Post-translational modifications and binding properties of the apically secreted 80-kDa glycoprotein from Madin-Darby canine kidney cells: similarities to the C-terminal portion of the basolaterally secreted fibronectin

Apically secreted 80-kDa glycoprotein (gp 80) from Madin-Darby canine kidney cells was found to be immunoprecipitated by the polyclonal antiserum against fibronectin or a monoclonal antibody specific for the fibronectin C-terminal fibrin binding domain. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), gp 80 migrated as a doublet band under nonreducing conditions. Under reducing conditions, gp 80 was resolved into three distinct bands, respectively of 45-, 40-, and 35-kDa molecular mass. Analysis by two-dimensional SDS-PAGE revealed that gp 80 exists in two molecular forms: one consisting of a 45-kDa subunit and a 40-kDa subunit, and one consisting of a 45-kDa subunit and a 35-kDa subunit. V-8 protease mapping indicated the 40 and 35-kDa subunits as being of the same homologous group and also as bearing partial homology to the 45-kDa subunit. Radioactive labeling revealed that labeled gp 80 was subjected to covalent modifications by sulfation and phosphorylation. Sulfate analysis showed that [35S]sulfate-labeled gp 80 contained ca. 2.45 +/- 0.07% tyrosine-bound [35S]sulfate with the rest being presumably carbohydrate-bound. [32P]-Phosphate-labeled gp 80, on the other hand, was found to contain serine-O-phosphate as the predominant phosphorylated amino acid residue. Employing the affinity gel fractionation technique, it was shown that gp 80 exhibited binding affinities toward heparin and fibrin. Binding of gp 80 to heparin-agarose or fibrin-Sepharose, however, was inhibited in the presence of added fibronectin or the monoclonal antibody. Tryptic peptide mapping revealed common peptide spots between fibronectin and the three subunits of gp 80. Furthermore, Western blot analysis showed that fibronectin could be recognized and bound by anti-gp 80 antibodies. These results indicate that gp 80 bears both structural and functional similarities to the C-terminal portion of the fibronectin molecule.     

Collagenase is a major gene product of induced rabbit synovial fibroblasts

We have investigated the effects of the tumor-promoting phorbol diester, 12-O-tetradecanoylphorbol-13-acetate (TPA), on rabbit synovial fibroblasts, and found that this agent induced a major switch in gene expression in these cells that was marked by the specific induction of the neutral proteinase, collagenase, and was always accompanied by alterations in cell morphology. Procollagenase synthesis and secretion was first observed 6-12 h after the addition of TPA. The rate of collagenase production (1-5 U, or approximately 0.2-1 micrograms secreted procollagenase protein per 10(5) cells per 24 h) depended on the TPA concentration (1-400 ng/ml) and time of exposure (1-72 h). Procollagenase was the most prominent protein visible by direct silver staining or by autoradiography after SDS PAGE of [35S]methionine-labeled proteins. The two procollagenase bands of Mr 53,000 and 57,000, which migrated as a family of spots on two-dimensional gels and were immunoprecipitated by antibodies to purified rabbit collagenase, accounted for 23% of the newly synthesized, secreted protein in TPA-treated cells. Cell-free translation of mRNA from TPA-treated cells in rabbit reticulocyte lysate produced a single band of immunoprecipitable preprocollagenase (Mr 55,000) as a major product (5% of total) that migrated as a single spot on two-dimensional gels. Secreted procollagenase, preprocollagenase , and active collagenase (purified to homogeneity; specific activity 1.2 X 10(4) U/mg protein) had related peptide maps. Two other major secreted proteins, a neutral metalloproteinase of Mr 51,000 and a polypeptide of Mr 47,000, were also induced by TPA. In contrast to the induction of these four polypeptides, TPA decreased synthesis and secretion of a number of proteins, including collagen and fibronectin. Thus, collagenase is a convenient marker for major alterations in the pattern of protein synthesis and secretion by rabbit synovial fibroblasts treated with TPA.     

Human eosinophil-derived neurotoxin and eosinophil protein X are likely the same protein

The human eosinophil granule contains a series of cationic proteins. Two of these, eosinophil-derived neurotoxin (EDN) and eosinophil protein X (EPX), are reported to have similar m.w. and both possess neurotoxic and helminthotoxic activities. Therefore, the properties of these molecules were analyzed to determine whether they differ. EDN was purified from eosinophils of patients with the hypereosinophilic syndrome and EPX from the buffy coat cells of normal individuals. By SDS-PAGE, both proteins showed a major band at 18.7 kDa and a minor band at 21.4 kDa. By two-dimensional non-equilibrium gel electrophoresis the proteins migrated identically. With radiolabeled proteins in reverse phase HPLC, both proteins eluted at the same concentration of acetonitrile and showed identical tryptic maps. Both proteins possessed comparable ribonuclease activity and both were comparably neurotoxic in the rabbit. By immunodiffusion the two proteins showed a reaction of identity; by RIA, with both polyclonal and monoclonal antibodies, the proteins had very similar inhibitory activities. These results indicate that EDN and EPX have virtually identical properties and are probably the same protein.     

Rabies mRNA translation in Xenopus laevis oocytes.

Two rabies virus-specific mRNA species were identified by analysis of their encoded proteins after translation of the partially purified species in Xenopus laevis oocytes. One of these coded for the virion surface glycoprotein (G protein), and the other coded for the major structural protein of the virion nucleocapsid (N protein). The G-mRNA sedimented in a sucrose density gradient at about 18S, and the N-mRNA had a sedimentation coefficient of approximately 16S. Their respective translation products were identified in a radioimmunoassay with specific monoclonal antibody probes that recognized only G or N proteins. Immunoprecipitates formed between the radiolabeled viral antigens synthesized in programmed oocytes and their respective monoclonal antibodies were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The glycoprotein antigen translated from G-mRNA in oocytes migrated in the gel ahead of the virion G protein with a migration rate that was similar to that of nonglycosylated intracellular glycoproteins from virus-infected cells. The results suggested that the branched-chain carbohydrate of G protein was not required for recognition by the particular monoclonal antibody used. The nucleocapsid antigen translated from N-mRNA in oocytes migrated to the same position in the gel as marker virion N protein. Both the electrophoretic mobility of virus-specific antigens in sodium dodecyl sulfate-polyacrylamide gel and the antibody concentration dependence for immunoprecipitations were criteria for identifying the individual viral proteins encoded by the two rabies mRNA's.     

Phagocytic cell molecules that bind the collagen-like region of C1q. Involvement in the C1q-mediated enhancement of phagocytosis

C1q binds to and elicits cellular responses by several cell types, including monocytes, macrophages, neutrophils, B cells, and fibroblasts. The cell-binding domain is located within the collagen-like pepsin-resistant region of the C1q molecule (C1q tails). An affinity matrix of C1q tails coupled to Sepharose was used to select C1q-binding proteins from detergent extracts of surface-iodinated human monocytes, polymorphonuclear leukocytes, and the U937 cells. The major radiolabeled polypeptide eluted specifically from the ligand affinity column had an apparent molecular mass (Mr) of 126,000. Minor iodinated components eluted from Sepharose-tails migrated with Mr of 216,000 and 55,000. When subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions no change in the migration of any of these polypeptide bands was detected. None of these polypeptides reacted with antibodies directed against the integrins alpha 5 beta 1 (fibronectin receptor) or alpha v beta 3 (vitronectin receptor), LFA-1, or to several other cell adhesion molecules. The Mr 126,000 band was found to contain more than one polypeptide. Lectin binding properties, susceptibility to glycosidases and proteases, and immunoreactivity with the monoclonal antibody L-10, indicated that CD43 (sialophorin/leukosialin) is a component of this band. However, further data show that a monoclonal antibody, generated by immunization with the isolated Clq-binding fractions, recognizes a cell surface sialoglycoprotein distinct from CD43 and inhibits the C1q-mediated enhancement of phagocytosis in monocytes. These latter observations provide the first definitive connection between a specific phagocytic cell surface protein and a known C1q-mediated function. While these proteins contain sialic acid, binding assays and functional assays using neuraminidase-treated cells demonstrate that the functional interaction between C1q and the cell surface is not via sialic acid. The data taken together indicate either that the functional C1q receptor on phagocytic cells is a multi-subunit complex or that multiple proteins can interact with the fragment of C1q containing the cell-binding domain, at least one of which is involved in the C1q-mediated enhancement of phagocytosis.     

Protective monoclonal antibody against Schistosoma mansoni: antigen isolation, characterization, and suitability for active immunization

Monoclonal antibodies that bind to the surface of developing schistosomula were generated from the spleens of chronically infected mice that were boosted with cercarial glycoproteins. The two most reactive monoclonal antibodies, denoted 152-66-9B and 152-66-1C, were used for identification of surface antigens. The antigen detected by these monoclonal antibodies persisted on the surface of the developing larva for 72 hr posttransformation. This monoclonal antibody effected complement-mediated killing of schistosomula in vitro as efficiently as infected mouse sera. It was also very efficient in inhibiting the infectivity of both cercariae and schistosomula. The antigen reactive with the 152-66-9B monoclonal antibody contains two major polypeptides (45 and 30 KD). These polypeptide chains might have originated from the same protein, because they have the same isoelectric point in two-dimensional gel electrophoresis. Moreover, the affinity-purified antigen migrated as only one protein band of approximately 200 KD in SDS-PAGE in nonreducing conditions. The 9B antigen was isolated, purified, and used for immunization, resulting in an antigen dose-dependent partial protection against S. mansoni infection.     

Fibronectin-binding proteins of Staphylococcus aureus mediate activation of human platelets via fibrinogen and fibronectin bridges to integrin GPIIb/IIIa and IgG binding to the FcgammaRIIa receptor

Staphylococcus aureus is a leading cause of infective endocarditis (IE). Platelet activation promoted by S. aureus resulting in aggregation and thrombus formation is an important step in the pathogenesis of IE. Here, we report that the fibrinogen/fibronectin-binding proteins FnBPA and FnBPB are major platelet-activating factors on the surface of S. aureus from the exponential phase of growth. Truncated derivatives of FnBPA, presenting either the fibrinogen-binding A domain or the fibronectin-binding BCD region, each promoted platelet activation when expressed on the surface of S. aureus or Lactococcus lactis, indicating two distinct mechanisms of activation. FnBPA-promoted platelet activation is mediated by fibrinogen and fibronectin bridges between the A domain and the BCD domains, respectively, to the low affinity form of the integrin GPIIb/IIIa on resting platelets. Antibodies recognizing the FnBPA A domain or the complex between the FnBPA BCD domains and fibronectin were essential for activation promoted by bacteria expressing the A domain or the BCD domain respectively. Activation was inhibited by a monoclonal antibody (IV-3) specific for the FcgammaRIIa IgG receptor on platelets. We propose that the activation of quiescent platelets by bacteria expressing FnBPs involves the formation of a bridge between the bacterial cell and the platelet surface by (i) fibronectin and fibrinogen interacting with the low affinity form of GPIIb/IIIa and (ii) by antibodies specific to FnBPs that engage the platelet Fc receptor FcgammaRIIa. Platelet activation by S. aureus clinical IE isolates from both the exponential and stationary phases of growth was completely inhibited by monoclonal antibody IV-3 suggesting that the IgG-FcgammaRIIa interaction is of fundamental importance for platelet activation mediated by this organism. This suggests new avenues for development of therapeutics against vascular infections.     

The leukotoxin of Pasteurella haemolytica binds to β2 integrins on bovine leukocytes

The putative receptor proteins of Pasteurella haemolytica leukotoxin were isolated from bovine polymorphonuclear neutrophil lysate by affinity chromatography on a leukotoxin-specific monoclonal antibody column to which the leukotoxin was pre-bound. SDS-PAGE of the purified proteins showed four bands at 180 kDa, 170 kDa, 150 kDa and 95 kDa, in addition to the expected 102-kDa leukotoxin band and a series of bands with molecular masses lower than 102 kDa representing the disintegrated leukotoxin. N-terminal amino acid sequencing of the 170-kDa band showed homology with human and murine CD11b. The purified proteins reacted specifically with monoclonal antibodies specific for CD11a, CD11b, CD11c (the alpha chains of beta(2) integrins), and CD18 (the beta chain of beta(2) integrins). Pre-incubation of polymorphonuclear neutrophils with a monoclonal antibody specific for CD18 reduced the cytotoxicity of the leukotoxin to the cells. These results indicate that the leukotoxin binds to the beta(2) integrins on bovine leukocytes, very likely via CD18.     

Use of specific monoclonal and polyclonal antibodies to define distinct antigens of the porcine zonae pellucidae

Specific monoclonal and polyclonal antibodies to solubilized porcine and rabbit zonae pellucidae (ZP) and to purified ZP glycoprotein components have been used to define distinct ZP antigens. These studies demonstrate that the individual ZP glycoproteins contain both unique and shared determinants. One monoclonal antibody (R5) has been used to demonstrate that the major porcine ZP glycoprotein, which has multiple charge species ranging in molecular weight from 42,000 to 120,000, is composed of two distinct polypeptide antigens unique to this glycoprotein class. These distinct antigens can be differentiated by immunoblotting after high-resolution two-dimensional polyacrylamide gel electrophoretic separation of trypsin-treated or deglycosylated glycoproteins. The two polypeptides also differ in their staining properties with the silver-based color stain and in their susceptibility to proteolysis. A second monoclonal antibody (PSI) has been used to define a determinant shared by all three major porcine ZP glycoprotein classes. This determinant appears to involve either a carbohydrate moiety or some other molecular feature related to post-translational modification, since the antibody recognizes only the acidic species of each glycoprotein class, and does not recognize the deglycosylated forms of the proteins. This work demonstrates that there are both unique and shared antigenic determinants present in the individual components of the ZP, but that the immunodominant determinants appear to be unique to each glycoprotein.     

A fibronectin-binding glycoprotein from human platelet membranes.

Fibronectin ('cold-insoluble globulin') has been suggested as a possible mediator of platelet adhesion. A fibronectin-binding protein as partially purified from washed solubilized human platelet membranes by affinity chromatography on fibronectin-Sepharose. The isolated protein migrated as a single band on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis with an Mr (relative molecular mass) of approx. 125 000 under reducing conditions. The protein migrated as a dimer in non-reduced gels. The purified protein did not react with immunoglobulins against fibrinogen or fibronectin when tested in crossed immunoelectrophoresis or electroimmunoassay. The protein and purified fibronectin formed a complex that had a significantly faster mobility in crossed immunoelectrophoresis than did native fibronectin. The presence of heparin in the binding-protein-fibronectin mixture resulted in an even faster mobility of the complex, whereas the mobility of native fibronectin was unaffected. Crossed affinoimmunoelectrophoresis of the complex using different lectins suggested that the binding protein is a glycoprotein containing N-acetylglucosamine residues. The complex, but not purified fibronectin, bound to phenyl-Sepharose on crossed hydrophobic-interaction immunoelectrophoresis. The results strongly suggest the presence of a fibronectin-binding glycoprotein in the platelet membrane.     

Purification and characterization of myrosinase from horseradish (Armoracia rusticana) roots.

Myrosinase (beta-thioglucoside glucohydrolase; EC 3.2.3.147) from horseradish (Armoracia rusticana) roots was purified to homogeneity by ammonium sulfate fractionation, Q-sepharose, and concanavalin A sepharose affinity chromatography. The purified protein migrated as a single band with a mass of about 65 kDa on SDS-polyacrylamide gel electrophoresis. Using LC-MS/MS, this band was identified as myrosinase. Western blot analysis, using the anti-myrosinase monoclonal antibody 3D7, showed a single band of about 65 kDa for horseradish crude extract and for the purified myrosinase. The native molecular mass of the purified myrosinase was estimated, using gel filtration, to be about 130 kDa. Based on these data, it appeared that myrosinase from horseradish root consists of two subunits of similar molecular mass of about 65 kDa. The enzyme exhibited high activity at broad pH (pH 5.0-8.0) and temperature (37 and 45 degrees C). The purified enzyme remained stable at 4 degrees C for more than 1 year. Using sinigrin as a substrate, the Km and Vmax values for the purified enzyme were estimated to be 0.128 mM and 0.624 micromol min(-1), respectively. The enzyme was strongly activated by 0.5 mM ascorbic acid and was able to breakdown intact glucosinolates in a crude extract of broccoli.     

Two-dimensional electrophoresis/phage panning (2D-PP): a novel technology for direct antibody selection on 2-D blots

We describe a novel method, two-dimensional electrophoresis/phage panning (2D-PP), for the generation of antibodies against proteins in crude biochemical samples, such as cellular membrane fractions. These sources have traditionally presented problems as to the development of antibodies by conventional techniques. 2D-PP involves two-dimensional resolution of proteins, blotting of the proteins onto a nitrocellulose membrane, and screening of a phage antibody library and isolation of corresponding antibodies. By 2D-PP with detergent-insoluble "lipid rafts" as a target protein complex, we obtained specific phage pools against eight antigen spots (from a total of 39 spots). These antibodies were functional in Western blotting, enzyme-linked immunosorbent assaying (ELISA), and immunoscreening of a cDNA expression library. Propagation of anti-nitrocellulose phages was the major problem in 2D-PP, but was overcome by the use of the soluble anti-nitrocellulose antibody fragment. 2D-PP constitutes a key tool for functional analysis of proteins in complex fractions.     

Purification of six human vitamin K-dependent proteins in a single chromatographic step using immunoaffinity columns

The major human vitamin K-dependent proteins were purified from plasma using immunoadsorbents made with antibodies specific for each protein. Monoclonal antibodies to Factor VII, Factor IX, Factor X, Protein C, and Protein S were prepared from mice immunized with isolated vitamin K-dependent antigens. Purified monoclonal antibodies and a purified burro polyclonal anti-prothrombin immunoglobulin were individually coupled to Sepharose and used in a tandem series of columns to purify each of the vitamin K-dependent proteins from eluates of barium citrate precipitates of plasma. The proteins were eluted from the columns by sodium thiocyanate and retained functional activity following dialysis. Prothrombin, Factor VII, Factor IX, Factor X and Protein C were essentially homogeneous as judged by NaDodSO4-PAGE; Protein S was isolated as a Protein S-C4b binding protein complex. These results indicate the utility of monoclonal antibody immunoadsorbents for purifying the human vitamin K-dependent proteins and represent a considerable simplification over other purification schemes.     

Ribosomes of Physarum polycephalum. Subunits and protein composition.

Ribosomes from Physarum polycephalum were purified. Optimal conditions for preparation and stability of subunits were determined. KCl concentration above 200 mM induced protein dissociation from the subunits. It was observed that dissociated ribosomes were more stable in a low ionic strength buffer than in 200 mM KCl, where the 40 S was preferentially degraded by ribonucleases. Ribosomal proteins were analyzed by two-dimensional gel electrophoresis. The first dimension was carried out at pH 8.6 while the second was run at pH 4.6. The monosome contained sixty seven proteins, of which six were acidic. Two proteins were lost after subunit dissociation. Twenty six basic and two acidic proteins were observed in the 40 S subunit while the largest subunit gave thirty nine spots on the basic part of the gel and three additional spots on the acidic side. Five proteins were shared by 40 S and 60 S.     

Thrombin-stimulated elevation of human endothelial-cell cytoplasmic free calcium concentration causes prostacyclin production.

The nucleoside transporter has been purified by passage of a preparation of human erythrocyte-membrane band-4.5 proteins through a column of immobilized antibodies specific for the glucose transporter. This procedure removed greater than 99.8% of the glucose transporters and achieved an approx. 18-fold purification of the nucleoside transporter, constituting a 478-fold purification from erythrocyte membranes. The isolated protein migrated as a single broad band of average apparent Mr 55,000 on SDS/polyacrylamide gels and bound approx. 0.6 mol of nitrobenzylthioinosine/mol of polypeptide, with a Kd of 1.1 +/- 0.14 (S.E.M.) nM. Upon reconstitution into large unilamellar phospholipid vesicles it catalysed the uptake of uridine with an apparent specific activity 6-fold greater than that of the unfractionated band-4.5 proteins. Furthermore, the purified nucleoside transporter was not labelled on Western blots by monoclonal antibody raised against the glucose transporter. It is concluded that the nucleoside transporter has been purified to near homogeneity.     

Mitogen-induced preferential synthesis of proteins during the G0 to S phase transition in human lymphocytes

We have followed the induction of protein synthesis in mitogen-activated human peripheral blood mononuclear cells during the transition from quiescence, or G0, through the prereplicative phase and into first S phase. Doses of mitogens optimal for proliferative response preferentially enhance the synthesis of a subset of intracellular proteins during the approximately 24-h lag interval. The mitogenic lectin phytohemagglutinin (PHA) and OKT3, a mitogenic monoclonal antibody to the CD3 component of the T cell antigen receptor, preferentially enhance bands of the same molecular weight in one-dimensional SDS-PAGE. The proteins are low detergent soluble (0.1% Triton X-100) "cytoplasmic" cellular components and some have been identified as single spots on two-dimensional gels. Bands of 51 and 66 kDa are induced early in lag phase (4 h after stimulation) but are transiently synthesized, decreasing later in lag phase. The majority of the mitogen-induced proteins, 39, 51, 55, 60, 73, and 95 kDa are enhanced by mid lag phase (12 h after stimulation). With the exception of the 55-kDa band, five of these proteins are clearly enhanced in T cells purified after mitogen stimulation. The same five bands show sustained synthesis in actively cycling cells 42-48 h after stimulation and are major synthesized proteins, and corresponding bands are synthesized in a transformed T cell line, MOLT-4. Two of the proteins in this group that are most prominently synthesized during the lag interval have been previously identified as the heat shock proteins, HSP 90 (95-kDa band) and HSC 70 (73-kDa band). We speculate that this group of five proteins, including HSP 90 and HSC 70, may be coordinately expressed in actively replicating T cells and may have some common structural or functional role in sustaining the replicative state.     

Prosomes and heat shock complexes in Drosophila melanogaster cells.

Prosomes and heat shock protein (HSP) complexes isolated from the cytoplasm of Drosophila cells in culture were biochemically and immunologically characterized. The two complexes were found to separate on sucrose gradients, allowing the analysis of their protein constituents by two-dimensional polyacrylamide gel electrophoresis and by reaction with anti-HSP sera and prosome-specific monoclonal antibodies. All of the prosomal proteins were found to be clearly distinct from the HSP; none of the prosomal proteins was synthesized de novo in heat shock. However, an antiprosome (anti-p27K) monoclonal antibody (mouse anti-duck) recognizing the Drosophila p29K prosomal protein allowed immunoprecipitation from a heat-shocked postmitochondrial supernatant of the crude HSP complex, including the low- and the high-molecular-weight components, in particular the 70 x 10(3)-molecular weight HSP. The highly purified small 16S HSP complex still contained this preexistent p29K prosomal protein, which thus also seems to be a metabolically stable constituent of the HSP complex. The significance of this structural and possibly functional relationship between prosomes and HSP, involving the highly ubiquitous and evolutionarily conserved prosomal protein p27/29K, remains to be elucidated.     

Mapping the proteome of Leishmania Viannia parasites using two-dimensional polyacrylamide gel electrophoresis and associated technologies

In this study we have demonstrated the potential of two-dimensional electrophoresis (2DE)-based technologies as tools for characterization of the Leishmania proteome (the expressed protein complement of the genome). Standardized neutral range (pH 5-7) proteome maps of Leishmania (Viannia) guyanensis and Leishmania (Viannia) panamensis promastigotes were reproducibly generated by 2DE of soluble parasite extracts, which were prepared using lysis buffer containing urea and nonidet P-40 detergent. The Coomassie blue and silver nitrate staining systems both yielded good resolution and representation of protein spots, enabling the detection of approximately 800 and 1,500 distinct proteins, respectively. Several reference protein spots common to the proteomes of all parasite species/strains studied were isolated and identified by peptide mass spectrometry (LC-ES-MS/MS), and bioinformatics approaches as members of the heat shock protein family, ribosomal protein S12, kinetoplast membrane protein 11 and a hypothetical Leishmania-specific 13 kDa protein of unknown function. Immunoblotting of Leishmania protein maps using a monoclonal antibody resulted in the specific detection of the 81.4 kDa and 77.5 kDa subunits of paraflagellar rod proteins 1 and 2, respectively. Moreover, differences in protein expression profiles between distinct parasite clones were reproducibly detected through comparative proteome analyses of paired maps using image analysis software. These data illustrate the resolving power of 2DE-based proteome analysis. The production and basic characterization of good quality Leishmania proteome maps provides an essential first step towards comparative protein expression studies aimed at identifying the molecular determinants of parasite drug resistance and virulence, as well as discovering new drug and vaccine targets.     

Effects of endothelial basement membrane on neutrophil adhesion and migration

The influence of the sub-endothelial basement membrane (BM) on the adhesion and migration of leukocytes is not well-defined. We therefore investigated the behaviour of human neutrophils on purified BM proteins and on BM deposited by short- or long-term cultures of endothelial cells (EC). The adhesion, but not migration velocities, of neutrophils activated with interleukin-8 was dependent on the coating concentrations of purified collagen, laminin or fibronectin. In contrast, adhesion was similar on matrices deposited by 3-day or 20-day cultures of EC, but neutrophils migrated more slowly on the distinct BM that formed over 20 days. In addition, while adhesion on all surfaces was greatly reduced when neutrophils were treated with antibody against β₂-integrins, antibody against β₁-integrins only inhibited adhesion to the 20-day BM. Thus, the native BM has distinct effects on integrin usage and migration by neutrophils, which are not reproduced by purified proteins or matrix deposited early during endothelial culture.     

Fibronectin is a component of the sodium dodecyl sulfate-insoluble transglutaminase substrate

Liver plasma membranes contain a morphologically distinct protein complex which serves as a substrate for the plasma membrane-associated transglutaminase. The complex, which appears as a two-dimensional sheet, is insoluble in sodium dodecyl sulfate and reducing agents and has been named SITS for sodium dodecyl sulfate-insoluble transglutaminase substrate (Tyrrell, D. J., Sale, W. S., and Slife, C. W. (1988) J. Biol. Chem. 263, 1946-1951). Polyclonal antibodies raised against SITS were used to probe for soluble constituents of the matrix. Immunoblots showed that proteins of 230, 35, and 32 kDa reacted with the anti-SITS antiserum when the soluble fraction from a liver homogenate was examined. The 230-kDa protein was identified as fibronectin after observing cross-reactivity of anti-SITS antiserum with authentic fibronectin and cross-reactivity of anti-fibronectin antiserum with the 230-kDa cytosolic protein and purified SITS. Preincubating anti-SITS antiserum with purified fibronectin decreased immunostaining of the 230-kDa cytosolic protein and authentic fibronectin. Immunoblots of the plasma membrane fraction using anti-SITS and anti-fibronectin antisera showed that both antisera reacted with proteins at the top of the stacking gel (SITS) and of 230 kDa. In addition, the anti-SITS antiserum reacted with proteins of 85, 35, and 32 kDa. Immunofluorescence microscopy revealed that the anti-SITS and anti-fibronectin antisera both react with isolated SITS and with the same filamentous structures associated with intact plasma membranes. These studies show that fibronectin is a component of the plasma membrane matrix, SITS. This finding is consistent with the proposed role of this matrix which is to mediate cell-cell adhesion between hepatocytes in the tissue.