Role Of Plasminogen Activator Research Articles

Urokinase-dependent plasminogen activation is required for efficient skeletal muscle regeneration in vivo

Plasminogen activators urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA) are extracellular proteases involved in various tissue remodeling processes. A requirement for uPA activity in skeletal myogenesis was recently demonstrated in vitro. The role of plasminogen activators in skeletal muscle regeneration in vivo in wild-type, uPA-deficient, and tPA-deficient mice is investigated here. Wild-type and tPA-/- mice completely repaired experimentally damaged skeletal muscle. In contrast, uPA-/- mice had a severe regeneration defect, with decreased recruitment of blood-derived monocytes to the site of injury and with persistent myotube degeneration. In addition, uPA-deficient mice accumulated fibrin in the degenerating muscle fibers; however, the defibrinogenation of uPA-deficient mice resulted in a correction of the muscle regeneration defect. A similar severe regeneration deficit with persistent fibrin deposition was also reproducible in plasminogen-deficient mice after injury, suggesting that fibrinolysis by uPA-mediated plasminogen activation plays a fundamental role in skeletal muscle regeneration. In conclusion, the uPA-plasmin system is identified as a critical component of the mammalian skeletal muscle regeneration process, possibly because it prevents intramuscular fibrin accumulation and contributes to the adequate inflammatory response after injury. These studies demonstrate the requirement of an extracellular proteolytic cascade during muscle regeneration in vivo.

Localization and the possible role of plasminogen activators and inhibitors in early stages of placentation

The distribution of mRNAs of tissue type (t) and urokinase type (u) plasminogen activator (PA) plus their corresponding inhibitors, type-1 (PAI-1) and type-2 (PAI-2) have been studied in the tissues of human first and second trimester placentae byin situ hybridization. The results show that: (i) All the molecules, tPA, uPA, PAI-1 and PAI-2, were identified in the blood vessels, the majority of extravillous trophoblastic cells of the decidual layer between Rohr’s and Nitabuch’s stria and in the trophoblast cells lining the chorionic plate, basal plate, intercotyledonary septae and cytotrophoblast cells of the chorionic villous tree. (ii) No expression of such probes was observed in the basal and chorionic plate, glandular cells of the decidua, the septal tissues or the villous core mesenchyme. The co-distribution of the molecules observed suggests that the co-ordinated expression of the activators and inhibitors in various cells of the placental tissue may play a role in angiogenesis related to conversion of spiral arteries into utero-placental arteries and establishment of a chorio-decidual blood flow during early stages of placentation.

Role of plasminogen activators and urokinase receptor in platelet kinetics

Plasminogen activators (PA) and plasmin are known to affect platelets but little is known of their role in platelet kinetics. We took advantage of genetically deficient mice to explore the role of urokinase (uPA) and tissue type (tPA) PAs, as well as the uPA receptor (uPAR, CD87) in platelet kinetics. Platelet shape and number were investigated by flow cytometry. Platelet kinetics was investigated by the in vivo biotinylation and FACS analysis. Platelet production was investigated by counting megakaryocytes in bone marrow. Platelets counts were within the same range in wild type (+/+), uPA, tPA and uPAR-deficient mice. Platelet survival was similar in +/+, uPA-/-, tPA-/- but markedly reduced in uPAR-/- mice. The number of megakaryocytes in bone marrow and spleen was increased 2-3-fold in uPAR-/- compared to +/+ mice. TGF-beta mRNA level within the bone marrow was also significantly increased in uPAR-/- mice. Consistent with an increased platelet production, platelets from uPAR-/- mice had a higher RNA content, as seen by Propidium Iodide (PI) labeling and FACS analysis. Since uPAR is detectable in both hemopoietic and non-hemopoietic cells, radiation chimera were prepared. Investigation of platelet kinetics in chimera showed that platelet survival is reduced with a deficit in either bone marrow-derived, or non-hemopoietic, host cells. These results demonstrate that uPAR, but not uPA or tPA, is essential for maintaining normal platelet survival. In addition, uPAR-/- mice maintain normal platelet numbers through increased production.

Roles of plasminogen activator inhibitor-1 and -2, and receptor of urokinase-type plasminogen activator (u-PA) in tumor growth and metastasis

Summary Aim: Roles of urokinase-type plasminogen activator (u-PA) and its receptor (u-PAR), and its inhibitors (PAI-1 and PAI-2) in colon and breast cancer growth and metastasis were investigated. Methods: Antigen levels of u-PA, u-PAR, PAI-1 and PAI-2 were measured in lung tumor sites and its normal neighboring tissues and metastasis sites. mRNA of these factors was measured by Northern blotting and localization of these factors was measured by in situ hybridization. Results: Antigen levels of u-PA, u-PAR, PAI-1 and PAI-2 were higher in both lung and colon cancer tissues than in normal tissues. mRNAs of u-PA, u-PAR, PAI-1 and PAI-2 were all detected in lung cancer tissues. The amounts of u-PA and PAI-2 mRNA were significantly higher in lung cancer tissues than in normal lung tissues. Both u-PAR and PAI-1 levels were significantly higher in large than in small colon tumors. Higher levels of u-PAR were found an independent prognostic value by multivariate analysis. Conclusion: Antigens and mRNAs of u-PA, u-PAR, PAIs were found in tumor tissues.

Role of plasminogen activators and inhibitors in reproduction

The recent progress in the studies on the role of local and directed fibrinolysis controlled by plasminogen activators (PAs) and regulated by their inhibitors (PAIs) in reproduction is summarized. Hormone-induced coordinated expression of tissue type PA (tPA) and PAI type-1 (PAI-1) in the ovary is involved in the processes of ovulation and luteal regression; increases in urokinase type PA (uPA) and PAI-1 activity in the early stage of luteinized follicles may be responsible for ovarian tissue remodeling and angiogenesis; the PA system has been found to play an important role in spermatogenesis in testis and modulation of sperm maturation in epididymis. PA and matrix matalloproteanase (MMP) and their respective inhibitors have also been identified in trophoblast and uterus. The targeted proteolytic activity generated by the two systems may play an essential role in the processes of the cyclic uterine angiogenesis, implantation and placentation as well as parturition.

The role of plasminogen activator inhibitor-1 as inhibitor of platelet and megakaryoblastic cell adhesion.

In the present study the ability of plasminogen activator inhibitor type-1 (PAI-1) to interfere with platelet and megakaryoblastic cell adhesion was investigated. Both cell types exhibited integrin-dependent adhesion in a static system, mediated by alphaIIb beta3 on platelets and alpha v-integrins on different megakaryoblastic cell lines, even though they also expressed alphaIIb beta3. In a concentration-dependent manner, active, but not latent or complexed, PAI-1 abrogated cell adhesion onto vitronectin but not onto fibrinogen or other matrix substrata. Urokinase as well as thrombin neutralized the anti-adhesive effect of active PAI-1. The direct binding of vitronectin, but not of other matrix proteins, to integrin alphaIIb beta3 was blocked by active PAI-1 in a purified system. Since activated platelets release active and latent PAI-1 as well as structurally and functionally distinct forms of vitronectin, the described interactions appear to be physiologically significant. Co-distribution of vitronectin and PAI-1 at sites of fibrin polymers within platelet thrombi was demonstrated by transmission electron microscopy, suggesting an extracellular functional relationship of both release products with regard to cell adhesion. Our data emphasize the regulatory role of active PAI-1 in platelet adhesion to provisional matrix proteins as found during wound healing independent of its anti-proteolytic activity. Furthermore, megakaryocyte maturation may depend on the intact vitronectin-integrin adhesion system that is influenced by PAI-1, thereby proposing a regulatory role for the inhibitor in cellular differentiation.

VITREOUS CONCENTRATIONS OF TPA AND PLASMINOGEN ACTIVATOR INHIBITOR ARE ASSOCIATED WITH VEGF IN PROLIFERATIVE DIABETIC VITREORETINOPATHY

Purpose: In angiogenesis, matrix degradation is an important step in endothelial cell migration and proliferation. There is evidence that serine proteases, such as tissue plasminogen activator (TPA), urokinase-type plasminogen activator (UPA), and plasminogen activator inhibitor (PAI), are involved in this process. We hypothesized that in eyes in which neovascularization is active, such as in proliferative diabetic vitreoretinopathy (PDVR), vitreous levels of these proteases are increased. Furthermore, correlation was sought between intraocular concentrations of serine proteases and vascular endothelial growth factor (VEGF), a multifunctional cytokine that has been shown to play a major part in mediating active neovascularization in patients with ischemic retinal diseases. Methods: Undiluted samples of vitreous fluid were obtained from patients who under-went vitreoretinal surgery for PDVR or retinal detachment. Vitreous levels of VEGF, TPA, UPA, and PAI were determined by enzyme-linked immunosorbent assay. Results: We found a statistically significant correlation between levels of VEGF and TPA (P < 0.01) and VEGF and PAI (P < 0.026) in the vitreous fluid of patients with PDVR. Concentrations of VEGF (P < 0.03), TPA (P < 0.042), and PAI (P < 0.0098) in diabetic eyes were significantly higher than in nondiabetic eyes. Of 14 eyes with PDVR, 6 contained detectable levels of UPA. Conclusions: A correlation between increased levels of VEGF and TPA or PAI in the vitreous fluid of eyes with PDVR reflects the possible role of plasminogen activators in the progression of this disease. An understanding of the endogenous inhibition of matrix degradation in ocular angiogenesis may be useful in the development of new treatment strategies.

Prevention of aneurysm development and rupture by local overexpression of plasminogen activator inhibitor-1.

Arterial aneurysms exhibit a loss of elastin and an increase in the plasminogen activators urokinase plasminogen activator (u-PA) and tissue plasminogen activator (t-PA). Because u-PA, t-PA, and plasmin have a limited proteolytic activity against elastin, the role of plasminogen activators in the aneurysmal disease is unclear. To investigate this question, we overexpressed plasminogen activator inhibitor-1 (PAI-1), an inhibitor of t-PA and u-PA, in a rat model of aortic aneurysm. Guinea pig-to-rat aortic xenografts were seeded with syngeneic Fischer 344 rat smooth muscle cells retrovirally transduced with the rat PAI-1 gene (LPSN group) or the vector alone (LXSN group). Some grafts were not seeded with cells (NO group). Western blots showed increased PAI-1 in grafts from the LPSN group compared with LXSN and NO groups. All grafts in the NO group (n=8) and 40% in the LXSN group ruptured between days 4 and 14. At 4 weeks in the LXSN group, the remaining unruptured grafts (n=6) were aneurysmal (diameter increase > or =100%), whereas in the LPSN group (n=6) none of the grafts had ruptured or were aneurysmal. Elastin was preserved in the LPSN group. t-PA, the major PA expressed in the model, was decreased in the LPSN group compared with the other groups, as determined by zymography. Quantitative zymography showed decreased levels of two matrix metalloproteinases (MMPs), a 28-kD caseinase, and activated MMP-9 in the LPSN group. The blockade of plasminogen activators prevents formation of aneurysms and arterial rupture by inhibiting MMP activation.

Role of plasminogen activator and plasminogen activator inhibitor type-1 in luteolysis—a minireview

This minireview summarized our recent studies on the role of plasminogen activator (PA) and inhibitor type-1 (PAI-1) in luteolysis. We have demonstrated that (1) both tissue type and urokinase type plasminogen activators (tPA and uPA) and a plasminogen activator inhibitor type-1 (PAI-1) were present in the corpus luteum of rat and rhesus monkey; (2) decrease in progesterone production in corpus luteum was well correlated with a sharp increase in tPA (but not uPA) and PAI-1 secretion; (3) exogenous tPA decreased luteal progesterone synthesis while monoclonal antibodies increased progesterone production; (4) interferony inhibited luteal progesterone synthesis and stimulated tPA production while LH plus prolactin increased progesterone production and decreased tPA (hut not uPA) activity in cultured luteal cells; (5) increase in proteolysis in the corpus luteum was also correlated with decrease in progesterone production in mouse. These data suggest that local degradation of extracellular matrix controlled by plasminogen activator and inhibitor is involved in the processes of luteolysis.

Structure, Function and Expression on Blood and Bone Marrow Cells of the Urokinase‐Type Plasminogen Activator Receptor, uPAR

Several important functions have been assigned to the receptor for urokinase-type plasminogen activator, uPAR. As implied by the name, uPAR was first identified as a high affinity cellular receptor for urokinase plasminogen activator (uPA). It mediates the binding of the zymogen, pro-uPA, to the plasma membrane where trace amounts of plasmin will initiate a series of events referred to as "reciprocal zymogen activation" where plasmin converts pro-uPA to the active enzyme, uPA, which in turn converts plasma membrane-associated plasminogen to plasmin. This is an efficient machinery to generate broad-spectrum proteolytic activity which is spatially restricted to the plasma membrane, since plasmin that diffuses away from the plasma membrane is rapidly inactivated by circulating inhibitors (i.e., alpha 2-antiplasmin). The system is controlled by a series of plasminogen activator inhibitors (PAIs), most importantly PAI-1 and PAI-2, providing means of temporally restricting the process of plasminogen activation. In addition to its role in plasminogen activation, compelling evidence has demonstrated a role for uPAR in cell-cell and cell-extracellular matrix adhesion, both directly and indirectly. uPAR is directly involved in binding to the extracellular matrix molecule, vitronectin, and the affinity of this binding is increased when uPAR is occupied by (pro-)uPA. A more indirect but presumably very important role of uPAR in cell adhesion seems to be mediated through interactions between uPAR and beta 1- or beta 2-integrins. It has been demonstrated that uPAR may bind physically to integrins in a reversible manner. The interaction seems to be of functional importance since the affinity of the integrin for its corresponding ligand is modulated by the association of integrin with uPAR. In some experimental setups uPAR has been shown to reduce the affinity of the associated integrin for certain ligands, while other experimental systems have demonstrated an increased affinity of the interaction between integrin and ligand after binding of uPAR to the integrin. Finally, uPAR has also been shown to participate in signal transduction events. Since uPAR is not a transmembrane molecule but belongs to the group of proteins that are tethered to the plasma membrane via a glycosyl-phosphatidylinositol anchor, association with a transmembrane adaptor is required for transmission of signals via uPAR. Integrins may serve as such signal transducers, and indeed uPAR has been shown to be associated in the plasma membrane with complexes of integrins and (phosphorylated) tyrosin kinases suggesting a role for these complexes in transmembrane transmission of signals via uPAR. In the hematopoietic system it has been shown that urokinase-type plasminogen activator (uPAR) is expressed as a differentiation antigen on cells of the myelomonocytic lineage and as an activation antigen on monocytes and T lymphocytes. Neutrophils contain intracellular reservoirs of uPAR that are translocated to the plasma membrane upon activation, and neutrophils from patients with the rare blood disease paroxysmal nocturnal hemoglobinuria (PNH) that fail to express glycosyl-phosphatidylinositol-anchored proteins including uPAR, show a very significantly reduced transmigration over an endothelial barrier. Cell-associated plasminogen activation by PNH-affected neutrophils is severely impaired, and it has been proposed that this may be causally related to the propensity for thrombosis in PNH. The pattern of expression of uPAR in hematological malignancies mirrors the expression by normal blood and bone marrow counterparts with some exceptions (differentiated myeloid leukemias are positive, undifferentiated myeloid may be negative and the majority of lymphoid leukemias and lymphomas are negative). The potential clinical relevance of uPAR expression in leukemias and lymphomas has not been determined.

The influence of somatic cell count on the heat stability of bovine milk plasmin activity

Abstract The heat stability of bovine milk plasmin activity and the role of plasminogen activators in milk of low and high somatic cell count (SCC) were examined, with or without KIO3 addition. The inactivation of plasmin was a first-order reaction and Arrhenius plots showed two-stage inactivation kinetics. Plasmin was more heat stable in high SCC milk than low SCC milk after low temperature treatments such as thermisation and pasteurisation, but less stable in high SCC milk under UHT-range thermal treatments. The addition of KIO3 to low SCC milk before heating resulted in considerably greater heat stability of plasmin at all heating temperatures. The activation energy, Ea, for the inactivation reaction in the temperature range 63–110°C was estimated as 52.75 and 74.44 kJ mol-1 for low and high SCC milk, respectively. The Ea for inactivation of plasmin in the temperature range 110–138°C was estimated as 22.03 and 24.70 kJ mol-1 for low and high SCC milk, respectively. The high SCC milk containing KIO3 showed evidence of considerable plasminogen activator activity, apparently leading to activation of plasminogen during the heating process itself. Overall, without the inactivating influence of denatured β-lactoglobulin, plasmin activity is extremely heat stable in native milk systems and plasminogen activators derived from somatic cells appear to be likewise very heat stable and active during heating processes.

Studies on the role of plasminogen activator in systemic infection by virulentYersinia pestisstrain C092

Plasminogen activator is an outer membrane protease ofYersinia pestisencoded by theplagene on plasmid pPst. Pla of the KIM-10 strain ofY. pestisappears to be required for the virulence from a subcutaneous (sc) but not an intraperitoneal (ip) or intravenous (iv) route of infection in mice. However, other strains ofY. pestisare highly virulent by the sc route yet lack pPst andpla. In this study, the pPst- Pestoides F strain was lethal to mice inoculated sc, with an LD50(3 cfu), equal to that of C092, a virulent pPst+ strain. To analyse further the role of Pla in invasive infection, isogenic derivatives of C092, including one harboringplawith a frameshift mutation and another cured of pPst, were made. Although the ip LD50of pPst- C092 and of theplamutant were nearly identical to that of the wild type, the subcutaneous LD50of the cured and mutant strains were 4 to 6 logs greater than that of wild type. Thus, pPst appears to be required for development of a lethal infection by some strains after sc inoculation but not after direct ip inoculation. Pla-associated virulence did not appear to be mediated by interference with the phagocyte chemoattractant C5a, as shown by the lack of correlation of C5a production with susceptibility toY. pestisin C5a+ and C5a- congenic mice. In a footpad model of the early host response to subcutaneous infection, pPst- C092 proliferated at the subcutaneous injection site to a similar extent as did the wild type parent strain, and elicited a similarly large, local inflammatory response. However, the wild type was present at higher concentrations at more distant sites such as the popliteal lymph node and spleen.

The effect of treatment of Helicobacter pylori infection on gastric mucosal plasminogen activators

The plasminogen activation system is known to be involved in several cell migration processes. A role for plasminogen activators in smooth muscle cell migration after vascular injury has been suggested from several animal studies. However, not much is known about their involvement in human vascular remodelling. In this study, the role of the plasminogen activation system in human smooth muscle cells was investigated in more detail using an in vitro wound assay. Confluent cultures were wounded by stripping the cells away from their extracellular matrix with the use of Millipore strips. After wounding, cells start to migrate from the wounded edge into the denuded area. Migration was followed during 24 hours and quantified by counting the number of cells that migrated into the denuded area. Migration was inhibited to 61.9 + 7.1 % of control by the addition of the plasmin inhibitor aprotinin (100 KIU/mL) to the culture medium. Blocking the activity of u-PA or t-PA using specific polyclonal antibodies reduced migration to 57.8 ±6.1% with anti-uPA and had no significant effect on migration with anti-tPA. Interference in the uPA/uPAR interaction by addition of soluble uPAR had a similar effect as for anti-uPA. A possible involvement of LRP or the VLDL receptor was shown by adding the receptor antagonist RAP to the culture medium, which inhibited migration to 61.0 ± 7.9 % of control. These results suggest an involvement of the plasminogen activation system and particularly surface bound u-PA in human smooth muscle cell migration.

The role of plasminogen activators in the development of atherosclerotic and restenotic lesions

The plasminogen activator (PA) system may participate in the pathogenesis of atherosclerosis and of restenosis after angioplasty by modulating the turnover of intimal fibrin and extracellular matrix deposits and by contributing to intimal cell migration. This paper summarise our results on the expression of tissue-type PA (t-PA), urokinase (u-PA), u-PA receptor (uPAR) and PAI-1 in atherosclerotic and restenotic lesions. In atherosclerotic arteries, t-PA, u-PA and PAI-1 were found in intimal smooth muscle cells (SMC) and macrophage-derived foam cells. A particularly high u-PA expression was noted on macrophages localised on the rims of the necrotic core. u-PA-dependent lytic activity was detected in macrophage rich areas of the advanced lesions. The similar distribution pattern of PAI-1 suggests its possible counterbalancing role in the local modulation PA dependent proteolysis within lesions. Time-course analysis of expression of PAs after balloon injury of rat and rabbit arteries have revealed that t-PA and PAI-1 antigen and mRNA are overexpressed by some SMC scattered in the subintimal area after 1–3 days following balloon injury. The neointimal SMC detected after 9 days have exhibited a strong expression of t-PA, PAI-1, u-PA and uPAR antigen and mRNA. PA dependent proteolytic activity was found in the neointimal area, especially after 14 days and it was inhibited in a large extent by anti t-PA antibodies. These results support the existence of a local dynamic process of PA dependent proteolysis in association with the advanced atherosclerotic plaque and with the hyperproliferative response of the SMC of injured arteries..

Preliminary studies on the role of plasminogen activator in seminal plasma of human and rhesus monkey.

Two types of plasminogen activators (PA), tissue type (tPA) and urokinase type (uPA), were identified in the seminal plasma of both the human and the rhesus monkey. We studied the possible relationship between PA activities in the seminal plasma and the sperm counts and motility and demonstrated that: (i) PA activity in human seminal plasma from infertile patients was associated with immotile spermatozoa; (ii) the treatment of fertile men with testosterone enanthate (TE) to induce azoospermia was accompanied by an increase in seminal PA activity; (iii) when monomer T4 (isolated from multiglycosides of Tripterygium wilforddi) was administered to fertile male rhesus monkeys to induce azoospermia, PA activities in seminal plasma increased considerably; and (iv) immunocytochemistry studies showed that both uPA and PAI-1 antigens were localized on the surface of human spermatozoa, indicating that human spermatozoa were capable of binding uPA and PAI-1 through their receptors or forming a complex. These data demonstrate that seminal PA activity may be related to azoospermia, and possibly, to the fertilizing capability of spermatozoa in primates.

Formation of the Hepatocyte Spheroid and Roles of Plasminogen Activator

For culturing hepatocytes, we generally use a matrix, collagen on which the cells proliferate and become confluent monolayer. Recently, a modified proteoglycan, chondroitin sulfatephosphatidylethanolamine (CS-PE), in stead of collagen, has been developed, and made possible a novel culture forming a multicellular assembling, spheroid. The spheroid is found to be highly differentiated, since it produces plasminogen and fibrinogen as well as albumin much more than the monolayer does, and it has an ability of being induced tyrosine aminotransferase by hormones. The mechanism with which hepatocytes form spheroid is unknown. Especially, it is not yet known how plasminogen activator (PA) plays in the spheroid or in the process of its formation. Our present study on the fibrinolytic factors revealed that the spheroid was in fairly hypofibrinolytic; t-PA activity in the conditioned media was one-tenth of that of monolayer (11U/106 cells versus 116U/106 cells), and the specific activity of t-PA was around one-fifth of monolayer. In addition, during the culture the mRNA for t-PA decreased in the spheroid, while it increased in monolayer. On the other hand, the mRNA for the PA inhibitor type 1 (PAI-1) was expressed higher in the spheroid. To form spheroid, addition of an anti-t-PA antibody to the media were not hampering although other protease inhibitors, including trypsin and plasmin inhibitors were of quite hampering and the cells remained monolayer. Thus, in the spheroid formation of hepatocytes, the cells would be in fibrinolytically inactive, however, they would require some proteolytic enzyme including plasmin.

Hormonal regulation of plasminogen activator in rat and mouse seminiferous epithelium.

To elucidate the possible role of plasminogen activator (PA) in spermatogenesis and spermiation in mammals, we studied the hormonal regulation of PA secretion in cultured rat and mouse seminiferous tubules during defined stages of spermatogenesis. Results indicated that: (1) under basal conditions, segments of rat seminiferous tubules released primarily urokinase-type PA (uPA) at all stages of the cycle. The highest level of PA secretion occurred at stages VIIab, VIIcd and VIII. FSH, 8-bromo cyclic AMP and forskolin (FK) stimulated PA secretion, predominantly tissue-type PA (tPA). (2) In contrast, mouse seminiferous tubules secreted only tPA under basal conditions. In the presence of 50 microM MIX, seminiferous tubules at stages VII and VIII secreted higher levels of both types of PA than at the other stages. Both tPA and uPA secretion was enhanced by addition of FSH and FK to the organ culture media. (3) Segments of both rat and mouse seminiferous tubules at stages IX-XII in which the sperm residual bodies are absorbed into the Sertoli cells were also very sensitive to the addition of FSH to the organ culture. These results suggest that tPA in rat and mouse testes may play an essential role in the process of spermatogenesis and spermiation as well as in sperm residual body absorption.

The Urokinase Receptor. Protein Structure and Role in Plasminogen Activation and Cancer Invasion

The Urokinase Receptor. Protein Structure and Role in Plasminogen Activation and Cancer Invasion

Role of plasminogen activators and their inhibitor PAI-1 in pericellular proteolysis of smooth muscle cells and endothelial cells

Role of plasminogen activators and their inhibitor PAI-1 in pericellular proteolysis of smooth muscle cells and endothelial cells

Modification of invasion and differentiation in human melanoma cell clones.

In an attempt to define the role of plasminogen activator in invasiveness and differentiation of human melanoma cells, the modulation of these parameters was studied in two melanoma clones characterized by marked differences in their basal features, using 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and retinoic acid, two differentiation inducers, and doxorubicin, a cytotoxic agent. TPA induced only slight reductions, whereas retinoic acid and doxorubicin caused an increase in invasiveness, enzymatic activity and differentiation in the clone showing low invasivity, low urokinase-type plasminogen activator levels and high differentiation. In contrast, in the clone showing high invasivity, high urokinase-type plasminogen activator levels and low differentiation it was found that: TPA was ineffective; retinoic acid induced a reduction of plasminogen activator but no modifications of invasiveness and differentiation; doxorubicin caused a decrease in invasiveness and plasminogen activator activity but no modification of morphological features. The different behaviour of the two clones thus could be related to the basal features of the clones. The results reported here indicate that in the presence of these drugs the associations between invasiveness and urokinase-type plasminogen activator activity and between invasiveness and differentiation are lost. Drug treatment therefore significantly affected the features of the clone characterized by low biological aggressiveness (high differentiation, low invasiveness), whereas the highly aggressive clone did not show a consistent response to drug treatment.