Lost in disruption: Role of proteases in glioma invasion and progression

A characteristic feature of malignant glial tumors (gliomas) is their tendency to diffusely infiltrate the nervous system preventing their complete surgical resection. Proteases play a decisive role in this malignant process, either by degradation of brain extracellular matrix (ECM) components, adhesion molecules, or by regulating the activity of growth and chemotactic factors. Secreted matrix metalloproteinases (MMPs) and ADAMTS proteases (ADAMs with thrombospondin motifs) cleave different ECM components like the proteoglycans (lecticans) aggrecan, versican, neurocan and brevican with selective preferences; they are further regulated by endogenous inhibitors and activating metallo- and serine proteases. Cell surface proteases of the ADAM family (A Disintegrin And Metalloproteinase), but also serine proteases regulate the activity of growth factors and chemokines that act as autocrine / paracrine stimulators within gliomas. Thus, proteases play a decisive role for the spread and growth of gliomas and are prominent targets for their therapy.     

Role of hyaluronan in glioma invasion

Gliomas are the most common primary intracranial tumors. Their distinct ability to infiltrate into the extracellular matrix (ECM) of the brain makes it impossible to treat these tumors using surgery and radiation therapy. A number of different studies have suggested that hyaluronan (HA), the principal glycosaminoglycan (GAG) in the ECM of the brain, is the critical factor for glioma invasion. HA-induced glioma invasion was driven by two important molecular events: matrix metalloproteinase (MMP) secretion and upregulation of cell migration. MMP secretion was triggered by HA-induced focal adhesion kinase (FAK) activation, which transmits its signal through ERK activation and nuclear factor kappa B (NFκB) translocation. Another important molecular event is osteopontin (OPN) expression. OPN expression by AKT activation triggers cell migration. These results suggest that HA-induced glioma invasion is tightly regulated by signaling mechanisms, and a detailed understanding of this molecular mechanism will provide important clues for glioma treatment.Key words: hyaluronan, matrix metalloproteinase, osteopontin, emodin, invasion, gliomaMalignant gliomas are highly invasive and infiltrative tumors that have a poor prognosis with a median survival of only one year.^1,2 A major barrier to effective malignant glioma treatment is the invasion of these cells into brain parenchyma. Because of this fact, local therapies such as surgery or radiation therapy are not effective.³ Glioma cells invade through the ECM of the brain by activating a number of coordinated cellular programs, which include those necessary for migration and invasion.³ Therefore, a detailed understanding of the mechanisms underlying this invasive behavior is essential for the development of novel effective therapies.During glioma invasion, tumor cells closely interact with the ECM. Although brain tumor cells may share some of the invasive characteristics with tumors that arise outside of the central nerve system (CNS), the particular structure and composition of the brain ECM suggest the existence of unique invasive mechanisms for brain tumors.⁴Brain ECM is composed of typical ECM proteins and a HA scaffold with associated glycoproteins and proteoglycans.⁵ Typical ECM proteins such as laminin, type-IV collagen and fibronectin have been implicated in the invasion of other tumors by regulating cell adhesion and migration.⁶ However HA, which is associated with proteoglycans and GAGs, is especially abundant in the brain parenchyma compared to other tissues.⁷ Furthermore, malignant gliomas contain higher amounts of HA than normal brain tissue.⁷ These facts raise the possibility that HA might play an important role in glioma invasion, a process that is distinct from other non-CNS derived tumors.     

Evolutionary game theory elucidates the role of glycolysis in glioma progression and invasion

Abstract. Objectives: Tumour progression has been described as a sequence of traits or phenotypes that cells have to acquire if the neoplasm is to become an invasive and malignant cancer. Although genetic mutations that lead to these phenotypes are random, the process by which some of these mutations become successful and cells spread is influenced by tumour microenvironment and the presence of other cell phenotypes. It is thus likely that some phenotypes that are essential in tumour progression will emerge in the tumour population only with prior presence of other different phenotypes. Materials and methods: In this study, we use evolutionary game theory to analyse the interactions between three different tumour cell phenotypes defined by autonomous growth, anaerobic glycolysis, and cancer cell invasion. The model allows us to understand certain specific aspects of glioma progression such as the emergence of diffuse tumour cell invasion in low‐grade tumours. Results: We have found that the invasive phenotype is more likely to evolve after appearance of the glycolytic phenotype which would explain the ubiquitous presence of invasive growth in malignant tumours. Conclusions: The result suggests that therapies, which increase the fitness cost of switching to anaerobic glycolysis, might decrease probability of the emergence of more invasive phenotypes.     

Rhomboid proteases in invasion and replication of Apicomplexa

In this issue of Molecular Microbiology, Rugarabamu and colleagues investigate the role of rhomboid proteases responsible for adhesin shedding during invasion of the apicomplexan parasite Toxoplasma gondii. This study, together with several other recent publications, raises new questions about the function of these rhomboids in Toxoplasma, while also strongly arguing against other recently proposed roles for these proteases.     

Membrane proteases: roles in tissue remodeling and tumour invasion.

The coordinated control of extracellular matrix degradation on the cell surface involves three crucial elements: secreted proteases and their inhibitors, surface protease receptors and integral membrane proteases. The roles that each of these elements play in cell surface proteolysis are described. The localization of proteases to the cell surface, protease activation, and regulation of cell surface proteolysis by protease inhibitors are key issues for elucidating the role of membrane proteases in tissue remodeling and tumour invasion.     

Malaria proteases and red blood cell invasion

Studies of malaria proteases have focused on two general groups, corresponding to activities specific to malaria parasites: (1) proteases involved in hemoglobin degradation which are active in the food vacuole and which exhibit optimal activity at low pH; and (2) proteases specific to schizonts and/or merozoites which are involved in merozoite maturation and red blood cell invasion and which exhibit optimal activity at neutral pH. In this paper, Catherine Braun Breton and Luis H. Pereira da Silva will focus on those activities necessary for the release of infectious merozoites and the entry of the parasite into its host cell.     

Malignant glioma progression and nitric oxide

Glioblastoma multiforme, the most common of the malignant gliomas, carries a dismal prognosis in spite of the most aggressive therapy and recent advances in molecular pathways of glioma progression. Although it has received relatively little attention in the setting of malignant gliomas, nitric oxide metabolism may be intimately associated with the disease process. Interestingly, nitric oxide has both physiological roles (e.g., neurotransmitter-like activity, stimulation of cyclic GMP), and pathophysiological roles (e.g., neoplastic transformation, tumor neovascularization, induction of apoptosis, free radical damage). Moreover, whether nitric oxide is neuroprotective or neurotoxic in a given disease state, or whether it enhances or diminishes chemotherapeutic efficacy in malignant neoplasia, is unresolved. This review discusses the multifaceted activity of nitric oxide with particular reference to malignant gliomas.     

Role of rhomboid proteases in bacteria

The first member of the rhomboid family of intramembrane serine proteases in bacteria was discovered almost 20 years ago. It is now known that rhomboid proteins are widely distributed in bacteria, with some bacteria containing multiple rhomboids. At the present time, only a single rhomboid-dependent function in bacteria has been identified, which is the cleavage of TatA in Providencia stuartii. Mutational analysis has shown that loss of the GlpG rhomboid in Escherichia coli alters cefotaxime resistance, loss of the YqgP (GluP) rhomboid in Bacillus subtilis alters cell division and glucose uptake, and loss of the MSMEG_5036 and MSMEG_4904 genes in Mycobacterium smegmatis results in altered colony morphology, biofilm formation and antibiotic susceptibilities. However, the cellular substrates for these proteins have not been identified. In addition, analysis of the rhombosortases, together with their possible Gly-Gly CTERM substrates, may shed new light on the role of these proteases in bacteria. This article is part of a Special Issue entitled: Intramembrane Proteases.     

Hybrid mathematical model of glioma progression

Objectives:  Gliomas are an important form of brain cancer, with high mortality rate. Mathematical models are often used to understand and predict their behaviour. However, using current modeling techniques one must choose between simulating individual cell behaviour and modeling tumours of clinically significant size.
Materials and Methods:  We propose a hybrid compartment-continuum-discrete model to simulate glioma growth and malignant cell invasion. The discrete portion of the model is capable of capturing intercellular interactions, including cell migration, intercellular communication, spatial cell population heterogeneity, phenotype differentiation, epigenetic events, proliferation, and apoptosis. Combining this with a compartment and continuum model allows clinically significant tumour sizes to be evaluated.
Results and Conclusions:  This model is used to perform multiple simulations to determine sensitivity to changes in important model parameters, specifically, the fundamental length parameter, necrotic cell degradation rate, rate of cell migration, and rate of phenotype transformation. Using these values, the model is able to simulate tumour growth and invasion behaviour, observed clinically. This mathematical model provides a means to simulate various tumour development scenarios, which may lead to a better understanding of how altering fundamental parameters can influence neoplastic progression.     

Role of proteases in activation of apoptosis

Programmed cell death, or apoptosis, is a physiological cell suicide mechanism, which is triggered in the cells by different stimuli. It has been shown that proteases play a significant role both in the target cell killing by cytotoxic lymphocytes and in the TNF- or anti-Fas-induced cell death. The proteases involved in the early (induction) and late (cell self-destruction) stages of apoptosis are reviewed. It is suggested that the late stages are connected with the activation of a cascade of intracellular proteases, which leads to massive protein destruction. It is likely that the protein destruction is mainly designed for preventing autoimmune response to proteins released from dying cells.     

Role of chloroplastidial proteases in leaf senescence

In this report the effect of hydrogen peroxide (H₂O₂) on peroxidase (POD) activity during leaf senescence was studied with and without phenylmethylsulfonyl fluoride (PMSF) pre-treatment in detached neem (Azadirachta indica A. juss) leaf chloroplasts. Increased POD activity was detected in natural and H₂O₂-promoted senescent leaf chloroplasts compared to untreated control mature green leaf chloroplasts. However, under H₂O₂ POD activity markedly increased at 1 day, and then significantly decreased until 4 days. In the presence of H₂O₂, PMSF, the induction of POD activity was alleviated at 1 day, whereas reduced after 4 days. In contrast, in the presence of H₂O₂, cycloheximide (CX), the induction of POD activity was reduced at 1 day, whereas alleviated after 4 days. The was a partial reduction in H₂O₂-induced POD activity with PMSF and CX, indicating the presence of pre-existing inactive PODs in chloroplasts. We also propose a new role for chloroplastidial proteases as activators of pre-existing inactive PODs during leaf senescence.Key words: chloroplast, leaf senescence, peroxidase, protease     

Role of ICE-related and other proteases in Fas-mediated apoptosis

Interleukin-1beta-converting enzyme (ICE)-like proteases comprise a novel family of unusual cysteine proteases which have been implicated in programmed cell death in both invertebrates and mammals. Current available evidence indicates a role of ICE proteases as central executioners of apoptosis triggered by the cell surface receptor Fas (APO-l). The presence of multiple mammalian ICE proteases with partially overlapping but distinct activities suggests a complex proteolytic cascade which is induced upon Fas ligation. The precise role of single members of the ICE family in Fas-mediated apoptosis, however, is still unclear. Here, we summarize the present knowledge about the relevance of ICE proteases, their potential targets, and interaction with unrelated proteases in cell death mediated by Fas and other apoptotic stimuli.     

Role of bacterial proteases in pseudomonal and serratial keratitis

Pseudomonas aeruginosa and Serratia marcescens can cause refractory keratitis resulting in corneal perforation and blindness. These bacteria produce various kinds of proteases. In addition to pseudomonal elastase (LasB) and alkaline protease, LasA protease and protease IV have recently been found to be more important virulence factors of P. aeruginosa . S. marcescens produces a cysteine protease in addition to metalloproteases. These bacterial proteases have a number of biological activities, such as degradation of tissue constituents and host defense-oriented proteins, as well as activation of zymogens (Hageman factor, prekallikrein and pro-matrix metalloproteinases) through limited proteolysis. In this article, the properties of these bacterial proteases are reviewed and the pathogenic roles of these proteases in pseudomonal keratitis are discussed.     

The role of malaria merozoite proteases in red blood cell invasion

Invasion of red blood cells by the malaria merozoite is an essential step in the life cycle of this obligate intracellular pathogen. The molecular details of invasion are only recently becoming understood, largely through studies in related apicomplexan parasites such as Toxoplasma. Protease activity is required for successful invasion to disengage interactions between parasite adhesins and host cell receptors. Shedding of at least two essential surface proteins from the merozoite is thought to occur continuously during invasion as the parasite moves into the nascent parasitophorous vacuole. This shedding is performed by way of juxtamembrane cleavage and is mediated by a sheddase, which probably belongs to the subtilisin-like superfamily. Recent revelations have shown that transmembrane adhesins that are secreted onto the Toxoplasma tachyzoite surface and capped to its posterior pole are shed by way of cleavage within their transmembrane domains. A family of intramembrane serine proteases called rhomboids have now been identified within Apicomplexa, and one Toxoplasma rhomboid has been localized to the posterior end of the parasite. This supports their role in capping proteolysis. Proteases involved in invasion constitute potential targets for the development of new protease inhibitor-based drugs.     

A role for ion channels in glioma cell invasion

Many cells, including neuronal and glial progenitor cells, stem cells and microglial cells, have the capacity to move through the extracellular spaces of the developing and mature brain. This is particularly pronounced in astrocyte-derived tumors, gliomas, which diffusely infiltrate the normal brain. Although a significant body of literature exists regarding signals that are involved in the guidance of cells and their processes, little attention has been paid to cell-shape and cell-volume changes of migratory cells. However, extracellular spaces in the brain are very narrow and represent a major obstacle that requires cells to dynamically regulate their volume. Recent studies in glioma cells show that this involves the secretion of Cl(-) and K(+) with water. Pharmacological inhibition of Cl(-) channels impairs their ability to migrate and limits tumor progression in experimental tumor models. One Cl(-)-channel inhibitor, chlorotoxin, is currently in Phase II clinical trials to treat malignant glioma. This article reviews our current knowledge of cell-volume changes and the role of ion channels during the migration of glioma cells. It also discusses evidence that supports the importance of channel-mediated cell-volume changes in the migration of immature neurons and progenitor cells during development. New unpublished data is presented, which demonstrates that Cl(-) and K(+) channels involved in cell shrinkage localize to lipid-raft domains on the invadipodia of glioma cells and that their presence might be regulated by trafficking of these proteins in and out of lipid rafts.     

RECK‐mediated inhibition of glioma migration and invasion

RECK is an anti‐tumoral gene whose activity has been associated with its inhibitory effects regulating MMP‐2, MMP‐9, and MT1‐MMP. RECK level decreases as gliobastoma progresses, varying from less invasive grade II gliomas to very invasive human glioblastoma multiforme (GBM). Since RECK expression and glioma invasiveness show an inverse correlation, the aim of the present study is to investigate whether RECK expression would inhibit glioma invasive behavior. We conducted this study to explore forced RECK expression in the highly invasive T98G human GBM cell line. Expression levels as well as protein levels of RECK, MMP‐2, MMP‐9, and MT1‐MMP were assessed by qPCR and immunoblotting in T98G/RECK+ cells. The invasion and migration capacity of RECK+ cells was inhibited in transwell and wound assays. Dramatic cytoskeleton modifications were observed in the T98G/RECK+ cells, when compared to control cells, such as the abundance of stress fibers (contractile actin–myosin II bundles) and alteration of lamellipodia. T98G/RECK+ cells also displayed phosphorylated focal adhesion kinase (P‐FAK) in mature focal adhesions associated with stress fibers; whereas P‐FAK in control cells was mostly associated with immature focal complexes. Interestingly, the RECK protein was predominantly localized at the leading edge of migrating cells, associated with membrane ruffles. Unexpectedly, introduced expression of RECK effectively inhibited the invasive process through rearrangement of actin filaments, promoting a decrease in migratory ability. This work has associated RECK tumor‐suppressing activity with the inhibition of motility and invasion in this GBM model, which are two glioma characteristics responsible for the inefficiency of current available treatments. J. Cell. Biochem. 110: 52–61, 2010. © 2010 Wiley‐Liss, Inc.     

Role of proteases in the pathophysiology of cardiac disease

Cardiovascular disease is a major cause of death and thus a great deal of effort has been made in salvaging the diseased myocardium. Although various factors have been identified as possible causes of different cardiac diseases such as heart failure and ischemic heart disease, there is a real need to elucidate their role for the better understanding of the cardiac disease pathology and formulation of strategies for developing newer therapeutic interventions. In view of the intimate involvement of different types of proteases in maintaining cellular structure, the role of proteases in various cardiac diseases has become the focus of recent research. Proteases are present in the cytosol as well as are localized in a number of subcellular organelles in the cell. These are known to use extracellular matrix, cytoskeletal, sarcolemmal, sarcoplasmic reticular, mitochondrial and myofibrillar proteins as substrates. Work from different laboratories using a wide variety of techniques has shown that the activation of proteases causes alterations of a number of specific proteins leading to subcellular remodeling and cardiac dysfunction. Inhibition of protease action by different drugs and agents, therefore, has a clinical relevance and is expected to form a part of new treatment paradigm for improving heart function. This review examines the biochemistry and localization of some of the proteases in the cardiac tissue in addition to identification of the sites of action of some protease inhibitors. (Mol Cell Biochem 263: 241–256, 2004)