Urokinase-type plasminogen activator (uPA) and its receptor (CD87): a new target in tumor invasion and metastasis

Discovery of a novel inhibitor against urokinase-type plasminogen activator, a potential enzyme with a role in atherosclerotic plaque instability

The buildup of lipids, cholesterol, and other substances in and on the walls of the arteries is known as atherosclerosis and deposition is known as atherosclerotic plaque. Urokinase-type plasminogen activator (uPA) has multiple roles in the atherosclerotic plaque formation and even work simultaneously in making the atherosclerotic plaque unstable. Extracellular matrix plays a major role in the plaque remodeling and rapture. In this study, we have accessed that a higher interaction was observed in the molecular interaction score for uPA with ZINC380065722 having a GOLD fitness score of about 67.60, which is much higher as compared to the known standard inhibitor UK 122 which has reported an interaction score of 59.14. Ser217 and Asp192 are found to be the key amino acid residues in almost all the interactions. Protein frustration analysis has shown that these amino acid residues play a crucial role in the retention of the active pocket conformation and any mutation of these two residues can causes serious decrease in the overall function of the protein. It was observed that the molecule ZINC380065722 remained bound to the protein till 100 ns of simulation time. The average SASA for the apo-uPA and uPA-ligand complex was found to be stable. The network of hydrogen bonds for the intramolecular protein secondary structure and with the solvent system for the apo-protein and the uPA-ligand complex was found to be consistent.Communicated by Ramaswamy H. Sarma.

Involvement of urokinase in cigarette smoke extract-induced epithelial-mesenchymal transition in human small airway epithelial cells

Urokinase-type plasminogen activator (uPA) augments inflammation and tissue remodeling during lung injury and repair. The uPA expression in small airway epithelium of chronic obstructive pulmonary disease (COPD) increases. Epithelial-mesenchymal transition (EMT) is important in the small airway fibrosis of COPD. This study shows the uPA regulation in cigarette smoke extract (CSE)-induced EMT in human small airway epithelial cell lines (HSAEpiCs). uPA is overexpressed in the small airway epithelium of COPD patients and CSE-treated cell lines. Furthermore, uPA expression correlated with vimentin expression in the small airway epithelium of COPD patients. uPA inhibition blocks CSE-induced EMT by reversing E-cadherin and α-catenin expression and retarding the induction of N-cadherin and vimentin, resulting in reduction in migration. uPA overexpression in HSAEpiC cells also promotes EMT and migration. EMT is partly reversed in uPA-overexpressing HSAEpiC cells through the silencing expression of uPA receptor. In conclusion, this study provides new insights into the contribution of uPA upregulation to EMT associated with small airway remodeling in COPD.

Involvement of urokinase-type plasminogen activator system in cancer: an overview

Currently, there are several studies supporting the role of urokinase-type plasminogen activator (uPA) system in cancer. The association of uPA to its receptor triggers the conversion of plasminogen into plasmin. This process is regulated by the uPA inhibitors (PAI-1 and PAI-2). Plasmin promotes degradation of basement membrane and extracellular matrix (ECM) components as well as activation of ECM latent matrix metalloproteases. Degradation and remodeling of the surrounding tissues is crucial in the early steps of tumor progression by facilitating expansion of the tumor mass, release of tumor growth factors, activation of cytokines as well as induction of tumor cell proliferation, migration, and invasion. Hence, many tumors showed a correlation between uPA system component levels and tumor aggressiveness and survival. Therefore, this review summarizes the structure of the uPA system, its contribution to cancer progression, and the clinical relevance of uPA family members in cancer diagnosis. In addition, the review evaluates the significance of uPA system in the development of cancer-targeted therapies.

Quantitative secretome analysis reveals that COL6A1 is a metastasis-associated protein using stacking gel-aided purification combined with iTRAQ labeling

In cancer metastasis, secreted proteins play an important role in promoting cancer cell migration and invasion and thus also in the increase of cancer metastasis in the extracellular microenvironment. In this study, we developed a strategy that combined a simple gel-aided protein purification with iTRAQ labeling to quantify and discover the metastasis-associated proteins in the lung cancer cell secretome. Secreted proteins associated with lung cancer metastasis were produced using CL1-0 and CL1-5 cells with different metastatic abilities. Quantitative secretomics analysis identified a total of 353 proteins, 7 of which were considered to be metastasis-associated proteins. These included TIMP1, COL6A1, uPA, and AAT, all of which were higher in CL1-5, and AL1A1, PRDX1, and NID1, which were higher in CL1-0. Six of these metastasis-associated proteins were validated with Western blot analysis. In addition, pathway analysis was performed in building the interaction network between the identified metastasis-associated proteins. Further functional analysis of COL6A1 on the metastatic abilities of CL1 cells was also carried out. An RNA interference-based knock-down of COL6A1 suppressed the metastatic ability of CL1-5 cells; in contrast, a plasmid-transfected overexpression of COL6A1 increased the metastatic ability of CL1-0 cells. This study describes a simple and high throughput sample purification method that can be used for the quantitative secretomics analysis of metastasis-associated proteins.

Anti-angiogenic activity of triptolide in anaplastic thyroid carcinoma is mediated by targeting vascular endothelial and tumor cells

Triptolide is confirmed to suppress angiogenesis of anaplastic thyroid carcinoma. Here we further expound the precise mechanism involved in this activity. Triptolide downregulated nuclear factor kappa B (NF-kappaB) pathway and its targeting genes associated with endothelial cell mobilization in human umbilical vein endothelial cells (HUVECs) and impaired VEGF expression in thyroid carcinoma TA-K cells. Furthermore, both triptolide and the conditioned medium from triptolide-treated TA-K cells (CMT) significantly attenuated proliferation, migration and tube formation of HUVECs. In vivo, triptolide inhibited TA-K cell-induced tumor growth, vascular formation and VEGF expression. Our data establish that triptolide inhibits tumor angiogenesis by the dual action on vascular endothelial cells and tumor cells, thus providing a novel and overall explanation for the anti-angiogenesis action of triptolide. The multicellular targets emphasize triptolide as a high-performance and potential angiogenesis inhibitor.

The urokinase plasminogen activator receptor promotes efferocytosis of apoptotic cells

The urokinase receptor (uPAR), expressed on the surface of many cell types, coordinates plasmin-mediated cell surface proteolysis for matrix remodeling and promotes cell adhesion by acting as a binding protein for vitronectin. There is great clinical interest in uPAR in the cancer field as numerous reports have demonstrated that up-regulation of the uPA system is correlated with malignancy of various carcinomas. Using both stable cell lines overexpressing uPAR and transient gene transfer, here we provide evidence for a non-reported role of uPAR in the phagocytosis of apoptotic cells, a process that has recently been termed efferocytosis. When uPAR was expressed in human embryonic kidney cells, hamster melanoma cells, or breast cancer cells (BCCs), there was a robust enhancement in the efferocytosis of apoptotic cells. uPAR-expressing cells failed to stimulate engulfment of viable cells, suggesting that uPAR enhances recognition of one or more determinant on the surface of the apoptotic cell. uPAR-mediated engulfment was not inhibited by expression of mutant beta5 integrin, nor was alphavbeta5 integrin-mediated engulfment modulated by cleavage of uPAR by phosphatidylinositol-specific phospholipase C. Further, we found that the more aggressive BCCs had a higher phagocytic capacity that correlated with uPAR expression and cleavage of membrane-associated uPAR in MDA-MB231 BCCs significantly impaired phagocytic activity. Because efferocytosis is critical for the resolution of inflammation and production of anti-inflammatory cytokines, overexpression of uPAR in tumor cells may promote a tolerogenic microenvironment that favors tumor progression.

Development of a Mammalian suspension culture for expression of active recombinant human urokinase-type plasminogen activator

The development of specific catalytic inhibitors for the serine protease urokinase-type plasminogen activator (uPA) has been hindered due to difficulties in producing sufficient amounts of active recombinant uPA that is catalytically equivalent to native uPA. The purpose of this study was to develop an efficient system for the expression of recombinant human uPA that exhibits comparable proteolytic activity to that of the native protein. Since post-translational modifications (e.g. glycosylations) of uPA are necessary for efficient proteolytic activity, we have used a mammalian cell line [Chinese hamster ovary (CHO)-S] to express recombinant human uPA. CHO-S cells were selected to stably express full-length recombinant human uPA containing a hexahistidine tag at its C-terminus to permit purification by nickel-based affinity chromatography. Secretion of recombinant uPA into the culture media was confirmed by immunoblotting and the presence of an N-linked glycosylation was confirmed by PNGase sensitivity. Enzymatic activity of purified recombinant uPA was demonstrated using zymography and quantitatively compared to native uPA by kinetic analysis using an uPA-specific substrate. Native uPA and the recombinant uPA demonstrated comparable K(m) values (55.7 and 39 muM, respectively). Furthermore, inhibition studies using benzamidine resulted in a K(i) of 195 muM for native uPA, while recombinant uPA had a K(i) of 112 muM. These data indicate that recombinant human uPA expressed by CHO-S cells is functionally comparable to native uPA.

Integrin alpha6 cleavage: a novel modification to modulate cell migration

Integrins play a major role in cell adhesion and migration. Previous work reported that a cleaved form of integrin alpha6 (alpha6p) was detected in invasive human prostate cancer tissue, absent in normal prostate tissue and was produced by urokinase-type Plasminogen Activator (uPA) in a plasmin-independent manner. Using site-directed mutagenesis we identified amino acid residues R594 and R595, located in the "stalk" region of integrin alpha6, as essential for cleavage. The cleavage site is located on the extracellular region of the protein between the beta-barrel domain and the thigh domain. Prostate cancer cells (PC3N) were stably transfected to overexpress the cleavable, wild-type (PC3N-alpha6-WT) or the non-cleavable form of integrin alpha6 (PC3N-alpha6-RR). The number of cells invading laminin 111- and laminin 332-coated filters by PC3N-alpha6-WT cells increased by threefold as compared to PC3N-alpha6-RR cells. Plasminogen activator inhibitor-1 (PAI-1) reduced the invasion of PC3N-alpha6-WT cells by approximately 42% through laminin 332-coated filters and plasmin inhibitor aprotinin had no significant effect. Linear cell migration increased production of integrin alpha6p in the PC3N-alpha6-WT cells and not in the PC3N-alpha6-RR cells and 32% of the PC3N-alpha6-WT cells migrated on laminin 111 in the linear migration assay as compared to the 5% PC3N-alpha6-RR cells. These data taken together suggest that the uPA-mediated cell surface cleavage of the alpha6 integrin extracellular domain is involved in tumor cell invasion and migration on laminin.

uPAR (CD87) as a biocompatibility marker of dialysis membrane

BACKGROUND/AIMS

Hemodialysis (HD) therapy may lead to functional changes in patient leukocytes. For example, the upregulation of inflammatory cytokines, such as IL-1beta and TNFalpha, has been well characterized. However, these findings do not explain the entire response of leukocytes in HD. In this study, we carried out a comprehensive gene expression analysis in leukocytes treated with various dialysis membranes using DNA microarrays. The identified gene has the potential to be a new marker for testing dialysis membrane biocompatibility.

METHODS

Gene expression profiles were compared between a group of leukocytes treated with various dialysis membranes and an untreated group by using DNA microarray analysis. Expression was confirmed by quantitative RT-PCR. The expression of the gene product (leukocyte surface protein) was examined in 20 chronic HD patients by flow cytometry.

RESULTS

In addition to the inflammatory cytokines, the urokinase plasminogen activator receptor (uPAR or CD87) gene was induced in leukocytes treated with each dialysis membrane. The extent of induction depended on the membrane's material composition. The expression of the uPAR (CD87) protein on leukocytes was markedly increased in patients undergoing dialysis therapy. The magnitude of uPAR (CD87) protein expression was correlated with clinical findings, i.e., the degree of leukopenia and the expression of adhesion molecules.

CONCLUSIONS

The gene and protein expression of uPAR (CD87) depended on the dialysis membrane material and correlated closely with clinical findings. These results suggest that uPAR has the potential to serve as a marker not only for clinical use but also for the development of new dialysis membranes.

Invasion and metastasis markers in cancers

Over 90% of all adults human cancers are of epithelial origin comprising mainly of skin and aero-digestive tract cancers. A significant proportion of our discipline's workload consists of management of these cancers. This review article is to provide clinicians with a summary of the current research findings in invasion and metastasis of epithelial cancers and the translation of some of this information to clinical use particularly related to skin and head and neck cancers (HNSCC). Metastasis is the leading cause of death in cancer patients. Although surgical resection of isolated metastases is beneficial for some patients, the overall efficacy of surgery, chemotherapy or radiotherapy is limited. Clearly, with today's advances in surgery a majority of these primary cancers are resectable and a cure attainable if surgeons could control or inhibit metastasis.

Urokinase receptor antagonists: novel agents for the treatment of cancer

The interaction between the urokinase receptor (uPAR) and its ligand urokinase (uPA) mediates phenomena such as tissue remodelling, chemotaxis, tumour invasion, dissemination, proliferation, and angiogenesis. The broad-spectrum of biological processes that the uPA/uPAR interaction plays a role in has led researchers to speculate that this interaction may be a useful molecular target for therapeutic intervention in several pathological conditions, particularly in the prevention and inhibition of the dissemination of cancer cells. In syngeneic and xenograft murine tumour models, in which metastasis is driven by the uPA/uPAR interaction, inhibition of primary tumour growth, metastasis and angiogenesis has been shown with several proteins acting as uPAR antagonists. Immunohistochemistry, in conjunction with prognostic studies, has implicated the uPA/uPAR interaction in the dissemination of tumours, such as malignant melanoma, colon cancer, non-small cell lung cancer (NSCLC) and stomach cancer, as well as breast and ovarian carcinomas. A potential inhibitor of the uPA/uPAR interaction should result in a significant increase in the disease-free interval and survival time following resection of the primary tumour in a clinical Minimal Residual Disease (MRD) setting. Low molecular weight uPAR antagonists should be orally active, and have few side-effects, excellent bioavailability, favourable pharmacokinetic properties and a long half-life. Furthermore, these compounds should be able to inhibit the dissemination of cancer cells without the need for targeted drug and vector delivery.

Correlation between metastatic potential and variants from colorectal tumor cell line HT-29

AIM: To evaluate the relationship between uPA, PAI-1, CEA, PI3K and metastatic potential in three colorectal tumor cell lines.

METHODS: Metastatic model in nude rats was established by variants HT-29c and HT-29d cell lines and the metastatic potential of two tumor cell variants was compared. Urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor type 1 (PAI-1) were determined using ELISA in colorectal carcinoma WiDr, HT-29 and HT-29d cell lines with different metastatic potentials. Expression of carcinoembryonic antigen (CEA) and phosphoinositide 3-kinase (PI3-Kinase) was analyzed using immunohistochemistry (IHC) in these cell lines in vitro and in vivo. CEA expression was compared using fluorescence activated cell sorter (FACS) in vitro.

RESULTS: The number of HT-29d cells arrested in liver dramatically decreased within the initial 24 h after injection. The taking rate of liver metastases in the variant HT-29d increased as compared with parental HT-29 cells (70% versus 50%) and a variant HT-29b cells (70% versus 60%), and extensive organs were synchronously involved in metastases. The uPA concentration of variant HT-29d cell line was significantly higher than that of the non-metastatic WiDr and the low metastatic HT-29 cell lines. The variant HT-29d cells produced stronger PI3-kinase expression as compared with the non-metastatic WiDr cells and the low metastatic HT-29 cells in vivo.

CONCLUSION: The selected variant HT-29d cell exhibited an enhanced metastatic potential. The level of uPA and PAI-1 is positively correlated with the metastatic capacity of tumor cells. The expression of PI3-kinase correlates with tumor development and metastasis.

2-(2-Hydroxy-3-alkoxyphenyl)-1H-benzimidazole-5-carboxamidine derivatives as potent and selective urokinase-type plasminogen activator inhibitors

The development of potent and selective urokinase-type plasminogen activator (uPA) inhibitors based on the lead molecule 2-(2-hydroxy-3-ethoxyphenyl)-1H-benzimidazole-5-carboxamidine (3a) is described.

Urokinase plasminogen activator amino-terminal peptides inhibit development of the rat ventral prostate

The plasma membrane urokinase plasminogen activator receptor (uPAR) localizes and enhances activation of pro-uPA. Active uPA, in turn, promotes increased degradation of the extracellular matrix (ECM) by activation of plasminogen. uPAR binds to ECM molecules and integrins, which can affect cellular adhesion, signal transduction, and gene regulation. The current study examines the expression and function of uPAR in developing rat ventral prostates (VPs). We report that newborn VPs express uPAR mRNA and protein. In addition, the function of uPAR-bound uPA during in vitro prostatic development was studied by adding recombinant peptide competitive inhibitors of uPA-uPAR binding. Newborn VP explants were cultured in serum-free media for one week with 10(-8) M testosterone plus chimeric peptides containing a human immunoglobulin G Fc domain and either human uPA amino acids 1-138 (hu-uPA 1-138) as a control or mouse uPA amino acids 1-138 (mo-uPA 1-138) or 1-48 (mo-uPA 1-48). Hu-uPA 1-138-treated VPs underwent normal ductal branching morphogenesis and tissue differentiation. In contrast, VPs treated with mo-uPA 1-138 or mo-uPA 1-48 displayed a dose-dependent perturbation of ductal branching. Differentiation of both epithelial and mesenchymal tissues was also impaired. Mo-uPA 1-48-treated VPs contained significantly more apoptotic cells. These observations suggest that disruption of uPA binding to uPAR results in a retardation of the development of newborn VPs.

Dolichol-phosphate-mannose-3 (DPM3)/prostin-1 is a novel phospholipase C-gamma regulated gene negatively associated with prostate tumor invasion

The most ominous development in tumor progression is the transition to an invasive and metastatic phenotype. Little is known, however, about the molecular alterations that cause a tumor to become invasive. In view of this, we have used microarray expression analysis to evaluate the expression profiles of a unique panel of human DU145 prostate cancer sublines that vary in their invasive potential. The three DU145 sublines expressed epidermal growth factor (EGF) receptors that differed in their ability to activate phospholipase C-gamma (PLC gamma). Three-way analyses yielded 11 genes out of 4608 genes screened that associated directly or inversely with invasive potential. The gene whose expression correlated most strongly with lack of invasion was identified as a potential invasion suppressor and called prostin-1. Pharmacological inhibition of PLC gamma (U73122) confirmed that PLC gamma signaling suppressed prostin-1 in that U73122 treatment caused induction of prostin-1 in PLC gamma competent cells. The prostin-1 gene, conserved through phylogeny, is induced by androgen in LNCaP cells and encodes a 92 amino acid protein. The protein shares no extensive homologies with other known genes, yet was recently identified as a small stabilizer subunit of the dolichol-phosphate-mannose (DPM) synthase complex. That DPM3/prostin-1 might suppress tumor progression was supported by the finding that exogenous expression in COS cells leads to apoptosis. These findings support the use of model cell lines to identify putative tumor suppressors and promoters.

New paradigms for the treatment of cancer: the role of anti-angiogenesis agents

Angiogenesis, the sprouting of new blood vessels, plays a role in diverse disease states including cancer, diabetic retinopathy, age-related macular degeneration, rheumatoid arthritis, psoriasis, atherosclerosis, and restenosis. With regard to cancer, the clinical association of tumor vascularity with tumor aggressiveness has been clearly demonstrated in numerous tumor types. The observation of increased microvessel density in tumors not only serves as an independent prognostic indicator, but also suggests that anti-angiogenic therapy may be an important component of treatment regimens for cancer patients. The complexity of the angiogenic process, which involves both positive and negative regulators, provides a number of targets for therapy. Many positive regulators, including growth factor receptors, matrix metalloproteinases, and integrins, have been correlated with increased vascularity of tumors and poor prognosis for patient survival. Thus, these serve as ideal targets for anti-angiogenesis therapy. Many inhibitors of these targets are currently undergoing clinical evaluation as potential anti-cancer agents. In this article, we discuss the role of positive regulators in angiogenesis and tumor growth and describe the anti-angiogenic agents under development.

Malignant progression in Barrett's esophagus: pathology and molecular biology

Due to its increasing incidence, esophageal adenocarcinoma and its precursor lesions have received increasing attention in recent years. The histopathologic steps in the process of malignant progression in Barrett's esophagus are well described and include the following: (a) metaplasia of the normal esophageal squamous epithelium to a specialized intestinal glandular epithelium, (b) development of dysplasia (classified histologically as low and high grade), and (c) development of adenocarcinoma characterized by invasive and metastatic potential. Intestinal metaplasia can be identified by the presence of goblet cells, the detection of which can be aided by finding mucin stained by Alcian blue at low pH. Despite this well-characterized sequence, the timing of the development of dysplasia and the subsequent transition to carcinoma and the risk of development of carcinoma in low- and high-grade dysplasia are not precisely known. In addition, there are problems in the identification of dysplasia, including sampling error and interobserver discrepancies among pathologists. A better understanding of the mechanisms of these events would allow early identification and elimination of high-risk lesions before adenocarcinoma with its attendant poor prognosis were able to develop. In order to better understand this process and to potentially identify early markers of malignant transformation, a variety of molecular studies have been carried out in recent years on adenocarcinoma and its precursor lesions in Barrett's esophagus. On the phenotypic level, increased expression and changes in pattern of expression of proliferation marker (Mib-1) Ki-67 antigen, overexpression of p53 protein, overexpression of growth factors such as epidermal growth factor (EGF), c-erbB2, and transforming growth factor (TGF)-a, decreased and abnormal expression of the cell adhesion molecule E-cadherin, and, in carcinomas, increased expression of serine proteases have all been described. A new area of interest is the family of rab proteins, which play an important role in maintaining cell polarity in the gastrointestinal tract. Increased expression of one of these proteins, rab11, has been described in low-grade, but not high-grade dysplasia. In cytogenetic studies, an increased S-phase fraction, followed by an increased tetraploid (4N) fraction and then aneuploidy, has been described. So far, the specific genes which have been most thoroughly investigated have been p53, APC, p16, and the sites of probable tumor suppressor genes, including 3p (FHIT), 13q, and 18q. With only a few exceptions (i.e., rab11 expression, and possibly mutations of FHIT), the numerous molecular abnormalities which have been described occur late in malignant progression, which means that the best marker which presently exists to identify high-risk lesions in Barrett's esophagus is the histologic identification of dysplasia in endoscopic biopsies, especially high-grade dysplasia. We are presently beginning studies using laser microdissection and competitive genomic hybridization (CGH), which could help to identify new chromosomal areas that might contain genes that are crucial in the early phases of malignant progression in Barrett's esophagus. In the future, identification of such early molecular events which predispose to carcinoma development will allow more precise and earlier risk assessment for individual patients, therefore, enabling more effective therapy.

Suppression of breast cancer growth and metastasis by a serpin myoepithelium-derived serine proteinase inhibitor expressed in the mammary myoepithelial cells

A serpin was identified in normal mammary gland by differential cDNA sequencing. In situ hybridization has detected this serpin exclusively in the myoepithelial cells on the normal and noninvasive mammary epithelial side of the basement membrane and thus was named myoepithelium-derived serine proteinase inhibitor (MEPI). No MEPI expression was detected in the malignant breast carcinomas. MEPI encodes a 405-aa precursor, including an 18-residue secretion signal with a calculated molecular mass of 46 kDa. The predicted sequence of the new protein shares 33% sequence identity and 58% sequence similarity to plasminogen activator inhibitor (PAI)-1 and PAI-2. To determine whether MEPI can modulate the in vivo growth and progression of human breast cancers, we transfected a full-length MEPI cDNA into human breast cancer cells and studied the orthotopic growth of MEPI-transfected vs. control clones in the mammary fat pad of athymic nude mice. Overexpression of MEPI inhibited the invasion of the cells in the in vitro invasion assay. When injected orthotopically into nude mice, the primary tumor volumes, axillary lymph node metastasis, and lung metastasis were significantly inhibited in MEPI-transfected clones as compared with controls. The expression of MEPI in myoepithelial cells may prevent breast cancer malignant progression leading to metastasis.

Urokinase and plasminogen activator-inhibitor (PAI-1) status in primary ovarian carcinomas and ovarian metastases compared to benign ovarian tumors as a function of histopathological parameters

Ninety-eight patients with histologically confirmed ovarian tumors (77 primary ovarian carcinomas of stages T1 to T3 according to the postoperative histopathological classification pTNM classification, 14 ovarian metastases of various origins and seven benign ovarian tumors) were investigated with regard to the concentration of urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor (PAI-1) in membrane extracts of tumors. The results were correlated with the clinical course and with histopathological findings. With more advanced stage of primary ovarian carcinomas, there was a highly significant rise in the membrane concentrations of both uPA and PAI-1. However, increasing dedifferentiation of the tumors correlated only with uPA, but not with PAI-1. There was no correlation between the number of steroid receptors for estradiol and progesterone and the content of uPA or PAI-1 in the primary ovarian carcinomas. In the 14 ovarian metastases of different origins incluced in the study, the contents of uPA and PAI-1 were comparable to those of primary ovarian carcinomas. Compared with the malignant ovarian tumors, the median uPA and PAI-1 concentrations in the membrane fraction were 2.5-6 fold lower (highly significant) in the group of seven benign tumors. A cut-off value of 4.8ng/mg pellet protein for a prognostically favorable (< 4.8) or unfavorable course (> 4.8) could be determined for uPA (p = 0.0392) but not for PAI-1 on the basis of the Kaplan and Meier survival curves in the malignant primary ovarian carcinomas.

Receptor-independent role of urokinase-type plasminogen activator in pericellular plasmin and matrix metalloproteinase proteolysis during vascular wound healing in mice

It has been proposed that the urokinase receptor (u-PAR) is essential for the various biological roles of urokinase-type plasminogen activator (u-PA) in vivo, and that smooth muscle cells require u-PA for migration during arterial neointima formation. The present study was undertaken to evaluate the role of u-PAR during this process in mice with targeted disruption of the u-PAR gene (u-PAR-/-). Surprisingly, u-PAR deficiency did not affect arterial neointima formation, neointimal cell accumulation, or migration of smooth muscle cells. Indeed, topographic analysis of arterial wound healing after electric injury revealed that u-PAR-/- smooth muscle cells, originating from the uninjured borders, migrated over a similar distance and at a similar rate into the necrotic center of the wound as wild-type (u-PAR+/+) smooth muscle cells. In addition, u-PAR deficiency did not impair migration of wounded cultured smooth muscle cells in vitro. There were no genotypic differences in reendothelialization of the vascular wound. The minimal role of u-PAR in smooth muscle cell migration was not because of absent expression, since wild-type smooth muscle cells expressed u-PAR mRNA and functional receptor in vitro and in vivo. Pericellular plasmin proteolysis, evaluated by degradation of 125I-labeled fibrin and activation of zymogen matrix metalloproteinases, was similar for u-PAR-/- and u-PAR+/+ cells. Immunoelectron microscopy of injured arteries in vivo revealed that u-PA was bound on the cell surface of u-PAR+/+ cells, whereas it was present in the pericellular space around u-PAR-/- cells. Taken together, these results suggest that binding of u-PA to u-PAR is not required to provide sufficient pericellular u-PA-mediated plasmin proteolysis to allow cellular migration into a vascular wound.

The 9E3/CEF4 gene and its product the chicken chemotactic and angiogenic factor (cCAF): potential roles in wound healing and tumor development

The 9E3/CEF4 gene was one of the first inducible chemokine genes to be discovered. Its product, the chicken chemotactic and angiogenic factor (cCAF), is highly homologous to IL-8. It is expressed at low levels in tissues of mesenchymal origin but is highly expressed shortly after wounding and persists throughout the period of granulation tissue formation. It also is highly expressed around Rous sarcoma virus-induced tumors. The most potent natural stimulator of this gene is thrombin and in vivo cCAF is chemotactic for monocytes and lymphocytes and is angiogenic. The chemotactic properties can be potentially important in the inflammatory response and in the deterrence of tumors, whereas the angiogenic properties could be important in wound repair and tumor growth. The very rapid stimulation of 9E3 by thrombin and fast synthesis and secretion of cCAF suggest that this is a new type of stress response protein whose rapid production is designed to protect tissues rather than individual cells.

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.

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.

The biochemistry of cancer dissemination

The progression of a tumor cell from one of benign delimited proliferation to invasive and metastatic growth is the major cause of poor clinical outcome of cancer patients. Recent research has revealed that this complex process requires many components for successful dissemination and growth of the tumor cell at secondary sites. These include angiogenesis, enhanced extracellular matrix degradation via tumor and host-secreted proteases, tumor cell migration, and modulation of tumor cell adhesion. Each individual component is multifaceted and is discussed within this review with respect to historical and recent findings. The identification of components and their interrelationship have yielded new therapeutic targets leading to the development of agents that may prove effective in the treatment of cancer and its metastatic progression.

Epigenetic modification of transgenes under the control of the mouse mammary tumor virus LTR: tissue-dependent influence on transcription of the transgenes

Transgenic mice expressing human urokinase, as well as animals expressing human urokinase receptor under the control of the murine mammary tumor virus (MMTV) long terminal repeat, were established. In the vast majority of the founder animals and their descendants, the transgene was completely methylated, corresponding to down-regulation of transgene expression in the mammary gland. Two lineages with human urokinase receptor as the transgene with mixed methylation of the transgenes were analyzed in more detail. We show here for the first time that the methylation status of the transgene is identical in different organs of an animal, but may differ from animal to animal among the descendents. In the mammary gland, complete methylation of the transgene was incompatible with expression; unmethylated and mixed methylation transgenes gave rise to expression at the RNA as well as at the protein level. The methylation observed was not the consequence of an imprinting process. Surprisingly, in organs other than the mammary gland, such as liver, kidney and spleen, weak expression of the transgene was noted independent of the methylation status of the MMTV promoter. With respect to the molecular mechanism it is unresolved whether the human growth hormone sequence of the transgene harbors a methylation inducing element responsible for the observed methylation pattern.

Systematic mutational analysis of the receptor-binding region of the human urokinase-type plasminogen activator

The amino-terminal fragment of human uPA (ATF; amino acids 1-135), which contains the binding site for the uPA receptor (uPAR, CD87) was expressed in the yeast Saccharomyces cerevisiae. Recombinant yeast ATF, modified and extended by an amino-terminal in-frame insertion of a His6 tract, was purified from total protein extracts by nickel chelate affinity chromatography and shown to be functionally active since it efficiently competes with uPA for binding to cell-surface-associated uPAR. The ATF expression plasmid served as a template for the construction of a series of site-directed mutants in order to define those amino acids that are important for binding to uPAR. All mutant ATF proteins but one (deletion of Ser26) were expressed in a stable form (about 20-30 ng/mg total protein) and the binding capacity of each mutant was tested by a uPA-ligand binding assay employing recombinant uPAR immobilized to a microtiter plate. Each of the 11 amino acids of loop B of the binding region of uPA (amino acids 20-30) were individually substituted with alanine. Lys23, Tyr24, Phe25, IIe28, and Trp30 were important determinants for uPAR binding. A systematic alanine scan was also performed with chemically synthesized linear peptides spanning amino acids 14-32 of ATF. Comparable results to those with the yeast ATF mutants were obtained. In a different set of experiments, those amino acids of the uPAR-binding region of uPA that are only conserved between man and baboon but not in other species were altered: whereas substitution of Thr18 by alanine or Asn32 by serine had hardly any effect, replacement of Asn22 by tyrosine and Trp30 by arginine (both positions are strictly conserved in other mammals) led to ATF variants incapable of interacting with human uPAR. Deletion of either Val20, Ser21, Lys23, His29 or Val20 plus Ser21, respectively, also generated non-reactive ATF mutants. Finally, Lys23 in ATF was substituted with certain amino acids: whereas the replacement of Lys23 by alanine, histidine or glutamine generated ATF variants with moderate uPAR-binding activity, the introduction of a negatively charged amino acid (exchange of Lys23 by glutamic acid) completely abolished uPAR-binding activity. The results presented for the ATF mutants and uPA-derived peptides may provide clues necessary to establish the nature of the physical interaction of uPA with its receptor and may help to develop uPA-derived peptide analogues as potential therapeutic agents to block tumor cell-associated uPA/uPAR interaction.

A competitive chromogenic assay to study the functional interaction of urokinase-type plasminogen activator with its receptor

Urokinase-type plasminogen activator (uPA) converts plasminogen to plasmin which degrades various extracellular matrix components. uPA is focused to the cell surface via binding to a specific receptor (uPAR, also termed CD87). uPAR-bound uPA mediates pericellular proteolysis in a variety of biological processes, e.g. cell migration, tissue remodeling and tumor invasion. We have developed a competitive microtiter plate-based chromogenic assay which allows the analysis of uPA/uPAR interaction. The plates are coated with recombinant uPAR expressed in Chinese hamster ovary (CHO) cells. Proteolytically active uPA (HMW-uPA) is added to the microtiter plate-attached uPAR. The amount of receptor-bound uPA is then determined indirectly via addition of plasminogen, which is activated to plasmin, followed by cleavage of a plasmin-specific chromogenic substrate. Substances interfering with binding of HMW-uPA to uPAR diminish the generation of plasmin, as indicated by a reduction of cleaved chromogenic substrate. This assay was used to analyze the inhibitory capacity of a variety of proteins and peptides, respectively, on the uPA/uPAR interaction: i) uPAR and uPAR-variants expressed in CHO cells, yeast or E. coli, ii) the aminoterminal fragment (ATF) of human uPA or yeast recombinant pro-uPA, iii) synthetic peptides derived from the sequence of the uPAR-binding region of uPA, and iv) antibodies directed against uPAR. This assay may be helpful in identifying uPA and uPAR analogues or antagonists which efficiently block uPA/uPAR interaction.