Extracellular matrix-modulated differential invasion of human meningioma cell lines in vitro

Molecular neuropathology of brain-invasive meningiomas

Invasion of brain tissue by meningiomas has been identified as one key factor for meningioma recurrence. The identification of meningioma tumor tissue surrounded by brain tissue in neurosurgical samples has been touted as a criterion for atypical meningioma (CNS WHO grade 2), but is only rarely seen in the absence of other high-grade features, with brain-invasive otherwise benign (BIOB) meningiomas remaining controversial. While post-surgery irradiation therapy might be initiated in brain-invasive meningiomas to prevent recurrences, specific treatment approaches targeting key molecules involved in the invasive process are not established. Here we have compiled the current knowledge about mechanisms supporting brain tissue invasion by meningiomas and summarize preclinical models studying targeted therapies with potential inhibitory effects.

Integrin-based meningioma cell migration is promoted by photon but not by carbon-ion irradiation

PURPOSE

Sublethal doses of photon irradiation (IR) are suspected to increase tumor cell migration and support locoregional recurrence of disease, which has already been shown in other cell lines. This manuscript describes the effect of photon and carbon-ion IR on WHO class I meningioma cell migration and provides an approach to the underlying cellular mechanisms.

MATERIALS AND METHODS

Meningioma cells were gained operatively at the university hospital in Homburg/Saar, Germany. For migration, membranes (8-µm pore sizes) were coated with collagen I, with collagen IV, and with fibronectin. Cells were analyzed in migration experiments with or without serum stimulation, with or without photon and carbon IR 24 h prior to experiments, and with or without integrin antibodies. Fluorescence-activated cell sorting (FACS) analyses of the integrins ανβ1, ανβ3, and ανβ5 were performed without IR and 6, 12 and 24 h after IR. Enzyme-linked immunosorbent assay (ELISA) analyses of matrix metalloproteinases (MMP)-2 and MMP-9 were realized with and without IR after cells were cultured on collagen I, collagen IV, or fibronectin for 24 h. Cells and supernatants for FACS and ELISA were stored at - 18 °C. The significance level was set at 5 % using both Student's t test and two-way ANOVA.

RESULTS

Migration of meningioma cells was serum-inducible (p < 0.001). It could be increased by photon IR (p < 0.02). The integrins ανβ1 and ανβ5 showed a 21 and 11 % higher expression after serum stimulation (not significant), respectively, and ανβ1 expression was raised by 14 % (p = 0.0057) after photon IR. Antibody blockage of the integrins ανβ1 and ανβ5 inhibited serum- and photon-induced migration. Expression of MMP-2 and MMP-9 remained unchanged after both IR and fetal bovine serum (FBS). Carbon-ion IR left both integrin expression and meningioma cell migration unaffected.

CONCLUSION

Photon but not carbon-ion IR promotes serum-based meningioma cell migration. Fibronectin receptor integrin ανβ1 signaling can be identified as an important mechanism for serum- and photon-induced migration of WHO class I meningioma cells.

Toward understanding recurrent meningioma: the potential role of lysosomal cysteine proteases and their inhibitors

OBJECT

The first aim of this study was to diagnose more aggressive and potentially recurrent meningiomas using an in vitro embryonic chick heart invasiveness assay in which lysosomal enzyme cathepsin B was used as the invasiveness marker. The second aim was to confirm if cathepsin B and/or cathepsin L and their endogenous inhibitors were also prognostic parameters in the clinical study of 119 patients with meningioma.

METHODS

Primary meningioma cultured spheroids were "confronted" with embryonic chick heart spheroids in vitro, and cathepsin B was used as molecular marker to immunolabel the invasive tumor cells. In vitro invasion assays of the malignant meningioma cells were used to assess the invasive potential related to the cysteine cathepsins. As to the second aim, the possible association of cathepsin B along with selected molecular markers, cathepsin L, and endogenous cysteine protease inhibitors (stefins A and B and cystatin C) with meningioma malignancy was determined using enzyme-linked immunosorbent assays in tumor homogenates. Univariate and multivariate analyses were used to compare these parameters with established biological markers of meningioma recurrence in 119 patients with meningiomas.

RESULTS

The more invasive tumors, which characteristically overgrew the normal tissue, were identified even within a group of histologically benign meningiomas. More intensive staining of cathepsin B in these tumors was not only found at the tumor front, but also in the invading pseudopodia of a single migrating tumor cells. Matrigel invasion of malignant meningioma cells was significantly altered by modulating cathepsin B activity and by stefin B silencing. In the clinical samples of meningioma, the levels of cathepsins B and L, stefin B, and cystatin C were highest in the tumors of higher histological grades, whereas stefin A and progesterone receptor were the only markers that were significantly increased and decreased, respectively, in WHO Grade III lesions. With respect to the prognosis of relapse, cathepsin L (p = 0.035), stefin B (p = 0.007), cystatin C (p = 0.008), and progesterone receptor (p = 0.049) levels were significant, whereas cathepsin B was not a prognosticator. As expected, WHO grade, age, and Simpson grade (complete tumor resection) were prognostic, with Simpson grade only relevant in the short term (up to 90 months) but not in longer-term follow-up. Of note, the impact of all these parameters was lost in multivariate analysis, due to overwhelming prognostic impact of stefin B (p = 0.039).

CONCLUSIONS

The data indicate that the cysteine cathepsins and their inhibitors are involved in a process related to early meningioma recurrence, regardless of their histological classification. Of note, the known tumor invasiveness marker cathepsin B, measured in whole-tumor homogenates, was not prognostic, in contrast to its endogenous inhibitor stefin B, which was highly significant and the only independent prognostic factor to predict meningioma relapse in multivariate analysis and reported herein for the first time. Stefin B inhibition of local invasion was confirmed by in vitro invasion assay, although its other functions cannot be excluded.

Immunohistochemical study of the extracellular matrix proteins laminin, fibronectin and type IV collagen in secretory meningiomas

The extracellular matrix plays a pivotal role in numerous cellular functions during normal and pathological processes. Secretory meningiomas are rare histological meningioma subtypes that have benign behavior, are highly vascularized and are frequently accompanied by massive peritumoral edema. The aim of this study was to assess in secretory meningiomas the immunohistochemical expression of laminin, fibronectin and type IV collagen, proteins found in the extracellular matrix. Extracellular matrix proteins were evaluated in samples from six secretory meningiomas using a semiquantitative scale ranging from not detected (0) to marked (3). Laminin expression was not detected in two cases, but was minimal in one, moderate in one and marked in the remaining cases. Fibronectin expression was absent in two cases, minimal in two, moderate in one and marked with generalized distribution in the remaining case. Type IV collagen expression was minimal in three cases, moderate in two and marked with generalized distribution in the remaining case. Our results are indicative of significant neoangiogenic activity. Meningiomas increase in size through increased production of extracellular matrix; furthermore, the proliferation of cells typically associated with neoplasia requires considerable interaction with the extracellular matrix.

Establishment of a benign meningioma cell line by hTERT-mediated immortalization

Meningioma represents the most common intracranial tumor, but well-characterized cell lines derived from benign meningiomas are not available. A major reason for the lack of benign tumor cell lines is senescence of nonmalignant cells in vitro, while malignant cells are often immortal. We have developed a meningioma cell line by retrovirally transducing primary cells derived from a human WHO grade I meningothelial meningioma with the human telomerase reverse transcriptase (hTERT) gene, which enables bypassing cellular senescence. Five clones have been cultured for more than 21 months so far, while corresponding nontransfected cells ceased proliferation within 3 months. Quantitative RT-PCR and a telomeric repeat amplification protocol (TRAP) assay revealed high hTERT mRNA levels and high telomerase activity in all transduced populations, while nontransduced cells were negative. The average telomere size of transduced cells was considerably longer than that of parental cells and the biopsy specimen. One clone, designated Ben-Men-1, was characterized in more detail, and exhibited typical cytological, immunocytochemical, ultrastructural and genetical features of meningioma, including whorl formation, expression of epithelial membrane antigen, desmosomes and interdigitating cell processes, as well as -22q. Following subdural transplantation into nude mice, tumor tissue with typical histological features of meningothelial meningioma was found. We conclude that Ben-Men-1 represents an immortalized yet differentiated cell line useful for biological and therapeutical studies on meningioma.

Regulation of human beta-cell adhesion, motility, and insulin secretion by collagen IV and its receptor alpha1beta1

Collagens have been shown to influence the survival and function of cultured beta-cells; however, the utilization and function of individual collagen receptors in beta-cells is largely unknown. The integrin superfamily contains up to five collagen receptors, but we have determined that alpha(1)beta(1) is the primary receptor utilized by both fetal and adult beta-cells. Cultured beta-cells adhered to and migrated on collagen type IV (Col-IV), and these responses were mediated almost exclusively by alpha(1)beta(1). The migration of cultured beta-cells to Col-IV significantly exceeded that to other matrix components suggesting that this substrate is of unique importance for beta-cell motility. The interaction of alpha(1)beta(1) with Col-IV also resulted in significant insulin secretion at basal glucose concentrations. A subset of beta-cells in developing islets was confirmed to express alpha(1)beta(1), and this expression co-localized with Col-IV in the basal membranes of juxtaposed endothelial cells. Our findings indicate that alpha(1)beta(1) and Col-IV contribute to beta-cell functions known to be important for islet morphogenesis and glucose homeostasis.

Invasion of human glioma biopsy specimens in cultures of rodent brain slices: a quantitative analysis

OBJECT

The reliable assessment of the invasiveness of gliomas in vitro has proved elusive, because most invasion assays inadequately model in vivo invasion in its complexity. Recently, organotypical brain cultures were successfully used in short-term invasion studies on glioma cell lines. In this paper the authors report that the invasiveness of human glioma biopsy specimens directly implanted into rodent brain slices by using the intraslice implantation system (ISIS) can be quantified with precision. The model was first validated by the demonstration that, in long-term studies, established glioma cells survive in the ISIS and follow pathways of invasion similar to those in vivo.

METHODS

Brain slices (400 microm thick) from newborn mice were maintained on millicell membranes for 15 days. Cells from two human and one rodent glioblastoma multiforme (GBM) cell lines injected into the ISIS were detected by immunohistochemistry or after transfection with green fluorescent protein-containing vectors. Preferential migration along blood vessels was identified using confocal and fluorescent microscopy. Freshly isolated (< or = 24 hours after removal) 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate-prelabeled human glioma biopsy specimens were successfully implanted in 19 (83%) of 23 cases, including 12 GBMs and seven lower grade gliomas (LGGs). Morphometric quantification of distance and density of tumor cell invasion showed that the GBMs were two to four times more invasive than the LGGs. Heterogeneity of invasion was also observed among GBMs and LGGs. Directly implanted glioma fragments were more invasive than spheroids derived from the same biopsy specimen.

CONCLUSIONS

The ISIS combines a high success rate, technical simplicity, and detailed quantitative measurements and may, therefore, be used to study the invasiveness of biopsy specimens of gliomas of different grades.

Lysosomal enzymes, cathepsins in brain tumour invasion

The expression patterns of different classes of peptidases in central nervous system (CNS) tumours have been most extensively studied in astrocytomas and meningiomas. Although the two types of tumours are very different in most respects, both may invade locally into normal brain. This process of invasion includes increased synthesis and secretion of lysosomal proteolytic enzymes - cathepsins. Aspartic endopeptidase cathepsin (Cat) D levels were found to be elevated in high-grade astrocytoma and partial inhibition of glioblastoma cell invasion by anti-Cat D antibody suggests that the enzyme activity is involved in the invasion process. Several studies on cysteine endopeptidase (CP) Cat B in gliomas agreed that transcript abundance, protein level and activity of Cat B increased in high-grade astrocytoma cultures compared with low-grade astrocytoma cultures and normal brain. Moreover, in glioma biopsies Cat B levels correlated with evidence of clinical invasion and it has been demonstrated that Cat B both in tumour cells and in endothelial cells can serve as a new biological marker for prognosis in glioblastoma patients. A high level of Cat B protein was also a diagnostic marker for invasive types of meningioma, distinguishing between histomorphologically benign, but invasive meningiomas and noninvasive, so-called clear-benign meningiomas. Cat L was also significantly increased in high-grade astrocytoma compared with low-grade astrocytoma and normal brain. Specific Cat L antibodies and antisense Cat L RNA transfection significantly lowered glioblastoma cell invasion. In meningioma, Cat L was a less-significant marker of invasion than Cat B. In contrast to cathepsins, the activities of endogenous cysteine peptidase inhibitors (CPIs), including stefins, cystatins and kininogens, were significantly higher in benign and atypical meningioma cell extracts than in malignant meningioma, and low-grade compared to high-grade astrocytoma. However, very low levels of stefins A and B were found in meningioma and glioblastoma tissues. Further studies on the expression levels and balance between cysteine endopeptidases (CPs) and CPIs would improve the clinical application of cathepsins in prognosis, which would lead to more-informed therapeutic strategies.