SECRETION OF PLASMINOGEN ACTIVATOR BY STIMULATED MACROPHAGES

Cultured thioglycollate-stimulated peritoneal macrophages synthesize, accumulate, and continuously release high levels of plasminogen activators for at least 4 days whereas cultures of unstimulated macrophages do not; the higher specific catalytic activity of released vs. cell-associated enzyme suggests that the plasminogen activators are actively secreted. The major macrophage plasminogen activator is a serine protease of mol wt 48,000, and thus resembles the comparable enzyme released by virally transformed fibroblasts. Macrophages release a second plasminogen activator of mol wt 28,000 that is also a serine enzyme. The secretion products released by stimulated and unstimulated macrophages have been compared by SDS-polyacrylamide gel electrophoresis after chemical labeling with ³H-DFP or biosynthetic labeling with ¹⁴C-amino acids. These procedures show that some proteins are formed in both cultures, whereas others are uniquely secreted by each type of macrophage. The serine enzymes released by the two kinds of macrophages differ in specificity and electrophoretic mobility.     

PROPERTIES OF PLASMINOGEN ACTIVATORS FORMED BY NEOPLASTIC HUMAN CELL CULTURES

A series of human cell lines has been examined for fibrinolysis in culture. The sera that are activating for fibrinolysis by human cells are mouse, monkey, human, horse, and bovine. Individual human sera show considerable variation in the ability to activate fibrinolysis. In common with other neoplastic or transformed mammalian and avian cell cultures, human cell lines of neoplastic origin produce substantial amounts of plasminogen activator. Several cultures of nonmalignant origin also produce plasminogen activator, whereas cultures obtained from trypsinized human embryos, or from human embryonic skin do not. The human melanoma plasminogen activators are of two kinds: a major component with a mol wt of 50,000, and a minor species with a mol wt of approximately 60,000. Both are DFP sensitive, serine proteases.     

Activation in vitro of rheumatoid synovial collagenase from cell cultures.

Rheumatoid synovial cells dissociated from matrix and adherent to culture dishes released a latent form of collagenase into culture medium. Previous studies have shown that the latent enzyme does not complex with alpha2-macroglobulin and binds to fibrillar substrate. We now show that serum-free culture medium of the synovial cells contains an inhibitor of collagenase as well as latent enzyme; the two were separated on a column of acrylamide/agarose. Latent collagenase (estimated mol wt 45,000-49,000) was transformed by trypsin to active collagenase of approximately equal to mol wt 33,000. When mixed with inhibitor the active enzyme formed an inactive complex again with approximately equal to mol wt 45,000-49,000. The inhibitor(s) itself was found in one major peak of mol wt 33,000-35,000 and several minor peaks eluting with lower apparent molecular weight. Mersalyl, an organic mercurial compound, effectively activated latent collagenase producing an active enzyme with approximately equal to mol wt 33,000. Bacterial collagenase did not activate latent enzyme. We suggest that latent rheumatoid synovial collagenase, as it is harvested from synovial cells in culture, is an enzyme-inhibitor complex.     

Immunological analysis of plasminogen activators from normal and transformed hamster cells. Evidence that the plasminogen activators produced by SV40 virus-transformed hamster embryo cells and normal hamster lung cells are antigenically identical

Rabbits were immunized against the plasminogen activator released by SV4- virus-transformed hamster embryo cells. The resulting antiplasminogen activator immunoglobulin (APA-IgG) inhibited the enzymatic activity of the plasminogen activator produced by SV40-transformed hamster cells, and the plasmin-catalyzed release of these cells from the tissue culture dish. APA-IgG was not cytotoxic for these cells even in the presence of complement and did not inhibit their release of plasminogen activator. APA-IgG formed a single precipitin line in immunodiffusion plates using highly purified plasminogen activator as antigen. APA-IgG inhibited the plasminogen activator produced by newborn hamster lung cells and by an established diploid line (DON) of hamster lung cells, but did not inhibit plasminogen activators produced by normal or transformed hamster kidney cells or by cells of other species (mouse and human). We derive three major conclusions from these data: (a) There are several immunologically distinguishable forms (isozymes) of plasminogen activators in normal hamster tissues. (b) The plasminogen activators produced by normal hamster lung cells and by SV40 virus-transformed hamster embryo cells share antigenic determinants and are presumably the same isozyme. (c) The plasminogen activators produced by different hamster tumor cells do not share antigenic determinants and are presumably different isozymes.     

Local fibrinolytic activity and its structural basis in experimental gastric ulcers

The stomach contains plasminogen activators localized to submucosal vessels and to the mucosa. To study the release of plasminogen activators from mucosal cells, we induced mucosal damage by pyloric ligature and instillation of 0.5 mol/l HCl in rats. After 4 h, all rats developed focal necrotic lesions and a diffuse mucosal damage, as studied both by light microscopy and by scanning electron microscopy. Diffuse mucosal damage was accompanied by significant increase (P less than 0.001) in mucosal fibrinolytic activity based on plasminogen activators. This activity was probably derived from injured mucosal cells since focal necrotic lesions (erosions and ulcers) with total denudation of the mucosal epithelium lacked fibrinolytic activity. The results obtained in this study support the hypothesis that plasminogen activators are released during cellular degeneration.     

Different inhibition of one and two chain tissue plasminogen activator by a placental inhibitor studied with two tripeptide-p-nitroanilide substrates

The interaction of tissue plasminogen activator derived from a melanoma cell line with a specific plasminogen activator inhibitor from placental tissue, which inhibits urokinase and tissue plasminogen activator but not plasmin, was studied. Tissue plasminogen activator exists in two forms, a one chain and a two chain molecule. It was found that the two enzyme species each form 1:1 complexes with the inhibitor and that the two chain enzyme binds the inhibitor very strongly, Ki = 3 X 10(-10) mol/l, whereas the one chain enzyme forms a much weaker complex, Ki is approximately 10(-7) to 10(-8) mol/l. Substrate hydrolysis is much more efficiently catalysed by the two chain plasminogen activator than by the one chain activator.     

Release of lysosomal enzymes and lactate dehydrogenase due to hematoporphyrin derivative and light irradiation of NHIK 3025 cells in vitro

NHIK 3025 cells in monolayer cultures were irradiated with near ultraviolet light in the presence of hematoporphyrin derivative (HPD). The release of lysosomal enzymes and the cytosol marker enzyme lactate dehydrogenase to the culture medium was determined 1, 3, 6 and 24 hours after irradiation. The enzyme activities of the cell pellet were investigated 24 hours after irradiating the cells. After exposure of HPD-labelled cells to light doses causing no cell inactivation, the leakage of enzymes was slightly inhibited in the first 6 hours followed by a period between 6 and 24 hours when the cells released the same amount or slightly more enzymes than the control. The enzyme activities of cell pellets made 24 hours after exposure were 40-75% of control values due to either a small inhibition of cellular enzyme activity or of inhibited cell growth by this dose. A higher light dose inactivating 80-90% of the cells, caused a rapid release of both lysosomal and cytosol enzymes. The cell pellets contained very little of the enzymes 24 hours after treatment and especially free intracellular enzymes had been released with high efficiency. Leupeptin, a lysosomal protease inhibitor, did not protect the cells from inactivation. We conclude that the release of lysosomal enzymes after porphyrins and light is of little significance in terms of cell killing.     

Increased sulfation of glycoconjugates by cultured nasal epithelial cells from patients with cystic fibrosis

Cystic fibrosis (CF) respiratory epithelia exhibit abnormal anion transport that may be linked to abnormal lung defense. In these studies, we investigated whether primary cultures of CF respiratory epithelial cells regulate abnormally the sulfate content of high molecular weight glycoconjugates (HMG) participating in airways' mucosal defense. HMG, including glycosaminoglycans and mucin-type glycoproteins released spontaneously into medium and HMG released from cell surfaces by trypsin, were metabolically labeled with 35SO4- and [6-3H]-glucosamine (GlcN) or 35SO4- and [3H]serine. All three classes of HMG from CF cells exhibited 35S/3H labeling ratios 1.5-4-fold greater than HMG from normal or disease control cells. Differences for labeling ratios of HMG from CF cells were shown to be the consequence of increased 35SO4- incorporation rather than decreased peptide synthesis and release or HMG glycosylation. The buoyant density of CF mucin-type HMG also was increased, consistent with increased sulfation. These observations suggest that oversulfation of a spectrum of HMG is a genetically determined characteristic of CF epithelial cells and may play an important pathophysiological role by altering the properties of mucous secretions and/or the interactions between selected bacteria and HMG at the airways' surface.     

DR (Ia-like) antigens on human melanoma cells. Serological detection and immunochemical characterization

11 cultured human melanoma cell lines were tested for the expression of DR antigens by using specific allo- and xenoantisera in an indirect rosette microassay. Four of these melanoma cell lines expressed DR antigens, but in lower amounts than expressed on cultured human B-lymphoid cells. Rabbits injected with the DR-positive melanoma cells produced antibodies that were serologically and immunochemically reactive with B-cell-derived DR antigens. Immunochemical studies indicate that melanoma cell-derived DR antigens have a two-chain structure with 34,000 and 27,000 mol wt components. The melanoma cell-derived DR beta-chain at 27,000 mol wt is slightly smaller than that of the Victor cell DR beta-chain whose mol wt is 29,000.     

Molecular cloning and nucleotide sequence of complementary DNAs encoding human short chain acyl-coenzyme A dehydrogenase and the study of the molecular basis of human short chain acyl-coenzyme A dehydrogenase deficiency.

Complementary DNAs encoding the precursor of human placental short chain acyl-coenzyme A (CoA) dehydrogenase (SCAD) (EC 1.3.99.2) were cloned and sequenced. The cDNA inserts in these clones were 1,852 bases in length combined, and encoded the entire 412-amino acid precursor SCAD (mol wt 44,303). This sequence included the 24-amino acid leader peptide moiety (mol wt 2,576) and 388 amino acids corresponding to the mature protein (mol wt 41,727). The comparison of SCAD and medium chain acyl-CoA dehydrogenase sequences revealed a high degree of homology, suggesting that these enzymes evolved from a common ancestral gene and belong to a gene family. We also studied mutant human SCAD in cultured skin fibroblasts from three patients with hereditary SCAD deficiency. Labeling fibroblast cultures with [35S]-methionine followed by immunoprecipitation with anti-SCAD antibody revealed that a normal size variant SCAD protein was synthesized. In all of the three SCAD-deficient cell lines, the size of variant SCAD mRNA as determined by Northern blotting using one of the normal SCAD cDNA as a probe was also normal, and no difference was observed on Southern blots in the restriction patterns of mutant genomic DNA using EcoRI, TaqI, HincII, and BamHI. These results suggest that the defects in SCAD in these cell lines are caused by a point mutation.     

Renin biosynthesis by human tumoral juxtaglomerular cells. Evidences for a renin precursor

Renin biosynthesis was studied in a juxtaglomerular cell tumor. The tumoral tissue had a high renin content (180 Goldblatt Units/g of tissue), was heavily stained by immunofluorescence using human renin antiserum, and exhibited numerous characteristic secretory granules by electron microscopy. In one series of experiments, renin biosynthesis was studied in tissue slices, by following the incorporation of radiolabeled amino acids into specific immunoprecipitable renin. Time course studies showed that renin was first synthesized in a high molecular weight form, 55,000 mol wt, i.e., 10,000 mol wt higher than that of active renin, and was then converted into a 44,000-mol wt form. In a second series of experiments renin tumoral cells were cultured. Small, round, birefringent cells obtained after collagenase digestion produced renin in both primary culture and subculture media. After 5 d most of the renin found in the culture medium was inactive, but could be activated by trypsin treatment. The tumoral tissue exhibited a strong renin immunofluorescence and numerous secretory granules were observed by electron microscopy. In contrast, the renin-producing cells isolated from this tumor and grown in culture showed little renin immunofluorescence and no secretory granule could be observed. The renin-producing cells in primary culture and subculture were pulsed with radiolabeled amino acids, and immunoprecipitable radiolabeled renin was found in the culture media, thus demonstrating the actual biosynthesis of the enzyme. This renin was not stored inside cultured cells but was rapidly released into the medium and had a molecular weight of 55,000. No conversion of this inactive high molecular weight renin into the active, 44,000 mol wt form of renin was observed. We postulate the existence of two pathways for the processing, packaging, and secretion of renin in the tumoral cells: in juxtaglomerular cells of tumoral tissue renin is synthesized as a preprorenin and rapidly converted into prorenin (55,000 mol wt), which is in turn packaged in secretory granules where it is processed into active renin (44,000 mol wt) and finally secreted; in the cultured tumoral cells renin is still biosynthesized as a preprorenin molecule and then converted into prorenin, but is neither stored as granules nor processed into active renin. In this case the renin is released in an inactive form.     

A role for dipeptidyl peptidase IV in suppressing the malignant phenotype of melanocytic cells.

Dipeptidyl peptidase IV (DPPIV) is a cell surface peptidase expressed by normal melanocytes, epithelial cells, and other cells. Malignant cells, including melanomas and carcinomas, frequently lose or alter DPPIV cell surface expression. Loss of DPPIV expression occurs during melanoma progression at a stage where transformed melanocytes become independent of exogenous growth factors for survival. Tetracycline-inducible expression vectors were constructed to express DPPIV in human melanoma cells. Reexpressing DPPIV in melanoma cells at or below levels expressed by normal melanocytes induced a profound change in phenotype that was characteristic of normal melanocytes. DPPIV expression led to a loss of tumorigenicity, anchorage-independent growth, a reversal in a block in differentiation, and an acquired dependence on exogenous growth factors for cell survival. Suppression of tumorigenicity and reversal of a block in differentiation were dependent on serine protease activity, assessed using mutant DPPIV molecules containing serine-->alanine substitutions. Surprisingly, dependence on exogenous growth factors was not dependent on serine protease activity. Reexpression of either wild-type or mutant DPPIV rescued expression of a second putative cell surface serine peptidase, fibroblast activation protein alpha, which can form a heterodimer with DPPIV. This observation suggests that rescue of fibroblast activation protein alpha may play a role in regulating growth of melanocytic cells. These results support the view that downregulation of DPPIV is an important early event in the pathogenesis of melanoma.     

Immunochemical analysis of the released Leu-2 (T8) molecule

We recently have found that the human T cell antigen Leu-2 was specifically released from Leu-2-bearing cells. The preliminary study showed that the released Leu-2 (RLeu-2) from HPB-ALL cells was composed of a single polypeptide chain of 27,000 molecular weight (mol wt), which was smaller than the subunit of the homodimeric molecule found on the cell surface. In the present study, RLeu-2 was further characterized and compared with cellular Leu-2 (CLeu-2). Metabolically radiolabeled Leu-2 was released from HPB-ALL cells and this released Leu-2 molecule had a mol wt of 27,000. Cell surface radioiodinated HPB-ALL cells were found to release radioactive Leu-2 molecules and this antigen also had the same mol wt of 27,000. In both experiments, the CLeu-2 was reconfirmed to be composed of a 33,000-mol wt subunit under reducing conditions. These experiments establish that the 27,000-mol wt single polypeptide chain of Leu-2 released from the cell is derived directly from the homodimeric Leu-2 molecule on the cell surface, presumably by a specific proteolytic cleavage. Two-dimensional gel analysis showed that CLeu-2 exhibited extensive charge heterogeneity with predominantly basic isoelectric points, whereas RLeu-2 was a group of more acidic proteins with less charge heterogeneity. Although CLeu-2 and RLeu-2 showed several different immunochemical characteristics, the homology between these two antigens was confirmed by the following results: CLeu-2 and RLeu-2 were found to share at least three different antigenic determinants, Leu-2a and Leu-2b, and those which were detected by a polyvalent rabbit antiserum. Significant similarities between CLeu-2 and RLeu-2 were demonstrated by peptide mapping analysis of these antigens. Therefore, RLeu-2 appears to be the specific, physiological product of the CLeu-2 protein.     

Molecular cloning and sequence of the complementary DNA encoding human mitochondrial acetoacetyl-coenzyme A thiolase and study of the variant enzymes in cultured fibroblasts from patients with 3-ketothiolase deficiency.

Complementary DNAs encoding the precursor of human hepatic mitochondrial acetoacetyl-CoA thiolase (T2) (EC 2.3.1.9) were cloned and sequenced. The cDNA inserts in these clones were 1,518 bases in length when overlapped, and encoded the 427-amino acid precursor of this enzyme (45,199 mol wt). This amino acid sequence included a 33-residue leader peptide moiety and a 394-amino acid subunit of the mature enzyme (41,385 mol wt). The T2 gene expression in fibroblasts from four patients with 3-ketothiolase deficiency was analyzed by Northern blotting. The T2 mRNA in all four cell lines had the same 1.7 kb as that of the control. However, the amounts of T2 mRNA differed: the content was reduced in two cell lines (cases 1 and 3), whereas it was within a normal range in others (cases 2 and 4). Pulse labeling followed by subcellular fractionation revealed that the T2 proteins in the fibroblasts from these patients are present in the mitochondria. These results suggest that different mechanisms are involved in the enzyme defects in the four patients.     

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.     

Novel surface antigen expressed on dividing cells but absent from nondividing cells

Radioimmunoprecipitation followed by sodium dodecyl sulfate- polyacrylamide gel electrophoresis was used to study the distribution on human lymphoid cells of a previously undescribed surface antigen recognized by several heteroantisera. A glycoprotein with a 90,000 mol wt (under reducing conditions) was detected on all cell lines tested including T, B, null, and myeloid cell lines, although the amount of antigen present varied considerably. The antigen was absent from normal peripheral blood lymphocytes (PBL), B and T cells, monocytes, granulocytes, thymocytes, and erythrocytes. After stimulation with lectins or allogeneic B cells, the antigen was induced on PBL T cells. A limited number of leukemic T cells tested all expressed the antigen, as did melanoma cell line and human embryonic lung fibroblasts. Hence, the antigen was present only on dividing lymphoid cells and absent from nondividing cells, but was also present on the two examples of dividing non-lymphoid cells tested. Under nonreducing conditions, the 90,000-mol wt band normally present disappeared to be replaced by another at approximately 200,000 mol wt. The glycoprotein bound to lectins from lentil and ricin, but not to wheat germ agglutinin. It could be readily labeled metabolically by [35S]methionine or by surface iodination, and appeared to be a major membrane protein on some cell lines.     

Biosynthesis of electron transfer flavoprotein in a cell-free system and in cultured human fibroblasts. Defect in the alpha subunit synthesis is a primary lesion in glutaric aciduria type II.

We investigated the biosynthesis of electron transfer flavoprotein (ETF) in a cell-free system. Both alpha-(alpha-ETF, 32,000 molecular weight [mol wt]) and beta-subunits (beta-ETF, 27,000 mol wt) were nuclear-coded, and synthesized in the cytosol. alpha-ETF was synthesized as a precursor (p alpha-ETF), 3,000 mol wt larger than its mature counterpart, and was translocated into the mitochondria and processed to the mature alpha-ETF. The newly synthesized beta-ETF was the same as the mature beta-ETF. Using [35S]methionine labeling, we also studied the biosynthesis in cultured normal human fibroblasts. p alpha-ETF was detected when the cells were labeled in the presence of dinitrophenol or rhodamine 6G. Among six glutaric aciduria type II (GAII) and two ethylmalonic-adipic aciduria cell lines, defective p alpha-ETF synthesis was observed in three GAII cell lines, and beta-ETF synthesis was normal. In one of them, no p alpha-ETF was synthesized at all, while in another, a faint p alpha-ETF band of normal size was detected, and was efficiently processed. In the third line, alpha-EFT was 1,000 mol wt smaller than the normal counterpart, both as the precursor and as the mature form.     

Sites of synthesis of urokinase and tissue-type plasminogen activators in the murine kidney.

Kidneys have long been recognized as a major source of plasminogen activators (PAs). However, neither the sites of synthesis of the enzymes nor their role in renal function have been elucidated. By the combined use of zymographies on tissue sections and in situ hybridizations, we have explored the cellular distribution of urokinase-type (u-PA) and tissue-type (t-PA) plasminogen activators and of their mRNAs in developing and adult mouse kidneys. In 17.5-d old embryos, renal tubules synthesize u-PA, while S-shaped bodies produce t-PA. In the adult kidney, u-PA is synthesized and released in urine by the epithelial cells lining the straight parts of both proximal and distal tubules. In contrast, t-PA is produced by glomerular cells and by epithelial cells lining the distal part of collecting ducts. The precise segmental distribution of PAs suggests that both enzymes may be implicated in the maintenance of tubular patency, by catalyzing extracellular proteolysis to prevent or circumvent protein precipitation.     

The Synthesis of Glycosaminoglycans by Cultures of Corneal Stromal Cells from Patients with Keratoconus

Keratoconus is a disease that results in thinning and ectasia of the central cornea. Cultures of corneal stromal cells from patients with keratoconus were established and the synthesis of glycosaminoglycans compared with the synthesis of glycosaminoglycans by normal human corneal stromal cells in culture.Keratoconus and normal control cell cultures were incubated with sodium [(35)S]sulfate and [(3)H]glucosamine for 4 h. After incubation, the labeled glycosaminoglycans were isolated from the medium fractions and cells. Keratoconus and normal control cultures synthesized similar amounts of sulfated glycosaminoglycans independent of the age of donors and(or) the number of subcultures. In contrast to normal control cultures, most of the newly synthesized glycosaminoglycans produced by keratoconus cells were found in the growth medium and much less were in the cell layer.Treatment with glycosaminoglycan-degrading enzymes followed by paper chromatography showed that keratoconus cells, as normal control cells, produced hyaluronic acid and various sulfated glycosaminoglycans. The production of cell layer-related heparan sulfate was markedly reduced in keratoconus cultures. Because heparan sulfate has been shown to be associated with cell surfaces, the decreased heparan sulfate content could reflect changes at this location.     

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.