Plasminogen activator in cultured Lewis lung carcinoma cells measured by chromogenic substrate assay

Methodologic Problems Encountered in the Assay of Proteinases in Lewis Lung Carcinoma, a Mouse Metastasizing Tumor

The proteolytic activity in homogenates and extracts of subcellular fractions prepared from subcutaneous Lewis lung carcinoma was determined using proteins and synthetic peptides as substrates. The presence of cathepsin D, plasminogen activator, cathepsin B-, cathepsin G-and elastase-like enzymes was observed. No difference was revealed between the proteolytic activity in homogenates of Lewis lung carcinoma, at the growth stage examined, and in homogenates of normal lung. High specific activities were found in the lysosomal extract, whereas decreasing activities were found in the nuclear extract, the homogenate and the post-lysosomal mitochondrial supernatant; no active or trypsin-activatable collagenase activity was detected. The presence in the tumor tissue of these enzymatic activities is in agreement with their proposed role in the process of metastasis. The lack of differences between homogenates of tumor and normal lung tissue suggests that the use of whole cells is required to selectively study tumor proteinases specifically involved in tumor malignancy.

Inhibition of metastasis of Lewis lung carcinoma by urinary trypsin inhibitor in experimental and spontaneous metastasis models

A purified human urinary trypsin inhibitor (UTI) and its related synthetic peptides were examined to determine whether they could inhibit production of experimental and spontaneous lung metastases by murine Lewis lung carcinoma (3LL) cells. Three peptides, peptide I, peptide 2 and peptide 3, representing the amino acid sequences within the UTI molecule, were synthesized. UTI and peptide 2 inhibited human leukocyte elastase (HLE). UTI and peptide 3 specifically inhibited human and murine plasmin activity. Peptide I had essentially no inhibitory activity. In an in vivo spontaneous metastasis model, multiple s.c. injections of UTI or peptide 3 for 7 days immediately after s.c. tumor cell inoculation significantly inhibited the formation of lung metastasis in C57BL/6 mice in a dose-dependent manner. UTI reduced lung tumor colonization more effectively than peptide 3. Peptides 1 and 2, however, did not affect the formation of lung metastasis. Inhibition of lung metastasis was not due to direct anti-tumor effects of UTI and peptide 3. In an in vivo experimental metastasis assay, multiple s.c. injections of UTI for 7 days after i.v. tumor cell inoculation inhibited metastatic lung tumor colonization, while peptide 3 did not affect metastasis. Peptides 1 and 2 did not affect the formation of lung metastasis. When examined with an in vitro assay system using a modified Boyden chamber, UTI and peptide 3 suppressed the invasion of tumor cells through Matrigel. UTI and peptide 3 inhibited neither cell proliferation nor the binding of tumor cells to Matrigel and showed no significant suppression of chemotactic migration of tumor cells to fibronectin. Our results suggest that UTI efficiently regulates the mechanism involved in not only the entry into vascular circulation of tumor cells (intravasation, though, at least in part, inhibition of the proteolytic enzyme plasmin) but also the extravasation step of the metastatic process.

Activity of interferon alpha, interleukin 6 and insulin in the regulation of differentiation in A549 alveolar carcinoma cells

The differentiation of A549, a human tumour cell line from type II pneumocytes, can be induced by a crude fibroblast-derived factor (FDF) isolated from the conditioned medium of glucocorticoid-treated lung fibroblasts. In the present report, we have used alkaline phosphatase as a differentiation marker to investigate the activity of a number of growth factors as potential candidates for this paracrine activity. This showed that insulin, interleukin 6 (IL-6), and interferon alpha (IFN-alpha) could simulate the activity of conditioned medium. Their effects were dexamethasone (DX) dependent, additive and reversible with a half-life of 1 week. Transforming growth factor alpha and beta, IL-1 alpha and epidermal growth factor, were all inhibitory, and inhibition was opposed, partially or completely, by DX. The most potent inducer was IL-6, but as DX was shown to decrease the concentration of IL-6 in lung fibroblast-conditioned medium it seems an unlikely candidate for FDF. Unlike FDF, all of the positive-acting factors were shown to induce plasminogen activator. FDF has also been shown to be active in the absence of DX. This suggests that differentiation-inducing activity may be present in several paracrine factors, but that so far a candidate for FDF has not been identified.

Inhibition of metastasis of Lewis lung carcinoma by a synthetic peptide within growth factor-like domain of urokinase in the experimental and spontaneous metastasis model

Four synthetic peptides (residues 20-30 and 17-34) within the growth factor-like domain (GFD) of murine and human urokinase-type plasminogen activator (uPA) were examined to determine whether they inhibit production of experimental and spontaneous lung metastasis by murine Lewis lung carcinoma (3LL) cells. In an in vivo experimental metastasis assay, which determines mainly the later steps of the metastatic migration process (extravasation from the bloodstream and then growth into pulmonary tumor), none of the peptides introduced by i.v. single co-injection into syngeneic C57B1/6 mice inhibited pulmonary metastasis, when 3LL cells were pre-incubated with the peptides followed by i.v. co-injection of the peptide and cells. In addition, none of the peptides, when injected i.p. daily for 7 days after i.v. tumor cell inoculation, reduced the number of lung tumor colonies. In a second in vivo assay that measures metastasis from a primary tumor (spontaneous metastasis model), multiple i.p. injections of the mouse peptide 17-34 for 7 days after s.c. tumor cell inoculation significantly inhibited metastatic lung tumor colonization in a dose-dependent manner, whereas human peptide 17-34 had no effect. Mouse and human peptide 20-30 had no effect either. The inhibition of lung metastasis was not due to direct antitumor effects of mouse peptide 17-34. Our results indicate that occupation of uPA receptors on 3LL cells by the enzymatically inactive mouse peptide 17-34 or prevention of rebinding of uPA synthesized by tumor cells to their receptor specifically reduced tumor cell invasion and formation of metastasis and that uPA may regulate more efficiently the mechanism involved in the entry of tumor cells into vascular circulation than extravasation during the metastatic process.

Urokinase-type plasminogen activator activity increases during the growth of two murine mammary adenocarcinomas with different metastasizing abilities

Urokinase-type plasminogen activator (u-PA) plays an important role in tumor growth and metastasis. The aim of this work was to study the u-PA production, in vitro and in vivo, in a transplantable murine mammary adenocarcinoma (M3), moderately metastatic to lung, and in a related tumor variant (MM3), highly metastatic to the same organ, during tumor development. At different times post-transplantation, tumors were employed to prepare either primary cell cultures or homogenates. PA activity from conditioned media (CM), cell lysates (CLs) and tumor homogenates (THs) was quantitated by means of a fibrinolytic assay. Immunoneutralization and zymographic assays were performed to identify the PA present in both tumors. PA activity in CM, CLs and THs, that was undetectable at early stages, increased significantly along the growth of M3 adenocarcinoma. Secreted PA activity in MM3 CM was measurable at early stages and consistently increased up to 37 days post-transplantation, but a marked fall of activity was found at 48 days. PA activity in MM3 THs exhibited the same enhancement and late fall found in vitro. A positive correlation was observed between tumor size and THs PA values in both tumors. The PA present in cell cultures and THs was identified as of the u-PA type. These results support the hypothesis that high u-PA levels are important for tumor invasion and that the stage of tumor development is a critical factor in their PA activity.

Paracrine control of differentiation in the alveolar carcinoma, A549, by human foetal lung fibroblasts

Synthesis of pulmonary surfactant (PS) is necessary for normal functioning of the lungs and its production is indicative of normal differentiated lung. The human alveolar carcinoma, A549, has been found to synthesis and secrete PS in vitro. The purpose of this study was to optimise the culture conditions for PS synthesis by A549 as well as to determine the potential role of foetal lung fibroblasts in the induction of PS by glucocorticoids. A549 cells growing in filter wells produced higher levels of PS in response to steroid, a 5-fold increase on the filter well compared to only a 1.5-fold increase when the cells were cultured on a conventional plastic substrate. A549 cells grown in filter wells responded to coculture with fibroblasts whether in direct contact or separated co-culture. A 20-fold increase in PS over control values was observed in separated steroid-treated co-cultures, suggesting the presence of a diffusible factor. A partially purified factor was isolated from fibroblast conditioned medium which was capable of inducing differentiation and other phenotypic changes in A549, namely induction of PS, reduction of plasminogen activator activity and reduction in the in vivo growth of A549 xenografts in nude mice. These results suggest that, under the correct conditions, A549 cells, although transformed, still retain the capacity to respond to differentiation-inducing signals from normal fibroblasts.

The role of urokinase-type plasminogen activator in aggressive tumor cell behavior

The correlation between urokinase-type plasminogen activator (uPA) expression and tumor cell invasion and metastasis has been well documented. Urokinase converts the zymogen plasminogen to plasmin, a trypsin-like enzyme with broad substrate specificities. Net uPA activity is determined not only by the amount of the enzyme itself, but also by its state of activation and the amount of specific plasminogen activator inhibitors (PAIs) present. Both uPA and its substrate, plasminogen, can bind to cells via specific membrane-associated receptors. Expression of uPA, uPA receptor (uPAR), and PAIs is regulated by growth factors, oncogenes, and other effector molecules. In the present review we discuss the interactions of uPA with its receptor, inhibitors, and substrate and how these interactions influence malignant behavior. We also review recent reports in which investigators have used anti-catalytic antibodies and/or gene transfection to demonstrate that uPA is directly involved in tumor cell invasion and metastasis.

Phenotypic properties of herpesvirus-transformed cells with high tumorigenic and metastatic ability

Herpes simplex virus type 2-transformed hamster embryo fibroblasts (333-8-9 cells) produce increased plasminogen activator (PA) compared with normal hamster cells. These cells produce undifferentiated fibrosarcomas at the inoculation site in newborn hamsters, and metastasize to the lungs. Using a direct PA assay, in which 125I-labeled plasminogen is cleaved, the optimum pH and osmolarity for detection of the 333-8-9 extracellular PA were pH 8.9 and approximately 150 mOsmol. Secretion of enzyme did not vary significantly on a per cell basis over cell densities from 0.1 to 8.0 X 10(7) cells/T-75 cm2 flask. This assay demonstrates that the 333-8-9 cells produce at least 20-fold greater levels of PA than normal cell counterparts. Based on the molecular weight (50-58 kDa) of secreted 333-8-9 cells PA and lack of fibrin stimulation, we conclude that it is a urokinase type PA. Subclonal lines of the 333-8-9 cells, selected for an increased PA phenotype were stable in culture, more tumorigenic and probably more metastatic. Correlation of these two events was examined by passaging 333-8-9 cells in vivo to select for greater tumorigenic potential and then determining the production of PA by the in vivo-derived sublines. The metastatic potential of the resulting cells was heterogeneous. Increased PA production upon increased passage in vivo did not always occur, whether the cells were passaged as subcutaneous tumors or as ascites tumors. Thus, while enzyme production correlated with tumorigenicity when selecting cells for an increased protease phenotype, this correlation was not observed when selecting for in vivo tumorigenicity. The results suggest that increased ability to make PA represents only one of multiple selective advantages for tumor growth.

Plasminogen activator activity of cultured murine macrophages and effects of isopropylmethylphosphonofluoridate (sarin)

Casein-elicited mouse peritoneal macrophages cultured in the presence of phorbol 12-myristate 13-acetate (PMA) express u-PA. Induction is maximal after 4 hr of stimulation and u-PA activity is mainly recovered with the membrane fraction of the cellular lysate. This enzymatic activity is inhibited by isopropylmethylphosphonofluoridate after stimulation by PMA. The presence of the organophosphorus compound before stimulation does not affect the activity. The results of the present study on the kinetics of u-PA activity in cultured macrophages, its subcellular localization and the effect of an organophosphorus ester are consistent with the concept that the development of pericellular proteolysis proceeds through a series of stages, namely, (a) synthesis of pro-u-PA, (b) binding to membrane receptors, (c) activation to a double-chain u-PA, and (d) conversion of plasminogen into plasmin. The assay procedure developed here provides a sensitive tool to investigate the mechanism of interference of chemicals with several steps of induction of this enzymatic activity in macrophages.

Do proteases play a role in cancer invasion and metastasis?

The main difference between a benign and malignant tumor is the ability of the malignant form to invade normal tissue and spread or metastasize to distant sites throughout the body. It is the ability to form metastasis which makes cancer such a difficult disease to treat. Evidence suggesting that proteolytic enzymes are involved in cancer spread is as follows: proteases are involved in normal destructive events and tissue remodelling, correlations exist between different protease activities and metastatic potential in model tumor systems, inhibitors and antibodies against proteases inhibit metastasis in model systems and the finding of highest levels of protease activity at the invading front in tumors. The most likely mechanism by which proteases could mediate metastasis is by catalyzing degradation of the extracellular matrix and basement membranes. It is concluded that if proteases could be proved to play a role in the spread of human cancers, inhibition of these enzymes could open up new therapeutic approaches for the control of malignancy.

Immunocytochemical localization of urokinase-type plasminogen activator in Lewis lung carcinoma

The invasively growing and metastasizing Lewis lung carcinoma consistently contained urokinase-type plasminogen activator (u-PA) enzyme activity. When investigated immunocytochemically with antibodies against u-PA, different parts of individual tumors showed a pronounced heterogeneity in staining intensity. Strong staining was found in areas with invasive growth and degradation of surrounding normal tissue, while other areas were completely devoid of staining. Immunoreactivity occurred both with a perinuclear cytoplasmic localization in tumor cells and associated with apparently extracellular material. SDS PAGE of tumor extracts, under both reducing and nonreducing conditions, followed by immunoblotting, showed only one immunocytochemically stainable band with an electrophoretic mobility corresponding to that of purified proenzyme to u-PA, while no two-chain u-PA was detected. This indicates that the major part of the activator in Lewis lung carcinoma is present as one-chain pro-u-PA.

A simple spectrophotometric assay of plasminogen activator: comparison with the fibrinolytic method

We describe a simple assay of plasminogen activator in which the enzyme reacts with a mixture of plasminogen and H-D-valyl-L-leucyl-L-lysine-p-nitroanilide for 1 h at 37 degrees C after which the absorbance is measured at 405 nm. The method detects as little as 2 CTA milliunits of activator and is linear over a 100-fold range of enzyme concentration. The new procedure has been used successfully for the assay of activator in breast tumor cytosols, cell culture supernatants, and pleural or ascitic fluids. Thirty-two biological samples have been assayed for plasminogen activator activity with both the spectrophotometric method and a classical fibrinolytic technique using radiolabeled fibrin. Although the two series of results are significantly correlated, the activities measured with the former assay are significantly different from those determined with the latter. It is shown that the spectrophotometric method is, in many respects, superior to the fibrinolytic procedure.

Interrelationship between differentiation and malignancy-associated properties in glioma

The phenotypic expression of cells derived from human anaplastic astrocytomas, rat glioma, normal human adult and foetal brain tissue have been examined for differentiated and malignancy-associated properties. Glial fibrillary acidic protein (GFAP), high affinity glutamate and gamma-amino butyric acid (GABA) uptake and glutamine synthetase were used as indicators of astroglial differentiation. Plasminogen activator and tumour angiogenesis factor were the malignancy-associated markers. The normal adult brain-derived lines showed some differentiated astroglial features and expressed low levels of the malignancy-associated properties. The foetal cultures contained highly differentiated astroglia while the glioma lines showed considerable phenotypic heterogeneity from highly differentiated to undifferentiated. The least differentiated glioma cells exhibited the highest plasminogen activator activities. The density-dependent control of phenotypic expression was also investigated. High affinity GABA uptake, and GFAP in rat C6 glioma cultures, increased with increasing monolayer cell density, events probably mediated by an increase in the formation of cell-cell contacts at confluence. Plasminogen activator activity decreased with increasing cell density.

Importance, localization and functional properties of the cell-associated form of plasminogen activator in mouse peritoneal macrophages

In inflammatory macrophages, plasminogen activator exists in two active forms, a soluble form released into the extracellular medium and a cell-associated form. This communication describes some properties of the cellular form of plasminogen activator, in intact macrophages and in cell lysates. Cellular plasminogen activator is a membrane protein, associated with the outer face of the plasma membrane; in intact macrophages, it participates in the activation of exogenous plasminogen and, thus, has to be considered as an ectoenzyme. A plasminogen activator activity can be detected in cell lysates (macrophage monolayers lysed in 0.1% Triton X-100) only when plasmin production is followed by the use of small synthetic substrates because a soluble inhibitor, released during extraction, blocks plasmin fibrinolytic activity. In these lysates, plasminogen activator molecules exist as high molecular weight unstable complexes exhibiting a high affinity for plasminogen.