Secretion of matrix metalloproteinase-2 (72 kD gelatinase/type IV collagenase = gelatinase A) by malignant human glioma cell lines: implications for the growth and cellular invasion of the extracellular matrix

GFAPδ: A Promising Biomarker and Therapeutic Target in Glioblastoma

GFAPδ, the delta isoform of the glial fibrillary acidic protein, is mainly expressed in the subventricular zone of the brain, together with other neural stem cell markers like nestin. The authors of this paper were among the first that described in detail the expression of GFAPδ and its correlation with malignancy and invasiveness in cerebral astrocytoma. Later, several papers confirmed these findings, showing that the alternative splice variant GFAPδ is overexpressed in glioblastoma (CNS WHO grade 4) compared with lower grade gliomas. Other studies suggested that a high GFAPδ/α ratio is associated with a more malignant and invasive behavior of glioma cells. Moreover, the changing of GFAPδ/α ratio affects the expression of high-malignant genes. It is now suggested that discriminating between predominant GFAP isoforms, GFAPδ or GFAPα, is useful for assessing the malignancy state of astrocytoma, and may even contribute to the classification of gliomas. Therefore, the purpose of this paper is to review the literature with emphasize on the role of GFAPδ as a potential biomarker, and as a possible therapeutic target in glioblastoma.

Beta-blockers and glioma: a systematic review of preclinical studies and clinical results

Given the median survival of 15 months after diagnosis, novel treatment strategies are needed for glioblastoma. Beta-blockers have been demonstrated to inhibit angiogenesis and tumor cell proliferation in various cancer types. The aim of this study was to systematically review the evidence on the effect of beta-blockers on glioma growth. A systematic literature search was performed in the PubMed, Embase, Google Scholar, Web of Science, and Cochrane Central to identify all relevant studies. Preclinical studies concerning the pharmacodynamic effects of beta-blockers on glioma growth and proliferation were included, as well as clinical studies that studied the effect of beta-blockers on patient outcomes according to PRISMA guidelines. Among the 980 citations, 10 preclinical studies and 1 clinical study were included after title/abstract and full-text screening. The following potential mechanisms were identified: reduction of glioma cell proliferation (n = 9), decrease of glioma cell migration (n = 2), increase of drug sensitivity (n = 1), induction of glioma cell death (n = 1). Beta-blockers affect glioma proliferation by inducing a brief reduction of cAMP and a temporary cell cycle arrest in vitro. Contrasting results were observed concerning glioma cell migration. The identified clinical study did not find an association between beta-blockers and survival in glioma patients. Although preclinical studies provide scarce evidence for the use of beta-blockers in glioma, they identified potential pathways for targeting glioma. Future studies are needed to clarify the effect of beta-blockers on clinical endpoints including survival outcomes in glioma patients to scrutinize the value of beta-blockers in glioma care.

Matrix protease production, epithelial-to-mesenchymal transition marker expression and invasion of glioblastoma cells in response to osmotic or hydrostatic pressure

Both hydrostatic and osmotic pressures are altered in the tumour microenvironment. Glioblastoma (GBM) is a brain tumour with high invasiveness and poor prognosis. We hypothesized that physical and osmotic forces regulate glioblastoma (GBM) invasiveness. The osmotic pressure of GBM cell culture medium was adjusted using sodium chloride or water. Alternatively, cells were subjected to increased hydrostatic force. The proteolytic profile and epithelial–mesenchymal transition (EMT) were investigated using zymography and real-time qPCR. The EMT markers assessed were Snail-1, Snail-2, N-cadherin, Twist and vimentin. Invasion was investigated in vitro using extracellular matrix-coated Transwell inserts. In response to osmotic and mechanical pressure, GBM cell lines U87 and U251 and patient-derived neural oncospheres upregulated the expression of urokinase-type plasminogen activator (uPA) and/or matrix metalloproteinases (MMPs) as well as some of the EMT markers tested. The adherent cell lines invaded more when placed in media of increased osmolality. Therefore, GBM respond to osmotic or mechanical pressure by increasing matrix degrading enzyme production, and adopting a phenotype reminiscent of EMT. Better understanding the molecular and cellular mechanisms by which increased pressure promotes GBM invasiveness may help to develop innovative therapeutic approaches.

GFAP alternative splicing regulates glioma cell-ECM interaction in a DUSP4-dependent manner

Gliomas are the most common primary brain tumors. Their highly invasive character and the heterogeneity of active oncogenic pathways within single tumors complicate the development of curative therapies and cause poor patient prognosis. Glioma cells express the intermediate filament protein glial fibrillary acidic protein (GFAP), and the level of its alternative splice variant GFAP-δ, relative to its canonical splice variant GFAP-α, is higher in grade IV compared with lower-grade and lower malignant glioma. In this study we show that a high GFAP-δ/α ratio induces the expression of the dual-specificity phosphatase 4 (DUSP4) in focal adhesions. By focusing on pathways up- and downstream of DUSP4 that are involved in the cell-extracellular matrix interaction, we show that a high GFAP-δ/α ratio equips glioma cells to better invade the brain. This study supports the hypothesis that glioma cells with a high GFAP-δ/α ratio are highly invasive and more malignant cells, thus making GFAP alternative splicing a potential therapeutic target.-Van Bodegraven, E. J., van Asperen, J. V., Sluijs, J. A., van Deursen, C. B. J., van Strien, M. E., Stassen, O. M. J. A., Robe, P. A. J., Hol, E. M. GFAP alternative splicing regulates glioma cell-ECM interaction in a DUSP4-dependent manner.

Overexpression of protease-activated receptor type 1 (PAR-1) in glioblastoma multiforme WHO IV cells and blood vessels revealed by NCAM-assisted glioblastoma border labeling

Glioblastomas are neuroepithelial tumors with lost cellular differentiation and tenfold increased growth rates compared to low-grade gliomas. Despite of very aggressive treatment options based on surgery, irradiation, and chemotherapy, the prognosis of affected patients has remained poor and showed only slight improvements during the last 30 years. Research on glioblastoma border zone was hindered by the tumor's intense invasion into the brain parenchyma and the lack of suitable tumor cell markers. Nevertheless, the compact tumor mass and tumor invasion zone are composed of distinct cell types that need to be distinguished from each other to be addressed selectively. As the isoform 140 of the neural cell adhesion molecule (NCAM-140) was recently demonstrated to be lost in human gliomas with rising WHO grade, human multiform glioblastomas were characterized as a NCAM-140 negative entity displaying three main distinct invasion patterns. Evaluation of putative therapy targets within the tumor tissue and tumor invasion zone has been made possible through NCAM-140 negativity. In the present study, brain tissue controls and human glioblastoma samples with compact tumor mass and invasion areas were analyzed for their vascularization at the tumor border and the expression of thrombin receptor protease-activated receptor type 1 (PAR-1) within tumor tissue and vascular vessel walls. Use of NCAM-140 enabled the identification of the tumor invasion zone and its experimental investigation. Tissue vascularization was found to be significantly increased in the compact tumor mass of glioblastomas compared to their invasion zone and tumor-free controls with a significantly high and specific overexpression of PAR-1 within tumor cells and within tumor blood vessels depending upon the tumor area. This suggests thereby a functional role of the thrombin receptor PAR-1 in glioma cell malignancy and glioblastoma neoangiogenesis.

The microtubule binding drug EM011 inhibits the growth of paediatric low grade gliomas

Low grade gliomas are a heterogeneous group of tumours representing the most common form of neoplasms in the central nervous system among children. Although gross total resection remains the principal treatment, it is often impractical especially for the resection of tumours within eloquent regions of the brain. Instead Radiotherapy is utilised in such cases, but because of its associated toxicities, it is refrained from use among younger children. These limitations coupled with hypersensitivity and toxicities associated with some commonly used chemotherapeutic agents, have ignited the need to search for safer and more effective treatments for paediatric low grade gliomas. In this study, we investigated the EM011 drug on the growth of two pilocytic and one diffuse paediatric astrocytoma cell lines, using an assortment of cancer assays. We discovered that treatments of low grade gliomas with EM011 abrogated cell viability by inducing a decrease in cell proliferation and an arrest in the S and G2M cell cycle phases, followed by a converse increase in apoptosis in a dose and time dependent manner. The cell migratory and invasion indices, as well as anchorage independent growth in soft agarose, were significantly attenuated. These findings were mechanistically associated with a transient release of AIF, a disruption of microtubule architecture, and a decline in the expression of key genes which drive cancer progression including EGFR, mTORC1, JUN and multiple MMPs. In fact, the activity of MMP2 was also perturbed by EM011. These findings, in conjunction with the insignificant adverse side effects established from other studies, make EM011 an appealing chemotherapeutic agent for the treatment of paediatric low grade gliomas.

Differential expression of oxidative stress and extracellular matrix remodeling genes in low- or high-dose-rate photon-irradiated skin

Changes in the expression of genes implicated in oxidative stress and in extracellular matrix (ECM) remodeling and selected protein expression profiles in mouse skin were examined after exposure to low-dose-rate or high-dose-rate photon irradiation. ICR mice received whole-body γ rays to total doses of 0, 0.25, 0.5 and 1 Gy at dose rates of 50 cGy/h or 50 cGy/min. Skin tissues were harvested for characterization at 4 h after irradiation. For oxidative stress after low-dose-rate exposure, 0.25, 0.5 and 1 Gy significantly altered 27, 23 and 25 genes, respectively, among 84 genes assessed (P < 0.05). At doses as low as 0.25 Gy, many genes responsible for regulating the production of reactive oxygen species (ROS) were significantly altered, with changes >2-fold compared to 0 Gy. For an ECM profile, 18-20 out of 84 genes were significantly up- or downregulated after low-dose-rate exposure. After high-dose-rate irradiation, of 84 genes associated with oxidative stress, 16, 22 and 22 genes were significantly affected after 0.25, 0.5 and 1 Gy, respectively. Compared to low-dose-rate radiation, high-dose-rate exposure resulted in different ECM gene expression profiles. The most striking changes after low-dose-rate or high-dose-rate exposure on ECM profiles were on genes encoding matrix metalloproteinases (MMPs), e.g., Mmp2 and Mmp15 for low dose rate and Mmp9 and Mmp11 for high dose rate. Immunostaining for MMP-2 and MMP-9 proteins showed radiation dose rate-dependent differences. These data revealed that exposure to low total doses with low-dose-rate or high-dose-rate photon radiation induced oxidative stress and ECM-associated alterations in gene expression profiles. The expression of many genes was differentially regulated by different total dose and/or dose-rate regimens.

Ionizing radiation enhances matrix metalloproteinase-2 secretion and invasion of glioma cells through Src/epidermal growth factor receptor-mediated p38/Akt and phosphatidylinositol 3-kinase/Akt signaling pathways

Glioblastoma is a severe type of primary brain tumor, and its highly invasive character is considered to be a major therapeutic obstacle. Several recent studies have reported that ionizing radiation (IR) enhances the invasion of tumor cells, but the mechanisms for this effect are not well understood. In this study, we investigated the possible signaling mechanisms involved in IR-induced invasion of glioma cells. IR increased the matrix metalloproteinase (MMP)-2 promoter activity, mRNA transcription, and protein secretion along with the invasiveness of glioma cells lacking functional PTEN (U87, U251, U373, and C6) but not those harboring wild-type (WT)-PTEN (LN18 and LN428). IR activated phosphatidylinositol 3-kinase (PI3K), Akt, and mammalian target of rapamycin, and blockade of these kinases by specific inhibitors (LY294002, Akt inhibitor IV, and rapamycin, respectively) and transfection of dominant-negative (DN) mutants (DN-p85 and DN-Akt) or WT-PTEN suppressed the IR-induced MMP-2 secretion in U251 and U373 cells. In addition, inhibitors of epidermal growth factor receptor (EGFR; AG490 and AG1478), Src (PP2), and p38 (SB203580), EGFR neutralizing antibody, and transfection of DN-Src and DN-p38 significantly blocked IR-induced Akt phosphorylation and MMP-2 secretion. IR-induced activation of EGFR was suppressed by PP2, whereas LY294002 and SB203580 did not affect the activations of p38 and PI3K, respectively. Finally, these kinase inhibitors significantly reduced the IR-induced invasiveness of these cells on Matrigel. Taken together, our findings suggest that IR induces Src-dependent EGFR activation, which triggers the p38/Akt and PI3K/Akt signaling pathways, leading to increased MMP-2 expression and heightened invasiveness of PTEN mutant glioma cells.

C6 glioma cell insoluble matrix components enhance interferon-gamma-stimulated inducible nitric-oxide synthase/nitric oxide production in BV2 microglial cells

Microglia are the primary central nervous system immune effector cells. Microglial activation is linked to interactions with extracellular cytokines and the extracellular matrix (ECM). Astrocytomas are characterized by their diffuse nature, which is regulated by insoluble ECM components produced by the tumor cells that are largely absent from normal central nervous system tissue. The present study examined the influence of astrocytoma (C6 rat glioma) insoluble matrix components on interferon-gamma (IFN-gamma)-mediated inducible nitric-oxide synthase (iNOS) induction in microglial cells. We found that IFN-gamma-stimulated iNOS induction and nitric oxide release was greater in microglia cultured on C6 glioma cell-derived matrices compared with microglia cultured on primary rat astrocyte-derived matrices. Culture of microglia on C6 glioma cell-derived matrices also led to activation of STAT1, augmentation of IFN-gamma-induced STAT-3 activation, and an increase in IFN-gamma-activated site (GAS)-luciferase reporter activity. In addition, culture of microglia on C6 glioma cell-derived matrices activated NF-kappaB DNA binding activity and transcriptional activity. The results suggest that insoluble matrix components derived from malignant glioma cells can regulate microglia activation. These factors may include ECM components, such as fibronectin, collagen, laminin, vitronectin, and other nondiffusible compounds, and laminin seems to a critical regulator of this process. Microglia activation and subsequent brain inflammation may influence tumor growth, treatment, and metastasis. Better understanding of the regulation of microglial activation by astrocytoma-derived insoluble matrix components may be important in the development of immune-based treatment strategies against malignant brain tumors.

Subventricular zone-derived neuroblast migration to the olfactory bulb is modulated by matrix remodelling

In the rodent brain neural progenitor cells are born in the subventricular zone and migrate along a pathway called the rostral migratory stream (RMS) into the olfactory bulb where they differentiate into several classes of interneurones. In the adult, tangential migration in the RMS takes place in 'chains' of cells contained within glial tubes. In contrast, neonatal neuroblasts along the RMS lack these defined glial tubes and chains, migrating instead as individual cells. Time-lapse confocal microscopy of neuroblasts at each of these ages shows that individual cells migrate in a saltatory manner with bursts of high speed followed by periods of slower speed. Tangential migration within a glial tube is 20% faster than migration as individual cells. Neuroblasts may also interact and modify the extracellular matrix during migration through expression of a family of proteins, the matrix metalloproteinases (MMPs). MMPs are present and active along the subventricular zone-olfactory bulb pathway. In the presence of inhibitors of MMPs, neuroblast migration rates were reduced only when cells migrate individually. Chain migration in the adult was unaffected by MMP inhibitors. Taken together, these data suggest that MMPs only influence migration as individual cells and not as chains.

Macrophage migration inhibitory factor: a mediator of matrix metalloproteinase-2 production in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by destruction of bone and cartilage, which is mediated, in part, by synovial fibroblasts. Matrix metalloproteinases (MMPs) are a large family of proteolytic enzymes responsible for matrix degradation. Macrophage migration inhibitory factor (MIF) is a cytokine that induces the production of a large number of proinflammatory molecules and has an important role in the pathogenesis of RA by promoting inflammation and angiogenesis. In the present study, we determined the role of MIF in RA synovial fibroblast MMP production and the underlying signaling mechanisms. We found that MIF induces RA synovial fibroblast MMP-2 expression in a time-dependent and concentration-dependent manner. To elucidate the role of MIF in MMP-2 production, we produced zymosan-induced arthritis (ZIA) in MIF gene-deficient and wild-type mice. We found that MMP-2 protein levels were significantly decreased in MIF gene-deficient compared with wild-type mice joint homogenates. The expression of MMP-2 in ZIA was evaluated by immunohistochemistry (IHC). IHC revealed that MMP-2 is highly expressed in wild-type compared with MIF gene-deficient mice ZIA joints. Interestingly, synovial lining cells, endothelial cells, and sublining nonlymphoid mononuclear cells expressed MMP-2 in the ZIA synovium. Consistent with these results, in methylated BSA (mBSA) antigen-induced arthritis (AIA), a model of RA, enhanced MMP-2 expression was also observed in wild-type compared with MIF gene-deficient mice joints. To elucidate the signaling mechanisms in MIF-induced MMP-2 upregulation, RA synovial fibroblasts were stimulated with MIF in the presence of signaling inhibitors. We found that MIF-induced RA synovial fibroblast MMP-2 upregulation required the protein kinase C (PKC), c-jun N-terminal kinase (JNK), and Src signaling pathways. We studied the expression of MMP-2 in the presence of PKC isoform-specific inhibitors and found that the PKCdelta inhibitor rottlerin inhibits MIF-induced RA synovial fibroblast MMP-2 production. Consistent with these results, MIF induced phosphorylation of JNK, PKCdelta, and c-jun. These results indicate a potential novel role for MIF in tissue destruction in RA.

Insoluble matrix components of glioma cells suppress LPS-mediated iNOS/NO induction in microglia

This study examines the influence of insoluble matrix components of glioma (astrocytoma) cells on LPS-mediated inducible nitric oxide (NO)/NO synthase (iNOS) induction in microglia cells. Insoluble matrix components prepared from C6 rat glioma cells strongly suppressed iNOS induction and subsequent NO release induced by LPS. Matrices prepared from several glioma cell lines displayed similar inhibitory effects on LPS-induced NO/iNOS induction, whereas matrices from primary cultured rat astrocytes had a minimal influence. Of the various purified ECM materials examined, collagen suppressed LPS-mediated iNOS/NO induction in microglia. C6 matrices potentiated LPS-induced NF-kappaB DNA binding/transcriptional activity, suggesting that the suppression of LPS-induced iNOS by C6 matrices is NF-kappaB independent. C6 matrices inhibited LPS-mediated activation of p38 and JNK MAP kinases. This study shows that non-diffusible factors derived from astrocytoma cells in the brain are critically involved in the suppression of microglial cell activation. Our results indicate that activation of microglia can be regulated by various cellular and pathological environmental conditions, not only through cell-cell contact or soluble factors, but also via insoluble matrix components.

Discoidin domain receptor-1a (DDR1a) promotes glioma cell invasion and adhesion in association with matrix metalloproteinase-2

Invasion of glioma cells involves the attachment of invading tumor cells to extracellular matrix (ECM), disruption of ECM components, and subsequent cell penetration into adjacent brain structures. Discoidin domain receptor 1 (DDR1) tyrosine kinases constitute a novel family of receptors characterized by a unique structure in the ectodomain (discoidin-I domain). These cell surface receptors bind to several collagens and facilitate cell adhesion. Little is known about DDR1 expression and function in glioblastoma multiforme. In this study we demonstrate that DDR1 is overexpressed in glioma tissues using cDNA arrays, immunohistochemistry and Western blot analysis. Functional comparison of two splice variants of DDR1 (DDR1a and DDR1b) reveal novel differences in cell based glioma models. Overexpression of either DDR1a or DDR1b caused increased cell attachment. However, glioma cells overexpressing DDR1a display enhanced invasion and migration. We also detect increased levels of matrix metalloproteinase-2 in DDR1a overexpressing cells as measured by zymography. Inhibition of MMP activity using MMP inhibitor suppressed DDR1a stimulated cell-invasion. Similarly, an antibody against DDR1 reduced DDR1a mediated invasion as well as the enhanced adhesion of DDR1a and DDR1b overexpressing cells. These results suggest that DDR1a plays a critical role in inducing tumor cell adhesion and invasion, and this invasive phenotype is caused by activation of matrix metalloproteinase-2.

Expression of extracellular matrix-degrading proteins in classic, atypical, and anaplastic meningiomas

Although the majority of meningiomas, commonly benign tumors (WHO I), are amenable to surgical resection, a percentage of up to 3% will recur as higher-grade meningiomas with potential brain invasion. Our study aims at the in situ identification of proteolytic, extracellular matrix-degrading enzymes in a broad spectrum of meningiomas. We examined 80 meningiomas (50 classic meningiomas WHO I, 19 meningiomas WHO II, including atypical, chordoid, and clear cell types, as well as 11 anaplastic meningiomas WHO III) for the immunohistochemical expression patterns of cathepsin D and metalloproteinases MMP-2 and MMP-9. Meningiomas of all types and grades revealed a distinct expression of MMP-9 and cathepsin D, while MMP-2 was found predominantly in WHO II and III meningiomas. There was a significant increase in positive tumor cells from WHO grade I to II and III for MMP-2 (p<0.001), but not for cathepsin D (p=0.099). MMP-9 displayed an increased number of positive tumor cells from WHO grade I to II, but a decrease in WHO III meningiomas (p<0.002). Routine screening for the expression of metalloproteinases and cathepsin D will not reveal any new diagnostically or prognostically relevant information. However, these factors may represent a potential target for pharmacological blocking as an anti-invasive therapy.

Activation of MMP-2 and MMP-9 in patients with oral squamous cell carcinoma

BACKGROUND AND OBJECTIVES

Oral cancer accounts for one third of all malignancies in India where habit of tobacco consumption is the major etiologic factor, which causes field cancerization in oral mucosa. Multiple molecular events in oral mucosa due to field cancerization may be the cause of local and regional lymph node involvement in oral cancer resulting into low overall survival, high recurrence rate, and poor prognosis. Several matrix metalloproteinases (MMPs) have been shown to play an important role in the invasion and metastasis of oral squamous cell carcinoma (SCC). MMP-2 and MMP-9 are capable of degrading type-IV collagen, which is a major component of basement membrane. Therefore, we studied MMP-2 and MMP-9 activation by gelatin zymography, which is cost effective alternate to ELISA method, in patients with oral SCCs to predict their role in metastatic potentials.

MATERIALS AND METHODS

Thirty-nine patients of oral SCCs were classified as non-metastatic (n = 28), and metastatic (n = 11) according to regional lymph node involvement. Malignant and adjacent normal tissues of the patients were collected at the time of surgery. Gelatin zymography was carried out using 7.5% polyacrylamide gel under non-denaturing and non-reducing conditions. Zymograms were analyzed densitometrically. Latent and active forms of MMP-2 and MMP-9 were expressed as ng/50 microg of protein.

RESULTS

Latent and active forms of MMP-2 and MMP-9 were significantly elevated in malignant tissues as compared to their adjacent normal tissues (P < 0.05). Total MMP-2 and MMP-9 activities were also significantly elevated in malignant tissues as compared to adjacent normal tissues (P = 0.005 and P = 0.028, respectively). Activation ratio of MMP-2 and MMP-9 were significantly elevated in malignant tissues as compared to adjacent normal tissues. Activation of MMP-2 was prominent (11%) than MMP-9 (5%) in malignant tissues. Activation ratio of MMP-2 was significantly elevated in patients with lymph node metastasis than patients without lymph node metastasis (P = 0.005). Receiver's operating characteristic (ROC) curve analysis revealed that activation ratio of MMP-2 discriminate better than and activation ratio of MMP-9 between patients with and without lymph node metastasis. Activation ratio of MMP-2 could predict risk of lymph node metastasis development in patients without lymph node involvement.

CONCLUSION

The study concluded that activation of MMP-2 and MMP-9 was significantly higher in malignant tissues as compared to adjacent normal tissues. Further, activation ratio of MMP-2 was significantly elevated in patients with lymph node metastasis as compared to patients without lymph node metastasis, which could predict risk of lymph node metastasis development in node negative patients.

ADAM23 methylation and expression analysis in brain tumors

The ADAMs comprises a family of cell surface proteins with putative roles in cell-cell and/or cell-matrix interactions and in protease activities. In this work, we have examined the expression level and the methylation status of the 5' upstream region of the adhesion molecule ADAM23 in two brain tumor cell lines (A172 and T98G) as well as in three primary brain tumors (one grade II astrocytoma and two meningiomas) and 15 glioblastoma xenografts. Using bisulfite sequencing we verified that the percentage of methylated dinucleotides is higher in T98G when compared to A172 and that methylation significantly correlates with ADAM23 mRNA and protein expression. However, we were unable to detect methylation and down-regulation of the ADAM23 gene in brain tumors. Together, these results indicate that ADAM23 down-regulation by methylation in brain tumors is a rare event and it may help explain why brain tumor metastases are rarely found elsewhere in the body.

Microregional extracellular matrix heterogeneity in brain modulates glioma cell invasion

The invasion of neoplastic cells into healthy brain tissue is a pathologic hallmark of gliomas and contributes to the failure of current therapeutic modalities (surgery, radiation and chemotherapy). Transformed glial cells share the common attributes of the invasion process, including cell adhesion to extracellular matrix (ECM) components, cell locomotion, and the ability to remodel extracellular space. However, glioma cells have the ability to invade as single cells through the unique environment of the normal central nervous system (CNS). The brain parenchyma has a unique composition, mainly hyaluronan and is devoid of rigid protein barriers composed of collagen, fibronectin and laminin. The integrins and the hyaluronan receptor CD44 are specific adhesion receptors active in glioma-ECM adhesion. These adhesion molecules play a major role in glioma cell-matrix interactions because the neoplastic cells use these receptors to adhere to and migrate along the components of the brain ECM. They also interact with the proteases secreted during glioma progression that degrade ECM allowing tumor cells to spread and diffusely infiltrate the brain parenchyma. The plasminogen activators (PAs), matrix metalloproteinases (MMPs) and lysosomal cysteine peptidases called cathepsins are also induced during the invasive process. Understanding the mechanisms of tumor cell invasion is critical as it plays a central role in glioma progression and failure of current treatment due to tumor recurrence from micro-disseminated disease. This review will focus on the impact of microregional heterogeneity of the ECM on glioma invasion in the normal adult brain and its modifications in tumoral brain.

The expression of matrix metalloproteinase-2 and -9 in human gliomas of different pathological grades

Matrix metalloproteinases (MMPs) have been implicated to play a critical role in glioma invasiveness. In this study, we aimed to investigate the expression of MMP-2 and MMP-9 in human gliomas of different degrees of malignancy, and evaluated the correlation between MMP-2 and MMP-9 expression in gliomas. The samples from 65 cases of glioma were divided into four groups according to the WHO classification: there were 16 cases of grade I, 17 cases of grade II, 20 cases of grade III, and 12 cases of grade IV. Normal brain samples served as the control group, and biopsy specimens were obtained from 8 glioma patients with a needle placed into the adjacent brain 1 cm from the margin after tumor resection. All the samples were stained with hematoxylin and eosin and immunohistochemistry. A computer-aided image-analysis system was employed to measure the integral optical density (IOD) of positive slides. No positive staining was found in the control group. The positive staining was localized in the cytoplasm of glioma cells, the extracellular matrix (ECM), the basement membrane (BM), and the endothelial cells of blood vessels. Positive staining rates increased significantly when the degree of malignancy of gliomas was elevated. The IOD value of MMP-2 and MMP-9 also indicated that the intensity of MMP-2 and MMP-9 expression was elevated significantly with the degree of malignancy of the gliomas. There was a positive correlation between MMP-2 and MMP-9 expression in gliomas. Glioma invasion and angiogenesis were particularly seen in the biopsied tissues, and MMP-9 immunostaining seemed to be much more intense and extensive than MMP-2 immunostaining in these samples. These results suggest that MMP-2 and MMP-9 staining in gliomas is localized in the cytoplasm of tumor cells, BM, and endothelial cells, and that MMP-2 and MMP-9 together play an important role in the invasiveness of gliomas, mediating the degradation of the ECM and angiogenesis. MMP-2 and MMP-9 could be molecular targets in the treatment of malignant glioma.

Anti-angiogenic agents for the treatment of brain tumors

It is accepted that novel therapeutic approaches are needed for the majority of patients with malignant brain tumors. The vascularity of many primary brain tumors and the encouraging preclinical studies suggest that antiangiogenic agents have the potential to become an important component of multimodality treatment of patients with brain tumors. The understanding of the biology of angiogenesis is improving rapidly, offering the hope for more specific vascular targeting of brain tumor neovasculature. Neuroimaging techniques evaluating the angiogenic process and the impact of antiangiogenic agents will be an important tool for the rapid development of these novel therapeutic agents.

Invasive behaviour of glioblastoma cell lines is associated with altered organisation of the cadherin-catenin adhesion system

As little is known about the role of cadherin-mediated cell-cell adhesion in astrocytes and its alteration in migrating and invasive glioblastomas, we investigated its molecular composition and organisation in primary cultured astrocytes and the T98G and U373MG glioblastoma cell lines. Biochemical and morphological analysis indicated that all three cell types express all of the structural components of the adhesion system, including the LIN-7 PDZ protein,a novel component involved in the organisation of the junctional domain in epithelia and neurons. However, only the astrocytes and T98G cells generated and maintained mature adhesive junctional domains to which LIN-7 was recruited. Alterations in the junctional domain of U373MG cells were associated with higher motility in a poly-L-lysine migration assay. When the T98G cells were cultured on Matrigel matrix, they acquired invasive properties but, despite unchanged cadherin adhesion system protein levels, the invasive T98G cell-cell contacts failed to accumulate LIN-7 and failed to mature. These results identify the LIN-7 PDZ protein as a marker of cell adhesion maturity and cell invasion and indicate that instability and disorganisation of cadherin-mediated junctions rather than reduced expression of cadherin-catenin system components are required to promote migration and invasiveness in glioblastoma cell lines.

Membrane-type matrix metalloproteinases (MT-MMPs): expression and function during glioma invasion

Membrane-type MMPs (MT-MMPs) constitute a growing subclass of recently identified matrix metalloproteinases (MMPs). In addition to the highly conserved MMP functional domains, the MT-MMPs have additional insertion sequences (IS) that confer unique functional roles. While most of the MMPs are secreted, the MT-MMPs are membrane associated and a number of these have cytoplasmic domains which may be important in cellular signaling. This membrane localization leads to focal areas of receptor recruitment and subsequent activity, thereby enhancing pericellular proteolysis in specific areas of contact within the brain interstitium. MT1-MMP is the best-characterized MT-MMP, the measure against which subsequently cloned homologues are compared. MT1-MMP activates proMMP2 via its interaction with TIMP2, which serves as an intermolecular bridge for proMMP2 binding to MT-MMPs. In addition to activation of proMMP2, MT-MMPs display intrinsic proteolytic activity towards extracellular matrix molecules (ECM), which is independent of MMP2 activation. The increased expression levels of several members of the MMP family have been shown to correlate with high-grade gliomas, including MTI-MMP. Despite improvements in the diagnosis and treatment of patients with glial tumors, they remain the most common and least curable brain cancer in adults. The ability of glioma cells to infiltrate surrounding brain tissue, and ultimately escape current therapeutic modalities, could potentially be minimized using anti-invasive therapies. Proteolysis is a necessary part of the invasion process, within which the MT-MMPs appear to play a central role. The development of pharmaceutical approaches that target expression and regulation of MT-MMPs may prove beneficial in targeting invading glioma cells.

Differential expression of matrix metalloproteinases 2 and 9 by glial Müller cells: response to soluble and extracellular matrix-bound tumor necrosis factor-alpha

Glial Müller cells are known to undergo functional and morphological changes during retinal proliferative disorders, but very little is known of the contribution of these cells to extracellular matrix deposition during retinal wound healing and gliosis. This study constitutes the first demonstration that retinal Müller cells express two major matrix metalloproteinases (MMPs), gelatinase A (MMP-2) and gelatinase B (MMP-9), implicated in cell migration and matrix degradation. Although mRNA and gelatinolytic activity of MMP-2 remained unchanged in cultured Müller cells, basal levels of MMP-9 mRNA observed after subculture at 24 hours, markedly declined after 48 or 72 hours. This correlated with the expression of MMP-9 gelatinolytic activity that peaked at 24 hours, but gradually decreased at 48 and 72 hours. Tumor necrosis factor-alpha, in both a soluble form or bound to collagen and fibronectin, increased MMP-9 mRNA and gelatinolytic activity, but not MMP-2 expression, and its effect could be blocked by anti-tumor necrosis factor-alpha antibodies. The results suggest that Müller cells may aid in the local control of extracellular matrix deposition during retinal proliferative disorders, and that interaction of these cells with matrix-bound cytokine may influence their pathological behavior. Control of Müller cell production of MMP-9 may constitute an important target for the design of new therapeutic approaches to treat and prevent retinal proliferative disease.

Membrane-type matrix metalloproteinases (MT-MMPs): expression and function during glioma invasion

Membrane-type MMPs (MT-MMPs) constitute a growing subclass of recently identified matrix metalloproteinases (MMPs). In addition to the highly conserved MMP functional domains, the MT-MMPs have additional insertion sequences (IS) that confer unique functional roles. While most of the MMPs are secreted, the MT-MMPs are membrane associated and a number of these have cytoplasmic domains which may be important in cellular signaling. This membrane localization leads to focal areas of receptor recruitment and subsequent activity, thereby enhancing pericellular proteolysis in specific areas of contact within the brain interstitium. MT1-MMP is the best-characterized MT-MMP, the measure against which subsequently cloned homologues are compared. MT1-MMP activates proMMP2 via its interaction with TIMP2, which serves as an intermolecular bridge for proMMP2 binding to MT-MMPs. In addition to activation of proMMP2, MT-MMPs display intrinsic proteolytic activity towards extracellular matrix molecules (ECM), which is independent of MMP2 activation. The increased expression levels of several members of the MMP family have been shown to correlate with high-grade gliomas, including MTI-MMP. Despite improvements in the diagnosis and treatment of patients with glial tumors, they remain the most common and least curable brain cancer in adults. The ability of glioma cells to infiltrate surrounding brain tissue, and ultimately escape current therapeutic modalities, could potentially be minimized using anti-invasive therapies. Proteolysis is a necessary part of the invasion process, within which the MT-MMPs appear to play a central role. The development of pharmaceutical approaches that target expression and regulation of MT-MMPs may prove beneficial in targeting invading glioma cells.

In vitro evaluation of reactive astrocyte migration, a component of tissue remodeling in glaucomatous optic nerve head

In order to improve understanding of remodeling events in the glaucomatous optic nerve head, the migration of optic nerve head astrocytes was studied in vitro. Since elevated intraocular pressure is an important stress factor identified in glaucomatous eyes, optic nerve head astrocytes were incubated under physical stress created by elevated hydrostatic pressure. In addition, they were incubated in the presence of a chemical stimulus, lipolysaccharide (LPS). Migration of reactivated astrocytes in the presence of these stressors was examined using chambers in which cell migration through extracellular matrix-coated pores is only possible following proteolytic digestion of the matrix. We observed that the migratory ability of optic nerve head astrocytes was approximately 4-6 times greater following exposure to elevated hydrostatic pressure or LPS for up to 48 h. Phosphoinositide 3-kinase, protein kinase C, and tyrosine kinase were found to be involved in the signal transduction for activated migration of optic nerve head astrocytes in response to elevated hydrostatic pressure or LPS. In addition, we observed that the stress-induced migration of optic nerve head astrocytes, which is accompanied by proteolytic degradation, resulted in the formation of culture cavities containing mucopolysaccharides. These in vitro findings provide a clearer understanding of the pathophysiologic mechanisms of characteristic tissue remodeling events that occur, in vivo, in the glaucomatous optic nerve head.

Production of MMPs in human cerebral endothelial cells and their role in shedding adhesion molecules

Matrix metalloproteinases (MMPs) are Zn2+-endopeptidases that seem to play an important role in chronic inflammatory diseases of the central nervous system by disrupting the blood-brain barrier (BBB) and mediating the destruction of myelin components. We therefore investigated the influence of the pro-inflammatory cytokine TNF-alpha. on the expression and activation of several MMPs in human cerebral endothelial cells (HCEC). HCEC constitutively express MMP-2 and MMP-3 mRNA, but only MMP-3 is upregulated on mRNA and protein level after TNF-alpha stimulation. MMP-9 and MMP-12 mRNA could only be detected under inflammatory conditions. Furthermore, MMPs are involved in shedding of cell surface molecules. We therefore investigated the influence of MMPs on the release of soluble adhesion molecules using marimastat, a specific broad-spectrum MMP inhibitor and other protease inhibitors like aprotinin or leupeptin. Only marimastat inhibited the TNF-alpha mediated release of sVCAM-1 in the supernatants of HCEC. Western blot results of culture supernatants supported the time dependent release of the complete extracellular portion of the VCAM-1 molecule. These data suggest that MMPs produced by HCEC are actively involved in the shedding of soluble adhesion molecules at the BBB.

Adhesive and invasive features in gliomas

This study aims at the in situ identification of factors mediating glioma cell invasion requiring adhesion, extracellular matrix degradation, and migration. Forty-five gliomas (astrocytomas, glioblastomas, oligodendrogliomas, and mixed gliomas) were investigated for the immunohistochemical expression of the membrane protein CD44s, the basal lamina proteins laminin, collagen IV, and fibronectin, the lectin galectin-3 recognizing tenascin and N-CAM, as well as for the matrix-degrading enzymes metalloproteinases MMP-2, MMP-9, and cathepsin D. Besides vessels expressing basal lamina proteins, tenascin, MMP-2, MMP-9, and galectin-3, tumor cells revealed strong immunoreactivity for CD44s, tenascin, galectin-3, and N-CAM, which was restricted to solid tumor masses. Single invading cells displayed distinct expression of MMP-2 and MMP-9, also found in solid tumor areas, as well as of cathepsin D. Restricted expression of CD44s, galectin-3, tenascin, and N-CAM in solid tumor masses seems to contribute to homotypical tumor cell adhesion. However, switching to an invasive phenotype, single tumor cells lack this expression pattern and acquire degrading and phagocytic activities by expressing cathepsin D, MMP-2, and MMP-9, which are also expressed by solid tumor masses facilitating the loosening and invasion of single neoplastic cells. The blocking of these factors may be of potential benefit in anti-invasive therapy.

Roles of membrane type 1 matrix metalloproteinase and tissue inhibitor of metalloproteinases 2 in invasion and dissemination of human malignant glioma

OBJECT

Acquisition of invasive and metastatic potentials through proteinase expression is an essential event in tumor progression. Among proteinases, matrix metalloproteinases (MMPs) are thought to play a key role in tumor progression through the degradation of the extracellular matrix. In the present study, the authors examined the role of MMP-2 (gelatinase A) and membrane type 1 MMP (MT1-MMP), an activator of the zymogen of MMP-2, proMMP-2, together with tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2) in the invasion of astrocytic tumors in humans.

METHODS

Analyses performed using sandwich enzyme immunoassays demonstrated that the production levels of pro-MMP-2 and TIMP-1, but not TIMP-2, are significantly higher in glioblastomas multiforme than in other grades of astrocytic tumors. Quantitative reverse transcription-polymerase chain reaction indicated that MT1-MMP is expressed predominantly in glioblastoma tissues, and its expression levels are significantly enhanced as tumor grade increases. In addition, the expression levels and proMMP-2 activation ratio were remarkably higher in glioblastomas associated with cerebrospinal fluid (CSF) dissemination than in those not associated with CSF dissemination. In contrast, an examination of TIMP-2 levels showed a reverse correlation. Like MT1-MMP, TIMP-1 and TIMP-2 were immunolocalized to neoplastic cells in glioblastoma samples. To study the roles of these molecules in the invasion of astrocytic tumors more fully, stable transfectants expressing the MT1-MMP gene were developed in a U251 human glioblastoma cell line. The MT1-MMP transfectants displayed prominent activation of proMMP-2 and invasive growth in three-dimensional collagen gel; however, mock transfectants and parental cells displayed noninvasive growth without the activation. The invasion and gelatinolytic activity of the transfectants were completely inhibited by addition of recombinant TIMP-2, but not recombinant TIMP-1.

CONCLUSIONS

These results indicate that MT1-MMP may contribute to tumor invasion and CSF dissemination of glioblastoma cells on the basis of an imbalance of TIMP-2.

Matrix metalloproteinase 2 (MMP-2) immunoreactive protein is associated with poor grade and survival in brain neoplasms

Matrix metalloproteinases play an important role in the invasion of tumor cells and the progression of cancer. The 72 kDa type IV collagenase, a matrix metalloproteinase 2 (MMP-2) has been shown to contribute to the invasion and metastasis in diverse malignant neoplasms.

OBJECT

To elaborate the potential role of MMP-2 in brain tumor invasion we studied the expression and localization of this enzyme protein in 101 brain tumors representing different types of brain neoplasms. For the first time, we also correlated the expression of MMP-2 protein to patient survival.

METHODS

Using immunohistochemistry and a monoclonal antibody specific for MMP-2 we found that MMP-2 protein was primarily localized in tumor cells and vasculature cells as well as inflammatory cells. The expression of MMP-2 was absent or negligible in benign tumors (pilocytic astrocytoma and meningioma). Thirty-three percent (6/18) of astrocytomas, 38% (3/8) of anaplastic astrocytomas, 14% (1/7) of anaplastic oligodendrogliomas, 54% (19/35) of glioblastomas and 100% (6/6) of metastatic brain tumors were positive for MMP-2. A correlation between MMP-2 expression and survival was found in malignant brain tumors. The mean survival of patients with an MMP-2 negative tumor was 36 months, when it was only 7-14 months in patients with an MMP-2 positive tumor.

CONCLUSIONS

Our data suggest that MMP-2 is associated with histological malignancy and poor survival in brain tumors.

The expression and activation of matrix metalloproteinase-2 in rat brain after implantation of C6 rat glioma cells

It has been reported that matrix metalloproteinases (MMPs) are highly expressed in malignant glioma cells and that this increased expression may facilitate the invasiveness of tumor cells. The authors investigated the expression and enzymatic activity of MMPs in rat brain during the growth of malignant gliomas at different time intervals. C6 rat glioma cells were unilaterally implanted into rat cerebral hemispheres. After 7 or 14 days, these brain tissues were prepared for SDS-PAGE zymography, Western blotting, immunohistochemistry, and in situ zymography. SDS-PAGE zymography and Western blotting revealed that the expression of proMMP-2 in rat brains with C6 glioma cells was significantly higher than that in normal or the sham-operated rat brains, and that the activated form of MMP-2 was detected only in the former but not in the latter. On immunohistochemistry, C6 glioma cells presenting invasive growth into the rat brain parenchyma and vessels demonstrated MMP-2 immunoreactivity. On in situ zymography, foci of invasive C6 glioma cells in rat brain tissue showed gelatinolytic activity. These results suggest that expression and activation of MMP-2 may be one of the crucial steps for glioma cell invasion into the brain parenchyma in vivo.

Multi-agent cytostatic treatment of 'low-grade' gliomas

The rationale and current supporting evidence for a complementary, multi-agent, low-toxicity, chronic, cytostatic therapeutic approach to treating patients with gliomas is presented in detail. This strategy would involve the simultaneous treatment of patients with DNA/chromosomal stabilizing agent(s), anti-angiogenesis agent(s), and anti- invasion agent(s), with or without the addition of a low-toxicity antiproliferation agent. Oral agents would be the ideal for this chronic, potentially life-long, therapeutic approach. The most logical target group would be patients with newly diagnosed "low-grade" gliomas rather than those with more malignant (usually recurrent) gliomas.

Expression of matrix metalloproteinase-2 and -9 in oral squamous cell carcinomas with regard to the metastatic potential

In order to evaluate the significance of matrix metalloproteinases (MMPs) in predicting the metastatic potential of oral squamous cell carcinomas (SCCs), we compared MMP-2 and -9 expression in 19 metastasizing oral SCCs with that in 25 non-metastasizing cases by immunohistochemistry and gelatin zymography. Immunohistochemistry showed that increased MMP-2 expression was not significantly related to metastasis; increased MMP-9 expression found in oral SCCs was, however, statistically significant (oral SCCs with metastasis, 73.7%; those without metastasis, 36.0%; P<0.05). Gelatin zymography revealed no significant difference in the activated form of MMP-2 between metastasizing and non-metastasizing oral SCCs. In metastasizing SCCs, on the other hand, increases in the activated form of MMP-9 were significant. These results suggest that oral SCCs express MMP-2 and -9, and that MMP-9 may play a more important role than MMP-2 in the metastasis of oral SCCs to adjacent tissue. An analysis of MMP-9 expression may be useful for predicting the metastatic potential of oral SCCs.

Expression of matrix metalloproteinase-2 in glial and neuronal tumor cell lines: inverse correlation with proliferation rate

The expression of matrix metalloproteinases (MMPs) has been found to be positively correlated to the degree of malignancy in gliomas, indicating that poorly differentiated brain tumor cells produce more MMPs than differentiated ones. We determined the production of active MMP-2 in five glial (U138MG, U373MG, A172, C6, GOS-3), two neuronal (SK-N-SH, SK-N-MC), and two pluripotent cell lines with facultative neuronal and glial differentiation (P19 and NT2) by gelatin zymography. The MMP-2 activity profiles were compared to the proliferative activities of the cell lines. MMP-2 expression varied from barely existent (P19 cells) to strong (U138MG and SK-N-SH). Interestingly, for the cell lines with high MMP-2 expression levels, low proliferative activities were recorded, and vice versa. Retinoic acid induced neuronal differentiation and a reduction of proliferation of P19 cells; the differentiated cells produced significantly more MMP-2 than untreated cells. Upon confluency, GOS-3 cells showed reduced proliferation, but increased MMP expression. Thus, proliferative activity was inversely correlated to MMP-2 expression in the tumor cell lines analyzed.

Effects of epidermal growth factor and dibutyryl cyclic adenosine monophosphate on the migration pattern of astrocytes grafted into adult rat brain

OBJECTIVE

Neonatal rat astrocytes transplanted into host brains migrate in specific patterns, which are determined by the developmental stage of the host brain and the region of implantation. We hypothesized that the differentiation state of the implanted astrocytes could also affect astrocyte migration.

METHODS

Astrocytes derived from neonatal rats (1-4 d) were placed in culture and exposed to growth- or differentiation-promoting agents (e.g., epidermal growth factor or dibutyryl cyclic adenosine monophosphate). Treated cells were then injected into different regions of the adult rat brain. At 3, 6, and 9 days after implantation, the extent and pattern of astrocyte migration after injection into the cortex, hippocampus, and corpus callosum were assessed.

RESULTS

Astrocytes pretreated with either factor did not migrate during the first 3 days after implantation into the host cortex and hippocampus, whereas untreated cells migrated extensively by Day 3. After 9 days, implanted cells that had been pretreated with dibutyryl cyclic adenosine monophosphate began to demonstrate migratory activity, whereas those exposed to epidermal growth factor remained at the site of implantation. These findings corresponded to the effects of these agents in culture. On the other hand, cells implanted into the corpus callosum migrated in spite of pretreatment.

CONCLUSION

Epidermal growth factor and dibutyryl cyclic adenosine monophosphate each altered the cells in culture such that they were inhibited from migrating after transplantation into the host cortex and hippocampus. This finding suggests that the activation of either growth or differentiation cascades partially inhibits the migratory ability in these cells either through effects on their internal migratory potentials or their responsiveness to external migratory signals. In contrast, cells implanted into the corpus callosum migrated in spite of pretreatment, suggesting that this structure may present migratory cues sufficient to override the effects of treatment.

Matrix metalloproteinase 2 (gelatinase A) is related to migration of keratinocytes

The role of matrix metalloproteinases (MMPs) in cell migration was studied by measuring cell growth, migration, and production of MMP-2 and -9 in oral mucosal and skin keratinocytes cultured in the presence of synthetic MMP inhibitors. MMP-2 was the major gelatinolytic MMP produced by these cells while MMP-9 was produced at a low basal level. Inhibitor effects on MMP-9 production were therefore studied in keratinocytes stimulated by tumor necrosis factor alpha (TNFalpha). Tetracycline analogues at concentrations that inhibited the production of MMP-2 but not MMP-9 were able to drastically inhibit migration of both mucosal and skin keratinocytes. Tetracycline analogues also inhibited keratinocyte growth, an effect not found for the other inhibitors tested. Heterocyclic carbonate-derived compounds (LWs) that inhibited MMP-9 but not MMP-2 production had no effect on cell migration. Batimastat, a potent MMP inhibitor, did not have any effect on MMP production or cell growth but did inhibit keratinocyte migration. Tumor growth factor beta (TGFbeta) increased keratinocyte migration as well as both cell-associated and secreted MMP-2 production in wounded cell cultures. The secreted enzyme was partially converted into an active form. In this model batimastat totally blocked TGFbeta-promoted keratinocyte migration. Immunostaining of keratinocytes advancing into the wound revealed that MMP-2 was localized in extracellular matrix contactlike structures against the endogenously produced laminin-5-rich matrix. MMP-9 was localized diffusely along the cell membranes. Using in situ hybridization we observed that in chronically inflamed human gingiva MMP-2 is expressed in epithelium extending into subepithelial connective tissue. These results suggest that MMP-2 plays a specific role in epithelial migration, possibly by detaching the advancing cells from the pericellular matrix or by activating other MMPs.

Gelatinase-A (MMP-2), gelatinase-B (MMP-9) and membrane type matrix metalloproteinase-1 (MT1-MMP) are involved in different aspects of the pathophysiology of malignant gliomas

Matrix metalloproteinases (MMPs) have been implicated as important factors in gliomas since they may both facilitate invasion into the surrounding brain and participate in neovascularization. We have tested the hypothesis that deregulated expression of gelatinase-A or B, or an activator of gelatinase-A, MT1-MMP, may contribute directly to human gliomas by quantifying the expression of these MMPs in 46 brain tumour specimens and seven control tissues. Quantitative RT-PCR and gelatin zymography showed that gelatinase-A in glioma specimens was higher than in normal tissue; these were significantly elevated in low grade gliomas and remained elevated in GBMs. Gelatinase-B transcript and activity levels were also higher than in normal brain and more strongly correlated with tumour grade. We did not see a close relationship between the levels of expression of MT1-MMP mRNA and amounts of activated gelatinase-A. In situ hybridization localized gelatinase-A and MT1-MMP transcripts to normal neuronal and glia, malignant glioma cells and blood vessels. In contrast, gelatinase-B showed a more restricted pattern of expression; it was strongly expressed in blood vessels at proliferating margins, as well as tumour cells in some cases. These data suggest that gelatinase-A, -B and MT1-MMP are important in the pathophysiology of human gliomas. The primary role of gelatinase-B may lie in remodelling associated with neovascularization, whereas gelatinase-A and MT1-MMP may be involved in both glial invasion and angiogenesis. © 1999 Cancer Research Campaign

Gelatinase-A (MMP-2), gelatinase-B (MMP-9) and membrane type matrix metalloproteinase-1 (MT1-MMP) are involved in different aspects of the pathophysiology of malignant gliomas

Matrix metalloproteinases (MMPs) have been implicated as important factors in gliomas since they may both facilitate invasion into the surrounding brain and participate in neovascularization. We have tested the hypothesis that deregulated expression of gelatinase-A or B, or an activator of gelatinase-A, MT1-MMP, may contribute directly to human gliomas by quantifying the expression of these MMPs in 46 brain tumour specimens and seven control tissues. Quantitative RT-PCR and gelatin zymography showed that gelatinase-A in glioma specimens was higher than in normal tissue; these were significantly elevated in low grade gliomas and remained elevated in GBMs. Gelatinase-B transcript and activity levels were also higher than in normal brain and more strongly correlated with tumour grade. We did not see a close relationship between the levels of expression of MT1-MMP mRNA and amounts of activated gelatinase-A. In situ hybridization localized gelatinase-A and MT1-MMP transcripts to normal neuronal and glia, malignant glioma cells and blood vessels. In contrast, gelatinase-B showed a more restricted pattern of expression; it was strongly expressed in blood vessels at proliferating margins, as well as tumour cells in some cases. These data suggest that gelatinase-A, -B and MT1-MMP are important in the pathophysiology of human gliomas. The primary role of gelatinase-B may lie in remodelling associated with neovascularization, whereas gelatinase-A and MT1-MMP may be involved in both glial invasion and angiogenesis.

Expression and tissue localization of membrane-type 1, 2, and 3 matrix metalloproteinases in human astrocytic tumors

Three different membrane-type matrix metalloproteinases (MT1-, MT2-, and MT3-MMPs) are known to activate in vitro the zymogen of MMP-2 (pro-MMP-2, progelatinase A), which is one of the key MMPs in invasion and metastasis of various cancers. In the present study, we have examined production and activation of pro-MMP-2, expression of MT1-, MT2-, and MT3-MMPs and their correlation with pro-MMP-2 activation, and localization of MMP-2, MT1-MMP, and MT2-MMP in human astrocytic tumors. The sandwich enzyme immunoassay demonstrates that the production levels of pro-MMP-2 in the anaplastic astrocytomas and glioblastomas are significantly higher than that in the low-grade astrocytomas (P<0.05 and P<0.01, respectively), metastatic brain tumors (P<0.05), or normal brains (P<0.01). Gelatin zymography indicates that the pro-MMP-2 activation ratio is significantly higher in the glioblastomas than in other astrocytic tumors (P<0.01), metastatic brain tumors (P<0.01), and normal brains (P<0.01). The quantitative reverse transcription polymerase chain reaction analyses demonstrate that MT1-MMP and MT2-MMP are expressed predominantly in glioblastoma tissues (17/17 and 12/17 cases, respectively), and their expression levels increase significantly as tumor grade increases. MT3-MMP is detectable in both astrocytic tumor and normal brain tissues, but the mean expression level is approximately 50-fold lower compared with that of MT1-MMP and MT2-MMP in the glioblastomas. The activation ratio of pro-MMP-2 correlates directly with the expression levels of MT1-MMP and MT2-MMP but not MT3-MMP. In situ hybridization indicates that neoplastic astrocytes express MT1-MMP and MT2-MMP in the glioblastoma tissues (5/5 cases and 5/5 cases, respectively). Immunohistochemically, MT1-MMP and MT2-MMP are localized to the neoplastic astrocytes in glioblastoma samples (17/17 cases and 12/17 cases, respectively), which are also positive for MMP-2. In situ zymography shows gelatinolytic activity in the glioblastoma tissues but not in the normal brain tissues. These results suggest that both MT1-MMP and MT2-MMP play a key role in the activation of pro-MMP-2 in the human malignant astrocytic tumors and that the gelatinolytic activity is involved in the astrocytic tumor invasion.

Role of glial fibrillary acidic protein expression in the biology of human glioblastoma U-373MG cells

OBJECT

The relationship between glial fibrillary acidic protein (GFAP) expression and glial tumor cell behavior has not been well defined. The goal of this study was to examine this relationship further.

METHODS

To investigate the relationship between GFAP expression and glial tumor cell behavior, the authors isolated clones from the human glioblastoma cell line, U-373MG, according to their level of GFAP expression. Immunochemical analysis demonstrated that one clone had consistently low GFAP expression (approximately 93% of cells were GFAP negative), whereas a second clone had consistently high GFAP expression (approximately 80% of the cells were GFAP positive). The structure, population doubling time, saturation density, anchorage-independent growth, migratory rate, and invasive potential of these two clones were determined in relation to their level of GFAP expression. Morphologically, both clones were composed of ameboid as well as stellate components. Although the population doubling times of the two clones were equally rapid, the clone with low GFAP expression demonstrated a slightly higher saturation density compared with the clone with high GFAP expression. In an anchorage-independent environment (soft agar), a greater difference in growth characteristics was noted between the two clones: the high-expression clone formed more colonies and these colonies were compact, well defined, and spherical, whereas the low-expression clone formed predominantly smaller, two-dimensional colonies with vague boundaries and isolated cells or groups of cells at the periphery. In contrast to these minor differences between the clones, the low-expression clone showed a markedly increased migratory rate and invasive potential compared with the high-expression clone. Therefore, the clone with reduced GFAP expression appeared more aggressive, demonstrating decreased contact inhibition, increased migratory rate, and increased invasive potential.

CONCLUSIONS

These results suggest a direct correlation between GFAP expression and some measures of aggressive tumor growth and transformation properties.