Fibrinolysis associated with oncogenic transformation. Requirement of plasminogen for correlated changes in cellular morphology, colony formation in agar, and cell migration

The ANXA2/S100A10 Complex—Regulation of the Oncogenic Plasminogen Receptor

The generation of the serine protease plasmin is initiated by the binding of its zymogenic precursor, plasminogen, to cell surface receptors. The proteolytic activity of plasmin, generated at the cell surface, plays a crucial role in several physiological processes, including fibrinolysis, angiogenesis, wound healing, and the invasion of cells through both the basement membrane and extracellular matrix. The seminal observation by Albert Fischer that cancer cells, but not normal cells in culture, produce large amounts of plasmin formed the basis of current-day observations that plasmin generation can be hijacked by cancer cells to allow tumor development, progression, and metastasis. Thus, the cell surface plasminogen-binding receptor proteins are critical to generating plasmin proteolytic activity at the cell surface. This review focuses on one of the twelve well-described plasminogen receptors, S100A10, which, when in complex with its regulatory partner, annexin A2 (ANXA2), forms the ANXA2/S100A10 heterotetrameric complex referred to as AIIt. We present the theme that AIIt is the quintessential cellular plasminogen receptor since it regulates the formation and the destruction of plasmin. We also introduce the term oncogenic plasminogen receptor to define those plasminogen receptors directly activated during cancer progression. We then discuss the research establishing AIIt as an oncogenic plasminogen receptor-regulated during EMT and activated by oncogenes such as SRC, RAS, HIF1α, and PML-RAR and epigenetically by DNA methylation. We further discuss the evidence derived from animal models supporting the role of S100A10 in tumor progression and oncogenesis. Lastly, we describe the potential of S100A10 as a biomarker for cancer diagnosis and prognosis.

Plasmin and Plasminogen System in the Tumor Microenvironment: Implications for Cancer Diagnosis, Prognosis, and Therapy

Simple Summary

In this review, we present a detailed discussion of how the plasminogen-activation system is utilized by tumor cells in their unrelenting attack on the tissues surrounding them. Plasmin is an enzyme which is responsible for digesting several proteins that hold the tissues surrounding solid tumors together. In this process tumor cells utilize the activity of plasmin to digest tissue barriers in order to leave the tumour site and spread to other parts of the body. We specifically focus on the role of plasminogen receptor—p11 which is an important regulatory protein that facilitates the conversion of plasminogen to plasmin and by this means promotes the attack by the tumour cells on their surrounding tissues.

Abstract

The tumor microenvironment (TME) is now being widely accepted as the key contributor to a range of processes involved in cancer progression from tumor growth to metastasis and chemoresistance. The extracellular matrix (ECM) and the proteases that mediate the remodeling of the ECM form an integral part of the TME. Plasmin is a broad-spectrum, highly potent, serine protease whose activation from its precursor plasminogen is tightly regulated by the activators (uPA, uPAR, and tPA), the inhibitors (PAI-1, PAI-2), and plasminogen receptors. Collectively, this system is called the plasminogen activation system. The expression of the components of the plasminogen activation system by malignant cells and the surrounding stromal cells modulates the TME resulting in sustained cancer progression signals. In this review, we provide a detailed discussion of the roles of plasminogen activation system in tumor growth, invasion, metastasis, and chemoresistance with specific emphasis on their role in the TME. We particularly review the recent highlights of the plasminogen receptor S100A10 (p11), which is a pivotal component of the plasminogen activation system.

Components of the Plasminogen-Plasmin System as Biologic Markers for Cancer

Members of the plasminogen-plasmin (PP) system participate in many physiologic functions. In particular, uPA, its receptor (uPAR) and its inhibitor PAI-1 play an important role in cell migration, cell proliferation and tissue remodeling. Through a number of interactions, these components of the PP system are also involved in the pathogenesis of many diseases. In cancer, they modulate the essential processes of tumor development, growth, invasion and metastasis as well as angiogenesis and fibrosis. Thus, quantification of uPA, uPAR and PAI-1 in tumors and, in some cases in the circulating blood, became of potential value in the prognostication of many types of cancer. These include cancer of the breast, stomach, colon and rectum, esophagus, pancreas, glioma, lung, kidney, prostate, uterine cervix, ovary, liver and bone. Published data are reviewed in this chapter. Clinical validation of the prognostic value has also been made, particularly in cancer of the breast. Inclusion of these biomarkers in the risk assessment of cancer patients is now considered in the risk-adapted management in carcinoma of the breast. Factors limiting its broader use are discussed with suggestions how these can be overcome. Hopefully the use of these biomarkers will be applied to other types of cancer in the near future.

DR-70 immunoassay for the surveillance of hepatocellular carcinoma

BACKGROUND AND AIM

Although alpha-fetoprotein (AFP) is a widely used serological marker for hepatocellular carcinoma (HCC), its utility is limited due to its unsatisfactory sensitivity. Meanwhile, a newly developed immunoassay-DR-70-has been reported to have a good sensitivity for HCC in a small-scale study. The aim of this study was to determine the clinical value of DR-70 for the surveillance of HCC.

METHODS

Serum levels of DR-70 and AFP were measured in 103 patients with HCC, 50 healthy volunteers, and 33 patients with chronic liver disease. In addition, we investigated the prognostic value of DR-70 in patients with HCC correlating with the clinical staging-Cancer of the Liver Italian Program (CLIP) score and Barcelona Clinic Liver Cancer (BCLC) classification.

RESULTS

Based on the receiver operating characteristic curve with area under the curve of 0.836, the DR-70 cut-off value for detecting HCC was determined to be 0.75 µg/mL. DR-70 provided a sensitivity of 81.6% and a specificity of 77.1%, and correlated well with the CLIP score and BCLC classification. The combination of DR-70 and AFP increased the sensitivity to 91.2%. The prognosis for patients with HCC with DR-70 level > 0.75 µg/mL was worse than that for those with DR-70 ≤ 0.75 µg/mL. Among the patients with early stage HCC (CLIP score 0-2), DR-70 > 0.75 µg/mL independently predicted a poor survival.

CONCLUSIONS

DR-70 immunoassay is complementary to AFP for the detection of HCC and has a good correlation with clinical staging and prognosis.

Serum concentration of AMDL DR-70 for the diagnosis and prognosis of carcinoma of the tongue

The aim of this study was to discover the clinical value of the tumour marker AMDL DR-70 in a group of patients with cancer of the tongue. Serum concentrations of AMDL DR-70 were estimated by enzyme linked immuno-sorbent assay in 52 patients with carcinoma of the tongue and compared with 40 controls and 42 patients with benign lesions in the tongue. Thirty-nine patients with carcinoma of the tongue had results above 6 mg/L (75%), compared with 3/40 (7%) in healthy controls and 4/42 (10%) in those with benign tumours. The concentration of AMDL DR-70 in serum correlated significantly with 3-year survival.

The new DR-70 immunoassay detects cancer of the gastrointestinal tract: a validation study

BACKGROUND

Malignant cells characteristically possess high levels of plasminogen activator, which induce local fibrinolysis. The DR-70 immunoassay is a newly developed test, which quantifies fibrin degradation products in serum by a proprietary antibody.

AIM

To evaluate the DR-70 immunoassay as a detection assay for the presence of gastrointestinal cancers.

METHODS

We prospectively collected blood sera of 85 patients with histologically proven tumour and 100 healthy blood donors. Ten microlitres of the sera was used for the DR-70 immunoassay. Nineteen patients had a hepatocellular and 10 cholangiocellular carcinoma, 13 cancer of the pancreas, 30 colorectal cancer, 10 stomach cancer and three cancer of the oesophagus.

RESULTS

Receiver-operator curve analysis revealed <0.7 microg/mL as the best cut-off value to distinguish between patients with cancer and healthy controls. Using this cut-off value, the DR-70 immunoassay showed a good clinical performance with a sensitivity of 91% and a specificity of 93%. Patients with advanced tumour spread showed significantly higher DR-70 values than those with early-stage tumours (P < 0.0003).

CONCLUSION

The DR-70 immunoassay reliably differs between cancer patients and healthy controls. Therefore, it promises to become a useful test for the detection of cancer in clinical practice.

Cancer cachexia: its correlations and causes

Cancer cachexia involves the loss of weight, mainly in skeletal muscle and adipose tissue, that is not caused simply by anorexia. The syndrome includes anemia and immunosuppression along with a number of biochemical changes indicating systemic effects of the cancer. It is a major factor in morbidity and mortality from cancer. For 30 years beginning in 1948, a large number of studies reported isolation from many tumors of a heterogeneous group of small peptides, generally labeled toxohormone, that caused various correlates of cachexia shortly after injection into mice. Interest in toxohormone-like peptides then fell off for diverse reasons that had little to do with their clinical significance and was shifted to cytokines, ILs, and ectopic hormones with catabolic consequences that were sporadically found in tumors. At the same time, evidence was accumulating for an important role of pericellular proteases in driving progressive stages of neoplastic development. A central part of that evidence was the inhibition of transformation-related changes by protease inhibitors, particularly the combination present in fetal bovine serum, which fully suppressed the expression of the transformed phenotype in discrete foci of chicken embryo fibroblasts (CEF) infected by Rous sarcoma virus against a confluent background of uninfected CEF. In contrast, CEF cultures heavily infected with Rous sarcoma virus in the same medium underwent pervasive transformation, which was correlated with the release of low molecular weight cytotoxic substances. Reevaluation of all of the evidence supports a central role for proteolytically generated peptides derived from tumors in producing cancer cachexia.

Microenvironmental Regulation of the Initiated Cell

In the classical skin model of tumor initiation, keratinocytes treated once with carcinogen retain their normal appearance and growth behavior indefinitely unless promoted to growth into papillomas. Because many of the papillomas regress and may recur with further promotion, their cells can also be considered as initiated. The growth of initiated keratinocytes can be inhibited either in vitro or in vivo by close association with an excess of normal keratinocytes, but it is enhanced by dermal fibroblasts. Chick embryo fibroblasts (CEF) in culture produce transformed foci after infection with Rous sarcoma virus (RSV) on a background of normal CEF in a medium containing 10% or less calf serum (CS), but they retain normal appearance and growth regulation in 10% fetal bovine serum (FBS) or 20% CS. Transformation of a carcinogen-treated line of mouse embryo fibroblasts is prevented, and can be reversed, in high concentrations of FBS in the presence of an excess of normal cells. FBS has high, broad-spectrum antiprotease activity. Increased protease production occurs in a variety of transformed cells and is correlated with progression in tumors. Protease treatment stimulates DNA synthesis and mitosis in confluent, contact-inhibited normal cell cultures. Synthetic inhibitors of proteases suppress transformation in carcinogen-treated cultures and inhibit tumor formation in animals. Several different classes of protease may be overexpressed in the same transformed cells. It is proposed that excessive protease production accounts for major features of neoplastic transformation of initiated cells, but that transformation can be held in check by protease inhibitors present in serum and released from surrounding cells. It would be informative to determine whether high concentrations of FBS would inhibit the neoplastic development of initiated keratinocytes.

Plasmin triggers rapid contraction and degradation of fibroblast-populated collagen lattices

We examined the role of the serine proteinase plasmin in regulating fibroblast-mediated tissue remodeling during wound healing. As an in vitro model system, collagen lattices were seeded with human dermal fibroblasts, and various concentrations of plasmin were added to the medium of the contracting lattices. Within 16 h, fibroblast-populated collagen lattices treated with plasmin rapidly contracted from approximately 20 mm to less than 2 mm in diameter. Measurements of collagen lattices with radiolabeled collagen indicated that, when these lattices included either fibroblasts or conditioned medium derived from fibroblast-populated collagen lattices, exogenous plasmin induced collagen degradation and rapid lattice contraction. Western blot analyses of conditioned medium demonstrated that fibroblasts in collagen lattices secreted the latent matrix metalloproteinase, MMP-1, which was subsequently cleaved by plasmin. Additionally, rapidlattice contraction and collagen degradation were blocked when collagen lattices were treated simultaneously with plasmin and aprotinin or a tissue inhibitor of metalloproteinases, TIMP-1. These results provide strong evidence that plasmin regulates rapid contraction of collagen lattices by activating fibroblast-secreted MMP-1 that triggers collagen degradation. The findings from this study suggest that fibroblast-populated collagen lattices can be used as an in vitro model system to investigate the mechanisms by which plasmin and cell-secreted plasminogen activators control MMP-1 mediated extracellular lattice degradation and remodeling during wound healing.

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

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

Plasminogen activator inhibitor-1 represses integrin- and vitronectin-mediated cell migration independently of its function as an inhibitor of plasminogen activation

Cell migration involves the integrins, their extracellular matrix ligands, and pericellular proteolytic enzyme systems. We have studied the role of plasminogen activator inhibitor-1 (PAI-1) in cell migration, using human amnion WISH cells and human epidermoid carcinoma HEp-2 cells in an assay measuring migration from microcarrier beads and a modified Boyden-chamber assay. Active, but not latent or reactive center-cleaved, PAI-1 inhibited migration. A PAI-1 mutant without ability to inhibit plasminogen activation was as active as wild-type PAI-1 as a migration inhibitor, showing that inhibition of plasminogen activation was not involved. PAI-1 specifically interfered with intergrin- and vitronectin-mediated migration: Migration onto vitronectin-coated but not onto fibronectin-coated surfaces was inhibited by PAI-1, a cyclic RGD peptide inhibited migration, and both cell lines expressed vitronectin-binding alpha v-integrins. In addition, active PAI-1, but not latent or reactive center-cleaved PAI-1, inhibited vitronectin binding to integrins in an in vitro binding assay, without affecting binding of fibronectin. Monoclonal antibodies against the urokinase receptor, another vitronectin binding protein, did not affect cell migration in the beads assay, while some inhibitory effect was observed in the Boyden-chamber assay. We conclude that PAI-1, independently of its role as a proteinase inhibitor, inhibits cell migration by competing for vitronectin binding to integrins, while the interference of PAI-1 with binding of vitronectin to the urokinase receptor may play a secondary role. These data define a novel function for the serpin PAI-1, enabling it to regulate cell migration over vitronectin-rich extracellular matrix in the body.

Immunoelectron microscopy of the receptor for urokinase plasminogen activator and cathepsin D in the human breast cancer cell line MDA-MB-231

Receptors for urokinase-type plasminogen activator (uPAR) are present on the surface of many cell types and appear to be the key determinant controlling extracellular proteolysis catalyzed by the urokinase-type plasminogen activator (uPA). Receptor-bound uPA may be inhibited by the specific inhibitors PAI-1 and PAI-2, and the complex thus formed may subsequently be internalized and degraded in lysosomes. Biochemical evidence has recently indicated that also uPAR is internalized with the uPA/uPAI complex. We report here the subcellular localization of uPAR and cathepsin D in the MDA-MB-231 human breast cancer cell line studied by immuno-electron microscopy of ultrathin cryosections using single or double immunostaining techniques. Cell surface uPAR was preferentially localized at cell-cell junctions; cytoplasmic uPAR was inside large vesicles of different morphology and in flat Golgi saccules. A number of vesicles also contained cathepsin D. The uPAR was exclusively membrane-bound at the cell surface and in cytoplasmic vesicles without cathepsin D. In lysosomal vesicles with both cathepsin D and u-PAR, uPAR was probably degraded as it was observed in the luminal contents.

Transduced endothelial cells expressing high levels of tissue plasminogen activator have an unaltered phenotype in vitro

Elevated cellular plasminogen activator activity has been associated with significant alterations in the in vitro phenotype of both malignant cell lines and nonmalignant endothelial cells. To examine the role of elevated cellular plasminogen activator activity in the production of altered endothelial cell behavior, bovine coronary artery endothelial cells were transduced with a retroviral vector expressing large amounts of tissue plasminogen activator. Cells transduced with the tissue plasminogen activator vector were compared with both untransduced cells and cells transduced with a control vector in a series of in vitro assays of cellular attachment, proliferation, migration, and invasion. The morphology of the 2 transduced populations was unchanged. There was a small decrease (5-15%) in the horizontal migration rate of both transduced cell populations, as compared with that of untransduced cells. No significant differences were detected among the three cell populations in any of the other assays. We conclude that expression of high levels of tissue plasminogen activator does not specifically affect endothelial cell phenotype in vitro. These data lend support to the hypothesis that elevated plasminogen activator activity is necessary but not sufficient to produce alterations in endothelial cell behavior.

Plasminogen activators in normal and malignant oral epithelium in vivo and in vitro

Urokinase-type (uPA) and tissue-type (tPA) plasminogen activators were identified by fibrinolytic autography in the sulcus epithelium of human gingival mucosa but not in the orthokeratinized gingival epithelium. Fibrinolytic activity was present only over blood vessels in frozen sections of oral squamous cell carcinomas, the malignant epithelial cells showing no plasminogen activator activity. Plasminogen activators could not be demonstrated in either the sulcus or gingival epithelium by immunofluorescence, but both uPA and tPA were found in occasional squamous carcinoma cells. Fibrinolytic activity of culture fluids from epithelial explants grown in vitro from human gingival mucosa showed marked variation, but activity was much higher in the culture supernatants than in the cell lysates. Fibrinolytic activity of culture fluids from epithelial explants of squamous cell carcinomas was low both in supernatants and lysates. Zymogram overlays of sodium dodecyl sulphate-polyacrylamide electrophoretic gels from culture supernatants showed that the low fibrinolytic activity of culture supernatants of oral squamous cell carcinomas was due to the associated presence of plasminogen activator inhibitors. The fibrinolytic activity in the zymogram was due predominantly to uPA but some lysis was due also to tPA.

Vascularization and endochondral bone development: changes in plasminogen activator activity

Changes in plasminogen activator activity were studied during the sequential developmental stages of matrix-induced cartilage, bone, and bone marrow development. The morphological transitions were correlated with biochemical parameters. Morphologic evidence of vascularization of calcified hypertrophic cartilage was accompanied by a concomitant rise in plasminogen activator activity. Thereafter, a steady decline during mineralization and deposition of new bone was observed. Maximal plasminogen activator activity occurs at approximately the same time as peak activity of alkaline and acid phosphatase. These results imply a role for plasminogen activator during angiogenesis, vascular invasion, and attendant bone differentiation.

Microglia isolated from rat brain secrete a urokinase-type plasminogen activator

In a previous study, we found particular proteases which degrade myelin basic protein (MBP) in a conditioned medium of cultured rat brain microglia. The MBP degrading activity in microglial-conditioned medium (Mic-CM) increased markedly in the presence of plasminogen. By Sephadex G-150 column chromatography, plasminogen-dependent MBP degrading activity was eluted at the position of about 47 kDa and 28 kDa. Furthermore slight plasminogen-dependent protease activity in the presence of fibrin (tissue plasminogen activator activity) was detected at a molecular weight of about 68 kDa. The two molecular forms (47 kDa and 28 kDa) of plasminogen-dependent protease were demonstrated by casein-zymography, and it was suggested that they were urokinase type-plasminogen activators (uPA). This suggestion was confirmed by immunoblotting using anti-uPA antiserum. The unique 28 kDa type was considered to be produced from the 47 kDa form by limited proteolysis. Secretion of PA from microglia was demonstrated by cell zymography. In contrast, significant secretion of plasminogen activator inhibitor could not be detected in the Mic-CM. In addition, lipopolysaccharide significantly decreased the secretion of PA from microglia, while interleukin-1 and basic fibroblast growth factor enhanced the secretion.

Serum protease inhibitors promote anchorage-independent growth of transformed cells in serum-free medium

The effect of three serum serine protease inhibitors on the serum-free agar growth of an SV40-transformed 3T3 cell line was investigated. Antithrombin III, alpha-2-macroglobulin and alpha-1-antitrypsin were found to potently stimulate colony growth in a semisolid medium because of their anti-proteolytic properties. These results indicate that protease inhibitors can facilitate tumor cell growth in serum-free agar cultures and suggest that the stimulatory effect of serum on the growth of certain transformed cells in agar may at least partially be due to the high levels of protease inhibitors found in serum.

Mediators, initiating the inflammatory response, released in organ culture by full-thickness human skin explants exposed to the irritant, sulfur mustard

Mediators released from injured human skin that initiate the inflammatory response have not been adequately identified. Organ culture of full-thickness skin explants enables us to do so, because injury to the skin can be made in vitro, eliminating the rapid leakage of serum and infiltration of leukocytes that occur in vivo. In our studies, the military vesicant sulfur mustard (SM) (10 microliters of a 0.01 to 1.0% dilution) was topically applied to injure the epidermis of the explant. Then, the explants were cultured in small Petri dishes, usually for 18 h at 36 degrees C, and the organ-culture fluids were assayed for various inflammatory mediators. We found that the culture fluids from SM-exposed and control explants contained similar amounts of angiotensin-converting enzyme, trypsin-like and chymotrypsin-like proteases, acid phosphatase, beta-glucuronidase, beta-galactosidase, lysozyme, deoxyribonuclease, ribonuclease, interleukin 1, and lactic dehydrogenase. However, the culture fluids from SM-exposed explants contained increased amounts of histamine and plasminogen-activating activity, and often prostaglandin E2, when compared to culture fluids from control explants. After 3 to 4 d in culture, full-thickness human skin explants, when exposed to 0.2% SM (but not when exposed to 1.0% SM), sometimes showed separation of the epidermis and increased collagenase activity (i.e., hydroxyproline release). Thus, histamine (from local mast cells), and prostaglandin E2 and plasminogen-activating activity (probably from both mast cells and epidermal cells) are apparently involved in early mediation of the inflammatory response.

Cell associated urokinase activity and colonic epithelial cells in health and disease

It is not known if urokinase-type plasminogen activator (uPA) is associated with normal colonic epithelial cells. The aims of this study were to determine if normal colonic epithelial cells have uPA activity and whether this is concentrated at the cell membrane. In addition, the contribution of colonic epithelial cell associated uPA activity to disease related pertubations of mucosal uPA activity were examined. A highly enriched population of colonic epithelial cells was isolated from resected colon or biopsy specimens by an enzymatic technique. uPA activity was measured in cell homogenates by a specific and sensitive colorimetric method and expressed relative to cellular DNA. In two experiments subcellular fractionation of colonic epithelial cells was performed by nitrogen cavitation followed by ultracentrifugation over a linear sucrose gradient. The fractions collected were analysed for uPA and organelle-specific enzyme activities. Normal colonic epithelial cells have cell associated uPA activity (mean (SEM) 5.6 (1.1) IU/mg, n = 18). This colocalised with fractions enriched for leucine-beta-naphthylamidase and 5'-nucleotidase, markers of plasma membrane. uPA activities in epithelial cells from cancerous colons (9.8 (3.1) n = 7) or from mucosa affected by inflammatory bowel disease (3.8 (0.7) n = 15) were not significantly different from normal (paired t test), while that in epithelial cells from greatly inflamed mucosa was similar to that from autologous normal or mildly inflamed areas (4.4 (1.2) v 5.9 (3.6), n = 9). Thus normal colonic epithelial cells have cell associated uPA activity which is concentrated on the plasma membranes, suggesting the presence of uPA receptors. Increased mucosal levels of uPA previously reported in patients with inflammatory bowel disease are not due to increased colonic epithelial cell associated uPA.

Identification of a plasminogen activator derived from nasopharyngeal carcinoma

The activity of plasminogen activator (PA) in tissue extracts from nasopharyngeal carcinoma (NPC) was determined by means of the fibrin plate method. Development of PA activity was observed in 16 out of 25 cases investigated. Furthermore, using tissue extract of NPC with PA activity, characterization and identification of the activator were carried out by means of electrophoretic analysis, fibrin zymography and immunological analysis. The molecular weight of this PA was found to be 38,000 daltons. Additionally, a urokinase type of plasminogen activator was contained in the tissue extracts.

Localization of urokinase-type plasminogen activator receptor on U937 cells: phorbol ester PMA induces heterogeneity

The binding of human urokinase-type plasminogen activator (u-PA) to the surface of the human monocytic cell line U937 was studied by immunological detection of bound u-PA or binding of biotinylated diisopropyl fluorophosphate-inactivated human u-PA visualized by light or electron microscopy. Untreated U937 cells showed a characteristic binding pattern, with the majority of the u-PA bound to the microvillar-containing protruding pole of the cells. After treatment with the phorbol ester PMA, the resulting adherent cell population was very heterogeneous with respect to both cellular morphology and u-PA binding. The bound u-PA was distributed on both the dorsal and the substrate side of the cells, and the patches of bound u-PA could not be correlated to any typical membrane conformations or cell-cell or cell-substratum contacts. When a monoclonal antibody directed against the amino-terminal fragment (ATF) of u-PA was used, the results were identical regardless of whether intact u-PA or ATF was used for binding to the cells. In contrast, when a monoclonal antibody recognizing the non-receptor-binding protease domain of u-PA was used, bound ATF showed no staining, while bound intact u-PA was stained as efficiently as above. The alteration of u-PA receptor distribution following treatment with PMA could be related to the changes in glycosylation and ligand affinity of the purified u-PA receptor previously described following PMA treatment of U937 cells.

Urokinase synthesis and binding by glomerular epithelial cells in culture

Fibrin deposits are frequently observed in the course of proliferative extracapillary glomerulonephritis and could be related to a defective local fibrinolysis. We studied human glomerular epithelial cells in culture which were found to release mainly a urokinase-type plasminogen activator (u-PA) identified on zymography by its molecular weight (53 kD), its plasminogen activator activity, and its neutralization by specific polyclonal anti-u-PA IgG. Trace amounts of tissue-type plasminogen activator (t-PA) complexed to a plasminogen activator inhibitor type 1 (PAI-1) were identified with specific antibodies. Specific binding sites were found at the surface of glomerular epithelial cells (kD: 2.10(-9) M), partially occupied by secreted u-PA. The spontaneous u-PA activity of the culture medium conditioned by glomerular epithelial cells was very low, suggesting that u-PA was released in its inactive single chain proenzyme form (SC-u-PA). After activation of SC-u-PA by plasmin, u-PA activity of the culture medium was found to increase in a time- and dose-dependent manner when cells were incubated with phorbol myristic acetate (PMA). This effect was inhibited by H7, a protein kinase C inhibitor. Stimulation of u-PA synthesis by PMA was also observed in two different epithelial tubular cell lines. LLC-PK1 and MDCK cells. However, 8 bromo cyclic AMP which increased u-PA release by LLC-PK1 cells was found to inhibit u-PA release by PMA-stimulated glomerular epithelial cells and MDCK cells. By Northern blot analysis we found that PMA induced an increase of u-PA mRNA level in glomerular epithelial cells and that cyclic AMP had an opposite effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Autocrine activities of basic fibroblast growth factor: regulation of endothelial cell movement, plasminogen activator synthesis, and DNA synthesis

We have found that the spontaneous migration of bovine aortic endothelial cells from the edge of a denuded area in a confluent monolayer is dependent upon the release of endogenous basic fibroblast growth factor (bFGF). Cell movement is blocked by purified polyclonal rabbit IgG to bFGF as well as affinity purified anti-bFGF IgG and anti-bFGF F(ab')2 fragments. The inhibitory effect of the immunoglobulins is dependent upon antibody concentration, is reversible, is overcome by the addition of recombinant bFGF, and is removed by affinity chromatography of the antiserum through a column of bFGF-Sepharose. Cell movement is also reversibly inhibited by the addition of protamine sulfate and suramin; two agents reported to block bFGF binding to its receptor. The addition of recombinant bFGF to wounded monolayers accelerates the movement of cells into the denuded area. Transforming growth factor beta which has been shown to antagonize several other effects of bFGF also inhibits cell movement. The anti-bFGF IgG prevents the movement of bovine capillary endothelial cells, BHK-21, NIH 3T3, and human skin fibroblasts into a denuded area. Antibodies to bFGF, as well as suramin and protamine sulfate also suppress the basal levels of plasminogen activator and DNA synthesis in bovine aortic endothelial cells.

Modulation of type IV collagenase and plasminogen activator in a hamster fibrosarcoma by basement membrane components and lung fibroblasts

The effect of basement membrane components (laminin, fibronectin and type IV collagen) and lung fibroblasts on type IV collagenase and plasminogen activator activity was investigated in a primary HSV-2-induced hamster fibrosarcoma, and its in vivo derived sublines and in vitro derived clones of varying metastatic potential. Fibronectin and type IV collagen were ineffective at influencing the expression of either type IV collagenase or plasminogen activator activity. Laminin, however, at concentrations of 1-10 micrograms ml-1 added to the serum-free culture supernatants, increased the release of type IV collagenase by up to 100% for the parental cell line. Three highly metastatic sublines (two from in vivo origin and one from in vitro cloning) showed increases of up to 300%. Non-metastatic sublines (two from in vivo origin and one from in vitro cloning), however, showed no increase in type IV collagenase activity. Plasminogen activator release from either the parental line cell or its metastatic sublines and clones, was unaffected by the addition of laminin. Addition of tumour cells to lung fibroblast monolayers resulted in an increased expression of PA activity in the supernatant, whilst type IV collagenase activity was reduced.

Localization of protease nexin-1 on the fibroblast extracellular matrix

Protease nexin-1 (PN-1) is a protease inhibitor that is secreted by fibroblasts and several other cultured cells. PN-1 forms complexes with certain serine proteases in the extracellular environment including thrombin, urokinase, and plasmin. The complexes then bind to the cells and are rapidly internalized and degraded. This report demonstrates that PN-1 is present on the surface of fibroblasts, bound to the extracellular matrix. Immunofluorescent studies showed that PN-1 colocalized with fibronectin on both intact cells and in preparations of extracellular matrix made from these cells. In contrast, PN-1 did not colocalize with the epidermal growth factor receptor, a plasma membrane marker. An enzyme-lined immunosorbent assay was developed which showed that the extracellular matrix contained at least 60-80% of the cellular immunoreactive PN-1. Extraction of the matrix with 2 M NaCl removed PN-1 in a form which reacted with 125I-thrombin to form complexes which were immunoprecipitated by anti-PN-1 IgG and were of identical size as complexes made from soluble PN-1 and 125I-thrombin. These data indicate that in addition to its role as a soluble protease inhibitor, PN-1 is also a component of the extracellular matrix and might control its proteolysis.

Urokinase-type plasminogen activator is induced in migrating capillary endothelial cells

Cellular migration is an essential component of invasive biological processes, many of which have been correlated with an increase in plasminogen activator production. Endothelial cell migration occurs in vivo during repair of vascular lesions and angiogenesis, and can be induced in vitro by wounding a confluent monolayer of cells. By combining the wounded monolayer model with a substrate overlay technique, we show that cells migrating from the edges of an experimental wound display an increase in urokinase-type plasminogen activator (uPA) activity, and that this activity reverts to background levels upon cessation of movement, when the wound has closed. Our results demonstrate a direct temporal relationship between endothelial cell migration and uPA activity, and suggest that induction of uPA activity is a component of the migratory process.

Secretion of plasminogen activator by cerebral astrocytes and its modulation

Plasminogen activator (PA) has been related to the neuron migration during brain development. PA has also been shown to degrade myelin basic protein. We present data to show that neonatal Balb/c astrocytes show PA activity on 125I-fibrin coated plates. Secreted and cell associated fibrinolytic activity is detected only in the presence of plasminogen. Modulants like concanavalin A and phorbol myristate acetate enhance PA production and this function involves a transcriptional event. Dexamethasone inhibits baseline as well as concanavalin A induced enhancement of PA activity. These results raise the possibility that astrocytes may have an active role in myelinoclastic disorders and CNS developmental defects.

Role of plasminogen, plasmin, and plasminogen activators in the migration of fibroblasts into plasma clots

Human diploid fibroblasts were seeded onto or into plasma clots and different aspects of cell adhesion and migration were measured. The roles of plasminogen activators and plasmin were studied by either the removal of plasminogen from plasma prior to clotting or by the addition of 10 mM epsilon-aminocaproic acid, which brings about an inhibition of plasmin in this system. When cells were seeded onto the surface of plasma clots, rates of attachment, spreading, and migration were unaffected by plasminogen depletion or plasmin inhibition. In contrast, when cells were seeded into plasma clots, then, although the rates of cells spreading were unaffected, cell migration was abolished by plasminogen depletion or by plasmin inhibition. When cells were seeded onto the surface of plasma clots and the rate of migration into the clots was measured, there was an absolute requirement for plasmin activity; while fibroblasts migrated rapidly into the fibrin lattice of control clots, in the case of plasminogen-depleted clots, cells failed to penetrate the lattice. Focussing through a plasma clot revealed that fibroblasts do not migrate through the fibrin lattice but instead, localized areas of fibrinolysis are generated and cells migrate over the surface of the area of lysis.

Cryoenzymology of human plasmin catalysis: comparison of cryosolvents and reactions with nitrophenyl ester and anilide substrates

A comparative study of nucleophilic (methanol), aprotic (dimethyl sulfoxide), and protic but non nucleophilic (ethylene glycol, ethylene glycol/dimethylformamide) solvents on the catalytic and structural properties of human plasmin has been made. All four solvent systems are potentially suitable as cryosolvents for plasmin catalysis at subzero temperatures although the solubility of plasmin is limited in the methanol and dimethyl sulfoxide systems. Each cryosolvent system caused minor effects on the catalytic properties of the enzyme, which could be rationalized in terms of the known physical properties of the cosolvent. Solvent systems containing ethylene glycol induce a minor conformational change which increases the catalytic efficiency of plasmin. The cosolvent effects on Km and Ki indicate that electrostatic interactions dominate the binding of both substrates and inhibitors such as benzamidine. A change in slope of the Arrhenius plots for catalysis, reflecting a temperature-induced isomerization, is observed around 0 degree C; the energies of activation being 13 +/- 2 kcal mol-1 at higher temperatures and 19 +/- 2 kcal mol-1 at subzero temperatures, and essentially independent of solvent. Deacylation was shown to be the rate-limiting step in the hydrolysis of specific p-nitrophenyl ester substrates. Previous stopped-flow studies at room temperature provided observations suggesting that a tetrahedral intermediate could be detected in the plasmin-catalyzed hydrolysis of p-nitroanilide substrates. Experiments at subzero temperatures with such substrates failed to reveal any buildup of a tetrahedral intermediate under the experimental conditions.

Alpha-1-antitrypsin in human brain tumors

This study was undertaken to confirm the presence of alpha-1-antitrypsin (alpha 1-AT) in human brain tumors and to attempt to elucidate its significance. Seventy-seven consecutive unselected patients with various brain tumors were entered in this study. The alpha 1-AT and alpha 2-macroglobulin contents of the tumor extracts were qualitatively assessed by Ouchterlony immunodiffusion techniques. Plasminogen activator (PA) activity was assayed electrophoretically on sodium dodecyl sulfate gels. The patients were were divided into two groups according to the positivity of their tumors to alpha 1-AT. Sixty-eight percent of the tumors were positive for alpha 1-AT, and all specimens were negative for alpha 2-macroglobulin. Clinical and biological parameters obtained in all study patients failed to show statistically significant differences between the two groups with the exception of PA activity (p = 0.001), the peritumoral edema as seen on computerized tomography, and the preoperative serum fibrinogen level. These three parameters were higher in the group with specimens positive to alpha 1-AT. This study supports the hypothesis that alpha 1-AT is produced primarily by tumor cells in proportion to the regional proteolytic and inflammatory activity, and may protect the tumor cells.

Proteolytic enzymes and arachidonic acid metabolites produced by MRC-5 cells on various microcarrier substrates

Human diploid fibroblasts were cultured on microcarriers made from DEAE-dextran, denatured collagen, DEAE-dextran linked to denatured collagen, and glass. Cells grown on these four substrates were examined for the production of proteolytic enzymes and arachidonic acid metabolites. Culture fluids from cells grown on the DEAE-dextran microcarriers contained the highest amounts of proteolytic enzyme activity. Both plasminogen-independent and plasminogen-dependent fibrinolytic activities were present and the plasminogen-dependent activity seemed to result from the presence of both urokinase and tissue plasminogen activator. Culture fluid from the cells grown on the glass microcarriers contained the least amount of protease activity, and nearly all of the plasminogen-activator activity seemed to be of the urokinase type. Protease activity in the culture fluids of cells grown on the other two substrates were intermediate. With regard to arachidonic acid metabolites, cells grown on the DEAE-dextran microcarriers produced the highest amounts of cyclooxygenase products but very low levels of lipoxygenase metabolites. Cells grown on the other three substrates produced comparable amounts of various cyclooxygenase products (lower than that produced by cells on the DEAE-dextran substrate). Cells grown on the glass microcarriers also produced detectable amounts of two lipoxygenase metabolites--leukotriene B4 and leukotriene C4. Inasmuch as both proteolytic enzymes and arachidonic acid metabolites regulate basic cell properties, the differential amounts of these metabolites observed in the culture fluids on the various substrates may contribute to the biological differences that exist on these substrates.

Contact inhibitory factor also restores anchorage and serum dependence to hamster melanoma cells

Conditioned medium (CM) from confluent cultures of the contact-inhibited hamster melanocytic cell line, FF, contains a biologic activity, contact inhibitory factor (CIF), which reversibly restores density-dependent growth to melanoma cells. When a hydrophobic affinity-concentrated extract of CIF-containing CM was incorporated in agarose at a concentration of 1000 micrograms protein/ml, it restored anchorage-dependent growth to RPMI 1846 hamster melanoma cells. Colony-forming efficiency in CIF-treated wells decreased to 5% from levels of 51.5% in controls prepared with regular growth medium. In addition, CIF-containing CM restored serum-dependent growth to RPMI 1846 cells, markedly restricting proliferation in 1% calf serum-containing medium. Control cultures containing 1% calf serum and either complete growth medium or CM from the non-contact-inhibited hamster melanoma line itself, supported proliferation of RPMI 1846 cells to levels 3.9 X and 3.7 X that of CIF-treated cultures, respectively. CIF is the first factor derived from contact-inhibited mammalian cell cultures that has been shown to restore density-, anchorage-, and serum-dependent growth to malignant melanoma cells.

A mouse model for vitiligo

As the result of a long search for a depigmenting mouse that could serve as a model for the study of vitiligo, we have located a strain that arose from the C57BL/6J. Its provisional genetic designation is C57BL/6J Ler-vit/vit. This vitiligo mouse has congenital dorsal and ventral white spots (piebaldism) as well as progressive replacement of pigmented hairs by white hairs with each spontaneous molt or after plucking. The lack of pigment is due to the absence of melanocytes from the amelanotic hair follicles and epidermis. As in human beings and the Smyth chicken model, there is also diminution of ocular pigment. Reciprocal skin transplants between C57BL/6J and vitiligo mice, and transplants into nude mice, suggest a programmed pigment cell death in the vitiligo mice. Like human beings with vitiligo, maximally depigmented vitiligo mice have a decreased contact sensitivity response in comparison to age-matched C57BL/6J controls. The resistance to injected B16 melanomas is lowered. Vitiligo mice show no signs of premature aging. Already at this early stage in the study of this new animal model, there are findings that open a range of new approaches to the study and treatment of patients with vitiligo and melanomas.

Isolation and characterization of a wheat germ agglutinin-binding glycoprotein from B16 mouse melanoma cells

Cells of B16 mouse melanoma grown in serum-free medium in the presence of [3H]glucosamine secreted or shed labeled glycoproteins. A wheat germ agglutinin-binding glycoprotein was isolated that accounted for 37% of the total [3H]glucosamine incorporated; it had a molecular weight of approximately 50,000 and was absent in less-tumorgenic wheat germ agglutinin (isolectin I)-resistant variants of the cells. The glycoprotein contained approximately 25% of serine and threonine plus equimolar amounts of glucosamine and galactosamine, indicating both N- and O-linked oligosaccharide chains. Neuraminidase treatment released approximately 60% of the glycoprotein's 3H radioactivity as N-acetylneuraminic acid. The sialoglycoprotein did not, but the desialylated species did, bind (97%) to ricin-Sepharose, suggesting the presence of terminal sialic acid and penultimate galactose residues in most of the saccharide units. Alkaline borohydride released 61% of the glycoprotein's radioactivity as oligosaccharide alcohols that were mainly tetrasaccharides (75%) with some branched trisaccharides (10%) from the O-linked structures. Hydrazinolysis and analysis of the alkaline borohydride-resistant portion of the glycoprotein indicated the presence of mainly triantennary, complex-type structures (N-linked) containing three sialic acids residues plus L-fucose. Serial lectin-affinity chromatography of the hydrazine-released saccharides with concanavalin A-agarose, pea lectin-agarose, L-PHA-agarose, and E-PHA-agarose, indicated the absence of high-mannose or hybrid-type structures and further confirmed the presence of triantennary, complex-type units.

Involvement of both heparanase and plasminogen activator in lymphoma cell-mediated degradation of heparan sulfate in the subendothelial extracellular matrix

The effect of plasminogen on the ability of highly metastatic ESb mouse lymphoma cells to degrade heparan sulfate (HS) in the subendothelial extracellular matrix (ECM) was studied. A metabolically sulfate-labeled ECM was incubated with the lymphoma cells, and labeled degradation products were analyzed by gel filtration on Sepharose 6B. Heparanase-mediated release of low-Mr (0.5 less than Kav less than 0.85) HS cleavage products was stimulated fourfold in the presence of plasminogen. Incubation of plasminogen alone with the ECM resulted in its conversion into plasmin, which released high-Mr (Kav less than 0.33) labeled proteoglycans from the ECM. Heating the ECM (80 degrees C, 1 hr) abolished its ability to convert plasminogen into plasmin, yet plasminogen stimulated, through its activation by the ESb plasminogen activator, heparanase-mediated release of low-Mr HS fragments. Heparin inhibited both the basal and plasminogen-stimulated degradation of HS side chains but not the total amount of labeled material released from the ECM. In contrast, aprotinin inhibited the plasminogen-stimulated release of high- as well as low-Mr material. In the absence of plasminogen, degradation of heated ECM by ESb cells was completely inhibited by aprotinin, but there was only a partial inhibition of the degradation of native ECM and no effect on the degradation of soluble HS proteoglycan. These results demonstrate that proteolytic activity and heparanase participate synergistically in the sequential degradation of ECM HS and that the ESb proteolytic activity is crucial for this degradation when the ECM-associated protease is inactivated. Plasminogen may serve as a source for the proteolytic activity that produces a more accessible substrate to the heparanase.

Occult pancreatic cancer with recurrent acute pancreatitis

A patient with occult pancreatic carcinoma associated with recurrent acute pancreatitis is reported. Endoscopic retrograde cholangiopancreatography after the first attack was normal, the diagnosis being made at repeat examination 10 months later.

An anticatalytic monoclonal antibody to avian plasminogen activator: its effect on behavior of RSV-transformed chick fibroblasts

A monoclonal antibody has been raised against the serine protease, plasminogen activator (PA) produced by Rous sarcoma virus-transformed chick embryo fibroblasts (RSVCEF), and selected for its ability to inhibit the catalytic activity of PA. The high specificity and anticatalytic nature of the antibody has allowed probing of the direct role of PA in cellular behavior. Microgram quantities of monoclonal IgG inhibit the overgrowth and the morphological changes associated with RSVCEF transformation and the degradation of extracellular matrix mediated by RSVCEF, indicating a catalytic role for PA in these cellular processes. Specific cleavage of extracellular matrix proteins by immunoaffinity-purified PA in the complete absence of plasminogen demonstrates a direct catalytic involvement of PA in matrix degradation.

Autocrine saturation of pro-urokinase receptors on human A431 cells

Single-chain pro-urokinase (pro-uPA) is present both in the medium and lysate of the A431 epidermoid carcinoma cell line. Most of the cell-associated pro-uPA is on the cell surface, as shown by indirect immunofluorescence and by surface iodination. Pro-uPA is not an integral membrane protein but is bound to a specific surface receptor that is completely saturated. A mild acid treatment uncovers the surface receptors by dissociating pro-uPA. Resaturation of uncovered receptors has been studied by reincubating cells in normal medium; within 40 min, 50% of the free sites are reoccupied. Excess uPA-specific antibodies prevent rebinding of ligand to the receptors. Thus, A431 cells first secrete uPA, which then binds to the surface receptor. We propose that the synthesis of uPA and uPA receptor by the same cell may provide a pathway for the activation of the metastatic potential of malignant cells.

Modulation of urokinase plasminogen activator gene expression during the transition from quiescent to proliferative state in normal mouse cells

We have investigated the regulation of urokinase (u-PA) mRNA in quiescent mouse fibroblasts and keratinocytes stimulated to divide by the addition of serum or epidermal growth factor (EGF), respectively. Serum stimulation of quiescent fibroblasts (BALB/c 3T3 or Swiss 3T3) results in an early and transient increase of u-PA mRNA level, which precedes by several hours the onset of DNA synthesis. A similar response is elicited by EGF stimulation of quiescent keratinocytes. The increase of u-PA mRNA parallels that of c-myc mRNA, does not require protein synthesis and is at least in part due to increase in template activity of the u-PA gene. Induction of terminal differentiation of mouse keratinocytes results in a decrease of u-PA mRNA which parallels the decrease of thymidine incorporation. In conclusion, variation in the level of u-PA mRNA is seen during G0/G1 transition and correlates with the proliferative state of these normal mouse cells.

Production of plasminogen activator by a primary HSV-2-induced hamster fibrosarcoma and its in vivo derived sublines

The plasminogen activator (PA) content of a primary HSV-2-induced hamster fibrosarcoma and sublines derived from its in vivo metastases was investigated using the indirect 125I-labeled fibrin plate method. Fresh tissue culture lines established from primary HSV-2-333-2-26 tumors were shown to produce levels of PA similar to sublines derived from lung or kidney foci that developed after resection of primary tumors. In comparison, normal hamster embryo fibroblast (NHEF) and baby hamster kidney cells produced little or no PA, although baby hamster lung fibroblasts produced intermediate levels of PA. In addition, no correlation was found between PA levels of the sublines and their ability to metastasize from subcutaneous tumors, although tumor cell lines were shown to produce significantly more PA than normal cells.

Effects of 1-hydroxyethylidene-1,1 bisphosphonate and (chloro-4 phenyl) thiomethylene bisphosphonic acid (SR 41319) on the mononuclear cell factor-mediated release of neutral proteinases by articular chondrocytes and synovial cells

Articular chondrocytes and synovial cells were stimulated to produce collagenase, neutral casein and proteoglycan-degrading proteinases by conditioned medium from human peripheral blood mononuclear cells. Collagenase, neutral casein and proteoglycan-degrading proteinase secretion was inhibited by SR 41319, a new bisphosphonate, in a concentration-dependent manner. Complete inhibition was achieved at about 0.3 mM. EHDP exhibited the same general profile but was about 10-fold less active and never completely inhibited the enzyme secretion. When added before MCF, SR 41319 had a protective effect against subsequent activation of the cells by MCF. SR 41319 also inhibited the increase of enzyme secretion by cells previously stimulated with MCF. The results suggest that the ability of SR 41319 to inhibit the MCF-mediated secretion of neutral enzymes involved in cartilage destruction could be valuable in the management of connective tissue damage in rheumatoid arthritis.

Differentiation-enhanced binding of the amino-terminal fragment of human urokinase plasminogen activator to a specific receptor on U937 monocytes

The purified amino-terminal fragment (ATF) of human urokinase plasminogen activator (residues 1-135), which is not required for activation of plasminogen, binds with high affinity to specific plasma membrane receptors on U937 monocytes. Intact urokinase efficiently competes for 125I-labeled ATF binding; 50% competition occurs with 1 nM urokinase. A large part of receptor-bound urokinase remains on the cell surface for at least 2 hr at 37 degrees C. Differentiation of U937 monocytes into macrophage-like cells specifically increases ATF binding 10- to 20-fold. These results suggest an important role for urokinase in monocyte/macrophage biology: the native enzyme binds to the cells with the amino-terminal domain; the catalytic, carboxyl-terminal domain remains exposed on the cell surface to stimulate localized proteolysis and facilitate cell migration.