Spatial differences of endogenous lectin expression within the cellular organization of the human heart: a glycohistochemical, immunohistochemical, and glycobiochemical study

Protein-carbohydrate recognition may be involved in an array of molecular interactions on the cellular and subcellular levels. To gain insight into the role of proteins in this type of interaction, surgically removed specimens of human endomyocardial tissue were processed for histochemical and biochemical analysis. The inherent capacity of these sections to bind individual sugar moieties, which are constituents of the carbohydrate part of cellular glycoconjugates, was assessed using a panel of biotinylated neoglycoproteins according to a standardized procedure. Together with appropriate controls, it primarily allowed localization of endogenous lectins. Differences in lectin expression were observed between layers of endocardial tissue, myocardial cell constituents, connective-tissue elements, and vascular structures. The endocardium proved to be positive with beta-galactoside-bearing probes; with neoglycoproteins carrying beta-xylosides, alpha-fucosides, and galactose-6-phosphate moieties; and with probes containing a carboxyl group within the carbohydrate structure, namely sialic acid and glucuronic acid. In contrast, only fucose-and maltose-specific receptors were apparent in the elastic layers of the endocardium. Aside from ascertaining the specificity of the protein-carbohydrate interaction by controls, i.e., lack of binding of the probe in the presence of the unlabelled neoglycoprotein and lack of binding of the labelled sugar-free carrier protein, respective sugar receptors were isolated from heart extracts by using histochemically effective carbohydrates as immobilized affinity ligand. Moreover, affinity chromatography using immobilized lactose as affinity ligand as well as the use of polyclonal antibodies against the predominant beta-galactoside-specific lectin of heart demonstrated that the lactose-specific neoglycoprotein binding was due to this lectin. Remarkably, the labelled endogenous lectin, preferred to plant lectins for detecting ligands of the endogenous lectin, localized ligands in tissue parts where the lectin itself was detected glycohistochemically as well as immunohistologically. This demonstration of receptor-ligand presence in the same system is a further step toward functional assignment of the recorded protein-carbohydrate interaction. Overall, the observed patterns of lectin expression may serve as a guideline to elucidate the precise physiological relevance of lectins and to analyze pathological conditions comparatively.     

Analysis of binding of mannosides in relation to Langerin (CD207) in Langerhans cells of normal and transformed epithelia

Tandem-repeat C-type lectins (pattern-recognition receptors) with specificity for mannosides are intimately involved in antigen recognition, uptake, routing and presentation in macrophages and dendritic cells. In Langerhans cells, Langerin (CD207), a type-II transmembrane protein with a single C-type carbohydrate recognition domain attached to a heptad repeat in the neck region, which is likely to establish oligomers with an -coiled-coil stalk, has been implicated in endocytosis and the formation of Birbeck granules. The structure of Langerin harbours essential motifs for Ca²⁺-binding and sugar accommodation. Lectin activity has previously been inferred by diminished antibody binding to cells in the presence of the glycan ligand mannan. In view of the complexity of the C-type lectin/lectin-like network, it is unclear what role Langerin plays for Langerhans cells in binding mannosides. In order to reveal in frozen tissue sections to what extent mannose-binding activity co-localizes with Langerin, we have used a synthetic marker, i.e. a neoglycoprotein carrying mannose maxiclusters, as a histochemical ligand, and computer-assisted fluorescence monitoring in a double-labelling procedure. Mannoside-binding capacity was detected in normal epithelial cells. Double labelling ensured the unambiguous assessment of the binding of the neoglycoprotein in Langerhans cells. Light-microscopically, its localization profile resembled the pattern of immunohistochemical detection of Langerin. This result has implications for suggesting rigorous controls in histochemical analysis of this cell type, because binding of kit reagents, i.e. mannose-rich glycoproteins horseradish peroxidase or avidin, to Langerin (or a spatially closely associated lectin) could yield false-positive signals. To show that recognition of carbohydrate ligands in dendritic cells is not restricted to mannose clusters, we have also documented binding of carrier-immobilized histo-blood group A trisaccharide, a ligand of galectin-3, which was not affected by the presence of a blocking antibody to Langerin. Remarkably, access to the carbohydrate recognition domain of Langerin appeared to be impaired in proliferatively active environments (malignancies, hair follicles), indicating presence of an endogenous ligand with high affinity to saturate the C-type lectin under these conditions.     

Conjugation of p-aminophenyl glycosides with squaric acid diester to a carrier protein and the use of neoglycoprotein in the histochemical detection of lectins

The coupling of p-aminophenyl 2-acetamido-2-deoxy-3-O-beta-D- galactopyranosyl-beta-D-galactopyranoside (gal-beta 1,3-galNAc) to bovine serum albumin (BSA) was achieved by using 1,2-diethoxycyclobutene-3,4-dione (squaric acid diester) as a new coupling reagent. Two selective consequential steps afforded the desired neoglycoprotein: reaction of the p-aminophenyl group of gal-beta 1,3-galNAc with squaric acid diester gave the corresponding squaric acid amide ester, which was transformed into the BSA conjugate by coupling with the lysyl epsilon-amino group of BSA through formation of a squaric acid 1,2-bisamide. The experimental conditions for the reactions and the optimization of average were performed by using p-anisidine as model substance, the methyl group substituting for the carbohydrate part of a p-aminophenylglycoside. Neoglycoproteins have proven to be valuable tools for lectin detection. To evaluate the properties of this type of probe, the obtained neoglycoprotein with the histochemically crucial T-antigen structure was used for glycocytological and glycohistochemical studies. Three cultured human tumor cell lines and tissue sections from human breast carcinomas were chosen. Its efficiency was similar in comparison to measurements with a probe, derived by diazotization with the p-aminophenyl glycosides of gal-beta 1,3-galNAc and already shown to be a reliable marker for lectin localization in tissue sections and cultured cells.     

Correlations between the binding of neoglycoproteins,bovine serum albumin (BSA) and lectins in 10 to 13-day-old mouse embryos

Summary In the present work we compared the appearance of carbohydrate binding sites for mannose, maltose, sialic acid and N-acetyl-glucosamine in the 11 to 13-day-old mouse embryo with the appearance of BSA and lectin binding sites. The carbohydrate-binding sites were localized with FITC-coupled neoglycoproteins, synthesized by chemical glycosylation of bovine serum albumin (BSA). These localizations were compared with binding of the FITC-labelled unglycosylated BSA. Furthermore the localizations of neoglycoprotein and BSA binding sites were correlated with binding of the FITC-labelled lectins WGA, RCA I and Con A. Initial appearance of neoglycoprotein binding sites occurred in the lens capsule of the 13 day old mouse embryo. Binding sites for the unglycosylated BSA appeared earlier, i.e. already in the 12-day-old embryo, in the basement membranes of the choroid plexus and the lung bud and lectin binding sites were seen in these structures in the 11-day-old embryo. The staining of the basement membrane and the lens capsule for BSA binding sites in the 12-and 13-day-old embryos correspond to WGA binding to these membranes. From these results we concluded that 1) specific carbohydrates which are probably involved in embryonic development appear much earlier in the embryo than the endogenous lectins which are able to react with these carbohydrates and 2) BSA is a protein which like WGA probably binds N-acetylglucosamine or sialic acid moieties.     

Glycopeptide-albumin derivative: Its preparation and histochemical ligand properties

Summary Carrier-immobilized mono-or disaccharides and other carbohydrate structures, derived by custom-made chemical synthesis, have already proven to be valuable ligands for localizing carbohydrate-binding proteins in tissue sections. Defined purified glycopeptides, as components of neoglycoproteins, offer the possibility of increasing their structural complexity and, thereby, their receptor selectivity. To test the feasibility of this approach, the glycopeptide man₆-glcNAc₂-asparagine derived from ovalbumin was purified after pronase digestion. It was coupled to bovine serum albumin as carrier protein with the homobifunctional linking agent bis-(sulphosuccinimidyl)suberate to yield the diglycosylated concanavalin A-reactive product. Following biotinylation, it was used to detect mannose-specific binding sites in fixed cells of seven human leukemia or lymphoma lines and in fixed, paraffin-embedded sections of human breast cancer. In comparison to chemically mannosylated bovine serum albumin with ten sites of glycosylation or to ovalbumin, this derivative produced a similar pattern of reaction with a quantitatively lower extent of staining in most cases. Remarkably, the presence of potential endogenous ligands for the detected receptor sites was ascertained using the plant lectin concanavalin A. Thus, the conjugation of a purified, deliberately selected glycopeptide to a suitable carrier produces a histochemical tool for detecting glycopeptide-specific binding sites.     

Regional differences in the distribution of endogenous receptors for carbohydrate constituents of cellular glycoconjugates, especially lectins, in cortex, hippocampus, basal ganglia and thalamus of adult human brain

Ten different types of labelled neoglycoproteins, exposing glycohistochemically pivotal carbohydrate moieties that mostly are constituents of naturally occurring glycoconjugates with an aromatic spacer, were synthesized. The panel was applied to fixed, paraffin-embedded sections of different cortical regions and white matter, of hippocampal gyrus, basal ganglia, thalamus nuclei and adjacent areas of adult human brain to comprehensively map the presence of respective binding sites in these parts. Compliance with accepted criteria for specificity of binding was routinely ascertained. Overall, not a uniform binding pattern, but a distinct distribution with regional differences on the level of specific cytoplasmic and nuclear staining in nerve cells was determined, fiber structures being generally labelled with medium or strong intensity. For example, among the neurons localized in the five cortical laminae the binding of N-acetyl-D-galactosamine varied from strong to undetectable. Biochemical analysis, employing carbohydrate residues as affinity ligands in chromatography, proved that the neuroanatomically different regions exhibited a pattern of receptors with notable similarities. These results on endogenous binding sites for glycoconjugates, especially lectins, are complementary to assessment of localization of cellular glycoconjugates by plant lectins and carbohydrate-specific monoclonal antibodies. They are thus a further obligatory step to substantiate the physiological roles of recognitive protein-carbohydrate interactions in the central nervous system.     

Correlations between the binding of neoglycoproteins, bovine serum albumin (BSA) and lectins in 10 to 13-day-old mouse embryos

In the present work we compared the appearance of carbohydrate binding sites for mannose, maltose, sialic acid and N-acetyl-glucosamine in the 11 to 13-day-old mouse embryo with the appearance of BSA and lectin binding sites. The carbohydrate-binding sites were localized with FITC-coupled neoglycoproteins, synthesized by chemical glycosylation of bovine serum albumin (BSA). These localizations were compared with binding of the FITC-labelled unglycosylated BSA. Furthermore the localizations of neoglycoprotein and BSA binding sites were correlated with binding of the FITC-labelled lectins WGA, RCA I and Con A. Initial appearance of neoglycoprotein binding sites occurred in the lens capsule of the 13 day old mouse embryo. Binding sites for the unglycosylated BSA appeared earlier, i.e. already in the 12-day-old embryo, in the basement membranes of the choroid plexus and the lung bud and lectin binding sites were seen in these structures in the 11-day-old embryo. The staining of the basement membrane and the lens capsule for BSA binding sites in the 12-and 13-day-old embryos correspond to WGA binding to these membranes. From these results we concluded that 1) specific carbohydrates which are probably involved in embryonic development appear much earlier in the embryo than the endogenous lectins which are able to react with these carbohydrates and 2) BSA is a protein which like WGA probably binds N-acetylglucosamine or sialic acid moieties.     

Carbohydrate binding properties of the stinging nettle (Urtica dioica) rhizome lectin

The interaction of the stinging nettle rhizome lectin (UDA) with carbohydrates was studied by using the techniques of quantitative precipitation, hapten inhibition, equilibrium dialysis, and uv difference spectroscopy. The Carbohydrate binding site of UDA was determined to be complementary to an N,N',N"-triacetylchitotriose unit and proposed to consist of three subsites, each of which has a slightly different binding specificity. UDA also has a hydrophobic interacting region adjacent to the carbohydrate binding site. Equilibrium dialysis and uv difference spectroscopy revealed that UDA has two carbohydrate binding sites per molecule consisting of a single polypeptide chain. These binding sites either have intrinsically different affinities for ligand molecules, or they may display negative cooperativity toward ligand binding.     

Regional differences in the distribution of endogenous receptors for carbohydrate constituents of cellular glycoconjugates,especially lectins,in cortex,hippocampus, basal ganglia and thalamus of adult human brain

Summary Ten different types of labelled neoglycoproteins, exposing glycohistochemically pivotal carbohydrate moieties that mostly are constituents of naturally occurring glycoconjugates with an aromatic spacer, were synthesized. The panel was applied to fixed, paraffin-embedded sections of different cortical regions and white matter, of hippocampal gyrus, basal ganglia, thalamus nuclei and adjacent areas of adult human brain to comprehensively map the presence of respective binding sites in these parts. Compliance with accepted criteria for specificity of binding was routinely ascertained. Overall, not a uniform binding pattern, but a distinct distribution with regional differences on the level of specific cytoplasmic and nuclear staining in nerve cells was determined, fiber structures being generally labelled with medium or strong intensity. For example, among the neurons localized in the five cortical laminae the binding of N-acetyl-d-galactosamine varied from strong to undetectable. Biochemical analysis, employing carbohydrate residues as affinity ligands in chromatography, proved that the neuroanatomically different regions exhibited a pattern of receptors with notable similarities. These results on endogenous binding sites for glycoconjugates, especially lectins, are complementary to assessment of localization of cellular glycoconjugates by plant lectins and carbohydrate-specific monoclonal antibodies. They are thus a further obligatory step to substantiate the physiological roles of recognitive protein-carbohydrate interactions in the central nervous system.     

Detection of binding sites for biotinylated neoglycoproteins and heparin (endogenous lectins) during cerebellar ontogenesis in the rat

Endogenous carbohydrate-binding sites were studied during rat cerebellar development on sections of fixed tissue using synthetic tools, biotinylated neoglycoproteins, in conjunction with subsequent avidinperoxidase staining. Neoglycoproteins were constructed by chemically coupling the histochemically pivotal carbohydrate moieties to an inert carrier protein. The sugar part of the neoglycoproteins included common constituents of the carbohydrate part of cellular glycoconjugates, namely mannose, galactose, fucose, N-acetyl-glucosamine, N-acetylgalactosamine and N-acetyl-neuraminic acid to probe for the presence of respective endogenous receptors. Heparin was biotinylated after mild cyanogen bromide activation and aminoalkylation. Specific positive reactions were obtained for all neoglycoproteins and heparin. The staining pattern with the individual probes disclosed variable developmental regulation. Consequently, these results suggest that recognition processes during cerebellar development may include several types of carbohydrate determinants. In two instances, the binding of neoglycoproteins could be compared to endogenous lectin-specific antibodies. Despite a significant extent of accordance the comparison revealed notable differences. These differences were attributed primarily to fixation and the presence of physiological ligands that can mask the active endogenous carbohydrate-binding proteins. In any case, histochemical application of labeled neoglycoproteins is valuable to discern the presence, localization and developmental pattern of binding sites for the carbohydrate part of glycoconjugates, on which further biochemical and cell biological studies can consequently be based.     

A new lectin-gold complex for ultrastructural localization of galacturonic acids

We report the development of a cytochemical affinity technique for detection of galacturonic acids at the ultrastructural level. The highly purified gonad lectin from Aplysia depilans (AGL) was tagged with colloidal gold particles and used for labeling carbohydrates in resin-embedded sections of various plant and fungal tissues. Patterns of AGL binding sites were compared to those obtained with a D-galactose-specific lectin, Ricinus communis agglutinin I. Differences in labeling patterns were noted, indicating that the lectins exhibited differential carbohydrate binding. In addition, the considerable loss of labeling over isolated wheat coleoptile walls treated for removal of pectin, after incubation with the AGL-gold complex, strongly suggested an affinity of AGL for pectic substances. A series of cytochemical controls, including sugar inhibition tests, has proven the specificity of the technique and the high affinity of AGL towards galacturonic acids. The potential value of this new lectin for ultrastructural studies on cell wall pectic substances in plant biology and pathology is demonstrated.     

Glycosyldisulfides from dynamic combinatorial libraries as O-glycoside mimetics for plant and endogenous lectins: their reactivities in solid-phase and cell assays and conformational analysis by molecular dynamics simulations

Dynamic combinatorial library design exploiting the thiol-disulfide exchange readily affords access to glycosyldisulfides. In order to reveal lectin-binding properties of this type of non-hydrolyzable sugar derivative, libraries originating from a mixture of common building blocks of natural glycans and thiocompounds were tested against three plant agglutinins with specificity to galactose, fucose or N-acetylgalactosamine, respectively, in a solid-phase assay. Extent of lectin binding to matrix-immobilized neoglycoprotein presenting the cognate sugar could be reduced, and evidence for dependence on type of carbohydrate was provided by dynamic deconvolution. Glycosyldisulfides also maintained activity in assays of increased physiological relevance, that is, using native tumor cells and also adding to the test panel an endogenous lectin (galectin-3) involved in tumor spread and cardiac dysfunction. N-Acetylgalactosamine was pinpointed as the most important building block of libraries for the human lectin and the digalactoside as most potent compound acting on the toxic mistletoe agglutinin which is closely related to the biohazard ricin. Because this glycosyldisulfide, which even surpasses lactose in inhibitory capacity, rivals thiodigalactoside as inhibitor, their degrees of intramolecular flexibility were comparatively analyzed by computational calculations. Molecular dynamics runs with explicit consideration of water molecules revealed a conspicuously high degree of potential for shape alterations by the disulfide's three-bond system at the interglycosidic linkage. The presented evidence defines glycosyldisulfides as biologically active ligands for lectins.     

Recognition and binding of template-primers containing defined abasic sites by Drosophila DNA polymerase alpha holoenzyme

Human DNA polymerase alpha holoenzyme follows an ordered sequential terreactant mechanism of substrate recognition and binding (Wong, S. W., Paborsky, L. R., Fisher, P. A., Wang, T. S.-F., and Korn, D. (1986) J. Biol. Chem. 261, 7958-7968). We confirmed this mechanism for the DNA polymerase alpha holoenzyme purified from Drosophila melanogaster embryos and studied the interaction of Drosophila pol alpha with synthetic oligonucleotide template-primers containing modified tetrahydrofuran moieties as model abasic lesions chemically engineered at a number of defined sites. Abasic lesions in the template had relatively little effect on the polymerase incorporation reaction at sites proximal to the lesion. However, incorporation opposite an abasic site was undetectable relative to that which occurred opposite a normal template nucleotide. Moreover, abasic residues in the primer region of the template-primer construct as far as 4 base pairs removed from the 3'-primer terminus prevented detectable nucleotide incorporation relative to that seen on an unmodified template-primer. Primer-region lesions had qualitatively similar effects whether they were located on the primer strand itself or on the complementary template strand. Data from polymerase incorporation experiments were corroborated by competitive binding assays performed under steady state reaction conditions. Results of these experiments suggested that polymerase binding to synthetic oligonucleotide template-primers was essentially unaffected by lesions located at sites that did not block incorporation. Lesions that did block incorporation apparently did so by abrogating template-primer binding. These observations have implications for understanding the mechanisms whereby DNA polymerase alpha recognizes noninformational template sites in vivo and prevents DNA synthesis from proceeding past these points.     

Lectin binding sites in normal and phenobarbitale/halothane treated rat liver. A histochemical study

The content of carbohydrate residues of both normal and phenobarbitale-halothane-hypoxia exposed rat liver has been examined by means of lectin histochemistry. Eight biotinylated lectins specific to galactose, N-acetyl-galactosamine, N-acetyl-glucosamine, fucose and mannose were applied to paraffin sections of rat liver at light microscopic level. The most distinct binding was observed at the structures of the "perisinusoidal functional unit": Kupffer cells are bound by S-WGA, SBA and PNA. Bile canaliculi display binding sites for RCA I and WGA. Cytoplasm of hepatocytes appears lectin-negative, except for PSA. The enhanced reaction of S-WGA, PNA and SBA after the preincubation of the sections with neuraminidase indicates the occurrence of sialic acid in Kupffer cells. The phenobarbitale-halothane-hypoxia exposed rat liver shows centrolobular degeneration of hepatocytes with a diminished amount of hepatocyte and Kupffer cells as well. The lectin binding pattern of sinusoidal walls, membranes of hepatocytes and bile canaliculi remains the same compared to that of normal rat liver. This finding suggests that at least the carbohydrate content of membranes in the liver resists severe destruction under phenobarbitale-halothane-hypoxia. It is assumed that there exists a connection between intact carbohydrate residues and the regeneration of liver parenchyma.     

Expression patterns of the T antigen and the cryptic T antigen in rat fetuses: detection with the lectin amaranthin

The lectin amaranthin, purified from the seeds of Amaranthus caudatus, has been shown to react specifically with the Gal beta 1,3GalNAc-alpha and the NeuAc alpha 2,3Gal beta 1,3GalNAc-alpha sequence which represent the T antigen and the cryptic T antigen, respectively. We report here the development of labeling techniques that apply amaranthin to stain paraffin sections from rat fetuses. Amaranthin staining was inhibited by pre-incubation of lectin-gold complexes with 10 mM Gal beta 1,3GalNAc-alpha-O-benzyl (synthetic T antigen) or 10 mM Gal beta 1,3GalNAc-alpha-O-aminophenylethyl-human serum albumin (T antigen neoglycoprotein), asialoglycophorin, asialofetuin, and asialomucin. The beta-elimination reaction also abolished the lectin staining demonstrating specificity for O-glycosidically linked structures. A comparison with monoclonal anti-T antigen antibody immunostaining demonstrated that amaranthin detects the T antigen and its cryptic form in tissue sections. Application of the galactose oxidase-Schiff sequence abolished amaranthin (and anti-T antibody) binding to the T antigen but not to its cryptic form, and therefore permitted their differentiation in tissue sections. Histochemical evidence was obtained indicating that amaranthin is a more specific anti-T reagent than peanut lectin. Data are presented that show the differential expression of the T antigen and the cryptic T antigen in organs and cells of rat fetuses late in gestation. Therefore, amaranthin can be used for histochemical detection of the T antigen and the cryptic T antigen, and facilitates discrimination between them.     

Binding and endocytosis of glycoproteins and neoglycoproteins by isolated rabbit hepatocytes.

Rabbit hepatocytes were isolated by a collagenase perfusion technique, and used to study the binding and endocytosis of the glycoprotein, asialo-orosomucoid, and the neoglycoprotein, Gal39-bovine serum albumin. Both of these proteins contain exposed galactosyl residues, and were avidly bound by the lectin on the hepatic parenchymal cell surface. Steady state and kinetic experiments performed at 2 degrees C and at 37 degrees C revealed the presence of two apparent classes of binding sites totalling 4.7 X 10(5) sites/cell at 2 degrees C, and 6.3 X 10(5) sites/cell at 37 degrees C. At 37 degrees C, both classes of sites participated in internalization of bound ligand. The cells were capable of internalizing about 60 000 molecules/min per cell. The process appeared to be first-order, with a rate constant k = 0.098 min-1 and t1/2 = 7.1 +/- 0.6 min. Binding could be inhibited by galactose-containing compounds, EGTA, and by anti-(hepatic lectin) immunoglobulin G. The inhibition by antibody appeared to be reversible upon removal of antibody-containing medium.     

Analysis of nuclear sugar-binding components in undifferentiated and in vitro differentiated human promyelocytic leukemia cells (HL60)

The nuclear sugar-binding components (i.e., lectin-like molecules) were analyzed using isolated and membrane-depleted nuclei after incubation in the presence of fluorescein-labeled neoglycoproteins. This analysis was performed before and during the in vitro differentiation of HL60 cells into monocytes by PMA treatment and into granulocytes by DMSO treatment. The nucleoli of undifferentiated and differentiated HL60 cells were not labeled, unlike the nucleoli of other mammalian cells studied so far. This peculiarity allowed us to quantitatively analyze by flow cytometry the changes in the lectin activity associated with the extranucleolar territories enriched in ribonucleoprotein complexes. The neoglycoprotein binding was found to be significantly lower in differentiated than in undifferentiated cells. The decrease in neoglycoprotein binding was observed within the first 24 h of DMSO or PMA treatment, just before the arrest of DNA synthesis. Taking into account that the granulocytic differentiation required 72 h of chemical treatment, the extra-nucleolar lectins might be involved in modulation of the DNA synthesis rather than in phenotypic differentiation. These data are discussed in an attempt to reconcile the association of lectins with RNP complexes and their possible involvement in modulation of HL60 cell proliferation.     

Analysis of nuclear sugar-binding components in undifferentiated and in vitro differentiated human promyelocytic leukemia cells (HL60)

The nuclear sugar-binding components (i.e., lectinlike molecules) were analyzed using isolated and membrane-depleted nuclei after incubation in the presence of fluorescein-labeled neoglycoproteins. This analysis was performed before and during the in vitro differentiation of HL60 cells into monocytes by PMA treatment and into granulocytes by DMSO treatment. The nucleoli of undifferentiated and differentiated HL60 cells were not labeled, unlike the nucleoli of other mammalian cells studied so far. This peculiarity allowed us to quantitatively analyze by flow cytometry the changes in the lectin activity associated with the extranucleolar territories enriched in ribonucleoprotein complexes. The neoglycoprotein binding was found to be significantly lower in differentiated than in undifferentiated cells. The decrease in neoglycoprotein binding was observed within the first 24 h of DMSO or PMA treatment, just before the arrest of DNA synthesis. Taking into account that the granulocytic differentiation required 72 h of chemical treatment, the extra-nucleolar lectins might be involved in modulation of the DNA synthesis rather than in phenotypic differentiation. These data are discussed in an attempt to reconcile the association of lectins with RNP complexes and their possible involvement in modulation of HL60 cell proliferation.     

Lactose-containing starburst dendrimers: influence of dendrimer generation and binding-site orientation of receptors (plant/animal lectins and immunoglobulins) on binding properties.

Starburst glycodendrimers offer the potential to serve as high-affinity ligands for clinically relevant sugar receptors. In order to define areas of application, their binding behavior towards sugar receptors with differential binding-site orientation but identical monosaccharide specificity must be evaluated. Using poly(amidoamine) starburst dendrimers of five generations, which contain the p-isothiocyanato derivative of p-aminophenyl-beta-D-lactoside as ligand group, four different types of galactoside-binding proteins were chosen for this purpose, i.e., the (AB)(2)-toxic agglutinin from mistletoe, a human immunoglobulin G fraction, the homodimeric galectin-1 with its two binding sites at opposite ends of the jelly-roll-motif-harboring protein and monomeric galectin-3. Direct solid-phase assays with surface-immobilized glycodendrimers resulted in obvious affinity enhancements by progressive core branching for the plant agglutinin and less pronounced for the antibody and galectin-1. High density of binding of galectin-3 with modest affinity increases only from the level of the 32-mer onwards points to favorable protein-protein interactions of the monomeric lectin and a spherical display of the end groups without a major share of backfolding. When the inhibitory potency of these probes was evaluated as competitor of receptor binding to an immobilized neoglycoprotein or to asialofetuin, a marked selectivity was detected. The 32- and 64-mers were second to none as inhibitors for the plant agglutinin against both ligand-exposing matrices and for galectin-1 on the matrix with a heterogeneous array of interglycoside distances even on the per-sugar basis. In contrast, a neoglycoprotein with the same end group was superior in the case of the antibody and, less pronounced, monomeric galectin-3. Intimate details of topological binding-site presentation and the ligand display on different generations of core assembly are major operative factors which determine the potential of dendrimers for applications as lectin-targeting device, as attested by these observations.     

Expression of endogenous receptors for neoglycoproteins, especially lectins, that allow fiber typing on formaldehyde-fixed, paraffin-embedded muscle biopsy specimens. A glycohistochemical, immunohistochemical, and glycobiochemical study

A panel of biotinylated (neo)glycoproteins was used for specific detection of endogenous sugar receptors, especially lectins, in formaldehyde-fixed, paraffin-embedded muscle biopsy specimens from human deltoid, quadriceps, and biceps muscles, tibial and quadriceps muscles of rat, and bovine masseter muscle. The glycohistochemical probes used consisted of conjugates of a labeled, histochemically inert carrier protein and various covalently linked, histochemically crucial sugar moieties. Specific binding of alpha-L-fucoside, beta-D-galactoside, beta-D-xyloside, and alpha-D-mannoside to muscle sections was detected, showing no species-specific differences. The presence of receptors for the N-acetylated sugars in natural glycoconjugates, and for sugars with a phosphate group, i.e., mannose-6-phosphate and galactose-6-phosphate, was demonstrated glycohistochemically. However, these binding specificities revealed species-specific differences, e.g., the absence of N-acetyl-D-galactosamine-specific receptors or galactose-6-phosphate-specific receptors in rat muscle. Other charged sugars included glucuronic acid and sialic acid, which bound only to ox and rat muscle or failed to reveal their respective receptors in all types of muscle investigated. This different extent of staining with anionic probes served as a further control to ascertain carbohydrate binding specificity. Positive glycohistochemical reaction developed within sarcomeres only at the level of A-bands. Granular staining was observed in the sarcoplasm among the myofibrils and also in the subsarcolemmal regions. Differences in expression of glycohistochemically detectable sugar receptors were noted between type 1, type 2A, and type 2B fibers. The molecular properties of one type of glycohistochemically detectable sugar receptor were inferred both immunohistochemically and biochemically. An antiserum against an endogenous beta-galactoside-specific lectin from muscle tissue localized this lectin within sections consistently similar to (neo)glycoproteins, detecting beta-galactoside-specific receptor(s). This similarity of binding patterns strongly supports the assumption that (neo)glycoproteins with beta-galactoside termini indeed bind to the respective endogenous lectin. The lectin-specific antiserum enabled us to ascertain that glycohistochemical fiber typing corresponds to enzyme histochemical typing. Moreover, biochemical purification using affinity chromatography and subsequent affinity elution revealed only the immunohistochemically detectable beta-galactoside-specific lectin. Consequently, use of a panel of neoglycoproteins, when frozen sections for histochemical analysis are not available, co