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PubMed1986

Characterization of mucus glycoconjugates in normal human conjunctiva by lectins in light microscopy, transmission and scanning electron microscopy.

Maintenance of tear film in normal conditions is dependent on mucus layer integrity and the presence and distribution of conjunctival epithelial cell microvilli. In the present work a new methodology has been developed to gain correlative information about microprojection assessment and mucus composition, from the same specimen, by Light Microscopy (LM), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). We have characterized the glycosidic residues secreted by goblet cells in normal human conjunctiva, by means of four lectins (WGA, ConA, PNA and SBA), conjugated with FITC for LM and with colloidal gold for TEM and SEM. The cytochemical reactions were performed on histological sections of paraffin-embedded material and on semithin and ultrathin sections of both Epon embedded material directly processed for TEM and of blocks recovered from SEM and reprocessed for TEM. WGA, ConA, PNA and SBA receptors were found to be constituents of the mucus produced by goblet cells in human conjunctiva. The granules of the so-called "second mucus system" (SMS) cells were labelled mainly by WGA. A difference in the quality of glycoconjugates between goblet cells and SMS cells has been also demonstrated. Our results provide an improved method to evaluate alterations of tear film that occur in many conjunctival diseases.

Carbohydrates↗

PubMed1988

The fucose-sulfate glycoconjugate that induces an acrosome reaction in spermatozoa stimulates inositol 1,4,5-trisphosphate accumulation.

The hydrolysis of phosphatidylinositol may generate multiple second messengers, including inositol phosphates, 1,2-diacylglycerol, arachidonic acid, and phosphatidic acid. Here, we describe for the first time in spermatozoa that accumulation of one of these potential second messengers, inositol 1,4,5-trisphosphate (1,4,5-IP3), can be stimulated by the fucose-sulfate glycoconjugate (FSG) that induces an acrosome reaction. Sea urchin spermatozoa were labeled with myo-[3H]inositol and incubated with FSG. The amount of [3H]1,4,5-IP3 obtained from FSG-treated cells was up to 10 times that from untreated cells. Increases in the amount of [3H]1,4,5-IP3 were detected within 30 s after addition of FSG (2.5-fold) and were highest at 2 min after addition. Previously, it was shown that FSG induces Ca2+-dependent increases in cyclic AMP concentrations (Kopf, G. S., and Garbers, D. L. (1980) Biol. Reprod. 22, 1118-1126). Increases in [3H]1,4,5-IP3 accumulation caused by FSG were also dependent on extracellular Ca2+. The Ca2+ channel blockers, verapamil and nifedipine, inhibited increases in both [3H]1,4,5-IP3 and cyclic AMP, and the addition of concentrations of extracellular Ca2+ higher than 9.6 mM could reduce the inhibition. When spermatozoa were incubated in Ca2+-free seawater, FSG-induced increases in [3H]1,4,5-IP3 and cyclic AMP concentrations were blocked; addition of extracellular Ca2+ restored the responses. Other treatments that result in the induction of an acrosome reaction, including the addition of monovalent cation H+ exchangers, nigericin and gramicidin S, and incubation in seawater at alkaline pH (pH 8.8), also stimulated accumulation of [3H]1,4,5-IP3 and cyclic AMP.

Acrosome↗

PubMed1989

Expression of a binding structure for sialic acid-containing glycoconjugates on rat bone marrow-derived macrophages and its modulation by IFN, TNF-alpha, and dexamethasone.

Rat macrophages express a binding structure for sialic acid-containing glycoconjugates (sialic acid-binding receptor, SAR) which can be detected by a rosette assay utilizing SRBC coated with bovine brain gangliosides (E-G). Freshly isolated rat bone marrow cells (BMC) contain about 5% SAR-positive cells. Rat BMC cultured for 1 wk with tissue culture media containing CSF-1 differentiate into a virtually pure population of bone marrow-derived macrophages (BMDM phi). All BMDM phi bound E-G coated with an optimal concentration of gangliosides (100 micrograms/ml). When BMC were cultured for 1 wk with murine recombinant granulocyte-macrophage CSF, irrespective of the dose of GM-CSF, approximately 90% of the cells were identified as rat macrophages, and practically all expressed SAR. Only about 50% of BMDM phi bound SRBC coated with a suboptimal concentration of gangliosides (20 micrograms/ml). However, this percentage increased markedly after 8 to 72 h incubation with 1 to 10,000 U/ml purified murine IFN-alpha or IFN-beta, whereas murine or rat rIFN-gamma at doses above 10 U/ml led to a decrease of E-G binding. Human and murine rTNF-alpha enhanced rosette formation in a dose-dependent manner. These effects could be blocked by the respective anti-cytokine antibodies. Treatment of BMDM phi with dexamethasone also augmented E-G rosetting. The enhancement of E-G binding was abolished by pretreatment of BMDM phi with cycloheximide and actinomycin D but not with mitomycin C, suggesting that de novo synthesis of protein and RNA, but not DNA, is required. Our results demonstrate that all rat BMDM phi constitutively bear SAR, and that murine IFN-alpha, IFN-beta, and TNF-alpha, as well as dexamethasone, may augment SAR expression.

Adjuvants, Immunologic↗

PubMed1987

Monoclonal antibodies and synthetic tumor-associated glycoconjugates in the study of the expression of Thomsen-Friedenreich-like and Tn-like antigens on human cancers.

Synthetic carbohydrate haptens, which are conjugated to carrier human serum albumin molecules [synthetic tumor-associated glycoconjugates (S-TAGs)], were used to immunize mice for monoclonal antibody (MoAb) production. Two of the S-TAGs were composed of haptens related to the Thomsen-Friedenreich (TF) antigen, and their structures are beta Gal(1----3)-beta GalNAc (TF-beta) and beta Gal(1----3) alpha GalNAc (TF-alpha) (Gal = galactose; GaNAc = N-acetylgalactosamine). The third S-TAG was made up of Tn hapten groups of the structure alpha GalNAc-O-serine. MoAbs specific for TF-alpha and Tn were able to be generated. All MoAbs generated against TF-beta cross-reacted with TF-alpha but not with Tn. None of the TF-alpha-specific MoAbs reacted with human carcinomas, whereas several TF-beta and Tn MoAbs were found to react with most human lung, colon, and breast carcinomas. It is believed that this is the first report of the use of synthetic carbohydrate cancer antigens for the production of anticancer MoAbs.

Antibodies, Monoclonal↗

PubMed1987

Isolation and characterization of chicken liver and hepatoma Mc-29 endoplasmic reticulum and Golgi apparatus membranes and biosynthesis of their glycoconjugates.

Rough and smooth endoplasmic reticulum (ER) membranes and trans-Golgi apparatus (GA) fraction, intermediate GA fraction, and cis-GA fraction from White Leghorn chicken liver and hepatoma Mc-29 were isolated. Their purity was checked by electron microscopy and by determination of the activity of the marker enzymes. Rough and smooth membranes were also identified by calculation of the ratio between the content of RNA and the total phospholipids. It was found that the membrane fractions were pure enough. The tumor exhibited a decreased amount of ER and a small GA when compared when the ER and GA in the liver. The biogenesis of membrane glycoconjugates was followed by in vivo experiments either with [14C]glucosamine or by double labeling with [14C]N-acetylmannosamine and [3H]leucine. The radioisotope studies indicated that the synthesis rate of protein in liver and hepatoma rough ER was nearly the same, but in the tumor cells the glycosylation of the nascent polypeptide chain and the formation of glycolipids were significantly decreased.

Animals↗

PubMedDate not supplied

Enhanced sialylation of the K 562 cell surface membrane glycoconjugates induced by adriamycin.

The antitumor agent Adriamycin (ADM) increases the sialic acid content of K 562 cell plasma membrane glycoconjugates. Total and neuraminidase-sensitive sialic acid are enhanced 3 to 4 times when expressed per 10(6) cells. This fact is a consequence of an increase in cell surface and in plasma membrane sialic acid density. Protein-bound and lipid-bound sialic acid are increased in the same way and exhibit the same ratio 90/10. After external radiolabelling by periodide-borotritide and neuraminidase-galactose oxidase-borotritide treatment, only some quantitative changes can be observed. Fractionation of gangliosides by thin layer chromatography gives the same results. Further experiments lead to the following conclusions: the hypersialylation cannot be explained by a G2-block in the cell cycle induced by ADM; it is not a consequence of a differentiation process; it is not observed in a population of adriamycin-resistant K 562 cells and can therefore be considered as a metabolic event linked to the cytotoxic activity of ADM.

Cell Cycle↗

PubMed1987

Light and electron microscopic localization of glycoconjugates with gold-labeled reagents.

This paper gives an overview of the use of lectins, glycoproteins, monoclonal anti-carbohydrate antibodies, toxins, and glycosyl-transferases for the detection and localization of cellular glycoconjugates in sections from embedded tissues by light and electron microscopy. In all these techniques particles of colloidal gold were used as a marker. For light microscopic studies routine conditions of embedding such as paraffin or Epon embedding could be employed. For electron microscopic studies the low temperature embedding technique using Lowicryl K4M was found to be the method of choice for the localization of sugar residues in intracellular compartments, the extracellular matrix and the plasma membrane. The applications of the various techniques will be illustrated with data about subcellular sites of certain glycosylation steps as well as the detection of glycocalyx domain formation and cellular heterogeneity in glycoclayx composition.

Animals↗

PubMed1987

Altered glycoconjugates in cultures of retinitis pigmentosa retinal pigment epithelium.

These studies have shown that these are some alterations in the complex carbohydrates associated with the cell surface of RPE cells from donors with dominant retinitis pigmentosa. Differences are found both in proteoglycans and in glycoproteins. Proteoglycans of different sizes and glycosaminoglycan composition are associated with distinct cellular compartments of normal RPE cells. In the case of dominant retinitis pigmentosa studied here, there are some alterations in RPE proteoglycans. Within a given cellular compartment, there may be differences in the size distribution and/or the ratios of the proteoglycan size classes. In addition, there may be altered glycosaminoglycan content found between peaks of comparable size. There also appears to be more microheterogenity in oligosaccharides derived from surface glycoproteins of retinitis pigmentosa RPE cells. This may be due to differences in the total number of carbohydrate units or in the organization of the branching structure as suggested by altered size distribution and lectin-reactivity, respectively. While the reason for these differences is not clear, they could be due to abnormal processing and/or increased degradation. Considering their importance, alterations in cell surface glycoconjugates could affect the ability of RPE cells to interact with their environment and to maintain a healthy status.

Adult↗

PubMed1985

Preliminary researches on the characterization of the glycoconjugates in the oviduct of Rana esculenta complex during its reproductive cycle.

Biochemical investigations were carried out on the oviduct of Rana esculenta. It was demonstrated that in the oviduct of Rana esculenta there is a heteropolysaccharide formed by sulphated acid glycoconjugates and neutral glycoproteins. The presence and the functional role of glucidic components are discussed and compared to previous histochemical data.

Animals↗

PubMed1985

Regional specificity of glycoconjugates in Xenopus and axolotl embryos.

This paper reviews work on the presence, synthesis and developmental regulation of glycoconjugates (proteoglycans, glycoproteins and glycolipids) in the early amphibian embryo. In the axolotl there is little regional specificity of protein synthesis until the tailbud stage, but substantial regional specificity of glycoprotein synthesis from the end of gastrulation. Glycolipid synthesis is more uniform although a number of unique species are made in the epidermis. Isolated explants from axolotl early gastrulae show three types of behaviour in terms of glycoprotein synthesis, corresponding to the classical germ layers. Xenopus embryos at this stage show a higher degree of mosaicism. Changes of glycoprotein synthesis in response to mesodermal or neural induction follow the predicted course depending on the regional character of the induced tissue. The regional binding patterns of a number of lectins and monoclonal antibodies specific for particular carbohydrate determinants are presented and their significance discussed.

Ambystoma↗

PubMed1985

Development of specific surface receptors recognizing mannose-terminal glycoconjugates in cultured monocytes: a possible early marker for differentiation of monocyte into macrophage.

Surface receptors for mannose-terminal glycoconjugates have been reported in various macrophage populations and are thought to be involved in specific binding and internalization of mannose-rich substances. They thereby may serve a function in such phenomena as phagocytosis of yeast and tumor cell recognition. Little is known of mannosyl receptors in blood monocytes. We synthesized a probe by covalently linking D-mannose to bovine serum albumin (BSA). Using this probe in fluoresceinated or latex minibead-derivatized forms, we searched the surface of human monocytes for the presence of mannosyl receptors. 125I-labeled probe was further used to quantify the number of receptors and the kinetics of the binding. Freshly isolated monocytes did not bind the probe, indicating the absence of mannosyl receptors. When placed in a culture system that preserves functional and morphological homogeneity of the cells, surface receptors for D-mannosyl glycoproteins developed within four days, reached a peak after one week, and then remained fairly stable. Binding parameters (Kd, Bmax, and receptor number) also remained stable and were not dissimilar to those reported for macrophages, although the Kd was consistently larger in cultured monocytes. When studied at 37 degrees C, the ligand-receptor complex was internalized through a system of coated pits and vesicles. The development of these receptors before evidence of morphological or functional differentiation suggests that these receptors may constitute an early marker for differentiation of monocytes into macrophages.

Cell Differentiation↗

PubMed1982

Glycoconjugate with Ulex europaeus agglutinin-I-binding sites in normal mucosa, adenoma, and carcinoma of the human large bowel.

Cancerous lesions and nonneoplastic mucosa of surgically extirpated specimens from 94 patients with colorectal carcinoma (of the right colon, 31 patients; of the left colon, 29 patients; and of the rectum, 34 patients) and endoscopically polypectomized specimens from 18 patients with rectal adenoma were examined with fluorescein isothiocyanate-conjugated or horse-radish peroxidase-conjugated Ulex europaeus agglutinin-I (UEA-I) specific to a certain terminal alpha-L-fucosyl residue in glycoconjugates. Of the 31 patients with right colon cancers, 22 showed positive UEA-I binding in the neoplastic cell apexes, apical luminal borders, and luminal secretions. The adjacent nonneoplastic mucosa of all 31 patients, however, demonstrated positive UEA-I binding in the goblet cell mucus. UEA-I binding was positive for 23 of the 29 left colon cancers and for 28 of the 34 rectal cancers, although UEA-I binding was not revealed in the adjacent nonneoplastic mucosa for most of the cases. Of the 18 rectal adenomas, 12 specimens showed positive UEA-I binding in the apical secretions of their adenoma cells. Marked regional differences of UEA-I binding in the nonneoplastic mucosae indicated that the constituents of glycoprotein with UEA-I binding sites in goblet cell mucus differed significantly between the human right and left large bowels. Positive UEA-I binding in many rectal cancerous and adenomatous lesions suggested that a neoplastic glycoprotein with alpha-L-fucosyl residue was produced or that the terminal carbohydrate structure of glycoprotein present in the nonneoplastic mucosa was altered to bind easily with UEA-I after the neoplastic transformation had occurred. A possible relation of this UEA-I binding to blood group H(O) substance is discussed.

Adenoma↗

PubMed1983

Distribution of glycoconjugates in the kidney studied by use of labeled lectins.

Distribution of glycoconjugates in different areas of the rat kidney was studied by light and electron microscopy using six different horseradish peroxidase-labeled lectins. Glomeruli and brush borders of the proximal tubules reacted differently to these lectins, which indicated differences in the carbohydrate compositions of those regions. The ascending limb of Henle's loop (ALH) had strong binding sites for peanut agglutinin (PNA) and soybean agglutinin (SBA). Dolichos biflorus agglutinin (DBA) did not stain the cells of ALH but did stain those of distal convoluted tubules (DCT). DBA is a good marker for distinguishing ALH from DCT. DBA, PNA, and SBA were also good markers of the collecting duct. Ricinus communis agglutinin (RCA-1) and wheat germ agglutinin (WGA) diffusely stained the various components of different parts of the kidney.

Animals↗

PubMed1983

Characterization of tumor-associated ganglio-N-triaosylceramide in mouse lymphoma and the dependency of its exposure and antigenicity on the sialosyl residues of a second glycoconjugate.

Ganglio-N-triaosylceramide (GalNAc beta 1 leads to 4Gal beta 1 leads to 4Glc beta 1 leads to 1Cer), a tumor-associated marker for L5178 cells, was previously reported to separate on thin layer chromatography into three distinct bands (bands a, b, and c). The present paper describes the characterization of these bands and the factor that determines the degree of glycolipid exposure at the cell surface and its antigenicity. 1) The resolution of ganglio-N-triaosylceramide into three bands was found to be due to molecules having different fatty acid compositions. Band a contained nervonic (C24:1) and lignoceric (C24:0) acids, band b contained palmitic acid (C16:0), and band c contained alpha-hydroxypalmitic acid. 2) Surface labeling of L5178c127 cells with galactose oxidase/sodium borotritide, followed by fluorography of the isolated glycolipids, revealed that all three bands were exposed on the surface of the cell. However, treatment of cells with sialidase before treatment with galactose oxidase resulted in a 10-fold increase of label incorporated into ganglio-N-triaosylceramide. Since no sialylated form of ganglio-N-triaosylceramide was detected on these cells, and no change in the chemical amount of this glycolipid could be detected, the increase of label into this molecule was due to the exposure by sialidase of a normally cryptic glycolipid. The exposure of ganglio-N-triaosylceramide after sialidase treatment was also reflected by the increased sensitivity of these cells to monoclonal antibodies to the glycolipid and complement after enzyme treatment. Thus, the results provide clear evidence that crypticity, as well as antigenicity, of a membrane glycolipid is determined by the degree of sialylation in a second membrane glycoconjugate.

Animals↗

PubMed1984

In situ distribution in different cell types of nuclear glycoconjugates detected by two lectins.

Nuclear glycoconjugates were detected in situ by two lectins--Concanavalin A and Wheat germ agglutinin--on tissue sections embedded in the hydrophilic resin glycol methacrylate. These lectins were conjugated with fluorescein isothiocyanate for fluorescence microscopy, and labelled with ferritin for electron microscopy. The ovarian follicle of the lizard Lacerta vivipara was chosen for this study, because it enables four types of nuclei, with different ultrastructures and physiology to be observed on the same section. In this material, all the nucleoli were found to contain a high concentration of receptors for both lectins. The distribution of the receptors located in the chromatin and nucleoli was observed to vary within the same type of nucleus, depending on the lectin used. Some of our results suggest that increased labelling by Wheat germ agglutinin might depend on increased production of ribosomal precursors.

Animals↗

PubMed1984

[Glycoconjugate cell surfaces as markers of differentiation and malignancy].

The composition of cell membrane-associated glycoproteins and glycolipids is changed during differentiation. Moreover, normal mature cells differ from transformed ones in regard to their glycoconjugate profile. These differences have been analyzed, by means of lectins, concerning intrathymic lymphocytes, T-lymphoma cell lines as well as epithelial carcinomas and tumor cell lines. It was found that lectins recognize molecular structures of the cell membrane which are characteristic of certain developmental stages of intrathymic T-lymphocyte differentiation and, moreover, "tumor"-associated determinants on T-lymphomas as well as on epithelial carcinoma cells.

Animals↗

PubMed1983

Decrease in human lymphocyte surface glycoconjugates in leukemia as demonstrated by lectin binding.

Qualitative variations in the glycoconjugates which make up the lectin receptor sites on the membranes of leukemic lymphocytes, compared with those of normal cells, have been studied by the use of three tritiated lectins: Robinia pseudoacacia lectin, Concanavalin A and Ricinus communis (var. Sanquineus) agglutinin (RCA 120). The binding specificity of these lectins has been demonstrated using specific determinants: alpha-methylmannoside and galactose for Concanavalin A and Ricinus communis agglutinin respectively. For the Robinia lectin this specificity was determined by saturation of the receptor sites with the unlabeled Robinia lectin before the addition of isotopically labeled Robinia lectin. The results show a decrease in the number of receptor sites on the leukemia cells, especially in chronic lymphoid leukemia, relative to that on normal cells. The apparent affinity constants of leukemic cells in all cases remain higher than those of normal cells.

Cell Membrane↗

PubMed1983

Membrane traffic in Dictyostelium discoideum: plasma membrane glycoconjugates internalized and recycled during fluid phase pinocytosis enter the Golgi complex.

Plasma membrane glycoconjugates, enzymatically labelled with [3H]galactose, were used as an autoradiographic membrane marker for a morphometric analysis of membrane traffic during fluid phase pinocytosis in the amoeba, Dictyostelium discoideum. The fraction of grains associated with the plasma membrane decreased exponentially from 99% for cells fixed directly after labelling on the cell surface, to a steady-state value of 45% after about 1 h of pinocytotic activity. The complementary fraction of grains was observed on vacuolar membranes. Only after a lag of about 20 min, a small but significant fraction (3%) of the total grains, was found in the region of the Golgi membranes. During two subsequent doublings of cell number, over a period of 24 h, label was lost into the medium at a constant rate of 1% per h. The cell bound label remained fully membrane bound over the entire period. The beta(1-4) linkage was not noticeably modified, as judged by its susceptibility to hydrolytic release by beta-galactosidase. An analysis by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) showed an identical labelling pattern for total membrane fractions when prepared directly after labelling or after 24 h of membrane flow.

Biological Transport, Active↗