Growth factor-like effect of urokinase type plasminogen activator in human renal cells

D2A sequence of the urokinase receptor induces cell growth through αvβ3 integrin and EGFR

The urokinase receptor (uPAR) stimulates cell proliferation by forming a macromolecular complex with αvβ3 integrin and the epidermal growth factor receptor (EGFR, ErbB1 or HER1) that we name the uPAR proliferasome. uPAR transactivates EGFR, which in turn mediates uPAR-initiated mitogenic signal to the cell. EGFR activation and EGFR-dependent cell growth are blocked in the absence of uPAR expression or when uPAR activity is inhibited by antibodies against either uPAR or EGFR. The mitogenic sequence of uPAR corresponds to the D2A motif present in domain 2. NMR analysis revealed that D2A synthetic peptide has a particular three-dimensional structure, which is atypical for short peptides. D2A peptide is as effective as EGF in promoting EGFR phosphorylation and cell proliferation that were inhibited by AG1478, a specific inhibitor of the tyrosine kinase activity of EGFR. Both D2A and EGF failed to induce proliferation of NR6-EGFR-K721A cells expressing a kinase-defective mutant of EGFR. Moreover, D2A peptide and EGF phosphorylate ERK demonstrating the involvement of the MAP kinase signalling pathway. Altogether, this study reveals the importance of sequence D2A of uPAR, and the interdependence of uPAR and EGFR.

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.

Plasminogen activator inhibitor-1 predicts coronary in-stent restenosis of drug-eluting stents

BACKGROUND

We tested the hypothesis that plasma levels of plasminogen activator inhibitor-1 (PAI-1) are influenced by percutaneous coronary intervention (PCI) with the implantation of drug eluting stents (DES) and are able to predict the occurrence of in-stent restenosis (ISR).

METHODS AND RESULTS

PAI-1 active antigen plasma levels were determined in 75 patients before and 24 h after PCI with DES implantation. Patients with ISR after six to eight months (16%) showed significantly lower PAI-1 plasma levels before PCI (ISR, 11.7 +/- 8.1 ng mL(-1); non-ISR, 22.8 +/- 18.8 ng mL(-1); P <0.05). PAI-1 levels in the lowest tertile were associated with a 9.5-fold increased risk of ISR, independent of clinical risk factors, angiographic or procedural characteristics, compared to the highest tertile (P < 0.05). The induced change of PAI-1 active antigen 24 h after PCI was significantly higher in patients with ISR (ISR, +5.6 +/- 8.0 ng mL(-1); non-ISR, -3.2 +/- 12.1 ng mL(-1); P < 0.05) with positive correlation to late lumen loss (r = 0.30; P < 0.05).

CONCLUSIONS

ISR after DES implantation is significantly related to plasma levels of PAI-1 active antigen before and after PCI. If confirmed by larger multicenter studies, the determination of PAI-1 plasma levels might be clinically helpful in the identification of patients at high risk of developing of ISR, even after DES implantation.

Urokinase plasminogen activator in injured adventitia increases the number of myofibroblasts and augments early proliferation

Myofibroblasts are involved in vessel remodeling during the development of hypertension as well as after angioplasty and aortocoronary grafting, but the mechanisms of myofibroblastic phenotypic modulation are not fully elucidated. We assessed the role of urokinase plasminogen activator (uPA) and its proteolytic activity in myofibroblast differentiation and the early proliferation following mechanical injury of the rat carotid adventitia. The effects of perivascular application of recombinant uPA (r-uPA), proteolytically inactive r-uPA(H/Q) and uPA neutralizing antibody were evaluated 4 days after surgical injury to the adventitia. The phenotype of adventitial cells was assessed using anti-alpha-smooth muscle actin (alpha-SM actin) antibody, anti-SM heavy chain myosin, anti-high-molecular-weight caldesmon, anti-smoothelin and anti-ED-1 antibodies, proliferation by the expression of proliferating cell nuclear antigen, and the size of the adventitia by quantitative morphometry. Four days after injury, the intensive immunostaining for urokinase appeared in the rat carotid artery adventitia. At the same time, the frequency of alpha-SM actin-positive adventitial cells was 1.8+/-1.1% in uninjured arteries and 25.2+/-5.4% in injured arteries (p<0.05), and the respective frequency of ED-1-positive cells 1.5+/-1.1 and 25.0+/-5.2%. The application of exogenous r-uPA doubled the numbers of alpha-SM actin-positive adventitial cells to 55.7+/-6.8% (p<0.05). ED-1-positive cells and proliferating cell nuclear antigen-positive cells as well as the size of the adventitia were also significantly increased after r-uPA compared with injury alone. In contrast, the proteolytically inactive r-uPA(H/Q) did not affect any parameters. The application of uPA neutralizing antibody attenuated the frequency of alpha-SM actin-positive cells to 12.6+/-3.5% (p<0.05), the frequency of ED-1-positive cells, and the numbers of adventitial cells. r-uPA stimulation of cultured human skin fibroblasts significantly increased the alpha-SM actin content in a concentration-dependent manner. In contrast, r-uPAH/Q did not induce changes in alpha-SM actin content. We conclude that uPA, which is upregulated in the injured adventitia, can augment adventitial cell accumulation, including myofibroblasts, and adventitia growth early after injury of the rat carotid artery adventitia by mechanisms involving proteolysis.

Cultured pressure ulcer fibroblasts show replicative senescence with elevated production of plasmin, plasminogen activator inhibitor-1, and transforming growth factor-beta1

In a 16-patient study, cultured fibroblast populations from normal skin were able to replicate an average of 14.8 +/- 2.2 times before becoming senescent, while fibroblast populations from the ulcer bed reached the end of their replicative life span after 7.2 +/- 1.9 population doublings (p= 0.001). Fibroblast populations from 10 of 16 pressure ulcers became senescent after fewer than five population doublings, whereas when populations of fibroblasts from adjacent normal skin were studied, only 2 of 16 became senescent within this same time period. In addition, only an occasional fibroblast from normal skin stained positively for senescence-associated beta-galactosidase compared to approximately 50% of equally aged ulcer bed fibroblasts (p = 0.0060). Senescent ulcer bed fibroblasts secreted significantly more plasmin than early passage ulcer bed fibroblasts (p= 0.0237), nearly six times as much plasmin as early passage normal skin fibroblasts (p < 0.0001), three and a half times the level of normal skin fibroblasts of the same age (11.52 +/- 4.58 microg/mg protein; p= 0.0003), and more than one and a half times the level of senescent normal skin fibroblasts (p= 0.0525). Senescent pressure ulcer fibroblasts generated significantly more plasminogen activator inhibitor-1 (1179.27 +/- 25.37 ng/mg protein) than normal skin fibroblasts of the same age (132.16 +/- 16.20 ng/mg protein; p = 0.0357). Also, senescent ulcer bed fibroblasts produced higher levels of transforming growth factor-beta1, but these were not significantly different from senescent normal skin fibroblasts. Although senescent ulcer fibroblasts produce elevated levels of plasminogen activator inhibitor-1 and transforming growth factor-beta1, the ratio of these factors to plasmin levels suggests that this may have little influence on extracellular matrix synthesis or maintenance in the chronic wound. These data show that cultured fibroblasts from most patient pressure ulcers profile a wound environment that is associated with an increasing population of senescent fibroblasts; however, factors within the chronic wound environment that promote cellular senescence remain unclear. We have proposed that a prolonged inflammatory response may be a contributing factor to the chronic wound condition.

Expression of E-Cadherin and uPA and their Association with the Prognosis of Pancreatic Cancer

OBJECTIVE

E-cadherin (ECD) and urokinase plasminogen activator (uPA) have been noted as markers for tumor metastasis and prognosis in several tumors. We thus investigated the relationship between the expression of ECD and uPA and the clinicopathological characteristics in pancreatic cancer.

METHODS

The expression of ECD and uPA was evaluated in pancreatic cancer tissues from 53 patients.

RESULTS

Among 53 tumor tissues, those from 29 (54.7%) patients showed positive ECD expression and those from 22 (41.5%) patients showed positive expression of uPA. There were four subgroups of ECD/uPA expression: ECD-positive/uPA-negative, ECD-negative/uPA-negative, ECD-positive/uPA-positive and ECD-negative/uPA-positive. These patterns were found in 14 (26.4%), 11 (20.8%), nine (17%) and 19 (35.8%) patients, respectively. The tumor tissues with ECD-negative and uPA-positive expression were associated with larger tumor, distant metastasis and an increased clinical stage. There was a difference in the median survival time between the patients with ECD-positive/uPA-negative pancreatic tissues (median: 18.7 months) and the patients with ECD-negative/uPA-positive pancreatic tissues (median: 7.5 months, P < 0.05), and there was a statistically significant difference in survival curves between these two groups.

CONCLUSION

The combined analysis concerning uPA and E-cadherin expression may be a useful predictor of metastasis in pancreatic cancer.

cDNA transfection of amino-terminal fragment of urokinase efficiently inhibits cancer cell invasion and metastasis

Focusing of urokinase-type plasminogen activator (uPA) to the cell surface via binding to its specific receptor (uPAR, CD87) is critical for tumor invasion and metastasis. Consequently, the inhibition of uPA-uPAR interaction on the cell surface might be a promising anti-invasion and anti-metastasis strategy. We examined the effects of cDNA transfection of the human uPA amino-terminal fragment (ATF) on invasion and metastasis of cancer cells. First, a highly metastatic human lung giant-cell carcinoma cell line (PG), used as the target cell for evaluation of this effect, was demonstrated to express both uPA and uPAR. Then, ATF, which contains an intact uPAR binding site but is catalytically inactive, was designed as an antagonist of uPA-uPAR interaction and was transfected into PG cells. [(3)H]-Thymidine incorporation and cell growth curves indicated that expressed ATF did not affect the proliferation of transfected cells. However, analysis by scanning electron microscopy revealed that ATF changed the host cells from the typical invasive phenotype to a noninvasive one. Correspondingly, the modified Boyden chamber test in vitro showed that ATF expression significantly decreased the invasive capacity of transfected cells. Furthermore, in the spontaneous metastasis model, it was confirmed in vivo that expressed ATF remarkably inhibited lung metastasis of implanted ATF-transfected PG cells. In summary, autocrine ATF could act as an antagonist of uPA-uPAR interaction, and ATF cDNA transfection could efficiently inhibit the invasion and metastasis of the cancer cells. Inhibition of uPA-uPAR interaction on the cell surface might be a promising anti-invasion and anti-metastasis strategy.

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.

Regulation of urokinase production by androgens in human prostate cancer cells: effect on tumor growth and metastases in vivo

During the complex multistep process of tumor progression, prostate cancer is initiated as an androgen-sensitive, nonmetastatic cancer, followed by a gradual transition into a highly metastatic and androgen-insensitive variety that lacks the expression of functional androgen receptors (AR). Urokinase (uPA), a member of the serine protease family, has been implicated in the progression of various human malignancies, including prostate cancer. Although uPA production is regulated by various growth factors and cytokines, the role of sex steroids (androgens) in regulating uPA gene expression in prostate cancer is poorly understood. In the current study, we have examined the role of androgens in regulating uPA production and the invasive capacity of the androgen insensitive PC-3 cells transfected with the full-length human AR complementary DNA (PC-3T). Restoration of androgen responsiveness in PC-3T cells caused a marked decrease in cell doubling time. Treatment of PC-3T cells with dihydroxytestosterone (DHT) caused a dose-dependent decrease in uPA messenger RNA and protein production, resulting in their decreased ability to invade through the Matrigel. Nuclear runoff assays revealed that these effects were attributable to the ability of DHT to inhibit uPA gene transcription. AR antagonist flutamide (Flu) reversed the effect of DHT on proliferation and invasion of PC-3T cells. Both control (PC-3) and experimental (PC-3T) cells were injected into the right flank of male BALB/c nu/nu mice. Control animals developed palpable tumors and microscopic tumor metastases at lymph nodes, lungs, and liver at 6-week posttumor cell inoculation. In contrast to this, because of androgen sensitivity of PC-3T cells, palpable tumors were observed only at week 12, with occasional tumor metastases in lungs. Furthermore, inoculation of PC-3T cells into surgically castrated host animals resulted in the development of tumors at a much earlier time (week 10) and a high incidence of metastases, compared with regular animals receiving PC-3T cells. Collectively, these results demonstrate the ability of androgen to regulate uPA production, which may directly effect prostate cancer growth, invasion, and metastasis in vitro and in vivo.

Plasmin activation system in restenosis: role in pathogenesis and clinical prediction?

During recent years it has become increasingly recognized that the plasmin activation system is involved in the development of atherosclerosis and restenosis. Responsible pathophysiologic mechanisms, however, remain elusive. This review focuses primarily on the clinicians, point of view, suggesting that increases in plasminogen activator inhibitor type-1 (PAI-1) plasma levels after balloon angioplasty or permanently elevated lipoprotein (a) (Lp(a)) plasma levels might be helpful in the prediction of restenosis after coronary angioplasty. In contrast, tissue-type plasminogen activator (tPA) plasma levels appear unrelated to restenosis, and data regarding a possible role of urokinase-type plasminogen activator (uPA) in circulation are not available at present. Furthermore, a new hypothesis on the pathophysiological role of local PAI-1 overexpression as a beneficial negative feedback mechanism to limit excess cellular proliferation in atherogenesis and restenosis is presented.

Urokinase plasminogen activator induces human smooth muscle cell migration and proliferation via distinct receptor-dependent and proteolysis-dependent mechanisms

In order to define the relative contribution of the proteolytic domain and the receptor-binding domain of urokinase plasminogen activator (uPA) toward its mitogenic properties we studied the effects of different uPA isoforms on migration and proliferation of human aortic smooth muscle cells (hSMC). The isoforms tested included native human glycosylated uPA, and two recombinant uPA forms, namely a recombinant uPA with wild type structure (r-uPA), and a uPA-mutant in which the first 24 N-terminal amino acid residues of the receptor binding domain were replaced by 13 foreign amino acid residues (r-uPAmut). Cell migration was evaluated using a micro-Boyden chamber assay, and cell proliferation assessed by measurement of [3H]-thymidine incorporation into DNA. Competition binding studies on hSMC using 125I-r-uPA as ligand demonstrated that r-uPA and r-uPAmut exhibited equivalent displacement profiles. However, migration of hSMC was promoted by r-uPA and not by r-uPAmut. r-uPA-induced migration occurred at concentrations (half-maximally effective concentration of 2 nM) approximating the Kd for uPA-uPAR binding (1 nM). r-uPA-induced migration was not affected by the plasmin inhibitor aprotinin. In contrast to their differential chemotactic properties, uPA, r-uPA and r-uPAmut, which possess similar proteolytic activities, all stimulated [3H]-thymidine incorporation in hSMC. Since the [3H]-thymidine incorporation response to each isoform occurred at concentrations (> 50 nM) much higher than necessary for uPAR saturation by ligand (1 nM), this mitogenic response may be independent of binding to uPAR. [3H]-thymidine incorporation responses to r-uPA and -uPAmut were sensitive to the plasmin inhibitor aprotinin, and uPA stimulated DNA synthesis was inhibited by plasminogen activator inhibitor. We conclude that hSMC migration in response to uPA depends upon on its binding to uPAR, whereas uPA-stimulated DNA synthesis in these cells requires proteolysis and plasmin generation.

Mitogenic effects of urokinase on melanoma cells are independent of high affinity binding to the urokinase receptor

The structural and functional properties of the urokinase-type plasminogen activator (u-PA) that are involved in the mitogenic effect of this proteolytic enzyme on human melanoma cells M14 and IF6 and the role of the u-PA receptor (u-PAR) in transducing this signal were analyzed. Native u-PA purified from urine induced a mitogenic response in quiescent IF6 and M14 cells that ranged from 25 to 40% of the mitogenic response obtained by fetal calf serum. The half-maximum response in M14 and IF6 cells was reached at u-PA concentrations of approximately 35 and 60 nM, respectively. Blocking the proteolytic activity of u-PA resulted in a 30% decrease of the mitogenic effect, whereas inhibition of plasmin activity did not alter the mitogenic effect. No mitogenic response was elicited by low molecular weight u-PA, lacking the growth factor domain and the kringle domain. The ATF domain of u-PA induced a mitogenic response that was similar to complete u-PA. Defucosylated ATF and recombinant u-PA purified from Escherichia coli lacking all post-translational modifications did not induce a mitogenic response. Blocking the interaction of u-PA with u-PAR, using a specific monoclonal antibody, did not alter the mitogenic effect induced by u-PA. The binding of radiolabeled u-PA to M14 and IF6 cells was characterized by high affinity binding mediated by u-PAR and low affinity binding to an unknown binding site. These results demonstrate that proteolytically inactive u-PA is able to induce a mitogenic response in quiescent melanoma cells in vitro by a mechanism that involves the ATF domain but is independent of high affinity binding to u-PAR. Furthermore, it suggests that u-PA is able to bind with low affinity to a hitherto unidentified membrane associated protein that could be involved in u-PA-induced signal transduction.

Urokinase induces proliferation of human ovarian cancer cells: characterization of structural elements required for growth factor function

Ovarian cancer metastasis is associated with an increase in the urokinase-type plasminogen activator (uPA) and its receptor uPAR. We present evidence that binding of uPA to uPAR provokes a mitogenic response in the human ovarian cancer cell line OV-MZ-6 in which endogenous uPA production had been significantly reduced by stable uPA 'antisense' transfection. High molecular weight (HMW) uPA, independent of its enzymatic activity, produced an up to 95% increase in cell number concomitant with 2-fold elevated [3H]thymidine incorporation as did the catalytically inactive but uPAR binding amino-terminal fragment of uPA, ATF. uPA-induced cell proliferation was significantly decreased by blocking uPA/uPAR interaction by the monoclonal antibody IIIF10 and by soluble uPAR. The efficiency of the uPAR binding synthetic peptide cyclo19,31 uPA19-31 to enhance OV-MZ-6 cell growth proved this molecular domain to be the minimal structural determinant for uPA mitogenic activity. Dependence of uPA-provoked cell proliferation on uPAR was further demonstrated in Raji cells which do not express uPAR and were thus not induced by uPA. However, upon transfection with full-length uPAR, Raji cells acquired a significant growth response to HMW uPA and ATF.

Oestradiol regulation of the components of the plasminogen-plasmin system in MDA-MB-231 human breast cancer cells stably expressing the oestrogen receptor

To understand the hormonal regulation of the components of the plasminogen-plasmin system in human breast cancer, we examined the oestradiol (E2) regulation of plasminogen activators (PAs), namely urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA), plasminogen activator inhibitor type 1 (PAI-1) and uPA receptor (uPAR), in our model system. We used stable transfectants of the MDA-MB-231 human breast cancer cells that express either the wild-type (S30 cells) or the mutant 351asp-->tyr oestrogen receptor (ER) (BC-2 cells). Northern blot analysis showed that there was a concentration-dependent down-regulation of uPA, tPA and PAI-1 mRNAs by E2. In contrast, uPAR mRNA was not modulated by E2. The pure anti-oestrogen ICI 182,780 was able to block E2 action, indicating that the regulation of these genes is ER mediated. The E2 also inhibited the expression and secretion of uPA, tPA and PAI-1 proteins as determined by enzyme-linked immunosorbent assay (ELISA) in cell extracts (CEs) and conditioned media (CM). Zymography of the CM confirmed the inhibitory effect of E2 on uPA activity. Thus, we now report the regulation of uPA, PAI-1 and tPA by E2 in both mRNA and protein levels in ER transfectants. The association between down-regulation of the uPA by E2 and known E2-mediated growth inhibition of these cells was also explored. Our findings indicate that down-regulation of uPA by E2 is an upstream event of inhibitory effects of E2 on growth of these cells as the addition of exogenous uPA did not block the growth inhibition by E2.

The urokinase-type plasminogen activator system in cancer metastasis: a review

The urokinase-type plasminogen activator (u-PA) system consists of the serine proteinases plasmin and u-PA; the serpin inhibitors alpha2-anti-plasmin, PAI-1 and PAI-2; and the u-PA receptor (u-PAR). Two lines of evidence have strongly suggested an important and apparently causal role for the u-PA system in cancer metastasis: results from experimental model systems with animal tumor metastasis and the finding that high levels of u-PA, PAI-1 and u-PAR in many tumor types predict poor patient prognosis. We discuss here recent observations related to the molecular and cellular mechanisms underlying this role of the u-PA system. Many findings suggest that the system does not support tumor metastasis by the unrestricted enzyme activity of u-PA and plasmin. Rather, pericellular molecular and functional interactions between u-PA, u-PAR, PAI-1, extracellular matrix proteins, integrins, endocytosis receptors and growth factors appear to allow temporal and spatial re-organizations of the system during cell migration and a selective degradation of extracellular matrix proteins during invasion. Differential expression of components of the system by cancer and non-cancer cells, regulated by paracrine mechanisms, appear to determine the involvement of the system in cancer cell-directed tissue remodeling. A detailed knowledge of these processes is necessary for utilization of the therapeutic potential of interfering with the action of the system in cancers.

Enhanced expression of urokinase plasminogen activator and its receptor in pancreatic carcinoma

Urokinase plasminogen activator (uPA) is a serine proteinase that has been suggested to play an important role in cancer invasion and metastasis. It binds to a specific membrane receptor denominated uPA receptor (uPAR). uPA activates plasminogen to form plasmin, which participates in tissue degradation and proteolysis. Binding of uPA to its receptor accelerates UPA's own activation from pro-uPA, enhancing the activity of the uPA/uPAR cascade. Using immunohistochemistry and Northern blot analysis, we analysed the role of uPA and uPAR in 30 human pancreatic cancers. Immunohistochemical analysis demonstrated moderate to strong immunostaining of both factors in most pancreatic cancers. Cancer lesions with signs of invasion exhibited the strongest immunohistochemical signals for both factors. In addition, in desmoplastic areas adjacent to the cancer cells, moderate uPA and uPAR immunoreactivity was detectable. Northern blot analysis revealed a sixfold and a fourfold increase in uPA and uPAR mRNA levels in pancreatic cancer, respectively, in comparison with normal controls (P<0.01). Correlation of the Northern blot data with the clinical parameters of the patients indicated that patients with concomitant overexpression of uPA and uPAR had a shorter post-operative survival (median 9 months; mean+/-s.d. 10.2+/-3.6 months) than patients in whom only one or none of these factors were overexpressed (median 18 months; mean+/-s.d. 20.3+/-8.7 months) (P<0.002). Our data suggest that uPA and uPAR may serve as prognostic markers in human pancreatic cancer and that the marked overexpression of both factors may create an environment that enables pancreatic cancer cells to invade surrounding tissues.

The role of plasminogen, plasminogen activators, and matrix metalloproteinases in primate arterial smooth muscle cell migration

The migration of arterial smooth muscle cells (SMCs) plays an important role in normal vessel development as well as the pathobiology of blood vessels. Because it is difficult to study cell migration in primates, we used ex vivo explants. The response of baboon aortic medial explants incubated in vitro in a serum-free medium with insulin and transferrin was compared with the response of whole artery injured in vivo by a balloon catheter to establish the validity of the explant model. Both the time course of entry of SMCs into the S phase and the changes in matrix metalloproteinase 9 were similar in the artery and the explants. SMCs began migrating from explants after a lag of 3 days. By day 11, > 90% of the explants exhibited SMC migration from the tissue (percent of explants with > or = 1 migrating cell). Basal migration was inhibited by antibodies to urokinase and tissue-type plasminogen activator, whereas addition of plasminogen to the explants increased migration. An inhibitor of matrix metalloproteinases. BB-94 (Batimistat), decreased migration, as did alpha 2-macroglobulin. These data demonstrate that proteinases of the matrix metalloproteinase and plasminogen/plasminogen activator families play an important role in the migration of primate arterial SMCs through the extracellular matrix.

Degradation of human plasma and extracellular matrix fibronectin by tissue type plasminogen activator and urokinase

Fibronectins and plasminogen activators, both tissue and urokinase types, are involved in the physiopathological degradation of the extracellular matrix. Previous reports indicate that fibronectin can be degraded by urokinase without plasminogen. Also, we have shown that tissue-type plasminogen activator can cleave fibronectin, without plasminogen, generating fragments of 30 and 220-250 kDa detectable by immunoblotting analysis. A comparison with urokinase-induced degradation indicates that the cleavage sites are the same for both plasminogen activators. One is close to the carboxyl-terminal, disrupting the fibronectin dimeric structure, and one is near the amino-terminal, generating a 30 kDa fragment. In solution, the activity of tissue-type plasminogen activator was prevalent on the amino-terminal site, while urokinase activity was prevalent on the carboxyl-terminal site. On fibronectin immobilized onto a gelatin coated surface, only the 30 kDa fragment was released when treated with both plasminogen activators. Plasminogen activators also were active on fibronectin assembled into the extracellular matrix of cultured fibroblasts. Urokinase caused the complete disappearance of extracellular matrix fibronectin, together with the release of the 30 and the 220-250 kDa fibronectin fragments, but left a flat morphology, while tissue-type plasminogen activator induced the release of the 30 kDa fragment associated with changes in cellular morphology. The plasminogen-independent fibronectin degradation exerted by tissue-type plasminogen activator and urokinase is 100 times lower than that exerted by plasmin. This may provide a mechanism for localized and limited degradation of fibronectin preventing the generalized proteolysis associated with plasminogen activation.

In vitro anti-proliferative and anti-invasive role of aminoterminal fragment of urokinase-type plasminogen activator on 8701-BC breast cancer cells

8701-BC cells, derived from a primary carcinoma of the breast, constitutively express mRNA for urokinase-type plasminogen activator (uPA). In this paper, we demonstrated the presence of uPA in the conditioned medium, and of uPA-receptor (uPAR) on the cell surface of 8701-BC cells, which therefore have the potential for an autocrine mechanism of uPA-mediated stimulation. We examined whether exogenous addition of either intact uPA, or its amino-terminal fragment (uPA-ATF), which lacks catalytic activity but retains the uPAR binding site and a growth factor-like domain, or immunoneutralisation of endogenous uPA-uPAR interactions could exert any effect on the proliferative and invasive behaviour of 8701-BC cells. The data demonstrate that, while uPA promotes growth and invasion of 8701-BC cells, its effect reversed by blocking uPA-uPAR interactions, uPA-ATF not only fails to impart growth factor-like signals, but also restrains cell invasion in vitro. In the light of these and other data, an active participation of ATF in the complex cell-ECM network of interactions underlying cancer progression can be postulated. In addition, it appears worth considering the possibility of testing the effect of this uPA fragment in vivo for the therapy of breast (and possibly other) human invasive carcinomas.

Differential growth state-dependent regulation of plasminogen activator inhibitor type-1 expression in senescent IMR-90 human diploid fibroblasts

The type-1 inhibitor of plasminogen activator (PAI-1) regulates pericellular proteolytic activity functioning, thereby to control matrix integrity, cell growth, and morphology. Subconfluent late-passage IMR-90 human fibroblasts and normal rat kidney (NRK) cells, both at the stage of replicative senescence accumulated 15- to 30-fold more undersurface PAI-1 protein compared to early-passage, actively-proliferating, cultures. Senescence-associated elevations in PAI-1 expression by IMR-90 cells reflected corresponding 11-fold increases in the 3.0- and 2.2-kb PAI-1 mRNA species. The 2.2-kb transcript exhibited a greater age-dependent increase (7.2-fold) compared to the 3.0-kb mRNA (3.7-fold). Since PAI-1 expression is coupled to growth activation in serum-deprived cultures (Ryan and Higgins, 1993, J. Cell. Physiol., 155:376-384), it was important to determine if PAI-1 gene regulation was altered as a function of cellular aging. In contrast to early-passage cultures, senescent IMR-90 fibroblasts did not down-regulate either PAI-1 protein expression or steady-state levels of PAI-1 mRNA transcripts upon serum-deprivation. Late-passage human fibroblasts at their proliferative end-stage, thus, appear to regulate PAI-1 mRNA levels through different mechanisms than do young, actively-proliferating, cells. PAI-1 overexpression during in vitro cellular aging, therefore, may contribute to the acquisition of specific senescence-associated phenotypic traits (e.g., enlarged cell morphology; increased adhesivity) by altering the pericellular proteolytic balance influencing, in turn, the formation or stability of cell-to-substrate attachment complexes.

Urokinase receptor is a multifunctional protein: influence of receptor occupancy on macrophage gene expression

Binding of urokinase to the glycolipid-anchored urokinase receptor (uPAR) has been implicated in macrophage differentiation. However, no biochemical markers of differentiation have yet been directly linked to uPAR occupancy. As extensive changes in proteolytic profile characterize monocytic differentiation, we have examined the role of uPAR occupancy on protease expression by differentiating phagocytes. Antibodies to either urokinase or to uPAR that prevent receptor binding inhibited induction of cathepsin B in cultured monocytes and both cathepsin B and 92-kD gelatinase mRNA and protein in phorbol diester-stimulated myeloid cells. Mannosamine, an inhibitor of glycolipid anchor assembly, also blocked protease expression. Anti-catalytic urokinase antibodies, excess inactive urokinase, or aprotinin had no effect, indicating that receptor occupancy per se regulated protease expression. Antibodies to the integrins CD11a and CD29 or to the glycolipid-anchored proteins CD14 and CD55 also had no effect. Protease induction was independent of matrix attachment. Antibodies to urokinase or uPAR affected neither the decrease in cathepsin G nor the increase in tumor necrosis factor-alpha in phorbol ester-stimulated cells. These data establish that uPAR is a multifunctional receptor, not only promoting pericellular proteolysis and matrix attachment, but also effecting cysteine- and metallo-protease expression during macrophage differentiation.

Regulation of mesothelial cell mitogenesis by antisense oligonucleotides for the urokinase receptor

The association of urokinase-type plasminogen activator (uPA) with its receptor (uPAR) influences various biologic functions, including cell migration, angiogenesis, differentiation, and wound healing. Expression of uPAR at the mesothelial surface could, therefore, influence cellular responses in the pleural space. We found that a line of cultured human mesothelial cells (MeT5A) expressed specific and saturable binding sites for uPA that increased on stimulation with PMA. Ligand blotting studies showed that the mesothelial receptor is a 50 kD protein similar to that in other cell lines. Binding of active and intact, but not amino terminal or low molecular weight fragment, uPA to mesothelial cells enhanced DNA synthesis and cell proliferation, and antibodies against either the active site of uPA or uPAR abrogated this effect. We reasoned that regulation of uPAR expression could control uPA-induced mitogenesis and tested this hypothesis with antisense oligonucleotides complementary to uPAR mRNA. Phosphorothioate-modified antisense oligonucleotides inhibited uPA-mediated mesothelial cell proliferation in a concentration-dependent manner. These effects were associated with decreased binding of 125I-uPA and reduced expression of the uPAR gene product. The results indicate that uPAR is involved in signal transduction pathways that control uPA-mediated mesothelial cell proliferation, a process implicated in the pathogenesis of mesothelial inflammation and pleural neoplasia. Antisense oligonucleotides to uPAR suppress mesothelial cell mitogenesis in vitro and offer a potential means of regulating the process in vivo.

Receptor binding and degradation of urokinase-type plasminogen activator by human mesangial cells

The binding of [125I] labeled urokinase-type plasminogen activator (u-PA) was studied on human mesangial cells (MC) in culture. The binding of active [125I]u-PA at 37 degrees C reached a plateau after 30 minutes of incubation and remained stable for at least four hours. When the supernatant was analyzed with trichloracetic acid (TCA), TCA soluble radioactive material could be detected after a lag phase of 30 minutes, and then increased linearly for four hours. Analysis by electrophoresis on SDS PAGE and autoradiography of the cell associated radioactivity and of the intracellular content showed that active u-PA and u-PA complexed to plasminogen activator inhibitor type-1 (PAI-1) were bound to the cell surface, but only u-PA/PAI-1 complexes were internalized and degraded. Therefore, the Kd and the number of binding sites were determined by competitive inhibition curves at 4 degrees C using diisopropyl-fluorophosphate (DFP) u-PA. Scatchard plots showed a Kd = 400 +/- 30 pM, and Bmax = 240,000 +/- 25,000 sites/cell. Excess of the amino terminal fragment of u-PA (ATF) completely blocked the specific binding of [125I]u-PA, confirming that the binding of u-PA was independent of the presence of the active site and/or of the formation of complexes with PAI-1. 3H thymidine incorporation by mesangial cells after stimulation with 100 nM active u-PA showed that u-PA had a moderate but significant mitogenic effect, in contrast to inactive u-PA and ATF. However, this mitogenic effect was not accompanied by a proliferative effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Gene transfer of metalloproteinase transin induces aberrant behavior of cultured mesangial cells

The aim of the present study is to clarify whether the cellular expression of a matrix-degrading metalloproteinase, transin, alters the behavior of cultured mesangial cells (MCs). The cDNA encoding rat transin was introduced into rat MCs and transcribed under the control of a Rous sarcoma virus promoter. The resulting transfectants were then investigated for cell shape, migration, proliferation, and expression of genes associated with matrix metabolism. Northern blot analysis routinely detected the transin transcript in two separate transfectants, MeTRN2 and MeTRN5. Transin expression was strong in MeTRN2, moderate in MeTRN5, but absent in mock transfectants. Immunoblot analysis revealed that these transin transfectants synthesized 59 and 62 kDa molecules, which correspond to transin gene products. Casein digestion assay detected enhanced proteolytic activity in MeTRN2 and MeTRN5. Microscopically, the transfected cells were somewhat elongated with accentuated margins compared with mock transfectants. [3H]-thymidine uptake studies revealed accelerated growth of the transfectants on a plastic substratum as well as within gel matrix. The migration of the transfectants into gel matrix was also significantly enhanced compared with that of mock transfectants. No obvious alteration, however, was found in transcripts of procollagen alpha 1(IV), laminin B2, or the metalloproteinase inhibitor TIMP. We hypothesize that the metalloproteinase transin has a potential for affecting the behavior of MCs and contributing to the pathogenesis of glomerular injury.

Functional roles of microglia in the brain

It has been suggested that microglia, a type of glial cells in the central nervous system, play various important roles in normal and pathologic brains. In this article, we discussed the association or roles of microglia in injury and in brain diseases such as Alzheimer's disease, AIDS dementia complex, multiple sclerosis and ischemia. Furthermore, microglia-derived cytotoxic products and other secretory factors were summarized. In addition to the pathological aspects, secretory factors that showed neurotrophic effects were described with special reference to their physiological significance in the neuronal growth, neuronal function and regeneration processes. Accumulated evidence suggests that microglia are associated with not only brain pathology but also normal physiology in the brain.

Proteinases and proteinase inhibitors as modulators of animal cell growth

1. Three distinct lines of evidence indicate that proteinases are involved in the growth of cultured animal cells. 2. Endogenous growth-related proteinases have been identified, and exogenous proteinases can also stimulate cell proliferation, probably by different mechanisms. In some cases, higher concentrations of proteinases are cytotoxic. 3. Proteinase inhibitors, not surprisingly, inhibit cell growth, but can also be mitogenic at sub-inhibitory concentrations. 4. There must, therefore, be at least three major cellular processes in which proteinases or proteinase inhibitors can operate to exert a direct effect on cell proliferation. 5. Details of one action of an exogenous proteinase, typified by thrombin and the thrombin receptor, are becoming clear at the molecular level, but thrombin probably activates at least two intracellular signalling systems, as well as acting as a growth inhibitor in some situations. 6. Much remains to be investigated in other examples.