Isolation of mannose-binding proteins from human and rat liver

Pattern of endogenous lectins of a human sarcoma (Ewing's sarcoma) reveals differences to human normal tissues and tumors of epithelial and germ cell origin

A human sarcoma, Ewing's sarcoma, contains activities of endogenous lectins. Fractionation of salt and detergent extracts by affinity chromatography on columns with immobilized sugars or glycoproteins results in the pattern of endogenous lectins for alpha- and beta-galactosides, alpha-mannosyl- and alpha-fucosyl-moieties. Whereas some lectins are known from normal, non-malignant human tissues or from a human epithelial tumor or a human germ cell tumor, a Ca2+-independent alpha- and beta-galactoside-binding protein at apparent molecular weight of 58 kilodaltons has so far not been characterized from any human source. The patterns for the tumors and human normal tissues reveal various differences in comparison between each other. These differences, documented for the first human sarcoma, human tumors of different histogenetic lineage and normal tissues are a first step to a lectin-based diagnosis and therapy of certain human cancer types.

Study of the plasma clearance of antibody--ricin-A-chain immunotoxins. Evidence for specific recognition sites on the A chain that mediate rapid clearance of the immunotoxin

In recent years, antibody--ricin-A-chain immunotoxins have been investigated as anti-neoplastic agents. To achieve in vivo therapy it is necessary that the immunotoxin remains in circulation at a sufficiently high level for a sufficiently long time to allow binding to tumor cells to occur. Therefore, examination of the pharmacology of immunotoxins may elucidate the reasons for the poor in vivo tumoricidal effect of immunotoxin described before. In this study the plasma clearance of antibody--ricin-A-chain immunotoxins, after intravenous injection in animals of different species, has been examined. Sensitive and reproducible techniques were developed to monitor the level of immunotoxin and its constituents in the blood. It is shown that immunotoxins are rapidly eliminated from the bloodstream. Neither the properties of the antibody moiety nor the nature of the linkage binding ricin A-chain to antibody account for the disappearance of immunotoxin from the plasma. On the other hand, we found that the rapid clearance of immunotoxin is due to the mannose residues on the ricin A-chain moiety which are specifically recognized by liver cells. When immunotoxin is administrated together with yeast mannan, which enhances the level of active immunotoxin in circulation by inhibition of liver uptake, the anti-cancer efficacy of immunotoxin in vivo is drastically improved.

Identification and isolation of an agglutinin from uterus of rats

A sialic acid-binding agglutinin was purified to apparent homogeneity by affinity chromatography on fetuin-sepharose column from the rat uterine homogenate in estrus. The agglutinin is Ca++ dependent, a glycoprotein, and composed of two very closely associated bands of molecular weights 28,000 and 30,000 and pIs of 4 and 4.1. Several sialoglycoproteins, sialic acid, EDTA, glucuronic acid and heparin acted as an inhibitor of the agglutinin.

Isolation and immunohistochemical characterization of two developmentally regulated highly insoluble antigens from the membrane of sinusoidal rat liver cells

Using sequential extractions with buffers containing or not containing neutral detergent, two highly insoluble protein components were found in livers of 30-day-old rats. These compounds (molecular weights (MW) 52 900 and 33 200 respectively) were practically absent from livers of young rats (between 5 and 8 postnatal days). After two-third hepatectomy performed on 30-day-old rats followed by a 24 h recovery, the level of these compounds is drastically decreased (about 50%). Monospecific antibodies against these components were obtained. Using immunohistochemical techniques, these antigens were localized in the membranes (essentially plasma membranes and sometimes internal membranes) of sinusoidal cells of adult rat livers. After partial hepatectomy, these antigens are no more present in the sinusoidal cells of the regenerating parts of the liver.

Separation of plasma membrane proteins of cultured human fibroblasts by affinity chromatography on bonded microparticulate silicas

Adsorbents for high-performance affinity chromatography were prepared by bonding proteins and reactive Procion triazine dyes to 3-isothiocyanatopropyl- and 3-aminopropylsilicas. The materials prepared were used successfully in the separation of hydrophobic plasma membrane proteins of cultured human fibroblasts. The data obtained show that the reaction of 3-isothiocyanatopropyltriethoxysilane (ITCPS) with the surface hydroxyl groups of silica yields a new and convenient route to preparing an "activated carrier" that is capable of coupling with potential affinity ligands containing amino functional groups. The reaction and bonding procedures of 3-isothiocyanatopropyltriethoxysilane and 3-aminopropyltriethoxysilane with silica were optimized with regard to a controlled and reproducible ligand density by adjusting the type of solvent and organic base as reaction catalyst. The ligand content of reactive triazine dyes directly coupled to 3-aminopropylsilica was significantly higher than that of the 6-aminohexyl derivatives coupled to 3-isothiocyanatopropylsilica. The stability of Procion Blue MX-R bonded to 3-aminopropylsilica and 3-isothiocyanatopropylsilica in phosphate-buffered aqueous solution at pH 5.0 and 8.0 was examined.

Subcellular distribution of the mannan-binding protein and its endogenous inhibitors in rat liver

The subcellular distribution of the mannan-binding protein from rat liver, a lectin specific for mannose and N-acetylglucosamine, was studied. Approximately 75% of the binding activity of the homogenate was recovered in microsomes, approximately 76% of which was accounted for by rough microsomes. Rough microsomes had the highest specific activity of binding, followed by the Golgi apparatus and smooth microsomes, whereas plasma membranes, lysosomes, mitochondria, and the soluble fraction had little or no binding activity. A topographical survey indicated that the binding protein was localized exclusively on the cisternal surface of microsomal vesicles. Thus, the binding protein of microsomal vesicles was protected from protease digestion and was released from the vesicles by mild detergent treatment. Competitive inhibitors, which presumably represent endogenous ligands of the binding protein, were found among subcellular fractions. More than 50% of the inhibitory activity of the homogenate was recovered in rough microsomes, while the highest specific activity of inhibition was found in lysosomes. The Ki values estimated for rough microsomes and lysosomes were 25.9 and 8.67 micrograms/ml, respectively. The distribution profiles of inhibitors were correlated roughly with those of the binding protein, resulting in masking of the binding activity in organelles up to the level of 86%. On the basis of the known localization and topology of the binding protein and endogenous inhibitors (ligands), possible physiological functions of the binding protein relevant to the transport of biosynthetic intermediates of glycoproteins from the rough endoplasmic reticulum to the Golgi apparatus and from the Golgi apparatus to lysosomes were discussed.

Alterations of lectin binding during chondrogenesis of mouse limb buds

The binding of six different FITC-labelled lectins to mesenchyme, blastemal cells and cartilage was investigated in limb buds of mouse embryos during their development from day 10 to day 13. Concanavalin A, wheat germ agglutinin and phaseolus vulgaris agglutinin labelled mesenchymal cells of earlier stages, day 10 or 11, distinctly more than those of later stages. Chondrogenic blastema, basement membrane and muscle were always strongly stained. The galactosamine-specific ricinus communis agglutinin (RCA) bound preferentially to the blastema, whereas the mesenchyme was only weakly labelled. The galactose-specific peanut agglutinin (PNA), however, stained solely the blastema. In the mesenchyme, no binding was detectable light microscopically with this lectin. In cartilage, RCA- and PNA-staining was found to a lesser extent. With the fucose-specific lectin Lotus A, no staining was detectable. Due to the apparent differences in the binding of PNA in mesenchyme and blastema, peroxidase-labelled PNA was used to study the binding behaviour electron microscopically. It is shown that peroxidase-PNA very strongly labelled the intercellular matrix and the plasma membrane of cells in the late blastemal stages, whereas in young blastema no reaction product was detectable. In contrast to light microscopic findings, some label could be demonstrated also in the mesenchyme. The results show a general reduction of lectin receptors in more developed mesenchyme of later stages and the occurrence of galactose and galactose derivatives during early chondrogenesis in the matrix and at the cell membrane. The significance of these changes for chondrogenesis, however, remains to be elucidated.