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

Fetal bovine and dog serum were selectively freed of plasminogen by affinity chromatography. The resulting serum as well as native and reconstituted serum (obtained by the addition of purified plasminogen to the plasminogen-depleted serum) were used to examine the role of plasminogen in (a) growth of normal and SV-40-transformed hamster embryo fibroblasts in liquid medium, (b) growth of SV-40-transformed hamster embryo fibroblasts in soft agar, (c) aggregation - a characteristic morphological change of SV-40-transformed hamster cells, and (d) migration of SV-40-transformed and control 3T3 cells from a monolayer into a "wound." The results demonstrated that exponential growth of both normal and transformed cells in liquid medium proceeded at the same rate in the presence or absence of plasminogen. In contrast, removal of plasminogen markedly depressed the plating efficiency of transformed cells in soft agar, eliminated their characteristic aggregation, and substantially reduced the extent of migration. The role of plasminogen and its activation in oncogenic transformation is discussed.

An enzymatic function associated with transformation of fibroblasts by oncogenic viruses. II. Mammalian fibroblast cultures transformed by DNA and RNA tumor viruses.

Chick, hamster, mouse, and rat embryo fibroblast cultures, transformed by either DNA or RNA viruses, show fibrinolytic activity under suitable conditions of growth and in appropriate media; normal counterpart cultures do not. The fibrinolysin is produced by the interaction of two protein factors: one of these, a cell factor, is released by transformed cells and accumulates in the medium when cultures are incubated in the absence of scrum. The second factor, the serum factor, is a specific protein that is present in sera of many avian and mammalian species, including man. Not all sera yield fibrinolysin on interaction with any given transformed cell factor, and the spectrum of activating sera is distinctive for each cell factor. This pattern appears to be determined by the cell type, rather than by the transforming virus. An important role for the fibrinolysin in oncogenic transformation is suggested by the following correlations. (a) The initial appearance of fibrinolysin precedes the morphological change after the transfer to permissive temperatures of chick fibroblast cultures infected with a temperature-sensitive mutant of RSV. (b) The initiation of fibrinolysis and of morphological change both require the synthesis of new protein, but not the synthesis of either DNA or rRNA. (c) The activity of the fibrinolysin is correlated with the retention of abnormal morphology in hamster cells transformed by SV-40. (d) The sera of normal chicks effectively activate fibrinolysis with the cell factor from transformed chick cells. In contrast the sera of chicks with RSV tumors do not; these contain an inhibitor of the fibrinolytic activity.

An enzymatic function associated with transformation of fibroblasts by oncogenic viruses. I. Chick embryo fibroblast cultures transformed by avian RNA tumor viruses.

Chick embryo fibroblast cultures develop fibrinolytic activity after transformation by Rous sarcoma virus (RSV). This fibrinolytic activity is not present in normal cultures, and it does not appear after infection with either nontransforming strains of avian leukosis viruses or cytocidal RNA and DNA viruses. In cultures infected with a temperature sensitive mutant of RSV the onset of fibrinolysis appears after exposure to permissive temperatures and precedes by a short interval the appearance of morphological evidence of transformation. See PDF for Structure The rate of fibrinolysis in transformed cultures depends on the nature of the serum that is present in the growth medium: some sera (e.g., monkey or chicken serum) promote high enzymatic activity, while others (calf, fetal bovine) do not. Some sera contain inhibitors of the fibrinolysin. Based on the effect of a small number of known inhibitors, at least one step of the fibrinolytic process shows specificity resembling that of trypsin. The sera of sarcoma-bearing chickens contain an inhibitor of the fibrinolysin, whereas normal chicken sera do not. For general discussion, conclusions, and summary see the accompanying paper, part II, (J. Exp. Med. 137:112).

Association of a protease (plasminogen activator) with a specific membrane fraction isolated from transformed cells.

The intracellular distribution of specific protease, plasminogen activator (PA), has been examined in Rous sarcoma virus-transformed chick embryo fibroblasts (RSV-CEF). Cellular homogenates were fractionated by differential centrifugation followed by sucrose gradient centrifugation. The activities and the percent distribution of a series of marker enzymes, specific for different subcellular organelles, were compared to those of PA. Normal CEF have been similarly fractionated and the relatively low amount of PA activity present in these cells has been analyzed in terms of its subcellular distribution. A membrane fraction was isolated from the RSV-CEF that contained the bulk of the PA activity and less than 8% of the total cellular protein. The specific activity of the PA in this fraction is 40-fold higher than that of a comparable fraction isolated from companion cultures of normal cells. This fraction contains little or no nuclear and cytoplasmic material and is contaminated only to a relatively small degree with mitochondria, lysosomes, endoplasmic reticulum. Significant amounts of a putative Golgi membrane marker are present in this fraction. The relatively high specific activities of Na+,K+-ATPase, 5'-nucleotidase, and [3H]fucose indicate that the fraction is enriched in surface membrane. Further purification of the fraction by equilibrium centrifugation on shallow sucrose gradients reduces further the contaminating activities and results in a PA distribution that closely parallels the distribution of the membrane enzyme, 5'-nucleotidase. PA was not released from its membrane association by hypotonic and hypertonic extraction and ultrasonication, while granule-bound enzymes were released by these treatments. The PA activity from hamster SV40 cells fractionated the same way as that of RSV-CEF. These results suggest that a protease that is dramatically enhanced upon malignant transformation is associated with "plasma membrane-like" elements of the cell and may serve as an intrinsic modifier of cell surface proteins after malignant transformation.

Subtractive immunization yields monoclonal antibodies that specifically inhibit metastasis.

Subtractive immunization allowed the isolation and characterization of monoclonal antibodies that specifically inhibit metastasis but not proliferation of highly metastatic human tumor cells. The tolerizing agent cyclophosphamide was used to suppress the immune system in mice to dominant immunodeterminants present on a non-metastatic variant (M-) of the human epidermoid carcinoma cell line (HEp3). Mice were then inoculated with a highly metastatic variant (M+) of HEp3 to enhance an immune response to antigenic determinants present on metastatic cells. Hybridomas were generated and screened by ELISA for differential reactivity to M+ HEp3 over M- HEp3 cells. This experimental approach, termed subtractive immunization (S.I.), was compared to a control immunization protocol, which eliminated the cyclophosphamide treatment. The S.I. protocol resulted in an eight-fold increase in the proportion of mAbs that react with molecules enriched on the surface of the M+ HEp3 cells. Two of the mAbs derived from the S.I. protocol, designated DM12-4 and 1A5, were purified and examined for their effect in a metastasis model system in which chick embryos are transplanted with primary HEp3 tumors. Purified mAbs DM12-4 and 1A5, inoculated i.v. into the embryos, inhibited spontaneous metastasis of HEp3 cells by 86 and 90%, respectively. The mAbs are specifically anti-metastatic in that they have no effect on the growth of HEp3 cells in vitro nor did they inhibit primary tumor growth in vivo. The mAbs recognize M+ HEp3 cell surface molecules of 55 kD and 29 kD, respectively. These data demonstrate that the S.I. protocol can be used for the development of unique mAbs that are reactive with antigenic determinants whose expression is elevated on metastatic human tumor cells and which function mechanistically in the metastatic cascade.

The extracellular matrix of normal chick embryo fibroblasts: its effect on transformed chick fibroblasts and its proteolytic degradation by the transformants.

Extracellular matrix (ECM), prepared from chick embryo fibroblasts, contains fibronectin as the major structural protein along with collagen and other polypeptides as less abundant protein components. When Rous sarcoma virus-transformed chick embryo fibroblasts are cultured on the ECM in the presence of the tumor promoter tetradecanoyl phorbol acetate, the transformed cells lose their characteristic rounded morphology and align on and within the ECM fibrillar network. This restrictive aspect of ECM is only temporary, however, and with time (24-72 h) the transformed cells progressively degrade the ECM fibers and resume their rounded appearance. The matrix degradation can be monitored by employing biosynthetically radiolabeled ECM. The addition of purified chicken plasminogen to the Rous sarcoma virus-transformed chick embryo fibroblast cultures enhances the rate and extent of ECM degradation, due to the elevated levels in the transformed cultures of plasminogen activator. Plasminogen-dependent and -independent degradation of ECM has been characterized with regard to sensitivity to various natural and synthetic protease inhibitors and to the requirement of cell/ECM contact. Plasminogen-dependent degradation of ECM occurs rapidly when ECM and cells are in contact or separated, whereas plasminogen-independent degradation is greatly reduced when ECM and cells are separated, which suggests that cell surface-associated proteolytic enzymes are involved. A possible role in ECM degradation has been indicated for cysteine proteases, metallo enzymes, and plasminogen activator, the latter as both a zymogen activator and a direct catalytic mediator.

Characterization of proinsulin- and proglucagon-converting activities in isolated islet secretory granules.

The conversion of proglucagon and proinsulin by secretory granules isolated from both prelabeled and unlabeled anglerfish islets was investigated. Either granules isolated from tissue labeled with [3H]tryptophan and [14C]isoleucine or [35S]cysteine, or lysed granules from unlabeled tissue to which exogenously labeled prohormones had been added were incubated under various conditions. Acetic acid extracts of these granule preparations were analyzed for prohormone and hormone content by gel filtration. Both prelabeled and lysed, unlabeled secretory granules converted radiolabeled precursor peptides (Mr 8,000-15,000) to labeled insulin and glucagon. The accuracy of the cleavage process was established by demonstrating comigration of products obtained from in vitro cleavage with insulin and glucagon extracted from intact islets using electrophoresis and high-pressure liquid chromatography (HPLC). The pH optimum for granule-mediated conversion was found to be in the range of pH 4.5-5.5. Conversion of both proglucagon and proinsulin by secretory granules was significantly inhibited in the presence of antipain, leupeptin, p-chloromercuribenzoate (PCMB) or dithiodipyridine (DDP) but not chloroquine, diisopropyl fluorophosphate, EDTA, p-nitrophenyl guanidinobenzoate, soybean trypsin inhibitor, or N-p-tosyl-L-lysine chloromethyl ketone HCl. The inhibitory action of PCMB and DDP was reversed in the presence of dithiothreitol. Both membranous and soluble components of the secretory granules possessed significant converting activity. HPLC and electrophoretic analysis of cleavage products demonstrated that the converting activities of the membranous and soluble components were indistinguishable. The amount of inhibition of proinsulin and proglucagon conversion caused by 600 micrograms/ml porcine proinsulin was significantly lower than that caused by the same concentration of unlabeled anglerfish precursor peptides. These results indicate that the proinsulin and proglucagon converting enzyme(s) in the anglerfish pancreatic islet is a unique intracellular thiol proteinase(s) that may be granule membrane-associated and may require the presence of prohormone sequences in addition to the dibasic residues at cleavage sites for substrate recognition and/or binding.

Synergistic effect of tumor virus transformation and tumor promoter treatment on the production of plasminogen activator by chick embryo fibroblasts.

Cultures of Rous sarcoma virus-transformed chick embryo fibroblasts (RSVCEF) produce 50-fold more of the protease plasminogen activator (PA), than do normal chick embryo fibroblasts. Treatment of RSVCEF cultures with the tumor promoter phorbol myristate acetate (PMA) further enhances (8- to 12-fold) the level of PA activity. Increased levels of PA activity in RSVCEF are observed as early as 1 to 2 hr after PMA treatment. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrates that the PA produced by PMA-treated cultures has a molecular weight identical to that of the PA produced by untreated cultures. PA induction by PMA cannot be accomplished in cell-free extracts, but requires protein synthesis in intact cells. Under serum-free conditions, PMA-treated RSVCEF secrete high levels of PA for 4 to 6 days and undergo pronounced morphological alterations. Modified culture conditions and the use of PMA to induce PA has allowed for the accumulation of large amounts of RSVCEF culture fluid and the subsequent purification of the enzyme. The sensitivity of transformed CEF to PMA and the generation of enhanced proteolytic activity in the cellular microenvironment may provide a model system to examine the role of both PA in malignant transformation and PMA in tumor promotion.

Fibronectin enhancement of directed migration of B16 melanoma cells.

The migration of B16 melanoma cells into porous nitrocellulose filters fitted between the upper and lower compartments of blindwell chemotactic chambers was examined by light microscopy. Human plasma fibronectin placed in the lower compartment of such chambers enhanced in a time-, temperature-, and dose-dependent manner the directed migration of B16 cells into the filter. Fibronectin placed either in the upper compartment alone or in equal concentrations in both compartments did not result in a significant increase in B16 cell migration, indicating that a positive gradient of fibronectin is required. Pretreatment of filters with fibronectin to establish a gradient of bound fibronectin also stimulated the directed migration of B16 cells. The response to fibronectin appeared to be specific, since other plasma proteins and reduced fibronectin or trypsin-digested fibronectin failed to enhance the migration over base-line values. These results suggest that a specific haptotactic-chemotactic response to fibronectin was responsible for enhanced B16 cell migration.

Transepithelial invasion and intramesenchymal infiltration of the chick embryo chorioallantois by tumor cell lines.

The ability of cultured tumor cell lines to invade across epithelia was studied by placing 10(4) to 10(6) dispersed cells on the chorionic epithelium (CE) of the chorioallantoic membrane of the 10-day chick embryo. Tumor lines included Walker carcinosarcoma, F87 cl 6T2 and B16-BL6 melanomas, and KiSV-NIH, 3B77SC4, and HT 1080 sarcomas. The CE is a bilayer of cells with a superficial periderm overlying a basal layer. Invasion across an intact CE was very weak (limited to the formation of "microtumors" by a small fraction of the inoculated cells in 5 to 50% of the embryos) but was massive (most or all of the inoculated cells invaded in over 99% of the embryos) if the chorioallantoic membrane was traumatized in a fashion which disrupted the periderm but left the basal layer intact. Normal fibroblasts also invaded across the traumatized CE. The histological picture of invasion suggests that cells inoculated on the traumatized CE induced large-scale active retraction of the basal layer, resulting in the formation of large gaps in its continuity. Migration into the subjacent mesoderm occurred through these gaps. The nodules formed by both tumorigenic and normal cells became extensively vascularized within 3 days.

Tumor promoter-stimulated Mr 92,000 gelatinase secreted by normal and malignant human cells: isolation and characterization of the enzyme from HT1080 tumor cells.

A Mr 92,000 metalloprotease, originally observed in neutrophils, has been found to be secreted by various normal and malignant cells of fibroblastic, hematopoietic, and epithelial origin. The responsiveness of the various cell types to the tumor promoter phorbol ester (phorbol myristate acetate) to secrete this enzyme and a corresponding Mr 72,000 gelatinase has been determined using gelatin zymograms. The latent zymogen form of the Mr 92,000 enzyme has been purified from phorbol myristate acetate-stimulated HT1080 human fibrosarcoma cells using sequential gelatin-Sepharose affinity chromatography and gel filtration. Selective elution from gelatin-Sepharose allows for a distinct separation of the Mr 92,000 gelatinase from the Mr 72,000 gelatinase. A fraction of the tumor cell derived latent Mr 92,000 enzyme is isolated as an apparent complex with human tissue inhibitor of metalloproteases, which is partially dissociated in sodium dodecyl sulfate and completely dissociated upon reduction of disulfide bonds and upon p-aminophenylmercuric acetate treatment. Organomercurial treatment rapidly allows for autoactivation of the proenzyme to active Mr 83,000 and Mr 75,000 species. At physiological pH, the enzyme rapidly degrades gelatin into small fragments and slowly cleaves native type V collagen at an apparent single site. Native type IV collagen is degraded to a much lesser extent. The NH2-terminal amino acid sequence of the Mr 92,000 proenzyme has been determined and is distinct from the Mr 72,000 gelatinase/type IV collagenase which is constitutively produced by fibroblasts. The Mr 92,000 enzyme is also immunologically distinct from the Mr 72,000 enzyme but immunologically cross-reactive with the neutrophil, high molecular weight gelatinase. The Mr 92,000 enzyme constitutes a distinct member of the matrix metalloprotease family. Its substrate specificity implies a broad physiological role, acting on basement membrane type V collagen as well as on denatured (gelatinized) collagens and thus may be involved in the invasive and migratory phenotype of human cells.

Eukaryotic expression cloning with an antimetastatic monoclonal antibody identifies a tetraspanin (PETA-3/CD151) as an effector of human tumor cell migration and metastasis.

A monoclonal antibody (mAb), 50-6, generated by subtractive immunization, was found to specifically inhibit in vivo metastasis of a human epidermoid carcinoma cell line, HEp-3. The cDNA of the cognate antigen of mAb 50-6 was isolated by a modified eukaryotic expression cloning protocol from a HEp-3 library. Sequence analysis identified the antigen as PETA-3/CD151, a recently described member of the tetraspanin family of proteins. The cloned antigen was also recognized by a previously described antimetastatic antibody, mAb 1A5. Inhibition of HEp-3 metastasis by the mAbs could not be attributed to any effect of the antibodies on tumor cell growth in vitro or in vivo. Rather, the antibodies appeared to inhibit an early step in the formation of metastatic foci. In a chemotaxis assay, HEp-3 migration was blocked by both antibodies. HeLa cells transfected with and overexpressing PETA-3/CD151 were more migratory than control transfectants expressing little CD151. The increase in HeLa migration was inhibitable by both mAb 50-6 and mAb 1A5. PETA-3 appears not to be involved in cell attachment because adhesion did not correlate with levels of PETA-3 expression and was unaffected by mAb 50-6 or mAb 1A5. The ability of PETA-3 to mediate cell migration suggests a mechanism by which this protein may influence metastasis. These data identify PETA-3/CD151 as the first member of the tetraspanin family to be linked as a positive effector of metastasis.

Proteinase inhibitory activity released from the horseshoe crab blood cell during exocytosis.

The blood cell of the horseshoe crab, Limulus, is packed with granules that can be stimulated to release their contents by exocytosis. We have identified a family of proteinase inhibitors in the released materials. Included is a factor similar to the alpha 2-macroglobulin homologue present in the plasma and acid-stable and acid-instable active-site inhibitors. The acid-stable factor is active against both serine (trypsin, chymotrypsin) and metal (thermolysin) proteinases. The trypsin- and chymotrypsin-inhibitory activity has a molecular weight of 6100, as determined by gel-filtration chromatography.

Involvement of alpha 2-macroglobulin and C-reactive protein in a complement-like hemolytic system in the arthropod, Limulus polyphemus.

Homologues of two plasma proteins of vertebrates, alpha 2-macroglobulin and C-reactive protein, participate in a hemolytic system of the ancient arthropod, Limulus polyphemus. C-reactive protein, which can under the appropriate circumstances activate the classical pathway of the mammalian complement system, is an essential element of the hemolytic system of Limulus. The selective removal of C-reactive protein from the plasma with phosphorylethanolamine-agarose inactivated hemolysis. Addition of affinity-purified C-reactive protein to inactive plasma restored activity. Exposure of plasma to phosphorylethanolamine in solution potentiated hemolysis. alpha 2-Macroglobulin is a member of the same protein family as the complement protein C3 and both require an intact thiol ester for activity. Treatment of Limulus plasma with methylamine under conditions that inactivate thiol-ester-containing proteins reduced the hemolytic activity of some plasma preparations. Addition of purified Limulus alpha 2-macroglobulin to the methylamine-treated plasma restored hemolytic activity. However, alpha 2-macroglobulin is not necessary for hemolysis since the hemolytic activity of some pooled plasma preparations was insensitive to methylamine treatment under conditions that inactivated alpha 2-macroglobulin. Purified C-reactive protein was hemolytic in the absence of alpha 2-macroglobulin. These observations suggest that the proteins in Limulus plasma that participate in hemolysis represent the components of an ancient invertebrate defense system with distant evolutionarily affinities to the vertebrate complement system.

Alpha2-macroglobulin does not function as a C3 homologue in the plasma hemolytic system of the American horseshoe crab, Limulus.

A major problem of comparative immunology is the characterization of the internal defense systems that lyse foreign cells, such as bacteria and other microbial pathogens that have gained entry into the body. The plasma cytolytic system of the American horseshoe crab, Limulus polyphemus, is sensitive to treatment with methylamine, which inactivates the abundant plasma defense protein alpha2-macroglobulin. This has been interpreted to mean that alpha2-macroglobulin plays an important role in hemolysis, analogous to the role of complement component C3 of the mammalian complement system (Enghild et al., 1990). Sensitivity to methylamine has been suggested to reflect an evolutionary homology with the plasma cytolytic system of mammals, in which the complement system is inactivated by the reaction of methylamine with complement components C3 and C4. C3, C4 and alpha2-macroglobulin contain an internal thiol ester bond linking cysteinyl and glutamic acid residues and methylamine inactivates all three proteins by reaction with the thiol-esterified glutamic acid. However, we have recently shown that the principal effector of hemolysis in Limulus is the plasma lectin, limulin (Armstrong et al., 1996). In this article we show that native, unreacted alpha2-macroglobulin is not involved directly in hemolysis but instead that methylamine-reacted alpha2-macroglobulin inhibits the hemolytic activity of limulin. Thus the thiol ester proteins alpha2-macroglobulin and C3 operate very differently in the hemolytic systems of Limulus and mammals and are not functionally homologous. Limulus alpha2-macroglobulin functions indirectly in hemolysis: its inactivation yields an inhibitory molecule for limulin-mediated hemolysis.

Co-inoculation of human and murine carcinoma cells induces reciprocal suppression of metastasis by both cell lines.

The interactions of two cell lines having different metastatic properties, and the subsequent effects on dissemination were investigated using the chicken embryo metastasis assay. The highly aggressive human epidermoid cell line HEp-3 was tested alone or mixed with the mouse colon carcinoma cell line CL26 in this assay. When inoculated individually, each cell line forms experimental metastases in the chicken embryo, but only the HEp-3 cells give rise to spontaneous metastases. In embryos co-inoculated with both cell lines there was an overall reduction in metastatic burden in both the spontaneous and experimental metastasis assays. Furthers studies revealed that CL26 cells, when co-inoculated with HEp-3 cells did not acquire the ability to spontaneously metastasize. However, in the presence of CL26 cells, spontaneous HEp-3 metastasis was reduced. Intravenous co-inoculation of HEp-3 and CL26 cells also resulted in a reciprocal suppression of experimental metastasis by both cell lines. These studies demonstrate that the interactions of adjacent, phenotypically different tumor cells can have a suppressive effect on dissemination of one or both cell types.

Role of endogenous proteinase inhibitors in the regulation of the blood clotting system of the horseshoe crab, Limulus polyphemus.

Blood clotting in Limulus is dependent on the activity of a proteinase which converts the zymogen, coagulogen, into a form that undergoes polymerization to form the clot. The abilities of a series of recently discovered endogenous proteinase inhibitors to inhibit this enzyme and thereby serve as potential regulators of its activity were explored. The blood plasma of Limulus contains a single inhibitor that is functionally and structurally homologous to vertebrate alpha 2 macroglobulin. During exocytosis, the blood cells (amebocytes) release a series of inhibitors, including small quantities of the alpha 2 macroglobulin homologue; a low molecular weight, acid-and heat-stable inhibitor; and an acid acid-labile activity. Of the three inhibitory activities, only the cell-released, acid-labile inhibitor is capable of inhibiting the clotting enzyme.

Alpha2-macroglobulin: an evolutionarily conserved arm of the innate immune system.

All animals and plants have immune systems that protect them from the diversity of pathogens that would otherwise threaten their survival. The different components of the immune system may inactivate the pathogens themselves or promote the inactivation and clearance of toxic products produced by the pathogens. An important category of virulence factors of bacterial and prokaryotic pathogens are the proteases, which act to facilitate the invasion of the pathogens and to promote their destructive growth in the host organism. The present review concentrates on the comparative biology of an evolutionarily conserved arm of the immune system, the protein, alpha2-macroglobulin. alpha2-Macroglobulin is an abundant protein of the plasma of vertebrates and members of several invertebrate phyla and functions as a broad-spectrum protease-binding protein. Protease-conjugated alpha2-macroglobulin is selectively bound by cells contacting the body fluids and alpha2-macroglobulin and its protease cargo are then internalized and degraded in secondary lysosomes of those cells. In addition to this function as an agent for protease clearance, alpha2-macroglobulin binds a variety of other ligands, including several peptide growth factors and modulates the activity of a lectin-dependent cytolytic pathway in arthropods.

Activation of proMMP-9 by a plasmin/MMP-3 cascade in a tumor cell model. Regulation by tissue inhibitors of metalloproteinases.

To examine MMP-9 activation in a cellular setting we employed cultures of human tumor cells that were induced to produce MMP-9 over a 200-fold concentration range (0.03 to 8.1 nM). The secreted levels of TIMPs in all the induced cultures remain relatively constant at 1-4 nM. Quantitation of the zymogen/active enzyme status of MMP-9 in the cultures indicates that even in the presence of potential activators, the molar ratio of endogenous MMP-9 to TIMP dictates whether proMMP-9 activation can progress. When the MMP-9/TIMP ratio exceeds 1.0, MMP-9 activation progresses, but only via an interacting protease cascade involving plasmin and stromelysin 1 (MMP-3). Plasmin, generated by the endogenous plasminogen activator (uPA), is not an efficient activator of proMMP-9. Plasmin, however, is very efficient at generating active MMP-3 from exogenously added proMMP-3. The activated MMP-3, when its concentration exceeds that to TIMP, becomes a potent activator of proMMP-9. Addition to the cultures of already-activated MMP-3 relinquishes the requirement for plasminogen and proMMP-3 additions and results in direct activation of the endogenous proMMP-9. The activated MMP-9 enhances the invasive phenotype of the cultured cells as their ability to transverse basement membrane is significantly increased following zymogen activation. That this enhanced tissue remodeling capability is due to the activation of MMP-9 is demonstrated through the use of a specific anti-MMP-9-blocking monoclonal antibody.

Properties of cloned human glioblastoma cells. Release of a specific protease.

We cloned a previously characterized glioblastoma-derived parent cell line (12-18) in order to obtain a relatively homogenous population of human neural cells of neoplastic origin. These cells reach high densities in culture (over 100,000 cells/cm2) and have a high mean DNA content per cell of 18.1 +/- 0.9 pg. A histogram of the cloned cells' chromosome numbers revealed one peak and a modal near diploid number of 52, whereas the parent cell line had expressed polyploidy, with several peaks (including 52) at population doubling level 16. Several consistent results were obtained by Giemsa staining. A persistent structural alteration was the duplication of the long arm of chromosome #9 on to another arm of #9, and the translocation of the short arm of #9 to chromosome #21. We further observed that these cloned cells secrete a specific protease, a plasminogen activator (PA), into serum-free medium (SFM). This enzyme was assayed by the conversion of purified plasminogen to plasmin and the subsequent degradation by plasmin of 125I-labelled fibrin. Glioblastoma-derived cells had higher levels of cell-associated PA activity (2.9-fold) and released more PA activity into SFM (22-fold) than human fetal neural cells. The presence of this protease suggests a mechanism for the invasive character of these neoplasms (glioblastoma multiforme) in vivo.