Interferon action: role of membrane gangliosides

Role of Globotriaosylceramide in Physiology and Pathology

At first glance, the biological function of globoside (Gb) clusters appears to be that of glycosphingolipid (GSL) receptors for bacterial toxins that mediate host-pathogen interaction. Indeed, certain bacterial toxin families have been evolutionarily arranged so that they can enter eukaryotic cells through GSL receptors. A closer look reveals this molecular arrangement allocated on a variety of eukaryotic cell membranes, with its role revolving around physiological regulation and pathological processes. What makes Gb such a ubiquitous functional arrangement? Perhaps its peculiarity is underpinned by the molecular structure itself, the nature of Gb-bound ligands, or the intracellular trafficking unleashed by those ligands. Moreover, Gb biological conspicuousness may not lie on intrinsic properties or on its enzymatic synthesis/degradation pathways. The present review traverses these biological aspects, focusing mainly on globotriaosylceramide (Gb3), a GSL molecule present in cell membranes of distinct cell types, and proposes a wrap-up discussion with a phylogenetic view and the physiological and pathological functional alternatives.

Molecular dynamics study of the conformations of glycosidic linkages in sialic acid modified ganglioside GM3 analogues

The objective of the present study is to model the analogues of monosialoganglioside (GM3) by making modifications in its sialic acid residue with different substitutions in aqueous environment and to determine their structural stability based upon computational molecular dynamics. Molecular mechanics and molecular dynamics investigation was carried out to study the conformational preferences of the analogues of GM3. Dynamic simulations were carried out on the analogues of GM3 varying in the substituents at C-1, C-4, C-5, C-8 and C-9 positions of their sialic acid or Neuraminic acid (NeuAc) residue. The analogues are soaked in a periodic box of TIP3P water as solvent and subjected to a 10 ns molecular dynamics (MD) simulation using AMBER ff03 and gaff force fields with 30 ps equilibration. The analogue of GM3 with 9-N-succNeuAc (analogue5, C9 substitution) was observed to have the lowest energy of -6112.5 kcal/mol. Graphical analysis made on the MD trajectory reveals the direct and water mediated hydrogen bonds existing in these sialic acid analogues. The preferable conformations for glycosidic linkages of GM3 analogues found in different minimum energy regions in the conformational maps were identified. This study sheds light on the conformational preferences of GM3 analogues which may be essential for the design of GM3 analogues as inhibitors for different ganglioside specific pathogenic proteins such as bacterial toxins, influenza toxins and neuraminidases.

Anti-ganglioside anti-idiotypic vaccination: more than molecular mimicry

Surgery, chemotherapy, and radiation therapy are standard modalities for cancer treatment, but the effectiveness of these treatments has reached a plateau. Thus, other strategies are being explored to combine with the current treatment paradigms in order to reach better clinical results. One of these approaches is the active immunotherapy based on the induction of anti-tumor responses by anti-idiotypic vaccination. This approach arose from Jerne’s idiotypic network theory, which postulates that B lymphocytes forms a functional network, with a role in the establishment of the immune repertoires, in the regulation of natural antibody production and even in the establishment of natural tolerance. Due to the large potential diversity of the immunoglobulin variable regions, the idiotypes repertoire can mimic the universe of self and foreign epitopes, even those of non-protein nature, like gangliosides. Gangliosides are sialic acid-containing glycolipids that have been considered attractive targets for cancer immunotherapy, based on the qualitative and quantitative changes they suffer during malignant transformation and due to their importance for tumor biology. Although any idiotype could be able to mimic any antigen, only those related to antigens involved in functions relevant for organism homeostasis, and that in consequence has been fixed by evolution, would be able not only to mimic, but also to activate the idiotypic cascades related with the nominal antigen. The present review updates the results, failures and hopes, obtained with ganglioside mimicking anti-idiotypic antibodies and presents evidences of the existence of a natural response against gangliosides, suggesting that these glycolipids could be idiotypically relevant antigens.

Conformations of higher gangliosides and their binding with cholera toxin - investigation by molecular modeling, molecular mechanics, and molecular dynamics

Molecular mechanics and molecular dynamics studies are performed to investigate the conformational preference of cell surface higher gangliosides (GT1A and GT1B) and their interaction with Cholera Toxin. The water mediated hydrogen bonding network exists between sugar residues in gangliosides. An integrated molecular modeling, molecular mechanics, and molecular dynamics calculation of cholera toxin complexed with GT1A and GT1B reveal that, the active site of cholera toxin can accommodate these higher gangliosides. Direct and water mediated hydrogen bonding interactions stabilize these binding modes and play an essential role in defining the order of specificity for different higher ganglioside towards cholera toxin. This study identifies that the binding site of cholera toxin is shallow and can accommodate a maximum of two NeuNAc residues. The NeuNAc binding site of cholera toxin may be crucial for the design of inhibitors that can prevent the infection of cholera.

Disialogangliosides and Their Interaction with Cholera Toxin—Investigation by Molecular Modeling, Molecular Mechanics and Molecular Dynamics

Molecular mechanics and molecular dynamics studies are performed to investigate the conformational preference of cell surface disialogangliosides (GD1A, GD1B and GD3) in aqueous environment. The molecular mechanics calculation reveals that water mediated hydrogen bonding network plays a significant role in the structural stabilization of GD1A, GD1B and GD3. These water mediated hydrogen bonds not only exist between neighboring residues but also exist between residues that are separated by 2 to 3 residues in between. The conformational energy difference between different conformational states of gangliosides correlates very well with the number of water mediated and direct hydrogen bonds. The spatial flexibility of NeuNAc of gangliosides at the binding site of cholera toxin is worked out. The NeuNAc has a limited allowed eulerian space at the binding site of Cholera Toxin (2.4%). The molecular modeling, molecular mechanics and molecular dynamics of disialoganglioside-cholera toxin complex reveal that cholera toxin can accommodate the disialoganglioside GD1A in three different modes. A single mode of binding is permissible for GD1B and GD3. Direct and water mediated hydrogen bonding interactions stabilizes these binding modes and play an essential role in defining the order of specificity for different disialogangliosides towards cholera toxin. This study not only provides models for the disialoganglioside-cholera toxin complexes but also identifies the NeuNAc binding site as a site for design of inhibitors that can restrict the pathogenic activity of cholera toxin.

Monosialogangliosides and Their Interaction with Cholera Toxin—Investigation by Molecular Modeling and Molecular Mechanics

Molecular mechanics and molecular dynamics studies are performed to investigate the conformational preference of cell surface monosialogangliosides (GM3, GM2 and GM1) in aqueous environment. Water mediated hydrogen bonding network plays a significant role in the structural stabilization of GM3, GM2 and GM1. The spatial flexibility of NeuNAc of gangliosides at the binding site of cholera toxin reveals a limited allowed eulerian space of 2.4% with a much less allowed eulerian space (1.4%) for external galactose of GM1. The molecular mechanics of monosialoganglioside-cholera toxin complex reveals that cholera toxin can accommodate the monosialogangliosides in three different modes. Direct and water mediated hydrogen bonding interactions stabilize these binding modes and play an essential role in defining the order of specificity for different monosialogangliosides towards cholera toxin. This study identifies the NeuNAc binding site as a site for design of inhibitors that can restrict the pathogenic activity of cholera toxin.

Cell membrane GM1 ganglioside is a functional coreceptor for fibroblast growth factor 2

Free gangliosides bind fibroblast growth factor 2 (FGF2), thus preventing cell interaction and biological activity of the growth factor in endothelial cells. Here we investigated the role of cell-associated gangliosides in mediating the biological activity of FGF2. Treatment of endothelial cells of different origin with the ganglioside biosynthesis inhibitors fumonisin B1, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol or D-1-threo-1-phenyl-2-hexa-decanoylamino-3-pyrrolidino-1-propanol-HCl, impairs their capacity to proliferate when exposed to FGF2. Also, the mitogenic activity of FGF2 is inhibited by the GM1-binding cholera toxin B subunit (CTB). Conversely, overloading of endothelial GM 7373 cell membranes with exogenous GM1 causes a 10-fold increase of the mitogenic potency of FGF2. 125I-FGF2 binds to cell membrane GM1 (K(d) = 3 nM) in complex ganglioside/heparan sulfate-deficient Chinese hamster ovary (CHO)-K1-pgsA745 cell mutants that were overloaded with exogenous GM1. Moreover, FGF2 competes with FITC-CTB for the binding to cell membrane GM1 in different CHO cell lines independently of their capacity to express heparan sulfate proteoglycans. Conversely, CTB inhibits cell proliferation triggered by FGF2 in CHO cells overexpressing the tyrosine kinase FGF receptor 1. Finally, GM1-overloading confers to FGF receptor 1-transfected, complex ganglioside-deficient CHO-K1 cell mutants the capacity to proliferate when stimulated by FGF2. This proliferation is inhibited by CTB. Cell proliferation triggered by serum or by phorbol 12-myristate 13-acetate is instead independent of the cell membrane ganglioside milieu. In conclusion, cell membrane GM1 binds FGF2 and is required for the mitogenic activity of the growth factor. Our data indicate that cell-associated gangliosides may act as functional FGF2 co-receptors in different cell types.

Interaction of fibroblast growth factor-2 (FGF-2) with free gangliosides: biochemical characterization and biological consequences in endothelial cell cultures

Exogenous gangliosides affect the angiogenic activity of fibroblast growth factor-2 (FGF-2), but their mechanism of action has not been elucidated. Here, a possible direct interaction of sialo-glycolipids with FGF-2 has been investigated. Size exclusion chromatography demonstrates that native, but not heat-denatured, 125I-FGF-2 binds to micelles formed by gangliosides GT1b, GD1b, or GM1. Also, gangliosides protect native FGF-2 from trypsin digestion at micromolar concentrations, the order of relative potency being GT1b > GD1b > GM1 = GM2 = sulfatide > GM3 = galactosyl-ceramide, whereas asialo-GM1, neuraminic acid, and N-acetylneuramin-lactose were ineffective. Scatchard plot analysis of the binding data of fluorochrome-labeled GM1 to immobilized FGF-2 indicates that FGF-2/GM1 interaction occurs with a Kd equal to 6 microM. This interaction is inhibited by the sialic acid-binding peptide mastoparan and by the synthetic fragments FGF-2(112-129) and, to a lesser extent, FGF-2(130-155), whereas peptides FGF-2(10-33), FGF-2(39-59), FGF-2(86-96), and the basic peptide HIV-1 Tat(41-60) were ineffective. These data identify the COOH terminus of FGF-2 as a putative ganglioside-binding region. Exogenous gangliosides inhibit the binding of 125I-FGF-2 to high-affinity tyrosine-kinase FGF-receptors (FGFRs) of endothelial GM 7373 cells at micromolar concentrations. The order of relative potency was GT1b > GD1b > GM1 > sulfatide a = sialo-GM1. Accordingly, GT1b,GD1b, GM1, and GM2, but not GM3 and asialo-GM1, prevent the binding of 125I-FGF-2 to a soluble, recombinant form of extracellular FGFR-1. Conversely, the soluble receptor and free heparin inhibit the interaction of fluorochrome-labeled GM1 to immobilized FGF-2. In agreement with their FGFR antagonist activity, free gangliosides inhibit the mitogenic activity exerted by FGF-2 on endothelial cells in the same range of concentrations. Also in this case, GT1b was the most effective among the gangliosides tested while asialo-GM1, neuraminic acid, N-acetylneuramin-lactose, galactosyl-ceramide, and sulfatide were ineffective. In conclusion, the data demonstrate the capacity of exogenous gangliosides to interact with FGF-2. This interaction involves the COOH terminus of the FGF-2 molecule and depends on the structure of the oligosaccharide chain and on the presence of sialic acid residue(s) in the ganglioside molecule. Exogenous gangliosides act as FGF-2 antagonists when added to endothelial cell cultures. Since gangliosides are extensively shed by tumor cells and reach elevated levels in the serum of tumor-bearing patients, our data suggest that exogenous gangliosides may affect endothelial cell function by a direct interaction with FGF-2, thus modulating tumor neovascularization.

Altered B-lymphocyte membrane architecture indicated by ganglioside accessibility in C3H/HeJ mice

We have analyzed both the total ganglioside composition and the surface accessibility of C3H/HeN B lymphocytes and C3H/HeJ B lymphocytes. Seventeen individual resorcinol-positive moieties were visualized by two-dimensional thin-layer chromatography of the purified gangliosides from both strains. Complete homology between strains was seen in the patterns of total gangliosides purified from the endotoxin-responsive and -hyporesponsive strains, with only minor differences in the relative concentrations of four gangliosides. In comparison, only 12 individual gangliosides were accessible to surface labeling following galactose oxidase treatment in these same strains, suggesting that some gangliosides are masked at the cell surface in both strains. However, labeling of the more polar components was greatly reduced in the endotoxin-hyporesponsive (C3H/HeJ) strain, suggesting that these gangliosides have decreased accessibility to galactose oxidase at the cell surface. Therefore, while the total ganglioside compositions of the two strains were nearly equivalent, there were dramatic differences in ganglioside surface accessibility. These findings indicate that an alteration in membrane structure that is associated with the endotoxin hyporesponsiveness observed in C3H/HeJ B lymphocytes exists.

Polymorphic effects of exogenous gangliosides on antigen-induced lymphoproliferation and generation of MHC unrestricted cell mediated cytotoxicity

Cell membrane gangliosides have been shown to be involved in a number of biological processes including cell adhesion, signal transduction and ligand receptor interactions. In this paper we analyzed the effects of a mixture of bovine brain gangliosides, currently in clinical use, on cell mediated immune responses in vitro. We show here that exogenous gangliosides inhibit mitogen and alloantigen induced lymphoproliferation. On the other hand effects on antigen induced blastogenesis were exquisitely dose dependent in that while high doses of gangliosides inhibited lymphoproliferation, probably by interfering in interleukin 2 receptor interactions, lower doses significantly enhanced antigen induced responsiveness. We also report that gangliosides inhibit the generation of lymphokine activated killer cells. Altogether, these data underline the immunoregulatory potential and the polymorphism of effects of exogenous gangliosides.

Mouse natural autoantibodies can interfere with murine alpha and beta interferons

Natural polyspecific autoantibodies could impede the establishment of an antiviral state by mouse alpha and beta interferons (IFN) as determined by an IFN assay with L929 cells and with vesicular stomatitis virus as the challenge virus. This anti-IFN effect was due to interactions with cell surface constituents rather than to antibody activity against IFN. This observation supports the hypothesis that natural autoantibodies participate in specific immune regulation as well as in the regulation of nonspecific host defense.

Combined treatment with Pseudomonas aeruginosa toxin and interferon on mouse and human cells

The combined biological effect of Pseudomonas toxin and beta-interferon on mammalian cells was studied on two cell lines. The first was a virus-producing clone derived from NIH/3T3 mouse fibroblasts transformed by Moloney murine sarcoma virus. The second was a clone derived from human amnion cells. The parameters examined were either retrovirus release from the mouse cells or the rate of protein synthesis in both cell lines. When applied together with Pseudomonas toxin, interferon inhibits virus release even at a Pseudomonas toxin concentration that by itself does not exhibit any biological effect on NIH/3T3 cells. This enhancement phenomenon is both Pseudomonas toxin and interferon dose-dependent. Likewise, the combined treatment of either mouse or human cells with Pseudomonas toxin and the appropriate species-specific interferon, inhibits protein synthesis to a much greater extent than either of these agents alone. The kinetics of the inhibition of virus release is different from that seen with protein synthesis indicating that the enhancement phenomenon observed on virus release is not a result of the inhibition of total cellular protein synthesis. Interferon potentiates the effect of Pseudomonas toxin in a species-specific manner, thus suggesting that this process does not occur at the level of cell receptors but is a consequence of a subsequent intracellular event. It is concluded that the enhancement phenomenon does not reflect a direct interaction between interferon and Pseudomonas toxin, since Pseudomonas incubated together with interferon retained its normal biological activity as indicated by the ability of the toxin molecule to transfer the adenine diphosphoribose (ADP-ribose) moiety of nicotinamide-adenine dinucleotide (NAD) onto elongation factor 2 (EF-2).

Evidence for the involvement of protein-carbohydrate interaction in hematopoietic, multipotential colony-stimulating factor-dependent stem cell proliferation

Immunologically important mediators have been shown to exhibit ability to specifically bind distinct carbohydrates. This type of protein-carbohydrate interaction is one mechanism how to explain involvement of glycochemical interactions in regulatory processes. Interference of certain saccharides with murine multipotential colony-stimulating factor (multi-CSF)-dependent colony formation from progenitor cells in semisolid agar raised evidence for similar potential involvement of protein-carbohydrate interactions. Affinity depletion of conditioned WEHI-3B-medium on resins, bearing saccharides that have been elucidated to be effective inhibitors (mannose and lactose), resulted in preparations with significantly reduced capability to sustain development and proliferation. Sequence comparison of multi-CSF to carbohydrate-binding proteins (lectins) with this specificity failed to uncover extended homologies in diagonal plots. But detailed sequence alignments revealed confined, high-scoring stretches of homology between various lectins and two types of CSF. These results prove the importance of protein-carbohydrate interactions in stem cell proliferation.

Reversible susceptibility to natural cell-mediated cytotoxicity observed in altered BHK cells resistant to HVJ (Sendai virus) infection

Altered baby hamster kidney (BHK-R) cells which were subcultured in the continuous presence of HVJ (hemagglutinating virus of Japan--the Sendai strain of parainfluenza 1 virus) showed a high susceptibility to natural cell-mediated cytotoxicity, although BHK-R cells are not transiently or persistently infected with HVJ but contain the restricted amount of sialic acid. By repeated subcultivation of BHK-R cells in growth medium free of HVJ, the sensitivity to natural killer cytotoxicity decreased to the level of normal BHK cells with a counter increase of cellular sialic acid, and the subsequent treatment of the cells with neuraminidase caused a loss of proper sialic acid residues, once again resulting in a significant enhancement of lysis by natural killer cells. In the BHK-R cell system which exhibits a reversible resistance to the interferon action, the enhancing effect induced by interferon on target cell susceptibility to natural killer activity became more pronounced in accord with the recovery of sensitivity to the antiviral action of interferon.

Gangliosides in the nervous system during development and regeneration

Gangliosides are present in nervous tissues of echinoderms and chordates, but the amounts and patterns differ widely. There are changes in the ganglioside contents of nervous tissues during development in most animals studied. To a large extent, regional differences and changes with development and degeneration in ganglioside composition reflect changing and different proportions of cellular types and subcellular organelles within the tissue. GM1 and GM4 are enriched in myelin; GD1a may be a marker for dendritic arborization. During regeneration of fish optic nerve and rat sciatic nerve there is an increased amount of ganglioside proximal to the regenerating axon tips, which may largely be a result of accumulation. This could provide a relatively large reservoir of ganglioside to become incorporated into the sprouting axolemma. Gangliosides added exogenously to growth medium can induce neuritogenesis of several types of neurons. The mechanisms of this action are unknown but may be related to nerve growth factor, microskeletal organization, membrane fluidity, and other factors. Gangliosides injected into young animals affect brain development, but further studies are required to determine these effects more specifically. Ganglioside administration increases the number of sprouts in regenerating peripheral nerves, but does not seem to accelerate axonal elongation. Parenterally administered gangliosides alter the recovery of brain tissue from a variety of types of lesions, and clinical trials are in progress to determine if they are of benefit in human neurological disorders. The biochemical mechanisms of these in vivo ganglioside effects are poorly understood, but may involve modulation of several enzyme systems as well as other properties of neural membranes, such as fluidity. It is possible that gangliosides may play similar roles and operate through some of the same mechanisms in developing and regenerating nervous tissues.

Inhibition of murine L cell interferon action by heparin

Heparin added together with murine L cell interferon inhibited the development of antiviral activity in mouse L cells. When added after interferon treatment, heparin had no effect on antiviral activity. There was also no inhibition of interferon action in L cells treated with heparin before addition of interferon. On the other hand, heparin did not inhibit antiviral activities of human interferon alpha and beta. Since murine L cell interferon, but not human interferon alpha and beta, binds to a heparin affinity column and can be eluted with a solution of high salt, it is presumed that murine L cell interferon and heparin must interact with each other. The apparent interaction of heparin with murine L cell interferon was prevented by protamine, a drug that neutralizes heparin. Dextran sulfate inhibited murine L cell interferon action, but dextran and chondroitin sulfate A did not. These results suggests that heparin inhibited murine L cell interferon action by the binding via sulfate groups on its molecules. Heparin also inhibited antiviral activity of murine L cell interferon in mice infected with herpes simplex virus (+GC Miyama strain).

The interferon receptors

Early studies on the mode of action of interferons have indicated that a receptor system on the cell surface is involved in its action. The first direct evidence to a high-affinity binding site was found only after pure interferon was available. Two different receptors, one specific for interferons-alpha and beta, and the other for interferon-gamma were recognized. A correlation between affinity to the receptor and specific activity was established. Cross-linked complexes of labeled interferons with their receptors were visualized on gel electrophoresis and even partially purified. Internalization of interferons after binding to the receptor was reported. The role of gangliosides as helpers of interferon binding was recently investigated. Fragments of interferons which still retained binding capacity were described and helped in elucidating the binding site on the interferon molecule.

Sensitivity to alpha/beta-interferon is independent of N-linked complex-type oligosaccharides on cell-surface-membrane glycoproteins

The extent of involvement of carbohydrate structures in the mechanism of action of alpha and beta-interferon (IFN-alpha, IFN-beta) is undefined. In this report we examine the role of complex-type N-linked oligosaccharides in the response to these interferons. The response of mouse leukemia L 1210S cells, grown in the presence of swainsonine, an inhibitor of Golgi mannosidase II [Tulsiani, D. R. P., Harris, T. M. and Touster, O. (1982) J. Biol. Chem. 257, 7936-7939; Elbein A. D., Solf, R., Dorling, P. R. and Vosbeck, K. (1981) Proc. Natl Acad. Sci. USA 78, 7393-7397], to mouse IFN-alpha/beta, both with respect to antiviral and antigrowth effects, remains intact in spite of the total absence of complex-type N-linked oligosaccharides. Also, there is no difference in the response to human IFN-beta of a parental Chinese hamster ovary cell line and a mutant lacking beta-N-acetylglucosaminyltransferase I and therefore unable to synthesize complex-type N-linked oligosaccharides [Stanley, P., Callibot, V. and Siminovitch, L. (1975) Cell 6, 121-128]. These results are significant in permitting the conclusion that the carbohydrate-specific binding of IFN-alpha and IFN-beta to gangliosides cannot be due to a similarity of the ganglioside carbohydrate to that of a glycoprotein containing a complex-type N-liked oligosaccharide.

Macrophage glycolipid receptors for human migration inhibitory factor (MIF): differentiated HL-60 cells exhibit MIF responsiveness and express surface glycolipids which both bind MIF and convert nonresponsive cells to responsiveness

The human promyelocytic leukemia line HL-60 when treated with a phorbol diester (TPA) differentiates into cells (HL60-TPA) that respond to human migration inhibitory factor (MIF). Unresponsive HL-60 cells became responsive to MIF when preincubated with a glycolipid-enriched preparation extracted from HL60-TPA cells, human monocytes, human macrophage-like (U937) cell line, or with the purified glycolipid receptor for MIF from guinea pig peritoneal macrophages. Human blood monocytes exhibited an increased response to MIF when preincubated with glycolipids from HL60-TPA and U937 cells but not from HL-60 cells. Finally, glycolipids from HL60-TPA cells but not from HL-60 cells were able to reversibly bind MIF when covalently coupled to agarose. These studies suggest that TPA induces the differentiation of HL-60 cells into MIF-responsive cells through the expression of a glycolipid receptor for MIF.

An inhibitor of interferon action: II. Biological properties of the IFN-gamma-associated inhibitor of interferon action

Previously an inhibitor of interferon action had been isolated from mitogen stimulated mouse spleen cells. This inhibitor was associated with the IFN-gamma molecule and might possibly represent an altered IFN-gamma molecule which can no longer induce an effective antiviral state. This report further investigates the biological properties of this inhibitor. Inhibitor activity is independent of the virus used in the interferon assay. Inhibitor activity has also been found to be species specific. Mouse inhibitor does not inhibit the antiviral activity of either human IFN-gamma or human IFN-beta. However, inhibitor production is not limited to the mouse system. Inhibitor is also present in preparations of human IFN-gamma. The inhibitor does not appear to directly compete with IFN-gamma for a specific cell surface receptor since inhibitor activity is independent of interferon concentration. The presence of inhibitor allows a unique, albeit reduced level of antiviral protection to develop. Increasing concentrations of interferon do not increase the level of antiviral protection allowed by the inhibitor. This inhibitor of interferon action may represent a natural mechanism whereby IFN-gamma-induced effects are regulated in vivo.

Inhibition of interleukin-2-dependent cytotoxic T-lymphocyte growth by gangliosides

Previous work has shown that exogenous gangliosides suppress lectin-induced T-lymphocyte mitogenesis in mixed populations of immune cells. As one potential cellular site of this inhibition, the influence of gangliosides on interleukin-2-dependent T-cell proliferation was tested, using cultures of cytotoxic T cells (strain CT-6). Incubation of CT-6 cells with mixed bovine brain gangliosides resulted in a dose-dependent inhibition of cell proliferation. Cell viability was unaffected by gangliosides, and the inhibition was totally reversed when the gangliosides were removed. Individual purified gangliosides were tested and GM2 was most inhibitory (I50 = 15 microM). GD1a and GT1b were somewhat less potent, whereas GM1 and GM3 were only weakly inhibitory. Various nonpolar lipids, sulfatides, and sialic acid did not inhibit CT-6 cell growth. The results suggest that a primary mechanism whereby gangliosides inhibit lectin-induced lymphocyte mitogenesis is by inhibition of the interleukin-2-stimulated proliferation of T cells in these cultures.

Antibodies to chromosome 21 coded cell surface components block binding of human alpha interferon but not gamma interferon to human cells

Antisera raised against a human X mouse hybrid cell line containing human chromosome 21 as its only human chromosome, block induction of an antiviral state by human alpha interferon (IFN-alpha), block induction of (2'-5')oligoisoadenylate synthetase [2'-5')A synthetase), and block binding of 125I-labeled and 35S-labeled recombinant, human IFN-alpha A, but not 125I-labeled IFN-gamma, to cell surface receptors. The data presented clearly demonstrate that the cell surface receptors for IFN-alpha and IFN-gamma are different, and provide independent evidence of the role of a chromosome 21 coded cell surface molecule in the pathway to the generation of the antiviral state.

Reversible resistance to the antiviral action of interferon observed in altered BHK cells resistant to HVJ (Sendai virus) infection. Brief report

Altered baby hamster kidney (BHK-R) cells which were subcultured in the continuous presence of HVJ (hemagglutinating virus of Japan--the Sendai strain of parainfluenza 1 virus) showed a resistance to the antiviral action of both type I and II interferons. No evidence for a direct inactivation of interferon molecules during incubation of BHK-R cells was obtained. After serial subculture of BHK-R cells in growth medium free of HVJ, surface membranes with the proper sialic acid residues were restored and the cells became susceptible to the interferon action. It is suggested that binding sites for interferons might be ranked above HVJ receptors in the "receptor gradient".

Receptors for human alpha interferon: are gangliosides involved?

Interferon (IFN) action on cells must begin with an interaction with cellular receptors. Binding and cross-linking experiments reported earlier with purified 125I-labeled recombinant human (Hu) IFN-alpha 2 have revealed that IFN-alpha 2 binds to a specific macromolecular receptor on human cells (Joshi et al., J. Biol. Chem. 257, 13884-13887, 1982). Based on indirect evidence such as neutralization of the antiviral action of IFN preparations by gangliosides and binding of IFNs to gangliosides coupled to solid supports, it has been suggested by various investigators that gangliosides may be a part of the IFN-alpha/beta receptors. Experiments presented here indicate that gangliosides could block the antiviral activity of HuIFN-beta, but not of HuIFN-alpha, although both species of IFN bound strongly to gangliosides coupled to poly-L-lysine-agarose. Furthermore, gangliosides did not inhibit the binding of 125I-labeled HuIFN-alpha 2 to specific receptors on human cells, and this binding was competed out by unlabeled HuIFN-alpha 2 and HuIFN-alpha(LE) which were preincubated with gangliosides. However, the capacity of HuIFN-beta to compete for the receptors was abolished by preincubation with gangliosides. These results were confirmed by cross-linking experiments to identify the IFN-receptor complex by gel electrophoresis. The results indicate that at least in the case of HuIFN-alpha species, the ganglioside binding is apparently not at the active site of the IFN molecules required for interaction with the receptors on the cell surface.

Antibodies to gangliosides inhibit goldfish optic nerve regeneration in vivo

Intraocular injection of antiserum to mixed ganglioside or to GM1 inhibited the regeneration of goldfish optic axons following an optic nerve crush. For example, injections of antiserum on 5 consecutive days beginning the day before the crush resulted in a decrease of about 40% in the axonal outgrowth distance measured at 10 days after the crush. The inhibition was observed even when the treatment was begun a few days after the lesion, and greater degrees of inhibition were observed when the treatment was given later in regeneration. This indicates that the antiganglioside serum interfered with axonal elongation more than with the initial sprout formation. The antiganglioside treatment did not impair the enlargement of the cell bodies and nucleoli that accompanies regeneration, nor did it affect fast axonal transport of protein, glycoprotein, or glycolipid in regenerating nerves. Thus inhibition of outgrowth by antiganglioside treatment was not mediated by a gross change in the metabolism of the regenerating neurons. Treatment of normal neurons with the antiserum produced a 20-30% increase in the amount of 3H-glucosamine-labeled glycoproteins and glycolipids conveyed by fast axonal transport. These results suggest that membrane gangliosides may normally influence the supply of axonally transported glycosylated macromolecules. However, the effect of antiganglioside on axonal transport of glycosylated molecules and on axonal outgrowth are not necessarily related to each other.

Inhibition of human lymphocyte activation by wheat germ agglutinin: a model for saccharide-specific suppressor factors

The suppressive effect of wheat germ agglutinin (WGA) on lectin-stimulated blastogenesis and immunoglobulin production was studied. Addition of WGA at 10 micrograms/ml inhibited phytohemagglutinin (PHA)-, concanavalin-A (Con-A)-, and pokeweed mitogen (PWM)-induced mitogenic responses by 70-80%. PWM-driven immunoglobulin synthesis was suppressed by 45% with WGA. The inhibitory effects of WGA were not due to cell death or to interference with lectin binding at the cell surface. Inhibition was dependent on the presence of WGA in the cell culture during the first 24 hr of mitogen exposure and was observed in cultures of both monocyte-depleted peripheral blood mononuclear cells as well as T-cell-enriched populations. WGA-induced inhibition of blastogenesis was blocked by the addition of N-acetylglucosamine (GluNAc) which prevents WGA binding to the cell surface. WGA was found to mimic the suppressive effect of a soluble immune suppressor supernatant (SISS) derived from Con-A-activated mononuclear cell cultures. PHA responses were inhibited by 80 and 95% with SISS and WGA, respectively. The inhibition by both WGA and SISS was totally reversed with addition of GluNAc. Furthermore, WGA and SISS demonstrated competition for the same cell surface receptor site. WGA may therefore be useful as an in vitro model of a saccharide-specific, biologically relevant, soluble mediator for the investigation of mechanisms of immunologic suppression.

Interferon-induced increase in neuraminidase-releasable sialic acid and glycosphingolipid metabolism in mouse lymphoma and L1210 leukemic cell lines: correlation with susceptibility to natural killer cell-mediated lysis

Changes in sialoglycoconjugates and glycosphingolipid (GSL)5 metabolism were demonstrated in mouse EL4, P52 and YAC-1 lymphoma and L1210 leukemia cell lines treated with beta-interferon (IFN). Expression of cell surface (neuraminidase-releasable) sialic acid on IFN-treated cells was markedly elevated (three- to six-fold). The increase in neuraminidase-releasable sialic acid is contributed by sialoglycoproteins and particularly by cell-surface gangliosides in IFN-treated cells. Incorporation of [3H]-galactose into all GSL was elevated in IFN-treated cells. Thin-layer chromatographic analysis of GSL of IFN-treated cells showed an increase in several GSL homologues with striking changes in ganglioside with chromatographic migration of GM2, GM1, and GD1a relative to control cells. IFN-treated tumor-cell lines became resistant to lysis by virus-induced IFN-activated natural killer (NK) cells, as shown previously, but addition of neuraminidase to IFN-treated and untreated cells caused only a moderate increase in NK-sensitivity. This suggests that IFN-mediated protection of target cells from NK lysis was not due to a preferential masking of target structure by elevated levels of sialic acid. These membrane-associated changes in GSL and sialic acid in IFN-treated cells may be potentially significant, because a correlation between certain GSL expression, sialic acid phenotype and susceptibility of target cells to NK-cell-mediated lysis have been found in several other systems.

Ultrastructural distribution of interferon receptor sites on mouse L fibroblasts grown in suspension: ganglioside blockade of ligand binding

Murine beta-interferon (IFN) receptors on L929 cells grown in suspension culture were visualized by indirect immunoferritin electron microscopy. Ferritin label on these cells was associated primarily with the coated areas and coated pits of the membrane, in contrast to previous observations with L929 cells grown in a monolayer, which did not reveal such coated areas or pits but showed ferritin label distributed randomly on the cell membrane (Kushnaryov et al., Infect. Immun. 36:811-821, 1982). On about 15% of the cell sections from suspension-grown cells, the ferritin label was found outside coated membrane areas. These findings suggest that different cell populations exist with respect to the localization and possibly the affinity of IFN receptors. In the same experiment, exogenously added gangliosides blocked the binding to cell surfaces not only of 125I-labeled IFN but also of unlabeled IFN as revealed by an immunospecific ferritin labeling technique, providing direct evidence that gangliosides interfere with the binding of IFN to specific receptor sites on the surface of mouse L929 cells. These studies establish that the binding of IFN to cell membranes, depending on cell growth conditions, can involve coated areas and coated pits, to which certain hormones and toxins have been shown to bind.

Selective inhibition by monosaccharides of tumor cell cytotoxicity mediated by mouse macrophages, macrophage-like cell lines, and natural killer cells

A series of monosaccharides were tested for their ability to inhibit the effector phase of macrophage-mediated cytolysis against two susceptible murine tumor target cells, L5178Y and RL male I. Two monosaccharides, D-mannose and N-acetyl-D-galactosamine, were found to decrease cytotoxicity consistently in a dose-dependent manner. However, D-mannose preferentially inhibited lysis of RL male I target cells with little effect on lysis of L5178Y target cells, while the reverse was found with N-acetyl-D-galactosamine. Neither monosaccharide interfered with the activation of macrophages by polyinosinic:polycytidylic acid. Natural killer cell activity was decreased by a 25 mM concentration of D-mannose but not by N-acetyl-D-galactosamine, although increasing concentrations of N-acetyl-D-galactosamine were inhibitory. Neither monosaccharide affected cytotoxicity by alloimmune T cells. Cytotoxicity of macrophage-like cell lines against tumor target cells was also decreased by monosaccharides but the pattern of inhibition was different from that seen with activated macrophage effector cells. Both D-mannose and N-acetyl-D-galactosamine inhibited glucose oxidation by activated macrophages but only D-mannose significantly decreased protein synthesis of activated macrophages. These results indicate that monosaccharides can inhibit macrophage-mediated cytotoxicity in a selective manner with the pattern dependent on the tumor target cell used in the assay.

Effect of exogenous gangliosides on human neural cell division

Human neural cells in exponential growth phase were transferred to a serum-free medium and maintained for 72 hr without any detectable loss in viability. The two normal fetal cell lines (CHI and CHII) showed a serum-dependent cell proliferation, but the glioblastoma multiforme cells (12-18) were able to continue proliferating in this totally synthetic medium. The incorporation of [3H]thymidine into the acid-precipitable fraction of both normal and neoplastic human neural cells was assayed in the presence and the absence of exogenous gangliosides by a convenient new method. In serum-free medium, gangliosides (50 microM) inhibited the thymidine incorporation into the normal fetal cells within 24 hr and, in serum containing medium, reduced their proliferation within 48 hr. No such effects were detectable in the glioma cells. The inhibition of thymidine incorporation in the normal cells was reversible upon removal of the gangliosides. These results indicate a role of gangliosides in the postmitotic phase of normal human neural cells resulting in the regulation of cell proliferation.

Effect of glycolipids and glycophorin on the activity of human interferon-beta and -gamma

We have studied neutralization of the antiviral activity of human fibroblast (IFN-beta) and immune interferon (IFN-gamma) by incubation with glycolipids (including the gangliosides GM1, GM2 and GM3, as well as various other glycolipids) and with the sialoglycoprotein, glycophorin. When 100 units/ml of IFN-beta were preincubated with 30-80 microM of the gangliosides, all antiviral activity was abolished. Similarly, 120 microM of glycophorin completely reversed the antiviral activity of 100 units/ml of IFN-beta. Glycolipids containing more than two sugars also showed moderate inhibitory effects. GM2 at a concentration of 200 microM almost completely inhibited the antiviral activity of 100 units/ml of IFN-gamma, but GM1, GM3 and glycophorin had only a moderate inhibitory effect. These results suggest that the terminal N-acetylneuraminic acid (NANA) residues of gangliosides and of glycophorin play an important role in the inhibition of IFN-beta, and that they may be similarly involved in the inhibition of IFN-gamma.

Inhibition of mouse fibroblast interferon by gangliosides. Differential effects on biological activity and on induction of (2'--5')oligoadenylate synthetase

Gangliosides are potent inhibitors of the antiviral activity of mouse fibroblasts and other beta-interferons. We have compared the effects of gangliosides on antiviral and antigrowth activities of mouse fibroblast interferon and on the induction of (2'--5')oligoadenylate synthetase, one of the enzymes implicated in the antiviral state induced by interferon. Whereas both biological effects appear to be inhibited by gangliosides in an analogous fashion, inhibition of induction of (2'--5')oligoadenylate synthetase does not correlate with inhibition of vesicular stomatitis virus replication. Ganglioside concentrations that inhibit the interferon-induced (2'--5')oligoadenylate synthetase to levels close to those of uninduced cells, still allow for a 100--1000-fold reduction of viral yield. Significantly higher ganglioside concentrations are required to prevent completely the antiviral effect. This biphasic relationship between (2'--5')oligoadenylate synthetase levels and inhibition of viral yield suggests that no or very small increases in synthetase levels are involved in inhibition of virus by between two and three orders of magnitude.

Ultrastructural localization of interferon receptors on the surfaces of cultured cells and erythrocytes

The bindings sites for interferon (IFN) on the limiting cell membranes of human and mouse fibroblasts and erythrocytes were revealed by an indirect immunoferritin technique. Mouse IFN-beta and human IFN-beta of high specific activity were used with the corresponding purified antibodies. Species-specific IFN binding was demonstrated by ferritin deposition on human erythrocytes and fibroblast membranes treated with human IFN and on mouse erythrocytes and fibroblast membranes treated with mouse IFN, but not on human erythrocytes or fibroblast membranes treated with mouse IFN. IFN binding sites on fibroblasts were located on regions of membranes between microvilli, whereas diphtheria toxin receptors were demonstrated mainly on microvilli. IFN binding altered the diphtheria toxin after IFN treatment. This reduced toxicity correlated with a decrease in the quantity of receptors for diphtheria toxin on the cell membrane. Thus, the species-specific binding of IFN appears to depend on membrane receptors in discrete regions of the limiting membrane which are present not only on functionally responsive fibroblasts but also on erythrocytes.