Urokinase and tissue-type plasminogen activator are required for the mitogenic and chemotactic effects of bovine fibroblast growth factor and platelet-derived growth factor-BB for vascular smooth muscle cells

Cellular diversity of the somatosensory cortical map plasticity

Sensory maps are representations of the sensory epithelia in the brain. Despite the intuitive explanatory power behind sensory maps as being neuronal precursors to sensory perception, and sensory cortical plasticity as a neural correlate of perceptual learning, molecular mechanisms that regulate map plasticity are not well understood. Here we perform a meta-analysis of transcriptional and translational changes during altered whisker use to nominate the major molecular correlates of experience-dependent map plasticity in the barrel cortex. We argue that brain plasticity is a systems level response, involving all cell classes, from neuron and glia to non-neuronal cells including endothelia. Using molecular pathway analysis, we further propose a gene regulatory network that could couple activity dependent changes in neurons to adaptive changes in neurovasculature, and finally we show that transcriptional regulations observed in major brain disorders target genes that are modulated by altered sensory experience. Thus, understanding the molecular mechanisms of experience-dependent plasticity of sensory maps might help to unravel the cellular events that shape brain plasticity in health and disease.

A Tubing-Free Microfluidic Wound Healing Assay Enabling the Quantification of Vascular Smooth Muscle Cell Migration

This paper presents a tubing-free microfluidic wound healing assay to quantify the migration of vascular smooth muscle cells (VSMCs), where gravity was used to generate a laminar flow within microfluidic channels, enabling cell seeding, culture, and wound generation. As the first systemic study to quantify the migration of VSMCs within microfluidic environments, the effects of channel geometries, surface modifications and chemokines on cellular migration were investigated, revealing that 1) height of the micro channels had a significant impact on cell migration; 2) the surface coating of collagen induced more migration of VSMCs than fibronectin coated surfaces and 3) platelet derived growth factor resulted in maximal cell migration compared to tumor necrosis factor alpha and fetal bovine serum. Furthermore, migrations of five types of VSMCs (e.g., the human vascular smooth muscle cell line, two types of primary vascular smooth cells, and VSMCs isolated from two human samples) were quantified, finding that VSMCs from the cell line and human samples demonstrated comparable migration distances, which were significantly lower than the migration distances of two primary cell types. As a platform technology, this wound healing assay may function as a new model to study migration of VSMCs within microfluidic environments.

Natural and engineered plasmin inhibitors: applications and design strategies

The serine protease plasmin is ubiquitously expressed throughout the human body in the form of the zymogen plasminogen. Conversion to active plasmin occurs through enzymatic cleavage by plasminogen activators. The plasminogen activator/plasmin system has a well-established function in the removal of intravascular fibrin deposition through fibrinolysis and the inhibition of plasmin activity; this has found widespread clinical use in reducing perioperative bleeding. Increasing evidence also suggests diverse, although currently less defined, roles for plasmin in a number of physiological and pathological processes relating to extracellular matrix degradation, cell migration and tissue remodelling. In particular, dysregulation of plasmin has been linked to cancer invasion/metastasis and various chronic inflammatory conditions; this has prompted efforts to develop inhibitors of this protease. Although a number of plasmin inhibitors exist, they commonly suffer from poor potency and/or specificity of inhibition that either results in reduced efficacy or prevents clinical use. Consequently, there is a need for further development of high-affinity plasmin inhibitors that maintain selectivity over other serine proteases. This review summarises clearly defined and potential applications for plasmin inhibition. The properties of naturally occurring and engineered plasmin inhibitors are discussed in the context of current knowledge regarding plasmin structure, specificity and function. This includes design strategies to obtain the potency and specificity of inhibition in addition to controlled temporal and spatial distribution tailored for the intended use.

A meta-analysis of microarray-based gene expression studies of olfactory bulb-derived olfactory ensheathing cells

Genome wide transcriptional profiling and large scale proteomics have emerged as two powerful methods to dissect the molecular properties of specific neural tissues or cell types on a global scale. Several genome-wide transcriptional profiling and proteomics studies have been published on cultured olfactory ensheathing cells (OEC). In this article we present a meta-analysis of all five published and publicly available micro-array gene expression datasets of cultured early-passage-OB-OEC with other cell types (Schwann cells, late-passage-OB-OEC, mucosa-OEC, an OEC cell line, and acutely dissected OEC). The aim of this meta-analysis is to identify genes and molecular pathways that are found in multiple instead of one isolated study. 454 Genes were detected in at least three out of five microarray datasets. In this "Top-list", genes involved in the biological processes "growth of neurites", "blood vessel development", "migration of cells" and "immune response" were strongly overrepresented. By applying network analysis tools, molecular networks were constructed and Hub-genes were identified that may function as key genes in the above mentioned interrelated processes. We also identified 7 genes (ENTPD2, MATN2, CTSC, PTHLH, GLRX1, COL27A1 and ID2) with uniformly higher or lower expression in early-passage-OB-OEC in all five microarray comparisons. These genes have diverse but intriguing roles in neuroprotection, neurite extension and/or tissue repair. Our meta-analysis provides novel insights into the molecular basis of OB-OEC-mediated neural repair and can serve as a repository for investigators interested in the molecular biology of OEC. This article is part of a Special Issue entitled: Understanding olfactory ensheathing glia and their prospect for nervous system repair.

Molecular regulation of thyroid gland function

PURPOSE OF REVIEW

For de-novo thyroid hormone synthesis ex vivo, thyroid follicular cells require a serum-free medium supplying nutrients, iodide, thyroid-stimulating hormone and insulin-like growth factor I (IGF-I) (or insulin). Under these conditions, T3 and T4 are secreted but so are other factors such as growth factors, plasminogen activators, their inhibitors known as serpins, and so on. What is the function of these factors? Do thyroid cells respond to them or are these paracrine/endocrine factors? The purpose of this review is to highlight the current developments in the identification and role of the signalling pathways that regulate thyroid growth and function and the putative role of endogenous thyroid proteases in regulating this.

RECENT FINDINGS

The roles of the mitogen-activated protein kinases and phosphoinositol 3 kinases and integrins in mediating growth and function in thyroid cancer cells and the roles of plasminogen activators, their receptors and the downstream signalling pathways they modulate have been developed. Discoveries of novel proteases, expressed in thyroid cancers, may be useful in diagnosis.

SUMMARY

The signalling pathways regulating thyroid activity are examined and the roles of follicular cell products in maintaining thyroid homeostasis evaluated. The possibility that thyroid cell products other than T3 and T4 may circulate and have extrathyroidal effects is proposed.

Urokinase-type plasminogen activator increases hepatocyte growth factor activity required for skeletal muscle regeneration

The plasminogen system plays a crucial role in the repair of a variety of tissues, including skeletal muscle. We hypothesized that urokinase-type plasminogen activator (uPA) promotes muscle regeneration by activating hepatocyte growth factor (HGF), which, in turn, stimulates proliferation of myoblasts required for regeneration. In our studies, levels of active HGF and phosphorylation of the HGF receptor c-met were increased after muscle injury in wild-type mice. Compared with wild-type animals, mice deficient in uPA (uPA(-/-)) had markedly reduced HGF levels and c-met activation after muscle damage. This reduced HGF activity in uPA(-/-) animals was associated with decreased cell proliferation, myoblast accumulation, and new muscle fiber formation. On the other hand, HGF activity was enhanced at early time points in PAI-1(-/-) mice compared with wild-type mice and the PAI-1(-/-) animals exhibited accelerated muscle fiber regeneration. Furthermore, administration of exogenous uPA rescued HGF levels and muscle regeneration in uPA(-/-) mice, and an HGF-blocking antibody reduced HGF activity and muscle regeneration in wild-type mice. We also found that uPA promotes myoblast proliferation in vitro through its proteolytic activity, and this process was inhibited by an HGF-blocking antibody. Together, our findings demonstrate that uPA promotes muscle regeneration through HGF activation and subsequent myoblast proliferation.

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.

Effect of the luteinising hormone surge on regulation of vascular endothelial growth factor and extracellular matrix-degrading proteinases and their inhibitors in bovine follicles

The aim of the present study was to evaluate the pattern of regulation of vascular endothelial growth factor (VEGF)-A (isoforms 121, 165, 189), VEGF receptor tyrosine kinases (VEGF-R1 and VEGF-R2), matrix metalloproteinase (MMP)-1, MMP-2, MMP-14, MMP-19, tissue-specific inhibitor of metalloproteinases (TIMP)-1, TIMP-2, tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), urokinase plasminogen activator receptor (uPAR) and plasminogen activator inhibitor-1 (PAI-1) in time-defined follicle classes before (0 h) and after the application of gonadotrophin-releasing hormone (GnRH). Bovine ovaries containing periovulatory follicles or new corpora lutea (CL; Days 1-2) were collected 0, 4, 10, 20 and 25 h (follicles) or 60 h (CL) after the injection of GnRH. Transcripts of VEGF isoforms (VEGF(121), VEGF(165), VEGF(189)) were upregulated 4 h after GnRH injection (during the luteinising hormone (LH) surge) and decreased thereafter to lowest levels around ovulation. All VEGF isoforms and their receptors were upregulated again after ovulation. The VEGF peptide concentration in follicular fluid decreased 20 h after GnRH injection, followed by an increase in follicles 25 h after GnRH. Expression of MMP-1 mRNA increased rapidly 4 h after GnRH injection and remained high during the entire experimental period. In contrast, MMP-19 mRNA increased significantly only after ovulation. Expression of TIMP-1 mRNA increased 4 h after GnRH and again after ovulation. Expression of tPA mRNA increased 4 h after GnRH and remained high during the entire experimental period, whereas expression of uPA transcripts increased significantly only after ovulation. Both uPAR and PAI-1 mRNA levels increased in follicles 4 h after GnRH and again after ovulation. The amount of MMP-1 protein (immunolocalisation) increased in follicles 10 h after GnRH: additional staining was observed in the granulosa cell layer. In conclusion, the temporal and spatial pattern of regulation of VEGF and extracellular matrix-degrading proteinases during periovulation suggests they are important mediators of the LH-dependent rupture of bovine follicles and for early CL formation (angiogenesis).

Mechanisms of vascular smooth muscle cell migration

Smooth muscle cell migration occurs during vascular development, in response to vascular injury, and during atherogenesis. Many proximal signals and signal transduction pathways activated during migration have been identified, as well as components of the cellular machinery that affect cell movement. In this review, a summary of promigratory and antimigratory molecules belonging to diverse chemical and functional families is presented, along with a summary of key signaling events mediating migration. Extracellular molecules that modulate migration include small biogenic amines, peptide growth factors, cytokines, extracellular matrix components, and drugs used in cardiovascular medicine. Promigratory stimuli activate signal transduction cascades that trigger remodeling of the cytoskeleton, change the adhesiveness of the cell to the matrix, and activate motor proteins. This review focuses on the signaling pathways and effector proteins regulated by promigratory and antimigratory molecules. Prominent pathways include phosphatidylinositol 3-kinases, calcium-dependent protein kinases, Rho-activated protein kinase, p21-activated protein kinases, LIM kinase, and mitogen-activated protein kinases. Important downstream targets include myosin II motors, actin capping and severing proteins, formins, profilin, cofilin, and the actin-related protein-2/3 complex. Actin filament remodeling, focal contact remodeling, and molecular motors are coordinated to cause cells to migrate along gradients of chemical cues, matrix adhesiveness, or matrix stiffness. The result is recruitment of cells to areas where the vessel wall is being remodeled. Vessel wall remodeling can be antagonized by common cardiovascular drugs that act in part by inhibiting vascular smooth muscle cell migration. Several therapeutically important drugs act by inhibiting cell cycle progression, which may reduce the population of migrating cells.

Targeting urokinase-type plasminogen activator and its receptor for cancer therapy

Cancer invasion and metastasis are highly complex processes and a serine protease urokinase-type plasminogen activator/urokinase-type plasminogen activator receptor system has been postulated to play a central role in the mediation of cancer progression. Of note, malignant tumor urokinase-type plasminogen activator and urokinase-type plasminogen activator receptor levels have been found to vary considerably, and to be related to patient prognosis. In mouse models, the urokinase-type plasminogen activator/urokinase-type plasminogen activator receptor system has been studied extensively as a target for anticancer therapy using a variety of approaches. In this review, we discuss the advances in the various modalities that have been used to target the urokinase-type plasminogen activator/urokinase-type plasminogen activator receptor system, including protein-based and peptide-based drugs, antisense therapy, and RNA interference technology. In particular, preclinical mouse model studies that used human tumor xenografts are reviewed.

Modulation of Smooth Muscle Cell Migration by Members of the Low-Density Lipoprotein Receptor Family

Low-density lipoprotein receptor family members (LRs) play a key role in the catabolism of many membrane-associated proteins, such as complexes between proteinases and their receptors, in addition to being involved in lipoprotein metabolism as suspected by the hitherto well-established functions of low-density lipoprotein receptor, in a variety of tissues. Recent studies using receptor-deficient or -overexpressing animals and cells have suggested that certain LRs are important regulators of the migration (and proliferation) of vascular smooth muscle cells (SMCs). LR expression is markedly induced in intimal or medial SMCs during the formation of atherosclerotic lesions. Because LRs can modulate the activity of the urokinase-type plasminogen activator (uPA) receptor and possibly of the platelet-derived growth factor (PDGF) receptor, LRs may influence the migration of SMCs through functional modulation of these membrane receptors. Therefore, SMC migration may be regulated by time-restricted expression of LRs. In agreement with the concept of functional interaction between LRs and membrane signaling receptors, a negative regulator of uPA receptor protein catabolism, LR11, has been identified. Statins modulate the PDGF-induced migration of intimal SMCs via the LR11/uPA receptor cascade. Selective modification of the LRs/uPA receptor/PDGF receptor systems in SMCs may be important for suppression of atherosclerotic plaque formation as well as for preventing intimal thickening after angioplasty.

Melanotransferrin stimulates t-PA-dependent activation of plasminogen in endothelial cells leading to cell detachment

Tissue plasminogen activator (t-PA) is an extracellular serine protease that converts the proenzyme plasminogen into the broad-spectrum substrate serine protease, plasmin. Plasmin, one of the most potent pro-angiogenic factors, is a key element in fibrinolysis, cell migration, tissue remodeling and tumor invasion. In the present investigation, we assessed the impact of the truncated form of soluble melanotransferrin (sMTf) on plasminogen activation by t-PA and subsequent endothelial cell detachment. Co-treatment of human endothelial microvessel cells with plasminogen, t-PA and sMTf significantly increased plasmin formation and activity in the culture medium. Plasmin generated in the presence of sMTf also led to a 30% reduction in fibronectin detection within cell lysates and to a 9-fold increase within the corresponding cell medium. Moreover, the presence of sMTf increases EC detachment by 6-fold compared to cells treated only with plasminogen and t-PA. Although the addition of alpha(2)-antiplasmin completely prevented plasmin formation and EC detachment, epigallocatechin gallate, GM6001 and a specific antibody directed against MMP-2 prevented cellular detachment without interfering with plasminogen activation. Overall, these data suggest that the anti-angiogenic properties of sMTf may result from local overstimulation of plasminogen activation by t-PA, thus leading to subsequent degradation of the Fn matrix and EC detachment.

Mactinin treatment promotes wound-healing-associated inflammation in urokinase knockout mice

Mactinin, a 31 kDa fragment from the amino-terminal end of alpha-actinin, is chemotactic for monocytes and can promote monocyte/macrophage maturation. Macrophages are essential for wound healing, in which they play key roles in debridement, angiogenesis, fibroblast proliferation, and collagen metabolism. We have previously determined that urokinase is necessary to form mactinin from extracellular alpha-actinin, which may be present at sites of inflammation as a result of cell movement. Thus, urokinase knockout mice are unable to form mactinin and therefore are an ideal model to study mactinin's effects on wound healing. Saline- and mactinin-treated wounds were analyzed in a subcutaneous sponge wound model in both wild-type and urokinase knockout mice. The wounded urokinase knockout mice had markedly decreased leukocyte infiltration compared with wounded wild-type mice. In addition, production of the proinflammatory cytokine, interleukin-12, and of collagen was also decreased in knockouts. Treatment of knockout mice with mactinin resulted in leukocyte infiltration numbers, interleukin-12 levels, and hydroxyproline measurements similar to those in wild-type mice. The results suggest that impaired wound healing in urokinase-deficient mice can be restored by administration of mactinin.

Characterization of SIS3, a Novel Specific Inhibitor of Smad3, and Its Effect on Transforming Growth Factor-β1-Induced Extracellular Matrix Expression

This is the first report that characterizes specific inhibitor of Smad3 (SIS3) as a potent and selective inhibitor of Smad3 function. In the reporter assay, the increased luciferase activity of p3TP-lux by the overexpression of constitutively active form of ALK-5 was abrogated by the treatment with SIS3 in a dose-dependent manner. Immunoprecipitation revealed that SIS3 attenuated the transforming growth factor (TGF)-beta1-induced phosphorylation of Smad3 and interaction of Smad3 with Smad4. On the other hand, this reagent did not affect the phosphorylation of Smad2. Thereafter, we evaluated the ability of SIS3 in the suppression of the TGF-beta1-induced type I procollagen up-regulation in human dermal fibroblasts. We found that the addition of SIS3 attenuated the effects of TGF-beta1 by reducing the transcriptional activity. SIS3 also inhibited the myofibroblast differentiation of fibroblasts by TGF-beta1. Moreover, we demonstrated that SIS3 completely diminished the constitutive phosphorylation of Smad3 as well as the up-regulated type I collagen expression in scleroderma fibroblasts. Together, our study suggested that SIS3 is a useful tool to evaluate the TGF-beta-regulated cellular mechanisms via selective inhibition of Smad3.

Plasmin-induced smooth muscle cell proliferation requires epidermal growth factor activation through an extracellular pathway

BACKGROUND

Plasminogen activators are used routinely for thrombolysis. They lead to the generation of the protease, plasmin, which can induce smooth muscle cell proliferation and may thus promote further intimal hyperplasia in the thrombolysed vessel. We have shown recently that plasmin induces extracellular signal-regulated kinase 1/2 (ERK1/2)-mediated cell proliferation. Plasmin can also activate metalloproteinases on the cell surface, which can release the tethered ligand heparin-binding epidermal growth factor (HB-EGF), which can in turn activate the epidermal growth factor receptor (EGFR).

METHODS

Murine aortic smooth muscle cells were cultured in vitro. Assays of DNA synthesis and cell proliferation, EGFR phosphorylation, and ERK1/2 activation were examined in response to plasmin in the presence and absence of the plasmin inhibitors (epsilon-aminocaproic acid and aprotinin), matrix metalloproteinase (MMP) inhibitor GM6001, HB-EGF inhibitor CRM197, HB-EGF inhibitory antibodies, EGF inhibitory antibodies, and the EGFR inhibitor AG1478.

RESULTS

Plasmin-induced smooth muscle cell DNA synthesis, which was blocked by EGFR and HB-EGF inhibition. Plasmin-induced time-dependent EGFR phosphorylation and ERK1/2 activation, which were inhibited by AG1478. This response was dependent on the proteolytic activity of plasmin since both plasmin inhibitors blocked the response. EGFR phosphorylation by plasmin was blocked by inhibition of MMP activity and the ligand HB-EGF. EGFR phosphorylation by EGF was not interrupted by inhibition of plasmin, MMPs, or HB-EGF. Direct blockade of the EGFR prevented activation by both plasmin and EGF.

CONCLUSIONS

Plasmin can induce smooth muscle cell proliferation through activation of EGFR by an extracellular MMP-mediated, HB-EGF-dependent process.

Plasmin Induces Smooth Muscle Cell Proliferation1,2

BACKGROUND

Plasminogen activators are routinely used for thrombolysis. They lead to the generation of the protease, plasmin, which can induce smooth muscle cell proliferation and may thus promote further intimal hyperplasia in the thrombolysed vessel. The signaling pathways used by plasmin are not understood.

METHODS

Murine aortic smooth muscle cells were cultured in vitro. Assays of DNA synthesis, cell proliferation, MAPKK and MAPK activation were examined in response to plasmin alone and in the presence of plasmin inhibitors (epsilon-aminocaproic acid and aprotinin), pertussis toxin (Galphai inhibitor, PTx), GP-2A (Galphaq inhibitor), wortmannin (PI3-K inhibitor, Wn), LY294002, (PI3-K inhibitor, LY), PD98059 (MEK inhibitor, PD), and SB203580 (p38MAPK inhibitor, SB).

RESULTS

Plasmin produced concentration dependent smooth muscle cells DNA synthesis and proliferation and induced ERK1/2 and p38MAPK phosphorylation. Inhibition of the proteolytic activity of plasmin prevented these responses. The ERK1/2 inhibitor, PD, but not the p38MAPK inhibitors, SB, blocked cell proliferation. The activation of the MEK1/2 and ERK1/2 pathway was both Galphai dependent (PTx-sensitive) and Galphaq dependent (GP-2A-sensitive). It was blocked by the PI3-K inhibitors, Wn and LY. PI3-K activation as measured by akt phosphorylation was dependent on Galphai, but was independent of Galphaq.

CONCLUSION

Plasmin induces smooth muscle cell proliferation. Plasmin induced ERK1/2 phosphorylation occurs through two pathways: one which is Galphai mediated/PI3-K dependent and a second which is Galphaq mediated/PI3K independent. p38MAPK appears not to be involved in plasmin-mediated cell proliferation. This pattern of activation is distinct from that seen with urokinase plasminogen activator.

Urokinase-induced signaling in human vascular smooth muscle cells is mediated by PDGFR-beta

Urokinase (uPA)-induced signaling in human vascular smooth muscle cells (VSMC) elicits important cellular functional responses, such as cell migration and proliferation. However, how intracellular signaling is linked to glycolipid-anchored uPA receptor (uPAR) is unknown. We provide evidence that uPAR activation by uPA induces its association with platelet-derived growth factor receptor (PDGFR)-beta. The interaction results in PDGF-independent PDGFR-beta activation by phosphorylation of cytoplasmic tyrosine kinase domains and receptor dimerization. Association of the receptors as well as the tyrosine kinase activity of PDGFR-beta are decisive in mediating uPA-induced downstream signaling that regulates VSMC migration and proliferation. These findings provide a molecular basis for mechanisms VSMC use to induce uPAR- and PDGFR-directed signaling. The processes may be relevant to VSMC function and vascular remodeling.

Urokinase-induced smooth muscle cell migration requires PI3-K and Akt activation

OBJECTIVE

To examine the role of the phospho-inositol-3'-kinase (PI3-K)-akt signaling axis during smooth muscle cell (SMC) migration in response to the aminoterminal fragment of urokinase (ATF).

BACKGROUND

Urokinase (uPA) is involved in vessel remodeling and mediates smooth muscle cell migration. Migration in response to urokinase is dependent on ATF. The role of PI3-K/akt signaling during migration in response to the uPA fragments is not understood.

METHODS

Murine arterial SMCs were cultured in vitro. Linear wound and Boyden microchemotaxis assays of migration were performed in the presence of ATF with and without the PI3-K inhibitors (Wortmannin, Wn [10 nm] and LY294002, LY [10 microm]) and an akt inhibitor (aktI, [10 microm]). Western blotting was performed for akt, ERK1/2, and GSK3beta phosphorylation after cells were stimulated with ATF in the presence and absence of the inhibitors. Statistics were analyzed by one-way ANOVA.

RESULTS

Both PI3-K and akt inhibitors blocked the migratory response to ATF in both assays. ATF induced time-dependent increases in akt phosphorylation at both S472 and T308 sites and ERK1/2 phosphorylation. Activation of akt and ERK1/2 was inhibited by Wn and LY. Manumycin A, a ras inhibitor, did not inhibit activation of akt but did inhibit ERK1/2 activation. Activation of akt and the dephosphorylation of its downstream kinase GSK3beta were inhibited by the akt inhibitor. Direct inhibition of akt did not influence ERK1/2 activation and inhibition of ERK1/2 did not influence akt activation.

CONCLUSION

ATF mediated migration is PI3-K dependent and activates two separate pathways: ERK1/2 and akt. ATF induces akt phosphorylation through a PI3K-mediated but ras-independent mechanism while both ras and PI3K are required for ERK1/2 activation. Defining key signaling pathways is vital to regulate vessel remodeling.

Urokinase-induced smooth muscle cell responses require distinct signaling pathways: A role for the epidermal growth factor receptor

OBJECTIVE

Urokinase plasminogen activator (uPA) a key serine protease during remodeling, is capable of inducing both smooth muscle cell migration and proliferation. However, the signals that produce these responses are poorly understood.

METHODS

Early passage rat aortic arterial smooth muscle cells were cultured in vitro and standard assays of DNA synthesis ([ 3 H]thymidine incorporation), cell proliferation (manual cell counting), and migration (linear wound assay and Boyden chamber) were used to study the cells responses to uPA. Activation of the mitogen-activated protein kinases (MAPK), extracellular signal-regulated kinase 1/2 (ERK1/2), p38 MAPK , Akt, MAP kinase/ERK kinase (MEK1/2), MAP kinase kinase (MKK)3/6, and epidermal growth factor receptor (EGFR) in response to uPA was assayed by Western blot analysis for the phosphorylated form of each kinase. These assays were repeated in the presence of the Galphai inhibitor pertussis toxin (PTx, 100 ng/mL), the Ras inhibitor manumycin A (MA, 10 microM), the phosphatidyl-inositol 3' kinase (PI3K) inhibitor wortmannin (WN, 1 microM), the EGFR inhibitor AG1478 (AG, 10 nM), the MEK1 inhibitor PD98059 (PD, 10 microM), the p38 MAPK inhibitor SB203580 (SB, 10 microM), and the plasmin inhibitors aprotinin and epsilon-aminocaproic acid.

RESULTS

uPA induced a twofold increase in smooth muscle cell migration and increased smooth muscle cell DNA synthesis and proliferation. The ERK1/2 and p38 MAPK inhibitors PD98059 (PD) and SB203580 (SB) blocked cell proliferation, but only PD blocked cell migration. Although uPA-induced phosphorylation of both ERK1/2 and p38 MAPK was blocked by Galphai inhibition, inhibition of PI3K and Ras decreased the uPA-induced phosphorylation of ERK1/2 but not p38 MAPK . Activation of MEK1/2 was abrogated by inhibitors of Galphai and Ras, but not by PI3K inhibition. In contrast, activation of MKK3/6 was abrogated by inhibition of Galphai, but not by Ras or PI3K inhibition. uPA induced time-dependent phosphorylation of EGFR, which was dependent on plasmin activity. Inhibition of EGFR reduced both ERK1/2 and p38 MAPK activation. uPA activation of PI3K and MKK3/6 was EGFR-dependent and that of MEK1 was EGFR-independent.

CONCLUSION

uPA induces smooth muscle cell proliferation through ERK1/2- and p38 MAPK -mediated pathways. Migration appears to be dependent on ERK1/2 activity alone. Activation of EGFR appears to be required. The differential activation of pathways for ERK1/2 and p38 MAPK by uPA allows for two distinct biologic responses that both require tyrosine kinase receptor transactivation.

CLINICAL RELEVANCE

Elevated urokinase-like plasminogen activator (uPA) and decreased plasminogen activator inhibitor-1 (PAI-1) levels are predictors for restenosis. Matrix remodeling and smooth muscle cell responses are integrally linked. Changes in smooth muscle cell migration and proliferation are dependent on the extracellular matrix environment in which they are encased. Proteases such as uPA can effect smooth muscle cells and alter the matrix; their activity is controlled by a series of inhibitors (eg, PAI-1). The balance of activation and inhibition forms the basis of the proteolytic thermostat in the vessel wall. Understanding the biology of the proteolytic thermostat will allow for structured therapeutic interventions to control restenosis and thus improve patient care and avoid secondary interventions. Our study demonstrates that uPA is capable of inducing separate responses through more than one signaling pathway, in part, by transactivation of a nearby receptor for the unrelated ligand epidermal growth factor receptor (EGFR). Blockade of EGFR can inhibit both cell migration and proliferation induced by uPA. This is the first description of cross talk between uPA and EGFR in vascular smooth muscle cells. Targeting a pivotal receptor such as EGFR, which can be transactivated by both G-protein-coupled receptors and receptor tyrosine kinases, is an attractive molecular target to control restenosis.

Regulation of fibrogenic/fibrolytic genes by platelet-derived growth factor C, a novel growth factor, in human dermal fibroblasts

Platelet-derived growth factor (PDGF) is a potent mitogenic and chemotactic cytokine, and PDGF-C is a novel growth factor belonging to the PDGF family. In this study, to determine whether this growth factor can contribute to fibrosis and tissue remodeling, we examined the effect of PDGF-CC on the expression of fibrogenic/fibrolytic genes such as type I collagen, fibronectin (FN), matrix metalloproteinases (MMPs), and their inhibitors (TIMPs) in normal human dermal fibroblasts in vitro. PDGF elevated the levels of MMP-1 or TIMP-1 protein as well as mRNA, whereas this cytokine had no influence on the expression of type I collagen, FN, or TIMP-2. PDGF-CC also increased the levels of MMP-1 catalytic activity in the cultured media and mRNA expression, which was paralleled that on the levels of promoter activation. Additionally, PDGF-CC induced the mitogenic and migratory activity of human dermal fibroblasts in a dose-dependent manner. On the other hand, we also determined the specificity of the inhibitory effect of monoclonal antibodies against PDGF-CC generated by immunizing balb/c mice with recombinant human PDGF-CC. This antibody could inhibit the regulatory effects of MMP-1 or TIMP-1 synthesis as well as the mitogenic effects on human dermal fibroblasts induced by PDGF-CC, whereas this antibody did not affect those induced by other PDGF forms such as PDGF-AA, -AB, or -BB. These results suggest that this cytokine plays a role in the tissue remodeling.

Contrasting Effects of Urokinase and Tissue-Type Plasminogen Activators on Neointima Formation and Vessel Remodelling after Arterial Injury

Urokinase-type plasminogen activator (uPA) has been implicated in neointima formation and arterial lumen narrowing after angioplasty. To determine the specificity of the action of uPA on vessel remodelling after arterial injury we compared the effects of the recombinant urokinase- and tissue-type plasminogen activators on vessel morphology, cell migration and proliferation. We used a standard model of the balloon catheter injury of the rat carotid artery followed by the periadventitial application to the injured vessel of the one of the recombinant PAs or recombinant alpha(2)-antiplasmin (alpha-AP) in pluronic gel with further immunohistochemistry and morphometry. The perivascular application of alpha-AP immediately after injury attenuated the healing response, significantly reducing neointima size and neointimal SMC numbers. The periadventitial application to the injured artery of recombinant uPA stimulated neointima formation as well as cell proliferation and migration in vivo and induced greater reductions in lumen size than injury alone. In contrast, recombinant tissue-type plasminogen activator reduced the number of neointimal smooth muscle cells and the neointimal area and increased both the lumen area and the area encompassed by the external elastic laminae after balloon catheter injury of the rat carotid artery. In the meantime both PAs nearly doubled medial and adventitial SMC numbers in the vessels. We conclude that the ability to stimulate neointima formation and inward arterial remodelling is a specific property for urokinase plasminogen activator that could not be mimicked by tissue-type plasminogen activator.

Growth inhibition of vascular smooth muscle cells derived from urokinase receptor (u-PAR)-deficient mice in the presence of carcinoma cells

The growth rate of vascular smooth muscle cells (VSMCs), which were derived from aorta of mice deficient in the fibrinolytic factors tissue-type plasminogen activator (t-PA(-/-)), urokinase (u-PA(-/-)), u-PA receptor (u-PAR(-/-)) and type 1 plasminogen activator inhibitor (PAI-1(-/-)), as well as wild-type (WT) mice, was investigated in the presence of mouse melanoma cells (B16). In the VSMCs cultured with a basal medium supplemented with 10% fetal calf serum (FCS), there was no difference in the growth rate among the gene-lacking VSMCs and WT VSMCs, indicating that these fibrinolytic factors were not involved in the FCS-mediated cell proliferation. On the other hand, when these VSMCs were cultured with B16 cells in either the mixed culture or a double-chamber, only u-PAR(-/-) VSMCs showed a significantly lower growth rate. In addition, these suppressive effects on u-PAR(-/-) VSMCs were also observed in the presence of B16-derived conditioned medium (B16/CM). The growth rate of all the VSMCs except u-PAR(-/-) VSMCs was increased in the presence of B16/CM. The degree of the increase in cell number was comparable to that obtained with FCS. These effects on growth activity were partially associated with the levels of mitogen-activated protein kinase (MAPK, p42/p44) activity. The findings suggest that u-PAR plays an important role in the proliferative response of VSMCs and that without u-PAR, there is no intracellular signaling for cell proliferation.

Vascular smooth muscle cells efficiently activate a new proteinase cascade involving plasminogen and fibronectin

The plasminogen/plasmin system is involved in vascular wall remodeling after injury, through extracellular matrix (ECM) degradation and proteinase activation. Vascular smooth muscle cells (VSMCs) synthesize various components of the plasminogen/plasmin system. We investigated the conversion of plasminogen into plasmin in primary cultured rat VSMCs. VSMCs efficiently converted exogenous plasminogen into plasmin in a time- and dose-dependent manner. We measured plasmin activity by monitoring the hydrolysis of Tosyl-G-P-R-Mca, a fluorogenic substrate of plasmin. Cell-mediated plasmin activation was associated with the degradation of ECM, as revealed by fibronectin proteolysis. Plasmin also activated a proteinase able to hydrolyze Mca-P-L-G-L-Dpa-A-R-NH(2), a fluorogenic substrate of matrix metalloproteinases (MMPs). However, this proteinase was not inhibited by an MMP inhibitor. Furthermore, this proteinase displayed similar biochemical and pharmacological properties to fibronectin-proteinase, a recently identified zinc-dependent metalloproteinase located in the gelatin-binding domain of fibronectin. These results show that VSMCs convert exogenous plasminogen into plasmin in their pericellular environment. By hydrolyzing matrix protein plasmin activates a latent metalloproteinase that differs from MMP, fibronectin-proteinase. This metalloproteinase may participate to vascular wall remodeling, in concert with other proteinases.

Gene transfer of the urokinase-type plasminogen activator receptor-targeted matrix metalloproteinase inhibitor TIMP-1.ATF suppresses neointima formation more efficiently than tissue inhibitor of metalloproteinase-1

Proteases of the plasminogen activator (PA) and matrix metalloproteinase (MMP) system play an important role in smooth muscle cell (SMC) migration and neointima formation after vascular injury. Inhibition of either PAs or MMPs has previously been shown to result in decreased neointima formation in vivo. To inhibit both protease systems simultaneously, a novel hybrid protein, TIMP-1.ATF, was constructed consisting of the tissue inhibitor of metalloproteinase-1 (TIMP-1) domain, as MMP inhibitor, linked to the receptor-binding amino terminal fragment (ATF) of urokinase. By binding to the u-PA receptor this protein will not only anchor the TIMP-1 moiety directly to the cell surface, it will also prevent the local activation of plasminogen by blocking the binding of urokinase-type plasminogen activator (u-PA) to its receptor. Adenoviral expression of TIMP-1.ATF was used to inhibit SMC migration and neointima formation in human saphenous vein segments in vitro. SMC migration was inhibited by 65% in Ad.TIMP-1.ATF-infected cells. Infection with adenoviral vectors encoding the individual domains, Ad.TIMP-1 and Ad.ATF, reduced migration by 32% and 52%, respectively. Neointima formation in saphenous vein organ cultures infected with Ad.TIMP-1.ATF was inhibited by 72% compared with 42% reduction after Ad.TIMP-1 infection and 34% after Ad.ATF infection. These data show that binding of TIMP-1.ATF hybrid protein to the u-PA receptor at the cell surface strongly enhances the inhibitory effect of TIMP-1 on neointima formation in human saphenous vein cultures.

Angiogenesis and the unique nature of tumor matrix

In this article we consider the factors responsible for the unique nature of the pericellular matrix of solid tumors and we discuss the role of alterations of tumor blood vessel structure. We examine the role of VEGF (vascular endothelial growth factor), a factor controlling permeability of capillaries, plasma protein extravasation, and the formation of a fibrin barrier. We discuss how this barrier could be destroyed by metalloproteinases bound on the surface of endothelial cells migrating through the matrix and how these enzymes are responsible for the activation of gelatinases that destroy basement membranes. The process called tubulogenesis, which gives rise to hyperpermeable tumor capillaries, will also be described. Alterations of the blood vessel structure leading to hypoxia of the matrix, and accumulation of plasma proteins and of blood cells will be treated. Finally, we review some of the strategies that might exploit this knowledge about the nature of the tumoral matrix for designing novel anticancer treatments.

The urokinase receptor mediates basic fibroblast growth factor-dependent smooth muscle cell migration through baboon aortic explants

The urokinase receptor is required for vascular smooth muscle cell migration in vitro, but may not be needed in vivo since smooth muscle cell migration and intimal hyperplasia after arterial injury in mice are not affected by urokinase receptor gene deletion. We have used baboon aortic explants as a bridge between cell culture and in vivo experiments to determine if the urokinase receptor is required for smooth muscle cell proliferation and smooth muscle cell migration in primate vessels. Levels of urokinase receptor in explants increased with time after explantation, while blockade of urokinase receptor with an antibody decreased smooth muscle cell proliferation and smooth muscle cell migration from the explants. A blocking antibody to basic fibroblast growth decreased levels of urokinase and urokinase receptor in explants, and it decreased smooth muscle cell migration and mitogenesis. These results suggest that the factor urokinase receptor plays a positive role in smooth muscle cell migration and proliferation in injured primate arterial tissue, in part mediating the pro-migratory and proliferative effects of basic fibroblast growth factor released by damaged smooth muscle cells.

Tissue plasminogen activator is required for the growth, invasion, and angiogenesis of pancreatic tumor cells

BACKGROUND & AIMS

Overexpression of tissue-type plasminogen activator (t-PA) in exocrine pancreatic tumors might be a determinant of the aggressive biological behavior of these tumors.

METHODS

Endogenous t-PA production was suppressed by antisense oligonucleotides or transcripts in CAPAN-1 and RWP-1 cell lines. Reciprocally, the t-PA non-expressing BxPC-3 and PANC-1 cells were stably transfected to overexpress t-PA. Recombinant t-PA and chemical inhibitors were also used on these cells. Clones were assayed for invasion and growth in vitro and in vivo.

RESULTS

In vitro, specific inhibition of t-PA expression or activity significantly inhibited the proliferation of t-PA-producing RWP-1, CAPAN-1, and SK-PC-1 cells. Antisense constructs were used to generate RWP-1 clones stably suppressed for t-PA expression (AS clones). These clones had a significantly reduced invasion and proliferation on plastic and in soft agar. The addition of recombinant t-PA rescued the growth of the AS clones to parental levels and was mitogenic for other independent pancreas cell lines. This effect did not require plasmin activity. In athymic mice, RWP-1 AS clones produced tumors fivefold smaller than control clones. AS tumors contained a significantly reduced number of Ki67-positive nuclei, fewer mitotic cells, and a remarkably reduced angiogenic network. Finally, the generation of tetracycline-repressed t-PA transfectants in PANC-1 cells confirmed the activity of t-PA in invasion and proliferation in vitro and in vivo.

CONCLUSIONS

t-PA, in addition to its known role in invasion, plays other critical roles in pancreas tumor progression, stimulating cancer cell proliferation and tumor-associated angiogenesis.

Urokinase plasminogen activator augments cell proliferation and neointima formation in injured arteries via proteolytic mechanisms

Urokinase plasminogen activator (uPA) has been implicated in the healing responses of injured arteries, but the importance of its various properties that influence smooth muscle cell (SMC) proliferation and migration in vivo is unclear. We used three recombinant (r-) forms of uPA, which differ markedly in their proteolytic activities and abilities to bind to the uPA receptor (uPAR), to determine, which property most influences the healing responses of balloon catheter injured rat carotid arteries. After injury, uPA and uPAR expression increased markedly throughout the period when medial SMCs were rapidly proliferating and migrating to form the neointima. Perivascular application of uPA neutralizing antibodies immediately after injury attenuated the healing response, significantly reducing neointima size and neointimal SMC numbers. Perivascular application of r-uPAwt (wild type uPA) or r-uPA/GDF (r-uPA with multiple mutations in its growth factor-like domain) doubled the size of the neointima. Four days after injury these two uPAs nearly doubled neointimal and medial SMC numbers in the vessels, and induced greater reductions in lumen size than injury alone. Proteolytically inactive r-uPA/H/Q (containing glutamine rather than histidine-204 in its catalytic site) did not affect neointima or lumen size. Also, in contrast to the actions of proteolytically active uPAs, tissue plasminogen activator (tPA) did not affect the rate of neointima development. We conclude that uPA is an important factor regulating the healing responses of balloon catheter injured arteries, and its proteolytic property, which cannot be mimicked by tPA, greatly influences SMC proliferation and early neointima formation.

Plasmin-mediated fibroblast growth factor-2 mobilisation supports smooth muscle cell proliferation in human saphenous vein

The focus of this study was identification of the contribution of the plasminogen activator-plasmin system to smooth muscle cell proliferation and migration in human saphenous vein. Segments of human saphenous vein were grown in organ culture for up to 14 days. Smooth muscle cell proliferation and migration were measured by incubating vein segments in bromodeoxyuridine, and smooth muscle cell death was detected by in situ end-labelling. Tissue-type (tPA) and urokinase-type (uPA) plasminogen activator enzymic activities were detectable in cultured saphenous vein segments, and were concentrated in focal zones. Inhibition of plasmin activity with alpha-N-acetyl-L-lysine methyl ester (NALME) or of uPA activity with a neutralising antibody caused significant decreases in smooth muscle cell proliferation in the media and the intima, but no significant changes in smooth muscle cell migration. Intimal thickness was also significantly decreased. Incubation with plasminogen or plasmin caused fibroblast growth factor-2 (FGF2) to be released into the medium. Addition of FGF2 to segments cultured with NALME reversed the inhibition of smooth muscle cell proliferation, and blocking the activity of FGF2 with a neutralising antibody caused a significant decrease in medial smooth muscle cell proliferation. These data suggest that plasmin mobilises FGF2 bound to the extracellular matrix of human saphenous vein, so that it can support smooth muscle cell proliferation and intimal thickening.

Integrin alpha(v)beta(3) is involved in stimulated migration of vascular adventitial fibroblasts by basic fibroblast growth factor but not platelet-derived growth factor

We examined the effects of basic fibroblast growth factor (bFGF) and platelet-derived growth factor (PDGF) on the migration of vascular adventitial fibroblasts (VAFs) isolated from rat aortic adventitiae. Both bFGF and PDGF significantly stimulated VAF migration in vitro. An antibody to rat beta(3) integrin reduced bFGF-stimulated migration in a dose dependent manner. Moreover, VAF migration was inhibited in the presence of cyclic RGD (cRGD) peptide. However, PDGF-directed migration was blocked only by equivalent cRGD peptide but not by antibody to beta(3) integrin. These data suggest that alpha(v)beta(3) integrin mediates VAF migration stimulated by bFGF and that chemoattractant directed migration may be through distinct integrins.

Mutational analyses of Aquifex pyrophilus DNA ligase define essential domains for self-adenylation and DNA binding activity

We constructed nine deletion mutants of NAD+-dependent DNA ligase from Aquifex pyrophilus to characterize the functional domains. All of DNA ligase deletion mutants were analyzed in biochemical assays for NAD+-dependent self-adenylation, DNA binding, and nick-closing activity. Although the mutant lsub1 (91-362) included the active site lysine (KxDG), self-adenylation was not shown. However, the mutants lsub6 (1-362), lsub7 (1-516), and lsub9 (1-635) showed the same adenylation activity as that of wild type. The lsub5 (91-719), which has the C-terminal domain (487-719) as to lsub4 (91-486), showed minimal adenylation activity. These results suggest that the presence of N-terminal 90 residues is essential for the formation of an enzyme-AMP complex, while C-terminal domain (487-719) appears to play a minimal role in adenylation. It was found that the presence of C-terminal domain (487-719) is indispensable for DNA binding activity of lsub5 (91-719). The mutant lsub9 (1-635) showed reduced DNA binding activity compared to that of wild type, suggesting the contribution of the domain (636-719) for the DNA binding activity. Thus, we concluded that the N-terminal 90 residues and C-terminal domain (487-719) of NAD+-dependent DNA ligase from A. pyrophilus are mutually indispensable for binding of DNA substrate.

In vivo suppression of restenosis in balloon-injured rat carotid artery by adenovirus-mediated gene transfer of the cell surface-directed plasmin inhibitor ATF.BPTI

Injury-induced neointimal development results from migration and proliferation of vascular smooth muscle cells (SMC). Cell migration requires controlled proteolytic degradation of extracellular matrix surrounding the cell. Plasmin is a major contributor to this process by degrading various matrix proteins directly, or indirectly by activating matrix metalloproteinases. This makes it an attractive target for inhibition by gene transfer. An adenoviral vector, Ad.ATF.BPTI, was constructed encoding a hybrid protein, which consists of the aminoterminal fragment (ATF) of urokinase-type plasminogen activator (u-PA) linked to bovine pancreas trypsin inhibitor (BPTI), a potent inhibitor of plasmin. This hybrid protein binds to the u-PA receptor, thereby inhibiting plasmin activity at the cell surface, and was found to be a potent inhibitor of cell migration in vitro. Local infection with Ad.ATF.BPTI of balloon-injured rat carotid artery resulted in detectable expression of ATF.BPTI mRNA and protein in the vessel wall. Morphometric analysis of arterial cross-sections revealed that delivery of Ad.ATF.BPTI to the carotid artery wall at the time of balloon injury inhibited neointima formation by 53% (P < 0.01) at 14 days and 19% (P = NS) at 28 days after injury when compared with control vector-infected arteries. Intima/media ratios were decreased by 60% (P < 0.01) and 35% (P < 0.05) at 14 and 28 days, respectively, when compared with control vector-infected arteries. Furthermore, a small but significant increase in medial area was found in the Ad.ATF.BPTI-treated arteries at 28 days (P < 0.05). These results show that local infection of the vessel wall with Ad.ATF.BPTI reduces neointima formation, presumably by inhibiting SMC migration, thereby offering a novel therapeutic approach to inhibiting neointima development.

Urokinase plasminogen activator enhances neointima growth and reduces lumen size in injured carotid arteries

OBJECTIVES

Increases in urokinase plasminogen activator (uPA) have been reported in tissues undergoing remodelling, but its effects on the vessel intima formation are not known. We investigated its effects on carotid artery intima, media and lumen size, as well as smooth muscle cell (SMC) proliferation and migration in vivo.

DESIGN AND METHODS

Carotid arteries of rats were distended with an inflated balloon catheter and uPA, or uPA-neutralizing antibodies were applied perivascularly in pluronic gel; control rats received vehicle. Carotid artery structure, cell migration and proliferation were assessed after 4 days by quantitative morphometry and immunohistochemistry.

RESULTS

Four days after increasing vessel uPA, the intima/media ratio was double compared to that in control rats (both P < 0.05). The size of the lumen reduced by 75%, compared to the vehicle-treated vessels (P < 0.05). The elevation in uPA also increased SMC numbers in the intima and media, compared to the vehicle-treated vessels (both P < 0.05). Antibody neutralizing endogenous uPA attenuated the growth responses in the distended arteries, reduced neointimal SMC numbers by approximately 50% and prevented much of the reduction in lumen size.

CONCLUSIONS

Thus, local increases in uPA in distended, injured arteries augment SMC migratory and proliferative responses, leading to increases in the thickness of the carotid artery intima and media and a reduction in lumen size; effects at least partially attributable to its proteolytic properties.

The chemotactic action of urokinase on smooth muscle cells is dependent on its kringle domain. Characterization of interactions and contribution to chemotaxis

Urokinase plasminogen activator (uPA) is thought to exert its effects on cell growth, adhesion, and migration by mechanisms involving proteolysis and interaction with its cell surface receptor (uPAR). The functional properties of uPA and the significance of its various domains for chemotactic activity were analyzed using human airway smooth muscle cells (hAWSMC). The wild-type uPA (r-uPAwt), inactive urokinase with single mutation (His(204) to Gln) (r-uPA(H/Q)), urokinase with mutation of His(204) to Gln together with a deletion of growth factor-like domain (r-uPA(H/Q)-GFD), the catalytic domain of urokinase (r-uPA(LMW)), and its kringle domain (r-KD) were expressed in Escherichia coli. We demonstrate that glycosylated uPA, r-uPAwt, r-uPA(H/Q), and r-uPA(H/Q)-GFD elicited similar chemotactic effects. Half-maximal chemotaxis (EC(50)) were apparent at approximately 2 nm with all the uPA variants. The kringle domain induced cell migration with an EC(50) of about 6 nm, whereas the denaturated r-KD and r-uPA(LMW) were without effect. R-uPAwt-induced chemotaxis was dependent on an association with uPAR and a uPA-kringle domain-binding site, determined using a monoclonal uPAR antibody to prevent the uPA-uPAR interaction, and a monoclonal antibody to the uPA-kringle domain. The binding of iodinated r-uPAwt with hAWSMC was due to interaction with a high affinity binding site on the uPAR, and a lower affinity binding site on an unidentified cell surface target, which was mediated exclusively through the kringle domain of urokinase. Specific binding of r-uPA(H/Q)-GFD to hAWSMC involved an interaction with a single site whose characteristics were similar to those of the low affinity site of r-uPAwt binding to hAWSMC. uPAR-deficient HEK 293 cells specifically bound r-uPAwt and r-uPA(H/Q)-GFD via a single, similar type of binding site. These cells migrated when stimulated by r-uPA(H/Q)-GFD and uPAwt, but not r-uPA(LMW). HEK 293 cells transfected with the uPAR cDNA expressed two classes of sites that bound r-uPAwt; however, only a single site was responsible for the binding of r-uPA(H/Q)-GFD. Together, these findings indicate that uPA-induced chemotaxis is dependent on the binding of the uPA-kringle to the membrane surface of cells and the association of uPA with uPAR.

FGF-2 isoforms of 18 and 22.5 kDa differentially modulate t-PA and PAI-1 expressions on the pancreatic carcinoma cells AR4-2J: consequences on cell spreading and invasion

Pancreatic tumors overexpress FGF-2 and t-PA, but the implication of the growth factor in t-PA synthesis and t-PA-dependent tumor invasion remains unknown. FGF-2 is present in different isoforms: The 18 kDa FGF-2 is secreted, while the 22.5 kDa one is nuclearized and exerts intracrine regulations bypassing cell-surface FGF receptors. Rat pancreatic carcinoma AR4-2J cells producing either the 18 or the 22.5 kDa FGF-2 after transfection with FGF-2 cDNAs have been used to analyze the role of FGF-2 in t-PA expression and t-PA-related cell spreading. The 22.5 kDa FGF-2 reduced t-PA and PAI-1 synthesis 2-fold. Addition of recombinant 18 kDa FGF-2 (rFGF-2) to cell cultures resulted in increased t-PA and decreased PAI-1 expression. By contrast, rFGF-2 did not significantly modify t-PA synthesis in cells producing the 22.5 kDa FGF-2. Cell spreading was t-PA-dependent. Furthermore, cells producing the 22.5 kDa FGF-2 migrated less than control cells and cells producing the 18 kDa FGF-2. Overall, our data show that secretory FGF-2 is involved in t-PA synthesis by pancreatic cancer cells and facilitates cell spreading. The 22.5 kDa FGF-2 exerts opposite effects by decreasing t-PA expression in basal conditions and during rFGF-2 stimulation. Since the expression of the 22.5 kDa FGF-2 is under specific controls, its up-regulation might have the potential to reduce spreading of pancreatic cancer cells.

Transgenic mouse models in angiogenesis and cardiovascular disease

Novel gene technologies have allowed us to manipulate the genetic balance of candidate molecules in mice in a controllable manner. Homologous or site-specific recombination in embryonic stem cells allows us to study the consequences of deficiencies, mutations, and conditional or tissue-specific expression of gene products in transgenic mice. These technological breakthroughs have significantly advanced biomedical research and broadened our understanding of the pathophysiological role of candidate disease genes. In addition, gene transfer allows us to test the possible therapeutic use of gene products for gene therapy. A variety of assays have been miniaturized, allowing analysis of cardiovascular physiology in the mouse. With the advent of genome sequencing programmes, these gene technologies provide means of studying gene function in a conclusive manner. Furthermore, disease models can be generated which can be used as test models for (gene) therapy or for the discovery of novel genes using differential gene profiling techniques. The present review will focus on the molecular basis of how blood vessels form (angiogenesis and arteriogenesis) and how they become diseased. A selected number of molecules that have been studied in the authors' laboratory will be reviewed in more detail.

Gene response of human skin fibroblasts to urokinase- and tissue-type plasminogen activators

In a previous work we have reported evidences on the mitogenic activity of urokinase-type and tissue-type plasminogen activator (u-PA, t-PA) on serum-deprived human dermal fibroblasts. In this work we have studied the transcription-dependent changes of some cell-cycle related genes associated with the biological activity of PAs, as well as the possible involvement of protein tyr kinases (PTK) and/or protein kinase C (PKC) in the mitogenic signal transduction. The data obtained demonstrate that the growth factor activity of PAs is associated with: - a rapid transient activation of early response genes, c-fos, c-jun and c-myc; - the subsequent coordinated down-regulation of p53 and p21CIP1; - the constant expression of the MEK1 mRNA in every phase of the cell cycle. Quiescent (G0) cells did not express c-fos, c-jun, c-myc and cyclin A, but upon stimulation with mitogens (fetal calf serum (FCS), u-PA, t-PA) the cyclin A mRNA expression was observed in concomitance with the activation of DNA synthesis. Therefore u-PA, t-PA and FCS similarly modulate the expression of c-fos, c-jun, c-myc, p53, p21CIP1 and cyclin A with only slight differences likely related to the time required for activation of DNA synthesis. The PAs mitogenic stimulation of serum-starved cells was associated with the internalization of their molecules, as revealed by immunostaining. The biological activity of u-PA, t-PA, as well as that of limiting concentration of FCS (1%), was mediated by PTK and PKC. Conversely, PTK, but not PKC, was involved in the activation of the proliferative response of basic fibroblast growth factor in the same experimental conditions. In conclusion, u-PA and t-PA can utilize two different pathways, one depending on PTK and the other on PKC in a way similar to the mitogenic activity induced by low concentration of FCS (1%).

Urokinase-induced mitogenesis is mediated by casein kinase 2 and nucleolin

BACKGROUND

Urokinase (uPA) and the urokinase receptor (uPAR) form a multifunctional system capable of concurrently regulating pericellular proteolysis, cell-surface adhesion, and mitogenesis. The role of uPA and uPAR in directed proteolysis is well established and its function in cellular adhesiveness has recently been clarified by numerous studies. The molecular mechanisms underlying the mitogenic effects of uPA and uPAR are still unclear, however.

RESULTS

We identified mechanisms that might participate in uPA-related mitogenesis in human vascular smooth muscle cells and demonstrated that uPA induces activation of a unique signaling complex. This complex contains uPAR and two additional proteins, nucleolin and casein kinase 2, which are implicated in cell proliferation. Both proteins were isolated by affinity chromatography on uPA-conjugated cyanogen-bromide-activated Sepharose 4B and were identified using nano-electrospray mass spectrometry and immunoblotting. We used laser scanning and immunoelectron microscopy studies to further demonstrate that nucleolin and casein kinase 2 are located on the cell surface where they colocalize with the uPAR. Moreover, the proteins were co-internalized into the cell as an entire complex. Immunoprecipitation experiments in combination with an in vitro kinase assay demonstrated a specific association of uPAR with nucleolin and casein kinase 2 and revealed a uPA-induced activation of casein kinase 2, which presumably led to phosphorylation of nucleolin. Blockade of nucleolin and casein kinase 2 with specific modulators led to the inhibition of uPA-induced cell proliferation.

CONCLUSIONS

We conclude that in human vascular smooth muscle cells, uPA induces the formation and activation of a newly identified signaling complex comprising uPAR, nucleolin, and casein kinase 2, that is responsible for the uPA-related mitogenic response. The complex is not a unique feature of vascular smooth muscle cells, as it was also found in other uPAR-expressing cell types.

Src-Dependence and Pertussis-Toxin Sensitivity of Urokinase Receptor-Dependent Chemotaxis and Cytoskeleton Reorganization in Rat Smooth Muscle Cells

The catalytically inactive precursor of urokinase-type plasminogen activator (pro-u-PA) induced a chemotactic response in rat smooth muscle cells (RSMC) through binding to the membrane receptor of urokinase (u-PA receptor [u-PAR]). A soluble form of u-PAR activated by chymotrypsin cleavage as well as a peptide located between domain 1 and 2 of u-PAR reproduced the effect of pro-u-PA on cell migration. The chemotactic pro-u-PA effect correlates with a dramatic reorganization of actin cytoskeleton, of adhesion plaques, and with major cell shape changes in RSMC. Pro-u-PA induced a decrease in stress fiber content, membrane ruffling, actin ring formation, and disruption leading to the characteristic elongated cell shape of motile cells with an actin semi-ring located close to the leading edge of cells. u-PAR effects on both chemotaxis and cytoskeleton were sensitive to pertussis toxin and, hence, possibly require G proteins. u-PAR effects are accompanied by a relocation of u-PAR, vitronectin receptor (VNR) vβ3, β1 integrin subunit, and Src tyrosine kinase to the leading membrane of migrating cells. In conclusion, our data show that pro-u-PA, via binding to u-PAR, controls a signaling pathway, regulated by tyrosine kinases and possibly G proteins, leading to cell cytoskeleton reorganization and cell migration.

Src-Dependence and Pertussis-Toxin Sensitivity of Urokinase Receptor-Dependent Chemotaxis and Cytoskeleton Reorganization in Rat Smooth Muscle Cells

The catalytically inactive precursor of urokinase-type plasminogen activator (pro-u-PA) induced a chemotactic response in rat smooth muscle cells (RSMC) through binding to the membrane receptor of urokinase (u-PA receptor [u-PAR]). A soluble form of u-PAR activated by chymotrypsin cleavage as well as a peptide located between domain 1 and 2 of u-PAR reproduced the effect of pro-u-PA on cell migration. The chemotactic pro-u-PA effect correlates with a dramatic reorganization of actin cytoskeleton, of adhesion plaques, and with major cell shape changes in RSMC. Pro-u-PA induced a decrease in stress fiber content, membrane ruffling, actin ring formation, and disruption leading to the characteristic elongated cell shape of motile cells with an actin semi-ring located close to the leading edge of cells. u-PAR effects on both chemotaxis and cytoskeleton were sensitive to pertussis toxin and, hence, possibly require G proteins. u-PAR effects are accompanied by a relocation of u-PAR, vitronectin receptor (VNR) vβ3, β1 integrin subunit, and Src tyrosine kinase to the leading membrane of migrating cells. In conclusion, our data show that pro-u-PA, via binding to u-PAR, controls a signaling pathway, regulated by tyrosine kinases and possibly G proteins, leading to cell cytoskeleton reorganization and cell migration.

Emphysematous lesions, inflammation, and fibrosis in the lungs of transgenic mice overexpressing platelet-derived growth factor

Because of its expression pattern and its potent effects on mesenchymal cells, platelet-derived growth factor (PDGF) has been implicated as an important factor in epithelial-mesenchymal cell interactions during normal lung development and in the pathogenesis of fibrotic lung disease. To further explore the role of PDGF in these processes, we have developed transgenic mice that express the PDGF-B gene from the lung-specific surfactant protein C (SPC) promoter. Adult SPC-PDGFB transgenic mice exhibited lung pathology characterized by enlarged airspaces, inflammation, and fibrosis. Emphysematous changes frequently occurred throughout the lung, but inflammation and fibrotic lesions were usually confined to focal areas. The severity of this phenotype varied significantly among individual mice within the same SPC-PDGFB transgenic lineage. A pathology similar to that observed in adult mice was noted in lungs from transgenic mice as young as 1 week of age. Neonatal transgenic mice exhibited enlarged saccules and thickened primary septa. Results of these studies indicated that overexpression of PDGF-B induced distinct abnormalities in the developing and adult lung and led to a complex phenotype that encompassed aspects of both emphysema and fibrotic lung disease.

Morphogenetic movements at gastrulation require the SH2 tyrosine phosphatase Shp2

The SH2 domain-containing tyrosine phosphatase Shp2 plays a pivotal role during the gastrulation of vertebrate embryos. However, because of the complex phenotype observed in mouse mutant embryos, the precise role of Shp2 during development is unclear. To define the specific functions of this phosphatase, Shp2 homozygous mutant embryonic stem cells bearing the Rosa-26 LacZ transgene were isolated and used to perform a chimeric analysis. Here, we show that Shp2 mutant cells amass in the tail bud of embryonic day 10.5 chimeric mouse embryos and that this accumulation begins at the onset of gastrulation. At this early stage, Shp2 mutant cells collect in the primitive streak of the epiblast and thus show deficiencies in their contribution to the mesoderm lineage. In high-contribution chimeras, we show that overaccumulation of Shp2 mutant cells at the posterior end of the embryo results in two abnormal phenotypes: spina bifida and secondary neural tubes. Consistent with a failure to undergo morphogenic movements at gastrulation, Shp2 is required for embryo fibroblast cells to mount a positive chemotactic response to acidic fibroblast growth factor in vitro. Our results demonstrate that Shp2 is required at the initial steps of gastrulation, as nascent mesodermal cells form and migrate away from the primitive streak. The aberrant behavior of Shp2 mutant cells at gastrulation may result from their inability to properly respond to signals initiated by fibroblast growth factors.

Functions of the fibrinolytic system in human Ito cells and its control by basic fibroblast and platelet-derived growth factor

During liver fibrogenesis, hepatic stellate cells (HSC) proliferate and migrate under the influence of growth factors, including platelet-derived growth factor (PDGF) and basic-fibroblast growth factor (b-FGF). The plasminogen activation system regulates extracellular matrix (ECM) catabolism and cell movement. We evaluated the expression and biological functions of the plasminogen activation system in human HSC and its interaction with PDGF and b-FGF. Urokinase-plasminogen activator receptors (u-PAR) were measured by radioligand binding, cell cross-linking, immunoassay, and RNAse protection assay. u-PA and plasminogen activator inhibitors (PAIs) expression and activities were analyzed by zymography, immunoassay, and RNase protection assay. Cell migration and proliferation, studied in Boyden chambers and by microscopic counting, were evaluated after the addition of PDGF, b-FGF, and blockade with anti-u-PA, anti-u-PAR antibodies, and antisense oligodeoxynucleotides (aODN) against u-PAR mRNA. We have shown that HSC produce u-PAR, u-PA, and PAI-1. PDGF and b-FGF up-regulate u-PA and u-PAR, but not PAI-1, and exogenous addition of u-PA stimulates HSC proliferation, chemotaxis, and chemoinvasion. Inhibition of u-PA/u-PAR with antibodies against u-PA or u-PAR and with u-PAR aODN inhibit the proliferative, chemotactic, and chemoinvasive activity of PDGF and b-FGF. These findings indicate that u-PA and u-PAR are required for the mitogenic and chemoinvasive activity of PDGF and b-FGF on HSC.

Plasminogen activator expression in rat arterial smooth muscle cells depends on their phenotype and is modulated by cytokines

Cultured rat aortic smooth muscle cells (SMCs) exhibit at least 2 phenotypic variants: (1) a spindle-shaped phenotype, obtained from normal adult media, and (2) an epithelioid phenotype, obtained from intimal thickening 15 days after endothelial injury. Both phenotypes can be cloned from each location, with normal media yielding a majority of spindle-shaped clones and intimal thickening yielding a majority of epithelioid clones. These findings suggest that intimal thickening develops essentially from a subpopulation of medial SMCs exhibiting epithelioid features in vitro. Using zymographic and Northern blot analyses, we have studied plasminogen activator (PA) expression by these SMCs. Our results show that epithelioid SMCs, cultured as whole SMC populations or as clones, display higher PA activity than do spindle-shaped SMCs, irrespective of their origin. This is mainly due to differences in the expression of tissue PA and, to a lesser extent, urokinase PA and is accompanied by a decrease in PA inhibitor 1. Tissue PA activity is increased by basic fibroblast growth factor and platelet-derived growth factor-BB, particularly in epithelioid SMCs. Taken together, these results indicate that SMCs are heterogeneous with respect to their proteolytic profile, at least as far as the PA system is concerned. Proteolytic activity of the different SMC populations is modulated by cytokines that play a role in intimal thickening. Our results are in agreement with the suggestion that epithelioid SMCs are mainly responsible for intimal thickening.