Expression of 72 kDa type IV collagenase and invasion activity of human glioma cells

Matrix metalloproteinase profiling and their roles in disease

Matrix metalloproteinases (MMPs) play roles in remodelling of the extracellular matrix that occurs during morphogenesis, repair, and angiogenesis. Dysregulation of extracellular matrix remodelling can lead to cell proliferation, invasion, and tissue fibrosis. Identification of a specific MMP(s) in a disease has been challenging due to the presence of 24 closely-related human MMPs, each existing in three forms, of which only one is active and capable of catalysis. This review focuses on methods for MMP profiling, with particular emphasis on the batimastat affinity resin that binds only to the active forms of MMPs and related ADAMs (a disintegrin and metalloproteinases), which are then identified by mass spectrometry. Use of the batimastat affinity resin has identified targets for intervention in several human diseases.

Gradient hydrogels for screening stiffness effects on patient-derived glioblastoma xenograft cellfates in 3D

Brain cancer is a devastating disease given its extreme invasiveness and intricate location. Glioblastoma multiforme (GBM) is one of the most common forms of brain cancer, and cancer progression is often correlated with significantly altered tissue stiffness. To elucidate the effect of matrix stiffness on GBM cell fates, previous research is largely limited to 2D studies using immortalized cell lines, which has limited physiological relevance. The objective of the study is to develop gradient hydrogels with brain-mimicking stiffness range as a 3Din vitro GBM model for screening of the effects of matrix stiffness on GBM. To increase the physiological relevance, patient-derived tumor xenograft (PDTX) GBM cells were used. Our gradient platform allows formation of cell-containing hydrogels with stiffness ranging from 40 Pa to 1,300 Pa within a few minutes. By focusing on a brain-mimicking stiffness range, this gradient hydrogel platform is designed for investigating brain cancer. Increasing stiffness led to decreased GBM proliferation and less spreading, which is accompanied by downregulation of matrix-metalloproteinases (MMPs). Using temozolomide (TMZ) as a model drug, we demonstrate that increasing stiffness led to higher drug resistance by PDTX GBM cells in 3D, suggesting matrix stiffness can directly modulate how GBM cells respond to drug treatment. While the current study focuses on stiffness gradient, the setup may also be adapted for screening other cancer niche cues such as how biochemical ligand gradient modulates brain cancer progression and drug responses using reduced materials and time.

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.

Extracellular diffusion quantified by magnetic resonance imaging during rat C6 glioma cell progression

Solution reflux and edema hamper the convection-enhanced delivery of the standard treatment for glioma. Therefore, a real-time magnetic resonance imaging (MRI) method was developed to monitor the dosing process, but a quantitative analysis of local diffusion and clearance parameters has not been assessed. The objective of this study was to compare diffusion into the extracellular space (ECS) at different stages of rat C6 gliomas, and analyze the effects of the extracellular matrix (ECM) on the diffusion process. At 10 and 20 days, after successful glioma modeling, gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) was introduced into the ECS of rat C6 gliomas. Diffusion parameters and half-life of the reagent were then detected using MRI, and quantified according to the mathematical model of diffusion. The main ECM components [chondroitin sulfate proteoglycans (CSPGs), collagen IV, and tenascin C] were detected by immunohistochemical and immunoblot analyses. In 20-day gliomas, Gd-DTPA diffused more slowly and derived higher tortuosity, with lower clearance rate and longer half-life compared to 10-day gliomas. The increased glioma ECM was associated with different diffusion and clearance parameters in 20-day rat gliomas compared to 10-day gliomas. ECS parameters were altered with C6 glioma progression from increased ECM content. Our study might help better understand the glioma microenvironment and provide benefits for interstitial drug delivery to treat brain gliomas.

Release of tissue inhibitor of metalloproteinase-2 from alginate microcapsule encapsulating genetically engineered cells

Background

In this study, 293T cells were genetically engineered to secrete tissue inhibitor of metalloproteinase-2 (TIMP2) and encapsulated into alginate microcapsules to continuously release TIMP2 protein.

Methods

The anti-invasive potential of the microcapsules was studied in vitro using brain tumor cells. The TIMP2 gene was transfected to 293T cells, and genetically engineered 293TIMP2 cells were encapsulated into alginate microcapsules. Release of TIMP2 protein was detected with Western blot analysis and the anti-invasive potential against U87MG cells was tested using gelatin zymography and a Matrigel assay.

Results

Cell viability within the alginate microcapsules was maintained at a cell density of 5 × 10⁶. Because polycationic polymers are helpful for maintaining the mechanical strength of microcapsules with good cell viability, the alginate microcapsules were reinforced with chitosan (0.1% w/v). Expression of TIMP2 protein in cell lysates and secretion of TIMP2 into the conditioned medium was confirmed by Western blot analysis. Alginate microcapsules encapsulating 293TIMP2 cells released TIMP2 protein into the medium efficiently, where the TIMP2 protein participated in degradation of the matrix metalloproteinase-2 enzyme and inhibited invasion of U87MG cells.

Conclusion

Alginate microcapsules encapsulating 293TIMP2 cells are promising candidates for anti-invasive treatment of glioma.

The pathobiology of collagens in glioma

Malignant gliomas are characterized by a diffuse infiltration into the surrounding brain parenchyma. Infiltrating glioma cells exist in close proximity with components of the tumor microenvironment, including the extracellular matrix (ECM). Whereas levels of collagens in the normal adult brain are low, in glioma, collagen levels are elevated and play a vital role in driving tumor progression. This article provides a comprehensive overview of the nature of collagens found in gliomas and offers unique insight into the mechanisms by which cancer cells interact with this ECM via cellular factors such as integrins, discoidin domain receptors, and mannose receptors. Also discussed are the major remodeling pathways of brain tumor collagen, mediated primarily by matrix metalloproteinases, and the reciprocal relationship between these enzymes and the collagen receptors. Finally, a concluding perspective is offered on how the biophysical properties of the collagen ECM, in particular, mechanical stiffness and compliance, influence malignant outcome. A better understanding of the complex molecular interactions between glioma cells and the collagen ECM will provide new avenues to combat the rampant tumor progression and chemoresistance in brain cancer patients.

Downregulation of PAK5 inhibits glioma cell migration and invasion potentially through the PAK5-Egr1-MMP2 signaling pathway

PAK5 (p21 activated kinase 5) is upregulated in human colorectal carcinoma cells and is a known tumor promoter in carcinogenesis of the colon. Little is known regarding the mechanisms underlying the downstream targets of PAK5, and information concerning its biological significance in glioma is lacking. In this study, we investigated the effects of PAK5 on proliferation, migration, invasion, and apoptosis in human U87 and U251 glioma cells and examined the underlying molecular mechanism. We performed cell growth assays and cell cycle analysis to observe the cell proliferation. Flow cytometry analysis was performed to evaluate apoptosis, and in vitro scratch assays, cell migration assays, and gelatin zymography were performed to examine cell migration. Western blot analysis was performed to examine signal transduction in the cells. We demonstrated that suppression of PAK5 in glioma cells significantly inhibited cell migration and invasion. We also observed that suppression of PAK5 in human glioma cell lines inhibited cell growth because of G1 phase arrest. Additionally, flow cytometry and Western blot analysis indicated that PAK5 could inhibit cell apoptosis. These results suggest that the PAK5-Egr1-MMP2 signaling pathway is involved in tumor progression and may have a potential role in cancer prevention and treatment.

A complete compilation of matrix metalloproteinase expression in human malignant gliomas

Glioblastomas are characterized by an aggressive local growth pattern, a marked degree of invasiveness and poor prognosis. Tumor invasiveness is facilitated by the increased activity of proteolytic enzymes which are involved in destruction of the extracellular matrix of the surrounding healthy brain tissue. Elevated levels of matrix metalloproteinases (MMPs) were found in glioblastoma (GBM) cell-lines, as well as in GBM biopsies as compared with low-grade astrocytoma (LGA) and normal brain samples, indicating a role in malignant progression. A careful review of the available literature revealed that both the expression and role of several of the 23 human MMP proteins is controversely discussed and for some there are no data available at all. We therefore screened a panel of 15 LGA and 15 GBM biopsy samples for those MMPs for which there is either no, very limited or even contradictory data available. Hence, this is the first complete compilation of the expression pattern of all 23 human MMPs in astrocytic tumors. This study will support a better understanding of the specific expression patterns and interaction of proteolytic enzymes in malignant human glioma and may provide additional starting points for targeted patient therapy.

Full-length L1CAM and not its Δ2Δ27 splice variant promotes metastasis through induction of gelatinase expression

Tumour-specific splicing is known to contribute to cancer progression. In the case of the L1 cell adhesion molecule (L1CAM), which is expressed in many human tumours and often linked to bad prognosis, alternative splicing results in a full-length form (FL-L1CAM) and a splice variant lacking exons 2 and 27 (SV-L1CAM). It has not been elucidated so far whether SV-L1CAM, classically considered as tumour-associated, or whether FL-L1CAM is the metastasis-promoting isoform. Here, we show that both variants were expressed in human ovarian carcinoma and that exposure of tumour cells to pro-metastatic factors led to an exclusive increase of FL-L1CAM expression. Selective overexpression of one isoform in different tumour cells revealed that only FL-L1CAM promoted experimental lung and/or liver metastasis in mice. In addition, metastasis formation upon up-regulation of FL-L1CAM correlated with increased invasive potential and elevated Matrix metalloproteinase (MMP)-2 and -9 expression and activity in vitro as well as enhanced gelatinolytic activity in vivo. In conclusion, we identified FL-L1CAM as the metastasis-promoting isoform, thereby exemplifying that high expression of a so-called tumour-associated variant, here SV-L1CAM, is not per se equivalent to a decisive role of this isoform in tumour progression.

Stictamides A-C, MMP12 inhibitors containing 4-amino-3-hydroxy-5-phenylpentanoic acid subunits

An extensive study of the secondary metabolites produced by a new Sticta sp. of lichen has led to the isolation of three new compounds containing the 4-amino-3-hydroxy-5-phenylpentanoic acid residue (Ahppa). The structures of stictamides A-C (1-3) were assigned by 2D NMR spectroscopic and chemical methods. Due to extensive epimerization of the Ahppa residue observed after acid hydrolysis, the configuration of this unit was deduced through conversion of 1 to an appropriate derivative and application of our recently developed statine NMR database. Evaluation of stictamide A against a panel of disease-relevant proteases showed that it inhibited MMP12 at 2.3 μM and significantly reduced invasion in the human glioma cell line U87MG. Docking studies suggest that stictamide A inhibits MMP12 by a non-zinc-binding mechanism.

Role of ZNF143 in tumor growth through transcriptional regulation of DNA replication and cell-cycle-associated genes

The cell cycle is strictly regulated by numerous mechanisms to ensure cell division. The transcriptional regulation of cell-cycle-related genes is poorly understood, with the exception of the E2F family that governs the cell cycle. Here, we show that a transcription factor, zinc finger protein 143 (ZNF143), positively regulates many cell-cycle-associated genes and is highly expressed in multiple solid tumors. RNA-interference (RNAi)-mediated knockdown of ZNF143 showed that expression of 152 genes was downregulated in human prostate cancer PC3 cells. Among these ZNF143 targets, 41 genes (27%) were associated with cell cycle and DNA replication including cell division cycle 6 homolog (CDC6), polo-like kinase 1 (PLK1) and minichromosome maintenance complex component (MCM) DNA replication proteins. Furthermore, RNAi of ZNF143 induced apoptosis following G2/M cell cycle arrest. Cell growth of 10 lung cancer cell lines was significantly correlated with cellular expression of ZNF143. Our data suggest that ZNF143 might be a master regulator of the cell cycle. Our findings also indicate that ZNF143 is a member of the growing list of non-oncogenes that are promising cancer drug targets.

Comparative expression pattern of Matrix-Metalloproteinases in human glioblastoma cell-lines and primary cultures

Background

Glioblastomas (GBM), the most frequent malignant brain tumors in adults, are characterized by an aggressive local growth pattern and highly invasive tumor cells. This invasion is facilitated by expression of matrix metalloproteinases (MMPs), a family of zinc-dependent endopeptidases. They mediate the degradation of protein components of the extracellular matrix. Twenty-three family members are known. Elevated levels of several of them have been reported in GBM. GBM cell-lines are used for in vitro studies of cell migration and invasion. Therefore, it is essential to know their MMP expression patterns. Only limited data for some of the cell-lines are published, yet. To fill the gaps in our knowledge would help to choose suitable model systems for analysis of regulation and function of MMPs during GBM tumorigenesis, cell migration and invasion.

Findings

We analysed MMP-1, -8, -9, -10, -11, -13, -17, -19, -20, -21, -23, -24, -26, -27, and MMP-28 expression in seven GBM cell-lines (SNB-19, GaMG, U251, U87, U373, U343, U138) and in four primary cell cultures by semiquantitative RT-PCR, followed changes in the MMP expression pattern with increasing passages of cell culture and examined the influence of TNF-α and TGF-β1 stimulation on the expression of selected MMPs in U251 and U373 cells.

MMP-13, -17, -19 and -24 were expressed by all analyzed cell-lines, whereas MMP-20 and MMP-21 were not expressed by any of them. The other MMPs showed variable expression, which was dependent on passage number. Primary cells displayed a similar MMP-expression pattern as the cell-lines. In U251 and U373 cells expression of MMP-9 and MMP-19 was stimulated by TNF-α. MMP-1 mRNA expression was significantly increased in U373 cells, but not in U251 cells by this cytokine. Whereas TGF-β1 had no impact on MMP expression in U251 cells, it significantly induced MMP-11 and MMP-24 expression in U373 cells.

Conclusions

Literature-data and our own results suggest that the expression pattern of MMPs is highly variable, dependent on the cell-line and the cell-culture conditions used and that also regulation of MMP expression by cytokines is cell-line dependent. This is of high impact for the transfer of cell-culture experiments to clinical implementation.

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

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

Adenovirus-mediated transfer of siRNA against MMP-2 mRNA results in impaired invasion and tumor-induced angiogenesis, induces apoptosis in vitro and inhibits tumor growth in vivo in glioblastoma

Invasive tumors, including gliomas, utilize proteinases to degrade extracellular matrix components and diffuse into the adjacent tissues or migrate toward distant ones. In addition, proteinase activity is required for the formation of new blood vessels within the tumor. Levels of the proteinase matrix metalloproteinase-2 (MMP-2) are highly increased in gliomas. In this study, we examined the effect of the downregulation of MMP-2 via adenovirus-mediated siRNA in gliomas. Here, we show that siRNA delivery significantly decreased levels of MMP-2 in the glioblastoma cell lines U-87 and U-251. U-87 and U-251 cells showed impaired invasion through matrigel as well as decreased migration from tumor spheroids transfected with adenoviral vector expressing siRNA against MMP-2. Additionally, tumor-induced angiogenesis was decreased in in vitro experiments in cultured human microvascular endothelial cells (HMECs) in serum-free conditioned medium of glioblastoma cells transfected with these constructs and co-cultures of glioma cells with HMECs. We also observed decreased angiogenesis in the in vivo dorsal skin-fold chamber model. Moreover, MMP-2 inhibition induced apoptotic cell death in vitro, and suppressed tumor growth of preestablished U-251 intracranial xenografts in nude mice. Thus, specific targeting of MMP-2 may provide a novel, efficient approach for the treatment of gliomas and improve the poor outcomes of patients with these brain tumors.

RNA interference-mediated simultaneous down-regulation of urokinase-type plasminogen activator receptor and cathepsin B induces caspase-8-mediated apoptosis in SNB19 human glioma cells

The invasive character of gliomas depends on proteolytic cleavage of the surrounding extracellular matrix. Cathepsin B and urokinase-type plasminogen activator receptor (uPAR) together are known to be overexpressed in gliomas and, as such, are attractive targets for gene therapy. In the present study, we used plasmid constructs to induce the RNA interference (RNAi)-mediated down-regulation of uPAR and cathepsin B in SNB19 human glioma cells. We observed that the simultaneous down-regulation of uPAR and cathepsin B induces the up-regulation of proapoptotic genes and initiates a collapse in mitochondrial Deltapsi. Cathepsin B and uPAR down-regulated cells showed increases in the expression of activated caspase-8 and DFF40/caspase-activated DNase. Nuclear translocation of AIF and Fas ligand translocation to the cell membrane were also observed. Ki67 and X-linked inhibitor of apoptosis protein levels decreased, thereby indicating apoptosis. These results suggest the involvement of uPAR-cathepsin B complex on the cell surface and its role in maintaining the viability of SNB19 glioma cells. In conclusion, RNAi-mediated down-regulation of uPAR and cathepsin B initiates a partial extrinsic apoptotic cascade accompanied by the nuclear translocation of AIF. Our study shows the potential of RNAi-mediated down-regulation of uPAR and cathepsin B in developing new therapeutics for gliomas.

Aberrant FoxM1B expression increases matrix metalloproteinase-2 transcription and enhances the invasion of glioma cells

We recently showed that FoxM1 is overexpressed in human glioblastomas and that forced FoxM1B expression in anaplastic astrocytoma cells leads to the formation of highly invasive glioblastoma multiforme (GBM) in nude mice. However, the molecular mechanisms by which FoxM1 enhances glioma invasion are unknown. In this study, we found that FoxM1 overexpression increased matrix metalloproteinase (MMP)-2 expression in glioma cells, whereas blockade of FoxM1 expression suppressed MMP-2 expression. Transfection of FoxM1 into glioma cells directly activated the MMP-2 promoter, whereas inhibition of FoxM1 expression by FoxM1-siRNA suppressed its activation. We identified a FoxM1-binding site in the MMP-2 promoter and demonstrated that FoxM1 protein bound directly to it. Mutation of this FoxM1-binding site significantly attenuated MMP-2 promoter activity. Furthermore, FoxM1 overexpression increased the invasiveness of glioma cells, whereas inhibition of FoxM1 expression suppressed the invasiveness of GBM cells. Inhibition of MMP-2 by a specific MMP-2 inhibitor reversed the invasive phenotype of glioma cells overexpressing FoxM1. Finally, immunohistochemical analysis of 45 human GBM specimens showed a significant correlation between FoxM1 overexpression and elevated MMP-2 expression. Collectively, these findings provide evidence that FoxM1 contributes to glioma progression by enhancing MMP-2 gene transcription and thus tumor-cell invasion.

Signaling Pathways Mediating Manganese-Induced Toxicity in Human Glioblastoma Cells (U87)

Although essential, manganese (Mn) intake in excess leads to neurotoxicity. Mn neurotoxicity induces impairment of energy metabolism and ultimately cell death. Nevertheless, the signaling mechanisms underlying Mn toxicity are unknown. Employing human glioblastoma (U87) cells, we investigated several signaling pathways (ones promoting cellular proliferation and invasion) underlying Mn toxicity. Mn-treatment of U87 cells induced a down-regulation of MAPK pathway but the AKT pathway was not markedly affected. Mn-treatment of these cells induced decreases in their levels of c-Jun and c-Fos transcription factors and extracellular matrix degrading enzymes like MMP-2, which are associated with glioblastoma invasiveness. Mn-treatment also induced apoptosis in U87 cells. Thus, our results indicate that other than inducing apoptosis in U87 cells, Mn exerts differential effects on several signaling pathways promoting glioblastoma proliferation and invasion. Consequently, Mn may have pathophysiological roles in inducing apoptosis and in blocking glioblastoma invasion. Our results may thus have therapeutic implications.

Inhibition of matrix degrading enzymes and invasion in human glioblastoma (U87MG) cells by isoflavones

Glioblastoma multiforme is a primary brain tumor associated with extensive invasion into surrounding brain tissue. Matrix metalloproteinases (MMPs) and urokinase plasminogen activation (uPA) system are shown to be involved in tumor invasion as they help in degradation of extracellular matrix (ECM) proteins and thus assist in the movement of cells. MMP-2 and 9 were shown to be upregulated in gliomas, suggesting their involvement in invasion. Genistein and biochanin A are isoflavones commonly known as phytoestrogens and have some anticancer properties. We hypothesize that these two isoflavones can induce a lowering of tumor invasion by decreasing the activity of matrix degrading enzymes. In this study we investigated the effects of genistein and biochanin A on invasive activity of U87MG cells using the Calbiochem in vitro invasion assay system. Our results suggest that genistein and biochanin A induced a decrease in invasive activity of U87MG cells in a dose-related manner. Genistein also induced a decrease in EGF-stimulated invasion thereby implicating an involvement of EGF-mediated signaling in invasion. Our results also show that treatment of U87MG cells with the two isoflavones induced decreases in the enzymatic activity of MMP-9 and the protein levels of MT1-MMP and uPAR.

Proteases and glioma angiogenesis

Angiogenesis, the process by which new branches sprout from existing vessels, requires the degradation of the vascular basement membrane and remodeling of the ECM in order to allow endothelial cells to migrate and invade into the surrounding tissues. Serine, metallo, and cysteine proteinases are 3 types of a family of enzymes that proteolytically degrade various components of extracellular matrix. These proteases release various growth factors and also increase adhesive molecules and signaling pathway molecules upon their activation, which plays a significant role in angiogenesis. Downregulation of these molecules by antisense/siRNA or synthetic inhibitors decreases the levels of these molecules, inhibits the release of growth factors, and decreases the levels of various signaling pathway molecules, thereby leading to the inhibition of angiogenesis. Furthermore, MMPs degrade specific substrates and release angiogenic inhibitors which inhibit angiogenesis. Downregulation of 2 molecules, such as uPA and uPAR, uPAR and MMP-9, or Cathepsin B and MMP-9, are more effective to inhibit angiogenesis rather than downregulation of single molecules. However, careful testing of these combinations are most important because multiple effects of these combinations play a significant role in angiogenesis.

The potential use of MMP inhibitors to treat CNS diseases

The matrix metalloproteinases (MMPs) are considered to be the physiological mediators of extracellular matrix remodelling. MMPs are involved in a variety of functions and in the nervous system, these include angiogenesis and the extension of neuronal growth cones during development. However, it has become increasingly evident that the aberrant expression of MMPs in the nervous system contributes to diseases that include among others, multiple sclerosis, malignant gliomas, Alzheimer's disease and stroke. This review highlights the evidence that MMPs are involved in diseases of the nervous system, and provides information for the potential beneficial use of MMP inhibitors in NS disorders. However, the application of MMP inhibitors to treat CNS diseases must be balanced carefully against the beneficial roles normally played by MMPs in CNS physiology or recovery.

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.

Characterization of Mca-Lys-Pro-Leu-Gly-Leu-Dpa-Ala-Arg-NH2, a fluorogenic substrate with increased specificity constants for collagenases and tumor necrosis factor converting enzyme

Matrix metalloproteinases (MMPs) and the related tumor necrosis factor converting enzyme (TACE) are involved in tissue remodeling, cell migration, and processing of signaling molecules, such as cytokines and adhesion molecules. Fluorescence-quenched peptide substrates have been widely used to quantitate the actual enzymatic activity of MMPs. However, the various MMPs have very different specific activities toward these substrates. This restricts their value for the determination of composite proteolytic activity of mixtures of metalloproteinases in biological fluids. The N-terminal elongation of the most widely used MMP substrate (FS-1) with a Lys to the sequence Mca-Lys-Pro-Leu-Gly-Leu-Dpa-Ala-Arg-NH(2) (FS-6) yields a fluorogenic peptide with improved substrate properties. As compared to FS-1, the specificity constant (kcat/Km) of FS-6 for collagenases (MMP-1, MMP-8, MMP-13) and MT1-MMP (MMP-14) is increased two- to ninefold and threefold, respectively, while those for gelatinases and matrilysin remain equally high. Using high-performance liquid chromatography-fluorescence detection, MMP activity can be quantitated in the picomolar range. FS-6 shows up to twofold higher specificity constants (kcat/Km of 0.8x10(6)M(-1)s(-1)) for TACE, as compared to standard substrates Mca-PLAQAV-Dpa-RSSSAR-NH(2) and Dabcyl-LAQAVRSSSAR-EDANS. FS-6 is fully water soluble and thus allows measurement of metalloproteinase activity in tissue culture conditions, e.g., on the surface of viable cells in situ.

Targeting the over-expressed urokinase-type plasminogen activator receptor on glioblastoma multiforme

A recombinant fusion protein targeting the urokinase-type plasminogen activator receptor (uPAR) and delivering a potent catalytic toxin has the advantage of simultaneously targeting both over-expressed uPAR on glioblastoma cells and on the tumor neovasculature. Such a hybrid protein was synthesized consisting of the noninternalizing amino-terminal fragment (ATF) of urokinase-type plasminogen activator (uPA) for binding, and the catalytic portion of diphtheria toxin (DT) for killing, and the translocation enhancing region (TER) of DT for internalization. The protein was highly selective for human glioblastoma in vitro and in vivo. In vivo, this DT/ATF hybrid called DTAT caused the regression of small subcutaneous uPAR-expressing tumors with minimal toxicity to critical organs. In vitro, DTAT killed only uPAR-positive glioblastoma cell lines and human endothelial cells in the form of the HUVEC cell line. Killing was selective and blockable with specific antibody. DTAT was highly effective against tumor cells cultured from glioblastoma multiforme patients and in vitro mixing experiments combining DTAT with DTIL13 another highly effective anti-glioblastoma agent showed that the mixture was as toxic as the most potent immunotoxin. In this article, we review our progress to date with DTAT.

Apoptotic induction by BE16627B on human malignant glioma cell lines by an anti-matrix metalloproteinase agent

We have elucidated the pharmacological action of the anti-matrix metalloproteinase inhibitor BE16627B on glioma cells. The study was limited to the noncytotoxic dose range. The aim of the study was to investigate whether the cytotoxicity of BE16627B, an anti-MMP agent, is related to apoptosis in the human malignant glioma cell lines U87MG, U251MG, and U373MG. MTT assay was performed to detect the cytotoxic dose range. Agarose gel electrophoresis was performed with purified genomic DNA following exposure to 20 to 500 microM BE16627B for 24 h, compared with 0 microM for the control group. Transmission electron microscopy (TEM) was employed to study nuclear fragmentation following exposure to 0, 20, and 500 microM of the agent for 24 h. An in situ endolabeling assay was performed to determine the index of apoptotic induction. MTT assay revealed that concentrations of 100 microM and above were cytotoxic. DNA laddering was demonstrated in agarose gel electrophoresis. TEM disclosed condensing and fragmentation of the chromatin. None of these changes were observed in the control group and the noncytotoxic dose group. The in situ endolabeling study disclosed that the apoptotic index was significantly elevated by cytotoxic doses of this agent (U373MG; control, 4.0%; 500 microM, 68.5%). These results indicated that cytotoxic concentrations of BE16627B induced apoptosis in human malignant glioma cell lines. In our previous report, this agent inhibited activity of MMP in noncytotoxic concentrations. Further study should be done to determine the pharmacological action of toxic BE16627B.

Modulation of tissue-type plasminogen activator expression by platelet activating factor in human glioma cells

PURPOSE

For tumor growth, proteolytic remodeling of the extracellular matrix (ECM) is a key factor. To determine proteolytic activity in human glioma cells, fibrinolytic activity, mRNA expression of fibrinolytic factors, and fibrinolytic inhibitors were studied in human glioma cell lines. The effect of platelet activating factor (PAF), a potent mediator of inflammatory and immune responses, on this fibrinolytic activity was also examined.

METHODS

The fibrinolytic activities of conditioned medium and cell lysates from human glioma cell lines, A172, T98G, U87 and TM1 were studied by fibrin plate zymography. mRNA expression of tissue plasminogen activator (tPA), urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitors (PAI-1, PAI-2) was measured by Northern blot analysis. PAF was added to the medium, and its effects on cell proliferation, fibrinolytic activity, mRNA expression of plasminogens and inhibitors were studied.

RESULTS

mRNA expression of plasminogens and inhibitors differed between individual cell lines. Only the medium and cell lysates from A172 cells revealed fibrinolytic activity. A172 cells showed mRNA expression of tPA. PAF at low concentrations, such as 1 nM, stimulated A172 cell proliferation, and high concentrations of PAF inhibited proliferation. PAF stimulated tPA release into the conditioned medium. mRNA expression of tPA was stimulated by low concentrations of PAF and inhibited by high concentrations.

CONCLUSION

The variability of mRNA expression of plasminogen activators (PAs) between different glioma cell lines may indicate that plasminogens and their inhibitors do not directly correlate with brain tumor growth. PAF may be an important factor in the local control of fibrinolytic activity in glioma and its proliferation.

The role of matrix metalloproteinase genes in glioma invasion: co-dependent and interactive proteolysis

Matrix metalloproteinases (MMPs) are cation-dependent endopeptidases which have been implicated in the malignancy of gliomas. It is thought that the MMPs play a critical role in both metastasis and angiogenesis, and that interference with proteases might therefore deter local tumor dissemination and neovascularization. However, the attempt to control tumor-associated proteolysis will rely on better definition of the normal tissue function of MMPs, an area of study still in its infancy in the central nervous system (CNS). Understanding the role of MMP-mediated proteolysis in the brain relies heavily on advances in other areas of molecular neuroscience, most notably an understanding of extracellular matrix (ECM) composition and the function of cell adhesion molecules such as integrins, which communicate knowledge of ECM composition intracellularly. Recently, protease expression and function has been shown to be strongly influenced by the functional state and signaling properties of integrins. Here we review MMP function and expression in gliomas and present examples of MMP profiling studies in glioma tissues and cell lines by RT-PCR and Western blotting. Co-expression of MMPs and certain integrins substantiates the gathering evidence of a functional intersection between the two, and inhibition studies using recombinant TIMP-1 and integrin antisera demonstrate significant inhibition of glioma invasion in vitro. Use of promising new therapeutic compounds with anti-MMP and anti-invasion effects are discussed. These data underline the importance of functional interaction of MMPs with accessory proteins such as integrins during invasion, and the need for further studies to elucidate the molecular underpinnings of this process.

Proteases and the biology of glioma invasion

Despite optimal clinical treatment, the prognosis for malignant gliomas remains poor. One of the primary reasons for treatment failure is not diffuse dissemination, but local invasion. Recently, there has been an increase in information regarding specific molecules that determine the aggressiveness and invasion potential of high-grade astrocytic tumors. In particular, expression of matrix metalloproteases in high-grade gliomas appears to correlate with tissue invasiveness. It is the purpose of the present review to describe the connection between alterations in growth-related genes, protease activity, and tumor biology, and how these connections may suggest potential novel therapeutic targets.

The role of matrix metalloproteinase genes in glioma invasion: co-dependent and interactive proteolysis

Matrix metalloproteinases (MMPs) are cation-dependent endopeptidases which have been implicated in the malignancy of gliomas. It is thought that the MMPs play a critical role in both metastasis and angiogenesis, and that interference with proteases might therefore deter local tumor dissemination and neovascularization. However, the attempt to control tumor-associated proteolysis will rely on better definition of the normal tissue function of MMPs, an area of study still in its infancy in the central nervous system (CNS). Understanding the role of MMP-mediated proteolysis in the brain relies heavily on advances in other areas of molecular neuroscience, most notably an understanding of extracellular matrix (ECM) composition and the function of cell adhesion molecules such as integrins, which communicate knowledge of ECM composition intracellularly. Recently, protease expression and function has been shown to be strongly influenced by the functional state and signaling properties of integrins. Here we review MMP function and expression in gliomas and present examples of MMP profiling studies in glioma tissues and cell lines by RT-PCR and Western blotting. Co-expression of MMPs and certain integrins substantiates the gathering evidence of a functional intersection between the two, and inhibition studies using recombinant TIMP-1 and integrin antisera demonstrate significant inhibition of glioma invasion in vitro. Use of promising new therapeutic compounds with anti-MMP and anti-invasion effects are discussed. These data underline the importance of functional interaction of MMPs with accessory proteins such as integrins during invasion, and the need for further studies to elucidate the molecular underpinnings of this process.

Suppression of matrix metalloproteinase-2 and -9 mediated invasiveness by a novel matrix metalloproteinase inhibitor, BE16627B

Cell invasion is a nature of malignant gliomas, demeriting to many efforts of the treatment. Matrix metalloproteinase (MMP) is acknowledged as a key factor in this complicated process. The aim of this study was to investigate whether inhibition of MMP activity in malignant glioma cells could be achieved by a novel agent, BE16627B (BE). Malignant glioma cell lines, U87MG, U251MG, and U373MG, were employed to evaluate inhibitory effect on zymogram, type IV collagenolysis assay, and haptoinvasion assay for 24 h exposure of BE, following preliminar

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.

Up-regulation of urokinase-type plasminogen activator and its receptor correlates with enhanced invasion activity of human glioma cells mediated by transforming growth factor-alpha or basic fibroblast growth factor

Glioblastoma multiforme is a highly malignant tumor that is extremely refractory to therapy. One reason is its highly invasive nature into brain tissue. Metalloproteinases and their inhibitors, plasminogen activators (PA) and their inhibitors and cathepsins are thought to be involved in invasion by tumor cells. In this study, we determined if the urokinase-type plasminogen activator (uPA) and/or the urokinase-type plasminogen activator receptor (uPAR) were responsible for the invasion activity of a human glioma cell line. We determined the invasion activity of a human glioma U251 cell line using an in vitro invasion assay system. A 2.4- to 5.8-fold increase in invasion activity was observed in the presence of basic fibroblast growth factor (bFGF) or transforming growth factor (TGF)-alpha. Northern blot analysis showed that bFCF and TGF-alpha treatment was associated with increases in cellular mRNA levels of uPA and uPAR. Zymographic activity correlated to mRNA levels of uPA and uPAR. Addition of an anti-uPAR monoclonal antibody significantly inhibited the invasion activity induced by bFGF- and TGF-alpha. Irsogladine, an inhibitor of uPA synthesis, also blocked the invasion activity. These observations suggest that uPA and its receptor have a role in the invasion process of human gliomas.

Suppression of cell invasion on human malignant glioma cell lines by a novel matrix-metalloproteinase inhibitor SI-27: in vitro study

Matrix metalloproteinase (MMP) has come to be highlighted by its close relation to the cell invasion of gliomas. Suppression of MMP activity in malignant glioma cells would be meriting to local delivery of genes or chemotherapeutic agents. In this study, we employed a novel MMP inhibitor, SI-27 to investigate inhibition of cell invasiveness in human malignant glioma cell lines, U87MG, U251MG, and U373MG. We evaluated with zymogram, reverse zymogram, and cell invasion assay after exposure of SI-27 for 24 h followed by preliminary MTT assay to find non-cytotoxic dose range, 5, 10, 50, 100 microg/ml compared with non-treatment group as the control. Common to three glioma cell lines, zymogram disclosed that expressions of MMP-2 and -9 were suppressed in a dose-dependent fashion, meanwhile those of tissue inhibitor of MMP (TIMMP) in reverse zymogram were not. The numbers of invading cells through Boyden chamber were significantly reduced in a dose-dependent manner, while those with 5 microg/ml were not diminished common to those three lines. In conclusion, dose concentration ranging 10-100 microg/ml of SI-27 inhibited MMP-2 and -9 mediated cell invasiveness in malignant glioma cell lines. This is the first report for chemotherapeutic effect of SI-27 on glioma cells.

High-molecular-weight serum protein complexes differentially promote cell migration and the focal adhesion localization of the urokinase receptor in human glioma cells

The distribution of the urokinase-type plasminogen activator receptor (uPAR) on human glioma cells was examined as a function of culture conditions, using immunofluorescence and immunophotoelectron microscopy. Both uPAR colocalization with focal adhesion proteins and glioma cell motility were maximal in medium containing whole serum or a serum fraction retained by a 500,000 mol wt cutoff centrifugal concentration filter. High motility also took place in medium containing a serum fraction passed by the 500,000 cutoff filter but retained by a 100,000 cutoff filter and in minimal medium containing added vitronectin; however, under these conditions only a small percentage of the otherwise abundant focal adhesions contained colocalized uPAR. Glioma cells in minimal medium with added laminin migrated with a highly elongated morphology but without either classical focal adhesions or well-defined uPAR labeling. In contrast, glioma cells in minimal medium with no additions did not migrate, nor did they adhere well or display defined labeling patterns for focal adhesion proteins or uPAR. The results indicate that high-molecular-weight serum protein complexes promote both uPAR-focal adhesion colocalization and cell migration in glioma cells. However, conditions can be selected in which migration takes place with minimal uPAR-focal adhesion localization, as well as in the absence of apparent focal adhesions.

The transcription factors Sp1, Sp3, and AP-2 are required for constitutive matrix metalloproteinase-2 gene expression in astroglioma cells

Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that contribute to pathological conditions associated with angiogenesis and tumor invasion. MMP-2 is highly expressed in human astroglioma cells, and contributes to the invasiveness of these cells. The human MMP-2 promoter contains potential cis-acting regulatory elements including cAMP response element-binding protein, AP-1, AP-2, PEA3, C/EBP, and Sp1. Deletion and site-directed mutagenesis analysis of the MMP-2 promoter demonstrates that the Sp1 site at -91 to -84 base pairs and the AP-2 site at -61 to -53 base pairs are critical for constitutive activity of this gene in invasive astroglioma cell lines. Electrophoretic gel shift analysis demonstrates binding of specific DNA-protein complexes to the Sp1 and AP-2 sites: Sp1 and Sp3 bind to the Sp1 site, while the AP-2 transcription factor binds the AP-2 element. Co-transfection expression experiments in Drosophilia SL2 cells lacking endogenous Sp factors demonstrate that Sp1 and Sp3 function as activators of the MMP-2 promoter and synergize for enhanced MMP-2 activation. Overexpression of AP-2 in AP-2-deficient HepG2 cells enhances MMP-2 promoter activation. These findings document the functional importance of Sp1, Sp3, and AP-2 in regulating constitutive expression of MMP-2. Delineation of MMP-2 regulation may have implications for development of new therapeutic strategies to arrest glioma invasion.

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.

"...those left behind." Biology and oncology of invasive glioma cells

Although significant technical advances in surgical and radiation treatment for brain tumors have emerged in recent years, their impact on clinical outcome for patients has been disappointing. A fundamental source of the management challenge presented by glioma patients is the insidious propensity of the malignant cells to invade into adjacent normal brain. Invasive tumor cells escape surgical removal and geographically dodge lethal radiation exposure. Recent improved understanding of the biochemistry and molecular determinants of glioma cell invasion provide valuable insight to the underlying biological features of the disease, as well as illuminating possible new therapeutic targets. Heightened commitment to migrate and invade is accompanied by a glioma cell's reduced proliferative activity. The microenvironmental manipulations coincident to invasion and migration may also impact the glioma cell's response to cytotoxic treatments. These collateral aspects of the glioma cell invasive phenotype should be further explored and exploited as novel antiglioma therapies.

Extracellular matrix degradation by metalloproteinases and central nervous system diseases

Matrix metalloproteinases (MMPs) are a gene family of neutral proteases involved in normal and pathological processes in the central nervous system (CNS). Normally released into the extracellular space, MMPs break down the extracellular matrix (ECM) to allow cell growth and to facilitate remodeling. Proteolysis becomes pathological when the normal balance between the proteases and their inhibitors, tissue inhibitors to metalloproteinases (TIMPs), is lost. Cancer cells secrete neutral proteases to facilitate spread through the ECM. MMPs increase capillary permeability, and they have been implicated in demyelination. Neurological diseases, such as brain tumors, multiple sclerosis, Guillain-Barré, ischemia, Alzheimer's disease, and infections, lead to an increase in the matrix-degrading proteases. Two classes of neutral proteases have been extensively studied, namely the MMPs and the plasminogen activators (PAs), which act in concert to attack the ECM. After proteolytic injury occurs, the process of ECM remodeling begins, which can lead to fibrosis of blood vessels and gliosis. TIMPs are increased after the acute injury and may add to the fibrotic buildup of ECM components. Thus, an imbalance in proteolytic activity either during the acute injury or in recovery may aggravate the underlying disease process. Agents that affect the proteolytic process at any of the regulating sites are potentially useful in therapy.

Direct evidence that hepatocyte growth factor-induced invasion of hepatocellular carcinoma cells is mediated by urokinase

BACKGROUND/AIMS

We have shown that hepatocyte growth factor secreted by human hepatic myofibroblasts increased the in vitro invasion of the hepatocarcinoma cell line HepG2 through Matrigel. Our aim in this study was to evaluate the role of urokinase in this process.

METHODS

Expression of urokinase in HepG2 cells was measured by Northern blot and zymography, and plasminogen activation was shown by a chromogenic substrate assay. Cell invasion was assayed on Matrigel-coated filters. Urokinase and urokinase receptor transcripts in hepatocarcinoma were detected by reverse transcription-polymerase chain reaction. Activated hepatocyte growth factor was detected by Western blot with a hepatocyte growth factor-beta chain-specific antibody.

RESULTS

HepG2 cells expressed urokinase mRNA and secreted active urokinase. Urokinase expression was enhanced by hepatocyte growth factor at the protein and mRNA level. Notably, cell-surface-associated urokinase was increased 22-fold by hepatocyte growth factor. Hepatocyte growth factor also increased urokinase receptor mRNA expression. B428, a urokinase inhibitor, decreased by up to 70% HepG2 invasion induced by myofibroblasts and by 90% that induced by recombinant hepatocyte growth factor. This was not due to a decrease in the generation of activated hepatocyte growth factor by myofibroblasts. Finally, all 17 hepatocarcinoma samples tested expressed urokinase and urokinase receptor transcripts.

CONCLUSION

Hepatocyte growth factor-dependent, myofibroblasts-induced invasion of HepG2 cells is secondary to the induction of urokinase expression on tumor cells.

Transcriptional Suppression of Matrix Metalloproteinase-2 Gene Expression in Human Astroglioma Cells by TNF-α and IFN-γ

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that function in the turnover of extracellular matrix components during development. In addition, MMPs also contribute to pathological conditions associated with inflammation, angiogenesis, and tumor invasion. A 72-kDa type IV collagenase, also referred to as gelatinase A or MMP-2, has been proposed to potentiate the invasion and metastasis of malignant tumors. In particular, MMP-2 activity has been shown to constitute an important component of human astroglioma invasion. We investigated the influence of various cytokines, both proinflammatory and immunosuppressive, on MMP-2 gene expression in two human astroglioma cell lines (U251-MG and CRT). Our results indicate that the cell lines constitutively express high levels of MMP-2 mRNA, protein, and bioactivity as assessed by ribonuclease protection assay, immunoblotting, and zymography assays, respectively. The proinflammatory cytokines TNF-α and IFN-γ individually can inhibit constitutive MMP-2 expression, and function in an additive manner for near-complete inhibition of MMP-2 expression. Inhibition of MMP-2 mRNA levels by TNF-α and IFN-γ is not due to destabilization of the MMP-2 message; rather, inhibition is mediated at the transcriptional level. Furthermore, TNF-α/IFN-γ inhibition of MMP-2 expression results in decreased invasiveness of the human astroglioma cells through an extracellular matrix. These results raise the possibility that TNF-α and IFN-γ may have beneficial effects in attenuating astroglioma invasive properties.

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.

Expression of multidrug resistance protein gene in patients with glioma after chemotherapy

Two different ATP-binding membrane glycoproteins, the 170 kDa P-glycoprotein (P-gp) and the 190 kDa multidrug resistance protein (MRP), are involved in the acquisition of multidrug resistance phenotypes in cancer cells. Overexpression of P-gp is often observed in various human tumors when treated with anticancer agents. In this study, we asked whether MRP was overexpressed in human gliomas after cancer chemotherapy. We investigated expression of MRP and P-gp before and after chemotherapy in tumor samples from patients with glioma. MRP expression was observed in 16 (70%) of 23 untreated patients, and the proportion of MRP-positive cells in the whole cell population ranged from 3 to 32% in the 16 MRP-positive patients. P-gp-positive tumors were observed in 4 (18%) of 23 patients, and the proportional rates of P-gp-positive cells in the whole cell population ranged from 4 to 23%. The proportional rate of MRP-positive or P-gp-positive glioma cells increased after chemotherapy when compared with that before chemotherapy in all patients examined. We could observe no statistically significant correlation between expression of MRP or P-gp and tumor grade. These results suggest that MRP as well as P-gp may be involved in acquired or intrinsic drug resistance in human glioma.

Dynamic determination of human glioma invasion in vitro

OBJECT

The goal of this study was to evaluate whether there is any relationship between survival of patients with brain tumor and tumor proliferation or tumor invasion in vitro.

METHODS

Samples of freshly resected brain tumors from 14 patients with glioblastoma multiforme (GBM) were directly grown as three-dimensional multicellular spheroids. The tumor spheroids were cocultured with fetal rat brain cell aggregates (BCAs), used to represent an organotypical normal brain tissue model. Before the coculture, the tumor spheroids and the BCAs were stained with two different carbocyanine dyes, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) and 3,3'-dioctadecycloxacarbocyanine perchlorate (DiO), respectively. During the coculture, confocal laser scanning microscopy allowed a sequential analysis of tumor cell invasion by visualizing dynamic aspects of the invasive process. Single cocultures were examined at three different time points (24, 48, and 96 hours). During the observation period there was a change in the structural morphology of the cocultures, with a progressive decrease in BCA volume. Furthermore, the scanning confocal micrographs revealed a bidirectional movement of tumor cells and normal cells into brain and tumor tissue, respectively. It is also shown that there is a considerable variation in the rate of BCA destruction in cocultures of glioma spheroids generated directly from biopsy specimens. This variation is seen both between spheroids generated from the same biopsy as well as between spheroids that are grown from different biopsy specimens. Cell proliferation measured by Ki-67 immunohistochemical analysis of biopsy samples obtained in the same patients revealed a correlation between tumor cell proliferation and tissue destruction of the BCAs, as determined by a reduction in BCA volume (p = 0.0338). No correlation was found when survival was related to the same parameters (p > 0.05).

CONCLUSIONS

The present work provides a model for quick and efficient assessment of dynamic interactions between tumor and normal brain tissue shortly after surgery.

Induction of matrix metalloproteinase-9 requires a polymerized actin cytoskeleton in human malignant glioma cells

Alterations in cytoskeleton and subsequent cell shape changes exert specific effects on the expression of various genes. Our previous results suggested that malignant human gliomas express elevated levels of matrix metalloproteinases compared with normal brain tissue and low grade gliomas. To understand the role of cell shape changes on matrix metalloproteinase expression in human glioma cells, we treated SNB19 cells with cytochalasin-D, an inhibitor of actin polymerization, and colchicine-B, a tubulin inhibitor, in the presence of phorbol 12-myristate 13-acetate. Cytochalasin-D treatment of SNB19 cells resulted in the loss of phorbol 12-myristate 13-acetate-induced matrix metalloproteinase-9 (also known as gelatinase-B) expression and coincided with inhibition of actin polymerization, resulting in cell rounding. Moreover, compared with monolayers, cells grown as spheroids or cell aggregates failed to express matrix metalloproteinase-9 in the presence of phorbol 12-myristate 13-acetate. Matrix metalloproteinase-9 expression was also inhibited by calphostin-C, a protein kinase inhibitor, suggesting the involvement of protein kinase C in matrix metalloproteinase-9 expression. Phorbol 12-myristate 13-acetate-induced invasion of SNB19 cells through Matrigel was inhibited by cytochalasin-D and calphostin-C. These results suggest that the actin polymerization transduces signals that modulate the expression of matrix metalloproteinase-9 expression and the subsequent invasion of human glioma cells.

Differential induction of cell death in human glioma cell lines by sodium nitroprusside

BACKGROUND

High grade gliomas represent very aggressive and lethal forms of human cancer, which often exhibit recurrence after surgical intervention and resistance to conventional chemotherapeutic and radiologic treatment. The clinically approved antihypertensive agent sodium nitroprusside (SNP) has been shown to induce cytotoxicity toward a number of carcinoma cell lines in vitro.

METHODS

Three human glioma cell lines were examined for susceptibility to the cytotoxic effects of SNP. The role of the protein kinase C (PKC)alpha gene in mediating resistance to SNP-induced killing in U343 cells was investigated using antisense oligonucleotide inhibition. Stable transfection and overexpression of the PKCalpha gene in the SNP-susceptible cell line U251 was performed to further implicate PKCalpha as a mediating factor in SNP cytotoxicity. In addition, the presence of bcl-2 protein in these cells was examined for possible correlation(s) with resistance to SNP.

RESULTS

Exposure of U251 cells and LN-Z308 cells to 0.5 mM SNP resulted in significant cytotoxicity over a 72-hour period. U343 cells were resistant to SNP killing. U343 cells were shown to exhibit higher basal levels of PKCalpha and bcl-2 than either U251 or LN-Z308 cells. bcl-2 expression and resistance to SNP toxicity both were decreased by the introduction of PKCalpha antisense oligonucleotides into U343 cells. Conversely, enhanced PKC activity in PKCalpha-transfected U251 clones was associated with increased bcl-2 expression and greater resistance to SNP-induced toxicity relative to control transfected cells.

CONCLUSIONS

SNP can induce cytotoxicity in glioma cells. The susceptibility of these glioma cells to nitroprusside-induced killing appears to be correlated inversely with bcl-2 and PKC activity. bcl-2 levels in these cells can be altered through modulation of PKC signaling, specifically, by induction or inhibition of PKCalpha. These in vitro results provide an interesting basis for further study into the potential use of SNP for treatment of human gliomas in patients receiving combination therapy with conventional chemotherapeutic agents that exhibit PKC inhibitory activity.

Overview of matrix metalloproteinase expression in cultured human cells

The matrix metalloproteinases (MMP) have been implicated in tumor invasion and metastasis both by immunohistochemical studies and from the observation that specific metalloproteinase inhibitors block tumor invasion and metastasis. Oligonucleotide primers for thirteen MMPs (MMP-1, MMP-2, MMP-3, MMP-7, MMP-8, MMP-9, MMP-10, MMP-11, MMP-12, MMP-13, MMP-14, MMP-15, MMP-16) were optimized for use in RT-PCR. A semi-quantitative RT-PCR assay was used to determine the pattern of MMP mRNA expression in 84 normal and transformed or carcinogen transformed human cell lines and strains derived from different tissues. The results demonstrate one or more cell lines which express thirteen members of the MMP family. In addition, various oncogene transfected human fibroblast cell strains were analyzed for MMP expression. We confirm that over-expression of the H-ras oncoprotein correlates with up-regulation of MMP-9 and demonstrate that over-expression of v-sis also up-regulates MMP-9. A cell line immortalized following myc expression was found to up-regulate MMP-7, MMP-11 and MMP-13. Inappropriate expression of several MMP mRNAs was detected in breast, prostate, bone, colon and oral tumor derived cell lines. Identification of at least one cell line expressing each of thirteen MMPs and the observation of oncogene induced expression of several MMPs should facilitate analysis of the transcriptional mechanisms controlling each MMP.