The plasminogen activation system in tumor growth, invasion, and metastasis

Generation of the serine proteinase plasmin from the extracellular zymogen plasminogen can be catalyzed by either of two other serine proteinases, the urokinase- and tissue-type plasminogen activators (uPA and tPA). The plasminogen activation system also includes the serpins PAI-1 and PAI-2, and the uPA receptor (uPAR). Many findings, gathered over several decades, strongly suggest an important and causal role for uPA-catalyzed plasmin generation in cancer cell invasion through the extracellular matrix. Recent evidence suggests that the uPA system is also involved in cancer cell-directed tissue remodeling. Moreover, the system also supports cell migration and invasion by plasmin-independent mechanisms, including multiple interactions between uPA, uPAR, PAI-1, extracellular matrix proteins, integrins, endocytosis receptors, and growth factors. These interactions seem to allow temporal and spatial reorganizations of the system during cell migration and a selective degradation of extracellular matrix proteins during invasion. The increased knowledge about the plasminogen activation system may allow utilization of its components as targets for anti-invasive therapy.     

Héparine et fibrinolyse

Summary In vitro study of the influence of heparin on fibrinolysis. Heparin, in high concentration, inhibits plasminogen activation by streptokinase or urokinase. The presence of some plasmatic component is herefore required. Heparin has no effect on the fibrinolytic activity of bovine plasmin orAspergillus protease. Heparin does not promote fibrinolysis.

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Travail réalisé avec l'aide financière de l'U.S. National Institute of Health (Grant H-5698).     

Mast cell tryptase,a still enigmatic enzyme

Tryptases constitute a subfamily of trypsin-like proteinases, stored in the mast cell secretory granules of all mammalian organisms. These enzymes are released along with other mediators into the extracellular medium upon mast cell activation/degranulation. Among the trypsin-like enzymes, tryptases are unique: they are present as active enzymes in the mast cell granules, but display activity only extracellularly, and have a specificity which is much more restricted than trypsin. Tryptases are mostly tetrameric, and in only few organisms (not in humans) are they inhibited by endogenous inhibitors in vitro. The enzymatic and molecular properties of tryptases are far better characterized that any of their plausible biological functions. On the basis of its structural and functional features it could be predicted that tryptase would not degrade a large number of proteins in vivo due to low accessibility to the tetramer central pore where the active sites face inwards. Although their biological function has not yet been clarified, tryptases seem to be involved in a number of mast cell-mediated allergic and inflammatory diseases. In particular, the involvement of tryptase in asthma, an inflammatory disease of the airways often caused by allergy, has been proposed. Here we review the present knowledge on the structure-function relationship of tryptases from different organisms, with special emphasis on human enzymes, and on their role in a variety of pathophsyiological processes.Received 29 October 2003; received after revision 3 December 2003; accepted 11 December 2003     

Maternal signals for progeny prevention against allergy and asthma

Allergy and asthma are chronic inflammatory diseases which result from complex gene–environment interactions. Recent evidence indicates the importance of prenatal and postnatal developmental processes in terms of maturation of balanced immune responses. According to the current view, gene–environment interactions during a restricted time frame are responsible for programming of the immune system in favor of allergic immune mechanisms later in life. The interaction between genes and environment is complex and only partially understood; however, heritable epigenetic modifications including chemical additions in and alternative packaging of the DNA have been shown to play a crucial role in this context. Novel data indicate that epigenetic mechanisms contribute to the development of T-helper cell function. Environmental factors, including diesel exhaust particles (DEP), vitamins and tobacco smoke, operate through such mechanisms. Furthermore, the role of environmental microbes provides another and maybe even more important group of exogenous exposures which operates in this critical time frame.     

Regulation and interactions in the activation of cell-associated plasminogen

The main components in plasminogen activation include plasminogen, tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), urokinase plasminogen activator receptor (uPAR), and plasminogen activator inhibitors-1 and –2 (PAI-1, PAI-2). These components are subject to extensive regulation and interactions with for example, pericellular adhesion molecules. Although uPA and tPA are quite similar in structure and have common inhibitors and physiological substrates, their physiological roles are distinct. Traditionally, the role of tPA has been in fibrinolysis and that of uPA in cell migration, especially in cancer cells. Recently several targets for tPA/plasmin have been found in neuronal tissues. The functional role of the PAIs is no longer simply to inhibit overexpressed plasminogen activators, and PAI-2 has an unidentified role in the regulation of cell death.Received 2 June 2004; received after revision 30 June 2004; accepted 20 July 2004     

The plasminogen activator system: biology and regulation

The regulation of plasminogen activation involves genes for two plasminogen activators (tissue type and urokinase type), two specific inhibitors (type 1 and type 2), and a membrane-anchored urokinase-type plasminogen-activator-specific receptor. This system plays an important role in various biological processes involving extracellular proteolysis. Recent studies have revealed that the system, through interplay with integrins and the extracellular matrix protein vitronectin, is also involved in the regulation of cell migration and proliferation in a manner independent of proteolytic activity. The genes are expressed in many different cell types and their expression is under the control of diverse extracellular signals. Gene expression reflects the levels of the corresponding mRNA, which should be the net result of synthesis and degradation. Thus, modulation of mRNA stability is an important factor in overall regulation. This review summarizes current understanding of the biology and regulation of genes involved in plasminogen activation at different levels. Received 21 December 1998; received after revision 8 March 1999; accepted 14 April 1999     

Regulation of myelopoiesis by proinflammatory cytokines in infectious diseases

Hematopoiesis is hierarchically orchestrated by a very small population of hematopoietic stem cells (HSCs) that reside in the bone-marrow niche and are tightly regulated to maintain homeostatic blood production. HSCs are predominantly quiescent, but they enter the cell cycle in response to inflammatory signals evoked by severe systemic infection or injury. Thus, hematopoietic stem and progenitor cells (HSPCs) can be activated by pathogen recognition receptors and proinflammatory cytokines to induce emergency myelopoiesis during infection. This emergency myelopoiesis counterbalances the loss of cells and generates lineage-restricted hematopoietic progenitors, eventually replenishing mature myeloid cells to control the infection. Controlled generation of such signals effectively augments host defense, but dysregulated stimulation by these signals is harmful to HSPCs. Such hematopoietic failure often results in blood disorders including chronic inflammatory diseases and hematological malignancies. Recently, we found that interleukin (IL)-27, one of the IL-6/IL-12 family cytokines, has a unique ability to directly act on HSCs and promote their expansion and differentiation into myeloid progenitors. This process resulted in enhanced production of neutrophils by emergency myelopoiesis during the blood-stage mouse malaria infection. In this review, we summarize recent advances in the regulation of myelopoiesis by proinflammatory cytokines including type I and II interferons, IL-6, IL-27, granulocyte colony-stimulating factor, macrophage colony-stimulating factor, and IL-1 in infectious diseases.     

Mitochondrial dysfunction and oxidative stress activate inflammasomes: impact on the aging process and age-related diseases

Oxidative stress and low-grade inflammation are the hallmarks of the aging process and are even more enhanced in many age-related degenerative diseases. Mitochondrial dysfunction and oxidative stress can provoke and potentiate inflammatory responses, but the mechanism has remained elusive. Recent studies indicate that oxidative stress can induce the assembly of multiprotein inflammatory complexes called the inflammasomes. Nod-like receptor protein 3 (NLRP3) is the major immune sensor for cellular stress signals, e.g., reactive oxygen species, ceramides, and cathepsin B. NLRP3 activation triggers the caspase-1-mediated maturation of the precursors of IL-1β and IL-18 cytokines. During aging, the autophagic clearance of mitochondria declines and dysfunctional mitochondria provoke chronic oxidative stress, which disturbs the cellular redox balance. Moreover, increased NF-κB signaling observed during aging could potentiate the expression of NLRP3 and cytokine proforms enhancing the priming of NLRP3 inflammasomes. Recent studies have demonstrated that NLRP3 activation is associated with several age-related diseases, e.g., the metabolic syndrome. We will review here the emerging field of inflammasomes in the appearance of the proinflammatory phenotype during the aging process and in age-related diseases.     

The role of the nuclear envelope in cellular organization

Over the last years it has become evident that the nuclear envelope (NE) is more than a passive membrane barrier that separates the nucleus from the cytoplasm. The NE not only controls the trafficking of macromolecules between the nucleoplasm and the cytosol, but also provides anchoring sites for chromosomes and cytoskeleton to the nuclear periphery. Targeting of chromatin to the NE might actually be part of gene expression regulation in eukaryotes. Mutations in certain NE proteins are associated with a diversity of human diseases, including muscular dystrophy, neuropathy, lipodistrophy, torsion dystonia and the premature aging condition progeria. Despite the importance of the NE for cell division and differentiation, relatively little is known about its biogenesis and its role in human diseases. It is our goal to provide a comprehensive view of the NE and to discuss possible implications of NE-associated changes for gene expression, chromatin organization and signal transduction. Received 8 August 2005; received after revision 13 October 2005; accepted 13 October 2005     

Novel insights into the biology of interleukin-32

Interleukin (IL)-32 is known as a proinflammatory cytokine that is likely involved in several diseases, including infections, chronic inflammation, and cancer. Since the first report in 2005, IL-32 has been the subject of numerous studies to unravel the biological function of this molecule. For example, silencing of endogenous IL-32 in primary or cell lines of human origin consistently suppressed responses to Toll-like receptors. The protein folding structure of the six isoforms of IL-32 does not resemble that of any classical cytokine and as of this writing, a specific IL-32 receptor has not been identified. Instead, we propose a mechanism by which exposure to extracellular IL-32 or overexpression of the molecule results in binding to intracellular partners that influences functions such as gene expression, cell death, or survival. As such, this review offers insights into the role of IL-32 in several diseases, host defense, inflammation, immune function, and cancer. Finally, possibilities to target IL-32 in several diseases are proposed.     

NOD-like receptors: Ancient sentinels of the innate immune system

NOD-like receptors (NLRs) comprise a family of cytosolic proteins that have been implicated as ancient cellular sentinels mediating protective immune responses elicited by intracellular pathogens or endogenous danger signals. Genetic variants in NLR genes have been associated with complex chronic inflammatory barrier diseases (e.g. Crohn disease, bronchial asthma). In this review, we focus on the molecular pathophysiology of NLRs in the context of chronic inflammatory diseases and pinpoint recent advances in the evolutionary understanding of NLR biology. We propose that the field of NLRs may serve as a prototype for how a comprehensive understanding of an element of the immunological barrier will eventually lead to the development of targeted diagnostic, therapeutic and/or preventive strategies. Received 29 October 2007; received after revision 10 December 2007; accepted 19 December 2007     

Redox-dependent thiol modifications: implications for the release of extracellular vesicles

Extracellular vesicles (EVs), including microvesicles and exosomes, are emerging as important regulators of homeostasis and pathophysiology. During pro-inflammatory and pro-oxidant conditions, EV release is induced. As EVs released under such conditions often exert pro-inflammatory and procoagulant effects, they may actively promote the pathogenesis of chronic diseases. There is evidence that thiol group-containing antioxidants can prevent EV induction by pro-inflammatory and oxidative stimuli, likely by protecting protein thiols of the EV-secreting cells from oxidation. As the redox state of protein thiols greatly impacts three-dimensional protein structure and, consequently, function, redox modifications of protein thiols may directly modulate EV release in response to changes in the cell’s redox environment. In this review article, we discuss targets of redox-dependent thiol modifications that are known or expected to be involved in the regulation of EV release, namely redox-sensitive calcium channels, N-ethylmaleimide sensitive factor, protein disulfide isomerase, phospholipid flippases, actin filaments, calpains and cell surface-exposed thiols. Thiol protection is proposed as a strategy for preventing detrimental changes in EV signaling in response to inflammation and oxidative stress. Identification of the thiol-containing proteins that modulate EV release in pro-oxidant environments could provide a rationale for broad application of thiol group-containing antioxidants in chronic inflammatory diseases.     

A novel fibrinolytic enzyme (nattokinase) in the vegetable cheese Natto; a typical and popular soybean food in the Japanese diet

Summary A strong fibrinolytic activity was demonstrated in the vegetable cheese Natto, which is a typical soybean food eaten in Japan. The average activity was calculated at about 40 CU (plasmin units)/g wet weight. This novel fibrinolytic enzyme, named nattokinase, was easily extracted with saline. The mol. wt and pI were about 20,000 and 8.6, respectively. Nattokinase not only digested fibrin but also the plasmin substrate H-D-Val-Leu-Lys-pNA (S-2251), which was more sensitive to the enzyme than other substrates tried. Diisopropyl fluorophosphate and 2,2,2-trichloro-1-hydroxyethyl-o,o-dimethylphosphate strongly inhibited this fibrinolytic enzyme.     

A novel fibrinolytic enzyme (nattokinase) in the vegetable cheese Natto; a typical and popular soybean food in the Japanese diet

A strong fibrinolytic activity was demonstrated in the vegetable cheese Natto, which is a typical soybean food eaten in Japan. The average activity was calculated at about 40 CU (plasmin units)/g wet weight. This novel fibrinolytic enzyme, named nattokinase, was easily extracted with saline. The mol. wt and pI were about 20,000 and 8.6, respectively. Nattokinase not only digested fibrin but also the plasmin substrate H-D-Val-Leu-Lys-pNA (S-2251), which was more sensitive to the enzyme than other substrates tried. Diisopropyl fluorophosphate and 2,2,2-trichloro-1-hydroxyethyl-o,o-dimethylphosphate strongly inhibited this fibrinolytic enzyme.     

Calcium and disease: molecular determinants of calcium crystal deposition diseases

Deposition of basic calcium phosphate (hydroxyapatite, octacalcium phosphate and tricalcium phosphate) (BCP) and crystalline calcium pyrophosphate dihydrate (CPPD) is associated with a variety of aging-related pathologies, including osteoarthritis, cartilage degeneration and pseudogout. These diseases of calcium deposition serve as some of the best-studied examples of how calcium-regulated changes in gene expression can directly lead to pathogenic consequences. Tissue damage can result when crystals stimulate cells to release matrix-degrading molecules or secrete cytokines that stimulate the release of matrix-degrading molecules. Exposure of cultured cells to crystals induces expression of cellular proto-oncogenes such as c-fos, c-myc and c-jun, by a calcium-dependent mechanism, and this response can be blocked by a potential therapeutic compound, phosphocitrate. Activation of the c-fos and c-jun genes is directly involved in expression of metalloproteinases such as collagenase and stromelysin, suggesting that crystal-mediated activation of these genes is directly involved in pathogenesis. In this review recent advances in the molecular mechanisms responsible for crystal-mediated cell activation are discussed.     

Serglycin – Structure and biology

Serglycin is a proteoglycan found in hematopoietic cells and endothelial cells. It has important functions related to formation of several types of storage granules. In connective tissue mast cells the covalently attached glycosaminoglycan is heparin, whereas mucosal mast cells and activated macrophages contain oversulfated chondroitin sulfate (type E). In mast cells, serglycin interact with histamine, chymase, tryptase and carboxypeptidase, in neutrophils with elastase, in cytotoxic T cells with granzyme B, in endothelial cells with tissue-type plasminogen activator and in macrophages with tumor necrosis factor-α. Serglycin is important for the retention of key inflammatory mediators inside storage granules and secretory vesicles. Serglycin can further modulate the activities of partner molecules in different ways after secretion from activated immune cells, through protection, transport, activation and interactions with substrates or target cells. Serglycin is a proteoglycan with important roles in inflammatory reactions. Received 2 October 2007; received after revision 7 November 2007; accepted 12 November 2007     

The cytotoxicity of eosinophil cationic protein/ribonuclease 3 on eukaryotic cell lines takes place through its aggregation on the cell membrane

Human eosinophil cationic protein (ECP)/ ribonuclease 3 (RNase 3) is a protein secreted from the secondary granules of activated eosinophils. Specific properties of ECP contribute to its cytotoxic activities associated with defense mechanisms. In this work the ECP cytotoxic activity on eukaryotic cell lines is analyzed. The ECP effects begin with its binding and aggregation to the cell surface, altering the cell membrane permeability and modifying the cell ionic equilibrium. No internalization of the protein is observed. These signals induce cell-specific morphological and biochemical changes such as chromatin condensation, reversion of membrane asymmetry, reactive oxygen species production and activation of caspase-3-like activity and, eventually, cell death. However, the ribonuclease activity component of ECP is not involved in this process as no RNA degradation is observed. In summary, the cytotoxic effect of ECP is attained through a mechanism different from that of other cytotoxic RNases and may be related with the ECP accumulation associated with the inflammatory processes, in which eosinophils are present. Received 26 October 2007; accepted 23 November 2007     

The plasmin–antiplasmin system: structural and functional aspects

The plasmin–antiplasmin system plays a key role in blood coagulation and fibrinolysis. Plasmin and α₂-antiplasmin are primarily responsible for a controlled and regulated dissolution of the fibrin polymers into soluble fragments. However, besides plasmin(ogen) and α₂-antiplasmin the system contains a series of specific activators and inhibitors. The main physiological activators of plasminogen are tissue-type plasminogen activator, which is mainly involved in the dissolution of the fibrin polymers by plasmin, and urokinase-type plasminogen activator, which is primarily responsible for the generation of plasmin activity in the intercellular space. Both activators are multidomain serine proteases. Besides the main physiological inhibitor α₂-antiplasmin, the plasmin–antiplasmin system is also regulated by the general protease inhibitor α₂-macroglobulin, a member of the protease inhibitor I39 family. The activity of the plasminogen activators is primarily regulated by the plasminogen activator inhibitors 1 and 2, members of the serine protease inhibitor superfamily.