Cytochemical detection of mannose-specific receptors for glycoproteins with horseradish peroxidase as a ligand

Lectins: a primer for histochemists and cell biologists

An experimental observation on selecting binding partners underlies the introduction of the term 'lectin'. Agglutination of erythrocytes depending on their blood-group status revealed the presence of activities in plant extracts that act in an epitope-specific manner like antibodies. As it turned out, their binding partners on the cell surface are carbohydrates of glycoconjugates. By definition, lectins are glycan-specific (mono- or oligosaccharides presented by glycoconjugates or polysaccharides) receptors, distinguished from antibodies, from enzymes using carbohydrates as substrates and from transporters of free saccharides. They are ubiquitous in Nature and structurally widely diversified. More than a dozen types of folding pattern have evolved for proteins that bind glycans. Used as tool, this capacity facilitates versatile mapping of glycan presence so that plant/fungal and also animal/human lectins have found a broad spectrum of biomedical applications. The functional pairing with physiological counterreceptors is involved in a wide range of cellular activities from cell adhesion, glycoconjugate trafficking to growth regulation and lets lectins act as sensors/effectors in host defense.

Introduction to glycopathology: the concept, the tools and the perspectives

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1670639891114983.

Analyzing the flow of biological information is a fundamental challenge for basic sciences. The emerging results will then lend themselves to the development of new approaches for medical applications. Toward this end, the products of protein/lipid glycosylation deserve special attention. The covalent attachment of sugars to these carriers means much more than just a change of the carriers’ physicochemical properties. In principle, the ubiquitous presence of glycoconjugates and the close inspection of the particular structural ‘talents’ of carbohydrates provide suggestive evidence for information coding by sugars. In fact, the theoretical number of ‘words’ (oligomers) formed by ‘letters’ (monosaccharides) is by far higher than by using nucleotides or amino acids. In other words, glycans harbor an unsurpassed coding capacity. The cyto- and histochemical detection of dynamic changes in the profile of cellular glycans (glycome, the equivalent of the proteome) by sugar receptors such as antibodies used as tools underscores the suitability of carbohydrates for such a task. The resulting staining patterns can be likened to a molecular fingerprint. By acting as ligand (counterreceptor) for endogenous receptors (tissue lectins), glycan epitopes become partners in a specific recognition pair, and the sugar-encoded information can then be translated into effects, e.g. in growth regulation. Of note, expression of both sides of such a pair, i.e. lectin and cognate glycan, can physiologically be orchestrated for optimal efficiency. Indeed, examples how to prevent autoimmune diseases by regulatory T cells and restrict carcinoma growth by a tumor suppressor attest occurrence of co-regulation. In consequence, these glycans have potential to establish a new class of functional biomarkers, and mapping presence of their receptors is warranted. In this review, the cyto- and histochemical methods, which contribute to explore information storage and transfer within the sugar code, are described. This introduction to the toolbox is flanked by illustrating the application of each type of tool in histopathology, with focus on adhesion/growth-regulating galectins. Together with an introduction to fundamental principles of the sugar code, the review is designed to guide into this field and to inspire respective research efforts.

Dendrobium findleyanum agglutinin: production, localization, anti-fungal activity and gene characterization

The recently reported Dendrobium findleyanum agglutinin (DFA) was identified and determined in different parts of D. findleyanum pseudobulbs by using Western blot analysis, LC-MS/MS, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and histochemical procedure. Western blot analysis of crude protein extract with horseradish peroxidase (HRP), a mannose-rich glycoprotein, showed only one band at 14.5 kDa, which had the same molecular mass as DFA. This band was a major band when the membrane was stained with Coomassie Brilliant Blue. The protein profiles from SDS-PAGE showed higher band intensity of the 14.5 kDa mannose-binding protein in nearly mature and mature stages, compared to very young and young stages of the orchid. In addition, the band intensity was to a great extent different between the swollen and the non-swollen internode of the pseudobulb. Using LC-MS/MS, the sequence tags of the 14.5-kDa protein bands from the node, swollen internode and non-swollen internode revealed that the protein was DFA. Histochemical procedure in the transverse section of the pseudobulbs demonstrated major HRP binding sites, which reflected the location of DFA, in periphery of parenchymal cells. The purified DFA showed anti-fungal activity against Alternaria alternata and Collectotrichum sp. Using reverse transcription polymerase chain reaction and DNA sequencing, the deduced amino acid sequence of the DFA precursor revealed 94% homology with a lectin precursor from D. officinale. N-terminal sequencing demonstrated the processing site between residues 24 and 25 of the DFA precursor.

Role of concanavalin A lectin in recognition of pterygium remnant after surgical excision: preliminary results of a prospective study

Background:

Pterygium is one of the most common conjunctival diseases among ophthalmic pathologies. The frequency of recurrences is high, either after surgical treatment or after treatment combined with mitomycin C or beta-radiation therapy.

Aims:

The purpose of this study was to determine whether concanavalin A (ConA) lectin bound to the pterygial surface can be used to detect recurrence or remnants of pterygium after surgical excision.

Materials and Methods:

This was a prospective study on 20 patients with pterygium, divided in five stages, pre-surgery, early post-surgery (24h), late post-surgery (seven days), very late post-surgery (four weeks) and two months after the procedure.

A drop of fluorescein-marked Con A (35 µg/mL) was instilled in the lower conjunctival eyelid sac and the eye was exposed to the light of a Wood′s lamp for an average of five seconds.

Results:

Out of the 20 patients, eight patients were found to have fluorescent stretch marks over the scar corresponding to residual pterygial tissue at four weeks; two months after the procedure of re-surgery we observed no fluorescent remnants. All residual pterygia were confirmed through histochemistry studies.

Conclusion:

It was possible to detect remnants of pterygium in postoperative patients and recurrences in early pre-clinical stages through the visualization of fluorescent ConA bound to the pterygial surface.

The expression of mannose receptors in skin fibroblast and their involvement in Leishmania (L.) amazonensis invasion

Leishmania are protozoa that invade mononuclear phagocytes with the involvement of different ligand-receptor systems, including mannose receptors. Until now, scant data are available concerning the mechanisms that govern the infection of Leishmania in other host cell types such as fibroblasts. Our aim was to analyze the expression of mannose receptors in primary cultures of skin fibroblasts (SF) further characterizing their role during the invasion of promastigotes of Leishmania (L.) amazonensis. Both fluorescent, light, and electron microscopy assays revealed that SF have mannose receptors since they bound and internalized mannosylated ligands in addition to being positively labeled by fuc-BSA-FITC probes. d-mannose competition assays revealed the participation of mannose receptors during the parasite association with SF presenting upregulated receptor expression during the initial steps of the infection. After longer periods of Leishmania:fibroblasts contact, the modulation noted in the host mannose receptors was reverted concomitantly to the infection control, suggesting that the parasites were required for the alteration maintenance and providing evidences that the SF may display microbicidal mechanisms to control the Leishmania infection.

Endocytic pathway in mouse cardiac cells

Primary cultures of heart muscle cells provide powerful tools for cardiac cell biological research that permits both physiological and biochemical approaches. In the present study we analyzed the endocytosis of cardiac cells and presented morphological characterization of the endocytic machinery using markers, which enabled us to follow the fluid-phase, receptor-mediated endocytosis and the internalization of large particles. Our results demonstrated the route of the internalized cargo to early endosomes followed or not by its discharge in the late compartments. We also confirmed the ability of cardiac muscle cells to ingest large particles such as the mannosylated ligand zymosan A, and even internalize whole eukaryotic cells such as the protozoan parasite Trypanosoma cruzi. Since endocytosis is involved in many important cellular functions, the present work contributes to the knowledge of possible additional roles played by cardiac muscle cells besides their well known ability to act as physically energetic cells in the body, constantly contracting without tiring.

Glycohistochemistry: the why and how of detection and localization of endogenous lectins

The central dogma of molecular biology limits the downstream flow of genetic information to proteins. Progress from the last two decades of research on cellular glycoconjugates justifies adding the enzymatic production of glycan antennae with information-bearing determinants to this famous and basic pathway. An impressive variety of regulatory processes including cell growth and apoptosis, folding and routing of glycoproteins and cell adhesion/migration have been unravelled and found to be mediated or modulated by specific protein (lectin)-carbohydrate interactions. The conclusion has emerged that it would have meant missing manifold opportunities not to recruit the sugar code to cellular information transfer. Currently, the potential for medical applications in anti-adhesion therapy or drug targeting is one of the major driving forces fuelling progress in glycosciences. In histochemistry, this concept has prompted the introduction of carrier-immobilized carbohydrate ligands (neoglycoconjugates) to visualize the cells' capacity to be engaged in oligosaccharide recognition. After their isolation these tissue lectins will be tested for ligand analysis. Since fine specificities of different lectins can differ despite identical monosaccharide binding, the tissue lectins will eventually replace plant agglutinins to move from glycan profiling and localization to functional considerations. Namely, these two marker types, i.e. neoglycoconjugates and tissue lectins, track down accessible binding sites with relevance for involvement in interactions in situ. The documented interplay of synthetic organic chemistry and biochemistry with cyto- and histochemistry nourishes the optimism that the application of this set of innovative custom-prepared tools will provide important insights into the ways in which glycans can act as hardware in transmitting information during normal tissue development and pathological situations.

A cardiomyocyte mannose receptor system is involved in Trypanosoma cruzi invasion and is down-modulated after infection

Mannosyl binding sites were detected "in vitro" on cardiomyocytes (CM) surface using horseradish peroxidase (HRP) as the ligand. Binding assays revealed a specific recognition system, which was time- and concentration-dependent. The binding required physiological pH and was inhibited by EDTA and trypsin treatments. HRP binding was reduced by pre-incubations with low concentrations of D-mannose. Ultrastructural analysis of the endocytic process was followed using HRP coupled to colloidal gold particles (HRP-Au). The tracer was found within caveolae characterizing early steps of the receptor-mediated endocytosis. The addition of 10 mM D-mannose to the interaction medium blocked Trypanosoma cruzi uptake by CM. The labeling of CM with a subsaturating concentration of HRP-Au before their infection showed, by ultrastructural studies, that its association with trypomastigote forms occurred frequently near to HRP-gold particles that could also be seen to comprise the parasitophorous vacuole. After infection of CM with T. cruzi, a considerable reduction on HRP binding was noticed. Binding was almost completely restored by treating the infected cultures with the trypanocidal drug Nifurtimox. Our "in vitro" findings suggest that cardiomyocyte's mannose receptors localized at the sarcolemma mediates T. cruzi recognition and can be down-modulated by parasite infection.

Beyond plant lectin histochemistry: preparation and application of markers to visualize the cellular capacity for protein-carbohydrate recognition

Oligosaccharides can store biological information. In this respect, their capacity even outmatches that of oligo- and polymeric structures of nucleotides and amino acids. Protein-carbohydrate interactions are thus considered to be involved in the regulation of diverse cellular activities. Over decades, plant lectins have proven valuable for assessing structural aspects of the enormous variety of carbohydrate epitopes and for monitoring spatially and/or temporally restricted patterns of expression. If the presence of these epitopes and the alterations in their occurrence bear physiological relevance, one reasonable possibility is that the visualized saccharides serve as ligands in an operative protein-carbohydrate recognition system. To support the validity of this hypothesis, receptor sites for a sugar compound must be localized. Carrier-immobilized carbohydrates (neoglycoconjugates) are adequate for this purpose. Chemical synthesis gains access to such probes. In the first stage, the presence of binding sites such as lectins in the tissue is ascertained. The next step toward proving the outlined hypothesis is the application of the first localized then purified endogenous receptors as glycohistochemical markers. It is essential to point out that the fine specificities of plant and animal lectins can differ, although they share an identical monosaccharide specificity. Thus, neoglycoconjugates for localizing sugar ligand-binding proteins and endogenous lectins to detect suitable binding partners are promising probes to enhance our knowledge about the capacities of cells to be engaged in protein-carbohydrate recognition in situ.

Secretion of plasminogen activator and lysosomal enzymes from mouse skeletal muscle: effect of denervation

Levels of hydrolytic enzymes increase in skeletal muscle after denervation and their activities in the extracellular matrix appear to be important for interaction between muscle and nerve. Using enzymatic assays for beta-glucuronidase, beta-galactosidase, and plasminogen activator, we show that secretion of these enzymes from mouse skeletal muscle increases after denervation and that drugs interfering with the secretory pathway or the reuptake of enzymes modulate this release. Thus, brefeldin A inhibited secretion of plasminogen activator activity and mannan increased secreted amounts of beta-glucuronidase, but not of beta-galactosidase, in denervated muscle. In innervated muscle, brefeldin A decreased secreted activity of plasminogen activator, but mannan had no effect on secretion of either beta-glucuronidase or beta-galactosidase. Furthermore, secretion of plasminogen activator was temperature dependent. These observations, together with previous studies, suggest that secretion of hydrolytic enzymes from adult skeletal muscle may be of physiological significance in nerve-muscle communication.

Enhanced intracellular stability of dextran-horse radish peroxidase conjugate: an approach to enzyme replacement therapy

Horse radish peroxidase (HRP), a mannose-containing glycoprotein was covalently modified by conjugation with dextran. The rapid uptake of HRP by the liver is markedly inhibited by mannan. The uptake of dextran-HRP conjugate by the liver, though lower compared to that of the free enzyme, is also partially inhibited by mannan. Liposomes were therefore used as carriers for delivering the free and the modified HRP to the liver. The dextran-HRP conjugate showed greater stability intracellularly as compared to the free enzyme. The enhanced stability of enzymes upon their extensive glycosylation with nondegradable sugar polymers would be of importance in extending the catalytic life of therapeutically active enzymes and thereby improve their therapeutic potential for the treatment of certain enzyme deficiency disorders.

Mannose-sensitive HRP endocytosis by the retinal pigment epithelium

Mannose-sensitive endocytosis by rat retinal pigment epithelium (RPE) explants was characterized using the mannose-rich glycoprotein horseradish peroxidase (HRP). The number of HRP-containing endosomes in the RPE was morphologically quantitated by light microscopy while the amount of HRP ingested was biochemically quantitated by enzyme assay. HRP internalized via a mannose-sensitive receptor was differentiated from fluid-phase uptake in competitive inhibition studies using D-mannose. Morphological results showed that most HRP-containing endosomes formed within the first 15 min of incubation and showed little increase in number during 4 hr of continued incubation with HRP. In contrast, the biochemical assay showed a steady increase in the amount of HRP in RPE endosomes measured over time. The addition of 10 mM D-mannose to the incubation medium was associated with a significant decrease in both the number of HRP-containing endosomes and the amount of HRP ingested by RPE explants. Values indicate that half of the total uptake of HRP is mediated by a mannose-sensitive receptor while the balance is ingested via non-specific fluid-phase endocytosis.

Neoglycoenzymes: a versatile tool for lectin detection in solid-phase assays and glycohistochemistry

Carbodiimide-mediated coupling of p-aminophenyl glycosides to a naturally nonglycosylated enzyme yields a neoglycoenzyme. This compound combines inherent enzymatic activity with synthetically conferred ligand properties to lectins. Appropriate choice of the ligand allows custom-made synthesis to reliably detect various types of lectins. To exemplify practical applications of this class of compounds, glycosylated bacterial beta-galactosidase has been employed to quantitate plant lectins, immobilized on plastic surfaces as well as on nitrocellulose. Competitive inhibition by specific sugar ascertained the dependence of binding on protein--carbohydrate interactions. In view of lectins as tools, a sandwich lectin-binding assay for high mannose-type glycoprotein detection has been modified to principally facilitate wide application to other lectin-reactive sugar chains by introducing the neoglycoenzyme. In addition to lectin determination in solid-phase assays, neoglycoenzymes allow one to glycohistochemically localize endogenous lectins in tissue prints and tissue sections with a minimum number of steps. This nonradioactive, rapid, sensitive, and convenient assay concept, based on conjugation of a ligand to an enzyme with maintenance of its receptor-binding activity, may find extended application beyond lectinology in receptor analysis.

Cytochemical detection of receptors specific for N-linked oligosaccharides of glycoproteins in the membrane of the human spermatozoon and their distribution in the different zones of that membrane

The horseradish peroxidase (HRP), a glycoprotein rich in mannose and N-acetylglucosamine residues has been used as a ligand to detect receptors for N-glycosidic linked oligosaccharides of glycoproteins in the human spermatozoon. Specific binding of HRP occurred to the membrane and the binding sites were visualized with 3,3'-diaminobenzidine-H2O2 (DAB-H2O2) reagent, and by fluorescence when the FITC-peroxidase was used. This specific binding was suppressed by alpha-D-methyl-mannoside and human chorionic gonadotropin, decreased by follicle stimulating and luteinizing hormones and slightly diminished by N-acetylglucosamine. The distribution of the N-linked oligosaccharide specific receptors for glycoproteins in the different zones of the membrane of the spermatozoon was determined by counting the spermatozoa labeled in those zones. The pattern of the distribution is similar to that found for N-linked oligosaccharides containing glycoproteins of the same membrane. The similarity of these distributions together with the general model for cell-to-cell recognition suggest that the sperm-egg interaction mechanism could consist of dual interactions by double binding receptors.

Concanavalin A binding sites on the surface of Drosophila melanogaster sperm: a fluorescence and ultrastructural study

The distribution of alpha-D-mannose/alpha-D-glucose terminal residues in the plasma membrane of Drosophila melanogaster spermatozoon has been investigated by fluorescence and electron microscopy using concanavalin A (Con A) labeling. The results indicate the presence of distinct domains on the sperm surface. Intense binding of Con A to the plasma membrane is highly restricted to the acrosomal region and to the endpiece of the tail. In the former, Con A receptors are not homogeneously distributed, suggesting the presence of microdomains in the acrosomal area. The main part of the tail contains very few Con A binding sites, which are confined to specific areas of the membrane. The sperm surface overlying the nucleus is completely negative. The labeling pattern is unchanged after storage in the female before fertilization. A preliminary analysis of the surface of mature oocytes using fluorochrome-conjugated horseradish peroxidase indicates that D-mannose binding molecules are specifically associated with the chorion of the micropyle anterior part, which might therefore be the site of a preliminary interaction between egg and spermatozoon.

Apical membrane endocytosis via coated pits is stimulated by removal of antidiuretic hormone from isolated, perfused rabbit cortical collecting tubule

Antidiuretic hormone increases the water permeability of the cortical collecting tubule and causes the appearance of intramembrane particle aggregates in the apical plasma membrane of principal cells. Particle aggregates are located in apical membrane coated pits during stimulation of collecting ducts with ADH in situ. Removal of ADH causes a rapid decline in water permeability. We evaluated apical membrane retrieval associated with removal of ADH by studying the endocytosis of horseradish peroxidase (HRP) from an isotonic solution in the lumen. HRP uptake was quantified enzymatically and its intracellular distribution examined by electron microscopy. When tubules were perfused with HRP for 20 min in the absence of ADH, HRP uptake was 0.5 +/- 0.3 pg/min/micron tubule length (n = 6). The uptake of HRP in tubules exposed continuously to ADH during the 20-min HRP perfusion period was 1.3 +/- 0.8 pg/min/micron (n = 8). HRP uptake increased markedly to 3.2 +/- 1.1 pg/min/micron (n = 14), when the 20-min period of perfusion with HRP began immediately after removal of ADH from the peritubular bath. Endocytosis of HRP occurred in both principal and intercalated cells via apical membrane coated pits. We suggest that the rapid decline in cortical collecting duct water permeability which occurs following removal of ADH is mediated by retrieval of water permeable membrane via coated pits.

Preparation of neoglycoprotein-enzyme conjugate using a heterobifunctional reagent and its use in solid-phase assays and histochemistry

A conjugate of a neoglycoprotein (chemically lactosylated bovine serum albumin) and an enzyme (horseradish peroxidase) has been prepared in solution using a heterobifunctional reagent, N-succinimidyl-3-(2-pyridyldithio)propionate, and has been purified by gel filtration on an Ultrogel AcA-44 column. To preclude any carbohydrate-dependent binding to the sugar residues on the glycoprotein peroxidase, the enzyme has to be treated with sodium periodate and sodium cyanoborohydride prior to coupling, which results in oxidative cleavage of the carbohydrates and reduction of the aldehydes thus formed to primary alcohols. Lactosylated bovine serum albumin-peroxidase conjugate has been employed to detect plastic-bound Ricinus communis agglutinin with dependence of the concentration of the lectin and with dependence of the presence of specific inhibitors. Enzyme-labeled conjugates with unmodified bovine serum albumin are completely ineffective in this assay. Localization of beta-galactoside-specific sugar receptors in connective tissue is used to demonstrate the feasibility of application of such neoglycoprotein-enzyme conjugates in histochemistry with a minimum number of steps.

Enzyme binding to detect carbohydrate expression in tissue sections. 1. Native and cross-linked glucose oxidase

Enzymes may be useful as highly specific histochemical probes to identify and localize macromolecular substrates in tissue sections. We have used glucose oxidase, a double-headed enzyme, to demonstrate beta-glucosyl groups in paraffin sections. Native glucose oxidase has two active sites per molecule. Soluble polymers formed by glutaraldehyde combine many active binding sites on to one molecule. Some of these bind to glucose in tissue sections, leaving others free to react with chromogenic substrate. The intensity of staining is directly related to the concentration of enzyme, duration of incubation with enzyme, temperature and pH. Polymeric forms of enzyme are about 100 times more effective than native. Glucose oxidase, particularly in a polymeric form, appears a simple reagent for the identification of glucose-containing structures. The use of native and polymerized enzymes as a histochemical probe has enormous potential in the analysis of normal tissues and in the detection of aberrant carbohydrate deposition in pathological tissues; this system serves as a useful model.

Rat liver endothelial cells have a greater capacity than Kupffer cells to endocytose N-acetylglucosamine- and mannose-terminated glycoproteins

The capacity of rat liver Kupffer and endothelial cells to endocytose glycoproteins with N-acetylglucosamine- or mannose-terminated oligosaccharide chains was studied. For this purpose, agalactoorosomucoid, ahexosaminoorosomucoid and horseradish peroxidase were used as ligands. A reliable determination of the amount of ligand endocytosed in vivo or in vitro was made possible by using the recently developed cold pronase method for the isolation and purification of Kupffer and endothelial cells. Both cell types participated in the uptake of the ligands in vivo as well as in vitro, but their endocytic capacity was several times greater in vivo than in vitro. Under both conditions, endothelial cells possessed a greater capacity to endocytose the ligands than did Kupffer cells. Since the total number of endothelial cells in the liver is at least twice the number of Kupffer cells, the contribution of endothelial cells to the liver uptake of N-acetylglucosamine-terminated glycoproteins in vivo was estimated to be 3 to 7 times higher than that of the Kupffer cells. In vitro experiments showed that the uptake of the glycoproteins followed saturation kinetics and was strongly inhibited at 4 degrees C and in the presence of mannan. Ultrastructural investigations revealed that horseradish peroxidase was taken up by all Kupffer and endothelial cells. These results emphasize the important role liver endothelial cells play in the clearance of specific glycoproteins from the circulation.

Mannose-specific binding sites in synoviocytes of rat synovial membrane: an ultrastructural-cytochemical study

Mannose-specific binding sites in the two types of synoviocytes (A and S) from the synovial membrane of normal rat knee joints were studied by an ultrastructural-cytochemical method using horseradish peroxidase (HRP) as a ligand. The A cells showed mannose-specific binding sites for HRP which were localized in coated pits and coated vesicles (110 nm) as well as in smooth-walled vesicles, vacuoles, and tubules. No mannose-specific binding sites for HRP were detected in the S cells. Together with previous observations on absorption of intraarticularly injected HRP in type A and type S synoviocytes, the present results strongly support the interpretation that the A cells internalize HRP by receptor-mediated endocytosis and that the S cells internalize HRP by fluid-phase endocytosis only. The present results agree with the suggestion that mannose-specific binding sites consist of two pools, the one concerned with internalization of ligand and the other with intracellular targeting of internalized ligand.

Unusual binding sites for horseradish peroxidase on the surface of cultured and isolated mammalian cells. Suppression of binding by certain nucleotides and glycoproteins, and a role for calcium

Binding sites for horseradish peroxidase (HRP), with unusual properties, were detected on the surface of cultured and isolated cells after the cells (on cover slips) had been quickly dried, fixed in cold methanol, and post-fixed in a paraformaldehyde solution. The reaction for surface-bound HRP was suppressed by micromolar concentrations of glycoproteins such as invertase, equine luteinizing hormone (eLH) or human chorionic gonadotropin (hCG). The reaction was also suppressed by 20 mM CDP, UDP, GTP, NAD, and ribose 5-phosphate. Two to six times higher concentrations of GMP, fructose 1-phosphate, galactose 6-phosphate, mannose 6-phosphate, fructose 6-phosphate, and glucose 6-phosphate were required to suppress the binding reaction. AMP, ATP, heparin, mannan, and eight non-phosphorylated sugars showed relatively low competing potencies but fucoidin and alpha-lactalbumin were strong inhibitors. No addition of Ca2+ was required for the binding of HRP to the cell surface. However, calcium-depleted, inactive HRP did not compete with the binding of native (calcium-containing) HRP whereas H2O2-inactivated HRP suppressed the binding. GTP, NAD, ribose 5-phosphate, and EGTA accelerated the release of previously-bound HRP from the cell surface whereas glycoproteins (invertase, eLH, and hCG) did not do so. Addition of Ca2+ to GTP, NAD, ribose 5-phosphate or to EGTA prevented the accelerated release of HRP from the cell surface. It is suggested that calcium, present either in the surface membrane or in HRP itself, is involved in the binding of HRP to the cell surface and in the inhibition of binding by GTP, NAD, and ribose 5-phosphate. It is also suggested that alpha-lactalbumin, GTP, UDP, and CDP compete with the binding of HRP to a glycosyltransferase on the cell surface.

Receptor-mediated uptake of horseradish peroxidase in innervated and denervated skeletal muscle

The in vitro uptake of [3H]inulin and horseradish peroxidase (HRP) has been studied in innervated and 6 days denervated extensor digitorum longus muscle of the mouse. Both markers were taken up at a higher rate in denervated muscle. The increase in uptake after denervation was, however, larger for HRP than for [3H]inulin. After 2 h incubation at 37 degrees C, pH 7.3, in the presence of equimolar concentrations of HRP and [3H]inulin (approx. 2.1 microM), the uptake of HRP was approx. 8 times as great as the uptake of [3H]inulin in the same innervated muscles. In denervated muscle the HRP uptake was approx. 19 times as great as the [3H]inulin uptake in the same muscles. Various possible explanations of these differences in uptake have been considered and tested experimentally. [3H]Inulin uptake in skeletal muscle has previously been shown to obey bulk kinetics. The present investigation shows the HRP uptake to obey saturation kinetics. The HRP uptake shows dependency on divalent cations and is reduced if incubation is carried out at pH 6.4. The uptake of HRP, when used at a low, non-saturating concentration (10 micrograms/ml approx. 0.25 microM), is inhibited greater than or equal to 60% by yeast mannan (0.1 mg/ml), ribonuclease B (0.1 mg/ml, approx. 7.4 microM), mannose (30 mM), monodansylcadaverine (1 mM), chloroquine (100 microM), trifluoperazine (25 microM) or maleic acid (2 mM). It is concluded that HRP is taken up in innervated and denervated skeletal muscle by a process of receptor-mediated endocytosis and that this uptake is under neurotrophic control.

Competition between glycoprotein hormones and horseradish peroxidase for mannose-specific binding sites in cells of endocrine organs

Mannose-specific binding sites for horseradish peroxidase (HRP) were studied in paraformaldehyde-fixed, frozen sections of endocrine organs by a cytochemical method reported previously. In the testis, HRP was bound to interstitial cells, probably macrophages, and to sites extending along the surface of spermatozoa in the seminiferous tubules. In the epididymis, cells in the connective tissue, probably fibroblasts or macrophages, showed the specific reaction. In the ovaries, the reaction for lectin-bound HRP was observed in connective tissue cells of the theca externa, and in the mucosa of the uterus, binding of HRP occurred to many fibroblasts. The glycoprotein was also bound to cells in the connective tissue of the thyroid, probably mast cells, as well as to endothelial cells in the adrenal medulla and cortex. In all cases, the binding reaction required Ca2+ and was suppressed by mannose or mannan. Partially purified and highly purified preparations of glycoprotein hormones [ovine follicle-stimulating hormone, ovine luteinizing hormone, bovine thyroid-stimulating hormone, and human chorionic gonadotropin] as well as bovine thyroglobulin and yeast invertase competed with the binding of HRP to all the cells mentioned thus showing that the hormones were bound to the same sites as HRP. When 1 microM HRP was present in the incubation medium, the addition of 15-25 microM of highly purified hormones almost suppressed the reaction for lectin-bound HRP and competitive effects could be observed at even lower concentrations of the hormones.

Horseradish peroxidase: a tool for study of the neuroendocrine cell and other peptide-secreting cells

The versatility of horseradish peroxidase is its usefulness both as an antigenic marker and as a probe molecule. We have demonstrated in the neuroendocrine cell that an HRP-bound antibody offers a high order of resolution for determining in which cellular compartment an antigen is located and where it is not. When native peroxidase is applied as an intracellular probe, it labels organelles associated with endocytosis in retrograde axonal transport and with the lysosomal system in both retrograde and orthograde axonal transport. The investigation that remains is the application of lectin-bound HRP to determine the pathways of membrane flow at the time when the neuroendocrine cell is stimulated to synthesize, transport, and secrete its peptide. For example, we are interested to know (1) whether internalized axon terminal membrane tagged with wheat germ agglutinin-HRP is channeled to all Golgi saccules engaged in the production of secretory granules in salt stimulated supraoptic neurons; and (2) if internalized cell membrane of the supraoptic cell body is tagged with wheat germ agglutinin-HRP and channeled to GERL, will this membrane be transferred from GERL to secretory granules, lysosomes in the cell body and axon, the axonal endoplasmic reticulum, and to autophagic/crinophagic vacuoles in axon terminals of salt-stressed supraoptic neurons? These additional studies should provide a more comprehensive, morphological picture of membrane flow in a neuroendocrine cell that is responding to the metabolic demands placed upon it.

Cytochemical observations on mannose-specific binding sites for horseradish peroxidase in liver sinusoidal cells

Paraformaldehyde-fixed, frozen sections of the liver of rats were processed for the detection of mannose-specific binding sites of horseradish peroxidase (HRP) by a method reported previously, with some modifications resulting in a more intense binding reaction. Before staining for peroxidase activity, the sections were held in buffered solutions of physiological saline at different temperatures and pH's, and in the presence or absence of added Ca2+, mannose or galactose. The gradual decrease and final disappearance of the binding reaction were observed. The release of HRP from the binding sites as determined by the disappearance of the cytochemical reaction was 50-100 times faster at 22 degrees C than at 4 degrees C and was 5-10 times faster at 37 degrees C than at 22 degrees C. The release was approximately twice as fast at pH 7.0 than at pH 9.0 and 20-30 times faster at pH 6.0 than at pH 7.0. The release of HRP was 10-15 times faster in the absence of 1 mM Ca2+ in the buffer solution and was approximately 100 times faster in the presence of 0.1 M D-mannose as compared to 0.1 M D-galactose. Pretreatment of the sections with trypsin abolished the binding reaction whereas neuraminidase, phospholipases A2 and C, and chondroitinase ABC were without effect. An acidic isoenzyme of HRP, Sigma type VIII, was bound more intensely and more widely to liver sinusoidal cells than another acidic isoenzyme, Sigma type VII, a basic isoenzyme, Sigma type IX, and the routinely used preparation, Sigma type VI. The effect of the temperature on the binding reaction was re-examined with an improved procedure. In contradistinction to the previous finding, strong binding of HRP after 2-4 h incubation at 4 degrees C was observed.