Synthesis and secretion of plasminogen activators and plasminogen activator inhibitors in cell lines of different groups of human lung tumors.

Several human lung tumor cell lines derived from large cell, squamous cell, and small cell carcinomas, as well as from mesotheliomas of the lung have been investigated for their gene expression and secretion of urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (t-PA), and plasminogen activator inhibitors 1 and 2. All bronchogenic non-small cell carcinoma-derived cell lines studied could produce either plasminogen activators, their inhibitors, or both components, whereas in small cell lung carcinoma cell lines and cell lines derived from mesothelioma of the lung, no substantial amounts of any of these substances were synthesized. In detail, a large cell carcinoma-derived cell line, LCLC 97TM1, constitutively secreted large amounts of plasminogen activator. Northern blot analysis revealed RNA specific for u-PA and t-PA. Another large cell carcinoma-derived cell line, LCLC 103H, secreted smaller amounts of plasminogen activator and, additionally, plasminogen activator inhibitor. Specific mRNAs for u-PA and plasminogen activator inhibitors 1 and 2 were found in this cell line. In contrast, squamous cell carcinoma-derived cell lines secreted plasminogen activator only after treatment with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate; enhanced levels of u-PA, t-PA, and plasminogen activator inhibitor 1 mRNAs could then be demonstrated. The different expression of the plasminogen activator enzyme system distinguishes cell lines derived of non-small cell lung carcinoma from those of small cell lung carcinoma and may also reflect significant differences in the biological behavior of these tumor types.

Phenotypical changes of a human pancreatic adenocarcinoma cell line after selection on laminin-1/nidogen (LM/Ng) substratum.

A cell line (PaTu 8902LM) exhibiting an altered phenotypic appearance was selected from a highly dedifferentiated established human pancreatic tumour cell line (PaTu 8902) by repetitive exposure to laminin-1/nidogen substratum and subsequent selection for adherent cells. Polymerase chain reaction analysis for repetitive DNA indicated that both cell lines are genetically very closely related. The original PaTu 8902 line consisted of flat cells growing in monolayers. In contrast, the obtained PaTu 8902LM cells exhibited a spherical morphology and tended to form clusters. Immunofluorescence analysis using antibodies against apical and basolateral marker enzymes indicated that the PaTu 8902LM cells were polarized, arranging their apical surfaces around central lumenal structures when growing in clusters. In addition, the selected PaTu 8902LM cell line exhibited altered levels of a number of differentiation marker enzymes like 5'-nucleotidase, transglutaminase and plasminogen activators. The different morphological characteristics of both cell lines were maintained even after injection into nude mice. In xenografts, PaTu 8902LM cells were grouped around lumenal, duct-like structures, whereas the original PaTu 8902 cell line formed solid tumours composed of undifferentiated cells. Evidence is presented that the PaTu 8902LM cells are not merely selected from preexisting cells, but that the exposure of PaTu 8902 cells to laminin-1/nidogen had induced a stable transdifferentiation towards the phenotype of the epithelial cells lining the pancreatic secretory ducts. Thus the PaTu 8902LM cells resemble more closely those cells from which tumours of the pancreas originate in vivo and therefore might be a useful cell system in future analyses of the biology of pancreatic tumours which are of increasing incidence and clinical importance.

Cathepsin B and cysteine proteinase inhibitors in human lung cancer cell lines.

Cell lines derived from human squamous cell (EPCL), large cell (LCLC), and small cell lung cancer (SCLC) lines were investigated for the expression of cathepsin B (Cat B) and cysteine proteinase inhibitors (CPIs). The EPLC and LCLC lines expressed 5- to 50-fold more Cat B activity and contained more mature Cat B of M(r) 27-29 kDa (> 2.5 microg/mg total protein) than the SCLC lines (< 1.0 microg/mg total protein). The LPLC lines also secreted the highest amounts of Cat B precursor of M(r) about 46 kDa. Inhibitory activities against Cat B and papain were associated with high molecular mass (HMM) and low molecular mass (LMM) inhibitory proteins, both in cell extracts and in media. About 75% of the inhibitory activity was associated with HMM inhibitors, the majority of which were kininogens (M(r) > or = 67 kDa). The LMM inhibitors of M(r) 10-15 kDa were cystatin C and stefins A and B, which were quantitated by ELISA: stefins A and B were present in cell extracts and medium in similar concentrations (5-200 ng/10(6) cells), while 80-99% of the cystatin C was released in the medium (10-195 ng/10(6) cells). Phorbol ester (PMA), which induces protein-kinase C mediated signal transduction and enhances cellular differentiation in many non-small cell lung cancer (NSCLC) cell lines, increased intracellular Cat B activity and Cat B protein as well as its secretion in some cell lines but not in others, regardless of their histological type. PMA significantly (P < 0.049) decreased intracellular stefin A concentrations in two EPLC lines and non-significantly in two LCLC lines. PMA decreased secretion of stefin A in all EPLC lines, but not in LCLC lines, while IGF-I significantly increased stefin B secretion in both SCLC lines. These data showed that lung tumor cells produce both cysteine proteinases and cystatins. As the antagonistic molecules are regulated differently in histologically different types of lung tumor cells, it is possible that an imbalance between the proteinases and their specific inhibitors plays a role in progression of certain types of lung tumors in vivo.

Studies on tumor-cell-induced platelet aggregation in human lung cancer cell lines.

We investigated the ability of human lung cancer cells of different histological subtypes to cause platelet aggregation. Tumor-cell-induced platelet aggregation (TCIPA) was studied in vitro in 13 human lung cancer cell lines [small-cell lung cancer (SCLC), squamous-cell lung cancer, large-cell lung cancer, adenocarcinoma and alveolar-cell lung cancer]. Three tumor cell lines failed to aggregate platelets in platelet-rich plasma, whereas platelet aggregation was induced by 12 cell lines when added to washed platelets and minimal amounts of platelet-poor plasma (0.5% v/v). The thrombin antagonist hirudin inhibited TCIPA in non-small-cell lung cancer cell lines (NSCLC). In SCLC, TCIPA was fully abolished only when the ADP scavenger apyrase was added to hirudin. Thus ADP and thrombin generation by these tumor cell lines are responsible for platelet aggregation. The ability to activate platelets independently of coagulation factors VII and X was demonstrated for 8 cell lines. Electron-microscopically, direct tumor-cell/platelet contact was found to be the initiating mechanism of TCIPA in SCLC, whereas tumor-cell/platelet contacts in NSCLC could only be observed at the peak of the aggregation curve. Lung cancer cells activate platelets in vitro by generation of thrombin and/or ADP.

Cloning and recombinant expression of mouse coagulation factor X.

Engineering of recombinant coagulation factor X variants, which can be activated by tumor-associated proteinases may lead to the development of new therapeutic molecules. However, the evaluation of such variants requires an appropriate animal model. Therefore, we isolated the complete coding sequence of mouse coagulation factor X from mouse liver cDNA by polymerase chain reaction. The deduced amino acid sequence codes for a prepro protein of 481 amino acids homologous to factor X sequences from various species. Recombinant mouse factor X was expressed in human embryonic kidney cells and secreted into cell culture supernatant as zymogen, which could be converted to catalytically active factor Xa by Russell's viper venom. Purified recombinant mouse factor X restored coagulation in human factor X deficient plasma, demonstrating that mouse factor X is able to functionally interact with the human blood coagulation system. Recombinant mouse factor X opens the possibility to analyze therapeutically useful variants in the mouse system.

Secretion of a latent, acid activatable cathepsin L precursor by human non-small cell lung cancer cell lines.

Secretion of pro-cathepsin L, the precursor of a lysosomal cysteine proteinase, has been described for ras-transfected mouse fibroblasts and several human cancer cell lines. The secretion of a latent but stable precursor might be a means for tumor cells to involve this proteinase in extracellular matrix breakdown. Since lung cancer is the leading cause of cancer death in the industrialized countries, we therefore studied the secretion of pro-cathepsin L in 11 human non-small cell lung cancer cell lines (EPLC 32M1, NCI H157, EPLC 272H, U1752, LCLC 103H, LCLC 97TM1, U 1810, NCI H661, NCI H23, NCI H125, and NCI H596) and 8 human small cell lung cancer cell lines (SCLC 22H, NCI H60, NCI H82, NCI H526, NCI H146, NCI H841, NCI H510, and DMS 79). Immunoblot analysis of cell conditioned media showed that latent pro-cathepsin L (M(r) 42 kDa) was secreted in all 11 non-small cell lung cancer cell lines. Three of these cell lines secreted an additional inactive form of cathepsin L of M(r) 24 kDa. In contrast, the 8 small cell lung cancer cell lines did not secrete any detectable cathepsin L-immunoreactive material. Phorbol-12-myristate-13-acetate increased the secretion of pro-cathepsin L in 6 of the non-small cell lung cancer cell lines. The cathepsin L precursor could be activated in vitro at pH 3, accompanied by a shift in molecular mass to 34 kDa. Chicken egg white cystatin prevented the acid activation. Specific antibodies against a synthetic peptide from the pro-sequence of cathepsin L reacted with the nonsmall cell lung cancer cathepsin L precursor. Extracellular pro-cathepsin L may be important in the tumor biology of non-small cell lung cancer and would be a good target for novel diagnostic and therapeutic approaches, since the majority of physiological lysosomal proteinases are contained in intracellular compartments only.

The role of chymase in ionophore-induced histamine release from human pulmonary mast cells.

Human pulmonary mast cells contain the serine proteases tryptase and chymase. Chymase is present in much smaller quantities than tryptase. The definite physiological role of both enzymes remains to be elucidated, angiotensin processing has been proposed as one possible function of chymase. A dose-dependent inhibition of A 23187-induced histamine release from dispersed human lung mast cells was observed after pretreatment with diisopropylfluorophosphate (DFP) or 1-1-tosyamide-2-phenylethyl chloromethyl ketone (TPCK) but not with N-2-p-tosyl-1-lysine chloromethyl ketone (TLCK). In contrast, no inhibition was observed under the same conditions with isolated rat peritoneal mast cells. These results indicate that a chymase is probably an important factor in a late phase of human lung mast cell activation. Current work focuses on the isolation of human lung chymase to further investigate this topic.

A novel chymotrypsin-like serine proteinase from human lung.

A novel chymotrypsin-like serine proteinase with an M(r) of 30,000 has been isolated from human lung tissue. The enzyme was active on both the synthetic substrate Suc-Ala-Ala-Pro-Phe-SBzl and azocasein, with a pH optimum of 8.0 and a preference for high concentrations of NaCl for maximum activity. The proteinase was inhibited by diisopropylfluorophosphate, tosyl-phenylalanyl-chloromethane, chymostatin, soybean trypsin inhibitor, alpha-1-antichymotrypsin, and alpha-2-macroglobulin. It was not inhibited by C-1 inhibitor or aprotinin. An N-terminal sequence of IIGGTESKPDSRPYMALLQIVEPAVH indicated that this enzyme is a member of a superfamily of serine proteinases comprising cathepsin G, chymase, and the granzymes; however, it is clearly distinct from these enzymes on the basis of both physical and chemical properties.

Assay of complexed alpha 1-antichymotrypsin in plasma.

We introduce an assay to measure complexed alpha 1-antichymotrypsin in human plasma. The assay works on the principle that the target proteinase cathepsin G has a very high affinity to the surface of microtiter plates, even if these surfaces are blocked with albumin and Tween 20. alpha 1-Antichymotrypsin, when complexed to cathepsin G, is thus immobilized and can be detected with specific antibodies. The mean (SD) concentration of alpha 1-antichymotrypsin in 50 healthy individuals was 1.73 (0.58) nmol/L. The detection limit was 0.84 nmol/L. The results of the assay are linear to at least 14 nmol/L. We propose to use this assay for diseases in which increased turnover of alpha 1-antichymotrypsin or cathepsin G can be expected to clarify further the function of this enzyme-inhibitor system.

Assay of functional activity of alpha 1-antichymotrypsin in plasma.

We introduce a novel assay for measuring active alpha 1-antichymotrypsin (alpha 1X) in human plasma. The assay works on the principle that cathepsin G, immobilized in microtiter plates, preferentially binds alpha 1X, which then can be specifically quantified immunologically. alpha 1X activity can be detected even after 50,000-fold dilution of normal plasma. A linear range was defined for reproducible quantification. There was no interference by alpha 1-proteinase inhibitor or alpha 2-macroglobulin. The assay is designed to detect conditions having decreased alpha 1X activity to further elucidate the biological function of this prominent acute-phase protein.

The effect of serine esterase inhibitors on ionophore-induced histamine release from human pulmonary mast cells.

The serine proteases tryptase and chymase are present in human pulmonary mast cells. About 10-100 times more tryptase than chymase is found in these cells. However, a clear physiological role for both enzymes remains to be elucidated; angiotensin processing has been proposed as one possible function of chymase. A dose-dependent inhibition of A23187-induced histamine release from dispersed human lung mast cells was observed after pretreatment with the serine protease inhibitor diisopropylfluorophosphate (DFP) or the chymotrypsin-like enzyme inhibitor N-tosyl-L-phenylalanine chloromethylketone (TPCK) but not with the trypsin-like enzyme inhibitor N-tosyl-L-lysine chloromethylketone (TLCK). These results indicate that a chymase is probably an important factor in a late phase of human lung mast cell activation.

APC resistance as an additional thrombotic risk factor in a patient suffering from polycythemia vera and recurrent thrombosis.

Patients with polycythemia vera (PV) have a high risk of thrombosis. However, thrombosis is not sufficiently predictable with standard diagnostic procedures. We report on a patient with PV and recurrent thrombosis who nevertheless had a low platelet count while under therapy with hydroxyurea. As a result of duodenal ulcer and gastrointestinal bleeding, treatment with phenprocoumon was stopped years ago. Recently, heterozygosity for the factor V gene defect was diagnosed and anticoagulation therapy was reconsidered. In conclusion, the presence of resistance to activated protein C was an additional thrombotic risk factor that was important for our decision to change the treatment strategy in our patient.

Neoantigenic group on Fc fragments in rheumatoid arthritis synovial fluids.

Expression of neoantigens during denaturation of IgG by oxygen radicals or proteolysis was assumed to be a possible mechanism for stimulation of rheumatoid factor (RF) formation and/or granulocyte dependent inflammative joint destruction. The so-called human leukocyte elastase (HLE) regularly released by stimulated neutrophils f.e. into the RA synovial fluid is known to split IgG in vitro into papain like fragments and low molecular weight peptides. The n-terminal site of the HLE related Fc is bearing a neoantigenic group which is located near the hinge region but not expressed by the native IgG. The neoantigen itself is represented by the low molecular weight peptides produced by prolonged HLE-IgG proteolysis. Detection of HLE generated Fc in synovial fluids was performed by radioimmunoassay specific for the neoantigen. Patients were divided into the three groups; I RA (n = 23), II inflammative joint effusions except RA (n = 23), III osteoarthritis and trauma (n = 19). The biological effect of the neoantigen on to granulocyte oxidative metabolism was tested by Cytochrome C reduction and chemiluminescence. Neoantigen bearing Fc could be detected in 15 of 23 cases of group I, in group II in 11 of 23 cases and only in 7 of 19 cases in group III. The median concentrations were 0.62 micrograms in group I and zero in II and III. The HLE derived Fc were able to inhibit the oxidative metabolism of activated granulocytes in vitro. The O2- production of stimulated granulocytes was depressed dose dependent by the neoantigen. The neoantigenic group itself does not react with RF as proved by nephelometric titration of HLE derived Fc, neoantigenic peptide and native IgG against a RF standard.

Control of proteinase expression by phorbol-ester- and Fos-dependent pathways in human non-small-cell lung-cancer cells.

Activation of protein kinase C- (PKC) and Fos/Jun-dependent signal transduction pathways are thought to be major effects of oncogene action in different tumor systems including human non-small-cell lung carcinoma (NSCLC). We have previously shown that the phorbol ester analogue phorbol-myristate-acetate (PMA), which is a potent activator of PKC, can induce squamous-type cellular differentiation and the expression of proteinases, such as plasminogen activators and pro-cathepsin L, in several NSCLC cell lines. To investigate the PMA-dependent effect on proteinase secretion in more detail, we have now analysed the role of a downstream transmitter of PKC activity in this process, namely Fos, which is part of the AP-1 transcription factor in the nucleus. We transfected a cell line derived from an undifferentiated squamous-cell lung carcinoma with different chimeric fos-estrogen receptor constructs (fos-ER) which makes selective activation of this transcription factor possible. The resulting clones were treated either with PMA as activator of PKC, or with diethylstilbestrol (DES), an estrogen analogue binding to and thereby activating preformed Fos-ER molecules. We show that cells treated with either substance undergo similar phenotypic changes (change from cuboidal to spindle-cell type) and decrease their doubling rates and cloning efficiencies. This is paralleled by the induction of several proteinase genes such as t-PA, urokinase, and pro-cathepsins B and L. Contrary to activated PKC, Fos in this system seems to be unable to initiate terminal squamous-cell differentiation, as assessed by the production of cornified envelopes. It is, however, efficient in the stimulation of neutral or lysosomal proteinase secretion as determined by Western-blot analysis and zymography. This Fos-ER expressing system thus seems to be a valuable tool in the molecular dissection of pathways that lead to the activation and secretion of proteinases in NSCLC cells.

Differentiation capacity of human non-small-cell lung cancer cell lines after exposure to phorbol ester.

Three cell lines of squamous-cell carcinoma and 3 of large-cell carcinoma origin were investigated for the expression of differentiation markers and functional parameters (proliferation, morphology, cornified envelope formation, involucrin staining, transglutaminase activity, adhesiveness and migration) under normal cell culture conditions and after treatment with the tumor promoter phorbol-12-myristate-13-acetate (PMA). Although all original tumors had been described as poorly differentiated by histological grading, we found significant heterogeneity in the expression of differentiation markers in cell culture. A systematic grading of the cell lines became possible only after PMA stimulation. PMA generally increased expression of differentiation markers in cell lines of comparably low grades of differentiation, as indicated by dose-dependent inhibition of proliferation and cloning efficiency, induction of squamous markers, and decreased adhesiveness and cell motility. In contrast, cell lines of apparently higher differentiation by these criteria showed little response to PMA. The results presented show that the assessment of differentiation capacity by comparison of differentiation markers under normal cell culture and PMA-stimulated conditions in established NSCLC cell lines allows for a refined cell culture grading, which might advance the classification and characterization of such cell lines which, otherwise, appear to be very heterogeneous. It may also help to correlate cellular functions with various states of differentiation in vitro.

Prognostic impact of an activation of coagulation in lung cancer.

BACKGROUND: There is evidence that activation of coagulation by influencing tumour biology may have impact on clinical course of lung cancer. PATIENTS AND METHODS: We measured the activation markers thrombin-antithrombin complex (TAT) and prothrombin fragment F1 + 2 in 99 lung cancer patients immediately after diagnosis, before antineoplastic treatment. Outcome was assessed at the end of appropriate standard primary therapy (four to six courses of chemotherapy, surgery or radiation). RESULTS AND CONCLUSIONS: The activation markers (means +/- SEM) were lower in the 33 responders (RSP; complete or partial remission) than in the 66 non-responders (NRSP): TAT 3.96 +/- 0.48 vs. 9.69 +/- 1.57 micrograms/l (P < 0.001), and F1 + 2 1.09 +/- 0.09 vs. 1.64 +/- 0.25 nmol/l (P < 0.05). TAT levels were > 6 micrograms/l in 30 of 66 (45%) NRSP, but only 4 of 33 (12%) RSP. 88% of patients with TAT < or = 6 micrograms/l achieved remission, and 45% with TAT > 6 micrograms/l (P = 0.0014). In the subgroup of 46 patients with advanced disease, the six RSP showed lower TAT than the 40 NRSP: 4.65 +/- 0.94 vs. 11.92 +/- 2.49 micrograms/l (P < 0.01); one of six (17%) RSP, but 21 of 40 (53%) NRSP showed TAT > 6 micrograms/l. These data suggest that in lung cancer the activation of coagulation is an independent prognostic factor, since TAT levels were different between RSP and NRSP, also within the homogeneously unfavourable metastatic subgroup. It should be further studied, whether TAT can identify patients, whose prognosis could be improved by anticoagulation as an adjunct to standard antineoplastic therapy.

Activators of coagulation in cultured human lung-tumor cells.

Tumor matrix generation and tumor cell growth are supported by coagulation processes within the tumor tissue. Activators of coagulation were searched for in suspensions of 9 permanent human squamous-cell lung-cancer (EPLC 32MI, U1752), large-cell lung-cancer (LCLC 97TMI, LCLC 103H, U1810), and small-cell lung-cancer (N-592, H-526, DMS79, 86MI) cell lines. Incubation with these cells shortened the recalcification time in normal plasma (also in the presence of antibodies against tissue factor) or coagulation-factor-VII-, VIII-, IX- or X-deficient plasmas. The activators of coagulation in the 2 most active cell lines (U1752 and LCLC 103H) were further characterized in purified systems: the cleavage of chromogenic substrates, and the generation of markers of pro-thrombin activation were assessed. Three activators of coagulation were found in intact or sonicated cell suspensions and culture supernatants: (i) a tissue factor (TF)-like activity; (ii) an activity activating factor X, which in contrast to "cancer pro-coagulant" was not inhibited by iodoacetamide; and (iii) an activity-activating pro-thrombin, which was inhibited by the serine protease inhibitor PMSF and appeared to require plasmatic co-factor(s). The heterogeneous expression of coagulation activators by lung-tumor cell lines might be of significance for tumor biology and response to therapy.

Three types of human lung tumour cell lines can be distinguished according to surface expression of endogenous urokinase and their capacity to bind exogenous urokinase.

This study evaluates the cell surface expression of urokinase-type plasminogen activator (u-PA) and the capacity to bind exogenous urokinase as possible parameters for the distinction of various types of human lung tumours. Twelve different tumour cell lines including four small cell carcinoma, two large cell carcinoma, three squamous cell carcinoma, one adenocarcinoma and two mesothelioma cell lines of lung origin were investigated. Surface expression of endogenous u-PA was determined in a cellular radioimmunoassay (CRIA) using the u-PA-specific monoclonal antibody 98/6. To estimate additional u-PA binding capacity, exogenous two-chain, 54 kDa u-PA was employed in the CRIA. The influence of phorbol ester (PMA) treatment on expression and binding of these molecules was studied. Three different groups of lung tumour cell lines could be distinguished according to their expression of u-PA and u-PA-binding ability: (i) non small cell lung carcinoma (NSCLC) cell lines of squamous cell carcinoma/adenocarcinoma origin expressed small amounts of u-PA and bound little u-PA. Large cell carcinoma cell lines expressed high amounts of u-PA and bound large amounts of u-PA. In general, expression of u-PA and u-PA binding was enhanced after PMA treatment. (ii) Mesothelioma cell lines did not express u-PA, but were able to bind u-PA. (iii) Small cell carcinoma (SCLC) lines were devoid of surface-expressed u-PA and could not bind u-PA, both under untreated and PMA-treated conditions. It could thus be demonstrated that these three groups of lung tumour cell lines differ in their ability to express u-PA and to bind external u-PA. This may reflect the different in vivo growth behaviour and origin of the respective tumour groups.

Synthesis and secretion of the anticoagulant protein S and coexpression of the Tyro3 receptor in human lung carcinoma cells.

BACKGROUND: Protein S is a plasma protein that serves as an important cofactor for activated protein C in the blood anticoagulation system. Protein S also acts as a mitogen on distinct cell types and is a ligand for Tyro3, a member of the Axl family of oncogenic receptor tyrosine kinases. This lends support to the hypothesis that protein S might also be involved in tumor cell regulation. METHODS: The expression of protein S and receptor Tyro3 was examined in 22 lung carcinoma cell lines and normal bronchial epithelial cells by reverse transcriptase-polymerase chain reaction. Secreted protein S was identified by Western blot analysis of cell supernatants and tested in a protein S-dependent clotting test for anticoagulant activity. Immunohistochemistry with anti-protein S polyvalent antiserum was also performed on 31 primary lung carcinoma specimens. RESULTS: Protein S mRNA and secreted protein were found in 11 of 12 cell lines of nonsmall cell lung carcinoma (NSCLC) origin and in normal bronchial epithelial cells, but they were found in only 4 of 10 small cell lung carcinoma (SCLC) cell lines. The majority of lung carcinoma cell lines that expressed protein S (13 of 15) also revealed expression of the cognate receptor, Tyro3. Protein S that was present in cell supernatant had anticoagulant activity comparable to that of plasma protein S, suggesting that it is gamma-carboxylated. In lung tumor tissue, protein S antigen was found in 20 of 31 cases examined, predominantly in tumors of the squamous cell and bronchioalveolar cell types. Protein S was found not only in tumor cells but also in cells of the normal bronchial epithelium, in alveolar macrophages, and in endothelium. CONCLUSIONS: To the authors' knowledge, their report is the first of the synthesis of an active anticoagulant protein in epithelial cells of human cancer. It suggests that protein S, by binding to a receptor (Tyro3), may influence local anticoagulation events or other, as yet unidentified, aspects of lung tumor development.

Generation of angiostatin-like fragments from plasminogen by prostate-specific antigen.

Angiostatin, a potent inhibitor of angiogenesis, tumour growth and metastasis, is a biologically active fragment of plasminogen, containing the kringle domains 1-4. It is generated from plasminogen by limited proteolysis. We show that prostate-specific antigen (PSA), a serine proteinase secreted by human prostate and human prostate cancer cells, is able to convert Lys-plasminogen to biologically active angiostatin-like fragments, containing kringles 1-4, by limited proteolysis of peptide bond Glu439-Ala440 in vitro. In an in vitro morphogenesis assay, the purified angiostatin-like fragments inhibited proliferation and tubular formation of human umbilical vein endothelial cells with the same efficacy as angiostatin. This finding might help to understand growth characteristics of prostate cancer, which usually has low microvessel density and slow proliferation.