Endogenous ganglioside GM1 modulates L-type calcium channel activity in N18 neuroblastoma cells

Digital imaging fluorescence microscopy was used to investigate the effect of the B subunit of cholera toxin on calcium homeostasis in neuroblastoma N18 cells. The B subunit, which binds specifically to ganglioside GM1 in the outer leaflet of the cell membrane, was found to induce a sustained increase of intracellular calcium concentration ([Ca2+]i). The increase in [Ca2+]i was not observed in the absence of extracellular calcium, or in the presence of the calcium chelator EGTA, and was blocked by nickel. The B subunit was also found to induce an influx of manganese ions, as indicated by a quench of the intracellular fura-2 fluorescence. These data suggest that the B subunit induces an increase in calcium influx in N18 cells. Potassium-induced depolarization also stimulated manganese influx; however, after the onset of depolarization-induced influx, the B subunit had no further effect. This occlusion suggests involvement of voltage-dependent calcium channels. Treatment with BayK8644, a dihydropyridine agonist selective for L-type calcium channels, induced manganese influx that was not altered by the B subunit and apparently blocked the effect of the B subunit itself. Furthermore, the dihydropyridine L-type channel antagonists niguldipine or nicardipine completely inhibited B subunit-induced manganese influx. Thus, the B subunit-induced manganese influx is likely due to activation of an L-type voltage-dependent calcium channel. Spontaneous influx of manganese ions was also inhibited by nicardipine or niguldipine and by exogenous gangliosides. Ganglioside GM1 was more potent than GM3, but globoside had no significant effect. The modulation of L-type calcium channels by endogenous ganglioside GM1 has important implications for its role in neural development, differentiation, and regeneration and also for its potential function in the electrical excitability of neurons.

Sulfate- and sialic acid-containing glycolipids inhibit DNA polymerase alpha activity

The effects of various glycolipids on the activity of immunoaffinity-purified calf thymus DNA polymerase alpha were studied in vitro. Preincubation with sialic acid-containing glycolipids, such as sialosylparagloboside (SPG), GM3, GM1, and GD1a, and sulfatide (cerebroside sulfate ester, CSE) dose-dependently inhibited the activity of DNA polymerase alpha, while other glycolipids, as well as free sphingosine and ceramide did not. About 50% inhibition was achieved by preincubating the enzyme with 2.5 microM of CSE, 50 microM of SPG or GM3, and 80 microM of GM1. Inhibition was noncompetitive with both the DNA template and the substrate dTTP, as well as with the other dNTPs. Since the inhibition was largely reversed by the addition of 0.05% Nonidet P40, these glycolipids may interact with the hydrophobic region of the enzyme protein. Apparently, the sulfate moiety in CSE and the sialic acid moiety in gangliosides were essential for the inhibition since neither neutral glycolipids (i.e., glucosylceramide, galactosylceramide, lactosylceramide) nor asialo-gangliosides (GA1 and GA2) showed any inhibitory effect. Furthermore, the ceramide backbone was also found to be necessary for maximal inhibition since the inhibition was largely abolished by substituting the lipid backbone with cholesterol. Increasing the number of sialic acid moieties per molecule further enhanced the inhibition, while elongating the sugar chain diminished it. It was clearly shown that the N-acetyl residue of the sialic acid moiety is particularly essential for inhibition by both SPG and GM3 because the loss of this residue or substitution with a glycolyl residue completely negated their inhibitory effect on DNA polymerase alpha activity.

GM3 directly inhibits tyrosine phosphorylation and de-N-acetyl-GM3 directly enhances serine phosphorylation of epidermal growth factor receptor, independently of receptor-receptor interaction

GM3 ganglioside (II3NeuAcLacCer) inhibits epidermal growth factor (EGF)-dependent receptor autophosphorylation and cell growth (Bremer, E.G., Schlessinger, J., and Hakomori, S. (1986) J. Biol. Chem. 261, 2434-2440), whereas de-N-acetyl-GM3 (deNAcGM3; II3NeuNH2Lac-Cer) promotes these processes (Hanai, N., Dohi, T., Nores, G. A., and Hakomori, S. (1988) J. Biol. Chem. 263, 6296-6301). Receptor-receptor interaction has been proposed as an essential initial mechanism for EGF-dependent activation of EGF receptor kinase (EGF-RK) (Schlessinger, J. (1988) Trends Biochem. Sci. 13, 443-447). We studied the effects of GM3 and deNAcGM3 on EGF-RK function and EGF-R dimerization, and observed that (i) EGF-dependent in vitro and in vivo (in situ) phosphorylation of A431 cells at both monomeric and dimeric forms of EGF-R was inhibited in a dose-dependent manner by GM3, but unaffected by GM1. (ii) Quantities of both forms of EGF-R remained constant regardless of addition of various quantities of GM3 or GM1, as revealed by blotting with antibodies directed to the C-terminal region of EGF-R, or by cell surface 125I-labeling followed by immunoprecipitation. (iii) DeNacGM3 in the absence as well as in the presence of a minimal quantity of detergent significantly enhanced EGF-R phosphorylation, particularly Ser phosphorylation. (iv) DeNAcGM3 was detected in a large variety of actively growing tumor cells. Findings i and ii above indicate that GM3 directly inhibits EGF-dependent Tyr phosphorylation but does not affect receptor-receptor interaction. Findings iii and iv suggest that deNAcGM3 strongly promotes serine phosphorylation (in addition to Tyr phosphorylation) of EGF-R and may function as a second messenger in the process of cell growth stimulation.

Assay for evaluation of rotavirus-cell interactions: identification of an enterocyte ganglioside fraction that mediates group A porcine rotavirus recognition

A virus-host cell-binding assay was developed and used to investigate specific binding between group A porcine rotavirus and MA-104 cells or porcine enterocytes. A variety of glycoconjugates and cellular components were screened for their ability to block rotavirus binding to cells. During these experiments a crude ganglioside mixture was observed to specifically block rotavirus binding. On the basis of these results, enterocytes were harvested from susceptible piglets and a polar lipid fraction was isolated by solvent extraction and partitioning. Throughout subsequent purification of this fraction by Sephadex partition, ion-exchange, silicic acid, and thin-layer chromatography, blocking activity behaved as a monosialoganglioside (GMX) that displayed a thin-layer chromatographic mobility between those of GM2 and GM3. The blocking activity of GMX was inhibited by treatment with neuraminidase and ceramide glycanase but not by treatment with protease or heat (100 degrees C). Further purification of GMX by high-pressure liquid chromatography resulted in the resolution of two monosialogangliosides, GMX and a band which comigrated with GM1 on thin-layer chromatography. These data suggest that a cell surface monosialoganglioside or family of monosialogangliosides may function as an in vivo relevant receptor for group A porcine rotavirus and that sialic acid is a required epitope for virus-binding activity.

Protein kinase C substrates and ganglioside inhibitors in bovine mammary nuclei

In cow mammary gland, unlike in other tissues, gangliosides (putative physiologic regulators of protein kinase C) may be distributed in nuclei and on the cell surface. This study was designed to determine whether gangliosides and the protein kinase C system (the enzyme and its substrate proteins) are present in cow mammary gland nuclei and to examine the effect of gangliosides detected in nuclei on protein phosphorylation catalyzed by protein kinase C. Gangliosides GM3, GD3, and GT1b were detected in the highly purified nuclear fraction. The nuclear ganglioside pattern was different from those of whole tissue and cytosol, thereby suggesting the presence of the gangliosides in nuclei. Protein kinase C and its substrate proteins (120, 97, 56, 43, 38, and 36 kDa) were extracted by Triton X-100 treatment of nuclei. Both protein kinase C activity (histone phosphorylation) and the nuclear substrate phosphorylation were effectively inhibited by the three gangliosides. Of the gangliosides, GT1b was the most potent in inhibiting phosphorylation, followed by GD3 and GM3. These results suggest that signal transduction mediated by protein kinase C in cow mammary gland nuclei may be regulated by gangliosides.

GM3 regulates protein kinase systems in cultured brain microvascular endothelial cells

The barrier function of endothelial cells is known to be positively regulated by protein kinase A (PKA) and negatively regulated by protein kinase C (PKC). We found that exogenously administered GM3(NeuAc) promoted PKA activity in cultured brain microvascular endothelial cells (BMECs). Other glycolipids, including GM1, sulfoglucuronyl paragloboside, and GM3(NeuGc), did not have any effect on the PKA activity of BMECs. PC12 cells did not respond to exogenously applied GM3(NeuAc). GM3(NeuAc) also suppressed the PKC activity of BMECs. Thus, GM3(NeuAc) may function as a modulator of blood-brain barrier function via the two different kinase systems.

Gangliosides stimulate synthesis of prostaglandin E2 and prostacyclin in fetal rat brain hemispheres after episodes of global intrauterine ischemia

The ability of brain preparations from 20-day-old rat fetuses to synthesize prostanoids in vitro before and after interruption of the maternal-fetal blood flow was examined using a radioimmunoassay technique. Synthesis of thromboxane B2 (TxB; the stable thromboxane A2 metabolite) decreased with increasing restriction time; conversely, it was elevated with reperfusion. Synthesis of 6-keto prostaglandin F1 alpha (PGF; the stable prostacyclin metabolite) and prostaglandin E2 (PGE) prostanoids remained unchanged after 20 min restriction and through a 2 hr reperfusion period. Intraperitoneal administration of GM1 (45 mg/kg) into the pregnant rat, 3 hr before restriction, stimulated synthesis of PGE and reduced synthesis of TxB. A prostanoid vasoactive index (PVI), which reflects the relative proportion of the three prostanoids synthesized and asserts the vasoactive potential of the brain tissue, was established. A rise in this value was attained after intrafetal administration into the peritoneal cavity of either GM1, GM3, or isopropyl-GM1 (AGF44) gangliosides, each given at 40 micrograms dose in 5 microliters volume, and N-dichloroacetyl-sphingosine (LIGA20; 15 micrograms/5 microliters) ganglioside analog, 1 hr before restriction. The effect was primarily due to an increase in the capacity of fetal brain tissue to synthesize PGE and, to a lesser extent PGF, vasodilating prostanoids. The N-methyl-D-aspartate (NMDA) receptor-blocker MK801 (6.6 micrograms/2 microliters) and the platelet activating factor (PAF) receptor antagonist BN52021 (0.1 mumol/2 microliters), given by the same route, effectively raised by 60-80% the vasodilating potential of the brain tissue following ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and characterization of N-parinaroyl analogs of ganglioside GM3 and de-N-acetyl GM3. Interactions with the EGF receptor kinase

A specific plasma membrane glycosphingolipid, known as ganglioside GM3, can regulate the intrinsic tyrosyl kinase activity of the epidermal growth factor (EGF) receptor; this modulation is not associated with alterations in hormone binding to the receptor. GM3 inhibits EGF receptor tyrosyl kinase activity in detergent micelles, in plasma membrane vesicles, and in whole cells. In addition, immunoaffinity-purified EGF receptor preparations contain ganglioside GM3 (Hanai et al. (1988) J. Biol. Chem. 263, 10915-10921), implying that the glycosphingolipid is intimately associated with the receptor kinase in cell membranes. Both the nature of this association and the molecular mechanism of kinase inhibition remain to be elucidated. In this report, we describe the synthesis of a fluorescent analog of ganglioside GM3, in which the native fatty acid was replaced with trans-parinaric acid. This glycosphingolipid inhibited the receptor kinase activity in a manner similar to that of the native ganglioside. A modified fluorescent glycosphingolipid, N-trans-parinaroyl de-N-acetyl ganglioside GM3, was also prepared. This analog, like the nonfluorescent de-N-acetyl ganglioside GM3, had no effect on receptor kinase activity. Results from tryptophan fluorescence quenching and steady-state anisotropy measurements in membranes containing these fluorescent probes and the human EGF receptor were consistent with the notion that GM3, but not de-N-acetyl GM3, interacts specifically with the receptor in intact membranes.

[Ganglioside GM3 from horse erythrocytes: structure and effect on cell proliferation]

An increase of the mouse fibroblast proliferation by ganglioside GM3 from equine erythrocytes is described. The structure of GM3 has been established on the basis of chemical methods, enzymatic degradation, GC-MS, as well as plasma desorption mass spectrometry and HPLC of 9-anthrylmethyl esters of gangliosides to characterize the long-chain base composition. The oligosaccharide moiety includes an N-glycolylneuraminic acid residue, whereas the main components of the lipid moiety are 20:1 sphingosine and 24:0 fatty acids.

Ganglioside GM3 inhibits the proliferation of cultured keratinocytes

Ganglioside GM3 is the predominant ganglioside of keratinocyte membranes. It has been proposed in other cell types that GM3 may participate in the regulation of cell proliferation. To examine the role of GM3 in keratinocyte proliferation, purified GM3 was added to cultured keratinocytes from normal foreskin, from lesional skin of patients with psoriasis and ichthyosis, and to cutaneous squamous carcinoma cell lines. Supplemental GM3 inhibited the growth of all cultured keratinocytes in a dose-dependent manner at concentrations of 10-100 microM. Keratinocytes from patients with psoriasis and ichthyosis were most sensitive to the inhibitory effects of GM3, and confluent undifferentiated keratinocytes were least sensitive. No change in differentiation was noted after addition of GM3. GD3, 9-0-acetyl-GD3, and GD1b also inhibited keratinocyte proliferation. Gangliosides GM1 and GD1a and sialic acid had little effect. Addition of 50 microM 3H-GM3 to cultured keratinocytes resulted in 1.7 times the amount of cellular GM3. These data suggest that hematoside (GM3) and "b" pathway gangliosides (GD3, GD1b), generated by the preferential activation of sialyltransferase II versus N-acetylgalactosaminyltransferase, may be involved in control of keratinocyte growth but not of differentiation.

Regulatory role of GM3 ganglioside in alpha 5 beta 1 integrin receptor for fibronectin-mediated adhesion of FUA169 cells

Mouse mammary carcinoma mutant cell line FUA169, characterized by high GM3 ganglioside content, was established from parent cell line FM3A/F28-7, which has high lactosyl ceramide (LacCer) content but no GM3. FUA169 displays no changes in protein glycosylation, and is a typical glycolipid mutant differing from its parent in that it contains high quantities of GM3 and GlcCer, but no LacCer (see accompanying paper; Tsuruoka, T., Tsuji, T., Nojiri, H., Holmes, E. H., Hakomori, S. (1993) J. Biol. Chem. 268, 2211-2216). In contrast to parent F28-7 cells, FUA169 cells showed clear adhesion to fibronectin (FN). Several lines of evidence indicate that adhesion of FUA169 cells to FN requires the presence of GM3, which supports the function of integrin receptor. (i) Both FUA169 and F28-7 cells express the same quantity of FN integrin receptor, which consists of alpha 5 beta 1 (sensitive to RGDS peptide) and alpha 4 beta 1 (sensitive to CS1 peptide). However, adhesion to FN-coated plates, regardless of type of FN, was much higher for FUA169 than for F28-7 cells. (ii) F28-7 cells, which normally lack GM3 and adhere only weakly to FN, acquired GM3 during incubation in GM3-containing medium, and subsequently adhered strongly to FN. (iii) Cholesterol-lecithin liposomes (cholesterol was 14C-labeled) incorporating alpha 5 beta 1 receptor isolated from human placenta showed clear adhesion to FN-coated plates, and this adhesion was completely inhibited by RGDS peptide and by anti-beta 1 mAb ZH1. When liposomes included a moderate quantity of GM3 (0.22-0.44 micrograms (0.2-0.4 nmol)/55 micrograms of phosphatidylcholine, 33 micrograms of cholesterol, 5 micrograms of alpha 5 beta 1 in liposome), adhesion was enhanced significantly. In contrast, adhesion was greatly reduced below control level for alpha 5 beta 1 liposomes containing a higher quantity (2.2 micrograms; > 2 nM) of GM3. Adhesion to FN was also inhibited, but never enhanced, for alpha 5 beta 1 liposomes with similar composition but containing 0.4 nmol (or other quantities) of LacCer or GlcCer instead of GM3. These findings suggest that the greater adhesion to FN by FUA169 cells, relative to parent F28-7 cells, is due to functional support by GM3 of alpha 5 beta 1 integrin receptor.

Characterization of the neutral pH-optimum sphingomyelinase from rat brain: inhibition by copper II and ganglioside GM3

A neutral pH-optimum sphingomyelinase (N-SMase), solubilized from rat brain membranes, was characterized with respect to metal and membrane lipid effects. Chromatofocusing chromatography, which separates proteins according to pI, showed two N-SMase activities. One eluted at pH 4.7 and the other required 0.4 M NaCl before elution. Kinetically, the two preparations appeared similar. The N-SMase eluting at pH 4.7 was most extensively studied here. Of the phospholipids studied, only phosphatidylserine showed any influence on N-SMase and that was to increase its activity by as much as 50%. Neither serine nor phosphatidic acid had any effect. Of the cations tested, none was able to replace Mg2+ as a required activator. However, it was found that several metals were inhibitory, with Cu2+ being most effective (IC50 = 5 microM). Gangliosides, particularly the monosialoganglioside, GM3 (IC50 approximately 50 microM), inhibited N-SMase. Other glycolipids showed little effect on activity, even the immediate precursor to GM3 - lactosylceramide. The ganglioside sugar, N-acetylneuraminic acid, also had no effect on N-SMase activity. None of these inhibitors affected the acidic pH-optimum sphingomyelinase. Other sphingolipid compounds such as ceramide - the enzymatic product - and sphingosylphosphorylcholine (lysosphingomyelin) showed no capacity to inhibit N-Smase, implying that the enzyme may have a selective substrate-binding site.

Full activation without calmodulin of calmodulin-dependent cyclic nucleotide phosphodiesterase by acidic glycosphingolipids: GM3, sialosylneolactotetraosylceramide and sulfatide

Among calmodulin-non-binding glycosphingolipids, GM3, sialosylneolactotetraosylceramide (LM1), and sulfatide potently activated calmodulin-dependent cyclic nucleotide phosphodiesterase with or without Ca2+ showing ED50 1-5 microM. In contrast to calmodulin-binding gangliosides, these glycosphingolipids activated the enzyme up to the maximum level achieved by Ca2+/calmodulin and did not inhibit the activity at higher concentrations. Competition studies with GD1b that bind both to calmodulin and the enzyme suggest that the calmodulin-non-binding glycosphingolipids activate the enzyme through interaction with the same site of the enzyme as GD1b interacts.

Angiogenesis can be stimulated or repressed in vivo by a change in GM3:GD3 ganglioside ratio

BACKGROUND

We had previously observed that rabbit cornea stimulated by an angiogenic factor 1) became richer in total gangliosides and 2) reduced the GM3:GD3 ganglioside ratio. Moreover, experimentally induced global enrichment of corneal gangliosides favors angiogenesis.

EXPERIMENTAL DESIGN

The objective of this work was to explain the possible relationship between angiogenic response and changes in the GM3:GD3 ratios observed in vivo. Cornea was utilized because it is avascular and transparent; i.e., the onset of opacity permitted exclusion of angiogenesis produced by a generic inflammatory response. Prostaglandin E1 or basic fibroblast growth factor were applied as angiogenesis triggers. Angiogenesis in vivo and mobilization and growth of microvascular endothelium in vitro were taken as parameters to indicate whether differences in GM3:GD3 ratios could modify the extent of the angiogenic response.

RESULTS

In vivo angiogenesis, whether prostaglandin E1 or basic fibroblast growth factor induced, was repressed by GM3 and enhanced by GD3 or GM1 enrichment of the cornea. In vitro growth and motility of microvascular endothelium were reduced by GM3 addition to the medium and returned to normal levels by addition of GD3.

CONCLUSIONS

Formation of new vessels induced by two different angiogenic factors could be stimulated or repressed in the cornea by reduction or enhancement of the GM3:GD3 ratio of tissue gangliosides. Changes in the relative proportion of molecules normally present in adult tissues, like prostaglandin E1, basic fibroblast growth factor, GM3, GD3, were sufficient to modulate or even block angiogenesis.

Alteration of the passive electrical properties of lymphocyte membranes induced by GM1 and GM3 glycolipids

The electrical conductivity of normal human lymphocyte suspensions has been measured in the frequency range from 10 kHz to 100 MHz, where a well-pronounced conductivity dispersion occurs, caused by the surface polarization at the interface between the cell membrane and the extracellular solution. We have investigated the alteration of the passive electrical properties of the cytoplasmatic cell membrane induced by two different gangliosides (GM1 and GM3) inserted, at various concentrations, into the outer leaflet of membrane double layer. The alterations observed in the dielectric parameters (the membrane conductivity and the membrane permittivity) derived on the basis of a 'double-shell' model, result in an overall increase of the ion permeation across the membrane and an enhanced polarizability of its hydrophilic region for both gangliosides investigated. The relevance of these alterations is discussed.

Regulatory role of GM3 ganglioside in integrin function, as evidenced by its effect on function of alpha 5 beta 1-liposomes: a preliminary note

Mouse mammary carcinoma mutant cell line FUA169, characterized by high GM3 ganglioside content, was established from parent cell line FM3A/F28-7, which has high LacCer content but no GM3. Although both cell lines showed the same quantity and quality of integrin receptors, FUA169 showed much stronger adhesion to fibronectin (FN)-coated plates than did F28-7. Liposomes containing phosphatidylcholine, cholesterol, alpha 5 beta 1, and a moderate amount of GM3 showed greatly enhanced adhesion to FN-coated plates, but adhesion of similar liposomes containing a large amount of GM3, or no GM3, was much lower. Our results suggest that GM3 regulates integrin receptor function essential for cell adhesion to FN.

Characteristics and regulation of ganglioside-induced elevation of free cytoplasmic Ca2+ in human blood platelets

We have found that gangliosides GD3 and GM3 induced rapid, reversible elevation of free cytoplasmic Ca2+ in fura-2-loaded human blood platelets. The effect persisted in Ca(2+)-free medium, indicating that gangliosides stimulated mobilization of intracellular stores. The action of gangliosides was concentration-dependent with EC50 of about 1 microM. The Ca(2+)-mobilizing effects of gangliosides were potentiated by epinephrine and inhibited by substances inducing activation of protein kinase C and cAMP-dependent protein kinases. Acidic phospholipids partially mimicked the Ca(2+)-mobilizing effects of gangliosides indicating that lipid head charge is essential for this activity. While the elevation of [Ca2+]i produced by arachidonic acid was almost completely blocked by aspirin pretreatment, the effects of gangliosides were diminished only 2-fold, indicating that gangliosides activate both aspirin-sensitive and aspirin-insensitive mechanisms of [Ca2+]i elevation.

Interaction of sialosyl cholesterol with the cell surface of rat astrocytes and its biological activities

The interaction between sialosyl cholesterol (alpha- or beta-D-N-acetyl neuraminyl cholesterol, alpha- or beta-SC) and the plasma membrane of astrocytes was investigated by the use of 14C-labeled alpha- or beta-SC. Both alpha- and beta-SC were dose-dependently and time-dependently bound to rat astrocytes. The Scatchard plot analyses showed that rat astrocytes bound apparently 9.69 x 10(9) molecules of both alpha-SC/cell (apparent Kd = 2.29 x 10(-5) M) and beta-SC/cell (apparent Kd = 5.39 x 10(-5) M) at 37 degrees C. Both the binding of alpha-SC to astrocytes and the subsequent inhibition of DNA synthesis were decreased at the low temperature (4 degrees C), and also suppressed by serum proteins including albumin. One molecule of bovine serum albumin (BSA) bound 2.3 molecules of alpha-SC with the slightly lower Kd-value (8.03 x 10(-6) M) than that for the binding site on astrocytes. BSA not only suppressed the alpha-SC-binding to astrocytes but also increased its release from the cells to the culture media. Gangliosides such as GM1 and GM3 unaffected the alpha-SC-binding, promoted the small release of alpha-SC from the cell surface, and inhibited the morphological changes of astrocytes induced by alpha-SC. The mechanism of alpha-SC-binding to cultured astrocytes with reference to the effects of serum or gangliosides is discussed.

Exogenous GM3 ganglioside stimulates process formation and glycoprotein release by cultured bovine oligodendrocytes

Isolated adult bovine oligodendrocytes maintained in vitro for 10 days were treated for 1 day with 50 micrograms/ml of GM3 ganglioside (NeuNac alpha 2-3Gal beta 1-4Glc beta 1-1'ceramide) in serum-free culture medium. The treated oligodendrocytes had significantly longer processes with more branching than control cells in the same medium without GM3. The treatment also stimulated the release of a series of 22-100-kDa, [3H]glucosamine-labeled glycoproteins into the culture medium. Treatment of oligodendrocytes maintained in vitro for 50 days with GM3 for 1 day resulted in a thickening of the processes and the appearance of many fine branches on existing processes as well as a similar stimulation of glycoprotein release into the medium.

Influence of ganglioside GM3 and its breakdown products on lymphoblastic transformation and T-suppressor activity

The influence of ganglioside GM3 and some of its breakdown products on phytohemagglutinin-induced blast transformation of human lymphocytes and concanavalin-A-induced T-suppressor activity was studied. The structures of two major hydrolysis products of GM3 were established by negative-ion fast-atom-bombardment mass spectrometry as neuraminyllactosylsphingosine (NeuLacSph) and neuraminyllactosylceramide (NeuLacCer). Both substances were shown to be potent inhibitors of mitogen-induced lymphoblastic transformation whereas their acetylation products NeuAcLacSphAc and GM3 did not affect the proliferative response of lymphocytes to phytohemagglutinin. On the other hand, only GM3 and NeuLacSph were able to enhance concanavalin-A-induced T-suppressor activity. On the basis of these data, it is suggested that the effects of GM3 and its breakdown products on lymphoblastic transformation and T-suppressor activity must rest on different mechanisms and that N-deacylation of GM3 appears to be an essential step in conversion of the ganglioside into an inhibitor of lymphocyte blast transformation.

Effects of gangliosides GM3 and De-N-acetyl GM3 on epidermal growth factor receptor kinase activity and cell growth

Previously it was reported (Bremer, E.G., Schlessinger, J., and Hakomori, S.-I. (1986) J. Biol. Chem. 261, 2434-2440) that ganglioside GM3 inhibited epidermal growth factor (EGF)-stimulated phosphorylation of the EGF receptor in Triton X-100-treated preparations of human epidermoid carcinoma (A431) cell membranes. In addition, these authors reported that GM3 inhibited the growth of A431 cells. In contrast, a modified ganglioside, de-N-acetyl GM3, enhanced the EGF-dependent tyrosine kinase activity of the EGF receptor. In this work and in subsequent studies (Hanai, N., Dohi, T., Nores, G. A., and Hakomori, S.-I. (1988) J. Biol. Chem. 263, 6296-6301), the tyrosine kinase activity of the receptor from A431 cell membranes was assayed in the presence of Triton X-100. In this report, we confirm that GM3 inhibited and de-N-acetyl GM3 stimulated EGF receptor autophosphorylation in the presence of Triton X-100. However, in the absence of detergents, ganglioside GM3 inhibited EGF-stimulated receptor autophosphorylation, whereas de-N-acetyl GM3 had no effect on EGF-stimulated receptor autophosphorylation. The effects of these gangliosides on receptor autophosphorylation were measured in both A431 cell plasma membranes and in 3T3 cell membranes permeabilized to [32P]ATP by a freeze-thaw procedure, in intact A431 cells permeabilized with alamethicin, and in intact A431 cells grown in the presence of [32P]orthophosphate. Thus, the inhibitory effect of GM3 on receptor autophosphorylation was demonstrated in the presence and in the absence of detergent; the stimulatory effect of de-N-acetyl GM3 was observed only in the presence of detergent. We also demonstrate that ganglioside GM3 inhibited EGF-stimulated growth of transfected murine fibroblasts (3T3) that express the gene for human EGF receptor (Velu, T. J., Beguinot, L., Vass, W. C., Zhang, K., Pastan, I., and Lowy, D. R. (1989) J. Cell. Biochem. 39, 153-166). De-N-acetyl ganglioside GM3 had no effect on the growth of these cells. Growth of control fibroblasts, which lack endogenous EGF receptors (Pruss, R. M., and Herschman, H. R. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 3918-3921), was not affected by the presence of either ganglioside. Similarly, ganglioside GM3, but not de-N-acetyl ganglioside GM3, inhibited the EGF-dependent incorporation of [3H]thymidine into DNA by transfected fibroblasts. Incorporation of labeled thymidine into DNA of control fibroblasts was not affected by the presence of either ganglioside. These studies indicate that ganglioside GM3, but not its deacetylated analogue, can affect EGF receptor kinase activity in intact membranes.(ABSTRACT TRUNCATED AT 400 WORDS)

Ganglioside GM3 stimulates the uptake and processing of low density lipoproteins by macrophages

Preincubation of low density lipoproteins (LDL) with low concentrations of the ganglioside GM3 (1-2x 10(-5) M/2.5 x 10(-6) M LDL-protein) results in an increase of LDL-uptake, enhances cholesterol accumulation and cholesteryl ester formation by macrophages. At the same time the lysosomal degradation of LDL in macrophages was inhibited under these conditions. These effects depended on the ganglioside structure and concentration. It is suggested that the effects observed could be caused by GM3-induced modification of LDL to a form that becomes recognized by macrophages.

Ganglioside GM3 can induce megakaryocytoid differentiation of human leukemia cell line K562 cells

The role of acidic glycosphingolipids in cell growth and differentiation was investigated using the multipotent leukemia cell line K562. When GM3 was added to cell culture media, the growth of K562 cells was remarkably inhibited and the cells were shown to have megakaryocytoid morphology. Ultrastructural study demonstrated that K562 cells treated with GM3 had platelet peroxidase-positive structures, which were considered to be the specific marker of megakaryocyte. Furthermore, AP-3 directed against an epitope present on membrane glycoprotein IIIa reacted with the GM3-treated cells. Free N-acetylneuraminic acid, GM1, GM2, GD1a, and a mixture of bovine brain gangliosides containing GD1a and GT1b did not affect growth of K562 cells or show morphological changes. According to chemical analyses, GM3 content increased in megakaryocytoid differentiation induced by tetradecanoylphorbol-13-acetate, whereas GM3 decreased in erythroid differentiation induced by hemin. Enzymatic analysis showed that the GM3 increase during megakaryocytoid differentiation was a result of the sialyltransferase activation. These results indicated that exogenous GM3 induced differentiation of K562 cells into a "GM3-rich" lineage, i.e., mainly megakaryocytoid lineage, and that GM3 accumulation in the GM3-rich lineage was the result of the activation of GM3 synthase. These findings strongly suggested that GM3 ganglioside, a minor membrane component, has a crucial role in not only the differentiation induction but also the determination of the differentiation direction in pluripotent K562 cells.

Nerve growth factor mediates monosialoganglioside-induced release of fibronectin and J1/tenascin from C6 glioma cells

C6 rat glioma cells incubated in serum-free medium with D-[14C]glucosamine secrete, on stimulation with nerve growth factor (NGF) or monosialogangliosides (MSGs), several glycoproteins (Gps), the most prominent of which are a 270-, 220-, and 69-kDa Gp. Several growth factors, hormones, phorbol ester, and disialo- and trisialogangliosides did not stimulate secretion. Western blot analysis of the conditioned medium from C6 cells stimulated with NGF or MSG identified one distinct band of approximately 220 kDa for fibronectin and J1/tenascin, which comigrated. Antiserum to NGF prevented NGF-stimulated release and also blocked MSG-evoked release. The 220-kDa band was labeled after pulse labeling with [35S]methionine in the presence of NGF, and by a 15-min chase period radioactively labeled J1/tenascin could be immunoprecipitated. Tunicamycin drastically inhibited almost completely release of the 220-kDa Gp labeled by D-[14C]glucosamine or [35S]methionine. These results extend the range of neurotrophic properties attributed to NGF to cells of glial origin and suggest that NGF regulates secretion of extracellular matrix proteins. MSG stimulation of fibronectin and J1/tenascin secretion may be mediated by NGF or an NGF-like molecule also secreted by the C6 glioma cells.

The influence of gangliosides on the hydrophilic pore edge line tension and monolayer fusion of lipid membranes

It is shown that inclusion of gangliosides into planar phospholipid bilayers leads to an essential suppression of their monolayer fusion. In contrast to phospholipid lysoforms, the gangliosides do not cause an associative decrease of the specific energy of the hydrophilic pore edge determined in the experiments on the electrical breakdown of membranes. This phenomenon depends on the effective size of the polar headgroup of the gangliosides. It is supposed that the effect of gangliosides on the parameters mentioned is based on the fact that they have large hydrated polar headgroups which create steric hindrances, which prevent (i) the membranes to come into contact during monolayer fusion; (ii) the gangliosides to take part in hydrophilic pore formation.