Cell surface carbohydrates and cell adhesion

Combining glycocluster synthesis with protein engineering: an approach to probe into the significance of linker length in a tandem-repeat-type lectin (galectin-4)

Complementarity in lectin-glycan interactions in situ is assumed to involve spatial features in both the lectin and the glycan, giving a functional meaning to structural aspects of the lectin beyond its carbohydrate-binding site. In combining protein engineering with glycocluster synthesis, it is shown that the natural linker length of a tandem-repeat-type human lectin (galectin-4) determines binding properties in two binding assays (using surface-presented glycoprotein and cell surface assays). The types of glycocluster tested included bivalent lactosides based on tertiary amides of terephthalic, isophthalic, 2,6-naphthalic and oxalic acids as well as bivalent H(type 2) trisaccharides grafted on secondary/tertiary terephthalamides and two triazole-linker-containing cores. The presented data reveal a marked change in susceptibility to the test compounds when turning the tandem-repeat-type to a proto-type-like display. The testing of glycoclusters is suggested as a general strategy to help to delineate the significance of distinct structural features of lectins beyond their contact sites to the glycan.

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.

Effects of monochromatic low-intensity light and laser irradiation on adhesion of HeLa cells in vitro

BACKGROUND AND OBJECTIVE

The adhesion of HeLa cells was evaluated after irradiation with monochromatic low-intensity light or laser irradiation. It is well known that the cell-cell and cell-matrix adhesion changes during wound repair. For better understanding of low-power laser light action on the wound healing process, it would be of interest to study the light action on cellular adhesion in vitro.

STUDY DESIGN/MATERIALS AND METHODS

The monochomatic light was in the range 580-860 nm (bandwidth 10 nm, 5-150 J/m2 1.3 W/m2) and the He-Ne laser irradiation was 632.8 nm (100 J/m2, 10 W/m2). Cell-cell and cell-glass adhesion were evaluated after irradiation of HeLa cells.

RESULTS

It was found that cell-cell and cell-glass adhesion increased following irradiation depending on the irradiation conditions (wavelength, dose) and the time elapsed after the irradiation. The cell attachment to glass surface increased after irradiation of samples of HeLa cells in suspension.

CONCLUSION

The adhesion was stimulated in the wavelength ranges 600-625, 645-700, and 720-850 nm with maxima at 620, 680, 750, and 820-830 nm, respectively.

Effect of tunicamycin, an inhibitor of protein glycosylation, on testicular cord organization in fetal mouse gonadal explants in vitro

The effect of tunicamycin (TM) on testicular cord organization in the fetal mouse was examined in vitro at light and electron microscopic levels, with special reference to the glycoprotein functions during Sertoli cell differentiation. In testicular explants treated with TM, testicular cord organization was inhibited. TM treatment affected basal lamina formation by Sertoli cells, resulting in a discontinuous basal lamina or none at all in certain areas. The disorganized Sertoli cells were amorphous in shape, exhibited poor epithelial polarity, and were irregularly arranged in the testicular parenchyma. Extracellular matrix and collagen fibers were often observed in the intercellular spaces between the disorganized Sertoli cells. Lectin histochemical observation revealed that the number of wheat germ agglutinin binding sites on the plasma membrane and basal lamina of disorganized Sertoli cells was significantly decreased by TM treatment. However, junctions were normally observed in the plasma membrane between disorganized Sertoli cells. Leydig cells showed a normal differentiation in the testicular parenchyma in the presence of TM. These observations suggest that basal lamina formation of Sertoli cells and/or the expression of their cell surface glycoconjugates may be crucial for the establishment of Sertoli cell polarity and/or the Sertoli-Sertoli cell interactions required for proper testicular cord formation. Sertoli cell organization into testicular cords and Leydig cell differentiation may be controlled by different regulatory mechanisms.

Lectin binding to injured corneal endothelium mimics patterns observed during development

Fluorochrome conjugated lectins were used to observe cell surface changes in the corneal endothelium during wound repair in the adult rat and during normal fetal development. Fluorescence microscopy of non-injured adult corneal endothelia incubated in wheat-germ agglutinin (WGA), Concanavalin A (Con A), and Ricinus communis agglutinin I (RCA), revealed that these lectins bound to cell surfaces. Conversely, binding was not observed for either Griffonia simplicifolia I (GS-I), soybean agglutinin (SBA) or Ulex europaeus agglutinin (UEA). Twenty-four hours after a circular freeze injury, endothelial cells surrounding the wound demonstrated decreased binding for WGA and Con A, whereas, RCA binding appeared reduced but centrally clustered on the apical cell surface. Furthermore, SBA now bound to endothelial cells adjacent to the wound area, but not to cells near the tissue periphery. Neither GS-I nor UEA exhibited any binding to injured tissue. By 48 h post-injury, the wound area repopulates and endothelial cells begin reestablishing the monolayer. These cells now exhibit increased binding for WGA, especially along regions of cell-to-cell contact, whereas, Con A, RCA and SBA binding patterns remain unchanged. Seventy-two hours after injury, the monolayer is well organized with WGA, Con A and RCA binding patterns becoming similar to those observed for non-injured tissue. However, at this time, SBA binding decreases dramatically. By 1 week post-injury, binding patterns for WGA, ConA and RCA closely resemble their non-injured counterparts while SBA continues to demonstrate low levels of binding. In early stages of its development, the endothelium actively proliferates and morphologically resembles adult tissue during wound repair.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of protein-linked glycoconjugates produced by identified neurons of Aplysia californica

The biosynthetic capabilities of individual neurons of the abdominal ganglion of the marine mollusc Aplysia californica have been analyzed after intrasomatic injection of 3H-monosaccharides. Glycopeptides prepared from the metabolically labeled cells were fractionated using serial lectin affinity and gel filtration chromatography. The fractionation procedure yielded eight populations of glycopeptides, and comparison of two different neurons (R2 and R14) showed that the quantity of the individual species produced is cell-dependent. Structural analysis indicated that the glycoconjugates produced by the Aplysia neuron constitute both O- and N-linked structures as well as an unusual class of oligosaccharide whose linkage to protein is unknown. The O-linked units are small and consist only of N-acetylglucosamine or N-acetylgalactosamine attached to protein. High-mannose-type asparagine-linked units are produced by the neurons, and some of these appear to be processed to biantennary complex-type units that bind to lentil lectin-agarose. Overall, although the Aplysia neurons produce oligosaccharides of a nature similar to that produced by higher eucaryotes, the N- and O-linked structures produced by the neurons do not achieve the complexity of the comparable structures produced by mammalian cells. The results provide a basis for further studies aimed at understanding the role of glycoconjugates in the development of the nervous system.

Identification of protein-bound oligosaccharides on the surface of growth cones that bind to muscle cells

In the accompanying paper (Gabel, Den, and Ambron, in press) it was shown that eight populations of glycopeptides are synthesized by single neurons of Aplysia californica. To see which glycopeptides might mediate interactions with target cells, we first identified glycopeptides that are transported selectively to synapses and growth cones. The giant neuron R2 was injected intrasomatically with 3H-glucosamine. Twenty-four hours later, 3H-glycopeptides in the axon and cell body were isolated and resolved by serial lectin affinity chromatography. Of the eight populations, the biantennary-type glycopeptides (GPbi) and those that bind to WGA (GPwga) were preferentially associated with rapidly transported glycoproteins. In contrast, the glycopeptide that consists of N-acetylglucosamine O-linked to ser/thr was mostly retained in the cell body. GPbi and GPwga were also preferentially transported to growth cones. Analyses of RUQ cells, exposed to 3H-glucosamine in vitro for 36 h showed an enrichment of GPbi and GPwga at the growth cone relative to the cell body. The disposition of the various glycopeptides in growing neurons was also examined using FITC lectins. FITC-coupled WGA, Vicia vellosa, and lentil lectin showed extensive staining of the cell body, but only WGA stained the growth cones. To investigate if GPwga interacts specifically with target cells, these glycopeptides were isolated from the neurons of 180 abdominal ganglia. GPwga, other Aplysia glycopeptides, and glycopeptides prepared from ovalbumin were coupled separately to fluorescent spheres. The spheres were then added to muscle cells isolated from the auricle of the heart, which is innervated by many neurons from the ganglion. While spheres coupled to GPwga bound to the muscle cell surface, the other glycopeptides did not. These results indicate that glycopeptides class GPwga, found among rapidly transported glycoproteins and on the growth cone surface, is able to bind to muscle cells and may therefore play some role in neuron-target interactions.

Human interferon-gamma increases adhesion of cultured carcinoma cells to the substratum

Effects of human recombinant-DNA derived interferon-gamma and -alpha 2 on the adhesion of cultured breast cancer cells (BT-20, ZR-75.1, MCF-7, 734-B and Hs-578-T), larynx carcinoma cells (HEP-2), epidermoid carcinoma cells (KB), lung carcinoma cells (CCL 185), and ovarian carcinoma cells (1847) to the surface of cell culture plastic dishes were studied. Layered cells were detached after a 3-day treatment with interferon either by trypsin-EDTA, trypsin, protease or cooling to 4 degrees C. Treatment with interferon-gamma (500 unit/ml) significantly increased the incubation time for trypsin-EDTA, EDTA and at 4 degrees C necessary to bring cells into suspension for the 4 cell lines BT-20, ZR-75.1, MCF-7 and HEP-2. Interferon-alpha 2 was not able to induce a similar effect. Reattachment of interferon-gamma treated ZR-75.1 cells was not increased after harvesting by trypsinization or EDTA action. Decreased adhesion of cultured cells is associated with transformation and the effects of interferon-gamma may be explained by reinforced normal phenotype. Interferon-gamma induced adhesion was not associated with other interferon effects especially the anti-proliferative activity or modulation of surface antigens.

Deglycosylation of a native, protease-sensitive glycoprotein by peptide N-glycosidase F without protease inhibitors

The glycoprotein fibrinogen was deglycosylated in its native state and in the absence of protease inhibitors by peptide N-glycosidase F following removal of protease contaminants from the enzyme by HPLC. Fibrinogen is sensitive both to proteolysis by contaminants which may constitute as little as 0.2% of the enzyme protein and to denaturation by 1,10-o-phenanthroline, the only substance known to inhibit the proteolysis. Thus removal of protease contaminants from the enzyme is a prerequisite for the deglycosylation of native fibrinogen. The starting material for the present method is the final material obtained from the purification described by A. L. Tarentino, C. M. Gomez, and T. H. Plummer (1985, Biochemistry 24, 4565). Three sequential passages over a PolyCAT A (20 X .46 cm) cation-exchange column and elutions with a linear gradient of NaCl from 0 to 0.4 M were necessary to completely overcome the tenacious but noncovalent association of peptide N-glycosidase F with contaminants that proteolyze fibrinogen. All three chromatographic runs could be completed in 1 day. Using this "protease-free" enzyme at up to a 1:20 molar ratio, fibrinogen that is completely deglycosylated and native has been generated in order to determine the role of the carbohydrate moieties in its function.

The biology and chemistry of fertilization

Fertilization of eggs by sperm, the means by which sexual reproduction takes place in nearly all multicellular organisms, is fundamental to the maintenance of life. In both mammals and nonmammals, the pathway that leads to fusion of an egg with a single sperm consists of many steps that occur in a compulsory order. These steps include species-specific cellular recognition, intracellular and intercellular membrane fusions, and enzyme-catalyzed modifications of cellular investments. In several instances, the molecular mechanisms that underlie these events during mammalian fertilization are beginning to be revealed.

Ricinus communis agglutinin-mediated agglutination and fusion of glycolipid-containing phospholipid vesicles: effect of carbohydrate head group size, calcium ions, and spermine

The glycolipids galactosylcerebroside (GalCer), lactosylceramide (LacCer), and trihexosylceramide (Gb3) were inserted into phospholipid vesicles, consisting of phosphatidylethanolamine and phosphatidic acid. The extent to which their carbohydrate head groups protruded beyond the vesicle surface and their interference with membrane approach were examined by determining vesicle susceptibility toward type I Ricinus communis agglutinin (RCA1) induced agglutination and Ca2+- and spermine-induced aggregation and fusion either in the presence or in the absence of the lectin. The initial agglutination rates increased in the order GalCer much less than LacCer less than Gb3, while a reversed order was obtained for Ca2+- and spermine-induced aggregation and fusion, indicating an enhanced steric interference on close approach of bilayers with increasing head group size. The lectin-mediated agglutination rates for LacCer- and Gb3-containing vesicles increased by an order of magnitude when Ca2+ was also included in the medium, at a concentration that did not induce aggregation per se. Charge neutralization could not account for this observation as the polyvalent cation spermine did not display this synergistic effect with RCA1. Addition of Ca2+ to preagglutinated vesicles substantially reduced the threshold cation concentration for fusion (micromolar vs. millimolar). Quantitatively, this concentration decreased with decreasing carbohydrate head group size, indicating that the head group protrusion determined the interbilayer distance within the vesicle aggregate. The distinct behavior of Ca2+ vs. spermine on RCA1-induced agglutination on the one hand and fusion on the other indicated that Ca2+ regulates the steric orientation of the carbohydrate head group, which appears to be related to its ability to dehydrate the bilayer. As a result, lectin agglutinability becomes enhanced while fusion will be interrupted as the interbilayer distance increases, the threshold head group size being three carbohydrate residues (Gb3). Finally, GalCer-containing vesicles were not agglutinated by RCA1 at ambient temperature, irrespective of the presence of Ca2+. Above 25 degrees C, RCA1 facilitated Ca2+-induced fusion of the vesicles, which was abolished by the haptenic sugar lactose. Since Gb3- and LacCer-containing vesicles displayed a similar behavior, a temperature-induced alteration in the supporting lipid matrix is suggested, which apparently affects lectin/glycolipid interaction.

Virosome-mediated implantation of red cell band 3 into the plasma membrane of cultured hepatoma cells

A method for implanting exogenous membrane proteins into recipient hepatoma cells is described. Red cell band 3 and Sendai virus envelope proteins HN and F were extracted from their respective sources and purified by centrifugation to equilibrium through sucrose step gradients in the presence of octyl-beta-D-glucopyranoside. 0.05-0.15 micron vesicles were formed by adding lipid to combined detergent solubilized, isolated membrane proteins and removing detergent by dialysis. The vesicles were hybrid band 3-Sendai envelope vesicles and not a mixture of two distinct vesicle types as judged by (1) the ability of Sendai specific antibody to immunoprecipitate greater than 99% of band 3 from vesicle suspensions and (2) comigration of band 3 and Sendai envelope proteins on isopyknic sucrose density gradients. The hybrid vesicles (virosomes) were not fusogenic but did bind to cultured hepatoma cells in the cold. Subsequent treatment of virosomes absorbed onto cultured cells with polyethylene glycol resulted in a stable association of 2-10% of added band 3 and Sendai envelope proteins with the cells. Efficient transfer of virosome-associated band 3 to the cells was dependent on both lipid and Sendai envelope proteins. Fluid phase marker transfer, immunofluorescence, and protease digestion experiments demonstrate that the majority of the virosomes were implanted into recipient hepatoma membranes and not simply adsorbed onto their surface or immediately endocytosed. The hybrid membrane protein-viral envelope vesicles thus offer an efficient means for insertion of foreign proteins into the membranes of recipient cultured cells.

Nonimmune lymphocyte-macrophage interaction. II. Evidence that the interaction involves sulfated polysaccharide recognition

This paper describes attempts to determine the molecular basis of the nonimmune interaction between lymphocytes and macrophages. Initial studies revealed that the interaction could be inhibited by simple sugars, six out of the thirty-five tested being inhibitory. Furthermore, the majority of the inhibitory sugars were charged and subsequent studies revealed that some sulfated polysaccharides, notably kappa-carrageenan, were potent inhibitors of the interaction. Further experiments revealed that the lymphocyte-macrophage interaction was indeed mediated by kappa-carrageenan-specific receptors on lymphocytes. The results supporting such a conclusion were as follows: When the interacting cells were preincubated with kappa-carrageenan, it was found that kappa-carrageenan exerted its inhibitory effect at the lymphocyte rather than the macrophage level. Separation of splenocytes into kappa-carrageenan-binding and -nonbinding subpopulations resulted in a corresponding enrichment and depletion of lymphocytes that reacted with macrophages. Lymphocytes were found to express kappa-carrageenan-reactive molecules, these molecules being detected on the surface of lymphocytes by rosetting and in detergent lysates as hemagglutinins. Furthermore, the polyanion specificity of these kappa-carrageenan-specific receptors/hemagglutinins closely resembled the specificity of inhibition of the lymphocyte-macrophage interaction. Pronase-resistant material in macrophage, but not lymphocyte lysates, effectively inhibited both the lymphocyte-macrophage interaction and the recognition of kappa-carrageenan by lymphocytes, suggesting that a kappa-carrageenan-like structure is expressed by macrophages.

Rat oligodendrocytes have cell adhesion molecules

The aggregation of isolated oligodendrocytes appears to be mediated by cell adhesion molecules. The cell adhesion molecules are inactivated by trypsin. Regeneration of the adhesion molecules is prevented by inhibitors of either protein synthesis or glycosylation. An immunological assay is described to quantitate the molecules involved in oligodendrocyte adhesion based on the following criteria: (a) treatment of oligodendrocytes with rabbit immunoglobulins against oligodendrocyte-conditioned medium prevented their aggregation; and (b) incubation of these immunoglobulins with oligodendrocyte-conditioned medium neutralized their ability to inhibit aggregation.

Glycosidases in cancer and invasion

Glycosidases have been demonstrated to be elevated in the interstitial fluid of tumors, sera of animals and patients with tumors, and in some tumor tissue as compared to normal adjacent tissue. Elevations of serum beta-N-acetylglucosaminidase and beta-glucuronidase most commonly have been found to occur and these enzymes have been shown to be secreted into the extracellular medium by many different tumor cell types in vitro. The mechanism of cellular release of these hydrolytic enzymes probably involves tumor lysosomal exocytosis. Increased tumor glycosidase levels may promote increased tumor cell shedding from primary tumors, local invasion and perhaps be responsible directly, or indirectly for structural changes in tumor cell surface glycoconjugates. These cell surface changes could facilitate tumor cell thrombus formation, secondary site implantation and attachment in the microcirculation to endothelial cells and/or subendothelial basement membrane components. Other studies have demonstrated a correlation between metastatic cell potential and increased endoglycosidase and polysaccharide lyase activity. Generally, metastatic tumor cell variants have been found to be more invasive and capable of degrading proteoglycan basement membrane components, in part due to these increased levels of degradative enzymes. Hence, it is of considerable interest to develop inhibitors against these enzymes. Initial studies with glucuronidase inhibitors in the therapy of bladder tumors have been promising and with the advent of better agents and the use of appropriate in vitro metastatic models it may be possible to design and develop agents which interfere in various metastatic events and limit tumor progression.