Synthesis, biological activity evaluation and mechanism analysis of new ganglioside GM3 derivatives as potential agents for nervous functional recovery

Neuronal regenerative ability is vital for the treatment of neurodegenerative diseases and neuronal injuries. Recent studies have revealed that Ganglioside GM3 and its derivatives may possess potential neuroprotective and neurite growth-promoting activities. Herein, six GM3 derivatives were synthesized and evaluated their potential neuroprotective effects and neurite outgrowth-promoting activities on a cellular model of Parkinson's disease and primary nerve cells. Amongst these derivatives, derivatives N-14 and 2C-12 demonstrated neuroprotective effects in the MPP + model in SH-SY5Y cells. 2C-12 combined with NGF (nerve growth factor) induced effecially neurite growth in primary nerve cells. Further action mechanism revealed that derivative 2C-12 exerts neuroprotective effects by regulating the Wnt signaling pathway, specifically involving the Wnt7b gene. Overall, this study establishes a foundation for further exploration and development of GM3 derivatives with neurotherapeutic potential.

Enhanced Anti-Atherosclerotic Efficacy of pH-Responsively Releasable Ganglioside GM3 Delivered by Reconstituted High-Density Lipoprotein

Recently, the atheroprotective role of endogenous GM3 and an atherogenesis-inhibiting effect of exogenous GM3 suggested a possibility of exogenous GM3 being recruited as an anti-atherosclerotic drug. This study seeks to endow exogenous GM3 with atherosclerotic targetability via reconstituted high-density lipoprotein (rHDL), an atherosclerotic targeting drug nanocarrier. Unloaded rHDL, rHDL loaded with exogenous GM3 at a low concentration (GM3_L-rHDL), and rHDL carrying GM3 at a relatively high concentration (GM3_H-rHDL) were prepared and characterized. The inhibitory effect of GM3-rHDL on lipid deposition in macrophages was confirmed, and GM3-rHDL did not affect the survival of red blood cells. In vivo experiments using ApoE^-/- mice fed a high fat diet further confirmed the anti-atherosclerotic efficacy of exogenous GM3 and demonstrated that GM3 packed in HDL nanoparticles (GM3-rHDL) has an enhanced anti-atherosclerotic efficacy and a reduced effective dose of GM3. Then, the macrophage- and atherosclerotic plaque-targeting abilities of GM3-rHD, most likely via the interaction of ApoA-I on GM3-rHDL with its receptors (e.g., SR-B1) on cells, were certified via a microsphere-based method and an aortic fragment-based method, respectively. Moreover, we found that solution acidification enhanced GM3 release from GM3-rHDL nanoparticles, implying the pH-responsive GM3 release when GM3-rHDL enters the acidic atherosclerotic plaques from the neutral blood. The rHDL-mediated atherosclerotic targetability and pH-responsive GM3 release of GM3-rHDL enhanced the anti-atherosclerotic efficacy of exogenous GM3. The development of the GM3-rHDL nanoparticle may help with the application of exogenous GM3 as a clinical drug. Moreover, the data imply that the GM3-rHDL nanoparticle has the potential of being recruited as a drug nanocarrier with atherosclerotic targetability and enhanced anti-atherosclerotic efficacy.

Synthesis and Evaluation of Liposomal Anti-GM3 Cancer Vaccine Candidates Covalently and Noncovalently Adjuvanted by αGalCer

GM3, a typical tumor-associated carbohydrate antigen, is considered as an important target for cancer vaccine development, but its low immunogenicity limits its application. αGalCer, an iNKT cell agonist, has been employed as an adjuvant via a unique immune mode. Herein, we prepared and investigated two types of antitumor vaccine candidates: (a) self-adjuvanting vaccine GM3-αGalCer by conjugating GM3 with αGalCer and (b) noncovalent vaccine GM3-lipid/αGalCer, in which GM3 is linked with lipid anchor and coassembled with αGalCer. This demonstrated that βGalCer is an exceptionally optimized lipid anchor, which enables the noncovalent vaccine candidate GM3-βGalCer/αGalCer to evoke a comparable antibody level to GM3-αGalCer. However, the antibodies induced by GM3-αGalCer are better at recognition B16F10 cancer cells and more effectively activate the complement system. Our study highlights the importance of vaccine constructs utilizing covalent or noncovalent assembly between αGalCer with carbohydrate antigens and choosing an appropriate lipid anchor for use in noncovalent vaccine formulation.

Effects of Gangliosides on Spermatozoa, Oocytes, and Preimplantation Embryos

Gangliosides are sialic acid-containing glycosphingolipids, which are the most abundant family of glycolipids in eukaryotes. Gangliosides have been suggested to be important lipid molecules required for the control of cellular procedures, such as cell differentiation, proliferation, and signaling. GD1a is expressed in interstitial cells during ovarian maturation in mice and exogenous GD1a is important to oocyte maturation, monospermic fertilization, and embryonic development. In this context, GM1 is known to influence signaling pathways in cells and is important in sperm-oocyte interactions and sperm maturation processes, such as capacitation. GM3 is expressed in the vertebrate oocyte cytoplasm, and exogenously added GM3 induces apoptosis and DNA injury during in vitro oocyte maturation and embryogenesis. As a consequence of this, ganglioside GT1b and GM1 decrease DNA fragmentation and act as H2O2 inhibitors on germ cells and preimplantation embryos. This review describes the functional roles of gangliosides in spermatozoa, oocytes, and early embryonic development.

[Effects of GM3 on proliferation, apoptosis and VEGF expression in human lung adenocarcinoma cell line A549 cells]

OBJECTIVE

To determine the effect of exogenous GM3 on proliferation, apoptosis and VEGF expression in human lung adenocarcinoma cell line A549 cells.

METHODS

A549 cells were treated with GM3 at different concentrations for 48 hours. MTT assay was used to detect the cell proliferation and flow cytometry was applied to analyze cell apoptosis. RT-PCR was used to detect the expression level of VEGF mRNA and confocal laser scanning microscopy was applied to observe the localization and fluorescence intensity of VEGF.

RESULTS

Comparing with the control, being treated with higher than 10 µmol/L GM3 significantly inhibited A549 cell proliferation (P < 0.05), and the suppressive effect could be enhanced following increasing doses. The IC(50) was 412 µmol/L. Comparing with the control, being treated with higher than 40 µmol/L GM3 significantly promoted the apoptotic rate of A549 cells (P < 0.05). Comparing with the control, being treated with higher than 40 µmol/L GM3 significantly decreased the VEGF mRNA level of A549 cells (P < 0.05), and the fluorescence intensity of VEGF distinctly weakened.

CONCLUSIONS

Exogenous ganglioside GM3 can inhibit the proliferation, promote apoptosis, and down-regulate the VEGF expression level in A549 cells. This may be considered as two mechanisms of GM3 for its anti-tumor effect by modulating cell apoptosis and angiogenesis.

Positive regulation of tumor necrosis factor-alpha by ganglioside GM3 through Akt in mouse melanoma B16 cells

GM3 has been shown to suppress TNFalpha expression in blood monocytes. However, we found that GM3 and TNFalpha were expressed in parallel in mouse melanoma B16 cells that were transfected with UDP-Gal:glucosylceramide beta-1,4-galactosyltransferase cDNA in a sense or antisense direction or CMP-NeuAc:lactosylceramide alpha-2,3-sialyltransferase siRNA. TNFalpha expression was increased by addition of GM3 to the B16 transfectants and decreased after treatment with D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, an inhibitor of glucosylceramide synthesis. These results clearly indicate that GM3 positively regulates TNFalpha expression in B16 cells. Phosphoinositide 3-kinase inhibitors, wortmannin and LY294,002, suppressed TNFalpha expression and Akt phosphorylation. GM3 was shown to increase phosphorylation of Akt in B16 cells and the B16-derived transfectants. Treatment of B16 cells with siRNA targeted to Akt1/2 resulted in TNFalpha suppression, indicating that Akt plays an important role in regulation of TNFalpha expression. Suppression of Akt1/2 rendered cells insensitive to GM3, suggesting that the GM3 signal may be transduced via Akt.

Gangliosides play an important role in the organization of CD82-enriched microdomains

Four-transmembrane-domain proteins of the tetraspanin superfamily are the organizers of specific microdomains at the membrane [TERMs (tetraspanin-enriched microdomains)] that incorporate various transmembrane receptors and modulate their activities. The structural aspects of the organization of TERM are poorly understood. In the present study, we investigated the role of gangliosides in the assembly and stability of TERM. We demonstrated that inhibition of the glycosphingolipid biosynthetic pathway with specific inhibitors of glucosylceramide synthase [NB-DGJ (N-butyldeoxygalactonojirimycin) and PPMP (D-threo-1-phenyl-2-hexadecanoylamino-3-morpholino-1-propanol.HCl)] resulted in specific weakening of the interactions involving tetraspanin CD82. Furthermore, ectopic expression of the plasma-membrane-bound sialidase Neu3 in mammary epithelial cells also affected stability of the complexes containing CD82: its association with tetraspanin CD151 was decreased, but the association with EGFR [EGF (epidermal growth factor) receptor] was enhanced. The destabilization of the CD82-containing complexes upon ganglioside depletion correlated with the re-distribution of the proteins within plasma membrane. Importantly, depletion of gangliosides affected EGF-induced signalling only in the presence of CD82. Taken together, our results provide strong evidence that gangliosides play an important role in supporting the integrity of CD82-enriched microdomains. Furthermore, these results demonstrate that the association between different tetraspanins in TERM is controlled by distinct mechanisms and identify Neu3 as a first physiological regulator of the integrity of these microdomains.

Inhibition of influenza-virus-induced cytopathy by sialylglycoconjugates

The anti-viral activity of gangliosides such as SPG (sialylparagloboside), GD1a, GM3, and GM4 was assessed by inhibition of the cytopathy of MDCK cells due to infection with the influenza virus A/PR/8/34. The inhibitory effect was in the following sequence: SPG>GD1a>GM3>GM4. The IC50 of SPG and GD1a was 7 and 70 microM, respectively, indicating that they are more effective than the representative inhibitor amantadine. Although 3'-sialyllactose (3'-SL) and 3'-sialyllactosamine (3'-SLN), which are identical to the terminal trisaccharides of GM3 and SPG, respectively, did not show any inhibitory effect, introduction of an amino group to the reducing end of 3'-SL following amidation with lauroyl chloride gave the inhibitory potency, which was comparable to that of GM3. These results suggest that the viral hemagglutinin recognizes exogenous sialyloligosaccharides rather than inherent sialyloligosaccharides expressed on MDCK cells, since introduction of the hydrophobic moiety to oligosaccharides might cause micelle formation.

Melanoma-derived gangliosides impair migratory and antigen-presenting function of human epidermal Langerhans cells and induce their apoptosis

Gangliosides are ubiquitous, membrane-associated, glycosphingolipids, the composition and production of which is altered in many tumour cells. They have been shown to inhibit the in vitro generation and differentiation of dendritic cells (DCs) from progenitors, but their effect on human tissue-residing DCs is yet to be investigated. In the present study, we analysed the effect of GM3 and GD3 gangliosides purified from human melanoma tumours on the phenotypic and functional maturation of human epidermal Langerhans cells (LCs), the first immune barrier against the tumour cells. We showed that both gangliosides impaired spontaneous LC maturation induced by a short in vitro culture, as assessed by significant down-regulation of co-stimulation (CD40, CD54, CD80, CD86) and maturation markers (CD83, CCR7), which correlated to an impaired ability of the cells to mount allogeneic T cell proliferation. Furthermore, the ganglioside-treated cells displayed less ability to migrate towards CCL19/macrophage inflammatory protein 3 beta, the chemokine that specifically binds CCR7 and mediates LC migration to lymph nodes. Lastly, we showed that both GM3 and GD3 gangliosides enhance LC spontaneous apoptosis. Globally, these in vitro results might explain, at least in part, the altered number and distribution of LCs in melanoma-bearing patients. They underscore a new mechanism for gangliosides to impede the host immune response by inducing LC dysfunction in the tumour microenvironment.

Ganglioside GM3 modulates tumor suppressor PTEN-mediated cell cycle progression--transcriptional induction of p21(WAF1) and p27(kip1) by inhibition of PI-3K/AKT pathway

The simple ganglioside GM3 has been shown to have anti-proliferative effects in several in vitro and in vivo cancer models. Although the exogenous ganglioside GM3 has an inhibitory effect on cancer cell proliferation, the exact mechanism by which it prevents cell proliferation remains unclear. Previous studies showed that MDM2 is an oncoprotein that controls tumorigenesis through both p53-dependent and p53-independent mechanisms, and tumor suppressor phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a dual-specificity phosphatase that antagonizes phosphatidylinositol 3-kinase (PI-3K)/AKT signaling, is capable of blocking MDM2 nuclear translocation and destabilizing the MDM2 protein. Results from our current study show that GM3 treatment dramatically increases cyclin-dependent kinase (CDK) inhibitor (CKI) p21(WAF1) expression through the accumulation of p53 protein by the PTEN-mediated inhibition of the PI-3K/AKT/MDM2 survival signaling in HCT116 colon cancer cells. Moreover, the data herein clearly show that ganglioside GM3 induces p53-dependent transcriptional activity of p21(WAF1), as evidenced by the p21(WAF1) promoter-driven luciferase reporter plasmid (full-length p21(WAF1) promoter and a construct lacking the p53-binding sites). Additionally, ganglioside GM3 enhances expression of CKI p27(kip1) through the PTEN-mediated inhibition of the PI-3K/AKT signaling. Furthermore, the down-regulation of the cyclin E and CDK2 was clearly observed in GM3-treated HCT116 cells, but the down-regulation of cyclin D1 and CDK4 was not. On the contrary, suppression of PTEN levels by RNA interference restores the enhanced expression of p53-dependent p21(WAF1) and p53-independent p27(kip1) through inactivating the effect of PTEN on PI-3K/AKT signaling modulated by ganglioside GM3. These results suggest that ganglioside GM3-stimulated PTEN expression modulates cell cycle regulatory proteins, thus inhibiting cell growth. We conclude that ganglioside GM3 represents a modulator of cancer cell proliferation and may have potential for use in colorectal cancer therapy.

Ganglioside GM3 inhibits proliferation and invasion of glioma

GM3, the simplest ganglioside, modulates cell adhesion, proliferation and differentiation in the central nervous system and exogenously added GM3 regulates cell-cell and cell-extracellular matrix adhesion and induces apoptosis. To assess the anti-tumor action of exogenous GM3, we examined its effect on the proliferation and invasion of glioma cells. Its inhibitory effect on cell proliferation was demonstrated in vitro by 3-(4,5-dimethyl-2-thiazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) assay and in vitro in rats with meningeal gliomatosis whose survival was significantly prolonged by the intrathecal injection of GM3. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) assay revealed that GM3 induced glioma cell apoptosis in vitro and in vitro. In rat brain slice cultures, GM3 suppressed the invasion of glioma cells; this effect manifested earlier than the inhibition of cell proliferation and before apoptosis induction. Our results suggest exogenous GM3 as a potential therapeutic agent in patients with glioma requiring adjuvant therapy.

Milk-Derived GM3 and GD3 Differentially Inhibit Dendritic Cell Maturation and Effector Functionalities

Gangliosides are complex glycosphingolipids, which exert immune-modulating effects on various cell types. Ganglioside GD(3) and GM(3) are the predominant gangliosides of human breast milk but during the early phase of lactation, the content of GD(3) decreases while GM(3) increases. The biological value of gangliosides in breast milk has yet to be elucidated but when milk is ingested, dietary gangliosides might conceptually affect immune cells, such as dendritic cells (DCs). In this study, we address the in vitro effect of GD(3) and GM(3) on DC effector functionalities. Treatment of bone marrow-derived DCs with GD(3) before lipopolysaccharide-induced maturation decreased the production of interleukin-6 (IL-6), IL-10, IL-12 and tumor necrosis factor-alpha as well as reduced the alloreactivity in mixed leucocyte reaction (MLR). In contrast, only IL-10 and IL-12 productions were significantly inhibited by GM(3,) and the potency of DCs to activate CD4(+) cells in MLR was unaffected by GM(3). However, both gangliosides suppressed expression of CD40, CD80, CD86 and major histocompatibility complex class II on DCs. Because GD(3) overall inhibits DC functionalities more than GM(3), the immune modulating effect of the ganglioside fraction of breast milk might be more prominent in the commencement of lactation during which the milk contains the most GD(3).

Elevated expression of GM3 in receptor-bearing targets confers resistance to human immunodeficiency virus type 1 fusion

GM3, a major ganglioside of T lymphocytes, promotes human immunodeficiency virus type 1 (HIV-1) entry via interactions with HIV-1 receptors and the viral envelope glycoprotein (Env). Increased GM3 levels in T lymphocytes and the appearance of anti-GM3 antibodies in AIDS patients have been reported earlier. In this study, we investigated the effect of GM3 regulation on HIV-1 entry by utilizing a mouse cell line (B16F10), which expresses exceptionally high levels of GM3. Strikingly, B16 cells bearing CD4, CXCR4, and/or CCR5 were highly resistant to CD4-dependent HIV-1 Env-mediated membrane fusion. In contrast, these targets supported membrane fusion mediated by CD4-requiring HIV-2, SIV, and CD4-independent HIV-1 Envs. Coreceptor function was not impaired by GM3 overexpression as indicated by Ca(2+) fluxes mediated by the CXCR4 ligand SDF-1alpha and the CCR5 ligand MIP-1beta. Reduction in GM3 levels of B16 target cells resulted in a significant recovery of CD4-dependent HIV-1 Env-mediated fusion. We propose that GM3 in the plasma membrane blocks HIV-1 Env-mediated fusion by interfering with the lateral association of HIV-1 receptors. Our findings offer a novel mechanism of interplay between membrane lipids and receptors by which host cells may escape viral infections.

GM3 content modulates the EGF-activated p185c-neu levels, but not those of the constitutively activated oncoprotein p185neu

The functional relationship between ganglioside GM(3) and two tyrosine-kinase receptors, the normal protein p185(c-neu) and the mutant oncogenic protein p185(neu), was examined in HC11 cells and in MG1361 cells, respectively. In the former, p185(c-neu) expression and activation are controlled by EGF addition to the culture medium and by epidermal growth factor receptor (EGFR) activity, whereas the latter express unchangingly high levels of constitutively activated p185(neu). Studies were carried out using (+/-)-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol hydrochloride ([D]-PDMP), which inhibits ganglioside biosynthesis resulting in ganglioside depletion, and addition of exogenous GM(3) to the culture medium. In HC11 cells treated with only [D]-PDMP, p185(c-neu) levels remain similar to control cells, whereas levels of tyrosine-phosphorylated p185(c-neu) increase after treatment with [D]-PDMP in combination with EGF. When exogenous GM(3) is added in combination with [D]-PDMP and EGF, the enhanced phosphorylated-p185(c-neu) returns to control levels. Interestingly, EGFR levels also vary and, analogously to phosphorylated-p185(c-neu), the increase of EGFR content consequent to the [D]-PDMP and EGF addition is reversed by exogenous GM(3). In contrast, the addition of neither [D]-PDMP nor exogenous GM(3) modifies expression and tyrosine-phosphorylation levels of p185(neu) in MG1361 cells. These findings indicate that changes in GM(3) content modulate the tyrosine-phosphorylated p185(c-neu) levels in a reversible manner, but this is not specific for p185(c-neu) because EGFR levels are also modified. Furthermore, these data suggest that GM(3) may play a functional role by affecting the internalisation pathway of p185(c-neu)/EGFR heterodimers, but not of p185(neu) homodimers.

Ganglioside GM3 inhibits matrix metalloproteinase-9 activation and disrupts its association with integrin

Gangliosides GM3 and GT1b both inhibit epithelial cell adhesion and migration on fibronectin. GT1b binds to integrin alpha5beta1 and blocks the integrin-fibronectin interaction; GM3 does not interact with integrin, and its effect is poorly understood. We evaluated the effects of endogenous modulation of GM3 expression on epithelial cell motility on several matrices and the mechanism of these effects. Endogenous accumulation of GM3 decreased cell migration on fibronectin, types I, IV, and VII collagen matrices; depletion of GM3 dramatically increased cell migration, regardless of matrix. GM3 overexpression and depletion in vitro correlated inversely with the expression and activity of matrix metalloproteinase-9; consistently, the cell migration stimulated by GM3 depletion is reversed by inhibition of matrix metalloproteinase-9 activity. Accumulation and depletion of GM3 in epithelial cells grown on fibronectin also correlated inversely with epidermal growth factor receptor and mitogen activated protein kinase phosphorylation and with Jun expression. Ganglioside depletion facilitated the co-immunoprecipitation of matrix metal-loproteinase-9 and integrin alpha5beta1, while endogenous accumulation of GM3, but not GT1b, blocked the co-immunoprecipitation. These data suggest modulation of epidermal growth factor receptor signaling and dissociation of integrin/matrix metalloproteinase-9 as mechanisms for the GM3-induced effects on matrix metalloproteinase-9 function.

Role of cell surface GM3 ganglioside and sialic acid in the antitumor activity of a GM3-based vaccine in the murine B16 melanoma model

PURPOSE

To examine the role of GM3 monosialoganglioside and sialic acid in the antitumor activity of a vaccine based on GM3, hydrophobically conjugated with the outer-membrane-protein complex from Neisseria meningitidis (GM3/VSSP).

METHODS

In order to evaluate the relationship between antitumor activity and the presence of GM3 on the surface of tumor cells, we used two murine tumor cell lines with different ganglioside expression. Syngeneic mice were immunized with four i.m. doses of GM3/VSSP (120 micro g) at 14-day intervals and challenged subcutaneously with tumor cells.

RESULTS

B16 melanoma cells showed GM3 on cell surface and GM3-dependent in vitro growth. As expected, preimmunization with the vaccine significantly inhibited tumor formation and prolonged survival in mice challenged with B16 cells. In contrast, no antitumor effect was observed in mice challenged with GM3-negative F3II mammary carcinoma cells. The reactivity of sera from immunized mice against B16 cells was confirmed by flow cytometry and immunoperoxidase staining. Depletion of sialic acid residues from the cell surface completely abolished antibody response against melanoma cells.

CONCLUSIONS

These results indicate that the antitumor activity of GM3/VSSP is associated with GM3 expression on tumor cell surface and demonstrate a major role of sialic acid in the humoral response of vaccinated mice.

Inhibition of human neuroblastoma cell proliferation and EGF receptor phosphorylation by gangliosides GM1, GM3, GD1A and GT1B

The inhibitory action of gangliosides GT1B, GD1A, GM3 and GM1 on cell proliferation and epidermal growth factor receptor (EGFR) phosphorylation was determined in the N-myc amplified human neuroblastoma cell line NBL-W. The IC50 of each ganglioside was estimated from concentration-response regressions generated by incubating NBL-W cells with incremental concentrations (5-1000 microm) of GT1B, GD1A, GM3 or GM1 for 4 days. Cell proliferation was quantitatively determined by a colourimetric assay using tetrazolium dye and spectrophotometric analysis, and EGFR phosphorylation by densitometry of Western blots. All gangliosides assayed, with the exception of GM1, inhibited NBL-W cell proliferation in a concentration-dependent manner. The IC50s for gangliosides GT1B [molecular weight (MW) 2129], GM3 (MW 1236), and GD1A (MW 1838) were (mean +/- SEM) 117 +/- 26, 255 +/- 29, and 425 +/- 44 m, respectively. In contrast, the IC50 for GM1 (MW 1547) could not be determined. Incubation of NBL-W cells with epidermal growth factor (EGF) concentrations ranging from 0.1 to 1000 ng/ml progressively increased cell proliferation rate, but it plateaued at concentrations above 10 ng/ml. EGFR tyrosine phosphorylation, however, was incrementally stimulated by EGF concentrations from 1 to 100 ng/ml. The suppression of EGF-induced EGFR phosphorylation differed for each ganglioside, and their respective inhibitory potencies were as follows: EGFR phosphorylation [area under curve (+ EGF)/area under curve (- EGF)]: control (no ganglioside added) = 8.2; GM1 = 8.3; GD1A = 6.7; GM3 = 4.87, and GT1B = 4.09. The lower the ratio, the greater the inhibitory activity of the ganglioside. Gangliosides GD1A and GT1B, which have terminal N-acetyl neuraminic acid moieties, as well as one and two N-acetyl neuraminic acid residues linked to the internal galactose, respectively, both inhibited cell proliferation and EGFR phosphorylation. However, GD1A was a more potent suppressor of cell proliferation and GT1B most effective against EGFR phosphorylation. GM3, which only has a terminal N-acetyl neuraminic acid, inhibited cell proliferation and EGFR phosphorylation almost equivalently. These data suggest that gangliosides differ in their potency as inhibitors of NBL-W neuroblastoma cell proliferation and EGFR tyrosine phosphorylation, and that perturbations in the differential expression of membrane glycosphingolipids may play a role in modulating neuroblastoma growth.

Ganglioside GM3 participates in the pathological conditions of insulin resistance

Gangliosides are known as modulators of transmembrane signaling by regulating various receptor functions. We have found that insulin resistance induced by tumor necrosis factor-alpha (TNF-alpha) in 3T3-L1 adipocytes was accompanied by increased GM3 ganglioside expression caused by elevating GM3 synthase activity and its mRNA. We also demonstrated that TNF-alpha simultaneously produced insulin resistance by uncoupling insulin receptor activity toward insulin receptor substrate-1 (IRS-1) and suppressing insulin-sensitive glucose transport. Pharmacological depletion of GM3 in adipocytes by an inhibitor of glucosylceramide synthase prevented the TNF-alpha-induced defect in insulin-dependent tyrosine phosphorylation of IRS-1 and also counteracted the TNF-alpha-induced serine phosphorylation of IRS-1. Moreover, when the adipocytes were incubated with exogenous GM3, suppression of tyrosine phosphorylation of insulin receptor and IRS-1 and glucose uptake in response to insulin stimulation was observed, demonstrating that GM3 itself is able to mimic the effects of TNF on insulin signaling. We used the obese Zucker fa/fa rat and ob/ob mouse, which are known to overproduce TNF-alpha mRNA in adipose tissues, as typical models of insulin resistance. We found that the levels of GM3 synthase mRNA in adipose tissues of these animals were significantly higher than in their lean counterparts. Taken together, the increased synthesis of cellular GM3 by TNF may participate in the pathological conditions of insulin resistance in type 2 diabetes.

Gangliosides GM1 and GM2 induce vascular smooth muscle cell proliferation via extracellular signal-regulated kinase 1/2 pathway

Gangliosides, sialic acid-containing glycophospholipids, accumulate in atherosclerotic vessels and appear to regulate the proliferation of various cell types. Furthermore, vascular smooth muscle cell (VSMC) proliferation is associated with the development and progression of cardiovascular diseases. To demonstrate whether gangliosides are able to modulate the VSMC growth, the effect of gangliosides GM1, GM2, and GM3 on cell DNA synthesis and cell number has been examined. Moreover, we investigated possible intracellular mechanisms by which GM1 and GM2 elicit their mitogenic effects. Stimulation of VSMCs with GM1 and GM2 resulted in a dose-dependent increase in DNA synthesis and cell number, whereas GM3 caused a decrease in DNA synthesis. GM1 and GM2 (50 micromol/L) stimulate phosphorylation of extracellular signal-regulated kinases (ERKs) 1 and 2 and phosphorylation of the c-Jun N-terminal kinase (JNK), with a maximum at 15 minutes, but they do not have an effect on the phosphorylation of p38 mitogen-activated protein kinase (MAPK). GM3 (50 micromol/L), on the other hand, does not stimulate any of the 3 aforementioned MAPKs. Pretreatment of the cells with 20 micromol/L PD 098,059 caused a complete inhibition of ERK1/2 and JNK MAPK, whereas pretreatment with a Ras (farnesyl transferase) inhibitor did not abrogate the GM1- and GM2-induced ERK1/2 phosphorylation. Furthermore, GM1 and GM2 did not activate Raf-1 kinase. Interestingly, pretreatment of VSMCs with 100 nmol/L pertussis toxin resulted in a complete inhibition of the ERK1/2 phosphorylation. Finally, the GM1- and GM2-induced increase in cell number was significantly inhibited by PD 098,059. We may conclude that GM1 and GM2 stimulate ERK1/2 via a pertussis toxin-sensitive G(i)-coupled receptor through a Raf-1 kinase-independent pathway. Moreover, the GM1- and GM2-induced VSMC growth is ERK1/2 dependent.

GM3 ganglioside inhibits endothelin-1-mediated signal transduction in C6 glioma cells

We found that sparse and confluent C6 glioma cells differ both in GM3 content, which increases with cell density, and in endothelin-1 (ET-1)-induced phosphoinositide hydrolysis, which was markedly higher in the sparse cells than in the confluent. Also after manipulation of the cellular GM3 content through treatment with exogenous GM3 or with drugs known to affect GM3 metabolism, the ET-1 effect was inversely related to GM3 cellular levels. Cell treatment with an anti-GM3 mAb resulted in the enhancement of ET-1-induced phospholipase C activation and restored the capacity of GM3-treated cells to respond to ET-1. These findings suggest that the GM3 ganglioside represents a physiological modulator of ET-1 signaling in glial cells.

GM3 Ganglioside Inhibits CD9-Facilitated Haptotactic Cell Motility: Coexpression of GM3 and CD9 Is Essential in the Downregulation of Tumor Cell Motility and Malignancy†

A cooperative inhibitory effect of GM3, together with CD9, on haptotactic cell motility was demonstrated by a few lines of study as described below. (i) Haptotactic motility of colorectal carcinoma cell lines SW480, SW620, and HRT18, which express CD9 at a high level, is inhibited by exogenous GM3, but not by GM1. (ii) Motility of gastric cancer cell line MKN74, which expresses CD9 at a low level, was not affected by exogenous GM3. Its motility became susceptible to and inhibited by exogenous GM3, but not GM1, when the CD9 level of MKN74 cells was converted to a high level by transfection with CD9 cDNA. Findings i and ii suggest that haptotactic tumor cell motility is cooperatively inhibited by coexpression of CD9 and GM3. (iii) This possibility was further demonstrated using cell line ldlD 14, and its derivative expressing CD9 through transfection of its gene (termed ldlD/CD9). Both of these cell lines are defective in UDP-Gal 4-epimerase and cannot synthesize GM3 unless cultured in the presence of galactose (Gal(+)), whereas GM3 synthesis does not occur when cells are cultured in the absence of Gal (Gal(-)). Haptotactic motility of parental ldlD cells is low, and shows no difference in the presence and absence of Gal. In contrast, the motility of ldlD/CD9 cells is very high in Gal(-) whereby endogenous GM3 synthesis does not occur, and is very reduced in Gal(+) whereby endogenous GM3 synthesis occurs. (iv) Photoactivatable (3)H-labeled GM3 added to HRT18 cells, followed by UV irradiation, causes cross-linking of GM3 to CD9, as evidenced by (3)H labeling of CD9, which is immunoprecipitated with anti-CD9 antibody. These findings suggest that CD9 is a target molecule interacting with GM3, and that CD9 and GM3 cooperatively downregulate tumor cell motility.

Selective cell-cycle arrest and induction of apoptosis in proliferating neural cells by ganglioside GM3

Control of cell proliferation and cell survival is critical during development of the vertebrate central nervous system (CNS). Much of the cell death seen during early stages of CNS development occurs through apoptosis; however, the factors that induce this early apoptosis are not clearly understood. Gangliosides, sialylated glycosphingolipids, are expressed in the CNS and have been proposed to regulate cell growth and differentiation. Here we show that the simple ganglioside GM3 selectively inhibits the proliferation of and induces apoptosis of actively dividing astrocyte precursors and other neural progenitors. The inhibition of astrocyte precursor proliferation by GM3 appears to be mediated in part by the cyclin-dependent kinase (Cdk) inhibitor p27(Kip1). During neonatal development there is extensive cell proliferation and little apoptosis in the ventricular and subventricular zones of the CNS. This proliferation was dramatically inhibited and the degree of apoptosis dramatically increased following intraventricular administration of GM3. These data suggest that GM3, a simple ganglioside, may regulate cell proliferation and death in the CNS and as such may have potential for brain tumor therapy.

GM3 as a novel growth regulator for human gliomas

The simple ganglioside GM3 inhibits proliferation and induces apoptosis in proliferating immature rodent CNS cells. To determine whether GM3 influenced the expansion of human neural tumors the effects of GM3 treatment on primary human brain tumors were assayed. Here we demonstrate that GM3 treatment dramatically reduces cell numbers in primary cultures of high-grade human glioblastoma multiforme (GBM) tumors and the rat 9L cell gliosarcoma cell line. By contrast, GM3 treatment had little effect on cell number in cultures of normal human brain. A single injection of GM3 3 days after intracranial implantation of 9L tumor cells in a murine xenograft model system resulted in a significant increase in the symptom-free survival period of host animals. The effects of GM3 were not restricted to GBMs and 9L cells. Cultures of high-grade ependymomas, mixed gliomas, astrocytomas, oligodendrogliomas, and gangliogliomas were all susceptible to GM3 treatment. These results suggest that GM3 may have considerable value as a selectively toxic chemotherapeutic agent for human high-grade gliomas.

Ganglioside control over IL-4 priming and cytokine production in activated T cells

Our previous studies have shown that the enzymatic activities of Neu-1, an endogenous sialidase encoded in the murine MHC, are involved in promoting IL-4 synthesis by naive CD4(+)T cells. Our present studies have characterized responsible sialoconjugate targets of Neu-1 and questioned possible biochemical mechanisms responsible for their regulatory influences on IL-4 gene expression. These studies determined that treatment of T cells with the naturally occurring ganglioside GM3 inhibited the production of IL-4 without affecting the production of IL-2. An analysis of IL-4-primed CD4(+)T cells further demonstrated that GM3 treatment specifically inhibited the restimulated production of IL-4, IL-5 and IL-13, without inhibiting the production of IL-2 and IFN-gamma. The inhibitory effects of GM3 could be overcome by treatment with thapsigargin or ionomycin, suggesting ganglioside regulation occurs upstream of activation-induced calcium mobilization. GM3 treatment attenuated the level of calcium influx following CD3epsilon crosslinking, and CD4(+)T cells from Neu-1-deficient B10.SM strain mice (neu-1(a)and IL-4-deficient) expressed reduced levels of intracellular calcium following activation. Our results indicate that activities by membrane gangliosides can influence the cytokine programs in CD4(+)T cells, possibly through the modulation of calcium responses induced by T cell activation.

Modulation of EGF receptor activity by changes in the GM3 content in a human epidermoid carcinoma cell line, A431

Gangliosides have been described as modulators of growth factor receptors. For example, GM3 addition in cell culture medium inhibits epidermal growth factor (EGF)-stimulated receptor autophosphorylation. Furthermore, depletion of ganglioside by sialidase gene transfection appeared to increase EGF receptor (EGFR) autophosphorylation. These data suggested that changes in GM3 content may result in different responses to EGF. In this study, the ceramide analog d-threo-1-phenyl-2-decannoylamino-3-morpholino-1-propanol ([D]-PDMP), which inhibits UDP-glucose-ceramide glucosyltransferase, and addition of GM3 to the culture medium were used to study the effects of GM3 on the EGFR. Addition of 10 microM [D]-PDMP to A431 cells resulted in significant GM3 depletion. Additionally, EGFR autophosphorylation was increased after EGF stimulation. When exogenous GM3 was added in combination with [D]-PDMP, the enhanced EGFR autophosphorylation was returned to control levels. [D]-PDMP also increased EGF-induced cell proliferation, consistent with its effect on autophosphorylation. Once again, the addition of GM3 in combination with [D]-PDMP reversed these effects. These results indicate that growth factor receptor functions can be modulated by the level of ganglioside expression in cell lines. Addition of GM3 inhibits EGFR activity and decrease of GM3 levels using [D]-PDMP treatment enhances EGFR activity. Modulation of growth factor receptor function may provide an explanation for how transformation-dependent ganglioside changes contribute to the transformed phenotype.

Mechanistic study of modulation of SR Ca2+-ATPpase activity by gangliosides GM1 and GM3 through some biophysical measurements

On the basis of confirming the antagonistic effects of GM1 and GM3 on the activity of Ca2+-ATPase, we further demonstrated that some of the components of these two gangliosides, including sialic acid (NeuNAc), asialo-GM1, asialo-GM3 and ceramide, failed to show any effects on the activity of Ca2+-ATPase. Thus it is apparent that the intact molecules of these two gangliosides with their specific conformations were needed to perform their effects on Ca2+-ATPase. From the fluorescence resonance energy transfer measurements, the energy transfer between Cys 670/674 and Lys 515 was decreased by GM1 and increased by GM3, indicating GM1 induced the conformation of the hydrophilic region of Ca2+-ATPase to be less compact, while GM3 induced it to be more compact. From the CD spectra measurements, GM1 and GM3 both reduced the content of alpha-helical structures of Ca2+-ATPase, but GM1 caused a stronger decrease than that of GM3. Using DPH as the probe, we found that the membrane lipid fluidity of the proteoliposomes containing Ca2+-ATPase was decreased by GM1 and tend to increase by GM3.

Immunosuppressive activity of glycosphingolipids. Influence of serum factors on ganglioside inhibition of IL-4-dependent cell proliferation

Gangliosides have been shown to inhibit proliferation of the interleukin-4 (IL-4) responsive cell line CT.4R. Kinetic analysis has revealed that ganglioside GT1b is a competitive inhibitor of proliferation, while GM and GM3 show a mixed pattern of inhibition, i.e., exhibit more than one inhibition type. Contribution of the competitive cell inhibition for GM1 and GM3 depends on serum factors added: the higher is the percentage of FCS, the larger is the contribution of competitive inhibition. The pattern of proliferation inhibition shown for GT1b does not depend on the FCS content. We have also studied the interaction of the recombinant IL-4 with fluorescent (anthrylvinyl-labelled) gangliosides GM1 and GM3 and lactosylceramide incorporated into liposomes. Dissociation constants of the IL-4-ganglioside complexes have been determined; lactosylceramide does not interact with rIL-4. The K(d) values for the lymphokine complexes with gangliosides support the conclusion based on the kinetic analysis that IL-4 has a higher affinity for GM3 (K(d) = 5 nM) than for GM1 (K(d) = 0.28 microM).

Commitment to apoptosis by GD3 ganglioside depends on opening of the mitochondrial permeability transition pore

We have studied the effects of GD3 ganglioside on mitochondrial function in isolated mitochondria and intact cells. In isolated mitochondria, GD3 ganglioside induces complex changes of respiration that depend on the substrate being oxidized. However, these effects are secondary to opening of the cyclosporin A-sensitive permeability transition pore and to the ensuing swelling and cytochrome c depletion rather than to an interaction with the respiratory chain complexes. By using a novel in situ assay based on the fluorescence changes of mitochondrially entrapped calcein (Petronilli, V., Miotto, G., Canton, M., Colonna, R., Bernardi, P., and Di Lisa, F. (1999) Biophys. J. 76, 725-734), we unequivocally show that GD3 ganglioside also induces the mitochondrial permeability transition in intact cells and that this event precedes apoptosis. The mitochondrial effects of GD3 ganglioside are selective, in that they cannot be mimicked by either GD1a or GM3 gangliosides, and they are fully sensitive to cyclosporin A, which inhibits both the mitochondrial permeability transition in situ and the onset of apoptosis induced by GD3 ganglioside. These results provide compelling evidence that opening of the permeability transition pore is causally related to apoptosis.

Sialic acid-containing components of lipoproteins influence lipoprotein-proteoglycan interactions

Sialic acid is a negatively charged sugar associated with the protein and lipid portions of lipoproteins. Sialic acid has been hypothesised to play an anti-atherogenic role in lipoprotein metabolism through the electrostatic inhibition of lipoprotein interactions with chondroitin-6-sulphate-rich arterial proteoglycans (APG). We conducted a series of studies using native and modified lipoproteins (VLDL1 Sf 60-400, VLDL2 Sf 20-60, IDL1 Sf 16-20, IDL2 Sf 12-16, LDL(A) Sf 8-12, and LDL(B) Sf0-8) that vary in their sialic acid content to examine the relationship between lipoprotein sialic acid content and its interaction with APG. Lipoprotein sialic acid was greatest in VLDL1 and decreased progressively with particle density until the IDL2 fraction (VLDL1 > VLDL2 > IDL1 > IDL2 = LDL(A) = LDL(B)). The pattern of reactivity of each fraction with APG was different from the pattern observed for lipoprotein sialic acid content (IDL2 > LDL(A) > LDL(B) > IDL1 > VLDL2 > VLDL1). Levels of sialic acid were lower in subjects with CHD as compared to control subjects but the presence of CHD had no effect on lipoprotein-APG complex formation when sex and plasma triglyceride levels were taken into account. There was also no significant relationship between the lipoprotein sialic acid content and the reactivity with APG within each lipoprotein fraction. Treatment of hypertriglyceridaemic subjects with ciprofibrate decreased lipoprotein-APG complex formation in all lipoprotein fractions. This was associated with a decrease in the total sialic acid content of apo B100-containing lipoproteins suggesting that the total sialic acid content of apo B100-containing lipoproteins has no influence on lipoprotein-APG complex formation. We next conducted in vitro experiments to manipulate LDL sialic acid content. Enzymatic removal of sialic acid from LDL with neuraminidase resulted in an increase in LDL-APG complex formation. This was accompanied by an increase in the exposure of free amino groups on LDL possibly due to disruption of interactions between free amino groups and sialic acid-containing components on LDL. Increasing LDL sialic acid content through incubation with ganglioside resulted in a decrease in lipoprotein-APG complex formation without any changes in the exposure of free amino groups on LDL. We conclude that total sialic acid content of lipoproteins is not a major determinant of their binding to APG. However, specific sialic acid-containing components on lipoproteins can affect their interaction with APG.

Gangliosides GD1a and GM3 induce interleukin-10 production by human T cells

Gangliosides are sialic acid-containing glycosphingolipids and exhibit various physiologic functions. Gangliosides GD1a and GM3 strongly induced interleukin-10 (IL-10) protein secretion and mRNA expression in T cells from normal human subjects while the other gangliosides were ineffective. IL-10 induction by both gangliosides was completely blocked by protein tyrosine kinase (PTK) inhibitors, herbimycin A, genistein, and tyrphostin AG 1288, but not by other signal transduction inhibitors. These results suggest that GD1a and GM3 may induce IL-10 production in T cells by regulating the PTK-dependent signaling pathway. These gangliosides may thus act as important immunoregulators via IL-10.

A novel mechanism of CD4 down-modulation induced by monosialoganglioside GM3. Involvement of serine phosphorylation and protein kinase c delta translocation

In this report the molecular mechanism(s) involved in the rapid and selective endocytosis of cell surface glycoprotein CD4 induced by exogenous monosialoganglioside GM3 in human peripheral blood lymphocytes have been investigated. Inhibition of the GM3-induced CD4 down-modulation was observed in the presence of specific protein kinase C (PKC) inhibitors. Scanning confocal microscopy revealed the translocation and clustering on the cell surface of PKC isozymes delta and theta (more evidently than alpha and beta) after GM3 treatment, suggesting the involvement of these isozymes in the ganglioside-induced CD4 down-modulation. Exogenous GM3 induced phosphorylation of CD4 molecule, which then dissociated from p56(lck), as early as after 5 min. Moreover, addition of GM3 resulted in a rapid (1 min) cytosolic phospholipase A2 activation with consequent arachidonic acid release, whereas no phosphatidylinositol-phospholipase C activity was observed. Both PKC translocation and CD4 down-modulation were blocked by the trifluoromethylketone analog of arachidonic acid, a selective inhibitor of cytosolic phospholipase A2 and by mitogen-activated protein kinase inhibitor PD98059. Taken together, these findings strongly suggest that GM3 may trigger a novel mechanism of modulation of the CD4 surface expression through the activation of enzyme(s) involved in the regulation of cellular functions.

Inhibition of hemopoiesis in vitro by neuroblastoma-derived gangliosides

Hemopoiesis is disturbed in bone marrow-involving cancers like leukemia and neuroblastoma. Shedding of gangliosides by tumor cells may contribute to this tumor-induced bone marrow suppression. We studied in vitro the inhibitory effects of murine neuroblastoma cells (Neuro-2a and C1300) and their gangliosides on hemopoiesis using normal murine hemopoietic progenitor colony-forming assays. Transwell cultured neuroblastoma cells showed a dose-dependent inhibition on hemopoiesis, indicating that a soluble factor was responsible for this effect. Furthermore, the supernatant of Neuro-2a cultured cells inhibited hemopoietic proliferation and differentiation. To determine whether the inhibitory effect was indeed due to shed gangliosides and not, for instance, caused by cytokines, the effect of DL-threo-1 -phenyl-2-decanoylamino-3-morpholino-1-propanol (DL-PDMP) on Neuro-2a cells was studied. DL-PDMP is a potent inhibitor of glucosylceramide synthase, resulting in inhibition of the synthesis and shedding of gangliosides. The initially observed inhibitory effect of supernatant of Neuro-2a cells was abrogated by culturing these cells for 3 days in the presence of 10 microM DL-PDMP. Moreover, gangliosides isolated from Neuro-2a cell membranes inhibited hemopoietic growth. To determine whether the described phenomena in vitro are a reflection of bone marrow suppression occurring in vivo, gangliosides isolated from plasma of neuroblastoma patients were tested for their effects on human hemopoietic progenitor colony-forming assays. These human neuroblastoma-derived gangliosides inhibited normal erythropoiesis (colony-forming unit-erythroid/burst-forming unit-erythroid) and myelopoiesis (colony-forming unit-granulocyte/macrophage) to a higher extent compared with gangliosides isolated from control plasma. Altogether these results suggest that gangliosides shed by neuroblastoma cells inhibit hemopoiesis and may contribute to the observed bone marrow depression in neuroblastoma patients.

Induction of nitric oxide production by ganglioside GM3 in murine peritoneal macrophages activated for tumor cytotoxicity

BACKGROUND

Recently, it was found that ganglioside GM3, known as a potent monocytic cell differentiation inducer, mimicked bacterial lipopolysaccharide (LPS) in the activation of macrophage-mediated tumor cytotoxicity (MTC). Since GM3 and LPS share partial structural and functional similarity, we postulate that the GM3-induced MTC was due to the induction of nitric oxide(NO) production in murine peritoneal macrophages (M phi s). MATERIALS RESULTS, CONCLUSIONS: Ganglioside GM3 was highly purified from canine erythrocytes by the authors. Murine peritoneal M phi s were used as the effector cells, and mouse ascites hepatoma cell line HCa-F25/16A3-F as the target cells. We found that: GM3 induced NO production by macrophages in a time- and dose-dependent manner; GM3 and IFN-gamma synergistically increased NO production; GM3 markedly enhanced MTC; both NO production and MTC were significantly inhibited by aminoguanidine. These results demonstrated for the first time that ganglioside GM3 in vitro induces the production of nitric oxide by macrophages, and the GM3-induced MTC is NO-dependent.

GM3-enriched microdomain involved in cell adhesion and signal transduction through carbohydrate-carbohydrate interaction in mouse melanoma B16 cells

Mouse melanoma B16 cells are characterized by the predominant presence of ganglioside GM3 and adhere to lactosylceramide- or Gg3-coated plates through interaction of GM3 with lactosylceramide or Gg3, whereby not only adhesion but also spreading and enhancement of cell motility occur (Kojima, N., Hakomori, S. (1991) J. Biol. Chem. 266, 17552-17558). We now report that the adhesion process is based essentially on a glycosphingolipid-enriched microdomain (GEM) at the B16 cell surface, since >90% of GM3 present in the original cells is found in GEM, and GEM is also enriched in several signal transducer molecules, e.g. c-Src, Ras, Rho, and focal adhesion kinase (FAK). GEM was isolated as a low density membranous fraction by homogenization of B16 cells in lysis buffer under two different conditions (i.e. buffer containing 1% Triton X-100, or hypertonic sodium carbonate without detergent), followed by sucrose density gradient centrifugation. A close association of GM3 with c-Src, Rho, and FAK was indicated by co-immunoprecipitation of GM3 present in GEM by anti-GM3 monoclonal antibody DH2, followed by Western blotting with antibodies directed to these transducer molecules. The following data indicate that GEM is a structural and functional unit for initiation of GM3-dependent cell adhesion coupled with signal transduction. 1) Tyrosine phosphorylation in FAK was greatly enhanced in B16 cells adhered to Gg3-coated plates but was minimal in cells adhered to GM3-coated, GlcCer-coated, or noncoated plates. 2) GTP loading on Ras and Rho increased significantly when cells were adhered to Gg3-coated plates, compared with GM3-coated, GlcCer-coated, or noncoated plates. Since Ras and Rho are closely associated with GM3 in GEM, cell adhesion/stimulation through GM3 in GEM may induce activation of Ras and Rho through enhanced GTP binding.

A streptavidin-based neoglycoprotein carrying more than 140 GT1b oligosaccharides: quantitative estimation of the binding specificity of murine sialoadhesin expressed on CHO cells

We prepared a streptavidin-based neoglycoprotein which carries more than 140 GT1b oligosaccharides. GT1b oligosaccharides were covalently coupled to streptavidin by reductive amination, yielding a monomer form of streptavidin carrying 13 oligosaccharides. The monomer form of glycosylated streptavidin was polymerized with biotinylated-bovine serum albumin, which yielded a polymer carrying more than 140 oligosaccharides. Both the monomer and the polymer bound to Chinese hamster ovary cells expressing murine sialoadhesin. The relative binding potencies determined with the polymer, monomer, and free GT1b oligosaccharides were 3,500, 83, and 1, respectively, indicating that an increase in the number of oligosaccharide ligands is critical for high avidity. The high avidity of the polymer enabled us to develop a sensitive and quantitative binding assay, and the assay was applied to characterization of the binding specificity of sialoadhesin. The polymer binding was inhibited by various gangliosides, the order of the inhibitory potencies being GM3 (IC50 = 40 microM) > GD1a (100 microM) > sialylparagloboside (120 microM) > GT1b (310 microM) > GM2 (640 microM) > GM4 (2,100 microM) > GD1b>LacCer = GM1 = paragloboside (no inhibition). These results indicate that the binding specificity is comparable to that reported, i.e. the determinant structure is NeuAcalpha2-3Galbeta1-linked to either 3GalNAc, 3(4)GlcNAc, or 4Glc, and that the oligosaccharide structure on the polymer is properly presented to sialoadhesin on the cell surface. To determine the precise requirement of the NeuAc structure for binding, NeuAc of GM3 was converted into various derivatives, the inhibitory potencies of which were examined; i.e. GM3 containing NeuAc, IC50 = 40 microM; C7- or C8-aldehyde, 500 microM; C7- or C8-alcohol, 700 microM; C1-alcohol, 2,000 microM; C1-amide, 2,200 microM; and NeuGc,>3,000 microM. These results confirmed the requirement of the hydroxyl group at C9 and/or C8, the carboxyl group at C1, and the methyl group of the N-acetyl residue of NeuAc in a quantitative manner. Thus, this streptavidin-based neoglycoprotein is a useful multivalent glycoprobe, which exhibits high affinity and specificity to murine sialoadhesin on the cell surface.

Gangliosides enhance apoptosis of thymocytes

Monosialogangliosides, normal components of cell membranes, regulate cell development and differentiation in several organs. Our previous observation of dramatic premature thymic involution in cats with feline GM1 gangliosidosis, whose thymocytes have abnormally high cell surface gangliosides, suggested that excess GM1 ganglioside (GM1) could modulate thymocyte apoptosis in this disease (Cox et al., "Thymic Alterations in Feline GM1 Gangliosidosis," submitted). In these studies, we added exogenous GM1 to murine primary thymocyte cultures and demonstrated enhanced apoptosis in treated cells by DNA fragmentation, apoptotic body, and electrophoretic analyses. GM1-enhanced apoptosis was blocked by common apoptotic pathway inhibitors including aurintricarboxylic acid (inhibitor of endonuclease activity), actinomycin D (inhibitor of RNA transcription), and cycloheximide (inhibitor of protein synthesis). GM1 treatment primarily affected the immature CD4+ CD8+ subset, as shown by flow cytometric evaluation of fetal thymic organ culture and primary thymocyte cultures. Apoptosis also could be induced by GM2, GM3, and GT1b, whereas asialo-GM1 failed to do so, suggesting that the sialic acid moiety may play an important role in the induction of thymocyte apoptosis.

Gangliosides inhibit growth factor-stimulated neurite outgrowth in SH-SY5Y human neuroblastoma cells

Exogenously added gangliosides are known to promote neurite outgrowth in a variety of cell types, including some neuroblastoma cell lines. To study neuritogenesis in SH-SY5Y human neuroblastoma we serum starved the cells for 24 hr and exposed them to gangliosides (GM1, GM3, or GT1b), platelet-derived growth factor (PDGF), insulin, nerve growth factor (NGF), insulin-like growth factor I (IGF-I), or combinations of these for 3 days. We measured four parameters of neurite outgrowth using image analysis. PDGF induced neurite outgrowth in SH-SY5Y and GM1 inhibited this. Both phenomena were dose-dependent with neurites/cell and neurite length being below controls with 100 microM GM1, and percent of neurite-bearing cells being below controls with 25, 50, and 100 microM GM1. Similar but more inhibitory results were obtained with GM3 and GT1b. Insulin and IGF-I induced a neuritogenic response that was less potent than that of PDGF and was also inhibited by gangliosides. NGF had no effect on neurite outgrowth but gangliosides were still inhibitory even in cells not treated with growth factors. From this we conclude that gangliosides inhibit spontaneous and trophic factor-induced neurite outgrowth in SH-SY5Y cells. For GM1 and GT1b, but not GM3, this probably involves inhibition of trophic factor receptor function.

The role of sphingolipids in the maintenance of fibroblast morphology. The inhibition of protrusional activity, cell spreading, and cytokinesis induced by fumonisin B1 can be reversed by ganglioside GM3

Previous studies demonstrated that inhibition of sphingolipid synthesis by the mycotoxin fumonisin B1 (FB1) disrupts axonal growth in cultured hippocampal neurons (Harel, R., and Futerman, A. H. (1993) J. Biol. Chem. 268, 14476-14481) by affecting the formation or stabilization of axonal branches (Schwarz, A., Rapaport, E., Hirschberg, K., and Futerman, A.H. (1995) J. Biol. Chem. 270, 10990-10998). We now demonstrate that long term incubation with FB1 affects fibroblast morphology and proliferation. Incubation of Swiss 3T3 cells with FB1 resulted in a decrease in synthesis of ganglioside GM3, the major glycosphingolipid in 3T3 fibroblasts and of sphingomyelin. The projected cell area of FB1-treated cells was approximately 45% less than control cells. FB1 had no affect on the organization of microtubules or intermediate filaments, but fewer actin-rich stress fibers were observed, and there was a loss of actin-rich lamellipodia at the leading edge. Three other processes involving the actin cytoskeleton, cytokinesis, microvilli formation, and the formation of long processes induced by protein kinase inhibitors, were all disrupted by FB1. All the effects of FB1 on cell morphology could be reversed by addition of ganglioside GM3 even in the presence of FB1, whereas the bioactive intermediates, sphinganine, sphingosine, and ceramide, were without effect. Finally, FB1 blocked cell proliferation and DNA synthesis in a reversible manner, although ganglioside GM3 could not reverse the effects of FB1 on cell proliferation. Together, these data suggest that ongoing sphingolipid synthesis is required for the assembly of both new membrane and of the underlying cytoskeleton.

Angiogenic and angiostatic microenvironment in tumors--role of gangliosides

Gangliosides are important components of the cell membrane that are usually shed in the surrounding microenvironment by neoplastic cells. Gangliosides can also modulate the angiogenic response of microvessels stimulated by angiogenic factors. The experiments reported here make a contribution to the assessment of the nature of this angiogenic modulation, by demonstrating that a) GM3 gangliosides can block the proliferation of endothelium induced by neoplastic cells from human tumors of five different origins; b) this block also occurs when the endothelial cells are preincubated with GM3 and disappears when the cells are returned to a medium poor in GM3; c) in the presence of GM3 the capacity of the endothelial cells to bind to fibronectin and to collagen types I and IV was sharply reduced; d) concentrations of GM3 able to block endothelial cell growth are counteracted by addition to the medium of GT1b ganglioside. The data suggest that the prevalence of a microenvironment rich in GM3 prevents proliferation of vascular endothelium, but the appropriate presence of another ganglioside, such as GT1b, nullifies the effect. Modulation of the angiogenic response of vascular endothelium to angiogenic factors released by tumors is probably dependent on the distribution and activity of growth factor receptors on the endothelial cell surface. The nature and concentration of the gangliosides in the endothelial microenvironment have a decisive influence on this event and possibly on the progression of tumor-induced angiogenesis.

Gangliosides GM1, GM2 and GM3 inhibit the platelet-derived growth factor-induced signalling transduction pathway in vascular smooth muscle cells by different mechanisms

Gangliosides appear to regulate proliferation of different cell types. In the present study, we investigated the effects of gangliosides GM1, GM2 and GM3 on platelet-derived growth factor (PDGF)-induced vascular smooth muscle cell (VSMC) growth. In addition, we examined the effects of gangliosides on the PDGF-BB-dependent signalling transduction pathway in rat aortic VSMC. GM2 and GM1 inhibit the PDGF-BB-dependent receptor tyrosine autophosphorylation, stimulation of the PLC-gamma 1, increase of inositol-1,4,5-trisphosphate (InsP3), elevation in cytosolic free Ca2+ ([Ca2+]i), expression of the immediate early growth response gene c-fos and cell proliferation with the following rank order of potency GM2 > GM1. Although GM3 did not influence the PDGF-BB-dependent receptor autophosphorylation and PLC-gamma 1 activation, it effectively inhibited the PDGF-BB-dependent InsP3 formation, [Ca2+]i and cell growth. Binding studies with 125I-PDGF-BB on VSMC in the presence and absence of 10 to 50 microM of each ganglioside revealed that GM1 and GM2 effectively inhibited the specific binding of PDGF-BB with an IC50 value of 20 microM for GM2 and 30 microM for GM1. GM3 had no significant effect on the specific 125I-PDGF-BB binding. These observations suggest that GM1 and GM2 may interact with PDGF-BB or its receptor resulting in a prevention of its binding. GM3 was able to suppress the PDGF-BB-dependent increase of InsP3 and [Ca2+]i downstream of the PDGF-BB-dependent receptor autophosphorylation and PLC-gamma 1 activity.

Effects of exogenous gangliosides on intracellular Ca2+ mobilization and functional responses in human platelets

Gangliosides, highly expressed in the outer leaflet of plasma membranes, mediate a variety of biological processes, including cell-cell and cell-matrix interactions. We examined the effects of exogenous gangliosides on intracellular Ca2+ mobilization and functional responses in human platelets. Gangliosides (GM3 and GM1) induced rapid and reversible elevation of intracellular Ca2+ in fura2-loaded platelets in a concentration-dependent manner. The Ca(2+)-mobilizing effect of gangliosides was not mimicked by deN-acetyl-GM3, lactosylceramide, or free sialic acid, suggesting that structural integrity as ganglioside is essential for this effect. GM3 and GM1 also induced platelet shape change by themselves and elicited aggregation in combination with epinephrine. Our observations suggest the involvement of ganglioside-activated platelets in atherosclerosis, in view of the high observed ganglioside levels in atherosclerotic lesions of human aorta.

Gangliosides of migrating and nonmigrating corneal epithelium in organ and cell culture

PURPOSE

To identify major gangliosides - the sialated glycolipids - of corneal epithelium; to determine which specific gangliosides, if any, are synthesized in a higher amount or are downregulated during corneal epithelial cell migration; and to determine what role, if any, they play in the modulation of corneal epithelial cell proliferation.

METHODS

[3H]-galactose-labeled and unlabeled glycolipids of migrating and nonmigrating rabbit corneal epithelium in cell and/or in organ culture were chromatographed on DEAE Sephadex to isolate gangliosides. The gangliosides eluted from the ion-exchange column were further characterized by thin-layer chromatography (TLC), glycosidase digestions, and TLC-immunostain analysis. A [3H]-thymidine incorporation assay was used to determine the effect of exogenous gangliosides on corneal epithelium cell proliferation.

RESULTS

Upon TLC of the acidic fraction eluted from the DEAE column, only two radiolabeled glycolipids (GL1 and GL2), migrating as a doublet, were detected. Regardless of whether the epithelia were prepared by cell culture or organ culture, both GL1 and GL2 were present in a significantly higher amount in migrating compared to nonmigrating epithelia. Further characterization of GL1 and GL2 identified them as gangliosides known as GM3. TLC-immunostain analysis, as well as orcinol staining of thin-layer chromatograms of gangliosides of unlabeled cells, revealed that GM3 also accumulates in a higher amount in migrating compared to nonmigrating epithelial cell cultures. Exogenous addition of GM3, but not various other gangliosides, inhibited corneal epithelial cell proliferation in a dose-dependent manner.

CONCLUSIONS

GM3 is the major ganglioside present in corneal epithelium, and its levels are elevated during corneal epithelial cell migration. It is suggested that the ganglioside plays a role in events that modulate corneal epithelial cell proliferation.

Ganglioside GM3 inhibits interleukin-3-dependent bone marrow-derived mast cell proliferation

To investigate the modulated proliferation of an interleukin-3(IL-3)-dependent cell by exogenous ganglioside GM3, mouse bone marrow-derived mast cells (BMMC) were cultured with various concentrations of GM3 in the presence of IL-3. By 4 weeks of culture, most of the nonadherent cells were alcian blue-positive mast cells. Culturing 2-week-cultured BMMC with GM3 for 1 week reduced the number of alcian blue-positive cells, but the increased total histamine content of BMMC was observed. To examine the effect of GM3 on the synergistic response by IL-3 and interleukin-4 (IL-4), 3-week-cultured BMMC were cultured with GM3 in the presence of IL-3 and IL-4 for 1 week. Although the addition of IL-4 to culture medium increased the number of BMMC, treatment with GM3 reduced its proliferative activity. Concerning the effect of GM3 on cell membrane, there are no changes in the expression of IgE receptors on BMMC treated with GM3 though a low concentration of GM3 increased it. However, the production of tumor necrosis factor-alpha from BMMC treated with GM3 was significantly suppressed. These results indicate that in vitro treatment with exogenous GM3 inhibited the proliferative response of IL-3-dependent mast cell populations and modulated its characteristics.

Inhibitory action of ganglioside GM3 on murine neuroblastoma cell proliferation: modulating effect of fetal calf serum

Exogenous gangliosides have been shown to exert a regulatory influence on the proliferation and differentiation of several cell lines in tissue culture. The effect of ganglioside GM3 on C-1300 murine neuroblastoma (MNB) cell proliferation and the modulating action of fetal calf serum (FCS) concentration in the culture media have been investigated. MNB cells were cultured in DMEM containing 1, 2.5, 5 or 10% FCS, and incubated with GM3 at concentrations ranging from 1.95 to 500 microM. Cell proliferation was assayed 4 days after the addition of GM3 using the CellTiter 96 Non-Radioactive Cell Proliferation Assay. GM3 inhibited MNB cell proliferation in a dose-dependent manner regardless of the FCS concentration in the culture media. However, the magnitude of this inhibitory effect was inversely proportional to the FCS concentration in the culture media. The addition of albumin to MNB cells cultured in DMEM containing 1% FCS exerted no effect on the antiproliferative action of GM3. FACS cell cycle analyses demonstrated that MNB cultured in DMEM containing 1% FCS had a higher proportion of cells in the G0/G1 compartment when compared to those cultured in 10% FCS. The enhanced response of MNB cells to GM3 observed in 1% FCS, may be due to a preferential action on cells in the G0/G1 stage of the cell cycle. These studies have demonstrated that the ganglioside GM3 inhibited MNB cell proliferation in tissue culture and this effect was modulated by FCS concentration in the culture media. Since protein-binding of GM3 by FCS does not appear to be the primary mechanism by which FCS exerts its antagonistic effects, we hypothesize that this may be due to the opposing action of stimulatory growth factors present in FCS.

Monosialoganglioside GM3 induces CD4 internalization in human peripheral blood T lymphocytes

Gangliosides modulate the expression of CD4 molecules on the cell surface of T lymphocytes. We report here that treatment of human peripheral blood lymphocytes with exogenous monosialoganglioside GM3 induces a rapid down-modulation of the CD4 molecules on the plasma membrane of CD4+ T lymphocytes, as assessed by cytofluorimetric analysis and quantitative immunoelectron microscopy. The CD4 down-modulation was ganglioside-dose dependent and was already evident after 5 min of treatment, reaching the maximum after 20 min. The expression of other surface antigens was not affected by GM3 treatment. The immunoelectron microscopic analysis showed that, following GM3 addition, gold labelled CD4 molecules were rapidly redistributed on the cell surface, clustered and internalized via endocytic pits and vesicles. These results indicate that CD4 down-modulation induced by GM3 occurs through an endocytic mechanism. A persistent low level of CD4 expression on the cell surface up to 24 h after GM3 treatment, compared with a stable expression of either CD4 in untreated cells and CD3 in GM3-treated cells, suggests intracellular degradation of the internalized CD4 molecules.

Differential effects of gangliosides on human IgE and IgG4 production

The effects of gangliosides on human IgE and IgG4 production were studied. Of the various gangliosides tested, only GM2 and GM3 inhibited the IgE and IgG4 production induced by interleukin (IL)-4 plus hydrocortisone (HC), or that induced by IL-13 plus HC, in human surface IgE- and IgG4-negative (sIgE-, sIgG4-) B cells without affecting the production of IgG1, IgG2, IgG3, IgM, IgA1 or IgA2. In contrast, GM1, GD1a, GD1b, GD3, GT1b and GQ1b were without effects. The GM2- and GM3-mediated inhibition was specific, since each was blocked by a corresponding antibody. Of the various factors tested. IL-6, IL-10, and tumor necrosis factor (TNF)-alpha enhanced the IgE and IgG4 production induced by IL-4 plus HC or by IL-13 plus HC, while IL-8 and transforming growth factor (TGF)-beta inhibited these responses. However, only TNF-alpha counteracted the GM2- and GM3-mediated inhibition of IgE and IgG4 production, while IL-6, IL-10, anti-IL-8 monoclonal antibody and anti-TGF-beta antibody failed to do so. Anti-TNF-alpha monoclonal antibody, but not control IgG1, not only inhibited IgE and IgG4 production in the absence of TNF-alpha but also blocked the counteraction of inhibition by TNF-alpha. In cultures containing IL-4 plus HC or IL-13 plus HC. GM2 and GM3 specifically inhibited TNF-alpha production without affecting TNF-alpha receptors, IL-6 production or IL-6 receptors. These results indicate that GM2 and GM3 inhibit IgE and IgG4 production by inhibiting endogenous TNF-alpha production.

A chemically synthesized sialic acid-containing glycoconjugate, 2-(tetradecylhexadecyl)-O-(5-acetamido-3,5-dideoxy-D-glycero-alpha-D-ga lacto-2-nonulopyranosylonic acid)-(2-->3)-O-beta-D-galactopyrannosyl-(1-->4)-beta-D- glucopyrannoside, is a potent inhibitor of cellular immune responses

Structural variations among gangliosides significantly influence their immunosuppressive activity. By total chemical synthesis, a sialic acid-containing glycoconjugate, 2-(tetradecylhexadecyl)-O-(5-acetamido-3,5-dideoxy-D-glycero-alpha -D-galacto-2-nonulopyranosylonic acid)-(2-->3)-O-beta-D-galactopyrannosyl-(1-->4)-beta-D- glucopyrannoside was synthesized. This glycoconjugate has the same carbohydrate structure as does GM3 ganglioside and a branched alkane in place of ceramide. It markedly inhibits the tetanus toxoid-induced human lymphoproliferative response in vitro (ID90 < 7 microM) and is five-fold more active than d18:1-C18:0 GM3 ganglioside, to which it is structurally related. This glycoconjugate is also a potent inhibitor of the murine alloimmune response in vivo: 10 nmol of the molecule injected subcutaneously together with an allogeneic cell challenge markedly inhibits the cellular immune response in the draining popliteal lymph node. In fact, the effect is quantitatively similar to that of systemically administered cyclosporin A, a well-studied immunosuppressive agent.

Differentiation of oligodendrocytes cultured from developing rat brain is enhanced by exogenous GM3 ganglioside

Cultures consisting primarily of O-2A progenitor cells and immature oligodendrocytes with a few microglia and astrocytes were obtained by shaking primary cultures from neonatal rat brain after 12-14 days in vitro. Addition of 50 micrograms/ml exogenous Neu-NAc alpha 2-3Gal beta 1-4Glc beta 1-1'ceramide (GM3 ganglioside) to the cultures resulted in an increase in the number and thickness of cell processes that stained intensely for sulfatide and galactocerebroside (galC) in comparison to control cultures without added GM3. The treated cultures also contained fewer astrocytes than control cultures as revealed by immunostaining for glial fibrillary acidic protein (GFAP). Cells that immunostained for both GFAP and sulfatide/galC were very rare in control cultures but were frequently seen in the GM3-treated cultures, suggesting that these may represent cells changing their direction of differentiation away from type II astrocytes toward oligodendrocytes under the influence of GM3. These effects on the developing rat oligodendrocytes were specific for GM3 ganglioside and were not produced by adding GM1, GM2, GD3, or GD1a to the cultures. Lactosyl ceramide and neuraminyl lactose were also ineffective. When control cultures were initially plated on polylysine and incubated with [14C]galactose, GD3 was the principal labeled ganglioside. However, as the control cells differentiated over time in culture without the addition of exogenous GM3 and produced increasing amounts of myelin-related components, the incorporation of [14C]galactose into endogenous GM3 increased to become the predominant labeled ganglioside by 6 days after plating. Metabolic labeling of the GM3-treated oligodendrocytes with [14C]galactose revealed increased incorporation into galC and sulfatide in comparison to control cultures, but a decreased labeling of endogenous GM3. Similarly, incorporation of an amino acid precursor into the myelin-associated glycoprotein (MAG) was increased by GM3 treatment, but incorporation into myelin basic protein (MBP) was not affected. Although the overall effect of added GM3 was to decrease the phosphorylation of most proteins in the oligodendrocytes, including MBP, GM3 enhanced the phosphorylation of MAG. These findings indicate that GM3 ganglioside has an important role in the differentiation of cells of the O-2A lineage toward myelin production, since differentiation is associated with increased metabolic labeling of endogenous GM3 in control cultures and is enhanced by the addition of exogenous GM3.

Significant inhibition of hybridoma cells by exogenous application of ganglioside GM3, a possible modulator of cell growth in vitro

Gangliosides of the mouse-rat hybridoma cell line 187.1, which secretes an antibody against kappa-light chain of mouse IgG, were isolated and structurally characterized by biochemical and immunological methods (overlay technique), and fast atom bombardment-mass spectrometry. Exclusively GM3, substituted with C24:1 and C16:0 fatty acid and C18:1 sphingosine, was found in this B cell derived cell line. A GM3(NeuGc) to GM3(NeuAc) ratio (80 to 20), was characteristic for 187.1 cells, and absolute GM3 amounts of about 0.3 mg 10(-9) viable cells were determined. Exogenous application of GM3, which has been isolated from large cell preparations, to 187.1 cells showed growth inhibition in a concentration dependent manner. Using the MTT-assay and the [3H]thymidine incorporation assay, the cells exhibited a strong reduction in metabolic and proliferative activity, respectively, after exposure of cells to GM3. GM3 was applied in concentrations between 3 microM and 30 microM, giving evidence for strong inhibitory effects at 30 microM GM3 and less but significant suppression after application of GM3 concentrations lower than 20 microM. No cellular response was observed at the lowest concentration (3 microM) used in this study. Hybridoma cells as well as other cell types like fibroblasts, muscle cells and endothelial cells, are in general characterized by high expression of the GM3 ganglioside, which is known to act as a modulator of cellular growth in monolayer cultures of adherent cells. Since gangliosides are released to the culture medium by cell lysis, i.e. cell death, and/or by active membrane shedding, the results obtained in this study suggest a growth regulatory role of GM3 in high density hybridoma cell cultures.