Characterization of a plasma membrane-associated plasminogen activator on thymocytes

Phenylmethylsulfonyl fluoride inhibits chemotactic peptide-induced actin polymerization and oxidative burst activity in human neutrophils by an effect unrelated to its anti-proteinase activity

Stimulation of polymorphonuclear leukocytes with the chemotactic peptide N-formylmethionylleucylphenylalanine (fMet-Leu-Phe) causes conversion of monomeric actin to polymeric actin. We studied the role of proteinase inhibitors phenylmethylsulfonyl fluoride PMSF) and diisopropyl fluorophosphate in fMet-Leu-Phe-induced actin polymerization in polymorphonuclear leukocytes. Pre-incubation of cells with PMSF (2 mM) for 1 min caused inhibition of fMet-Leu-Phe-induced actin polymerization, as studied by 7-nitrobenz-2-oxa-1,3-diazole (NBD) -phallacidin labeling and flow cytometry. PMSF also inhibited fMet-Leu-Phe-induced hydrogen peroxide release, superoxide anion generation and chemiluminescence. In contrast, diisopropyl fluorophosphate (5 mM) was unable to inhibit fMet-Leu-Phe-induced actin polymerization and superoxide generation, but was effective in inhibiting hydrogen peroxide production and chemiluminescence. PMSF did not cause any change in membrane potential by itself and failed to inhibit the membrane potential changes induced by fMet-Leu-Phe, indicating that PMSF does not affect the binding of fMet-Leu-Phe to the receptors. The high concentration of PMSF required coupled with the fact that diisopropyl fluorophosphate was unable to inhibit fMet-Leu-Phe-induced actin polymerization suggested that this activity of PMSF might be unrelated to proteinase inhibitory activity. Polymyxin B, a membrane-active antibiotic, had an effect similar to PMSF on fMet-Leu-Phe-induced actin polymerization. This suggests that PMSF may also be acting via its membrane effect rather than its anti-proteinase effect.

Differences between the F10, BL6 and F1 sublines of the B16 melanoma in the enhancement of plasminogen activator and plasminogen activator inhibitor secretion by phorbol myristate acetate

Analysis of conditioned medium from three sublines of the B16 melanoma [F1 (parental), BL6 (invasive), F10 (metastatic)] by SDS-PAGE and zymography revealed the presence of plasminogen activator activity at 60,000 daltons. The relative activity was F10 greater than F1 greater than or equal to BL6. Treatment of the cells with the tumor promoter, phorbol myristate acetate (PMA) led to increased secretion of PA by F10 cells and a lesser increase in secretion by F1 cells and BL6 cells. In addition, a second plasminogen activator activity at 45,000 daltons was detected in conditioned medium from PMA treated F10 cells. Conditioned medium from F10 and F1 cells was also shown to contain a 33,000 dalton plasminogen activator binding protein. Upon PMA treatment the concentration of the binding protein increased in medium from F10 cells but not in similarly treated F1 cells. The binding protein, very likely a plasminogen activator inhibitor, was nearly undetectable in conditioned medium from control and PMA-treated BL6 cells. Therefore, the three sublines, which differ in in vivo phenotypic characteristics, also differ in their in vitro regulation of proteinase and proteinase inhibitor synthesis.

A specific serine proteinase is inducible in Lyt-2+,L3T4- and Lyt-2-,L3T4+ T cells in vitro but is mainly associated with Lyt-2+,L3T4- effector cells in vivo

Recently, we and others reported on the expression of a serine proteinase in long-term cultured murine T lymphocyte cell lines. In an attempt to explore the distribution and possible regulation of this enzyme in T lymphocyte subsets, we performed the presented detailed study. We found that the proteinase is not expressed by thymocytes and resting T cells but can be induced by lectin or antigen in combination with lymphokine sources in vitro in macrophage-depleted unselected T cells as well as in both T cell subsets (Lyt-2+,L3T4- and Lyt-2-,L3T4+) separated by flow cytofluorometry. Furthermore, it appears that cell-associated proteinase activity is increasing with prolonged culture period of sensitized T lymphocytes and that it is higher in antigen-activated as compared to lectin-activated T cells. When tested for substrate specificity the T cell-associated proteinase was shown to preferentially cleave model peptide substrates carrying L-arginine at position P1 in combination with nonpolar amino acids at position P2 and P3. As concluded from its sensitivity to proteinase inhibitors the enzyme can be classified as a serine proteinase and by molecular sieving at high ionic strength it was shown to have a mol. mass of approximately 50-60 kDa. Analysis of in vivo activated T cells revealed that this particular proteinase was expressed in flow cytofluorometry sorted lymphocytic choriomeningitis virus-specific Lyt-2+,L3T4- cytolytic T lymphocytes but not in Lyt-2-,L3T4+ T cells presensitized with either Listeria monocytogenes or I-A alloantigens. The data demonstrate that the two T cell subsets (Lyt-2+,L3T4-; Lyt-2-,L3T4+) have distinct in vitro induction requirements for the expression of proteinase and that after activation of T cells in vivo the enzyme is preferentially associated with Lyt-2+,L3T4- effector cells.

Human neutrophil plasminogen activator is localized in specific granules and is translocated to the cell surface by exocytosis

The subcellular localization of plasminogen activator (PA) in human neutrophils was studied. The cells were disrupted by nitrogen cavitation and fractionated on Percoll density gradients into three major components containing the plasma membranes, the specific granules, and the azurophilic granules. The biochemical markers we used to identify these organelles were alkaline phosphatase, vitamin B12-binding protein, and beta-glucuronidase, respectively. Using the radioactive fibrin plate method, PA activity and plasminogen-independent fibrinolytic activity were measured. In resting neutrophils, PA was associated mainly with the membranes of the specific granules. In five individual experiments the activity of this fraction varied from 79 to 100% of the total; the remaining activity was found to be associated with the plasma membrane, and no activity was present in the azurophilic granules. In neutrophils that were activated by exposure to PMA (20 ng/ml for 15 min at 37 degrees C), the total recoverable PA activity remained unchanged; however, the main peak of activity (85% of total) shifted from the specific granules to the plasma membranes. The magnitude of the reduction of the enzyme in the specific granules paralleled that of vitamin B12-binding protein. PMA-activated, intact neutrophils had approximately 12-fold more surface-bound PA activity than resting cells. Recovery of PA activity from neutrophils was critically dependent on pretreatment of the intact cells with DFP before cavitation; 100-fold more PA activity was detected in DFP-pretreated cells. At the same time, this pretreatment reduced the plasminogen-independent fibrinolytic activity by approximately sevenfold. We determined that PA present in the neutrophils is of the urokinase (UK) type and that the enzyme is produced and stored as a pro-UK, a form insensitive to DFP inhibition. The reduction in the level of proteases (measured as fibrinolytic activity) and the resistance of pro-UK to DFP are most likely the two major reasons for the greatly improved recovery of PA from the DFP-pretreated cells. These findings show that in resting neutrophils PA is stored in the specific granules, and that during activation, it translocates to the outer surface of the plasma membranes, thus equipping the cell with an ecto-proteolytic potential.

Species differences in the expression of caseinolytic proteinases and plasminogen activators by bone marrow cells

Intact viable bone marrow cells from hamsters (Mesocricetus aruatus), rat (Rattus norvegicus), guinea pig (Cavia porcella) and rabbit (Oryctolagus cuniculus) were analyzed for caseinolytic proteinases and plasminogen activator activity. Species specific quantitative and qualitative differences in caseinolytic activity were detected. Quantitative and qualitative differences in plasminogen activator expression were observed. Cellular fractionation experiments revealed a heterogenous distribution of plasminogen activator activity among subpopulations of cells. The plasminogen activator activity associated with bone marrow cells behaved as ectoenzymes. These results indicated that different species may regulate bone marrow cell proteinase activity in a species-specific manner, compatible with their unique regulatory requirements.

Plasminogen-dependent fibrinolytic activity in normal human lymphocytes: diminished lymphocyte plasminogen activator in chronic lymphocytic leukemia

Discrepancies in correlations between fibrinolytic activity and metastatic potential of malignant cells has resulted in speculation on the putative role of plasminogen activators (PA) in cancer. In this report we have compared lymphocyte PA from 40 patients with chronic lymphocytic leukemia (CLL) to normal human B- and T-lymphocytes. Lymphocytes were isolated from peripheral blood by Ficoll-Hypaque centrifugation. The B- and T-cells were further separated on nylon wool columns. Cell PA activity and cell membrane PA were determined using 3H-fibrin-coated plates with added human plasminogen. Lymphocytes did not lyse 3H-fibrin in the absence of plasminogen. Plasminogen-dependent fibrinolytic activities of normal B- and T-lymphocytes were comparable. The addition of protease inhibitors with trypsin or plasmin specificity to lymphocytes significantly inhibited normal PA, thus substantiating the serine protease spectrum of lymphocyte PA. Examination of lymphocytes from greater than 95% of patients with chronic lymphocytic leukemia revealed a marked decrease in lymphocyte and cell membrane PA as compared to normals. No correlation between Stage of CLL and lymphocyte PA was observed. Likewise, an inhibitor of PA in CLL lymphocytes was not detected. The function of PA in normal B-lymphocyte physiology and the potential pathogenetic role of diminished PA in CLL lymphocytes remain to be explored.

Characterization of an extracellular matrix-degrading protease derived from a highly metastatic tumor cell line

A proteolytic activity associated with the microsomal fraction of L-5178Y/Esb tumor cells has been characterized. The enzyme has a molecular weight of 80-90 kD as determined by affinity-labelling with [3H]DFP and SDS-gel electrophoresis. It cleaves ester substrates at the carboxyl position of lysine and arginine and can activate the proenzyme plasminogen. The enzyme is found to be associated with the plasma membranes of high and low metastatic tumor cell lines and is shed in high-molecular-weight form mainly by the high metastatic variant. The pH optimum for esterase and protease activities was 7.5-8.5. Although similar to trypsin in substrate specificity, the enzyme was not inhibited by lima-bean trypsin inhibitor but was inhibited by DFP, PMSF, aprotinin and leupeptin. Partially purified preparations of the protease can alone degrade 125I-labelled endothelial cell extracellular matrix, pointing at the putative role of this enzyme in tumor invasion.

Production of plasminogen activator by human natural killer cells. Large granular lymphocytes

In this report we have used highly purified populations of natural killer (NK) cells: large granular lymphocytes (LGL). This study demonstrates that freshly isolated and interleukin 2-cultured LGL produce the specific neutral serine protease, plasminogen activator (PA). We have found that the enzyme is expressed in both an extracellular form as well as in a cell-associated form. Upon subcellular distribution the latter form of the enzyme is associated with a cell-surface membrane-enriched fraction. LGL PA exists in multiple molecular weight forms ranging from 100,000 to 26,000. Interferon (IFN), the major positive regulator of NK cytolytic activity, caused a substantial enhancement of cell-associated, but not extracellular, PA. In contrast, LGL isolated from patients with Chediak-Higashi syndrome, who are known to be defective in NK activity, displayed low PA activity, altered morphology, and low NK killing relative to LGL isolated from normal donors. The possible role of LGL PA in the lysis of tumor cells by NK cells, either directly or indirectly, is discussed.

Murine lymphocyte cell surface proteolytic activity is strain related

A/J and C57 Br/cdj mice bear the H-2 haplotypes which are generally associated with high responses to bovine gamma globulin and type 3 pneumococcal polysaccharide. A/J has been reported, however, to produce higher levels of antibody than C57 Br/cdj mice against the antigens. The two strains of mice were used as model systems in this study to determine whether the level of lymphoid cell surface proteolytic activity is also genetically controlled. The results of this study illustrate that the level of lymphoid cell surface proteolytic activity is strain related. Since A/J lymphocytes were found to have a significantly higher rate of proteolysis than C57 Br/cdj lymphocytes, a correlation between lymphoid cell surface caseinolytic activity and immune responsiveness is suggested.

Morphological transformation of cells induced by Kirsten sarcoma virus transforming factor is independent of serine proteases

Reports from several laboratories have suggested that the virus transformed state may be maintained either by ectopically produced growth factors or alternatively by ectopically produced serine proteases including plasminogen activator. Here we show that the maintenance of transformation induced by Kirsten sarcoma virus induced growth factor(s) is independent of serine proteases in that 1) the factors are not themselves serine proteases, and 2) the growth factors do not induce the expression of detectable serine proteases or plasminogen activator.