Interferon action: role of membrane gangliosides

Interferon interactions with thyroid cells

Iodide uptake by functioning rat thyroid (FRTL) cells is increased by mouse interferon. The effect is detectable using purified interferon; it is not accompanied by an increase in intracellular cyclic AMP levels, is measurable within 20 min, and is prevented by cholera toxin, an agent which inhibits interferon's antiviral activity. The effect of interferon is biphasic with maximally increased iodide uptake (approximately 2-fold) evident at about 300 international mouse units per ml (U/ml) and lesser effects evident at higher concentrations (greater than 1000 U/ml). The effect of mouse interferon on iodide uptake is accompanied by an extremely sensitive antiviral response. Thus, significant antiviral protection is evident at 1 U/ml with FRTL cells, as opposed to 1000 U/ml for nonfunctioning rat thyroid (FRT) cells. Functioning FRTL thyroid cells are also more sensitive to mouse interferon (10-fold) with respect to 2',5'-polyadenylate (An) synthetase activity or to 125I-thyrotropin binding to membrane preparations than are nonfunctioning FRT cells. Antiviral protection in FRTL cells is evident as early as 1 h after exposure to mouse interferon, and is accompanied by a nearly 100-fold increase in the measurable titer of 2'5'-An synthetase activity. Actinomycin D blocks the antiviral effect of interferon, but not its effect on iodide uptake. The results are discussed with respect to the unusually sensitive response of heterologous (rat) cells to mouse interferon: a possible relationship between thyrotropin and interferon receptors; and, the difference in interferon sensitivity exhibited by differentiated (functioning) as opposed to undifferentiated (nonfunctioning) thyroid cells.

Interferon-mediated inhibition of adenylate cyclase in mouse cells

Adenylate cyclase activity was measured in mouse cell plasma membrane after 30 units/ml of interferon (IFN) treatment. The basal and Gpp(NH)p stimulated enzyme activity in LB cell was inhibited by 20%-40% throughout the time course of treatment (30 min to 18 h). The reduced enzyme activity was not associated with enhanced breakdown of cAMP, but was related to alteration in the catalytic component of the enzyme. Moreover, there was no change in the affinity for guanine-nucleotide regulatory unit and 1 X 10(-7) M Gpp(NH)p was required to obtain half-maximal activation with either type of membrane. Interferon action on adenylate cyclase was biphasic, at 10 u/ml it was stimulatory and between 30 and 1000 u/ml it inhibited the enzyme activity to a great extent; but IFN did not exert its effect directly on the enzyme. The reduction in enzyme activity was comparable to a reduction in the intracellular level of cAMP in most of the interferon-sensitive cell lines studied. We propose, therefore, that the inhibitory effect on adenylate cyclase is related to a step in the development of antiviral activity.

Inhibition of beta-interferon augmentation of murine natural killer cytotoxicity by gangliosides

Interferons cause augmentation of natural killer (NK) cell activity, which might be a major reason for their antitumor effect. Antiviral and antigrowth effects of mouse beta interferon are inhibited by mono-, di-, and trisialogangliosides commonly found in brain extracts, but also in membranes of many other cells. Results presented in this report show that preincubation of mouse beta interferon with a brain ganglioside mixture or its isolated major components Gm1, Gd1a, Gd1b, and Gt1b (see Aberrations) prior to addition to effector spleen cells, inhibits NK-cell enhancement due to interferon in a dose-dependent manner. When spleen cells are treated with individual gangliosides alone, spontaneous NK cell activity is not affected. Pretreatment of effector cells with gangliosides prior to addition of interferon does not inhibit subsequent augmentation of NK cell activity by beta interferon. Also, target susceptibility remains unaltered in the presence of gangliosides. Thus the inhibitory effect of gangliosides appears to involve competition for interaction of beta interferon with the NK cells.

Ganglioside stimulation of axonal sprouting in vitro

Bovine brain gangliosides were applied to primary and established neuronal cultures to examine the role of gangliosides in neuronal development. Media containing gangliosides enhanced the degree of axonal elongation exhibited by sensory ganglia neurons and increased the length and number of Neuro-2a neuroblastoma cell processes. Ganglioside-supplemented media caused a twofold increase in ornithine decarboxylase activity in both culture systems. These experiments suggest that gangliosides function as acceptor molecules for growth-promoting substances in embryonic and tumor-derived neurons.

Electron paramagnetic resonance studies on the fluidity and surface dynamics of egg phosphatidylcholine vesicles containing gangliosides

The influence of different gangliosides (GM1, GD1a, GT1b) on the fluidity and surface dynamics of phosphatidylcholine small unilamellar vesicles was studied by electron paramagnetic resonance. 5- and 16-nitroxystearic acid, sounding respectively the region close to the surface and that close to the hydrophobic core of the vesicle, were employed as spin-label probes. The signals released by 5-nitroxystearic acid showed that the presence of gangliosides reduced the mobility of the hydrocarbon chains around the probe. The effect increased by increasing ganglioside concentration, and diminished from GM1 to GD1a and GT1b. The decrease of membrane fluidity was also monitored by the 16-nitroxystearic acid probe. On addition of Ca2+ the fluidity of ganglioside-containing vesicles (as signalled by the 5-nitroxystearic acid probe) promptly decreased, therefore returning slowly to the original value. It is suggested that gangliosides cause strong side-side head group interactions on the bilayer surface--between ganglioside oligosaccharide chains and between ganglioside and phosphatidylcholine polar portions--which lead the lipid chains to assembly in a more rigid fashion. The influence of Ca2+ is interpreted as due to lateral phase separation in the vesicle membrane. This phenomenon can be related to the formation or stabilization of ganglioside clusters on the vesicle surface.

Interferon induces an antiviral state in ganglioside-deficient transformed mouse fibroblasts

The antiviral activity of mouse fibroblast interferon against vesicular stomatitis virus was investigated in L-929 mouse fibroblasts and the ganglioside-deficient L-929 mutant cells (ATCC clone NCTC 2071). Although it has been widely reported that gangliosides serve as primary receptors for interferon at the cellular membrane, only a small difference in interferon sensitivity was observed between the wild-type L-929 and the ganglioside-deficient NCTC 2071 cells. It was not possible, however, to overcome this difference by administration of exogenous gangliosides.

Inhibition of secondary IgG responses by N-acetyl-D-galactosamine

A range of monosaccharides were tested for their ability to inhibit a variety of in vitro immune response. The most striking specific inhibition was produced by N-acetyl-D-galactosamine (GalNAc). This sugar strongly inhibited the secondary IgG antibody response to two different hapten-carrier systems, but had no effect on primary and secondary IgM responses, generation of cytotoxic T cells to alloantigens and mixed lymphocyte reactions. By exposing secondary antibody cultures to GalNAc for varying periods of time, it was observed that GalNAc only exerted its inhibitory effect on day 4 of the culture, the day when IgG plaque-forming cells first appeared. Furthermore, GalNAc could override the action of T helper factor in T cell-depleted cultures. Collectively, these data indicate that GalNAc inhibits the initiation of IgG synthesis probably by blocking the interaction of a helper factor for IgG synthesis with its target cell.

Topographic studies of gangliosides of intact synaptosomes from rat brain cortex

Gangliosides in the external surface of intact synaptosomes from rat brain cortex have been studied by oxidation of exposed galactose and galactosamine groups with galactose oxidase followed by reduction with labeled sodium borohydride. Purified synaptosomes were labeled, disrupted by osmotic shock, and the particulate components fractionated on diatrizoate to give four synaptosomal membrane fractions (A-D) and a mitochondrial pellet (E). Fractions A and B represent synaptosomal plasma membranes. When intact synaptosomes were labeled, the major portion of the total radioactivity incorporated into ganglioside fraction was found to be in GM1 3 species. With isolated membrane fractions little selectivity was seen: (1) more label was present compared to intact synaptosomes, and (2) zones corresponding to GM2, GM1, GD1a, GD1b were the major gangliosides labeled. The results confirm the conclusion that membrane fractions A and B are derived from the exposed synaptosome surface and also show that GM1 is the major ganglioside species available for enzyme oxidation at the surface.

Inhibitory effect of cholera toxin on human natural cell-mediated cytotoxicity and its augmentation by interferon

Cholera toxin inhibits human natural cell-mediated cytotoxicity in a dose- and time-dependent manner. Pretreatment of lymphocytes with 10 ng/ml of cholera toxin for 2 h almost completely inhibited cytolysis. Interferon augmented human natural cell-mediated cytolysis, but when lymphocytes were pretreated with cholera toxin before interferon treatment, no enhancement of cytolysis occurred. Cholera toxin could inhibit the enhancement of cytolysis by interferon even when lymphocytes were treated with cholera toxin after 2 h interferon treatment. Cholera toxin subunit B which binds cell surface ganglioside galactosyl-N-acetylgalactosaminyl - [N-acetylneuraminyl] - galactosylglucosylceramide (GM1) without activating adenyl cyclase had no effect either on natural cytolysis or on the enhancement of natural cytolysis by interferon, suggesting that mere binding of cholera toxin to the cellular receptor was not enough to inhibit natural cell-mediated cytolysis. Cyclic adenosine 3',5'-monophosphate (cAMP) levels increased in cholera toxin-treated lymphocytes and the time course of cAMP accumulation was similar to that of cytotoxicity inhibition. Exogenous dibutyryl-cAMP (db-cAMP) and theophylline inhibited cytolysis, while exogenous dibutyryl cyclic guanosine 3',5'-phosphate (db-cGMP) enhanced cytolysis slightly, suggesting that the process of inhibition of human natural cell-mediated cytolysis was at least partly modulated by intracellular cyclic nucleotides.

Beta-interferon-induced time-dependent changes in the plasma membrane lipid bilayer of cultured cells

The time-dependent interferon-induced structural changes in the plasma membrane lipid bilayer have been investigated in cultured cells using spin label electron spin resonance techniques. Treatment of human HeLa-S3 cells in suspension culture with human beta 1 interferon (640 u/ml) for as short a time as 30 min causes an increase in the rigidity of the plasma membrane lipid bilayer (Landsberger, Pfeffer and Tamm, in preparation). The plasma membrane rigidity of interferon-treated cells returns to the level of control cells within 3 to 5 hr, but by 24 hr after beginning of treatment, the rigidity of the plasma membrane is increased again and remains so for at least 2 days. Mouse beta interferon causes both an early (Landsberger, Pfeffer and Tamm, in preparation) and a late increase in membrane rigidity in homologous mouse L-929 cells, but not in heterologous HeLa-S3 cells. Thus, the interferon-induced perturbation of membrane structure is species specific. The late increase in membrane rigidity may have a different underlying mechanism from that of the early increase. While the early and transient change probably is related to signal generation and transmission, the later and persistent change may be an aspect of the phenotype and interferon-treated cells and may reflect changes in the plasma membrane-cytoskeletal complex.

A simple radioimmunoassay to determine binding of antibodies to lipid antigens

A solid-phase radioimmunoassay to determine the binding of antibodies to lipid antigens is described. Polyvinyl chloride microtiter plates were coated with lipid antigens by placing in each well 25--100 microliters of solutions of the antigens in ethanol and evaporation of the solvent. The wells were than washed with 0.3% gelatine solution to remove loosely bound antigens and to saturate the plastic with an unrelevant protein to prevent unspecific binding of antibodies to the plates. About one-third of [3H] phosphatidylcholine adsorbed in this way (out of 1 nmole) was firmly attached to the plastic and was not washed away during a standard assay. The rest, loosely bound lipid, was washed away in the first 5 washings before the primary antibodies were applied. The technique is rapid and convenient and is as sensitive as a conventional solid-phase radioimmunoassay with protein antigens. It requires minute amounts of antigen. Less than 10(-12) moles of lipid antigen can be detected by this technique.

Effects of concanavalin A on the antiviral and cell growth inhibitory action of human interferons

Sensitivities of human transformed cell line RSa and its variant cell line IFr to the cytotoxicity of Con A were compared. IFr cells were more resistant than RSa to Con A. Con A-resistant cell lines, Con Ar-1 and Con Ar-3, were isolated from RSa, and they were slightly more sensitive than RSa cells to the cell growth-inhibitory actions of interferons. Agglutinability of RSa, IFr, and Con Ar cells by Con A was compared and found to be almost equal. The combined effects of Con A and interferon upon growth and viability of these cell lines were tested. When RSa and IFr cells were treated simultaneously with Con A and Le-IF, growth of the cells was suppressed more markedly than when treatment was with Con A or Le-IF alone. To clarify the mechanism of this phenomenon, binding of 125I-labeled Con A was examined. Though ther wee some differences, both leukocyte and fibroblast interferon enhanced the binding of Con A to RSa cells and also in Con Ar cells but, in interferon-resistant IFr and HEC cells, enhancement of Con A binding was low or not observed. Therefore, the combined effect of Con A and interferon on the inhibition of cell growth is not considered to be merely due to the enhanced binding of Con A by interferon action. Successive treatment of RSa or Con Ar cells with Con A and interferon did not enhance the antiviral action of interferon at all. On the contrary, simultaneous treatment with Con A and interferon suppressed the antiviral action of interferon, depending on the concentration of Con A used. Thus, the effect of Con A on the antiviral and cell growth-inhibitory actin of interferon seems rather different.

Mouse fibroblast (type I) and immune (type II) interferons: pronounced differences in affinity for gangliosides and in antiviral and antigrowth effects on mouse leukemia L-1210R cells

Different interferons can be obtained from the same animal species depending on the cells and (or) the inducers used. Interferons of type I and type II differ not only antigenically but also in molecular weight and stability at low pH. We have investigated whether mouse type I and type II interferons also differ in properties relating to their biological action. We present evidence which suggests that the molecular mechanism leading to antiviral and antigrowth effects induced by both types of interferon in susceptible cells must differ in at least one important step. Antiviral and antigrowth activities of type I but not of type II interferon are both inhibited when gangliosides are added to cell cultures together with the interferon. Whereas type I interferon strongly binds to ganglioside affinity columns and can be eluted with solutions of N-acetylneuraminyllactose, type II interferon passes through such columns unretarded. L-1210 mouse leukemia cells (L-1210S) respond equally well to antiviral and antigrowth activities of type I and type II interferons. Type I interferon-resistant L-1210 cells (L-1210R), derived from L-1210S cells after continuous culture in the presence of mouse fibroblast interferon, lack antiviral and antigrowth response to mouse type I interferon [Gresser, I., Bandu, H.T. & Brouty-Boyé, D. (1974) J. Natl. Cancer Inst. 52, 553-559]. However, these cells display the same sensitivity toward type II interferon as do the parent L-1210S cells from which they were derived and respond equally well to its antiviral and antigrowth activities.

High-affinity binding of 125I-labelled mouse interferon to a specific cell surface receptor

Previous research suggests that interferon binds to the cell surface, possibly by attachment to gangliosides. A two-component receptor system consisting of binding and activation sites has been proposed. This hypothesis is supported by the finding that interferon inhibits binding of cholera toxin and thyrotropin to their receptors suggesting possible common receptor sites. Moreover, an antiserum against cell surface components of interferon-sensitive cells has been shown to inhibit the action of interferon. However, to understand the interaction of interferon with the cell surface requires direct ligand-binding studies. I present here direct evidence that high-affinity binding of interferon to a specific cell surface receptor is an initial step in interferon action using biologically active purified 125I-labelled mouse interferon. Labelled interferon binds specifically to interferon-sensitive mouse leukaemia L1210 cells, whereas binding to interferon-resistant L1210 cells is nonspecific. Furthermore, specific binding to monolayer cultures of mouse L929 cells is compared with nonspecific binding to chick embryo fibroblasts insensitive to the action of mouse interferon.

Interferon-treated cells release vesicular stomatitis virus particles lacking glycoprotein spikes: correlation with biochemical data

Earlier we reported a reduction to 1/30th-1/100th of the original number of infectious particles in the infectious vesicular stomatitis virus (VSV) released from L cells treated with 10 or 30 reference units of interferon per ml. However, in these cultures virus particle production, as measured by VSV particle-associated viral RNA, virus nucleocapsid protein, and viral transcriptase, was inhibited by less than 10%. Data reported in this paper show that there was a significant reduction in glycoprotein and membrane protein of VSV particles released from interferon-treated cells. Evidence supporting the deficiency of glycoprotein in VSV released from interferon-treated cells was derived from electron microscopic studies. Under conditions where glycoprotein spikes or projections were clearly detectable on the surface of VSV released from cells not treated with interferon, very few spikes were observed on VSV released from interferon-treated cells. These results suggested that interferon-treated cells produced VSV particles with low infectivity and that this low infectivity may be related to the reduced amount of glycoprotein and membrane protein incorporated into such particles.

Sendai virus receptor: proposed recognition structure based on binding to plastic-adsorbed gangliosides

The binding of Sendai virus to polystyrene petri dishes to which various gangliosides of defined structures had been adsorbed was determined. The ganglioside-bound virus was visualized either by a water vapor condensation method or by a hemadsorption method. By either assay, specific virus binding of high affinity was demonstrated to the gangliosides GT1a, GQ1b, and GPlc which have a common end sequence in the oligosaccharide moiety: NeuAc alpha 2 leads to 8NeuAc alpha 2 leads to 3Gal beta 1 leads to 3GalNAc leads to. Binding also occurred to the GD1a and GT1b gangliosides, which have the same end carbohydrate sequence except for the terminal N-acetylneuraminic acid, but the affinity was only 1-9% of that of the gangliosides with a terminal disialosyl linkage. It is proposed that the structure NeuAc alpha 2 leads to 8NeuAc alpha 2 leads to 3Gal beta 1 leads to 3GalNAc is the recognition-specific structure of the receptor for Sendai virus that is present on cell membrane gangliosides and possibly also glycoproteins. Binding tests to plastic-adsorbed glycolipids are suggested to be a useful tool for identification of the receptor recognition structure.

Laser-light scattering investigation of the micellar properties of gangliosides

The micellar properties of gangliosides in water solutions were investigated by quasielastic light scattering measurements. GM1 and GD1a gangliosides were isolated from calf brain, purified to more than 99% and dissolved in 0.025 M Tris--HCl buffer (pH 6.8) at 37 degrees C. The average intensity of scattered light and the intensity correlation function were measured by an apparatus including a 5145 A argon laser and a real-time digital correlator. The scattered intensity data allowed the derivation of an upper limit to the critical micelle concentration (c0) and the evaluation of the molecular weight (M) of the micelle. The intensity correlation function gave the diffusion coefficient D, and hence the hydrodynamic radius RH, and also contained information on the polydispersity of the sample. We find co less than 1 x 10(-6) M for both GM1 and GD1a, M = 532000 +/- 50000 and RH = 63.9 +/- 2 A for GM1, and M = 417000 +/- 40000 and RH = 59.5 +/- 2 A for GD1a. The mixture 3:1 of the two gangliosides gave intermediate values for all examined parameters. The presence of cations, within the physiological concentration range, and, in particular of Ca2+, did not influence significantly the values of co and the main features of the micelle.

Adsorption of interferon to homologous and heterologous cells. Brief report

Mouse and human interferons adsorbed well both to human and mouse cells. There was no difference in the recovering of homologous and heterologous interferons from the cells. Pretreatment of the cells with heterologous interferon did not prevent adsorption of subsequently applied homologous interferon and did not interfere with the antiviral activity of homologous interferon.

Selective inhibition of glycoprotein and membrane protein of vesicular stomatitis virus from interferon-treated cells

A 200-fold inhibition in the titer of infectious vesicular stomatitis virus (VSV) was produced in cultures of Ly cells treated with 30 reference units of interferon per milliliter. Virus particle production, as measured by VSV particle-associated transcriptase, or nucleocapsid protein was inhibited by a maximum of tenfold. The glycoprotein and membrane protein content was reduced in VSV derived from interferon-treated cells. Thus interferon-treated cells may have produced VSV particles with low infectivity, which may be related to the reduced amount of glycoprotein incorporated into such particles. These findings resemble those reported in interferon-treated cells infected with murine leukemia viruses.

Decreased sensitivity to interferon associated with in vitro transformation of X-ray-transformed C3H/10T1/2 cells

We have compared the interferon sensitivity of parental 10T1/2 cells, having a phenotype characteristic of normal cells, with that of transformed cells isolated after X-irradiation of treatment with methylcholanthrene. Transformed cells were 10- to 20-fold less sensitive than the parental untransformed cells to the antiviral action of interferon and were also less sensitive to the inhibitory effect of interferon on cell multiplication. The decreased sensitivity of these cells to interferon is a useful marker of the transformed phenotype.

Possible role for glycosphingolipids in the control of immune responses

Preparations of gangliosides from bovine brain contain material which acts as a strong mitogen on murine spleen cells. This material is highly lipophilic and co-purifies with the ganglioside fraction. It contains saccharides of a similar composition to those found in monosialogangliosides, as well as a spinogsine base and an appreciable amount of peptide. The common brain gangliosides GM1, GD1a and GD1b, on the other hand, are not mitogenic and act as suppressors of the mitogenic activity of bacterial lipopolysaccharide on murine spleen cells. Both the mitogenically active and suppressive fractions of bovine brain glycosphingolipid were found to act exclusively on B lymphocytes. Since gangliosides and related compounds are components of plasma membranes and of amphipathic nature, they may passively migrate between the lymphocyte subpopulations and thus act as physiological modulators of immune responses.

Membrane alterations following interferon treatment

Interferon treatment appears to induce a number of changes in the plasma membrane of uninfected cells. Interferon treatment altered the surface exposure of gangliosides of both Ly and KB cell membranes. The differences were found in the amount and pattern of incorporation of tritium after galactose oxidase treatment. In AKR,C- (AKR-2B) mouse cells, not only was there an apparent increase in the number of intramembranous particles in response to treatment with interferon but also the kinetics of the increase followed that of the establishment of the antiviral activity. The buoyant density of plasma membrane was also found to be significantly increased in interferon-treated cells. Moloney murine leukemia virus produced in interferon-treated mouse thymus and bone marrow cells had a high particle to infectivity ration. This virus contained a prominent glycoprotein with a molecular weight of about 85,000. This large glycoprotein was only a very minor component of Moloney leukemia virus produced in control TB cells and might be an uncleaved precursor to gp 69-71.

The effect of interferon on de novo infection of Moloney murine leukemia virus

The mode of action of interferon in de novo Moloney murine leukemia virus (Mo-MuLV) infection of mouse bone marrow/thymus (TB) cells was studied. Our results indicate that in interferon-treated cells, there is approximately a 2000 fold decrease in the production of infectious MuLV, but only a 10-20 fold decrease in the level of viral specific extracellular reverse transcriptase activity, and only about a 2 fold difference in the number of virus particles observed on the cell membrane as determined by scanning electron microscopic (SEM) studies. Transmission electron microscopic (TEM) studies showed that the proportion of early budding virions, which have shallow crescent-shaped ribonucleoprotein cores (Figure 3A), to virions in later stages of assembly (Figures 3B-3D) is relatively higher in interferon-treated cells than in the untreated controls. From a temperature shift-down experiment on a temperature-sensitive mutant of MuLV, ts 3, which produces viral particles that fail to dissociate from the cell surface at the nonpermissive temperature, we demonstrated that ts 3 virions partially assembled on the cell membrane prior to the addition of interferon are able to complete assembly and to dissociate from the cell membrane on temperature shift-down in the presence of interferon action. Our data suggest that interferon neither inhibits the late stages of virion assembly at which ts 3 virions are arrested at the nonpermissive temperature nor prevents release of the virions. Our findings also indicate that in interferon-treated cells, most of the extracellular virions are noninfectious.

Biosynthesis and function of gangliosides

Gangliosides are unique acidic glycolipids that are selectively concentrated in the plasma membrane of cells. Surface labeling studies have demonstrated that at least a portion of the oligosaccharde chain of gangliosides extends beyond the hydrophe) is imbedded in the membrane bilayer. It is becoming increasingly apparent that gangliosides participate in the internalization of environmental signals elicited by cholera toxin and glycoprotein hormones such as thyrotropic hormone and chorionic gonadotropin as well as other substances such as interferon and possibly serotonin. The mechanism by which cholera toxin binds to a specific ganglioside receptor on the celraction of trophic agents with gangliosides. We would predict that analyogous phenomena involving gangliosides will be discovered in brain. The biosynthesis of gangliosides proceeds by the ordered sequential addition of sugars to the lipid moiety. These reactions are catalyzed by a cluster of membrane-bound glycosyltransferases. Any alteration in the activity or specificity of one of these enzymes will result in a dramatic change in the ganglioside pattern of an afflicted cell or organ. The drastic consequences that accompany abnormalities of ganglioside synthesis have been documented in a heritable metabolic disorder in vivo and in tumorigenic transformation of cells in vitro. In this article, we have attempted to unify these observations and to provide a reasonable interpretation of the role of gangliosides in mediating cell surface phenomena.