Multifunctional glyceraldehyde-3-phosphate dehydrogenase of Streptococcus pyogenes is essential for evasion from neutrophils

Streptococcus pyogenes is an important pathogen that causes pharyngitis, sepsis, and rheumatic fever. Cell-associated streptococcal C5a peptidase (ScpA) protects S. pyogenes from phagocytosis and has been suggested to interrupt host defenses by enzymatically cleaving complement C5a, a major factor in the accumulation of neutrophils at sites of infection. How S. pyogenes recognizes and binds to C5a, however, is unclear. We detected a C5a-binding protein in 8 M urea extracts of S. pyogenes by ligand blotting using biotinylated C5a. Searching of genome databases showed that the C5a-binding protein is identical to the streptococcal plasmin receptor (Plr), also known as streptococcal surface dehydrogenase (SDH) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). In the present study we identified a novel function of this multifunctional protein. Western blotting and immunofluorescence microscopy with anti-Plr/SDH/GAPDH showed that Plr/SDH/GAPDH is located on the bacterial surface and released into the culture supernatant. Next, we examined whether the streptococcal Plr/SDH/GAPDH inhibits the biological effects of C5a on human neutrophils. We found that soluble Plr/SDH/GAPDH inhibits C5a-activated chemotaxis and H2O2 production. Furthermore, our results suggested that soluble Plr/SDH/GAPDH captures C5a, inhibiting its chemotactic function. Also, cell-associated Plr/SDH/GAPDH and ScpA were both necessary for the cleavage of C5a on the bacterial surface. Together, these results indicate that the multifunctional protein Plr/SDH/GAPDH has additional functions that help S. pyogenes escape detection by the host immune system.     

Role of a streptococcal antigen in the pathogenesis of acute poststreptococcal glomerulonephritis. Characterization of the antigen and a proposed mechanism for the disease.

We studied the significance of a streptococcal protein (preabsorbing Ag) (PA-Ag) in the pathogenesis of acute poststreptococcal glomerulonephritis (APSGN). This protein was isolated from nephritogenic streptococci. Purification of PA-Ag was achieved by chromatography, followed by Sephadex IEF. A single protein band at pH 4.7 was identified as PA-Ag. The m.w. was 43,000. Rabbit antisera against PA-Ag and sera of patients with APSGN showed identical precipitation lines by immunodiffusion. Antibodies to PA-Ag were found to be present in 30 of 31 patients with APSGN, in 1 of 36 patients with uncomplicated group A streptococcal upper respiratory tract infections, and in 1 of 36 normal adults. By using immunoelectrophoresis, it was found that PA-Ag activates the alternate pathway of C. Other water-soluble streptococcal fractions, used as controls, did not activate the C system. The demonstration that PA-Ag is present in the glomeruli in the early phase of APSGN and its ability to activate C3 and factor B suggest that PA-Ag may be involved in the pathogenesis of APSGN, via in situ C activation.     

Analysis of expression of a cytosolic enzyme on the surface of Streptococcus pyogenes

The normally cytosolic glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase, (GAPDH) has been reported to be expressed on the surface of Streptococcus pyogenes, group A, where it can act as a plasmin binding protein (Plr), and potentially a signaling molecule. In studies of wild-type and isogenic mutants, an association between surface expression of antigenic GAPDH/Plr and M and M-related fibrinogen-binding proteins was identified. Inactivation of the mga gene, whose product controls expression of M and M-related proteins also influenced expression of surface GAPDH/Plr. Revertants or pseudorevertants of mga mutants led to concomitant re-expression of surface GAPDH/Plr and M and M-related proteins. Using surface enhanced laser desorption ionization (SELDI) mass spectroscopy, a physical association between GAPDH/Plr and streptococcal fibrinogen-binding proteins was demonstrated. These studies support the hypothesis that surface M and M-related proteins are involved in anchoring GAPDH/Plr on the surface of group A streptococci.     

Characterization of group B streptococcal glyceraldehyde-3-phosphate dehydrogenase: surface localization,enzymatic activity,and protein-protein interactions

During characterization of the surface antigens of serotype III group B streptococci (GBS), a protein with an apparent M(r) of approximately 173,500 migrating on a SDS--polyacrylamide gel was found to have an N-terminal amino acid sequence identical to that of the plasmin receptor (Plr) of group A streptococci, a surface-localized glyceraldehyde-3-phosphate dehydrogenase (GAPDH). This work begins to characterize GBS GAPDH and to assess its functional activity on the cell surface. The 1.0-kb gapC gene of GBS was amplified by PCR. plr and gapC demonstrated 87% homology. An anti-Plr monoclonal antibody reacted with GBS whole cells, suggesting GBS GAPDH is surface localized. Multiple serotypes of GBS demonstrated functional GAPDH on their surfaces. The anti-Plr monoclonal antibody recognized GBS protein bands of approximately 41 and 173.5 kDa, by Western blot. Presumably, these represent monomeric and tetrameric forms of the GAPDH molecule. GBS GAPDH was demonstrated by Western blot analysis to interact with lys- and glu-plasminogens. Fluid-phase GBS GAPDH interacted, by means of ELISA, with immobilized lys-plasminogen, glu-plasminogen, actin, and fibrinogen. Enzymatically active GAPDH, capable of binding cytoskeletal and extracellular matrix proteins, is expressed on the surface of GBS.     

Differential localization within human kidney of five membrane proteins expressed on acute lymphoblastic leukemia cells

The reactivity of a panel of monoclonal antibodies (MAb) produced against non-T, non-B acute lymphoblastic leukemia cells was investigated by immunoperoxidase staining of sections of normal human kidney. The antigens of kidney reactive with the MAb were isolated by immunoaffinity chromatography and were purified further by immunoprecipitation. Two MAb, 44D7 and 44H9, reacted with determinants found exclusively on the basolateral membranes of proximal convoluted tubules. The 44D7 antigen isolated from kidney was biochemically similar to that isolated from leukemic cells. It was resolved as a multimeric complex with an apparent m.w. of 120,000 when analyzed by SDS-PAGE under nonreducing conditions. The 44H9 antigen has not yet been purified from kidney. MAb 50B4 reacted with components of the interstitium and with the mesangium of glomeruli. It immunoprecipitated a polypeptide chain of apparent m.w. 85,000, similar to that of the 50B4 antigen isolated from leukemic cells. MAb 44G4 also reacted with the mesangium of glomeruli and with the interstitium of the kidney. However, the endothelium of glomerular capillaries and of interstitial blood vessels has also reacted with MAb 44G4. The kidney antigen recognized by MAb 44G4 was characterized as a major polypeptide band, 95,000 m.w. (reduced) and 125,000 m.w. (nonreduced), a subunit structure analogous to the 44G4 antigen isolated from leukemic cells. MAb 44E3 reacted with all cellular elements of glomeruli, tubules, blood vessels, and interstitium. Two polypeptide chains of apparent m.w. 94,000 and 90,000 were immunoprecipitated from kidney by MAb 44E3, while a single polypeptide chain of 94,000 m.w. was precipitated from leukemic cells. Our results describe five new antigens with distinctive cellular distributions within kidney.     

The primary inhibitor of plasmin in human plasma.

A complex between plasmin and an inhibitor was isolated by affinity chromatography from urokinase-activated human plasma. The complex did not react with antibodies against any of the known proteinase inhibitors in plasma. A rabbit antiserum against the complex was produced. It contained antibodies agianst plasminogen+plasmin and an alpha2 protein. By crossed immunoelectrophoresis the alpha2 protein was shown to form a complex with plasmin, when generated by urokinase in plasma, and with purified plasmin. The alpha2 protein was eluted by Sephadex G-200 gel filtration with KD approx. 0.35, different from the other inhibitors of plasmin in plasma, and corresponding to an apparent relative molecular mass (Mr) of about 75000. By sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, the Mr of the complex was found to be approx. 130000. After reduction of the complex two main bands of protein were observed, with Mr, about 72000 and 66000, probably representing an acyl-enzyme complex of plasmin-light chain and inhibitor-heavy chain, and a plasmin-heavy chain. A weak band with Mr 9000 was possibly an inhibitor-light chain. The inhibitor was partially purified and used to titrate purified plasmin of known active-site concentration. The inhibitor bound plasmin rapidly and strongly. Assuming an equimolar combining ratio, the concentration of active inhibitor in normal human plasma was estimated to be 1.1 mumol/1. A fraction about 0.3 of the antigenic inhibitor protein appeared to be functionally inactive. In plasma, plasmin is primarily bound to the inhibitor. Only after its saturation does lysis of fibrinogen and fibrin occur and a complex between plasmin and alpha2 macroglobulin appear.     

Purification of the Epstein-Barr virus-determined nuclear antigen from Epstein-Barr virus-transformed human lymphoid cell lines.

The Epstein-Barr virus-determined nuclear antigen (EBNA) was purified from extracts of the human lymphoid cell lines Raji, Namalwa, and B95-8/MLD by two different methods. In the first approach, the apparently native antigen was purified 1,200-fold by a four-step procedure involving DNA-cellulose chromatography, blue dexptran-agarose chromatography, hydroxyapatite chromatography, and gel filtration, employing complement fixation as the assay procedure. Such EBNA preparations specifically inhibited the anticomplement immunofluorescence test for EBNA and bound to methanol/acetic acid-fixed metaphase chromosomes. The purified antigen, which has a molecular weight of 170,000 to 200,000, yielded a single protein band of molecular weight about 48,000 by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. These data indicate that native EBNA has a tetrameric structure. In the second purification method, EBNA-containing cell extracts containing radioactively labeled proteins were incubated with anti-EBNA-positive sera, and antigen-antibody complexes were adsorbed to matrix-bound staphylococcal protein A. The bound proteins were then released with an SDS-containing buffer, and denatured EBNA was separated from antibody chains by SDS-polyacrylamide gel electrophoresis and visualized by fluorography. The denatured EBNA obtained in radiochemically pure form by this procedure has a molecular weight of about 48,000, so both methods yield an EBNA monomer of the same size.     

Fluorescent antibody study of diseased, end-stage human kidneys.

Forty cases of diseased kidneys at end-stage were studied by fluorescent antibody technique in search for viral etiology of glomerulonephritis and other renal diseases. Among these 40 cases, 12 (30%) were ascribed to immune complex disease because of detection of immunoglobulins and complement in glomeruli of the same kidney specimen. In 8 cases (20%) only complement was detected in glomeruli. In the remaining 50% neither complement nor immunoglobulin deposit was found in glomeruli. The etiologies of the latter cases remain unknown. Of 12 cases of kidney disease of immune complex origin, hepatitis virus type B surface antigen was detected in 2 cases. In these 2 cases the magnitude of immune complex deposits with complement was greater than that of other cases. Other than hepatitis B virus antigen, no other viruses including Coxsackieviruses, ECHO viruses, and HSV-1 could be detected by indirect fluorescent antibody techniques. The proportion of complement deposit to the deposition of complement with immune complex in the diseased kidneys at end-stage was calculated and statistically analyzed.     

Activation of pro-urokinase and plasminogen on human sarcoma cells: a proteolytic system with surface-bound reactants

Human HT-1080 fibrosarcoma cells produce urokinase-type plasminogen activator (u-PA) and type 1 plasminogen activator inhibitor (PAI-1). We found that after incubation of monolayer cultures with purified native human plasminogen in serum-containing medium, bound plasmin activity could be eluted from the cells with tranexamic acid, an analogue of lysine. The bound plasmin was the result of plasminogen activation on the cell surface; plasmin activity was not taken up onto cells after deliberate addition of plasmin to the serum-containing medium. The cell surface plasmin formation was inhibited by an anticatalytic monoclonal antibody to u-PA, indicating that this enzyme was responsible for the activation. Preincubation of the cells with diisopropyl fluorophosphate-inhibited u-PA led to a decrease in surface-bound plasmin, indicating that a large part, if not all, of the cell surface plasminogen activation was catalyzed by surface-bound u-PA. In the absence of plasminogen, most of the cell surface u-PA was present in its single-chain proenzyme form, while addition of plasminogen led to formation of cell-bound two-chain u-PA. The latter reaction was catalyzed by cell-bound plasmin. Cell-bound u-PA was accessible to inhibition by endogenous PAI-1 and by added PAI-2, while the cell-bound plasmin was inaccessible to serum inhibitors, but accessible to added aprotinin and an anticatalytic monoclonal antibody. A model for cell surface plasminogen activation is proposed in which plasminogen binding to cells from serum medium is followed by plasminogen activation by trace amounts of bound active u-PA, to form bound plasmin, which in turn serves to produce more active u-PA from bound pro-u-PA. This exponential process is subject to regulation by endogenous PAI-1 and limited to the pericellular space.     

Use of the surface proteins GapC and Mig of Streptococcus dysgalactiae as potential protective antigens against bovine mastitis

Streptococcus dysgalactiae is a significant pathogen associated with bovine mastitis in lactating and nonlactating dairy cows, causing a severe inflammatory response of the mammary gland, which results in major economic losses to the dairy industry. Two proteins from S. dysgalactiae strain SDG8 were tested for their protective capacity against a homologous bacterial challenge in a dry cow model. The first was a bovine plasmin receptor protein (GapC), which shares 99.4% sequence identity to the plasmin-binding Plr protein of group A streptococci. The second protein product was Mig, a alpha2-M-, IgG-, and IgA-binding protein present on the cell surface of SDG8. We investigated the efficacy of immunization with purified recombinant forms of GapC and Mig by measuring the number of somatic cells and assessing the presence of the challenge strain in mammary secretions following challenge. In this model, we found that, although the number of quarters containing SDG8 was significantly reduced in the GapC- but not in the Mig-immunized animals, the somatic cell counts from teat secretions were significantly decreased in both the GapC and Mig vaccinates.     

Purification of epidermal plasminogen activator inhibitor

A plasminogen activator inhibitor was purified from human cornified cell extract by DEAE-Sepharose, Sephacryl S-200, and high-performance liquid chromatographies on hydroxyapatite HPHT and anion-exchanger Mono Q at pH 7.2 and 8.0. The purified inhibitor showed Mr 43,000 and pI 5.2 50% inhibition of fibrinolytic activity (1.5 IU) of urokinase and tissue-type plasminogen activator was attained by 0.60 ng and 11.0 ng purified inhibitor, respectively. Synthetic substrate assay demonstrated slow tight-binding inhibition to both urokinase and tissue-type plasminogen activator. The inhibitor did not inactivate plasmin, thrombin, glandular kallikrein or trypsin.     

Schistosoma mansoni: Anodic polysaccharide antigen in glomerular immune deposits of mice with unisexual infections

In mice infected with unisexual Schistosoma mansoni, circulating anodic antigen was detected by immunofluorescence in glomeruli of 20 out of 22 animals from 7 to 30 weeks after infection. Circulating anodic antigen was present as finely granular deposits in the mesangium. The amount of circulating anodic antigen in the glomeruli was not clearly related to the worm burden but it increased during the course of the infection. These circulating anodic antigen deposits were accompanied by deposits of immunoglobulins, sometimes found in the same precise localization, and of complement. They probably represent the antigen part of immune complexes. Circulating anodic antigen appears to be a major candidate among the antigens involved in schistosomal glomerulopathy.     

Purification and functional characterization of glutamate-1-semialdehyde aminotransferase from Chlamydomonas reinhardtii

The formation of delta-aminolevulinic acid, the first committed precursor of chlorophyll biosynthesis, occurs in the chloroplast of plants and algae by the C5-pathway, a three-step, tRNA-dependent transformation of glutamate. Previously, we reported the purification and characterization of the first two enzymes of this pathway, glutamyl-tRNA synthetase and Glu-tRNA reductase from the green alga Chlamydomonas reinhardtii (Chen, M.-W., Jahn, D., Sch?n, A., O'Neill, G. P., and S?ll, D. (1990) J. Biol. Chem. 265, 4054-4057 and Chen, M.-W., Jahn, D., O'Neill, G. P., and S?ll, D. (1990) J. Biol. Chem. 265, 4058-4063). Here we present the purification of the third enzyme of the pathway, the glutamate-1-semialdehyde aminotransferase from C. reinhardtii. The enzyme was purified from the membrane fraction of a whole cell extract employing four different chromatographic separations. The apparent molecular mass of the protein was approximately 43,000 Da as analyzed by denaturing sodium dodecyl sulfate-polyacrylamide gel electrophoresis, by nondenaturing rate zonal sedimentation on glycerol gradients, and by gel filtration. By these criteria, the enzyme in its active form is a monomer of 43,000 Da. In the presence of pyridoxal 5'-phosphate, purified glutamate-1-semialdehyde aminotransferase converts synthetic glutamate 1-semialdehyde to delta-aminolevulinic acid. The enzyme is inhibited by gabaculine and aminooxyacetate, both typical inhibitors of aminotransferases. The purified glutamate-1-semialdehyde aminotransferase successfully reconstitutes the whole C5-pathway in vitro from glutamate in the presence of purified glutamyl-tRNA synthetase, glutamyl-tRNA reductase, Mg2+, ATP, NADPH, tRNA, and pyridoxal 5'-phosphate.     

Misfolded forms of glyceraldehyde-3-phosphate dehydrogenase interact with GroEL and inhibit chaperonin-assisted folding of the wild-type enzyme

We studied the interaction of chaperonin GroEL with different misfolded forms of tetrameric phosphorylating glyceraldehyde-3-phosphate dehydrogenase (GAPDH): (1) GAPDH from rabbit muscles with all SH-groups modified by 5,5'-dithiobis(2-nitrobenzoate); (2) O-R-type dimers of mutant GAPDH from Bacillus stearothermophilus with amino acid substitutions Y283V, D282G, and Y283V/W84F, and (3) O-P-type dimers of mutant GAPDH from B. stearothermophilus with amino acid substitutions Y46G/S48G and Y46G/R52G. It was shown that chemically modified GAPDH and the O-R-type mutant dimers bound to GroEL with 1:1 stoichiometry and dissociation constants K(d) of 0.4 and 0.9 muM, respectively. A striking feature of the resulting complexes with GroEL was their stability in the presence of Mg-ATP. Chemically modified GAPDH and the O-R-type mutant dimers inhibited GroEL-assisted refolding of urea-denatured wild-type GAPDH from B. stearothermophilus but did not affect its spontaneous reactivation. In contrast to the O-R-dimers, the O-P-type mutant dimers neither bound nor affected GroEL-assisted refolding of the wild-type GAPDH. Thus, we suggest that interaction of GroEL with certain types of misfolded proteins can result in the formation of stable complexes and the impairment of chaperonin activity.     

Down-regulation of plasmin receptors on human sarcoma cells by glucocorticoids

After incubation of confluent monolayer cultures of human HT-1080 fibrosarcoma cells with purified native human plasminogen in plasminogen-depleted serum-containing medium, bound plasmin activity could be specifically eluted from the cells with tranexamic acid, an analogue of lysine. Dexamethasone reduced the amount of recoverable bound plasmin activity in a dose-dependent manner. Dexamethasone was also found to induce a time- and dose-dependent decrease in the ability of the cells to bind added plasmin. Untreated HT-1080 cells bound added plasmin with a high capacity (600,000 molecules bound per cell), and this decreased to an undetectable level after treatment with 100 nM dexamethasone. The kinetics of the loss of plasmin binding by the dexamethasone-treated sarcoma cells, a clear decrease after 4 h, correlated with those for the loss of cell-bound urokinase (u-PA) activity. Plasmin was not, however, bound to the active site of u-PA: an anti-catalytic monoclonal antibody to u-PA had no effect on plasmin binding. Other glucocorticoids, such as hydrocortisone and corticosterone, had a similar effect to dexamethasone on plasmin binding to HT-1080 cells. The effect of glucocorticoids on the plasmin receptor seemed to occur at least partly via a decrease in the affinity for plasmin, since the Kd for plasmin with untreated cells was 5.4 x 10(-9) M, and with cells treated with 5 nM dexamethasone, the Kd value for plasmin was 1.2 x 10(-7) M. These results show that glucocorticoids induce down-regulation of plasmin receptors on the surface of HT-1080 cells: a novel mechanism, in addition to the known effects of glucocorticoids on u-PA and PA inhibitors, by which human tumor cells may be disarmed of their pericellular proteolytic activity.     

Endothelial cell-derived heparan sulfate binds basic fibroblast growth factor and protects it from proteolytic degradation

Cultured bovine capillary endothelial (BCE) cells were found to synthesize and secrete high molecular mass heparan sulfate proteoglycans and glycosaminoglycans, which bound basic fibroblast growth factor (bFGF). The secreted heparan sulfate molecules were purified by DEAE cellulose chromatography, followed by Sepharose 4B chromatography and affinity chromatography on immobilized bFGF. Most of the heparinase-sensitive sulfated molecules secreted into the medium by BCE cells bound to immobilized bFGF at low salt concentrations. However, elution from bFGF with increasing salt concentrations demonstrated varying affinities for bFGF among the secreted heparan sulfate molecules, with part of the heparan sulfate requiring NaCl concentrations between 1.0 and 1.5 M for elution. Cell extracts prepared from BCE cells also contained a bFGF-binding heparan sulfate proteoglycan, which could be released from the intact cells by a short proteinase treatment. The purified bFGF-binding heparan sulfate competed with 125I-bFGF for binding to low-affinity binding sites but not to high-affinity sites on the cells. Heparan sulfate did not interfere with bFGF stimulation of plasminogen activator activity in BCE cells in agreement with its lack of effect on binding of 125I-bFGF to high-affinity sites. Soluble bFGF was readily degraded by plasmin, whereas bFGF bound to heparan sulfate was protected from proteolytic degradation. Treatment of the heparan sulfate with heparinase before addition of plasmin abolished the protection and resulted in degradation of bFGF by the added proteinase. The results suggest that heparan sulfate released either directly by cells or through proteolytic degradation of their extracellular milieu may act as carrier for bFGF and facilitate the diffusion of locally produced growth factor by competing with its binding to surrounding matrix structures. Simultaneously, the secreted heparan sulfate glycosaminoglycans protect the growth factor from proteolytic degradation by extracellular proteinases, which are abundant at sites of neovascularization or cell invasion.     

Immunoaffinity purification of Schistosoma mansoni soluble egg antigens

Schistosoma mansoni egg antigens were purified from a heterogeneous mixture of soluble egg antigens (crude SEA) with an immunoaffinity column that consisted of the specific anti-SEA antibodies contained in 16-week S. mansoni-infected mouse serum bound to Sepharose 4B. On sodium dodecyl sulfate (SDS) gel electrophoresis, the purified antigen fraction yielded at least eight bands staining with Coomassie blue and at least five bands staining with Coomaisse blue and at least five bands reacting with periodic acid-Schiff (PAS). All of the proteins in the antigenic fraction appear to contain carbohydrate residues. Upon immunoelectrophoresis the antigen yielded four precipitin arcs. The antigenic fraction isolated by means of the immunoaffinity column was then compared to various fractions obtained from concanavalin A (Con A) chromatography of SEA. The results of Ouchterlony immunodiffusion and immunoelectrophoresis indicate that the antigenic fraction isolated by immunoaffinity purification of SEA contains the major antigens found in the fractions obtained from Con A chromatography of SEA. The results of SDS gel electrophoresis indicate that the major PAS-reacting bands of the antigenic fraction isolated by immunoaffinity purification are found in the 3rd peak (bound fraction) resulting from Con A chromatography of SEA, whereas the major Coomaisse blue-staining band in the isolated antigenic fraction is found in the 2nd peak (unbound fraction) from Con A chromatography of SEA.     

Purification and partial characterization of glyceraldehyde-3-phosphate dehydrogenase from the ciliate Tetrahymena thermophila

In the present study, we purified the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) which is involved in cellular energy production and has important housekeeping functions, from the ciliate Tetrahymena thermophila using a three-step procedure. The enzyme was purified ~68 folds by ammonium sulfate precipitation, followed by two steps of column chromatography (DEAE-cellulose and Mono-S). The purified enzyme is a homotetramer with a molecular weight of ~120 kDa. Isoelectric focusing analysis showed the presence of only one basic GAPDH isoform with an isoelectric point of 8.8. Western blot analysis showed a single 32-kDa band corresponding to the enzyme subunit using a monospecific polyclonal antibody against the T. thermophila GAPDH. The maximum of enzyme activity occurred at pH 8.0 and at 30-35°C. The apparent K(m) values for both NAD(+) and D-glyceraldehyde-3-phosphate were 0.102 ± 0.012 and 0.360 ± 0.018 mM, respectively. The maximal velocity (V(max)) was 39.40 ± 2.95 U/mg. The T. thermophila GAPDH is inhibited by oxidative and nitrosative stress reagents.     

Detection and partial characterization of a specific plasminogen activator inhibitor in human chondrocyte cultures

Serum-free culture medium collected from primary monolayer cultures of human articular chondrocytes was found to inhibit human urokinase [EC 3.4.21.31] activity. Although chondrocyte culture medium contained a small amount of endothelial-type plasminogen activator inhibitor which could be demonstrated by reverse fibrin autography, most of the urokinase inhibitory activity of chondrocyte culture medium was shown to be due to a different molecule from endothelial-type inhibitor, since it did not react with a specific antibody to this type of inhibitor. The dominant urokinase inhibitor in chondrocyte culture medium was partially purified by concanavalin A-Sepharose affinity chromatography. The partially purified inhibitor inhibited high-Mr urokinase more effectively than low-Mr urokinase, but no obvious inhibition was detected against tissue-type plasminogen activator, plasmin, trypsin, and thrombin. The inhibitor had an apparent Mr of 43,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis, and it was unstable to sodium dodecyl sulfate, acid, and heat treatments. Inhibition of urokinase by the inhibitor was accompanied with the formation of a sodium dodecyl sulfate-stable high-Mr complex between them. Inhibition and complex formation required the active site of urokinase. The partially purified inhibitor was thought to be immunologically different from the known classes of plasminogen activator inhibitors, including endothelial-type inhibitor, macrophage/monocyte inhibitor, and protease nexin, since it did not react with specific antibodies to these inhibitors.