Structural requirements for the growth factor activity of the amino-terminal domain of urokinase

The Plasminogen Activation System Promotes Neurorepair in the Ischemic Brain

The plasminogen activation (PA) system was originally thought to exclusively promote the degradation of fibrin by catalyzing the conversion of plasminogen into plasmin via two serine proteinases: tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA). However, experimental evidence accumulated over the last 30 years indicates that tPA and uPA are also found in the central nervous system (CNS), where they have a plethora of functions that not always require plasmin generation or fibrin degradation. For example, plasminogen-dependent and - independent effects of tPA and uPA play a central role in the pathophysiological events that underlie one of the leading causes of mortality and disability in the world: cerebral ischemia. Indeed, recent work indicates that while the rapid release of tPA from the presynaptic compartment following the onset of cerebral ischemia protects the synapse from the deleterious effects of the ischemic injury, the secretion of uPA and its binding to its receptor (uPAR) during the recovery phase promotes the repair of synapses that have been lost to the acute ischemic insult. This restorative role of uPA has high translational significance because to this date there is no effective approach to induce neurorepair in the ischemic brain. Here we will discuss recent evidence that bridges the gap between basic research in the field of the PA system and the bedside of ischemic stroke patients, indicating that uPA and uPAR are potential targets for the development of therapeutic strategies to promote neurological recovery among ischemic stroke survivors.

Epiregulin promotes trophoblast epithelial-mesenchymal transition through poFUT1 and O-fucosylation by poFUT1 on uPA

Objectives

The transformation of cytotrophoblasts into mesenchymal‐like extravillous trophoblasts is necessary for successful embryo implantation, and the inadequate transformation may cause abortion. Epiregulin, which is a new growth factor, plays important roles in the reproductive processes. The glycosylation of many proteins in reproduction processes is critical. Protein O‐fucosyltransferase 1 (poFUT1) is the key enzyme for the biosynthesis of O‐fucosylation on the specific glycoproteins. Urokinase‐type plasminogen activator (uPA) contains O‐fucosylated domain on Thr¹⁸. However, the functions of epiregulin and poFUT1 in the trophoblast epithelial–mesenchymal transition (EMT) process, the regulatory mechanism of epiregulin on poFUT1 and the resulting O‐fucosylated uPA remain unclear.

Materials and methods

We employed ELISA and Western blot to detect serum levels of epiregulin and poFUT1 from non‐pregnancy women, pregnancy women and abortion patients. Using two trophoblast cell lines and a mouse pregnancy model, we investigated the underlying mechanisms of epiregulin and poFUT1 in trophoblast EMT process.

Results

Serum levels of epiregulin and poFUT1 were higher in pregnant women compared with non‐pregnant women, and their levels were significantly decreased in abortion patients compared with pregnant women. The results showed that epiregulin upregulated poFUT1 expression and increased O‐fucosylation on uPA, which further activated the PI3K/Akt signalling pathway, facilitating EMT behaviour of trophoblast cells and embryo implantation in the mouse pregnant model.

Conclusions

Level of epiregulin and poFUT1 is lower in abortion patients than early pregnancy women. Epiregulin promotes trophoblast EMT through O‐fucosylation on uPA catalysed by poFUT1. Epiregulin and poFUT1 may be suggested as the potential diagnostic biomarkers and useful treatment targets for abortion.

poFUT1 promotes uterine angiogenesis and vascular remodeling via enhancing the O-fucosylation on uPA

Uterine angiogenesis and vascular remodeling play critical roles in determing the normal menstrual cycle and successful pregnancy. Poor uterine angiogenesis usually results in pregnancy failure. Protein O-fucosyltransferase 1 (poFUT1) is the key enzyme responsible for O-fucosylated glycan biosynthesis on glycoproteins. However, the dynamic expression and regulation of poFUT1 on the uterine angiogenesis and vascular remodeling remain unknown. Here, we showed that the enlargement of the vascular lumen in the secretory phase was greater than that in the proliferative phase of the uterine endometrium during menstrual cycle; whereas there was a narrower vessel lumen and fewer blood vessels in the decidua from miscarriage patients than in that from healthy pregnancy women. Additionally, the expression of poFUT1 was increased in the uterine endometrium during the secretory phase compared with that in the proliferation phase, and its expression was decreased in the uterus of miscarriage patients compared with that of the healthy pregnancy women. Using hESCs and a mouse model, we demonstrated that poFUT1 increased the O-fucosylation on uPA, and activated of the RhoA signaling pathway, thus facilitating uterine angiogenesis and vascular remodeling. We also provide evidence that poFUT1 promotes hESCs angiogenesis by the decreased stemness of hESCs. These findings reveal a new insight into the uterine angiogenesis and vascular remodeling. The study suggests that poFUT1 could be seen as a novel potential diagnostic and therapeutic target for miscarriage.

Biosynthetic Routes for Producing Various Fucosyl-Oligosaccharides

Fucosyl-oligosaccharides (FOSs) play physiologically important roles as prebiotics, neuronal growth factors, and inhibitors of enteropathogens. However, challenges in designed synthesis and mass production of FOSs hamper their industrial applications. Here, we report flexible biosynthetic routes to produce various FOSs, including unnatural ones, through in vitro enzymatic reactions of various sugar acceptors, such as glucose, cellobiose, and agarobiose, and GDP-l-fucose as the fucose donor by using α1,2-fucosyltransferase (FucT2). Also, the whole-cell conversion for fucosylation of various sugar acceptors by overexpressing the genes associated with GDP-l-fucose production and fucT2 gene in Escherichia coli was demonstrated by producing 17.74 g/L of 2'-fucosylgalactose (2'-FG). Prebiotic effects of 2'-FG were verified on the basis of selective fermentability of 2'-FG by probiotic bifidobacteria. These biosynthetic routes can be used to engineer industrial microorganisms for more economical, more flexible, and safer production of FOSs than chemical synthesis of FOSs.

Multifaceted Role of the Urokinase-Type Plasminogen Activator (uPA) and Its Receptor (uPAR): Diagnostic, Prognostic, and Therapeutic Applications

The plasminogen activator (PA) system is an extracellular proteolytic enzyme system associated with various physiological and pathophysiological processes. A large body of evidence support that among the various components of the PA system, urokinase-type plasminogen activator (uPA), its receptor (uPAR), and plasminogen activator inhibitor-1 and -2 (PAI-1 and PAI-2) play a major role in tumor progression and metastasis. The binding of uPA with uPAR is instrumental for the activation of plasminogen to plasmin, which in turn initiates a series of proteolytic cascade to degrade the components of the extracellular matrix, and thereby, cause tumor cell migration from the primary site of origin to a distant secondary organ. The components of the PA system show altered expression patterns in several common malignancies, which have identified them as ideal diagnostic, prognostic, and therapeutic targets to reduce cancer-associated morbidity and mortality. This review summarizes the various components of the PA system and focuses on the role of uPA-uPAR in different biological processes especially in the context of malignancy. We also discuss the current state of knowledge of uPA-uPAR-targeted diagnostic and therapeutic strategies for various malignancies.

A structural mechanism of flavonoids in inhibiting serine proteases

The crystal structure of quercerin:uPA reveals that catechol serves as the functional group in inhibiting serine proteases.

Zinc phthalocyanine conjugated with the amino-terminal fragment of urokinase for tumor-targeting photodynamic therapy

Photodynamic therapy (PDT) has attracted much interest for the treatment of cancer due to the increased incidence of multidrug resistance and systemic toxicity in conventional chemotherapy. Phthalocyanine (Pc) is one of main classes of photosensitizers for PDT and possesses optimal photophysical and photochemical properties. A higher specificity can ideally be achieved when Pcs are targeted towards tumor-specific receptors, which may also facilitate specific drug delivery. Herein, we develop a simple and unique strategy to prepare a hydrophilic tumor-targeting photosensitizer ATF-ZnPc by covalently coupling zinc phthalocyanine (ZnPc) to the amino-terminal fragment (ATF) of urokinase-type plasminogen activator (uPA), a fragment responsible for uPA receptor (uPAR, a biomarker overexpressed in cancer cells), through the carboxyl groups of ATF. We demonstrate the high efficacy of this tumor-targeting PDT agent for the inhibition of tumor growth both in vitro and in vivo. Our in vivo optical imaging results using H22 tumor-bearing mice show clearly the selective accumulation of ATF-ZnPc in tumor region, thereby revealing the great potential of ATF-ZnPc for clinical applications such as cancer detection and guidance of tumor resection in addition to photodynamic treatment.

Multi-tissue microarray analysis identifies a molecular signature of regeneration

The inability to functionally repair tissues that are lost as a consequence of disease or injury remains a significant challenge for regenerative medicine. The molecular and cellular processes involved in complete restoration of tissue architecture and function are expected to be complex and remain largely unknown. Unlike humans, certain salamanders can completely regenerate injured tissues and lost appendages without scar formation. A parsimonious hypothesis would predict that all of these regenerative activities are regulated, at least in part, by a common set of genes. To test this hypothesis and identify genes that might control conserved regenerative processes, we performed a comprehensive microarray analysis of the early regenerative response in five regeneration-competent tissues from the newt Notophthalmus viridescens. Consistent with this hypothesis, we established a molecular signature for regeneration that consists of common genes or gene family members that exhibit dynamic differential regulation during regeneration in multiple tissue types. These genes include members of the matrix metalloproteinase family and its regulators, extracellular matrix components, genes involved in controlling cytoskeleton dynamics, and a variety of immune response factors. Gene Ontology term enrichment analysis validated and supported their functional activities in conserved regenerative processes. Surprisingly, dendrogram clustering and RadViz classification also revealed that each regenerative tissue had its own unique temporal expression profile, pointing to an inherent tissue-specific regenerative gene program. These new findings demand a reconsideration of how we conceptualize regenerative processes and how we devise new strategies for regenerative medicine.

Potential role of kringle-integrin interaction in plasmin and uPA actions (a hypothesis)

We previously showed that the kringle domains of plasmin and angiostatin, the N-terminal four kringles (K1–4) of plasminogen, directly bind to integrins. Angiostatin blocks tumor-mediated angiogenesis and has great therapeutic potential. Angiostatin binding to integrins may be related to the antiinflammatory action of angiostatin. We reported that plasmin induces signals through protease-activated receptor (PAR-1), and plasmin-integrin interaction may be required for enhancing plasmin concentration on the cell surface, and enhances its signaling function. Angiostatin binding to integrin does not seem to induce proliferative signals. One possible mechanism of angiostatin's inhibitory action is that angiostatin suppresses plasmin-induced PAR-1 activation by competing with plasmin for binding to integrins. Interestingly, plasminogen did not interact with αvβ3, suggesting that the αvβ3-binding sites in the kringle domains of plasminogen are cryptic. The kringle domain of urokinase-type plasminogen activator (uPA) also binds to integrins. The uPA-integrin interaction enhances uPA concentrations on the cell surface and enhances plasminogen activation on the cell surface. It is likely that integrins bind to the kringle domain, and uPAR binds to the growth factor-like domain (GFD) of uPA simultaneously, making the uPAR-uPA-integrin ternary complex. We present a docking model of the ternary complex.

Targeting the embryonic gene Cripto-1 in cancer and beyond

IMPORTANCE OF THE FIELD

Emerging evidence has clearly implicated an inappropriate activation of embryonic regulatory genes during cell transformation in adult tissues. An example of such a case is the embryonic gene Cripto-1. Cripto-1 is critical for embryonic development and is considered a marker of undifferentiated embryonic stem cells. Critpo-1 is expressed at low levels in adult tissues, but is re-expressed at a high frequency in a number of different types of human carcinomas, therefore, representing an attractive therapeutic target in cancer.

AREA COVERED IN THIS REVIEW

This review surveys different approaches that have been used to target Cripto-1 in cancer as reflected by the relevant patent literature as well as peer-reviewed publications. Potential involvement and targeting of Cripto-1 in neurodegenerative and degenerative muscle diseases are also discussed.

WHAT THE READER WILL GAIN

The reader will gain an overview of different mAbs, vaccines or oligonucleotides antisense targeting Cripto-1. A humanized anti-Cripto-1 antibody is currently being tested in a Phase I clinical trial in cancer patients.

TAKE HOME MESSAGE

Targeting Cripto-1 in human tumors has the potential to eliminate not only differentiated cancer cells but also destroy an undifferentiated subpopulation of cancer cells with stem-like characteristics that support tumor initiation and self-renewal.

O-GlcNAc modification of the extracellular domain of Notch receptors

Epidermal growth factor (EGF) domains are posttranslationally modified with unique O-linked glycans. The classical types of O-glycans on EGF domains are O-fucose and O-glucose glycans, found on many plasma glycoproteins and signaling molecules, whose biological functions have been demonstrated especially in the context of the Notch signaling pathway. We recently discovered O-GlcNAc modification as a new modification of the EGF domain that occurs on the conserved Ser/Thr residue located between the fifth and sixth cysteine residues within the EGF domain of Notch receptors in Drosophila. Here, we describe the methods employed to detect the O-GlcNAc modification of EGF repeats of Notch receptors. These methods include mass spectrometric analysis, galactosyltransferase labeling, immunoblotting with a specific antibody, and beta-N-acetyl-hexosaminidase digestion experiments. We also describe a method to detect O-GlcNAc transferase activity from crude membrane fraction proteins prepared from cultured S2 cells.

Soluble urokinase receptor conjugated to carrier red blood cells binds latent pro-urokinase and alters its functional profile

Coupling plasminogen activators to carrier red blood cells (RBC) prolongs their life-time in the circulation and restricts extravascular side effects, thereby allowing their utility for short-term thromboprophylaxis. Unlike constitutively active plasminogen activators, single chain urokinase plasminogen activator (scuPA) is activated by plasmin proteolysis or binding to its receptor, uPAR. In this study we conjugated recombinant soluble uPAR (suPAR) to rat RBC, forming RBC/suPAR complex. RBC carrying suPAR circulated in rats similarly to naïve RBC and markedly prolonged the circulation time of suPAR. RBC/suPAR carrying approximately 3x10(4) suPAR molecules per RBC specifically bound up to 2x10(4) molecules of scuPA, retained approximately 75% of scuPA-binding capacity after circulation in rats and markedly altered the functional profile of bound scuPA. RBC carrying directly conjugated scuPA adhered to endothelial cells, while showing no appreciable fibrinolytic activity. In contrast, RBC/suPAR loaded with scuPA did not exhibit increased adhesion to endothelium, while effectively dissolving fibrin clots. This molecular design, capitalizing on unique biological features of the interaction of scuPA with its receptor, provides a promising modality to deliver a pro-drug for prevention of thrombosis.

Regulation of arterial remodeling and angiogenesis by urokinase-type plasminogen activatorThis article is one of a selection of papers from the NATO Advanced Research Workshop on Translational Knowledge for Heart Health (published in part 2 of a 2-part Special Issue)

A wide variety of disorders are associated with an imbalance in the plasminogen activator system, including inflammatory diseases, atherosclerosis, intimal hyperplasia, the response mechanism to vascular injury, and restenosis. Urokinase-type plasminogen activator (uPA) is a multifunctional protein that in addition to its fibrinolytic and matrix degradation capabilities also affects growth factor bioavailability, cytokine modulation, receptor shedding, cell migration and proliferation, phenotypic modulation, protein expression, and cascade activation of proteases, inhibitors, receptors, and modulators. uPA is the crucial protein for neointimal growth and vascular remodeling. Moreover, it was recently shown to be implicated in the stimulation of angiogenesis, which makes it a promising multipurpose therapeutic target. This review is focused on the mechanisms by which uPA can regulate arterial remodeling, angiogenesis, and cell migration and proliferation after arterial injury and the means by which it modulates gene expression in vascular cells. The role of domain specificity of urokinase in these processes is also discussed.

Notch-dependent control of myelopoiesis is regulated by fucosylation

Cell-cell contact-dependent mechanisms that modulate proliferation and/or differentiation in the context of hematopoiesis include mechanisms characteristic of the interactions between members of the Notch family of signal transduction molecules and their ligands. Whereas Notch family members and their ligands clearly modulate T lymphopoietic decisions, evidence for their participation in modulating myelopoiesis is much less clear, and roles for posttranslational control of Notch-dependent signal transduction in myelopoiesis are unexplored. We report here that a myeloproliferative phenotype in FX(-/-) mice, which are conditionally deficient in cellular fucosylation, is consequent to loss of Notch-dependent signal transduction on myeloid progenitor cells. In the context of a wild-type fucosylation phenotype, we find that the Notch ligands suppress myeloid differentiation of progenitor cells and enhance expression of Notch target genes. By contrast, fucosylation-deficient myeloid progenitors are insensitive to the suppressive effects of Notch ligands on myelopoiesis, do not transcribe Notch1 target genes when cocultured with Notch ligands, and have lost the wild-type Notch ligand-binding phenotype. Considered together, these observations indicate that Notch-dependent signaling controls myelopoiesis in vivo and in vitro and identifies a requirement for Notch fucosylation in the expression of Notch ligand binding activity and Notch signaling efficiency in myeloid progenitors.

O-glucosylation and O-fucosylation occur together in close proximity on the first epidermal growth factor repeat of AMACO (VWA2 protein)

AMACO (VWA2 protein) is an extracellular matrix protein of unknown function associated with certain basement membranes in skin, lung, and kidney. AMACO is a member of the von Willebrand factor A-like (VWA) domain containing protein superfamily and in addition to three VWA domains it also contains two epidermal growth factor-like domains. One of these contains the rare, overlapping consensus sequences for both O-glucosylation and O-fucosylation. In earlier studies of other proteins the attachment of either core glucose and fucose moieties or of the respective elongated glycans starting with these monosaccharides has been described. By a detailed mass spectrometric analysis we show that both elongated O-glucosylated (Xyl1-3Xyl1-3Glc) and elongated O-fucosylated glycan chains (NeuAc2-3Gal1-4GlcNAc1-3Fuc) can be attached to AMACO in close proximity on the same epidermal growth factor-like domain. It has been reported that the lack of O-fucosylation can markedly decrease secretion of proteins. However, the secretion of AMACO is not significantly affected when the glycosylation sites are mutated. The number of extracellular matrix proteins carrying the overlapping consensus sequence is very limited and it could be that these modifications have a new, yet unknown function.

Biological functions of glycosyltransferase genes involved in O-fucose glycan synthesis

Rare types of glycosylation often occur in a domain-specific manner and are involved in specific biological processes. Well-known examples of such modification are O-linked fucose (O-fucose) and O-linked glucose (O-glucose) glycans on epidermal growth factor (EGF) domains. In particular, O-fucose glycans are reported to regulate the functions of EGF domain-containing proteins such as urinary-type plasminogen activator and Notch receptors. Two glycosyltransferases catalyze the initiation and elongation of O-fucose glycans. The initiation process is catalyzed by O-fucosyltransferase 1, which is essential for Notch signalling in both Drosophila and mice. O-fucosyltransferase 1 can affect the folding, ligand interaction and endocytosis of Notch receptors, and both the glycosyltransferase and non-catalytic activities of O-fucosyltransferase 1 have been reported. The elongation of O-fucose monosaccharide is catalyzed by Fringe-related genes, which differentially modulate the interaction between Notch and two classes of ligands, namely, Delta and Serrate/Jagged. In this article, we have reviewed the recent reports addressing the distinctive features of the glycosyltransferases and O-glycans present on the EGF domains.

Structural basis of specificity of a peptidyl urokinase inhibitor, upain-1

Urokinase-type plasminogen activator (uPA) plays a crucial role in the regulation of plasminogen activation, tumor cell adhesion and migration. The inhibition of uPA activity is a promising mechanism for anti-cancer therapy. A cyclic peptidyl inhibitor, upain-1, CSWRGLENHRMC, was identified recently as a competitive and highly specific uPA inhibitor. We determined the crystal structure of uPA in complex with upain-1 at 2.15 A. The structure reveals that the cyclic peptide adopts a rigid conformation stabilized by a disulfide bond (residues 1-12) and three tight beta turns (residues 3-6, 6-9, 9-12). The Glu7 residue of upain-1 forms hydrogen bonds with the main chain nitrogen atoms of residues 4, 5, and 6 of upain-1, and is also critical for maintaining the active conformation of upain-1. The Arg4 of upain-1 is inserted into the uPA's specific S1 pocket. The Ser2 residue of upain-1 locates close to the S1beta pocket of uPA. The Gly5 and Glu7 residues of upain-1 occupy the S2 pocket and the oxyanion hole of uPA, respectively. Furthermore, the Asn8 residue of upain-1 binds to the 37- and 60-loops of uPA and renders the specificity of upain-1 for uPA. Based on this structure, a new pharmacophore for the design of highly specific uPA inhibitors was proposed.

O-fucosylation is required for ADAMTS13 secretion

ADAMTS13 is a plasma metalloproteinase that cleaves von Willebrand factor to smaller, less thrombogenic forms. Deficiency of ADAMTS13 activity in plasma leads to thrombotic thrombocytopenic purpura. ADAMTS13 contains eight thrombospondin type 1 repeats (TSR), seven of which contain a consensus sequence for the direct addition of fucose to the hydroxyl group of serine or threonine. Mass spectral analysis of tryptic peptides derived from human ADAMTS13 indicate that at least six of the TSRs are modified with an O-fucose disaccharide. Analysis of [(3)H]fucose metabolically incorporated into ADAMTS13 demonstrated that the disaccharide has the structure glucose-beta1,3-fucose. Mutation of the modified serine to alanine in TSR2, TSR5, TSR7, and TSR8 reduced the secretion of ADAMTS13. Mutation of more than one site dramatically reduced secretion regardless of the sites mutated. When the expression of protein O-fucosyltransferase 2 (POFUT2), the enzyme that transfers fucose to serines in TSRs, was reduced using siRNA, the secretion of ADAMTS13 decreased. A similar outcome was observed when ADAMTS13 was expressed in a cell line unable to synthesize the donor for fucose addition, GDP-fucose. Although overexpression of POFUT2 did not affect the secretion of wild-type ADAMTS13, it did increase the secretion of the ADAMTS13 TSR1,2 double mutant but not that of ADAMTS13 TSR1-8 mutant. Together these findings indicate that O-fucosylation is functionally significant for secretion of ADAMTS13.

The threonine that carries fucose, but not fucose, is required for Cripto to facilitate Nodal signaling

Cripto is a membrane-bound co-receptor for Nodal, a member of the transforming growth factor-beta superfamily. Mouse embryos lacking either Cripto or Nodal have the same lethal phenotype at embryonic day 7.5. Previous studies suggest that O-fucosylation of the epidermal growth factor-like (EGF) repeat in Cripto is essential for the facilitation of Nodal signaling. Substitution of Ala for the Thr to which O-fucose is attached led to functional inactivation of both human and mouse Cripto. However, embryos null for protein O-fucosyltransferase 1, the enzyme that adds O-fucose to EGF repeats, do not exhibit a Cripto null phenotype and die at about embryonic day 9.5. This suggested that the loss of O-fucose from the EGF repeat may not have led to the inactivation of Cripto in previous studies. Here we investigate this hypothesis and show the following: 1) protein O-fucosyltransferase 1 is indeed the enzyme that adds O-fucose to Cripto; 2) Pofut1(-/-) embryonic stem cells behave the same as Pofut1(+/+) embryonic stem cells in a Nodal signaling assay; 3) Pofut1(-/-) and Pofut1(+/+) embryoid bodies are indistinguishable in their ability to differentiate into cardiomyocytes; and 4) none of 10 amino acid substitutions at Thr(72), including Ser which acquires O-fucose, rescues the activity of mouse Cripto in Nodal signaling assays. Therefore, the Thr to which O-fucose is linked in Cripto plays a key functional role, but O-fucose at Thr(72) is not required for Cripto to function in cell-based signaling assays or in vivo. By contrast, we show that O-fucose, and not the Thr to which it is attached, is required in the ligand-binding domain of Notch1 for Notch1 signaling.

Urokinase Induces Matrix Metalloproteinase-9/Gelatinase B Expression in THP-1 Monocytes via ERK1/2 and Cytosolic Phospholipase A2 Activation and Eicosanoid Production

OBJECTIVE

Urokinase-type plasminogen activator (uPA) regulates cell migration and invasion by pericellular proteolysis and signal transduction events. We characterized the mechanisms by which uPA regulates matrix metalloproteinase-9 (MMP9) function in THP-1 monocytes.

METHODS AND RESULTS

In THP-1 monocytes, MMP9 production induced by urokinase was completely inhibited by the ERK1/2 inhibitor, PD98059, but not by the p38 mitogen-activated protein kinase inhibitor, SB202190. A dominant negative MEK1 adenovirus also blocked MMP9 expression. The effect of urokinase was completely suppressed by genistein and by herbimycin A indicating that tyrosine kinase(s) are required for MMP9 production. Bisindolylmaleimide, a protein kinase C (PKC) inhibitor, did not decrease MMP9 expression suggesting that PKC activation is not required. Key roles for cytosolic phospholipase A2 (PLA2) and eicosanoid production were shown by complete inhibition with methyl arachidonyl fluorophosphonate (an inhibitor of cytosolic PLA2), and indomethacin (a cyclooxygenase inhibitor), with no effect of monoalide, a secretory PLA2 inhibitor. uPA stimulated phosphorylation of cytosolic PLA2.

CONCLUSIONS

Induction of MMP9 by uPA in THP-1 monocytes is via a pathway involving MEK1-ERK1/2-mediated activation of cytosolic PLA2 and eicosanoid generation. These data suggest important roles for eicosanoids in monocyte migration induced by uPA and MMP9.

Urokinase induces activation of STAT3 in lung epithelial cells

Urokinase-type plasminogen activator (uPA) is a serine protease that plays a major role in diverse physiological and pathological processes. Studies from our laboratory have shown that exposure of human lung epithelial cells to uPA induces proliferation. To understand uPA mitogenic signaling events, we sought to elucidate its effects on tyrosine phosphorylation in a human bronchial epithelial cell line (Beas2B). uPA induced tyrosine phosphorylation of several proteins in a time-dependent manner. One of these proteins was identified as the 91-kDa signal transduction activator transcription (Stat)3 moiety. Tyrosine phosphorylation of Stat3 by uPA was time dependent. uPA induced Stat3-DNA binding activity in a time-dependent manner. uPA-induced Stat3 activation does not require uPA catalytic activity, as the uPA amino-terminal fragment alone was as potent as active two-chain uPA (tcuPA) in causing this effect. Single-chain uPA likewise induced tyrosine phosphorylation of Stat3 to a similar extent as intact tcuPA. Plasmin did not alter uPA-induced Stat3 activation. Furthermore, transfection of Beas2B cells with dominant-negative Stat3 blocked uPA-induced DNA synthesis. These results reveal for the first time that the uPA-uPAR interaction leads to activation of Stat3, independent of its catalytic activity but dependent on its interaction with its receptor, uPAR, leading to DNA synthesis in lung epithelial cells.

Protein expression and preliminary crystallographic analysis of amino-terminal fragment of urokinase-type plasminogen activator

The amino-terminal fragment (ATF, Ser1-Glu143) of urokinase-type plasminogen activator (uPA) is responsible for some important functions of uPA, such as receptor binding and chemotactic activity. To dissect the function and structure-activity relationship of ATF, recombinant human ATF was expressed in Pichia pastoris system at a yield of about 30 mg/L. The recombinant ATF was captured by a cation exchange column, further purified up to 99% purity by a gel filtration column, and characterized in terms of its receptor binding capability. The purified ATF was then crystallized by the method of sitting-drop vapor diffusion with magnesium sulfate as the precipitating agent at 298 K. The crystals belong to space group P1 with unit cell dimensions of a=47.5A, b=64.7A, c=65.4A, alpha=71.6 degrees , beta=92.1 degrees , gamma=84.0 degrees .

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.

Production and purification of urokinase: A comprehensive review

An increased emphasis on prevention of fatalities due to thrombovascular disorders is broadening opportunities for several cardiovascular agents, especially plasminogen activators, for preventing strokes and heart attacks. Hence, urokinase, as one of the most potent plasminogen activators is attracting a great deal of attention. Developments in cell lines and bioprocess technology have made it possible to produce urokinase from in vitro cell culture. Attempts are now underway to enhance urokinase production from cell culture through media manipulation, bioreactor cultivation, and innovative purification techniques. Downstream processing also poses an intricate problem due to the complexity of cell culture extracts, susceptibility of urokinase to autocatalytic and proteolytic degradation and due to the presence of plasminogen activator inhibitors in the culture media. Hence, enhancing cellular productivity and downstream product recovery continue to be major challenges as discussed in this review. Furthermore, an approach for integrated upstream and downstream processing is needed to develop an economically viable technology. In the present review the emerging trends in urokinase production and purification have been discussed in detail.

Prostate secretory protein of 94 amino acids (PSP-94) and its peptide (PCK3145) as potential therapeutic modalities for prostate cancer

This review focuses on the promising roles of prostate secretory protein of 94 amino acids (PSP-94) and one of its derived peptides (PCK3145) as potential therapeutic modalities for prostate cancer and its associated complications. Evaluation of these compounds was carried out in vitro and in vivo using syngeneic models of rat prostate cancer. Overproduction of parathyroid hormone-related protein (PTHrP) results in the development of hypercalcemia of malignancy in several malignancies including prostate cancer. In order to evaluate the effect of PSP-94 and PCK3145 on prostate cancer progression, the rat Dunning R3227 MatLyLu cell line transfected with full-length cDNA encoding PTHrP (MatLyLu-PTHrP) was used. As the main pathogenetic factor of hypercalcemia of malignancy, overexpression of PTHrP was aimed at mimicking the hypercalcemic nature seen in patients suffering from late-stage cancer. In vitro studies showed that PSP-94 and PCK3145 can cause a dose-dependent inhibition in the growth of MatLyLu-PTHrP cells. For in vivo studies, male Copenhagen rats were inoculated either s.c. into the right flank or directly into the left ventricle via intracardiac (i.c.) inoculation with MatLyLu-PTHrP cells. In these models, s.c. injection of MatLyLu cells results in the development of primary tumor growth, whereas i.c. inoculation routinely results in the development of experimental skeletal metastases in the lumbar vertebrae causing hind-limb paralysis. Administration of PSP-94 and PCK3145 into tumor-bearing animals resulted in a dose-dependent inhibition of primary tumor growth, and tumoral and plasma PTHrP levels, and in the reduction of plasma calcium levels. Additionally, treatment with PSP-94 or PCK3145 caused an inhibition of skeletal metastases resulting in a significant delay in the development of hind-limb paralysis. Interestingly, equimolar concentrations of PCK3145 were shown to be more effective in delaying the development of experimental skeletal metastases as compared to PSP-94. One of the possible mechanisms of action of these modalities is through the induction of apoptosis which was observed by both in-vitro and in-vivo analyses of MatLyLu-PTHrP cells and tumors. Several intracellular mechanisms can also be involved in inhibiting PTHrP production and anti-tumor effects of PSP-94 and PCK3145. Collectively, these studies warrant the continued clinical development of these agents as therapeutic agents for patients with hormone-refractory prostate cancer.

Evolution of distinct EGF domains with specific functions

EGF domains are extracellular protein modules cross-linked by three intradomain disulfides. Past studies suggest the existence of two types of EGF domain with three-disulfides, human EGF-like (hEGF) domains and complement C1r-like (cEGF) domains, but to date no functional information has been related to the two different types, and they are not differentiated in sequence or structure databases. We have developed new sequence patterns based on the different C-termini to search specifically for the two types of EGF domains in sequence databases. The exhibited sensitivity and specificity of the new pattern-based method represents a significant advancement over the currently available sequence detection techniques. We re-annotated EGF sequences in the latest release of Swiss-Prot looking for functional relationships that might correlate with EGF type. We show that important post-translational modifications of three-disulfide EGFs, including unusual forms of glycosylation and post-translational proteolytic processing, are dependent on EGF subtype. For example, EGF domains that are shed from the cell surface and mediate intercellular signaling are all hEGFs, as are all human EGF receptor family ligands. Additional experimental data suggest that functional specialization has accompanied subtype divergence. Based on our structural analysis of EGF domains with three-disulfide bonds and comparison to laminin and integrin-like EGF domains with an additional inter-domain disulfide, we propose that these hEGF and cEGF domains may have arisen from a four-disulfide ancestor by selective loss of different cysteine residues.

The role of urokinase in innate immunity against Staphylococcus aureus

Urokinase (uPA) is a serine protease that not only displays fibrinolytic function but also promotes host leukocytes to home to inflammatory sites. We have recently demonstrated that staphylokinase (SAK), which is a fibrinolytic protein secreted by Staphylococcus aureus, forms complexes with human neutrophil peptides (HNPs), which are members of the defensin family and have anti-microbial properties, thereby inhibiting the bactericidal effects of the HNPs. The aim of this study was to assess whether endogenous uPA, which has fibrinolytic properties similar to those of SAK, binds to HNPs and interferes with SAK/HNPs interaction. To this end, an ELISA was used to analyze the interactions between uPA and HNPs. HMW uPA had the ability to bind to both HNP types. The biological consequences of the formation of this complex were analyzed with respect to its bactericidal properties. HMW uPA killed S. aureus, albeit at relatively high doses (50-100 mug/ml). In contrast, the binding of HMW uPA to HNPs had no impact on the bactericidal functions of the HNPs. Importantly, the addition of HMW uPA to SAK eliminated the ability of SAK to neutralize HNPs. Our results demonstrate that endogenous HMW uPA inhibits S. aureus growth both directly, by cytolysis, and indirectly, by abrogation of the neutralizing effect of SAK on the bactericidal activities of HNPs. These findings indicate novel functions of HMW uPA in the host defense against staphylococcal infections.

Induction of p53 by urokinase in lung epithelial cells

Urokinase plasminogen activator (uPA) is a serine protease that catalyzes the conversion of plasminogen to plasmin. The plasminogen/plasmin system includes the uPA, its receptor, and its inhibitor (plasminogen activator inhibitor-1). Interactions between these molecules regulate cellular proteolysis as well as adhesion, cellular proliferation, and migration, processes germane to the pathogenesis of lung injury and neoplasia. In previous studies, we found that uPA regulates cell surface fibrinolysis by regulating its own expression as well as that of the uPA receptor and plasminogen activator inhibitor-1. In this study, we found that uPA alters expression of the tumor suppressor protein p53 in Beas2B airway epithelial cells in both a time- and concentration-dependent manner. These effects do not require uPA catalytic activity because the amino-terminal fragment of uPA lacking catalytic activity was as potent as two chain active uPA. Single chain uPA also enhanced p53 expression to the same extent as intact two chain active uPA and the amino-terminal fragment. Pretreatment of cells with anti-beta1 integrin antibody blocked uPA-induced p53 expression. uPA-induced p53 expression occurs without increased p53 mRNA expression. However, uPA induced oncoprotein MDM2 in a concentration-dependent manner. uPA-induced p53 expression does not require activation of tyrosine kinases. Inactivation of protein-tyrosine phosphatase SHP-2 inhibits both basal and uPA-induced p53 expression. Plasmin did not alter uPA-mediated p53 expression. The induction of p53 expression by exposure of lung epithelial cells to uPA is a newly recognized pathway by which urokinase may influence the proliferation of lung epithelial cells. This pathway could regulate pathophysiologic alterations of p53 expression in the setting of lung inflammation or neoplasia.

Dynamics of Urokinase Receptor Interaction with Peptide Antagonists Studied by Amide Hydrogen Exchange and Mass Spectrometry

Using amide hydrogen exchange combined with electrospray ionization mass spectrometry, we have in this study determined the number of amide hydrogens on several peptides that become solvent-inaccessible as a result of their high-affinity interaction with the urokinase-type plasminogen activator receptor (uPAR). These experiments reveal that at least six out of eight amide hydrogens in a synthetic nine-mer peptide antagonist (AE105) become sequestered upon engagement in uPAR binding. Various uPAR mutants with decreased affinity for this peptide antagonist gave similar results, thereby indicating that deletion of the favorable interactions involving the side chains of these residues in uPAR does not affect the number of hydrogen bonds established by the main chain of the peptide ligand. The isolated growth factor-like domain (GFD) of the cognate serine protease ligand for uPAR showed 11 protected amide hydrogens in the receptor complex. Interestingly, a naturally occurring O-linked fucose on Thr(18) confers protection of two additional amide hydrogens in GFD when it forms a complex with uPAR. Dissociation of the uPAR-peptide complexes is accompanied by a correlated exchange of nearly all amide hydrogens on the peptide ligand. This yields bimodal isotope patterns from which dissociation rate constants can be determined. In addition, the distinct bimodal isotope distributions also allow investigation of the exchange kinetics of receptor-bound peptides providing information about the local structural motions at the interface. These exchange experiments therefore provide both structural and kinetic information on the interaction between uPAR and these small peptide antagonists, which in model systems show promise as inhibitors of intravasation of human cancer cells.

Role of glycosylation in development

Researchers have long predicted that complex carbohydrates on cell surfaces would play important roles in developmental processes because of the observation that specific carbohydrate structures appear in specific spatial and temporal patterns throughout development. The astounding number and complexity of carbohydrate structures on cell surfaces added support to the concept that glycoconjugates would function in cellular communication during development. Although the structural complexity inherent in glycoconjugates has slowed advances in our understanding of their functions, the complete sequencing of the genomes of organisms classically used in developmental studies (e.g., mice, Drosophila melanogaster, and Caenorhabditis elegans) has led to demonstration of essential functions for a number of glycoconjugates in developmental processes. Here we present a review of recent studies analyzing function of a variety of glycoconjugates (O-fucose, O-mannose, N-glycans, mucin-type O-glycans, proteoglycans, glycosphingolipids), focusing on lessons learned from human disease and genetic studies in mice, D. melanogaster, and C. elegans.

Gene expression in cancer cells is influenced by contact with bone cells in a novel coculture system that models bone metastasis

Contact between bone cells and cancer cells (heterotypic cell contact) is thought to play a central role in the initial growth and progression of metastatic cells. Attempts at studying heterotypic contact in vitro and in vivo have been confounded by difficulty in controlling how and when heterotypic contact occurs between unlike cells. A novel model, the micropatterned coculture system, is described that quantifies and controls heterotypic contact between cancer cells and bone cells in vitro. The micropatterned coculture system is biocompatible, and is modified easily to accommodate two or more different populations of cells. Immunofluorescence of cocultures of prostate cancer-3 cells and osteoblasts show the precise control of cell interactions. Ribonucleic acid of sufficient quantity and quality is isolated readily from cells cocultured on the micropatterned coculture system. The expression of the metastasis associated genes urokinase plasminogen activator, insulinlike growth factor binding protein-1 and insulinlike growth factor binding protein-3 are regulated in response to heterotypic contact and soluble factors respectively. A model of bone metastasis based on the micropatterned coculture system technology will streamline the process for testing therapeutic agents, so that more molecules can be identified for animal and clinical testing at less cost and in less time than using conventional methods.

Design of Novel and Selective Inhibitors of Urokinase-type Plasminogen Activator with Improved Pharmacokinetic Properties for Use as Antimetastatic Agents

The serine protease urokinase-type plasminogen activator (uPA) interacts with a specific receptor (uPAR) on the surface of various cell types, including tumor cells, and plays a crucial role in pericellular proteolysis. High levels of uPA and uPAR often correlate with poor prognosis of cancer patients. Therefore, the specific inhibition of uPA with small molecule active-site inhibitors is one strategy to decrease the invasive and metastatic activity of tumor cells. We have developed a series of highly potent and selective uPA inhibitors with a C-terminal 4-amidinobenzylamide residue. Optimization was directed toward reducing the fast elimination from circulation that was observed with initial analogues. The x-ray structures of three inhibitor/uPA complexes have been solved and were used to improve the inhibition efficacy. One of the most potent and selective derivatives, benzylsulfonyl-D-Ser-Ser-4-amidinobenzylamide (inhibitor 26), inhibits uPA with a Ki of 20 nm. This inhibitor was used in a fibrosarcoma model in nude mice using lacZ-tagged human HT1080 cells, to prevent experimental lung metastasis formation. Compared with control (100%), an inhibitor dose of 2 x 1.5 mg/kg/day reduced the number of experimental metastases to 4.6 +/- 1%. Under these conditions inhibitor 26 also significantly prolonged survival. All mice from the control group died within 43 days after tumor cell inoculation, whereas 50% of mice from the inhibitor-treated group survived more than 117 days. This study demonstrates that the specific inhibition of uPA by these inhibitors may be a useful strategy for the treatment of cancer to prevent metastasis.

Small interfering RNA urokinase silencing inhibits invasion and migration of human hepatocellular carcinoma cells

The serine protease urokinase-type plasminogen activator (u-PA) is involved in a variety of physiologic and pathological processes; in particular, u-PA mRNA is up-regulated in human hepatocellular carcinoma (HCC) biopsies and its level of expression is inversely correlated with patients' survival. To determine the role of u-PA in the invasiveness properties of HCC, we successfully down-regulated u-PA by RNA interference (RNAi) technology, in an HCC-derived cell line at high level of u-PA expression. RNAi is a multistep process involving generation of small interfering RNAs (siRNA) that cause specific inhibition of the target gene. SKHep1C3 cells were transfected with a U6 promoter plasmid coding for an RNA composed of two identical 19-nucleotide sequence motifs in an inverted orientation, separated by a 9-bp spacer to form a hairpin dsRNA capable of mediating target u-PA inhibition. Stable transfectant cells showed a consistently decreased level of u-PA protein. In biological assays, siRNA u-PA–transfected cells showed a reduction of migration, invasion, and proliferation. In conclusion, u-PA down-regulation by RNAi technology decreases the invasive capability of HCC cells, demonstrating that stable expression of siRNA u-PA could potentially be an experimental approach for HCC gene therapy.

The kringle stabilizes urokinase binding to the urokinase receptor

The structural basis of the interaction between single-chain urokinase-type plasminogen activator (scuPA) and its receptor (uPAR) is incompletely defined. Several observations indicated the kringle facilitates the binding of uPA to uPAR. A scuPA variant lacking the kringle (Delta K-scuPA) bound to soluble uPAR (suPAR) with the similar "on-rate" but with a faster "off-rate" than wild-type (WT)-scuPA. Binding of Delta K-scuPA, but not WT-scuPA, to suPAR was comparably inhibited by its growth factor domain (GFD) and amino-terminal fragment (ATF). ATF and WT-scuPA, but not GFD, scuPA lacking the GFD (Delta GFD-scuPA), or Delta K-scuPA reconstituted the isolated domains of uPAR. ATF completely inhibited the enzymatic activity of WT-scuPA-suPAR unlike comparable concentrations of GFD. Variants containing mutations that alter the charge, length, or flexibility of linker sequence (residues 43-49) between the GFD and the kringle displayed a lower affinity for uPAR, were unable to reconstitute uPAR domains, and their binding to uPAR was inhibited by GFD in the same manner as Delta K-scuPA. A scuPA variant in which the charged amino acids in the heparin binding site (HBS) in the kringle domain were mutated to alanines behaved like Delta K-scuPA, indicating that that the structure of the kringle as well as its interaction with the GFD govern receptor binding. These data demonstrate an important role for the kringle in stabilizing the binding of scuPA to uPAR.

The role of urokinase-type plasminogen activator (uPA)/uPA receptor in HIV-1 infection

The binding of urokinase-type plasminogen activator (uPA) to its glycosyl-phosphatidyl-inositol (GPI) anchored receptor (uPAR) mediates a variety of functions in terms of vascular homeostasis, inflammation and tissue repair. Both uPA and uPAR, as well as their soluble forms detectable in plasma and other body fluids, represent markers of cancer development and metastasis, and they have been recently described as predictors of human immunodeficiency virus (HIV) disease progression, independent of CD4+ T cell counts and viremia. A direct link between the uPA/uPAR system and HIV infection was earlier proposed in terms of cleavage of gp120 envelope by uPA. More recently, a negative regulatory effect on both acutely and chronically infected cells has been linked to the noncatalytic portion of uPA, also referred to as the amino-terminal fragment (ATF). ATF has also been described as a major CD8+ T cell soluble HIV suppressor factor. In chronically infected promonocytic U1 cells this inhibitory effect is exerted at the very late stages of the virus life cycle, involving virion budding and entrapment in intracytoplasmic vacuoles, whereas its mechanism of action in acutely infected cells remains to be defined. Since uPAR is a GPI-anchored receptor it requires association with a signaling-transducing component and different partners, which include CD11b/CD18 integrin and a G-protein coupled receptor homologous to that for the bacterial chemotactic peptide formyl-methionyl-leucyl-phenylalanine. Which signaling coreceptor(s) is(are) responsible for uPA-dependent anti-HIV effect remains currently undefined.

neurotic, a novel maternal neurogenic gene, encodes an O-fucosyltransferase that is essential for Notch-Delta interactions

Notch signalling, which is highly conserved from nematodes to mammals, plays crucial roles in many developmental processes. In the Drosophila embryo, deficiency in Notch signalling results in neural hyperplasia, commonly referred to as the neurogenic phenotype. We identify a novel maternal neurogenic gene, neurotic, and show that it is essential for Notch signalling. neurotic encodes a Drosophila homolog of mammalian GDP-fucose protein O-fucosyltransferase, which adds fucose sugar to epidermal growth factor-like repeats and is known to play a crucial role in Notch signalling. neurotic functions in a cell-autonomous manner, and genetic epistasis tests reveal that Neurotic is required for the activity of the full-length but not an activated form of Notch. Further, we show that neurotic is required for Fringe activity, which encodes a fucose-specific beta1, 3 N-acetylglucosaminyltransferase, previously shown to modulate Notch receptor activity. Finally, Neurotic is essential for the physical interaction of Notch with its ligand Delta, and for the ability of Fringe to modulate this interaction in Drosophila cultured cells. We present an unprecedented example of an absolute requirement of a protein glycosylation event for a ligand-receptor interaction. Our results suggest that O-fucosylation catalysed by Neurotic is also involved in the Fringe-independent activities of Notch and may provide a novel on-off mechanism that regulates ligand-receptor interactions.

Inhibition of the tumor-associated urokinase-type plasminogen activation system: effects of high-level synthesis of soluble urokinase receptor in ovarian and breast cancer cells in vitro and in vivo

Tumor cell invasion and metastasis depend on the coordinated and temporal expression of proteolytic enzymes to degrade the surrounding extracellular matrix and of adhesion molecules to remodel cell-cell and/or cell-matrix attachments. The tumor cell-associated urokinase-type plasminogen activator system, consisting of the serine protease uPA, its substrate plasminogen, its membrane-bound receptor uPAR, as well as its inhibitors PAI-1 and PAI-2, plays an important role in these pericellular processes. Especially, association of the proteolytic activity of uPA with the cell surface via interaction with uPAR significantly increases the invasive capacity of tumor cells. Consequently, various approaches have been pursued to interfere with the expression or activity of uPA and/or uPAR, including antisense strategies and the development of active-site inhibitors of uPA or inhibitors of uPA/uPAR interaction. In this review, we focus on the results obtained in vitro and in vivo with tumor cells producing high levels of a recombinant soluble form of uPAR, which efficiently inhibits uPA binding to cell surface-associated uPAR and, by this, acts as a scavenger for uPA.

Critical role of integrin alpha 5 beta 1 in urokinase (uPA)/urokinase receptor (uPAR, CD87) signaling

Urokinase-type plasminogen activator (uPA) induces cell adhesion and chemotactic movement. uPA signaling requires its binding to uPA receptor (uPAR/CD87), but how glycosylphosphatidylinositol-anchored uPAR mediates signaling is unclear. uPAR is a ligand for several integrins (e.g. alpha 5 beta 1) and supports cell-cell interaction by binding to integrins on apposing cells (in trans). We studied whether binding of uPAR to alpha 5 beta 1 in cis is involved in adhesion and migration of Chinese hamster ovary cells in response to immobilized uPA. This process was temperature-sensitive and required mitogen-activated protein kinase activation. Anti-uPAR antibody or depletion of uPAR blocked, whereas overexpression of uPAR enhanced, cell adhesion to uPA. Adhesion to uPA was also blocked by deletion of the growth factor domain (GFD) of uPA and by anti-GFD antibody, whereas neither the isolated uPA kringle nor serine protease domain supported adhesion directly. Interestingly, anti-alpha 5 antibody, RGD peptide, and function-blocking mutations in alpha 5 beta 1 blocked adhesion to uPA. uPA-induced cell migration also required GFD, uPAR, and alpha 5 beta 1, but alpha 5 beta 1 alone did not support uPA-induced adhesion and migration. Thus, binding of uPA causes uPAR to act as a ligand for alpha 5 beta 1 to induce cell adhesion, intracellular signaling, and cell migration. We demonstrated that uPA induced RGD-dependent binding of uPAR to alpha 5 beta 1 in solution. These results suggest that uPA-induced adhesion and migration of Chinese hamster ovary cells occurs as a consequence of (a) uPA binding to uPAR through GFD, (b) the subsequent binding of a uPA.uPAR complex to alpha 5 beta 1 via uPAR, and (c) signal transduction through alpha 5 beta 1.

Differential terminal fucosylation of N-linked glycans versus protein O-fucosylation in leukocyte adhesion deficiency type II (CDG IIc)

LAD II/CDG IIc is a rare autosomal recessive disease characterized by a decreased expression of fucosylated antigens on cell surfaces that results in leukocyte adhesion deficiency and severe neurological and developmental abnormalities. Its molecular basis has been identified as a defect in the transporter of GDP-l-fucose into the Golgi lumen, which reduces the availability of the substrate for fucosyltransferases. During metabolic radiolabeling experiments using [3H]fucose, LAD II fibroblasts incorporated significantly less radiolabel compared with control cells. However, fractionation and analysis of the different classes of glycans indicated that the decrease in [3H]fucose incorporation is not generalized and is mainly confined to terminal fucosylation of N-linked oligosaccharides. In contrast, the total levels of protein O-fucosylation, including that observed in Notch protein, were unaffected. This finding demonstrates that the decrease in GDP-l-fucose levels in the fibroblast Golgi caused by the LAD II defect does not impair bulk protein O-fucosylation, but severely affects the bulk addition of fucose as a terminal modification of N-linked glycans. These data suggest that the severe clinical abnormalities including neurological and developmental ones observed in at least some of the LAD II patients may be related to alteration in recognition systems involving terminal fucose modifications of N-glycans and not be due to a defective O-fucosylation of proteins such as Notch.

Increased bone formation in mice lacking plasminogen activators

Plasminogen activators tPA and uPA are involved in tissue remodeling, but their role in bone growth is undefined. Mice lacking tPA and uPA show increased bone formation and bone mass. The noncollagenous components of bone matrix are also increased, probably from defective degradation. This study underlines the importance of controlled bone matrix remodeling for normal endochondral ossification.

INTRODUCTION

Proteolytic pathways are suggested to play a role in endochondral ossification. To elucidate the involvement of the plasminogen activators tPA and uPA in this process, we characterized the long bone phenotype in mice deficient in both tPA and uPA (tPA-/-:uPA-/-).

MATERIALS AND METHODS

Bones of 2- to 7-day-old tPA-/-:uPA-/- and wild-type (WT) mice were studied using bone histomorphometry, electron microscopy analysis, and biochemical assessment of bone matrix components. Cell-mediated degradation of metabolically labeled bone matrix, osteoblast proliferation, and osteoblast differentiation, both at the gene and protein level, were studied in vitro using cells derived from both genotypes.

RESULTS

Deficiency of the plasminogen activators led to elongation of the bones and to increased bone mass (25% more trabecular bone in the proximal tibial metaphysis), without altering the morphology of the growth plate. In addition, the composition of bone matrix was modified in plasminogen activator deficient mice, because an increased amount of proteoglycans (2x), osteocalcin (+45%), and fibronectin (+36%) was detected. Matrix degradation assays showed that plasminogen activators, by generating plasmin, participate in osteoblast-mediated degradation of the noncollagenous components of bone matrix. In addition, proliferation of primary osteoblasts derived from plasminogen activator-deficient mice was increased by 35%. Finally, osteoblast differentiation and formation of a mineralized bone matrix were enhanced in osteoblast cultures derived from tPA-/-:uPA-/- mice.

CONCLUSIONS

The data presented indicate the importance of the plasminogen system in degradation of the noncollagenous components of bone matrix and suggest that the accumulation of these proteins in bone matrix--as occurs during plasminogen activator deficiency--may in turn stimulate osteoblast function, resulting in increased bone formation.

Fucose: biosynthesis and biological function in mammals

Fucose is a deoxyhexose that is present in a wide variety of organisms. In mammals, fucose-containing glycans have important roles in blood transfusion reactions, selectin-mediated leukocyte-endothelial adhesion, host-microbe interactions, and numerous ontogenic events, including signaling events by the Notch receptor family. Alterations in the expression of fucosylated oligosaccharides have also been observed in several pathological processes, including cancer and atherosclerosis. Fucose deficiency is accompanied by a complex set of phenotypes both in humans with leukocyte adhesion deficiency type II (LAD II; also known as congenital disorder of glycosylation type IIc) and in a recently generated strain of mice with a conditional defect in fucosylated glycan expression. Fucosylated glycans are constructed by fucosyltransferases, which require the substrate GDP-fucose. Two pathways for the synthesis of GDP-fucose operate in mammalian cells, the GDP-mannose-dependent de novo pathway and the free fucose-dependent salvage pathway. In this review, we focus on the biological functions of mammalian fucosylated glycans and the biosynthetic processes leading to formation of the fucosylated glycan precursor GDP-fucose.

Induction of plasminogen activator inhibitor-1 by urokinase in lung epithelial cells

The plasminogen/plasmin system, urokinase-type plasminogen activator (uPA), its receptor (uPAR), and its inhibitor (PAI-1), influence extracellular proteolysis and cell migration in lung injury or neoplasia. In this study, we sought to determine whether tcuPA (two chain uPA) alters expression of its major inhibitor PAI-1 in lung epithelial cells. The expression of PAI-1 was evaluated at the protein and mRNA level by Western blot, immunoprecipitation, and Northern blot analyses. We found that tcuPA treatment enhanced PAI-1 protein and mRNA expression in Beas2B lung epithelial cells in a time- and concentration-dependent manner. The tcuPA-mediated induction of PAI-1 involves post-transcriptional control involving stabilization of PAI-1 mRNA. Inactivation of the catalytic activity of tcuPA had little effect on PAI-1 induction and the activity of the isolated amino-terminal fragment was comparable with full-length single- or two-chain uPA. In contrast, deletion of either the uPA receptor binding growth factor domain or kringle domain (kringle) from full-length single chain uPA markedly attenuated the induction of PAI-1. Induction of PAI-1 by exposure of lung epithelial cells to uPA is a newly recognized pathway by which PAI-1 could regulate local fibrinolysis and urokinase-dependent cellular responses in the setting of lung inflammation or neoplasia.

A proteome study of secreted prostatic factors affecting osteoblastic activity: identification and characterisation of cyclophilin A

Prostate cancer cells metastasise to bone causing a predominantly osteosclerotic response. It has previously been shown that PC3 cells secrete factors which stimulate the mitogenic activity of human bone marrow stromal (hBMS) cells. Some of these mitogens have been found to be proteins with a molecular weight between 20 and 30 kDa. Even though a number of investigations have been performed to identify the osteoblastic mitogenic factor or factors produced by prostate cancer cells, it is still unknown what causes the mitogenic activation of osteoblasts. Therefore, the aim of this study was to characterise the protein profile of conditioned medium (CM) from PC3 cells in the molecular weight range of 5-30 kDa using proteome analysis. A protein profile of the CM from PC3 cells was performed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Thirty protein spots with molecular weights ranging from 5 to 30 kDa were analysed by matrix-assisted laser desorption/ionisation time of flight mass spectrometry (MALDI-TOF MS). One of these spots was identified as cyclophilin A. We examined whether cyclophilin A alone or in combination with insulin-like growth factor-I (IGF-I) had any effects on the proliferation or differentiation of hBMS cells. Cyclophilin A at 1, 10, and 100 nM and cyclophilin A at 10 nM combined with 10 ng/ml IGF decreased the proliferation of hBMS cells up to 49+/-30, 38+/-29, 50+/-8 and 60+/-16%, respectively [mean (treated/control)+/-standard error of the means (SEM)] of control. IGF-I did not significantly affect these decreases. Cyclophilin A alone or in combination with IGF-I did not have any effect on differentiation (assessed by measuring the activity of alkaline phosphatase (ALP)). In conclusion, these results suggest cyclophilin A is not involved in the osteosclerotic effects seen when prostate cancer metastasises to bone.

Protein O-fucosyltransferase 1 is an essential component of Notch signaling pathways

Notch receptor signaling regulates cell growth and differentiation, and core components of Notch signaling pathways are conserved from Drosophila to humans. Fringe glycosyltransferases are crucial modulators of Notch signaling that act on epidermal growth factor (EGF)-like repeats in the Notch receptor extracellular domain. The substrate of Fringe is EGF-O-fucose and the transfer of fucose to Notch by protein O-fucosyltransferase 1 is necessary for Fringe to function. O-fucose also occurs on Cripto and on Notch ligands. Here we show that mouse embryos lacking protein O-fucosyltransferase 1 die at midgestation with severe defects in somitogenesis, vasculogenesis, cardiogenesis, and neurogenesis. The phenotype is similar to that of embryos lacking downstream effectors of all Notch signaling pathways such as presenilins or RBP-J kappa, and is different from Cripto, Notch receptor, Notch ligand, or Fringe null phenotypes. Protein O-fucosyltransferase 1 is therefore an essential core member of Notch signaling pathways in mammals.

Convergence of the adhesive and fibrinolytic systems: recognition of urokinase by integrin alpha Mbeta 2 as well as by the urokinase receptor regulates cell adhesion and migration

Previous studies demonstrated that integrin alpha(M)beta(2) (CD11b/18, Mac-1) forms a physical complex with the urokinase-type plasminogen activator receptor (uPAR/CD87) on leukocytes. In this study, we used human peripheral blood neutrophils and transfected cells expressing alpha(M)beta(2), uPAR, or both receptors to show that the integrin can directly interact with urokinase (uPA). We demonstrate that alpha(M)beta(2) supported adhesion and migration of these cells to uPA, and, in each case, blockade of alpha(M)beta(2) suppressed the response. Within uPA, both the kringle and proteolytic domains are recognized by alpha(M)beta(2), which are distinct from the growth factor domain that binds to uPAR. Within the alpha(M) subunit of the integrin, the I domain interacts with uPA, which is distinct from the region that interacts with uPAR. On cells expressing uPAR and alpha(M)beta(2), both receptors mediated adhesion and migration. This cooperation was particularly apparent in the responses of neutrophils to uPA, where blockade of alpha(M)beta(2) reduced uPAR-mediated responses and engagement of uPAR enhanced recognition of uPA by alpha(M)beta(2). Thus, recognition of uPA by alpha(M)beta(2) allows for formation of a multicontact trimolecular complex, in which a single uPA ligand may bind simultaneously to both uPAR and alpha(M)beta(2). This complex may play an important role in the control of inflammatory cell migration and vascular homeostasis.