Increased responsiveness of hypoxic endothelial cells to FGF2 is mediated by HIF-1α-dependent regulation of enzymes involved in synthesis of heparan sulfate FGF2-binding sites

2002 ◽  
Vol 115 (9) ◽  
pp. 1951-1959
Author(s):  
Jian Li ◽  
Nicholas W. Shworak ◽  
Michael Simons
Keyword(s):  
Endothelial Cells ◽  
Endothelial Cell ◽  
Cell Surface ◽  
Heparan Sulfate ◽  
Binding Sites ◽  
Cell Mass ◽  
Growth Stimulation ◽  
Receptor Expression ◽  
Hypoxic Conditions

Binding of basic fibroblast growth factor (FGF2) to its high affinity receptors requires the presence of specific heparan sulfate (HS) moieties on the cell surface that act as coreceptors. To determine the contribution of cell-surface HS to modulation of FGF2-dependent cell growth, we studied the changes in the cell mass and FGF2 binding of endothelial cell HS under normoxic and hypoxic conditions in vitro. Both large vein and cardiac microvascular endothelial cells cultured under hypoxic conditions demonstrated an increase in the ratio of cell-surface HS to chondroitin sulfate (CS), as well as an increase in the number of low affinity (HS-associated) binding sites for FGF2 with no change in the apparent Kd. This increase in the number of HS-FGF2 binding sites, in the absence of a significant change in FGF receptor expression, resulted in enhanced responsiveness of hypoxic,compared with normoxic, endothelial cells to FGF2 stimulation. Gene expression studies demonstrated increased expression of the key regulatory enzyme responsible for HS chain synthesis, 1,4 GlcNAc transferase(GlcNAcT-I), as well as increased expression of 2-O sulfotransferase (HS2ST),the enzyme responsible for sulfation of IdoA, a crucial part of the HS-FGF2 binding site. Transduction of cells with an adenovirus encoding a HIF-1αexpression construct resulted in a similar increase in GlcNAcT-I and HS2ST expression. We conclude that hypoxia increases endothelial cell responsiveness to FGF2 by promoting preferential synthesis of HS rather than CS chains and increasing the number of FGF2-binding sites on HS chains. Both of these events are mediated by a HIF-1α-dependent increase in expression of the enzymes GlnNAcT-I and HS2ST. This shift in cell-surface HS composition results in enhanced cell sensitivity to FGF2-induced growth stimulation.

CULTURED HUMAN ENDOTHELIAL CELLS BIND AND INTERNALIZE HIGH MOLECULAR WEIGHT KININOGEN

1987 ◽  
Author(s):  
Freek van Iwaarden ◽  
G Philip ◽  
de Groot ◽  
Bonno N Bouma
Keyword(s):  
Molecular Weight ◽  
Endothelial Cells ◽  
Endothelial Cell ◽  
Cell Surface ◽  
High Molecular Weight ◽  
Binding Sites ◽  
High Molecular Weight Kininogen ◽  
Human Endothelial Cells ◽  
Endothelial Cell Surface ◽  
Coagulation Pathway

The presence of High Molecular Weight kininogen (HMWK) was demonstrated in cultured human endothelial cells (EC) by immunofluorescence techniques. Using an enzyme linked immunosorbent assay a concentration of 58 ng HMWK/10 cells was determined. Immunoprecipitation studies performed with lysed metabolically labelled endothelial cells and mono-specific antisera directed against HMWK suggested that HMWK is not synthesized by the endothelial cells. Endothelial cells cultured in the presence of HMWK-depleted serum did not contain HMWK. This, suggests that endothelial cells can internalize HMWK. Using 125I-HMWK it was demonstrated that cultured endothelial cells bind HMWK in a time-dependent, specific and saturable.way. The cells were found to internalize 125I-HMWK, since I-HMWK was detected in solubilized endothelial cells after the cell bound 125I-HMWK had been eluted with dextran sulphate.The binding of I-HMWK required the presence of zinc ions. Optimal binding of 125I-HMWK was observed at 50 μM Zn++ . Calcium ions inhibited the Zn++ dependent binding of 125I-HMWK |25EC. In the presence of 3 mM CaCl2 the total binding of 125I-HMWK was significantly decreased, and a .concentration of 200 μM Zn++ was Required for the binding of 125I-HMWK to thecells. Higher,. Ca concentrations did not further decrease the binding of 125I-HMWK. Analysis of tl^e binding data by the ligand computer program indicated 3.2 x 10 binding sites per cell for HMWK with a Kd of 35 nM at 50 μM ZnCl2 and 1 mM CaCl2. Specify binding of HMWK did also occur at physiological plasma Zn++ concentrations. Half maximal binding was observed at HMWK concentrations of ± 105 nM at 10 μM ZnCl2 and 45 nM at 25 μM ZnCl2. The HMWK binding sites were saturatecT at HMWK concentrations of 130 nM with 1.6 x 10 molecules of HMWK bound per cell and at 80 nM with 2.8 x 10 molecules of HMWK bound per cell at 10 and 25 pM ZnCl2 respectively. These results suggest that at physiological zinc, calcium and HMWK concentrations the HMWK binding sites on the endothelial cell are saturated. The presence of HMWK on the endothelial cell surface may play a role in the initiation of the intrinsic coagulation pathway. M ZnCl2 and 45 nM at 25 μM ZnCl2. The HMWK binding sites were saturatecT at HMWK concentrations of 130 nM with 1.6 x 10 molecules of HMWK bound per cell and at 80 nM with 2.8 x 10 molecules of HMWK bound per cell at 10 and 25 μM ZnCl2 respectively. These results suggest that at physiological zinc, calcium and HMWK concentrations the HMWK binding sites on the endothelial cell are saturated. The presence of HMWK on the endothelial cell surface may play a role in the initiation of the intrinsic coagulation pathway. M ZnCl2 and 45 nM at 25 μM ZnCl2. The HMWK binding sites were saturatecT at HMWK concentrations of 130 nM with 1.6 x 10 molecules of HMWK bound per cell and at 80 nM with 2.8 x 10 molecules of HMWK bound per cell at 10 and 25 μM ZnCl2 respectively. These results suggest that at physiological zinc, calcium and HMWK concentrations the HMWK binding sites on the endothelial cell are saturated. The presence of HMWK on the endothelial cell surface may play a role in the initiation of the intrinsic coagulation pathway. M ZnCl2 and 45 nM at 25 μM ZnCl2. The HMWK binding sites were saturatecT at HMWK concentrations of 130 nM with 1.6 x 10 molecules of HMWK bound per cell and at 80 nM with 2.8 x 10 molecules of HMWK bound per cell at 10 and 25 μM ZnCl2 respectively. These results suggest that at physiological zinc, calcium and HMWK concentrations the HMWK binding sites on the endothelial cell are saturated. The presence of HMWK on the endothelial cell surface may play a role in the initiation of the intrinsic coagulation pathway.M ZnCl2 and 45 nM at 25 μM ZnCl2. The HMWK binding sites were saturatecT at HMWK concentrations of 130 nM with 1.6 x 16 molecules of HMWK bound per cell and at 80 nM with 2.8 x 106 molecules of HMWK bound per cell at 10 and 25 μM ZnCl2 respectively. These results suggest that at physiological zinc, calcium and HMWK concentrations the HMWK binding sites on the endothelial cell are saturated. The presence of HMWK on the endothelial cell surface may play a role in the initiation of the intrinsic coagulation pathway.

THE BINDING OF ANTITHROMBIN TO CAPILLARY ENDOTHELIAL CELLS GROWN IN VITRO

1987 ◽  
Author(s):  
A de Agostini ◽  
J Marcum ◽  
R Rosenberg
Keyword(s):  
Endothelial Cells ◽  
Endothelial Cell ◽  
Heparan Sulfate ◽  
Cell Monolayer ◽  
Whole Cells ◽  
Cell Monolayers ◽  
Bacterial Enzyme ◽  
Capillary Endothelial Cells ◽  
Binding Cell

Cloned endothelial cells from rat epididymal fat pads synthesize anticoagulantly active heparan sulfate proteoglycans containing the disaccharide, GlcA→ AMN-3,6-O-SO3, which is a marker for the antithrombin-binding domain of heparin. To demonstrate that antithrombin (AT) binds to cell surface heparan sulfate, a binding assay employing 125I-AT and cell monolayers has been developed. Post-confluent endothelial cells (7 days) were incubated with radiolabeled AT for 1 h at 4° and washed with PBS. Bound radioactivity was quantitated after solubilizing whole cells. Under these conditions, ∼1% (2174±50 cpm/5x104 cells) of the 125I-AT bound to the endothelial cell monolayer, whereas none of the radiolabeled protein bound to CHO cells or bovine smooth muscle cells. Utilization of unlabeled AT (1 μM) in experiments conducted as described above resulted in a reduction (73%) of the binding of the labeled species to endothelial cells. To assess whether heparan sulfate was responsible for AT binding, cell monolayers were incubated for 1 h at 37° with purified Flavobacterium heparinase (0.2 units). Over 90% of 125I-AT binding to these cellular elements was suppressed with the bacterial enzyme. Internalization of radiolabeled AT by endothelial cells was examined by incubating the protease inhibitor and cells at 4° and 37 . An initial rapid binding was observed at both temperatures. At 4° AT binding plateaued within 15 min, whereas at 37° binding did not plateau until 60 min and was 30% greater than that observed at 4. These data suggest that surface-associated AT can be internalized by endothelial cells. In addition, AT binding was shown to increase with the length of endothelial cell postconfluence, indicating an accumulation of heparan sulfate by these cells during quiescence. In conclusion, our studies support the hypothesis that the vascular endothelium is coated with heparan sulfate-bound AT, which is responsible for the antithrombotic properties of these natural surfaces.

scholarly journals High-resolution probing heparan sulfate–antithrombin interaction on a single endothelial cell surface: single-molecule AFM studies

2015 ◽  
Vol 17 (20) ◽  
pp. 13301-13306 ◽  
Author(s):  
Cunlan Guo ◽  
Xian Fan ◽  
Hong Qiu ◽  
Wenyuan Xiao ◽  
Lianchun Wang ◽  
...  
Keyword(s):  
Endothelial Cell ◽  
High Resolution ◽  
Cell Surface ◽  
Heparan Sulfate ◽  
Single Molecule ◽  
Binding Sites ◽  
Specific Interactions ◽  
Endothelial Cell Surface ◽  
Afm Probe

Using an antithrombin functionalized AFM probe, the specific interactions between antithrombin and heparan sulfate on endothelial cell surface were determined, revealing previously unexpected diverse binding sites as well as critical roles of N-, 2-O- and 6-O-sulfation in the interactions.

Endothelial adhesion molecules and their role in inflammation

1993 ◽  
Vol 71 (1) ◽  
pp. 76-87 ◽  
Author(s):  
C. Wayne Smith
Keyword(s):  
Endothelial Cells ◽  
Monoclonal Antibodies ◽  
Endothelial Cell ◽  
Cell Surface ◽  
Adhesion Molecules ◽  
Surrounding Tissue ◽  
Intercellular Adhesion Molecule ◽  
Intercellular Adhesion Molecule 1 ◽  
Endothelial Cell Surface

The emigration of leukocytes such as neutrophils into inflammatory sites requires adhesion to the endothelium of small venules. The initial adhesive event is margination characterized by rolling of neutrophils along the luminal surface of the endothelium. Each member of the selectin family of adhesion molecules has been shown to support neutrophil rolling under conditions of flow. E-selectin is synthesized by endothelial cells following cytokine stimulation, P-selectin is rapidly mobilized from Weibel–Palade bodies to the endothelial cell surface following stimulation with agents such as histamine, and L-selectin is constitutively expressed on the surface of leukocytes. Each selectin functions primarily as a lectin, recognizing carbohydrate structures on the leukocyte or endothelial cell surface. Once the marginated neutrophil forms a stationary adhesion with endothelial cells, it is stimulated by chemotactic factors to downregulate the selectin-based adhesion and upregulate adherence dependent on β2-integrins, principally CD11a/CD18 (LFA-1) and CD11b/CD18 (Mac-1). These adhesion molecules interact with intercellular adhesion molecule 1 (ICAM-1) and possibly other structures on the endothelial cell, and the leukocyte rapidly emigrates into surrounding tissue. Transendothelial migration in vitro is markedly inhibited by monoclonal antibodies against CD18 integrins or ICAM-1. Monoclonal antibodies against the selectins, CD18, CD11a, CD11b, and ICAM-1 have all been shown to significantly reduce the influx of neutrophils into sites of inflammation in various animal models.Key words: adhesion, integrins, selectins, leukocytes, endothelial cells.

scholarly journals Functional interactions of T cells with endothelial cells: the role of CD40L-CD40-mediated signals.

1995 ◽  
Vol 182 (6) ◽  
pp. 1857-1864 ◽  
Author(s):  
M J Yellin ◽  
J Brett ◽  
D Baum ◽  
A Matsushima ◽  
M Szabolcs ◽  
...  
Keyword(s):  
T Cells ◽  
Endothelial Cells ◽  
Endothelial Cell ◽  
Cell Surface ◽  
Cell Activation ◽  
Endothelial Cell Activation ◽  
Cd40 Expression

CD40 is expressed on a variety of cells, including B cells, monocytes, dendritic cells, and fibroblasts. CD40 interacts with CD40L, a 30-33-kD activation-induced CD4+ T cell surface molecule. CD40L-CD40 interactions are known to play key roles in B cell activation and differentiation in vitro and in vivo. We now report that normal human endothelial cells also express CD40 in situ, and CD40L-CD40 interactions induce endothelial cell activation in vitro. Frozen sections from normal spleen, thyroid, skin, muscle, kidney, lung, or umbilical cord were studied for CD40 expression by immunohistochemistry. Endothelial cells from all tissues studied express CD40 in situ. Moreover, human umbilical vein endothelial cells (HUVEC) express CD40 in vitro, and recombinant interferon gamma induces HUVEC CD40 upregulation. CD40 expression on HUVEC is functionally significant because CD40L+ Jurkat T cells or CD40L+ 293 kidney cell transfectants, but not control cells, upregulate HUVEC CD54 (intercellular adhesion molecule-1), CD62E (E-selectin), and CD106 (vascular cell adhesion molecule-1) expression in vitro. Moreover, the kinetics of CD40L-, interleukin 1-, or tumor necrosis factor alpha-induced CD54, CD62E, and CD106 upregulation on HUVEC are similar. Finally, CD40L-CD40 interactions do not induce CD80, CD86, or major histocompatibility complex class II expression on HUVEC in vitro. These results demonstrate that CD40L-CD40 interactions induce endothelial cell activation in vitro. Moreover, they suggest a mechanism by which activated CD4+ T cells may augment inflammatory responses in vivo by upregulating the expression of endothelial cell surface adhesion molecules.

scholarly journals Mechanism and effects of the binding of lupus anticoagulant IgG and prothrombin to surface phospholipid

Blood ◽  
1996 ◽  
Vol 88 (11) ◽  
pp. 4173-4182 ◽  
Author(s):  
LV Rao ◽  
AD Hoang ◽  
SI Rapaport
Keyword(s):  
Endothelial Cells ◽  
Endothelial Cell ◽  
Cell Surface ◽  
Binding Sites ◽  
Lupus Anticoagulant ◽  
Umbilical Vein ◽  
Protein A ◽  
Thrombotic Risk ◽  
Cell Monolayers ◽  
Umbilical Vein Endothelial Cells

Abstract We report here experiments on how lupus anticoagulant antibodies (LA IgG) that react with prothrombin bind to surface phospholipid and affect prothrombin's affinity for surface phospholipid and activation to thrombin. LA IgG was purified by protein A chromatography from the plasma of 16 patients of whom four had associated hypoprothrombinemia and 10 had experienced thrombosis. Many LA IgG bound, in the absence of phospholipid and calcium, not only to immobilized prothrombin but to both prothrombin 1 and fragment 1, which established at least an oligoclonal origin of LA IgG. No LA IgG bound to thrombin. Although prothrombin and Ca2+ were required to support binding of LA IgG to immobilized phosphatidylserine (PS), prothrombin at higher concentrations inhibited binding, presumably by competing with prothrombin/LA IgG complexes for PS binding sites. Prothrombin 1, which cannot bind to PS, also inhibited binding of many LA IgG to PS, presumably by forming competing soluble prothrombin 1/LA IgG complexes. Despite their ability to react with prothrombin independent of phospholipid, LA IgG enhanced binding of prothrombin to immobilized phospholipid and to cultured human umbilical vein endothelial cells. Prothrombin bound with LA IgG to the surface of endothelial cell monolayers could be activated to thrombin after supernatant prothrombin and LA IgG were washed away. The relation is discussed of these observations to a hypothesis that LA IgG mediated concentration of prothrombin on cell surface phospholipid represents a mechanism by which LA IgG could increase thrombotic risk.

scholarly journals Dysregulation of the EphrinB2−EphB4 ratio in pediatric cerebral arteriovenous malformations is associated with endothelial cell dysfunction in vitro and functions as a novel noninvasive biomarker in patients

2020 ◽  
Vol 52 (4) ◽  
pp. 658-671 ◽  
Author(s):  
Katie Pricola Fehnel ◽  
David L. Penn ◽  
Micah Duggins-Warf ◽  
Maxwell Gruber ◽  
Steven Pineda ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Endothelial Cell ◽  
Cerebrovascular Disease ◽  
Cell Function ◽  
Index Patient ◽  
Receptor Expression ◽  
Endothelial Cell Function ◽  
Angiogenic Potential ◽  
The Impact

Abstract We investigated (1) EphrinB2 and EphB4 receptor expression in cerebral AVMs, (2) the impact of an altered EphrinB2:EphB4 ratio on brain endothelial cell function and (3) potential translational applications of these data. The following parameters were compared between AVM endothelial cells (AVMECs) and human brain microvascular endothelial cells (HBMVECs): quantified EphrinB2 and EphB4 expression, angiogenic potential, and responses to manipulation of the EphrinB2:EphB4 ratio via pharmacologic stimulation/inhibition. To investigate the clinical relevance of these in vitro data, Ephrin expression was assessed in AVM tissue (by immunohistochemistry) and urine (by ELISA) from pediatric patients with AVM (n = 30), other cerebrovascular disease (n = 14) and control patients (n = 29), and the data were subjected to univariate and multivariate statistical analyses. Compared to HBMVECs, AVMECs demonstrated increased invasion (p = 0.04) and migration (p = 0.08), impaired tube formation (p = 0.06) and increased EphrinB2:EphB4 ratios. Altering the EphrinB2:EphB4 ratio (by increasing EphrinB2 or blocking EphB4) in HBMVECs increased invasion (p = 0.03 and p < 0.05, respectively). EphrinB2 expression was increased in AVM tissue, which correlated with increased urinary EphrinB2 levels in AVM patients. Using the optimal urinary cutoff value (EphrinB2 > 25.7 pg/μg), AVMs were detected with high accuracy (80% vs. controls) and were distinguished from other cerebrovascular disease (75% accuracy). Post-treatment urinary EphrinB2 levels normalized in an index patient. In summary, AVMECs have an EphrinB2:EphB4 ratio that is increased compared to that of normal HBMVECs. Changing this ratio in HBMVECs induces AVMEC-like behavior. EphrinB2 is clinically relevant, and its levels are increased in AVM tissue and patient urine. This work suggests that dysregulation of the EphrinB2:EphB4 signaling cascade and increases in EphrinB2 may play a role in AVM development, with potential utility as a diagnostic and therapeutic target.

scholarly journals Tumor cell surface beta 1-4-linked galactose binds to lectin(s) on microvascular endothelial cells and contributes to organ colonization.

1990 ◽  
Vol 111 (2) ◽  
pp. 773-781 ◽  
Author(s):  
I Cornil ◽  
R S Kerbel ◽  
J W Dennis
Keyword(s):  
Endothelial Cells ◽  
Endothelial Cell ◽  
Cell Surface ◽  
Tumor Cell ◽  
Tumor Cells ◽  
Tumor Cell Line ◽  
Microvascular Endothelial Cells ◽  
Class 1 ◽  
Microvascular Endothelial

Cell surface carbohydrate structures acting as ligands for tissue specific mammalian lectins have been implicated in cell-cell interactions during embryogenesis, lymphocyte homing, and tumor cell metastasis. In this report, we provide evidence that beta 1-4 linked galactose (Gal) residues in N-linked oligosaccharides on the surface of blood born tumor cells serve as a ligand for binding to microvascular endothelial cells. D36W25, a class 1 glycosylation mutant of the MDAY-D2 lymphoreticular tumor cell line, lacks sialic acid and Gal in cellular glycans due to a defect in the Golgi UDP-Gal transporter. Using UDP-Gal and bovine galactosyltransferase in vitro, beta 1-4 Gal was restored to the surface of the cells and 70% of the galactosylated glycans persisted for 8 h in vitro at 37 degrees C. Compared to mock-treated D36W25 cells, galactosylated D36W25 cells showed an 80% increase in binding to microvascular endothelial cell monolayers in vitro. The enhanced binding of galactosylated D36W25 cells to endothelial cell was inhibited by the addition of lactosamine-conjugated albumin to the assay. Consistent with these observations, swainsonine and castinospermine, two inhibitors of N-linked processing that result in loss of lactosamine antennae inhibited the binding of wild-type MDAY-D2 cells to endothelial cells in vitro. Injection of radiolabeled tumor cells into the circulation of syngeneic mice, showed that galactosylation of D36W25 cells resulted in 2-3 more tumor cells retained in the lungs and livers. In addition, galactosylation of D36W25 cells increased by 30-fold the number of visible liver metastases on inspection 4 wk after tumor cell injection. These results suggest that beta 1-4Gal-binding lectins on microvascular endothelial cells can contribute to retention and secondary tumor formation of blood born tumor cells. With the increasing availability of purified glycosyltransferases, reconstruction of a variety of carbohydrate sequences on the surface of class 1 mutants provides a controlled means of studying carbohydrate-lectin interactions on viable cells.

scholarly journals Mechanism and effects of the binding of lupus anticoagulant IgG and prothrombin to surface phospholipid

Blood ◽  
1996 ◽  
Vol 88 (11) ◽  
pp. 4173-4182 ◽  
Author(s):  
LV Rao ◽  
AD Hoang ◽  
SI Rapaport
Keyword(s):  
Endothelial Cells ◽  
Endothelial Cell ◽  
Cell Surface ◽  
Binding Sites ◽  
Lupus Anticoagulant ◽  
Umbilical Vein ◽  
Protein A ◽  
Thrombotic Risk ◽  
Cell Monolayers ◽  
Umbilical Vein Endothelial Cells

We report here experiments on how lupus anticoagulant antibodies (LA IgG) that react with prothrombin bind to surface phospholipid and affect prothrombin's affinity for surface phospholipid and activation to thrombin. LA IgG was purified by protein A chromatography from the plasma of 16 patients of whom four had associated hypoprothrombinemia and 10 had experienced thrombosis. Many LA IgG bound, in the absence of phospholipid and calcium, not only to immobilized prothrombin but to both prothrombin 1 and fragment 1, which established at least an oligoclonal origin of LA IgG. No LA IgG bound to thrombin. Although prothrombin and Ca2+ were required to support binding of LA IgG to immobilized phosphatidylserine (PS), prothrombin at higher concentrations inhibited binding, presumably by competing with prothrombin/LA IgG complexes for PS binding sites. Prothrombin 1, which cannot bind to PS, also inhibited binding of many LA IgG to PS, presumably by forming competing soluble prothrombin 1/LA IgG complexes. Despite their ability to react with prothrombin independent of phospholipid, LA IgG enhanced binding of prothrombin to immobilized phospholipid and to cultured human umbilical vein endothelial cells. Prothrombin bound with LA IgG to the surface of endothelial cell monolayers could be activated to thrombin after supernatant prothrombin and LA IgG were washed away. The relation is discussed of these observations to a hypothesis that LA IgG mediated concentration of prothrombin on cell surface phospholipid represents a mechanism by which LA IgG could increase thrombotic risk.

scholarly journals Upregulation of urokinase receptor expression on migrating endothelial cells

1993 ◽  
Vol 122 (3) ◽  
pp. 673-684 ◽  
Author(s):  
MS Pepper ◽  
AP Sappino ◽  
R Stöcklin ◽  
R Montesano ◽  
L Orci ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Cell Migration ◽  
Endothelial Cell ◽  
Cell Monolayer ◽  
Receptor Expression ◽  
Endothelial Cell Migration ◽  
Extracellular Proteolysis ◽  
Migrating Cells

One of the phenotypic hallmarks of migrating endothelial cells, both in vivo and in vitro, is expression of the urokinase-type plasminogen activator (u-PA), a key mediator of extracellular proteolysis. In the study reported here, we have used an in vitro model of endothelial cell migration to explore the mechanism of this phenomenon. We have found that wounding of an endothelial cell monolayer triggers a marked, rapid and sustained increase in expression of a specific high-affinity receptor for u-PA (u-PAr) on the surface of migrating cells. Migrating cells displayed an increase in the levels of u-PA and u-PAr mRNAs, and this increase was mediated by endogenous basic fibroblast growth factor (bFGF). We also show that the increase in u-PA activity on migrating cells can be accounted for by an increase in receptor-bound u-PA, and that the increase in activity is also dependent on endogenous bFGF. These results demonstrate that the expression of plasmin-mediated proteolytic activity by migrating endothelial cells is a consequence of increased production of both u-PA and its receptor, and that this in turn is mediated by endogenous bFGF. This suggests that u-PA, produced at increased levels by migrating cells, binds to u-PAr whose expression is upregulated on the same cells. These observations are in accord with the postulated role of u-PAr in mediating efficient and spatially restricted extracellular proteolysis, particularly in the context of cell migration.

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