suggest that the down-regulation of cadherin-11 is a frequent molecular event in the neoplastic transformation of astrocytes and that this down-regulation may be initiated and/or amplified by TGF-alpha autocrine/paracrine loops during tumor progression.