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PubMed1986

Hormonal regulation of extracellular plasminogen activators and Mr approximately 54,000 plasminogen activator inhibitor in human neoplastic cell lines, studied with monoclonal antibodies.

We have studied the regulation by glucocorticoids and dibutyryl cAMP of the amounts of urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (t-PA) and a Mr approximately 54000 plasminogen activator inhibitor accumulated in serum-free conditioned culture fluid by a human fibrosarcoma, a human glioblastoma and a human melanoma cell line (HT-1080, UCT/gl-1 and Bowes). For the quantitation of u-PA and t-PA, we used sandwich-type ELISA with a combination of polyclonal and monoclonal antibodies. For an estimation of variations in the amount of the inhibitor, we used sodium dodecyl sulphate-polyacrylamide gel electrophoresis followed by Coomassie blue staining of conditioned culture fluid proteins, the inhibitor protein band being identified by its selective removal by passage of the conditioned culture fluids through a column with monoclonal antibodies against the inhibitor. The modulation of the 3 proteins by the hormonal agents varied greatly between the cell lines. The proteins were independently regulated, in the sense that the hormonal agents did not concomitantly change their levels in the direction expected either to increase or decrease total extracellular plasminogen activator activity. In conditioned culture fluids containing both t-PA and inhibitor, the two were present in the medium as a Mr approximately 120 000 complex. In contrast, no u-PA inhibitor complexes were found in conditioned culture fluid from any of the cell lines; this is likely to be due to the occurrence of u-PA in the culture fluid in the one-chain proenzyme form, which, unlike active u-PA, does not react with the inhibitor. These findings illustrate the complexity of the regulation of extracellular plasminogen activator activity, and imply that the presumed functional diversity of u-PA and t-PA may be related to their independent regulation.

Antibodies, Monoclonal↗
PubMed2004

Epithelial tissue-type plasminogen activator expression, unlike that of urokinase, its receptor, and plasminogen activator inhibitor-1, is increased in chronic venous ulcers.

BACKGROUND: The plasminogen activation system represents a potent mechanism of extracellular proteolysis and is an essential component of normal wound healing. It has also been implicated in the pathogenesis of chronic, nonhealing ulcers. Traditionally, urokinase-type plasminogen activator (uPA) has been associated with pericellular proteolytic activity involved in tissue remodelling processes, and tissue-type plasminogen activator (tPA) mainly with intravascular fibrinolysis. OBJECTIVES: The present study was conducted to characterize the spatial distribution of the various plasminogen activation system components in chronic ulcers and acute, well-granulating wounds. METHODS: The expression of uPA, tPA, urokinase receptor (uPAR), plasminogen activator inhibitor-1 (PAI-1), and vitronectin was investigated by immunohistochemical staining, in addition to uPA, tPA and PAI-1 expression by in-situ hybridization, in samples from eight chronic venous ulcers, five decubitus ulcers, five well-granulating acute wounds and five normal skin samples. RESULTS: In chronic venous leg ulcers tPA mRNA was detected in basal and suprabasal keratinocytes at the leading wound edge, while in well-granulating wounds and in decubitus ulcers tPA mRNA was expressed only in a few keratinocytes. However, tPA was widely expressed in fibroblast- and macrophage-like cells in the stroma of well-granulating wounds, while less tPA was detected in the granulation tissue of chronic ulcers. tPA mRNA and protein were localized in the superficial granular layers in normal skin. Although no qualitative differences in expression of uPA, PAI-1 or uPAR in the wound edge keratinocytes in chronic ulcers vs. normally granulating wounds were found, their expressions were more pronounced in the granulation tissue of well-granulating wounds. CONCLUSIONS: These results suggest that in poorly healing venous leg ulcers, the pattern of tPA expression is altered in keratinocytes at the leading edge of the wound, and the patterns of tPA, uPA and PAI-1 expression are altered in the granulation tissue.

Acute Disease↗
PubMed1989

Anticoagulant low molecular weight heparin does not enhance the activation of plasminogen by tissue plasminogen activator.

The activity of tissue plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA) is stimulated by heparin. Heparin binds tightly to t-PA, u-PA, and plasminogen and decreases the usual stimulatory effect of fibrin on t-PA activity. In the present study we have found that low molecular weight heparin (LMW-heparin) preparations obtained by nitrous acid depolymerization or heparinase treatment of standard heparin have different properties with respect to their interaction with the fibrinolytic system. LMW-heparin prepared by either method does not stimulate plasmin formation by t-PA. However, these preparations of heparin still efficiently accelerate the inhibition of thrombin by antithrombin III. Binding data show that LMW-heparin does not bind t-PA and Glu-plasminogen and only binds very weakly to Lys-plasminogen. These results illustrate that it is possible to selectively destroy the fibrinolytic stimulating properties of heparin while leaving the classical anticoagulant characteristics intact.

Animals↗
PubMed1996

Phorbol-ester-stimulated human lymphoid cell lines produce a plasminogen activator modulator inducing cell-bound urokinase-type plasminogen activator in malignant tumor cell lines.

The importance of cell-associated plasminogen activation in tumor invasion and metastasis is becoming increasingly evident. To clarify the modulators of cell-associated plasminogen activation in malignant states, we have recently established an assay system utilizing endogenous plasminogen activators on the cell surface. In the present study using the assay system, we found that the conditioned medium from phorbol 12-myristate 13-acetate (PMA)-stimulated human lymphoid cell lines, HUT 78 and Raji, strongly enhanced plasminogen activator (PA) activity on the surface of human malignant tumor cell lines (WI-38 VAI3 2RA, A431, A549 and HT-1080). The enhancing effect was inhibited by the addition of actinomycin D. By gel filtration, the active substances in PMA-stimulated HUT 78- and Raji-conditioned media were eluted in similar fractions corresponding to molecular weights of 60 to 80 kDa. The active substance was heat-labile. The enhanced PA activities were completely inhibited by anti-urokinase-type plasminogen activator (uPA) IgG. Moreover, the active substance was found to increase in cell-bound uPA antigen. These findings suggest that a population of activated lymphocytes produces a plasminogen activator modulator that induces uPA on the surface of malignant tumor cells.

Cell Line↗
PubMed1996

Promoter (4G/5G) plasminogen activator inhibitor-1 genotype in Pima Indians: relationship to plasminogen activator inhibitor-1 levels and features of the insulin resistance syndrome.

Elevated plasminogen activator inhibitor-1 may contribute to vascular disease in diabetes mellitus. Pima Indians have a low incidence of cardiovascular disease despite having a high prevalence of non-insulin-dependent diabetes mellitus (NIDDM) which in this population is not associated with elevated plasminogen activator inhibitor-1 activity. In Caucasians an insertion/deletion (4G/5G) polymorphism in the promoter region of the plasminogen activator inhibitor-1 gene that has been related to activity levels of its protein in plasma differentially binds repressor and enhancer elements. In 265 Pima Indians (133 diabetic, 132 non-diabetic, 129 male, 136 female, male, mean age 46.6, range 34-68 years) the promoter genotype frequencies were 23.0% for 4G/4G, 49.8% for 4G/5G and 27.2% for 5G/5G compared to 35.4%, 50.8% and 13.8% respectively, (chi 2 = 15.3, 2 df, p < 0.0005) previously reported in Caucasians with NIDDM. The mean plasma activity levels in the three genotypes in the Pima Indians were 18.2, 19.1 and 18.1 U/ml, respectively. Plasminogen activator inhibitor-1 activities correlated with plasma insulin (r = 0.38, p < 0.0001), body mass index (r = 0.24, p < 0.0001), and with triglyceride level (r = 0.12, p = 0.054) but there was no relationship between promotor genotype and activity. A steeper regression slope between plasminogen activator inhibitor-1 activity and triglycerides has been observed in Caucasians with the 4G/4G genotype as compared to Caucasians with the other genotypes. This was not found in the Pima population which may indicate a functional difference in this gene associated with reduced cardiovascular risk and may be involved in the lack of association of plasminogen activator inhibitor-1 levels with NIDDM in Pima Indians.

Adult↗
PubMed1984

The role of the lysine binding sites of human plasminogen in the fibrinogen stimulated rate of active site formation in the streptokinase-plasminogen equimolar complex.

The effect of various concentrations of epsilon-amino caproic acid (EACA) on the rate of active site formation in the human plasminogen moiety of the streptokinase-plasminogen equimolar complex has been studied in the absence and presence of human fibrinogen fragment D1 (FD1). In the absence of FD1, the pseudo first order rate constant (kobs) for active site development in this complex ranges from 8.4-17.9 x 10(-3) sec-1 with Glu1-plasminogen (Glu1-Pg), Lys77-plasminogen (Lys77-Pg), and Val442-plasminogen (Val442-Pg), at levels of EACA from 0-25 mM. In the presence of 2 microM FD1, the kobs for active site formation in the SK . Glu1-Pg complex, of 60.1 x 10(-3) sec-1, was not altered significantly as the EACA level was increased to 25 mM. Similarly, in the SK . Lys77-Pg complex, the kobs for active site formation, of 62.1 x 10(-3) sec-1, was essentially unchanged as the EACA level was increased to 25 mM. Finally, the kobs for active site formation in the SK . Val442-Pg complex, of 113.6 x 10(-3) sec-1, was also unaffected at levels of EACA up to 5 mM, with a slight inhibition at 25 mM EACA. These results show that the stimulation of active site formation in the equimolar Sk . Pg complex by fibrinogen fragment D1 is mediated by sites separate from the lysine binding sites of plasminogen.

Aminocaproic Acid↗
PubMed2004

Complex interactions between bovine plasminogen and streptococcal plasminogen activator PauA.

The interactions between bovine plasminogen and the streptococcal plasminogen activator PauA that culminate in the generation of plasmin are not fully understood. Formation of an equimolar activation complex comprising PauA and plasminogen by non-proteolytic means is a prerequisite to the recruitment of substrate plasminogen; however the determinants that facilitate these interactions have yet to be defined. A mutagenesis strategy comprising nested deletions and random point substitutions indicated roles for both amino and carboxyl-terminal regions of PauA and identified further essential residues within the alpha domain of the plasminogen activator. A critical region within the alpha domain was identified using non-overlapping PauA peptides to block the interaction between PauA and bovine plasminogen, preventing formation of the activation complex. Homology modelling of the activation complex based upon the known structures of streptokinase complexed with human plasmin supported these findings by placing critical residues in close proximity to the plasmin component of the activation complex.

Amino Acid Sequence↗
PubMed2005

Specific conformational changes of plasminogen induced by chloride ions, 6-aminohexanoic acid and benzamidine, but not the overall openness of plasminogen regulate, production of biologically active angiostatins.

The overall conformation of plasminogen depends upon the presence of anions and molecules such as AHA (6-aminohexanoic acid) and BZ (benzamidine). The purpose of the present study was to determine the effect of conformation on the initial and secondary cleavages of plasminogen to generate active angiostatins. Plasminogen was digested with the physiologically relevant neutrophil elastase in one of the four Tris/acetate buffers: buffer alone or buffer plus NaCl, AHA or BZ. The initial cleavage of Glu1-plasminogen was much slower in the tight NaCl-induced alpha-conformation, fastest in the intermediate BZ-induced beta-conformation and intermediate both in the control and in the AHA-induced open gamma-conformation. Although the buffer system determined the relative amounts of the initial cleavage products, the same four cleavage sites were utilized under all conditions. A fifth major initial cleavage within the protease domain was observed in the presence of BZ. N-terminal peptide cleavage required for angiostatin formation occurred as either the initial or the secondary cleavage. Angiostatins were generated fastest in the presence of BZ and slowest in the presence of NaCl. Both the initial and secondary cleavages were affected by the modifying agents, indicating that they influence the conformation of both Glu-plasminogen and the initial cleavage products. The angiostatins produced under the different conditions inhibited proliferation of human umbilical-vein endothelial cells. These results suggest that plasminogen conversion into active angiostatins is dependent more on the specific conformation changes induced by the various modifying reagents rather than on the overall openness of the molecule.

Aminocaproic Acid↗
PubMed2004

Thrombin activatable fibrinolysis inhibitor (TAFI) affects fibrinolysis in a plasminogen activator concentration-dependent manner. Study of seven plasminogen activators in an internal clot lysis model.

TAFIa was shown to attenuate fibrinolysis. In our in vitro study, we investigated how the inhibitory effect of TAFIa depended on the type and concentration of the plasminogen activator (PA). We measured PA-mediated lysis times of plasma clots under conditions of maximal TAFI activation by thrombin-thrombo-modulin in the absence and presence of potato carboxypeptidase inhibitor. Seven different PAs were compared comprising both tPA-related (tPA, TNK-tPA, DSPA), bacterial PA-related (staphylokinase and APSAC) and urokinase-related (tcu-PA and k2tu-PA) PAs. The lysis times and the retardation factor were plotted against the PA concentration. The retardation factor plots were bell-shaped. At low PA concentrations, the retardation factor was low, probably due to the limited stability of TAFIa. At intermediate PA concentrations the retardation factor was maximal (3-6 depending on the PA), with TNK-tPA, APSAC and DSPA exhibiting the strongest effect. At high PA concentrations, the retardation factor was again low, possibly due to inactivation of TAFIa by plasmin or to a complete conversion of glu-plasminogen into lys-plasminogen. Using individual plasmas with a reduced plasmin inhibitor activity (plasmin inhibitor Enschede) the bell-shaped curve of the retardation factor shifted towards lower tPA and DSPA concentrations, but the height did not decrease. In conclusion, TAFIa delays the lysis of plasma clots mediated by all the plasminogen activators tested. This delay is dependent on the type and concentration of the plasminogen activator, but not on the fibrin specificity of the plasminogen activator. Furthermore, plasmin inhibitor does not play a significant role in the inhibition of plasma clot lysis by TAFI.

Antifibrinolytic Agents↗
PubMed1992

Regulation of plasminogen activators and type-1 plasminogen activator inhibitor by cyclic AMP and phorbol ester in rat astrocytes.

Two plasminogen activators (PAs): tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA), as well as the type-1 plasminogen activator inhibitor (PAI-1) are synthesized and secreted by rat astrocytes. Preliminary studies suggest that PA activity plays a role in astrocyte development and differentiation. We have examined the regulation of the PA system by the cAMP-dependent protein kinase (PKA) and protein kinase C (PKC) in purified rat astrocyte cultures. PKA activity was increased by exposing cultured astrocytes to forskolin or dibutyryl cyclic AMP, whereas PKC activity was stimulated with phorbol-12-myristate 13-acetate (PMA). Activation of both second-messenger pathways produced a time- and dose-dependent increase in the total PA activity. However, based on SDS-PAGE/zymography we found that forskolin increased t-PA activity and reduced u-PA activity, whereas PMA treatment caused a significant increase in u-PA activity without altering t-PA activity. Reverse zymography analysis revealed that astrocyte PAI-1 activity is decreased by forskolin and increased by PMA. Together, these results demonstrate that the components of the PA system in rat astrocytes are independently and reciprocally regulated by PKA and PKC. Our findings raise the possibility that the plasminogen activator system could be involved in some of the actions of growth factors and/or neuromodulators that modulate PKC or PKA in astrocytes.

Animals↗
PubMed1994

Initiation of a fibrinolytic system in hepatic resection: the roles of tissue-type plasminogen activator and plasminogen activator inhibitor-1.

The factors related to the initiation of fibrinolysis, especially with regard to the tissue-type plasminogen activator (tPA) and the plasminogen activator inhibitor-1 (PAI-1), were investigated in 15 patients who underwent hepatic resection, and the findings were compared between those with normal livers and those with diseased livers. It was found that tPA increased before hepatic division, whereas PAI-1 increased after hepatic division and reached a peak immediately following the operation. Plasminogen decreased during hepatectomy, reaching its lowest point on postoperative day 1, and increasing later. Decreased levels of both plasminogen and the alpha 2-plasmin inhibitor were considered to be partly due to plasmin formation in the blood. Patients with a diseased liver tended to have higher intraoperative values of euglobulin lysis activity and higher postoperative values of plasminogen activator, but significantly lower postoperative values of alpha 2-plasmin inhibitor than those with a normal liver. The results of this study suggest that activation of the fibrinolytic system occurs both during hepatectomy and in the early postoperative period, and that patients with a diseased liver are prone to develop hyperfibrinolysis during hepatectomy. Moreover, the increased levels of both tPA and PAI-1 can serve as one of the most sensitive markers for the vital reaction against surgical stress.

Aged↗
PubMed1987

The genetic relationships between the kringle domains of human plasminogen, prothrombin, tissue plasminogen activator, urokinase, and coagulation factor XII.

A computer-based statistical evaluation of the optimal alignments of the kringle domains of human plasminogen, human prothrombin, human tissue plasminogen activator, human urokinase, and human coagulation Factor XIIa, as well as the putative kringle of human haptoglobin, has been performed. A variety of different alignments has been examined and scores calculated in terms of the number of standard deviations (SD) of a given match from randomness. With the exception of human haptoglobin, it was found that very high alignment scores (8.9-23.0 SD from randomness) were obtained between each of the kringles, with the kringle 1 and kringle 5 regions of human plasminogen displaying the highest similarity, and the S kringle of human prothrombin and the human Factor XII kringle showing the least similarity. The relationships obtained were employed to construct an evolutionary tree for the kringles. The predicted alignments have also allowed nucleotide mutations in these regions to be evaluated more accurately. For those regions for which nucleotide sequences are known, we have employed the maximal alignments from the protein sequences to assess nucleotide sequence similarities. It was found that a range of approximately 40-55% of the nucleotide bases were placed at identical positions in the kringles, with the highest number found in the alignment of the two kringles of human tissue plasminogen activator and the lowest number in the alignment of the S kringle of prothrombin with the second kringle of tissue plasminogen activator. From both protein and nucleotide alignments, we conclude that haptoglobin is not statistically homologous to any other kringle. Secondary structural comparisons of the kringle regions have been predicted by a combination of the Burgess and Chou-Fasman methods. In general, the kringles display a very high number of beta-turns, and very low alpha-helical contents. From analysis of the predicted structures in relationship to the functional properties of these domains, it appears as though many of their functional differences can be related to possible conformational alterations resulting from amino acid substitutions in the kringles.

Amino Acid Sequence↗
PubMed1998

Production of urokinase-type plasminogen activator (u-PA) and plasminogen activator inhibitor-1 (PAI-1) in human brain tumours.

We investigated the role of plasminogen activators (PAs) and their inhibitor (plasminogen activator inhibitor-1, PAI-1) in human brain tumours. The amounts of urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (t-PA), and plasminogen activator inhibitor-1 (PAI-1), and the activity of u-PA and t-PA were determined by enzyme-linked immunosorbent assay (ELISA), and u-PA and PAI-1 were immunolocalized using monoclonal antibodies in human brain tumours and normal brain tissues. The tissues were surgically removed from 64 patients; normal brain tissue (5 cases), low-grade glioma (4 cases), high-grade glioma (17 cases), metastatic tumour (9 cases), meningioma (benign 12 cases, malignant 6 cases), acoustic schwannoma (11 cases). u-PA activity and u-PA and PAI-1 antigen levels were significantly elevated in malignant brain tumours (malignant meningiomas, high-grade gliomas, and metastatic tumours) and acoustic schwannomas but very low in benign meningiomas, low-grade gliomas and normal brain. There was no difference in t-PA antigen levels among normal and malignant tissues, however levels of t-PA activity were markedly decreased in metastastic tumours. All malignant brain tumour tissues showed positive immunostaining for u-PA and PAI-1, however, some tumour cells showed negative intensity while others showed strong intensity for these antibodies. This contrasts to the homogeneous staining pattern found in acoustic schwannoma. These findings indicate that malignancy in human brain tumours is associated with elevated levels of u-PA and PAI-1 and that an imbalance between these proteins in a micro-environment contributes (ascribes) to tumour cell invasion.

Adolescent↗
PubMed1988

Kinetic analysis of the interactions between plasminogen activator inhibitor 1 and both urokinase and tissue plasminogen activator.

Plasminogen activator inhibitor 1 (PAI-1) was purified from medium conditioned by cultured bovine aortic endothelial cells by successive chromatography on concanavalin A Sepharose, Sephacryl S-200, Blue B agarose, and Bio-Gel P-60. As shown previously for conditioned media (C. M. Hekman and D. J. Loskutoff (1985) J. Biol. Chem. 260, 11581-11587) the purified PAI-1 preparation contained latent inhibitory activity which could be stimulated 9.4-fold by sodium dodecyl sulfate and 45-fold by guanidine-HCl. The specific activity of the preparation following treatment with 0.1% sodium dodecyl sulfate was 2.5 X 10(3) IU/mg. The reaction between purified, guanidine-activated PAI-1 and both urokinase and tissue plasminogen activator (tPA) was studied. The second-order rate constants (pH 7.2, 35 degrees C) for the interaction between guanidine-activated PAI-1 and urokinase (UK), and one- and two-chain tPA are 1.6 X 10(8), 4.0 X 10(7), and 1.5 X 10(8) M-1 S-1, respectively. The presence of CNBr fibrinogen fragments had no affect on the rate constants of either one- or two-chain tPA. Steady-state kinetic analysis of the effect of PAI-1 on the rate of plasminogen activation revealed that the initial UK/PAI-1 interaction can be competed with plasminogen suggesting that the UK/PAI-1 interaction may involve a competitive type of inhibition. In contrast, the initial tPA/PAI-1 interaction can be competed only partially with plasminogen, suggesting that the tPA/PAI-1 interaction may involve a mixed type of inhibition. The results indicate that PAI-1 interacts more rapidly with UK and tPA than any PAI reported to date and suggest that PAI-1 is the primary physiological inhibitor of single-chain tPA. Moreover, the interaction of PAI-1 with tPA differs from its interaction with UK, and may involve two sites on the tPA molecule.

Animals↗
PubMed2004

Plasminogen mediates the pathological effects of urokinase-type plasminogen activator overexpression.

Increased expression of urokinase-type plasminogen activator (uPA) and its receptor (uPAR) is associated with different pathological conditions. Both uPAR-mediated signaling and plasmin-catalyzed extracellular proteolysis may contribute to pathogenesis. To evaluate the involvement of plasminogen in such circumstances, we have taken advantage of transgenic mouse models in which overexpression of uPA and/or uPAR in enamel epithelium, basal epidermis, and hair follicles leads to a pathological phenotype; uPA transgenic mice have chalky-white incisors and, when uPAR is co-expressed, develop extensive alopecia, epidermal thickening, and subepidermal blisters. We report here that when these transgenic mice were backcrossed into a plasminogen-deficient (Plg-/-) background, the dental and skin phenotypes appeared completely normal. Heterozygous Plg+/- transgenic mice exhibited a haplo-insufficiency, with an intermediate or normal phenotype. These results do not argue in favor of a role for uPAR-mediated signaling in our experimental model; rather, they demonstrate an essential, dose-dependent, requirement for plasminogen in uPA-mediated tissue alterations. They also support the hypothesis that plasminogen could play a part in certain skin diseases.

Animals↗
PubMed1997

Elevations of tissue-type plasminogen activator and differential expression of urokinase-type plasminogen activator in diseased aorta.

PURPOSE: Elevations of plasmin have been implicated in the pathogenesis of abdominal aortic aneurysms (AAA) because of its ability to digest extracellular matrix proteins. Plasminogen activators regulate the conversion of plasminogen to plasmin. Tissue-type plasminogen activator (tPA) is more important in modulation of fibrinolysis, and urokinase-type plasminogen activator (uPA) is predominant in tissue remodeling. The purpose of this study was to determine the levels of plasminogen activators in diseased aorta because they may be responsible for the increased plasmin levels previously described in AAA. METHODS: Levels of tPA and uPA in AAA, occlusive, and normal (organ donor) aorta were studied in tissue explant supernatants. Supernatant tPA and uPA levels were measured with an enzyme-linked immunosorbent assay. Northern analysis was used to quantitate uPA messenger RNA (mRNA) levels in aortic tissue. RESULTS: Levels of tPA in the supernatants were similar in occlusive (20 +/- 4 ng/ml) and AAA (23 +/- 8) aorta, but threefold higher than in normal aorta (7 +/- 5; p < 0.005 for normal vs occlusive and p < 0.001 for normal vs AAA). In contrast, uPA supernatant levels were differentially expressed, with the highest level existing in AAA (9.7 +/- 2.7 ng/ml), followed by occlusive (4.9 +/- 3.5), and the lowest levels in normal aorta (1.2 +/- 0.7; p < 0.05 for normal vs occlusive, p < 0.001 for normal vs AAA, and p < 0.005 for occlusive vs AAA). Inhibition of protein or RNA synthesis by addition of cyclohexamide or actinomycin D, respectively, revealed no significant difference between treated and control supernatants, suggesting that the increases were caused by protein release rather than active synthesis. Levels of uPA mRNA followed the same trend as the supernatant uPA levels (AAA 1.07 +/- 0.54, occlusive 0.54 +/- 0.08, and normal aorta 0.01 +/- 0.01). CONCLUSIONS: Levels of tPA were similar in aneurysmal and occlusive aorta, but exhibited a threefold increase over normal aorta, suggesting that the elevations of tPA are associated with the arteriosclerosis present in both aneurysmal and occlusive disease. Differences in uPA levels were significant between all three groups, with the highest levels in AAA and the lowest levels in normal specimens. Northern analysis of uPA mRNA followed the same trend, suggesting that the increase in uPA may be regulated at the level of transcription. As uPA plays an important role in tissue remodeling, our findings may also reflect the relative tissue repair activities in these three types of specimens and may explain the previously reported increased levels of plasmin seen in AAA.

Adult↗
PubMed1990

Prourokinase activation on the surface of human rhabdomyosarcoma cells: localization and inactivation of newly formed urokinase-type plasminogen activator by recombinant class 2 plasminogen activator inhibitor.

Recombinant class 2 plasminogen activator inhibitor (PAI-2) was used in an approach to probe the formation and location of enzymatically active urokinase-type plasminogen activator (u-PA) sites on the surface of cultured human rhabdomyosarcoma cells (RD cells). Activation of pro-u-PA on the cell surface and consequent binding of PAI-2 was dependent on the addition of native plasminogen to serum cultures of the cells. Inhibition of the enzyme activity of surface-bound u-PA by the added PAI-2 resulted in a 79% reduction in the capacity of the RD cells to generate cell surface-associated plasmin activity from bound plasminogen. Under these conditions, the PAI-2 probe was localized at focal adhesions of RD cells, where it colocalized with both extracellular u-PA and intracellular vinculin antigens in double immunofluorescence labeling. Specificity of the probe's interaction with cell surface-bound u-PA was confirmed by blocking with a monoclonal antibody to human u-PA, which could also inhibit the formation of bound plasmin activity. These results showed the assembly of the plasmin-generating system at focal adhesions and the accessibility of bound u-PA on which it depends to added PAI-2. Therefore, PAI-2 has the potential both to localize at sites of tumor expression of functionally active u-PA and simultaneously to inhibit cell surface plasminogen activation.

Cell Line↗
PubMed1996

Urokinase-type plasminogen activator is effective in fibrin clearance in the absence of its receptor or tissue-type plasminogen activator.

The availability of gene-targeted mice deficient in the urokinase-type plasminogen activator (uPA), urokinase receptor (uPAR), tissue-type plasminogen activator (tPA), and plasminogen permits a critical, genetic-based analysis of the physiological and pathological roles of the two mammalian plasminogen activators. We report a comparative study of animals with individual and combined deficits in uPAR and tPA and show that these proteins are complementary fibrinolytic factors in mice. Sinusoidal fibrin deposits are found within the livers of nearly all adult mice examined with a dual deficiency in uPAR and tPA, whereas fibrin deposits are never found in livers collected from animals lacking uPAR and rarely detected in animals lacking tPA alone. This is the first demonstration that uPAR has a physiological role in fibrinolysis. However, uPAR-/-/tPA-/- mice do not develop the pervasive, multi-organ fibrin deposits, severe tissue damage, reduced fertility, and high morbidity and mortality observed in mice with a combined deficiency in tPA and the uPAR ligand, uPA. Furthermore, uPAR-/-/tPA-/- mice do not exhibit the profound impairment in wound repair seen in uPA-/-/tPA-/- mice when they are challenged with a full-thickness skin incision. These results indicate that plasminogen activation focused at the cell surface by uPAR is important in fibrin surveillance in the liver, but that uPA supplies sufficient fibrinolytic potential to clear fibrin deposits from most tissues and support wound healing without the benefit of either uPAR or tPA.

Animals↗