Urokinase and urokinase receptor: a paracrine/autocrine system regulating cell migration and invasiveness

Plasminogen activator system modulates invasive capacity and proliferation in prostatic tumor cells

The malignant phenotype of prostatic tumor cells correlates with the expression of both uPA and its cell-membrane receptor (uPAR); however, there is little information concerning the role of cell-bound uPA in matrix degradation and invasion. Our results suggest that cell-associated uPA plays a key role in regulating the amount of plasmin present at the surface of prostatic carcinoma (PRCA) cells and show that differential production of uPA corresponds with the capacity to bind and activate plasminogen. In addition, we provide direct evidence that both uPA secretion and the presence of uPA-uPAR complexes characterize the invasive phenotype of PRCA cells and suggest the existence of several pathways by which tumor cells acquire plasmin activity. LNCaP cells (which do not produce uPA but express uPAR) may activate plasmin through exogenous uPA. In vivo, the source of uPA may be infiltrating macrophages and/or fibroblasts as observed in several other systems. PAI-1 accumulation in the conditioned medium (CM) limits plasmin action to the pericellular microenvironment. Our results indicate that MMP-9 and MMP-2 are also activated by plasmin generated by cell-bound but not by soluble, extracellular uPA. Plasmin activation and triggering of the proteolytic cascade involved in Matrigel invasion is blocked by antibodies against uPA (especially by anti- A-chain of uPA which interacts with uPAR) and by PA inhibitors such as p-aminobenzamidine which may regulate levels of cell-bound uPA. uPA may also regulate growth in PRCA cells. Indeed, antibodies against uPA A-chain (and also p-aminobenzamidine treatment) interfere with the ATF domain and inhibit cell growth in uPA-producing PC3 and DU145 prostate cancer cell lines, whereas exogenous uPA (HMW-uPA with ATF) induces growth of LNCaP prostate tumor cell line. These data support the hypothesis that in prostatic cancer patients at risk of progression, uPA/plasmin blockade may be of therapeutic value by blocking both growth of the primary tumor and dissemination of metastatic cells.

Absence of host plasminogen activator inhibitor 1 prevents cancer invasion and vascularization

Acquisition of invasive/metastatic potential through protease expression is an essential event in tumor progression. High levels of components of the plasminogen activation system, including urokinase, but paradoxically also its inhibitor, plasminogen activator inhibitor 1 (PAI1), have been correlated with a poor prognosis for some cancers. We report here that deficient PAI1 expression in host mice prevented local invasion and tumor vascularization of transplanted malignant keratinocytes. When this PAI1 deficiency was circumvented by intravenous injection of a replication-defective adenoviral vector expressing human PAI1, invasion and associated angiogenesis were restored. This experimental evidence demonstrates that host-produced PAI is essential for cancer cell invasion and angiogenesis.

Protein kinase C-alpha activity inversely modulates invasion and growth of intestinal cells

The phorbol ester phorbol 12-myristate 13-acetate induces remarkable phenotypic changes in intestinal HT-29 M6 cells; these changes consist of loss of homotypic adhesion and inactivation of E-cadherin. In parallel, cell growth is retarded. We have transfected HT-29 M6 cells with an activated form of the conventional protein kinase Calpha (cPK-Calpha). Expression of this isoform induced the acquisition of a scattered phenotype, similar to that adopted by cells after addition of phorbol 12-myristate 13-acetate, with very low cell-to-cell aggregation and undetectable levels of functional E-cadherin. These cell clones were highly motile and rapidly invaded embryonic chick heart fragments. Furthermore, cells expressing activated-cPK-Calpha showed decreased proliferation in comparison to control clones. We have also studied how these two apparently antagonistic changes affect the tumorigenic ability of HT-29 M6 cells. When the different cell clones were xenografted into athymic mice, the effect on cell growth seemed to predominate. Expression of activated-cPK-Calpha significantly reduced the size of the tumors; the cells with the highest level of expression did not even form subcutaneous tumors. Besides their smaller size, the morphology of these tumors was clearly different from those originated by HT-29 M6 cells, and they could be defined as infiltrative on anatomo-pathological basis. These results indicate that cPK-Calpha controls both cell-to-cell adhesion and proliferation of intestinal cells.

Time and dose dependency of the suppression of pulmonary metastases of rat mammary cancer by amiloride

Amiloride is an inhibitor of urokinase plasminogen activator (uPA), an essential component of the plasminogen/plasmin enzyme system. Inhibition of uPA prevents the conversion of plasminogen to tumor cell surface bound plasmin which is required for initiation of the metastatic process. MATB rat mammary cancer cells were introduced into the jugular venous system of 80 Fisher 344 female rats. Amiloride at high and low dosages was administered in the drinking water at the time of, prior to or several days following the tumor cell inoculation and continued daily for 10 days post inoculation. Control rats were maintained on water alone. The middle lobe of the right lung was examined microscopically for numbers of metastases. Suppression of metastases was significant at high amiloride dosages in all groups, and at low dosage when administered prior to inoculation. We conclude that amiloride suppresses induced metastases of rat mammary cancer, the effect being dose- and time-dependent.

Effects of collagenase-cleavage of type I collagen on alpha2beta1 integrin-mediated cell adhesion

In this paper we show that collagenase-3 cleavage of type I collagen has a marked effect on alpha2beta1 integrin-mediated interactions with the collagen fragments generated. Isolated alpha2beta1 integrin and alpha2 integrin A-domain were found to bind to both native collagen and native 3/4 fragment and, to a lesser degree, native 1/4 fragment. Whole integrin and integrin A-domain binding were lost after heat denaturation of the collagen fragments. At physiological temperature, cell adhesion to triple-helical 3/4 fragment via alpha2beta1 integrin was still possible; however, no alpha2beta1 integrin-mediated adhesion to the 1/4 fragment was observed. Unwinding of the collagen fragment triple helices by heating to physiological temperatures prior to adsorption to plastic tissue culture plates resulted in total abrogation of HT1080 cell attachment to either fragment. These results provide significant evidence in support of a role for matrix-metalloproteinase cleavage of the extracellular matrix in modifying cell-matrix interactions.

The effect of thrombospondin-1 and TGF-beta 1 on pancreatic cancer cell invasion

We have previously shown that thrombospondin-1 (TSP-1) and TGF-beta 1 upregulate the urokinase plasminogen activator (uPA) and its receptor (uPAR) and promote tumor cell invasion in breast cancer. To date, the effect of TSP-1 and TGF-beta 1 on the plasminogen/plasmin system in gastrointestinal epithelial malignancies has not been investigated. In this study, we determined the effect of TSP-1 and TGF-beta 1 on uPA and uPAR expression and on tumor cell invasion in pancreatic cancer. ASPC1 human pancreatic adenocarcinoma cells were incubated for 48 h on cell-conditioned media (CCM) either alone (Control) or with the addition of either TSP-1 (40 micrograms/ml) or TGF-beta 1 (5 ng/ml). uPA and uPAR expression were determined by ELISA. ASPC1 cell invasion was determined in a modified Boyden chamber type I collagen invasion assay. The upper chamber was treated with CCM either alone (Control) or with the addition of anti-uPA (10 micrograms/ml) or anti-uPAR (10 micrograms/ml). The lower chamber was treated with CCM either alone (Control) or with the addition of either TSP-1 (40 micrograms/ml) or TGF-beta 1 (5 ng/ml). TSP-1 and TGF-beta 1 induced a twofold increase on uPAR expression but only a slight increase on total uPA. Tumor cell invasion was upregulated 3.5 to 4.5-fold by TSP-1 and TGF-beta 1, respectively. Anti-uPA and anti-uPAR antibodies completely blocked the TSP-1 and TGF-beta 1-mediated pancreatic tumor cell invasion. We conclude that TSP-1 and TGF-beta 1 mediate pancreatic tumor cell invasion through upregulation of the plasminogen/plasmin system.

Tumor-associated proteases and inhibitors in gastric cancer: analysis of prognostic impact and individual risk protease patterns

Expression of proteolytic parameters of the urokinase-type plasminogen activator (uPA) system [uPA receptor (uPA-R), plasminogen activator inhibitor (PAI)-1] has been proven to be an independent prognostic parameter in cancer. However, it has not been considered that the uPA system is interacting with several other protease/inhibitor systems, neither has a comparable prognostic role of these factors been investigated. Moreover, studies evaluating specific protease patterns indicating high individual risk are missing completely. Therefore, in a consecutive prospective series of 203 gastric cancer patients, the expression of activators (plasminogen, tPA, MMP-2, cathepsin D, antithrombin 3) and inhibitors (alpha-2-antiplasmin, alpha-2-macroglobulin, alpha-1-antitrypsin, alpha-1-antichymotrypsin) of proteolysis was studied immunohistochemically in the tumor epithelium semiquantitatively (score 0-3) in addition to the uPA system. Kaplan-Meier analysis (median time of follow-up 31 months) revealed a significant association of cathepsin D (P=0.0042), alpha-2-macroglobulin (P=0.0281) and antitrypsin (P=0.0372) with disease-free survival and of cathepsin D (P=0.0018), antitrypsin (P=0.0112) and antichymotrypsin (P=0.0002) with overall survival. Multivariate Cox analysis performed to correct these results for relative impact of the uPA system and established prognostic factors showed PAI-1 (disease-free survival: P=0.002, relative risk 1.86; overall survival: P=0.005, relative risk 1.39), pT and pN as independent parameters. Cathepsin D was shown to have an independent impact on disease-free survival (P=0.020, relative risk 2.98). Comparative chi-square analysis of cases with poor and good prognoses revealed that in patients with good clinical outcome, inhibitors of proteolysis are correlated significantly, whereas in patients with poor prognosis activators of proteolysis are significantly associated preferentially and significant correlations with the uPA-R are dominant. For detailed pattern analysis, stepwise overall Kaplan-Meier analyses were performed in subgroups of high uPA-R-, uPA-, PAI1- and cathepsin D expression for two additional proteases each. From these analyses, the combination of high (score 2/3) expression of uPA-R, PAI-1, antichymotrypsin and alpha-2-macroglobulin was identified as a high-risk pattern, representing parameters known to be essential for uPA-R internalization and recycling. This suggests some of the uPA-associated proteases and inhibitors investigated as univariate prognostic parameters in gastric cancer. Cathepsin D is a new independent parameter for disease-free survival. The study further demonstrates that a protease pattern promoting uPA-R recycling in tumor cells especially indicates high individual risk tumors in gastric cancer.

Prognostic factors in gastric cancer

BACKGROUND

Despite gastric cancer being common, its prognosis has not been improved significantly in recent years. Now, greater insight has been gained into the biological properties of tumour cells, how they become malignant and what mechanisms they may use to invade and metastasize. This involves tumour-associated protease systems, loss or mutation of adhesion molecules and changes in genetics. The view of gastric cancer is changing: it is not only a solid tumour but also exhibits a minimal residual disease component even in the early stages of disease. Such biological tumour characteristics may provide new prognostic factors and also potential new therapeutic options.

METHODS

This is an update of prognostic factors in gastric cancer, emphasizing new biological features, some of which have been investigated by this group over the past few years. Current results are discussed in the light of 212 references obtained from the Medline database from 1979 to 1997.

RESULTS

There is high probability that some of the factors reviewed, such as c-erbB-2, individual course and phenotyping of disseminated tumour cells will become significant new prognostic variables. This is true also, to a lesser extent, of cathepsin D, matrix metalloproteinase 2 combined with activators or tissue inhibitor of metalloproteinases 2, CD44, E-cadherin, p53 and cripto. Plasminogen activator inhibitor 1 (PAI-1), a member of the urokinase-type plasminogen activator (uPA) system, can already be defined as an established new prognostic factor in gastric cancer.

CONCLUSION

PAI-1 should be considered prognostically in addition to established tumour classifications. Moreover, the uPA system is a target for future therapeutic concepts. Further analysis of factors describing tumour biology should lead to new, functionally orientated, tumour classifications in gastric cancer.

In vitro regulation of pericellular proteolysis in prostatic tumor cells treated with bombesin

Bombesin is a potent inducer of signal trasduction pathways involved in the proliferation and invasion of androgen-insensitive prostatic tumor cells. This study examines the bombesin-mediated modulation of pericellular proteolysis, monitoring cell capability to migrate and invade basement membranes, using a chemo-invasion assay and analyzing protease production. The results suggest that bombesin could modulate the invasive potential of prostatic cell lines regulating secretion and cell-surface uptake of uPA and MMP-9 activation. In fact, in PC3 and DU145 cells but not in LNCaP cells, urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor-1 (PAI-1) are induced by bombesin treatment. Bombesin also stimulates cell proliferation and this effect can be inhibited blocking uPA by antibodies and/or uPA inhibitor p-aminobenzamidine. Moreover, HMW-uPA induces cell proliferation in LNCaP cells, which do not produce uPA in the basal conditions, while PC3 and DU145 cell growth is supported by autocrine production of uPA. The increment of uPA activity on the external plasma membrane causes an increased pericellular plasmin activation. This effect is inhibited by antibodies against uPA and by p-aminobenzamidine. Similarly to EGF, bombesin stimulates secretion and activation of MMP-9 and TIMP-1 production. MMP-9 activation can be also obtained by HMW-uPA treatment, suggesting that plasma-membrane-bound uPA can start a proteolytic cascade involving MMP-9. Therefore, in in vitro assays, bombesin is able to modulate pericellular proteolysis and cell proliferation, differently distributing and activating proteolytic activities. This effect can be related to the "non-random" degradation of the extracellular matrix in which membrane uPA-uPAreceptor complexes could start bombesin-induced directional protein degradation during metastatic spread.

Agonistic monoclonal antibodies against the Met receptor dissect the biological responses to HGF

Hepatocyte growth factor, also known as scatter factor, is a pleiotropic cytokine, which stimulates cell motility, invasion, proliferation, survival and morphogenesis, and induces the expression of specific genes by activating its receptor tyrosine kinase. In this work we have isolated, characterized and used as agonists two monoclonal antibodies (mAbs) directed against the extracellular domain of HGF receptor to investigate the requirements for receptor activation and for the different biological responses. The two mAbs display similar affinities, react with epitopes different from the hepatocyte growth factor binding site, and behave as either full or partial agonists. The full agonist mAb (DO-24) triggers all the biological effects elicited by hepatocyte growth factor, namely motility, proliferation, cell survival, invasion, tubulogenesis and angiogenesis. The partial agonist mAb (DN-30) induces only motility. Only the full agonist mAb is able to induce and sustain the expression of urokinase-type plasminogen activator receptor for prolonged periods of time, while both mAbs up-regulate the constitutive expression of urokinase-type plasminogen activator. Both mAbs activate receptor phosphorylation, which, being strictly dependent on mAb bivalence, requires receptor dimerization. Since simple receptor dimerization is not sufficient to trigger full biological responses, we propose that the region on the ss chain of the receptor recognized by the full agonist mAb is crucial for optimal receptor activation.

The Jak/Stat pathway and urokinase receptor signaling in human aortic vascular smooth muscle cells

The binding of urokinase plasminogen activator (uPA) to its specific receptor (uPAR) facilitates migration of vascular smooth muscle cells (VSMC). However, the signaling cascade utilized by the urokinase receptor is only incompletely understood. We investigated intracellular uPA/uPAR signaling in human aortic VSMC from the cell membrane to the nucleus. uPA binding to VSMC induced a rapid and pronounced increase in tyrosine phosphorylation of several proteins with molecular masses of 53-60, 85-90, and 130-140 kDa. By using co-immunoprecipitation techniques and in vitro kinase assays, the uPAR-associated proteins were identified as Janus (Jak) and Src non-receptor protein-tyrosine kinases (PTK) Jak1, Tyk2, and p59(fyn), p53/56(lyn), p53/59(hck), and p55(fgr). Furthermore, uPA induced a time-dependent reversible translocation of the Stat1 (signal transducer and activator of transcription) protein to the VSMC nuclei, as shown by confocal microscopy studies. Using an electrophoretic mobility shift assay, we then demonstrated that Stat1 is rapidly activated in response to stimulation with uPA and specifically binds to the DNA regulatory elements GAS (interferon-gamma activation site) and ISRE (interferon-stimulated response element). Mobility supershift experiments confirmed DNA-protein complexes containing Stat1 protein. Migration experiments with double immunofluorescence staining revealed polarization of uPAR, and colocalization with Jak1 and Tyk2 to the leading edge of the migrating cells. Under the same conditions, Jak2, Jak3, and the Src-PTKs remained randomly distributed over the entire body of the cells. Our studies therefore suggest that, in VSMC, the uPAR-signaling complex utilizes at least two different mechanisms, a direct signaling pathway utilizing the Jak/Stat cascade and a second signal transduction mechanism via Src-like protein-tyrosine kinases. uPA-induced signaling via Jak/Stat is most likely involved in the regulation of cell migration, while the functional purpose of the uPA-associated Src-PTK activation remains to be elucidated.

Transforming growth factor beta 1 and sodium butyrate differentially modulate urokinase plasminogen activator and plasminogen activator inhibitor-1 in human breast normal and cancer cells

The effects of transforming growth factor beta 1 (TGF-beta1) and sodium butyrate on cell proliferation and the urokinase plasminogen activator (uPA) system were examined in normal human breast epithelial cells (HBECs) and in a breast cancer cell line, MDA-MB-231. In HBECs, TGF-beta1 inhibited cell proliferation and uPA activity, while it augmented plasminogen activator inhibitor-1 (PAI-1) antigen level. Sodium butyrate inhibited both cell proliferation and uPA activity but did not affect the level of PAI-1. In MDA-MB-231, TGF-beta1 had no effect on cell proliferation but increased uPA activity and PAI-1 antigen level; sodium butyrate inhibited both cell proliferation and uPA activity but had no effect on PAI-1 level. Moreover, in the presence of plasminogen, cell detachment could be modulated by the level of cell-associated uPA. Our results indicate (1) that the effects of TGF-beta1 on cell growth can be dissociated from its effects on the uPA/PAI system; (2) that, while TGF-beta1 is a potent inhibitor of cell proliferation and uPA activity in normal cells, it may promote invasion and metastasis of tumour cells by increasing uPA activity and PAI-1 levels; and (3) that sodium butyrate offers a potential approach to preventing tumour development by inhibiting both cell proliferation and invasion.

Inhibition of establishment of primary and micrometastatic tumors by a urokinase plasminogen activator receptor antagonist

Tumor establishment and metastasis are dependent on extracellular matrix proteolysis, tumor cell migration, and angiogenesis. Urokinase plasminogen activator (uPA) and its receptor are essential mediators of these processes. The purpose of this study was to investigate the effect of a recombinant human uPAR antagonist on growth, establishment, and metastasis of tumors derived from human cancer cell lines. A noncatalytic recombinant protein, consisting of amino acids 1-137 of human uPA and the CH2 and CH3 regions of mouse IgG1 (uPA-IgG), was expressed, purified, and shown to bind specifically to human uPAR and to saturate the surface of human tumor cells which express uPAR. Daily i.p. administration of uPA-IgG to nude mice extended latencies of unstaged tumors derived from Lox melanoma and SW48 colon carcinoma cells by 7.7 and 5.5 days, respectively. uPA-IgG treatment did not affect the growth of Lox or KB tumors staged to 200 mg before antagonist treatment commenced. The effect of uPA-IgG on the establishment of micrometastases was assessed in SCID mice. KB head/neck tumor cells were injected in the tail vein and allowed to seed for 48 h before initiation of daily i.p. injections of uPA-IgG for 24 days. The number of lung colonies ranged between 5 and 30% of vehicle-treated mice in two separate experiments. Furthermore, a single 800 microg dose of uPA-IgG administered 1 h prior to tail vein injection of KB cells reduced lung colony formation to just 3.5% of vehicle-treated SCID mice. These data demonstrate that antagonism of uPAR arrested metastasis and inhibited the establishment of primary tumors and micrometastases. Thus, small molecule uPAR antagonists may serve as useful adjuvant agents in combination with existing cancer chemotherapy.

Tumor-associated proteases and inhibitors in gastric cancer: analysis of prognostic impact and individual risk protease patterns

Expression of proteolytic parameters of the urokinase-type plasminogen activator (uPA) system [uPA receptor (uPA-R), plasminogen activator inhibitor (PAI)-1] has been proven to be an independent prognostic parameter in cancer. However, it has not been considered that the uPA system is interacting with several other protease/inhibitor systems, neither has a comparable prognostic role of these factors been investigated. Moreover, studies evaluating specific protease patterns indicating high individual risk are missing completely. Therefore, in a consecutive prospective series of 203 gastric cancer patients, the expression of activators (plasminogen, tPA, MMP-2, cathepsin D, antithrombin 3) and inhibitors (alpha-2-antiplasmin, alpha-2-macroglobulin, alpha-1-antitrypsin, alpha-1-antichymotrypsin) of proteolysis was studied immunohistochemically in the tumor epithelium semiquantitatively (score 0-3) in addition to the uPA system. Kaplan-Meier analysis (median time of follow-up 31 months) revealed a significant association of cathepsin D (P=0.0042), alpha-2-macroglobulin (P=0.0281) and antitrypsin (P=0.0372) with disease-free survival and of cathepsin D (P=0.0018), antitrypsin (P=0.0112) and antichymotrypsin (P=0.0002) with overall survival. Multivariate Cox analysis performed to correct these results for relative impact of the uPA system and established prognostic factors showed PAI-1 (disease-free survival: P=0.002, relative risk 1.86; overall survival: P=0.005, relative risk 1.39), pT and pN as independent parameters. Cathepsin D was shown to have an independent impact on disease-free survival (P=0.020, relative risk 2.98). Comparative chi-square analysis of cases with poor and good prognoses revealed that in patients with good clinical outcome, inhibitors of proteolysis are correlated significantly, whereas in patients with poor prognosis activators of proteolysis are significantly associated preferentially and significant correlations with the uPA-R are dominant. For detailed pattern analysis, stepwise overall Kaplan-Meier analyses were performed in subgroups of high uPA-R-, uPA-, PAI1- and cathepsin D expression for two additional proteases each. From these analyses, the combination of high (score 2/3) expression of uPA-R, PAI-1, antichymotrypsin and alpha-2-macroglobulin was identified as a high-risk pattern, representing parameters known to be essential for uPA-R internalization and recycling. This suggests some of the uPA-associated proteases and inhibitors investigated as univariate prognostic parameters in gastric cancer. Cathepsin D is a new independent parameter for disease-free survival. The study further demonstrates that a protease pattern promoting uPA-R recycling in tumor cells especially indicates high individual risk tumors in gastric cancer.

Regulation of the uPAR/uPA system expressed on monocytes by the deactivating cytokines, IL-4, IL-10 and IL-13: consequences on cell adhesion to vitronectin and fibrinogen

Urokinase (uPA) and its receptor (uPAR) have been proposed to be involved in monocyte migration by inducing degradation of matrix proteins. In addition, uPAR is also implicated in cell adhesion to the vascular wall. The adhesive function of uPAR depends on a direct interaction with vitronectin which is increased by uPA and by modification of cell surface integrin (such as CD11b-CD18) when associated to uPAR. In this study we analysed the role of three deactivating cytokines, IL-4, IL-10 and IL-13, on the surface expression of uPA, uPAR and CD11b by monocytes and their consequences on monocyte adhesion to immobilized fibrinogen and vitronectin. IL-10 induced a decrease in uPA and CD11b after 18 h incubation and a delayed decrease in uPAR which was only significant after 48 h incubation. These results may explain the decrease in monocyte adhesion, which was observed after an 18 h incubation with IL-10, on immobilized vitronectin and fibrinogen. In contrast, IL-4 and IL-13 induced a decrease in uPAR after 18 h and a significant increase in uPA both in the cell lysates and at the cell surface, as well as an increase in cell surface associated CD11b. These cytokines did not modify cell adhesiveness to vitronectin or fibrinogen despite the increase in CD11b-CD18. This could be due to the decrease in uPAR because CD11b-CD18/uPAR forms a cell adhesion complex. In addition, the increase in uPA induced by IL-4 could counterbalance the direct interaction of uPAR with vitronectin. The increase in uPA suggests that IL-4 and IL-13 could induce plaque fissuring by monocytes, whereas IL-10 may induce protection against matrix protein degradation by decreasing uPA.

The migration of purified osteoclasts through collagen is inhibited by matrix metalloproteinase inhibitors

The most obvious proteolytic event controlled by the osteoclast is bone matrix removal in the resorption compartment. Here, however, we investigated whether matrix metalloproteinase (MMP) activity of the osteoclast might be involved in its migration to its future bone resorption site. We seeded either nonpurified or purified osteoclasts onto either uncoated or collagen-coated dentine slices and cultured them in the presence or absence of specific MMP inhibitors. When nonpurified osteoclasts were cultured on uncoated dentine, MMP inhibitors did not prevent pit formation, as previously reported. However, when collagen-coated dentine was used, pit formation was strongly inhibited by MMP inhibitors. The same results were obtained when performing these experiments with purified osteoclasts, thus demonstrating the ability of osteoclasts by themselves to migrate through collagen via an MMP-dependent pathway. This demonstration was confirmed by using collagen-coated invasion chambers. In addition, the invasions were not, or only slightly, inhibited by inhibitors of serine proteinases, cysteine proteinases, and carbonic anhydrase, though the latter two are well established bone resorption inhibitors that strongly inhibited pit formation. It is concluded that osteoclasts can migrate through collagen in the absence of other cells and that this migration relies on MMP activity, whereas other enzymes typically required for bone removal in the resorption compartment are not essential for migration. Some of the osteoclast MMPs might thus be relevant to the migratory/invasive activity of the osteoclast, rather than to its bone resorptive activity itself.

Plasminogen activator inhibitor type 2 is expressed in keratinocytes during re-epithelialization of epidermal defects

Plasminogen activation is observed in the human epidermis during re-epithelialization of epidermal defects. The activation reaction depends on plasminogen activators (PAs) associated with re-epithelializing keratinocytes. PA inhibitor type 2 (PAI-2) is thought to be a major epidermal PA inhibitor in keratinocytes. However, no data are available on the expression of PAI-2 in keratinocytes during epidermal regeneration. We have therefore analysed PAI-2 at the mRNA and protein level in keratinocyte cultures as well as in epidermal lesions in which re-epithelializing keratinocytes were apparent. We found that PAI-2 expression at the mRNA and protein level was negatively correlated with the cell density in regular keratinocyte cultures. In organotypic cocultures, in which the transition from a re-epithelializing to a sedentary phenotype can be studied, PAI-2 was most strongly expressed in early cultures prior to formation of a differentiated epidermis-like structure. We found a strong expression of PAI-2 in keratinocytes that re-epithelialized dermal burn wounds or lesions caused by the autoimmune blistering disease pemphigus vulgaris. Our results suggest that not only PAs, but also a major PA inhibitor, PAI-2, are expressed in keratinocytes that are actively involved in re-epithelialization.

Tissue-specific expression of the relaxed conformation of plasminogen activator inhibitor-2 and low-density lipoprotein receptor-related protein in human term gestational tissues

The relaxed conformation of plasminogen activator inhibitor-2 (PAIr) is formed during inactivation of the matrix-degrading enzyme urokinase plasminogen activator (uPA). The presence of PAIr in tissues, therefore, indicates the in situ inhibition of uPA-mediated proteolysis. In addition, PAIr functions as a ligand for the clearance receptor low-density lipoprotein receptor-related protein (LRP), thereby promoting internalization of receptor-bound uPA-PAIr complexes from the cell surface. The rapid internalization of receptor-bound, inactivated uPA has been suggested to be characteristic of invasive cell phenotypes. The aims of this study were to characterize the immunohistochemical localization of PAIr in human term gestational tissues (amnion, choriodecidua, and placenta) and to establish its co-expression with other components of the uPA cascade. The results obtained indicate that PAIr immunoreactivity was exclusively localized to amnion epithelial cells, with only minimal staining in the underlying chorion. PAIr immunoreactivity was not detectable in any of the trophoblastic tissues examined (villous and extravillous). The tissue-specific expression of PAIr immunoreactivity was not significantly altered in association with labor onset. uPA and PAI-2 staining was localized predominantly to amnion epithelial cells, underlying chorion, and trophoblast cells of villous and extravillous tissue. Amnion and trophoblasts of extravillous and chorionic tissue showed uPAR immunoreactivity, whereas staining in placenta was absent. Immunoreactive LRP was confined to trophoblasts of the chorion, and the villous and extravillous tissue. For the first time, localization of PAIr at the tissue level has been identified. The data obtained are consistent with the hypothesis that cells of invasive phenotype, although expressing all components of the uPA cascade, do not accumulate immunoreactive PAIr, because it is rapidly internalized from the cell surface. Conversely, cells of noninvasive phenotype will accumulate PAIr immunoreactivity only in the absence of LRP expression. We propose that the presence of PAIr and the absence of LRP at the cell surface are putative markers of noninvasive phenotypes.

Clinical value of extended biologic staging by bone marrow micrometastases and tumor-associated proteases in gastric cancer

OBJECTIVE

To investigate whether extended staging, including biologic grading and aspects of an early systemic disease component, would give additional prognostic information on patients with curatively resected gastric cancer.

BACKGROUND

Tumor-associated proteolytic mechanisms have been shown to be essential for invasion and metastasis. The urokinase-type plasminogen activator (uPA) system is of major biologic impact, but different interactive proteases and inhibitors with modulating effects also must be considered. The detection of early tumor cell dissemination indicates the systemic character of a primarily local gastric cancer. The confrontation of the organism with these cells determines the often unpredictable course of an individual tumor after presumed curative primary treatment.

METHODS

In a prospective study of 247 consecutive patients with gastric cancer, detection of disseminated tumor cells in bone marrow aspirates was immunocytochemically performed in 180 patients. The expression of uPA, activators of uPA (cathepsin D, antithrombin III), uPA substrates (plasminogen, matrix-metalloproteinase 2 [collagenase IV, 72 kD; MMP-2]), uPA/plasmin inhibitors (plasminogen activator inhibitor type 1 and 2 [PAI-1, PAI-2], alpha1-antitrypsin, alpha2-antiplasmin), uPA receptor (uPA-R), and parameters of the uPA-R cycle (alpha2-macroglobulin, alpha1-antichymotrypsin) could be determined immunohistochemically and were scored semiquantitatively in 203 patients. Kaplan-Meier statistical techniques and multivariate Cox regression models were used for prognostic analyses.

RESULTS

In multivariate analysis considering all the established risk factors, disease-free survival was independently predicted by PAI-1 (relative risk 2.21, 1.32-3.73) and cathepsin D (relative risk 2.98, 1.28-6.91) besides pT, pN, and extended resection. Tumor cell dissemination was found to be an additional prognostic factor in early tumor stages (pT1, T2) and lymphnode-negative patients. Stepwise regression analysis revealed an extended staging system with new risk groups. Node-positive, curatively resected pT1/2 patients with low expression of PAI-1 had a favorable prognosis (mean recurrence-free survival [MRT] 54.84 months), similar to that of node-negative patients (MRT 54.76 months). In node-negative, curatively resected pT1/2 patients, detection of bone marrow tumor cells and high expression of PAI-1 defined a subgroup with a steep decrease of prognosis (MRT 36.60 months), which was worse than that of node-positive patients (MRT 45.81).

CONCLUSION

This new staging model gives better prognostic differentiation of subgroups, which should be considered in future adjuvant therapy protocols. In addition, it indicates that the uPA system might be a future therapeutic target.

Regulation of urokinase expression in the developing avian heart: a role for the Ets-2 transcription factor

During heart development, cells of the endocardial cushions undergo an epithelial-mesenchymal transformation and migrate into the surrounding extracellular matrix. This event is required for the normal formation of valves and chamber septation. Coincident with this phenotypic change is the expression of the serine protease urokinase by the mesenchymal cells. This protease plays an important role in remodeling of the matrix, promotion of cell migration by regulating cell-matrix interactions, and the activation of growth factors. To understand the mechanisms underlying the expression of urokinase during heart development, studies were designed to analyze the role of the Ets transcription factors in the regulation of the avian urokinase gene promoter. Deletion or mutagenesis of the Ets consensus sites significantly decreased the activity of the promoter in isolated cushion tissue cells. Proteins were identified by electrophoretic mobility shift analysis and UV-crosslinking which bound to a specific region of the promoter shown to be required for full transcriptional activity. Analyses based upon protein molecular weight and interaction with specific antibodies suggest a role for the Ets-2 protein in promoter binding and activity. The expression of Ets-2 in the cushion tissue cells was confirmed by RT-PCR analysis and in situ hybridization. The mRNA levels and the DNA binding activity of the Ets-2 protein were found to change during development paralleling the increase in urokinase activity. Overexpression of the full-length Ets-2 protein or a dominant-negative form of the protein altered the activity of the promoter and significantly affected the production of urokinase in these cells. The results from these studies suggest an important role for the Ets-2 protein in heart development and may contribute to a better understanding of the inductive factors present in the heart which facilitate the normal morphogenesis of this organ.

Induction of vascular SMC proliferation by urokinase indicates a novel mechanism of action in vasoproliferative disorders

The urokinase-type plasminogen activator (UPA) and its receptor are expressed in the vasculature and are involved in cell migration and remodeling of the extracellular matrix in the neointima. Vessels with atherosclerosis or neointimal hyperplasia, when compared with normal vessels, contain high UPA activity as well as increased levels of UPA receptor. In this study, we have identified the stimulation of vascular smooth muscle cell proliferation as a novel activity for UPA in the vessel wall. High-molecular-weight-UPA (12-200 nmol/L range) stimulated DNA synthesis and cell proliferation, which was half that induced by fetal calf serum or by platelet-derived growth factor-BB. UPA did not induce growth of endothelial cells, and tissue-type plasminogen activator showed no activity on either cell type. Induction of proliferation required the complete UPA molecule but was independent of the proteolytic activity of UPA, whereas neither the amino-terminal fragment nor the catalytic domain by itself was mitogenic. UPA also stimulated c-fos/c-myc mRNA expression and mitogen-activated protein kinase activity in smooth muscle cells. Blocking monoclonal antibodies against the UPA receptor and the enzymatic removal of receptors were ineffective in inhibiting the mitogenic effect of UPA, suggesting a UPA receptor-independent mechanism. Thus, we provide evidence for a novel function of UPA on vascular smooth muscle cell proliferation that, together with its previously documented involvement in regulating pericellular proteolysis-related events and cell migration, provides additional evidence for a role in the pathogenesis of atherosclerosis/restenosis.

Production and activation of matrix metalloprotease-9 (MMP-9) by HL-60 promyelocytic leukemia cells

Human promyelocytic HL-60 cells have been used as a model of acute leukemia to investigate the expression and the regulation of matrix metalloproteases (MMPs), known to contribute to the degradation of extracellular matrix components. As shown by gelatin zymography, HL-60 cells constitutively released significant amounts of proMMP-9 (92 kDa) and moderate amounts of proMMP-2 (72 kDa). Furthermore, casein zymography confirmed the presence of serine proteases in the form of pro-urokinase. Activation of proMMP-9 was dependent on the plasminogen activator/plasmin (PA/plasmin) system and was inhibited by aprotinin. MMP-9 was only detected in cellular extracts or conditioned media incubated with HL-60 cells, indicating that cells are essential to the activation process. Addition of plasminogen increased by 3-fold the basal invasive rate of these cells across a matrigel layer (2.1% versus 0.7% in control cells after 4 h of incubation). Taken together, these results indicate that HL-60 cells exhibit an autocrine activation mechanism of proMMP-9 via the PA/plasmin system and that activation of proMMP-9 increases their invasive potential.

Induction in human osteoblastic cells (SaOS2) of the early response genes fos, jun, and myc by the amino terminal fragment (ATF) of urokinase

Previous studies have demonstrated that overexpression of urinary plasminogen activator (uPA) in rat prostate cancer cells results in increased skeletal metastases, which are primarily of the osteoblastic variety. The osseous activation induced by the metastases appears to be mediated through the amino terminal fragment (ATF) of uPA, which lacks the catalytic domain and can act as a growth factor for osteoblasts. To explore further the mechanism of action of uPA in bone cells, we evaluated the effects of ATF on modulating the expression of various proto-oncogenes. Human-osteoblast-derived osteosarcoma cells, SaOS2, were treated with graded doses of ATF for 10-120 min, and effects on early response proto-oncogenes were monitored. ATF increased c-myc, c-jun, and c-fos gene expression in a time-dependent manner for up to 60 min, after which mRNA levels fell. The maximum induction was seen in c-fos gene expression, which was found to be dose dependent. This effect of ATF was localized to its growth-factorlike domain. Examination of the half life of these transcripts in the presence of the transcriptional inhibitor actinomycin D demonstrated that ATF does not alter the stability of c-fos mRNA in these bone cells. Nuclear run-off assays indicated that ATF effects were due to stimulation of c-fos gene transcription. An increase in c-fos protein levels was correlated with the augmentation of its mRNA in ATF-treated SaOS2 cells. Pretreatment of SaOS2 cells with the protein tyrosine kinase inhibitor herbimycin and recombinant soluble uPA receptor (uPAR) caused a significant reduction in the ability of ATF to induce c-fos expression. These results demonstrate a novel role for uPA in activating early response proto-oncogenes, in particular c-fos, which plays an important role in bone cell growth and differentiation and may be a key factor in the signal transduction pathway of ATF.

Thrombospondin-1 and transforming growth factor-beta l promote breast tumor cell invasion through up-regulation of the plasminogen/plasmin system

BACKGROUND

Pericellular proteolysis is crucial in tumor cell invasion. The plasminogen/plasmin system is one of the main protease systems involved in cancer progression. Thrombospondin-1 (TSP-1), through activation of transforming growth factor-beta 1 (TGF-beta 1), up-regulates the main plasminogen activator, the urokinase-type plasminogen activator (uPA). The objectives of this study were to determine the role of TSP-1 and TGF-beta 1 in the localization of the plasminogen/plasmin system to the tumor cell surface by the uPA receptor (uPAR) and to determine its effect in breast tumor cell invasion.

METHODS

The effect of TSP-1 and TGF-beta 1 in uPAR expression was determined in MDA-MB-231 human breast cancer cells by enzyme-linked immunosorbent assay and Western blot analysis. Their effect and the role of the plasminogen/plasmin system in breast tumor cell invasion were studied with a Boyden Chamber assay.

RESULTS

uPAR expression was up-regulated more than twofold by both TSP-1 and TGF-beta 1. The effect of TSP-1 involved its receptor and the activation of TGF-beta 1 by TSP-1. Breast tumor cell invasion was up-regulated sevenfold to eightfold by both TSP-1 and TGF-beta 1 compared with the control group. Antibodies against uPA or uPAR neutralized the TSP-1- and TGF-beta 1-promoted breast tumor cell invasion.

CONCLUSIONS

TSP-1, through the activation of endogenous TGF-beta 1, up-regulates the plasminogen/plasmin system and promotes tumor cell invasion in breast cancer cells.

An immunohistochemical assessment of cathepsin D in gastric carcinoma: its impact on clinical prognosis

BACKGROUND

In the context of tumor-associated proteolysis, the prognostic value of cathepsin D in breast carcinoma has been studied but its role is controversial in relation to gastrointestinal carcinoma. The aim of the current study was to determine whether cathepsin D is a prognostic parameter for gastric carcinoma, and also to consider interaction with the urokinase-plasminogen activator (uPA) system as an established risk factor for tumor-associated proteolysis.

METHODS

In a consecutive prospective series of 203 gastric carcinoma patients, expression of cathepsin D in tumor cells was semiquantitatively analyzed with immunohistochemistry (scored 0-3). Median follow-up time was 31 months (range, 9-56 months). Kaplan-Meier (log rank) and multivariate Cox analyses were used to analyze survival.

RESULTS

Kaplan-Meier analysis (log rank statistics) revealed significant association of increasing cathepsin D detection with poorer disease free survival (P = 0.0042) and poorer overall survival (P = 0.0018) of curatively resected patients. Overall survival of all patients was not significantly correlated. Multivariate analysis of established risk factors for gastric carcinoma, including the uPA system, identified cathepsin D as a new and independent prognostic parameter for disease free survival (P = 0.020; relative risk, 2.98; 95% confidence interval, 1.28-6.91). Plasminogen activator inhibitor type-1 as a representative of the uPA system was confirmed as a strong independent factor for disease free and overall survival. Chi-square analysis showed significant correlation of higher cathepsin D levels with Laurén's diffuse-type carcinomas and strong evidence of uPA receptor in tumor cells. However, a subgroup analysis performed according to Laurén's classification revealed a univariate prognostic impact of cathepsin D on both diffuse and intestinal types without independent value. For patients with high levels of uPA receptor (scores of 2 and 3, n = 132), a highly significant association of increasing evidence of cathepsin D with disease free survival (P < 0.0001) and overall survival (P < 0.0001) was observed for curatively resected patients. Significant association with survival was also observed for all patients (P = 0.0407).

CONCLUSIONS

Cathepsin D is a new functional prognostic parameter for gastric carcinoma patients with independent value for disease free survival. Moreover, this study indicates that consideration of more than one tumor-associated protease could lead to a more individualized estimation of risk for carcinoma patients.

Plasmin and plasminogen activator inhibitor type 1 promote cellular motility by regulating the interaction between the urokinase receptor and vitronectin

The urokinase receptor (uPAR) coordinates plasmin-mediated cell-surface proteolysis and promotes cellular adhesion via a binding site for vitronectin on uPAR. Because vitronectin also binds plasminogen activator inhibitor type 1 (PAI-1), and plasmin cleavage of vitronectin reduces PAI-1 binding, we explored the effects of plasmin and PAI-1 on the interaction between uPAR and vitronectin. PAI-1 blocked cellular binding of and adhesion to vitronectin by over 80% (IC50 approximately 5 nM), promoted detachment of uPAR-bearing cells from vitronectin, and increased cellular migration on vitronectin. Limited cleavage of vitronectin by plasmin also abolished cellular binding and adhesion and induced cellular detachment. A series of peptides surrounding a plasmin cleavage site (arginine 361) near the carboxy-terminal end of vitronectin were synthesized. Two peptides spanning res 364-380 blocked binding of uPAR to vitronectin (IC50 approximately 8-25 microM) identifying this region as an important site of uPAR-vitronectin interaction. These data illuminate a complex regulatory scheme for uPAR-dependent cellular adhesion to vitronectin: Active urokinase promotes adhesion and also subsequent detachment through activation of plasmin or complex formation with PAI-1. Excess PAI-1 may also promote migration by blocking cellular adhesion and/or promoting detachment, possibly accounting in part for the strong correlation between PAI-1 expression and tumor cell metastasis.

Constitutive activation of NF-kappaB during progression of breast cancer to hormone-independent growth

Breast cancers often progress from a hormone-dependent, nonmetastatic, antiestrogen-sensitive phenotype to a hormone-independent, antiestrogen- and chemotherapy-resistant phenotype with highly invasive and metastatic growth properties. This progression is usually accompanied by altered function of the estrogen receptor (ER) or outgrowth of ER-negative cancer cells. To understand the molecular mechanisms responsible for metastatic growth of ER-negative breast cancers, the activities of the transcription factor NF-kappaB (which modulates the expression of genes involved in cell proliferation, differentiation, apoptosis, and metastasis) were compared in ER-positive (MCF-7 and T47-D) and ER-negative (MDA-MB-231 and MDA-MB-435) human breast cancer cell lines. NF-kappaB, which is usually maintained in an inactive state by protein-protein interaction with inhibitor IkappaBs, was found to be constitutively active in ER-negative breast cancer cell lines. Constitutive DNA binding of NF-kappaB was also observed with extracts from ER-negative, poorly differentiated primary breast tumors. Progression of the rat mammary carcinoma cell line RM22-F5 from an ER-positive, nonmalignant phenotype (E phenotype) to an ER-negative, malignant phenotype (F phenotype) was also accompanied by constitutive activation of NF-kappaB. Analysis of individual subunits of NF-kappaB revealed that all ER-negative cell lines, including RM22-F5 cells of F phenotype, contain a unique 37-kDa protein which is antigenically related to the RelA subunit. Cell-type-specific differences in IkappaB alpha, -beta, and -gamma were also observed. In transient-transfection experiments, constitutive activity of an NF-kappaB-dependent promoter was observed in MDA-MB-231 and RM22-F5 cells of F phenotype, and this activity was efficiently repressed by cotransfected ER. Since ER inhibits the constitutive as well as inducible activation function of NF-kappaB in a dose-dependent manner, we propose that breast cancers that lack functional ER overexpress NF-kappaB-regulated genes. Furthermore, since recent data indicate that NF-kappaB protects cells from tumor necrosis factor alpha-, ionizing radiation-, and chemotherapeutic agent daunorubicin-mediated apoptosis, our results provide an explanation for chemotherapeutic resistance in ER-negative breast cancers.

Urokinase and the urokinase receptor: association with in vitro invasiveness of human bladder cancer cell lines

BACKGROUND AND PURPOSE

The plasminogen activators urokinase and tissue plasminogen activator are enzymes that degrade proteins in tissue basement membranes and the extracellular matrix (a biomolecular complex surrounding individual cells in tissues that serves as a barrier between the cells and the vascular and lymph systems). The action of these enzymes allows tumor cells to escape their local environment and metastasize. Plasminogen activator activity can be influenced by the urokinase receptor, which is expressed on the surface of cells, and by the plasminogen activator inhibitors 1 and 2. Because bladder tumors differ in their propensity to invade local areas and distant sites, we studied the expression of both plasminogen activators, the two plasminogen activator inhibitors, and the urokinase receptor in four human bladder cancer cell lines (RT4, 253J, EJ, and T24) to see if there was an association between the expression of these proteins and tumor cell invasiveness in vitro.

METHODS

The expression of urokinase, tissue plasminogen activator, and the two inhibitors was measured by enzyme-linked immunosorbent assays of serum-free, cell-conditioned media (i.e., culture fluids). Cell surface expression of the urokinase receptor was assayed by flow cytometry, using an anti-receptor monoclonal antibody (Mab3936). The invasive capacity of untreated cells and of cells exposed to exogenous, high-molecular-weight urokinase was analyzed by use of Matrigel invasion chambers.

RESULTS

The four bladder cancer cell lines demonstrated differential expression of both plasminogen activators and both inhibitors; three of the cell lines (T24, EJ, and 253J) expressed the urokinase receptor. The four cell lines differed in their invasive potential in vitro. Neither expression of tissue plasminogen activator nor production of the inhibitors appeared to influence Matrigel invasion. EJ cells and 253J cells produced the highest levels of urokinase and demonstrated the greatest propensity for invasion; T24 cells, which produced only small amounts of urokinase, exhibited a low invasive potential. Pretreatment of T24 cells with exogenous high-molecular-weight urokinase markedly increased their invasiveness. Similar pretreatment of EJ and 253J cells increased their invasiveness as well. RT4 cells, which lacked urokinase receptor expression but produced moderate amounts of urokinase, were not invasive and did not become so after exposure to exogenous high-molecular-weight urokinase. Binding of Mab3936 to urokinase receptors inhibited Matrigel invasion.

CONCLUSIONS

To our knowledge, this is the first study demonstrating that bladder tumor cells express the urokinase receptor and that both receptor expression and urokinase expression are required for bladder tumor cell invasion in vitro.

Reduction in surface urokinase receptor forces malignant cells into a protracted state of dormancy

Considerable evidence links urokinase plasminogen activator (uPA) bound to its surface receptor (uPAR) with enhanced invasiveness of cancer cells. By blocking uPAR expression in human epidermoid carcinoma cells (HEp3), we have now identified an additional and novel in vivo function for this receptor by showing that receptor-deficient cells enter a state of dormancy reminiscent of that observed in human cancer metastasis. Its main characteristic is survival without signs of progressive growth. Five clones transfected with a vector expressing uPAR antisense RNA under the beta-actin promoter were isolated and shown to have uPAR (at the mRNA and protein levels) reduced by 50 to 80%; four clones, transfected with vector alone and having uPAR levels similar to those of parental cells, served as controls. In confirmation of our previous results, reduced uPAR always coincided with a significantly reduced invasiveness. Each of the control clones produced rapidly growing, highly metastatic tumors within 2 wk of inoculation on chorioallantoic membranes (CAMs) of chick embryos. In contrast, each of the clones with low surface uPAR, whose proliferation rate in culture was indistinguishable from controls, remained dormant for up to 5 mo when inoculated on CAMs. Thus, the reduction in uPAR altered the phenotype of HEp3 tumor cells from tumorigenic to dormant. Although protracted, tumor dormancy was not permanent since in spite of maintaining low uPAR levels, each of the in vivo-passaged antisense clones eventually reemerged from dormancy to initiate progressive growth and to form metastases at a level of 20 to 90% of that of fully malignant control. This observation suggested that other factors, whose expression is dependent on cumulative and prolonged in vivo effects, can compensate for the lack of a full complement of surface uPAR required for the expression of malignant properties. These "reemerged," uPAR-deficient clones were easily distinguishable from the vector-transfected controls by the fact that after only 1 wk in culture, the invasion of CAM by all five clones and tumorigenicity of four of the five clones were reduced back to the values observed before in vivo maintenance. In contrast, dissociated and in vitro-grown cells of control tumors were fully invasive and produced large, metastatic tumors when reinoculated on CAMs. Quantitation of the percent of apoptotic and S-phase cells in vivo, in the control and uPAR-deficient, dormant clones, showed that the mechanism responsible for the dormancy was a diminished proliferation.

Mutational analysis of the genes encoding urokinase-type plasminogen activator (uPA) and its inhibitor PAI-1 in advanced ovarian cancer

Evidence has accumulated that urokinase-type plasminogen activator (uPA), its inhibitor (PAI-1) and receptor (uPAR) are involved in tumor invasion and metastasis. We analyzed the DNA sequences encoding these factors to see if they are altered in the ovarian cancer cell lines OV-MZ-6, OV-MZ-19, and OVCAR-3. In the uPA-encoding cDNA derived from OV-MZ-6 cells (but not in the uPA-cDNA from OVCAR-3 and OV-MZ-19), a so-far unknown mutation was identified in codon 121, resulting in a proline to leucine exchange. This exchange creates an AluI restriction site making restriction fragment length polymorphism (RFLP) analyses possible. Previously published PAI-1 sequences pointed to a variation of amino acid 15 of the PAI-1 signal sequence representing either threonine or alanine, which was confirmed in the present study. The uPAR cDNAs of all three cell lines encoded the published wild-type sequence. In order to elucidate the possible role of the Pro121Leu exchange in uPA and the Ala/Thr variants in the signal sequence of PAI-1 in the development and/or progression of human ovarian cancer, we studied the presence of these mutants or variants in a series of 22 ovarian cancer tissues. In addition to the wild-type sequence, the Pro121Leu exchange in the uPA sequence was detected in 10 out of 22 tumor tissues; 11 tumors carried exclusively the Pro121 allele; in one case exclusively the Leu121 allele was detected. In 18/22 tumors, triplet 15 in the signal sequence of PAI-1 encoded alanine, four DNAs contained both the Ala and the Thr allele. Furthermore, we analyzed another known common single-base-pair insertion/deletion polymorphism (ins/del allele) found in the promoter region of the PAI-1 gene and thought to be of functional importance in regulating PAI-1 gene expression. The PAI-1 ins-allele was found in 3/22, the del-allele in 6/22 and both alleles in 13/22 ovarian cancer tissues. In genomic DNA isolated from peripheral blood of 23 healthy donors, we observed similar allele frequencies of the three polymorphisms as found in the 22 ovarian carcinomas. Taken together, these results suggest that the polymorphisms observed in the uPA and PAI-1 genes may not be linked to ovarian cancer.

Beta 2 (CD11/CD18) integrins can serve as signaling partners for other leukocyte receptors

Fig. 1 depicts our current thinking about the ways in which Mo1 and p150,95 form cis interactions with other leukocyte receptors. With respect to the associations of Mo1 with Fc gamma RIIIB and uPAR, the inhibitory effect of saccharides such as NADG suggests a lectin-carbohydrate interaction that may involve the recognition of Mo1's beta-glucan site for N-linked carbohydrates4 that are expressed by both Fc gamma RIIIB and uPAR. This hypothesis is supported by the results of Stockl et al., who showed that the binding of C-terminal-specific mAb VIM12 to Mo1, which enhances the phospholipase C-mediated release of Fc gamma RIIIB, was inhibited by NADG. However, unlike the sample lectin-carbohydrate interaction that appears to govern the association between Mo1 and Fc gamma RIIIB, effective Mo1-dependent uPAR signaling also depends on the binding of intact uPA to uPAR (the receptor-binding ATF of uPA proving insufficient to prime neutrophils for an enhanced burst response to FMLP). We speculate that ATF (residues 6-135) binds to uPAR while the carboxyl terminal fragment (residues 136-411), which includes a glycosylation site at residue 144, binds to the lectinlike site of Mo1, thus fostering the linkage between the two receptors. In support of this model is the fact that exposure of neutrophils to ATF reduced the degree of molecular proximity between Mo1 and uPAR (the latter probably occupied by endogenous intact uPA) and increased the molecular association between Mo1 and Fc gamma RIIIB (both as detected by quantitative RET). This hypothesis is analogous to the concept proposed by Nykjaer et al in which plasminogen activator inhibitor-1 initially binds to uPA to form a complex that secondarily binds to the alpha 2 macroglobulin receptor, leading to internalization of the complex. Whereas the contribution of intact uPA to the interaction between Mo1 and uPAR remains speculative (based on the indirect data available), no such ambiguity exists for the role of the LPS/LBP ligand in regulating the association between Mo1 and CD14. In this circumstance, no physical linkage exists between the two receptors without the ligand complex. This observation is consistent with the previously described affinity of the beta 2 integrins for LPS, leading to the notion that the LPS portion of the LPS/LPB complex binds to Mo1, serving to link it with LPS/LBP bound to CD14. The observed reversibility of the interactions between the integrin glycoproteins and uPAR or CD14 illustrates the fact that these associations can be highly dynamic and tied to cellular processes that include directed motility (Mo1-uPAR), adherence to substrates (Mo1-CD14), and energy metabolism (p150,95-uPAR). We speculate that the GPI-anchored receptor proteins serve as rapidly diffusible, expendable "scouts" for the beta 2 integrins, which serve to expand their ligand binding repertoire in a cis-acting fashion.

Evidence of a non-conventional role for the urokinase tripartite complex (uPAR/uPA/PAI-1) in myogenic cell fusion

Urokinase can form a tripartite complex binding urokinase receptor (uPAR) and plasminogen activator inhibitor type-1 (PAI-1), a component of the extracellular matrix (ECM). The components of the tripartite complex are modulated throughout the in vitro myogenic differentiation process. A series of experiments aimed at elucidating the role of the urokinase tripartite complex in the fusion of human myogenic cells were performed in vitro. Myogenic cell fusion was associated with increased cell-associated urokinase-type plasminogen activator (uPA) activity, cell-associated uPAR, and uPAR occupancy. Incubation of cultures with either uPA anticatalytic antibodies, or the amino-terminal fragment of uPA (ATF), which inhibits competitively uPA binding to its receptor, or anti-PAI-1 antibodies, which inhibit uPA binding to PAI-1, resulted in a 30 to 47% decrease in fusion. Incubation of cultures with the plasmin inhibitor aprotinin did not affect fusion. Decreased fusion rates induced by interfering with uPAR/uPA/PAI-1 interactions were not associated with significant changes in mRNA levels of both the myogenic regulatory factor myogenin and its inhibitor of DNA binding, Id. Incubation of cultures with purified uPA resulted in a decrease in fusion, likely due to a competitive inhibition of PAI-1 binding of endogenous uPA. We conclude that muscle cell fusion largely depends on interactions between the members of the urokinase complex (uPAR/uPA/PAI-1), but does not require proteolytic activation of plasmin. Since the intrinsic muscle cell differentiation program appears poorly affected by the state of integrity of the urokinase complex, and since cell migration is a prerequisite for muscle cell fusion in vitro, it is likely that the urokinase system is instrumental in fusion through its connection with the cell migration process. Our results suggest that the urokinase tripartite complex may be involved in cell migration in a non conventional way, playing the role of an adhesion system bridging cell membrane to ECM.

Production of a urokinase plasminogen activator-IgG fusion protein (uPA-IgG) in the baculovirus expression system

Numerous studies have demonstrated the importance of urokinase plasminogen activator (uPA) and its receptor, uPAR, in the processes of tumor progression and metastasis. Thus, the uPA/uPAR interaction may represent an important target for inhibiting metastatic disease. The baculovirus expression system was used to produce high levels of a secreted uPA-Immunoglobulin G fusion protein (uPA-IgG) which could then be used for displacing uPA from the surface of tumor cells. The recombinant uPA-IgG fusion protein was placed under the control of either the viral polyhedrin promoter or a copy of the viral basic protein promoter. Recombinant viruses were then used to infect Sf9 and BTI-Tn-5B1-4 cells. Infection of both cell types resulted in the production of secreted uPA-IgG. The molecular mass of the secreted protein as determined by SDS-PAGE was approximately 40 kDa. The highest level of secreted uPA-IgG, 444 microg/ml, was found in the culture medium of BTI-Tn-5B1-4 cells 72 h post-infection with the basic protein promoter-uPA-IgG virus. In the case of Sf9 cells, the highest level of secreted protein was 195 microg/ml. The amount of cell-associated uPA-IgG in infected BTI-Tn-5B1-4 cells was significantly less than that of infected Sf9 cells, reflecting the superior secretory capability of the BTI-Tn-5B1-4 cells. The uPA-IgG was readily purified using a combination of zinc chelate and sephacryl S-100 column chromatography. Routinely, greater than 100 mg of greater than 95% pure protein could be obtained per liter of culture medium collected at 72 h post-infection of BTI-Tn-5B1-4 cells with the basic protein promoter virus. BIAcore analysis and competition binding assays using LOX human malignant melanoma cells expressing uPAR indicated that the purified recombinant protein possessed similar ligand binding characteristics to that of human uPA.

Liver regeneration

Liver regeneration after the loss of hepatic tissue is a fundamental parameter of liver response to injury. Recognized as a phenomenon from mythological times, it is now defined as an orchestrated response induced by specific external stimuli and involving sequential changes in gene expression, growth factor production, and morphologic structure. Many growth factors and cytokines, most notably hepatocyte growth factor, epidermal growth factor, transforming growth factor-alpha, interleukin-6, tumor necrosis factor-alpha, insulin, and norepinephrine, appear to play important roles in this process. This review attempts to integrate the findings of the last three decades and looks toward clues as to the nature of the causes that trigger this fascinating organ and cellular response.

Differential expression of the urokinase receptor (CD87) in arthritic and normal synovial tissues

AIM

To determine whether the urokinase plasminogen activator receptor (u-PAR; CD87) exhibits a possible pathogenic role in rheumatoid and osteoarthritis.

METHODS

A semiquantitative, indirect immunoperoxidase histochemical analysis was performed on frozen synovial tissue sections. The recently characterised monoclonal antibody 10G7 recognising transfectants bearing u-PAR was used. Synovial tissue was obtained from 10 patients with rheumatoid arthritis, 10 patients with osteoarthritis, and four normal subjects.

RESULTS

u-PAR was expressed on 70-90% of synovial tissue lining cells and subsynovial, interstitial macrophages from the arthritis patients, but only on a few myeloid cells from the normal subjects. It was also present on more endothelial cells from the rheumatoid and osteoarthritis patients, than from normal synovial tissue.

CONCLUSIONS

Plasminogen activators are important in joint destruction underlying arthritis. The up-regulated expression of u-PAR in diseased versus normal synovial tissue suggests a role for this antigen in the inflammatory and angiogenic mechanisms underlying rheumatoid and osteoarthritis.

Inhibition of the interaction of urokinase-type plasminogen activator (uPA) with its receptor (uPAR) by synthetic peptides

Focusing of the serine protease urokinase-type plasminogen activator (uPA) to the cell surface via interaction with its specific receptor (uPAR, CD87) is an important step for tumor cell invasion and metastasis. The ability of a synthetic peptide derived from the uPAR-binding region of uPA (comprising amino acids 16-32 of uPA; uPA(16-32)) to inhibit binding of fluorescently labeled uPA to uPAR on human promyeloid U937 cells was assessed by quantitative flow cytofluorometric analysis (FACS) and compared to the inhibitory capacities of other synthetic peptides known to interfere with uPA/uPAR-interaction. An about 3000-fold molar excess of uPA(16-32) resulted in 50% inhibition of pro-uPA binding to cell surface-associated uPAR. Using a solid-phase uPA-ligand binding assay employing recombinant soluble uPAR coated to microtiter plates, the minimal binding region of wild-type uPA was determined. The linear peptide uPA(19-31) and its more stable disulfide-bridged cyclic form (cyclo(19,31)uPA(19-31)) displayed uPAR-binding activity whereas other peptides such as uPA(18-30), uPA(20-32) or uPA(20-30) did not react with uPAR. Cyclic peptide derivatives of cyclo(19,31)uPA(19-31) in which certain amino acids were deleted and/or replaced by other amino acids as well as uPAR-derived wild-type peptides did also not inhibit uPA/uPAR-interaction. Therefore, the present investigations identified cyclo(19,31)uPA(19-31) as a potential lead structure for the development of uPA-peptide analogues to block uPA/uPAR-interaction.

Characterization of downstream Ras signals that induce alternative protease-dependent invasive phenotypes

Invasive and metastatic cells require protease expression for migration through the extracellular matrix. Metastatic NIH 3T3 fibroblasts transformed by different activated ras genes showed two different protease phenotypes, rasuPA+/CL- and rasCL+/uPA- (Zhang, J-Y., and Schultz, R. M. (1992) Cancer Research 52, 6682-6689). Phenotype rasuPA+/CL- is dependent on expression of the serine-type protease urokinase plasminogen activator (uPA) and the phenotype rasCL+/uPA- on the cystine-type protease cathepsin L (CL) for lung colonization in experimental metastasis. The existence of multiple invasive phenotypes on ras-isoform transformation implied the activation of alternative pathways downstream from Ras. We now show that c-Raf-1, extracellular signal-regulated protein kinase (ERK)-1, and ERK-2 are hyperphosphorylated, and the ERK activity is high in both the uPA- and CL-dependent ras-transformed invasive phenotypes. Levels of c-Jun and c-Jun NH2-terminal kinase (JNK) activity are also high in the uPA-dependent phenotype, but they are almost undetectable in the CL-dependent phenotype. The uPA Ras-response element is a PEA3/URTF element, and mobility shift assays show a strong PEA3/URTF protein band in the uPA-dependent phenotype. This band is competed by a consensus AP-1 DNA sequence and by antibodies to PEA3 and c-Jun. Thus, the uPA-invasive phenotype appears to require the activation of Ets/PEA3 and c-Jun transcription factors activated by the ERK and JNK pathways, while the CL-invasive phenotype appears to require ERK activity with suppression of JNK and c-Jun activities. These postulates are supported by the introduction of a dominant negative c-Jun, TAM67, into cells of phenotype rasuPA+/CL-, which down-regulated the high uPA mRNA levels characteristic of this phenotype to basal levels and up-regulated basal levels of CL mRNA to levels similar to those observed in cells of phenotype rasCL+/uPA-. We conclude that the JNK pathway acts as a switch between two distinct protease phenotypes that are redundant in their abilities to grow tumors and metastasize.

Endothelial and macrophage upregulation of urokinase receptor expression in human renal cell carcinoma

The binding of urokinase-type plasminogen activator (u-PA) to a specific cell surface receptor (uPA-R) has been shown to enhance plasminogen activation, a process involved in extracellular matrix degradation and cell migration during angiogenesis and tumor growth. We investigated the expression of u-PA and uPA-R in renal cell carcinomas (n = 11). By immunohistochemistry using monoclonal and polyclonal anti-uPA-R antibodies, we found that tumoral capillary endothelial cells (von Willebrand factor and CD31 positive cells) overexpressed uPA-R, whereas vascular endothelial cells of the normal human kidney do not. In addition, tumor-associated macrophages (CD68-positive cells) strongly expressed uPA-R. In contrast, few tumoral cells and stromal fibroblasts expressed uPA-R. By in situ hybridization using a cDNA S35-labeled probe specific for uPA-R, we confirmed the local expression of uPA-R messenger RNA. We also detected the induction of u-PA in tumoral capillary endothelial cells and in tumor-associated macrophages. In two cases, tumoral cells themselves were also stained by anti-u-PA antibodies in focal areas. Finally tissue-type plasminogen activator (t-PA) was also overexpressed by tumoral capillary endothelial cells as compared with endothelial cells of normal human kidney vessels. These findings indicate an active invasive phenotype of endothelial cells in renal cell carcinoma and suggest a role for the plasminogen activation system in tumoral angiogenesis and invasion.

Immunocytochemical phenotyping of disseminated tumor cells in bone marrow by uPA receptor and CK18: investigation of sensitivity and specificity of an immunogold/alkaline phosphatase double staining protocol

Phenotyping of cytokeratin (CK)18-positive cells in bone marrow is gaining increasing importance for future prognostic screening of carcinoma patients. Urokinase-type plasminogen activator receptor (uPA-R) is one example of a potential aggressive marker for those cells. However, a valid and reliable double staining method is needed. Using monoclonal antibodies against uPA-R and CK18, we modified an immunogold/alkaline phosphatase double staining protocol. UPA-R/CK18-positive tumor cell controls exhibited black uPA-R staining in 15-80% of cases and red CK18 staining in almost 100% of tumor cells. Isotype- and cross-matched controls were completely negative. Bone marrow from healthy donors was always CK18-negative. Reproducibility of CK18-positive cell detection was estimated in a series of specimens from 61 gastric cancer patients comparatively stained with the single alkaline phosphatase-anti-alkaline phosphatase (APAAP) and our double staining method (10(6) bone marrow cells/patient). In four cases, double staining could not reproduce CK18-positive cells. In 34 cases it revealed fewer or equal numbers, and in 23 cases more CK18-positive cells than the APAAP method. Overall quantitative analysis of detected cell numbers (838 in APAAP, range 1-280 in 10(6); double staining 808, range 0-253) demonstrated relative reproducibility of APAAP results by double staining of 97%. Correlation of results between both methods was significant (p < 0.001, linear regression). Sensitivity of double staining tested in logarithmic tumor cell dilutions was one CK18-positive cell in 300,000. Specific uPA-R staining was seen on CK18-positive cells in bone marrow from 29 of 61 patients, and also on single surrounding bone marrow cells. To test the specificity of this staining, bone marrow cytospins from 10 patients without tumor disease were stained for uPA-R with the APAAP method. uPA-R expression was confirmed in all 10 cases, with a mean of 6.5% uPA-R-positive cells in 1000 bone marrow cells (SEM 1.2%). These results suggest that our double staining protocol is a sensitive, reproducible, and specific method for routine uPA-R phenotyping of disseminated CK18-positive cells in bone marrow of carcinoma patients.

Role of fibrin and plasminogen activators in repair-associated angiogenesis: in vitro studies with human endothelial cells

Angiogenesis, the formation of new blood vessels from existing ones, plays a central role in development and in a number of pathological conditions. Tissue repair-associated angiogenesis usually involves cell invasion into a fibrin structure and the presence of inflammatory cells. In this chapter the role of plasminogen activators in the dissolution of fibrin and the invasion of endothelial cells into a fibrin matrix is described. Tissue-type plasminogen activator is stored in endothelial cells and can be released acutely into the vessel lumen upon stimulation of the endothelium to activate fibrinolysis and to prevent fibrin deposition. At the basolateral side of the cell, urokinase-type plasminogen activator (uPA) bound to a specific cellular receptor is involved in the proteolytic modulation of matrix proteins and cell-matrix interaction. The cytokine tumor necrosis factor-alpha (TNF-alpha) cooperates with the angiogenic factors basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) in inducing human microvascular endothelial cells in vitro to invade a three dimensional fibrin matrix and to form capillary-like tubular structures. The formation of these capillary-like tubules requires cell-bound uPA activity.

Characterization of the murine plasminogen/urokinase-type plasminogen-activator system

The murine plasminogen/urokinase-type plasminogen-activator (u-PA) system was studied using purified proteins, plasma and endothelioma cells. Recombinant murine u-PA was obtained as a single-chain molecule of 45 kDa which was converted to two-chain u-PA with plasmin by cleavage of the Lys159-Ile160 peptide bond. Murine plasminogen, purified from plasma as a single-chain protein of 95 kDa, was resistant to quantitative activation with murine recombinant two-chain u-PA: only 15% activation within 1 h at 37 degrees C was obtained in mixtures of 1 microM plasminogen and 5 nM recombinant two-chain u-PA, whereas quantitative activation was observed in the autologous human system. Addition of 6-aminohexanoic acid to native murine plasminogen resulted in quantitative activation within 1 h. In murine plasma in vitro, plasminogen was also resistant to quantitative activation with u-PA (50% activation within 1 h at 37 degrees C with 50 nM recombinant two-chain u-PA, whereas in the human system nearly quantitative activation was obtained). Murine plasma clots submerged in murine plasma were resistant to lysis with u-PA; < or = 2% clot lysis in 2 h was obtained with 80 nM recombinant two-chain u-PA in the autologous murine system whereas 50% clot lysis in 2 h required only 15 nM recombinant two-chain u-PA in the autologous human system. Saturable binding of murine recombinant two-chain u-PA was observed to murine endothelioma cells that are genetically deficient in u-PA (u-PA-/- End cells). Binding was characterized by a Kd of 5.5 nM and 800000 binding sites/cell. However, u-PA-/- End cells did not significantly stimulate the activation rate of murine plasminogen by murine recombinant two-chain u-PA and did not enhance the plasmin-mediated conversion rate of murine recombinant single-chain u-PA to its two-chain derivative. Murine recombinant two-chain u-PA bound to murine endothelioma cells was quantitatively inhibited by murine plasminogen-activator inhibitor-1 (PAI-1). Thus, the interactions between murine plasminogen, u-PA and PAI-1 are qualitatively similar to those between their human counterparts. However, quantitative differences were observed both in the presence of cells and in plasma which may contribute to a reduced u-PA-mediated fibrinolytic activity in the murine systems.

Urokinase-type plasminogen activator regulates cranial neural crest cell migration in vitro

Proper migration and differentiation of neural crest (NC) cells are required for normal development of craniofacial structures, heart and great vessels, sensory and autonomic nervous systems, and other organs with vertebrate embryos. Serine-protease inhibitors reduce NC cell migration in vitro, suggesting the extracellular proteases are important mediators of NC cell migration. While plasminogen activator activity levels are high in NC cells relative to other embryonic tissue, its ability to regulate NC cell migration has not been specifically tested in vivo or in vitro through its ability to convert plasminogen to plasmin. Using a transfilter migration assay, NC cell migration was measured in the presence or absence of plasminogen. Our results showed that plasminogen significantly enhanced NC cell migration. This increase could not be attributed to differences in initial NC cell attachment or cytotoxicity and did not require a chemotactic gradient. The plasminogen-enhanced NC cell migration was blocked by aprotinin (a plasmin inhibitor) and was mimicked by the direct addition of plasmin to the NC cells, indicating that the plasminogen effect was mediated through plasmin generation. Furthermore, anticatalytic-uPA antibody blocked the plasminogen-enhanced NC cell migration showing that NC cell-associated uPA activity was required for this effect. Finally, decreasing NC-uPA activity by treating cells with transforming growth factor-Beta, also blocked the plasminogen-dependent increase in cell migration. These data show that in vitro, NC cell migration is regulated by NC-associated uPA activity suggesting that growth factor-regulation of this activity may play a major role in regulating NC cell migratory capacity in vivo.

Contrasting effects of plasminogen activators, urokinase receptor, and LDL receptor-related protein on smooth muscle cell migration and invasion

Smooth muscle cell (SMC) migration is an early response to vascular injury and contributes to the development of intimal thickening. Upregulation of several components of the plasminogen activator (PA) system has been documented after vascular injury. Utilizing a Transwell filter assay system and human umbilical vein SMCs, we sought to define the role of four different PA system components on SMC migration and matrix invasion: (1) PAs, (2) plasmin, (3) PA receptors, and (4) PA clearance receptors (ie, low density lipoprotein receptor-related protein [LRP]). Addition of active two-chain urokinase-type PA (UPA) stimulated random migration (192 +/- 30% of control, 0.36 nmol/L, P < .001). The stimulation was inhibited by pretreatment with diisopropylfluorophosphate, PA inhibitor type 1 (PAI-1), or aprotinin, a plasmin inhibitor. Augmented migration was also observed with either low-molecular-weight UPA or the amino terminal fragment of UPA (ATF), with the effects being additive. Stimulation by ATF alone, however, was not inhibited by aprotinin. The stimulatory effect was not specific for UPA, in that tissue-type PA (TPA) also increased migration (169 +/- 9% of control, 10 nmol/L, P < .001); the augmentation was inhibited by pretreatment with DFP, PAI-1, or aprotinin and was additive to the UPA effect. Antibodies to the UPA receptor but not 5'-nucleotidase (another glycosylphosphatidylinositol-anchored cell surface protein) inhibited baseline and UPA-stimulated migration. Similarly, both UPA and TPA stimulated invasion of a collagen gel; this augmentation was inhibited by aprotinin, whereas antibodies to the UPA receptor reduced baseline invasion. Finally, we tested whether inhibition of LRP function, which mediates internalization of PA/inhibitor complexes, affected either process. Both antibodies to LRP and recombinant receptor associated protein, a known inhibitor of ligand binding to the LRP, significantly inhibited migration but did not affect collagen gel invasion. These data demonstrate the ability of several components of the PA system to modulate SMC migration and invasion in vitro via plasmin-dependent and -independent mechanisms.

The proteolytic potential of normal human melanocytes: comparison with other skin cells and melanoma cell lines

To understand the contribution of epidermal melanocytes in the proteolytic potential of human skin, we have studied melanocytes grown in a low-serum medium deprived of phorbol esters, cholera toxin, and other non-physiological supplements. We focused on the plasminogen activation system and certain matrix metalloproteinases (gelatinases). Supposing that the proteolytic activity of cells can influence binding to collagen matrix and its reorganization, we have analyzed these parameters as well. We found that human melanocytes secreted tissue-type plasminogen activator and utilised it to generate cell-bound plasmin. No urokinase-type plasminogen activator was detected in the cultures but its receptor was found in cell extracts. Both the 72 kDa and 92 kDa gelatinases were secreted by the cells and in equal amounts. In addition, melanocytes secreted the wide-spectrum proteinase inhibitor alpha-2-macroglobulin. Melanocytes cast into collagen matrices retained a rounded morphology, did not extend processes, and were unable to contract collagen lattices. As a control, these parameters were investigated in parallel in cultures of human keratinocytes, dermal fibroblasts, and two melanoma cell lines. The obtained characteristics suggest that normal human melanocytes are proteolytically active cells. This function may pertain to skin physiology and pathophysiology.

Human glioma U-251 cells contain type 1 plasminogen activator inhibitor in a rapidly releasable form

Because recent information suggests that the localized deposition of protease inhibitors is one mechanism by which cells regulate pericellular proteolysis during tissue invasion, the distribution of type 1 plasminogen activator inhibitor (PA1-1) associated with the invasive human glioma cell line U-251 was investigated. Direct and reverse fibrin zymography indicated the presence of urokinase-like plasminogen activator (u-PA) and PAI-1 in U-251 conditioned media and cell lysates. PA1-1 antigen was detected immunologically in cytoplasmic granules present within cellular processes of U-251 cells and these organelles could be isolated on Percoll density gradients in a high density band. In contrast, u-PA activity and another secreted protein, amyloid beta-protein precursor, were only present in the low density region of the gradients. Functional analysis of PAI-1 in the granules contained within the high density fractions revealed the presence of active PAI-1. Incubation of U-251 cells with the secretagogue, 8-bromoadenosine 3':5'-cyclic monophosphate, resulted in a 3-fold increase in the release of PAI-1 in the media conditioned by these cells. These data suggest that the human glioma cell line U-251 contains PAI-1 in a rapidly releasable form, which may provide another mechanism by which these tumors could regulate proteolytic activity in a localized manner.