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

Calmodulin inhibitors trigger the proteolytic processing of membrane type-1 matrix metalloproteinase, but not its shedding in glioblastoma cells

Most transmembrane proteins are subjected to limited proteolysis by cellular proteases, and stimulation of cleavage of membrane proteins by calmodulin (CaM) inhibitors was recently shown. The present study investigated the ability of several CaM inhibitors to induce the proteolytic cleavage of the membrane type-1 matrix metalloproteinase (MT1-MMP) from the cell surface of highly invasive U-87 glioblastoma cells. Although no shedding of a soluble MT1-MMP form was induced by CaM inhibitors in the conditioned media, we showed that these inhibitors induced MT1-MMP proteolytic processing to the 43 kDa membrane-bound inactive form that was not correlated with an increase in proMMP-2 activation but rather with an increase in tissue inhibitor of MMPs (TIMP)-2 expression levels. Moreover, this proteolytic processing was sensitive to marimastat suggesting the involvement of MMPs. Interestingly, CaM inhibitors antagonized concanavalin A- and cytochalasin D-induced proMMP-2 activation, and affected the cytoskeletal actin organization resulting in the loss of migratory potential of U-87 glioblastoma cells. Cytoplasmic tail-truncated MT1-MMP constructs expressed in COS-7 cells were also affected by CaM inhibitors suggesting that these inhibitors stimulated MT1-MMP proteolytic processing by mechanisms independent of the CaM-substrate interaction. We also propose that TIMP-2 acts as a negative regulator of MT1-MMP-dependent activities promoted by the action of CaM inhibitors in U-87 glioblastoma cells.

Modulation of endothelial cell morphogenesis in vitro by MMP-9 during glial-endothelial cell interactions

The purpose of this study was to investigate the roles of matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1) in the formation of capillary structures by human brain microvascular endothelial cells cocultured with SNB19 glioblastoma cells. Unstimulated cocultures did not form capillaries and produce MMP-9 but stimulation with the protein kinase C (PKC) activator 4-phorbol-12-myristate 13-acetate (PMA) produced MMP-9 and capillary networks. Addition of recombinant MMP-9 increased capillary formation. Anti-MMP-9 antibodies, TIMP-1, the synthetic MMPs inhibitor Batimastat (BB-94), and the PKC inhibitor calphostin-C all reduced MMP-9 activity and capillary network formation in these cocultures. Cytochalasin-D in the presence of PMA suppressed MMP-9 expression and capillary formation, but colchicine-B had no such effect. Finally, PMA-induced MMP-9 expression and capillary formation were inhibited by the MEKK-specific inhibitor PD98059. These results suggest that MMP-9 is important in endothelial cell morphogenesis and the formation of capillaries in glial/endothelial cocultures in vitro.

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.

Interleukin-1beta gene transcription in U937 cells is modulated by type I collagen and cytoskeletal integrity via distinct signaling pathways

Type I collagen (Col), an extracellular matrix molecule highly expressed in injured tissues, stimulates interleukin-1beta (IL-1beta) expression in monocytic cells. Using U937 cells transfected with the human IL-1beta gene promoter connected to a reporter gene, we examined how the organizational state of the cytoskeleton modulates the expression of IL-1beta after Col stimulation. We found the same degree of stimulation of IL-1beta gene transcription in cells exposed to Col presented in different fashions (i.e., soluble Col, Col-coated plate, three-dimensional Col lattice), suggesting that stimulation of IL-1beta is independent of the mode of presentation of Col. The Col-stimulated response was associated with induction of the transcription factor activator protein-1 (AP-1) and was abolished by a protein kinase C (PKC) inhibitor, by a mitogen-activated protein kinase (MAPK) inhibitor, and by cotransfection of cells with a competing AP-1 oligo. Disruption of cytoskeletal organization with colchicine or cytochalasin B stimulated IL-1beta gene transcription and enhanced the cells' response to Col. The effects of cytochalasin and colchicine were inhibited by the PKC inhibitor but were not affected by the MAPK inhibitor or the AP-1 oligo. These findings suggest that the cytoskeletal integrity modulates the constitutive and Col-stimulated transcription of the IL-1beta gene via distinct signaling mechanisms.

Tumor biology and experimental therapeutics

Recent research using multicellular tumor spheroids has resulted in new insights in the regulation of invasion and metastasis, angiogenesis and cell cycle kinetics. The onset and expansion of central necrosis in tumor spheroids has been characterized to be a complex interaction of several mechanisms; in a number of cases, necrosis is not a consequence of hypoxia or anoxia, but emerges as secondary necrosis following an accumulation of apoptosis in spheroids. Recent therapeutically oriented studies have been directed towards novel hypoxic markers, targeted therapy, multicellular-mediated drug resistance, and heavy ion irradiation of spheroids. Research efforts should be enhanced mainly in the fields of tumor tissue modeling by heterotypic three-dimensional (3D) cultures and of apoptotic versus necrotic cell death. Based on the fundamental differences between monolayer and 3D cultures, spheroids should become mandatory test systems in therapeutic screening programs.

Activation of MMP-2 by Clostridium difficile toxin B in bovine smooth muscle cells

Matrix metalloproteinase-2 (MMP-2) plays critical roles in cell migration through the breakdown of the extracellular matrix. Cell movements require dynamic actin reorganization, which is controlled by Rho family GTPases. In order to examine the relation between MMP-2 regulation and actin reorganization, we used several inhibitors of Rho family GTPases. Treatment of smooth muscle cells with Clostridium difficile toxin B known to inactivate Rho family GTPases activated MMP-2. However, neither C3 transferase, a Rho inhibitor, nor Y-27632, a specific inhibitor of Rho-kinase, induced MMP-2 activation. Treatment with C3 transferase and Y-27632 caused morphological changes into the round and stellate shape, respectively, by inhibition of actin stress fiber formation. In addition, toxin B treatment induced expression and processing of MT1-MMP, a major activator of MMP-2. Taken together, we suggest the involvement of Rho family GTPases, although inhibition of neither Rho nor Rho-kinase is sufficient, in the activation of MMP-2 through expression and activation of MT1-MMP.

Regulation and significance of hepatocyte-derived matrix metalloproteinases in liver remodeling

Regulation in expression and activation of proteinases is one of the most important mechanisms in organ morphogenesis. In this study, we investigated the expression of MMPs in primary hepatocytes and their roles in liver remodeling. A hepatocyte proliferation initiating cytokine, TNFalpha, induced MMP-9 expression in these cells while the expression of MMP-2 did not change by zymography analysis. Interestingly, both the induced MMP-9 expression and hepatocyte proliferation by TNFalpha were synergistically enhanced by HGF in vitro. The increased proliferation was suppressed by MMP inhibitor TIMP-1, suggesting that cytokine-induced MMP regulates proliferation. The increased expression of MMP-9 by the cytokines was inhibited by cytochalasin D or colchicine but not by PI3 kinase inhibitor wortmannin. In addition, co-stimulation by TNFalpha and HGF of spheroidal hepatocytes cultured in 3-dimensional collagen gel drastically induced morphological changes by cell extension and migration in the gel, which was in parallel with the induced expression of MMP-9 and was inhibited by TIMP-1 and -2. The MMP activity was also detected in vivo in the regenerating liver after partial hepatectomy by in situ zymography. These results suggest the roles of MMPs produced by parenchymal cells in liver remodeling.

Invasive potential and substrate dependence of attachment in the dunning R-3327 rat prostate adenocarcinoma model

Cancer cell attachment to and invasion of the extracellular matrix has been associated with the metastatic potential of cell lines of the Dunning R-3327 rat prostatic adenocarcinoma model. We investigated the cell-matrix interactions of prostate tumor cells by comparing the invasive ability through reconstructed extracellular matrix and attachment upon EHS NATRIX (natural extracellular matrix), fibronectin, laminin, and collagen Type IV. We observed a correlation between metastatic potential and substrate dependence of attachment in prostate cancer cells. Nonmetastatic AT-1 cells possessed a higher adhesive potential to extracellular matrix components than the highly metastatic cells (ML, MLL and AT-3). It was also found that the invasive potential of the three highly metastatic cell lines was significantly higher than that of the nonmetastatic cell line. Here, it is reported that the ability to traverse a matrigel matrix correlates with their metastatic potential. These observations suggest that the extracellular matrix components are highly involved in influencing prostate cancer cell activities. In addition, we investigated the effects of two differentiation agents, retinoic acid (RA) and difluoromethylornithine (DFMO), on the adhesive and invasive profiles of the tumor cells. After treatment with both agents, adhesion was increased to levels not different from nonmetastatic cells. Furthermore, the ability of highly metastatic cells to traverse a matrigel barrier was significantly reduced after treatment with both differentiation agents. These results suggest that RA and DFMO are capable in reversing the metastatic potential of prostate cancer cells in vitro and may give a possible insight into their role as potential therapeutic agents in vivo.

Function of alpha3beta1-tetraspanin protein complexes in tumor cell invasion. Evidence for the role of the complexes in production of matrix metalloproteinase 2 (MMP-2)

Tumor cell migration through the three- dimensional extracellular matrix (ECM) environment is an important part of the metastatic process. We have analyzed a role played by the integrin-tetraspanin protein complexes in invasive migration by culturing MDA-MB-231 cells within Matrigel. Using time-lapse video recording, we demonstrated that the Matrigel-embedded cells remain round and exhibit only limited ability for migration by extending short, highly dynamic pseudopodia. The alpha3beta1-tetraspanin protein complexes were clustered on the thin microvilli-like protrusions extending from both the main cell body and pseudopodia. Ligation of the alpha3beta1-tetraspanin protein complexes with monoclonal antibodies specifically stimulates production of matrix metalloproteinase 2 (MMP-2) and induces formation of long invasive protrusions within Matrigel. Accordingly, treatment with the monoclonal antibodies to various tetraspanin proteins and to the alpha3 integrin subunit increases invasive potential of the MDA-MB-231 cells in the Matrigel-penetration assay. A specific inhibitor of phosphoinositide 3-kinase (PI3K), LY294002, negated the effect of the monoclonal antibodies on the morphology of the Matrigel-embedded cells and on production of MMP-2. Interestingly, broad-spectrum inhibitors of protein tyrosine kinases (genistein) and protein tyrosine phosphatases (orthovanadate), and actin filament stabilizing compound (jasplakinolide), also block protrusive activity of the Matrigel-embedded cells but have no effect on the production of MMP-2. These results indicate that alpha3beta1-tetraspanin protein complexes may control invasive migration of tumor cells by using at least two PI3K-dependent signaling mechanisms: through rearrangement of the actin cytoskeleton and by modulating the MMP-2 production.

Matrix metalloproteinases and their biological function in human gliomas

Gliomas, a type of devastating primary brain tumors, are distinct from other solid, non-neural primary neoplasms, in that they display extensive infiltrative invasive behavior but seldom metastasize to distant organs. This invasiveness into the surrounding normal brain tissue makes gliomas a major challenge for clinical intervention. Total surgical resection of gliomas is not possible, and recurrence of tumor growth is common; mean survival time is 8-12 months. Although substantial progress has been made recently toward understanding the behavior of gliomas, the mechanisms that facilitate invasion are still poorly documented. Clues to the invasion process have been ascertained through clarification of the key roles played by the extracellular matrix (ECM), cell-adhesion molecules and matrix degrading proteases. Serine proteases and metalloproteinases have been implicated in glioma tumor cell-invasion. Matrix metalloproteinases (MMPs) in particular can degrade almost all known ECM components and seem to play important roles in mediating glioblastoma tumor cell invasion. This review focuses on recent developments concerning the role of MMPs in the invasiveness of human gliomas.

Airway epithelial cell migration dynamics. MMP-9 role in cell-extracellular matrix remodeling

Cell spreading and migration associated with the expression of the 92-kD gelatinase (matrix metalloproteinase 9 or MMP-9) are important mechanisms involved in the repair of the respiratory epithelium. We investigated the location of MMP-9 and its potential role in migrating human bronchial epithelial cells (HBEC). In vivo and in vitro, MMP-9 accumulated in migrating HBEC located at the leading edge of a wound and MMP-9 expression paralleled cell migration speed. MMP-9 accumulated through an actin-dependent pathway in the advancing lamellipodia of migrating cells and was subsequently found active in the extracellular matrix (ECM). Lamellipodia became anchored through primordial contacts established with type IV collagen. MMP-9 became amassed behind collagen IV where there were fewer cell-ECM contacts. Both collagen IV and MMP-9 were involved in cell migration because when cell-collagen IV interaction was blocked, cells spread slightly but did not migrate; and when MMP-9 activation was prevented, cells remained fixed on primordial contacts and did not advance at all. These observations suggest that MMP-9 controls the migration of repairing HBEC by remodeling the provisional ECM implicated in primordial contacts.