Ganglioside GM2 mediates migration of tumor cells by interacting with integrin and modulating the downstream signaling pathway

The definitive role of ganglioside GM2 in mediating tumor-induced growth and progression is still unknown. Here we report a novel role of ganglioside GM2 in mediating tumor cell migration and uncovered its mechanism. Data shows differential expression levels of GM2-synthase as well as GM2 in different human cancer cells. siRNA mediated knockdown of GM2-synthase in CCF52, A549 and SK-RC-26B cells resulted in significant inhibition of tumor cell migration as well as invasion in vitro without affecting cellular proliferation. Over-expression of GM2-synthase in low-GM2 expressing SK-RC-45 cells resulted in a consequent increase in migration thus confirming the potential role GM2 and its downstream partners play in tumor cell migration and motility. Further, treatment of SK-RC-45 cells with exogenous GM2 resulted in a dramatic increase in migratory and invasive capacity with no change in proliferative capacity, thereby confirming the role of GM2 in tumorigenesis specifically by mediating tumor migration and invasion. Gene expression profiling of GM2-synthase silenced cells revealed altered expression of several genes involved in cell migration primarily those controlling the integrin mediated signaling. GM2-synthase knockdown resulted in decreased phosphorylation of FAK, Src as well as Erk, while over-expression and/or exogenous GM2 treatment caused increased FAK and Erk phosphorylation respectively. Again, GM2 mediated invasion and Erk phosphorylation is blocked in integrin knockdown SK-RC-45 cells, thus confirming that GM2 mediated migration and phosphorylation of Erk is integrin dependent. Finally, confocal microscopy suggested co-localization while co-immunoprecipitation and surface plasmon resonance (SPR) confirmed direct interaction of membrane bound ganglioside, GM2 with the integrin receptor.

Gangliosides inhibit the development from monocytes to dendritic cells

Dendritic cell (DC) development and function is critical in the initiation phase of any antigen-specific immune response against tumours. Impaired function of DC is one explanation as to how tumours escape immunosurveillance. In the presence of various soluble tumour-related factors DC precursors lose their ability to differentiate into mature DC and to activate T cells. Gangliosides are glycosphingolipids shed by tumours of neuroectodermal origin such as melanoma and neuroblastoma. In this investigation we address the question of whether gangliosides suppress the development and function of monocyte-derived DC in vitro. In the presence of gangliosides, the monocytic DC precursors showed increased adherence, cell spreading and a reduced number of dendrites. The expression of MHC class II molecules, co-stimulatory molecules and the GM-CSF receptor (CD116) on the ganglioside-treated DC was significantly reduced. Furthermore, the function of ganglioside-treated DC was impaired as observed in endocytosis, chemotactic and T cell proliferation assays. In contrast to monocytic DC precursors, mature DC were unaffected even when higher doses of gangliosides were added to the culture. With regard to their carbohydrate structure, five different gangliosides (GM2, GM3, GD2, GD3, GT1b), which are typically shed by melanoma and neuroblastoma, were tested for their ability to suppress DC development and function. Suppression was induced by GM2, but not by the other gangliosides. These data suggest that certain gangliosides impair DC precursors, implying a possible mechanism for tumour escape.

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.

Apoptosis of Neuro2a cells induced by lysosphingolipids with naturally occurring stereochemical configurations

Lysosphingolipids, which lack the fatty acid moiety of sphingolipids, are known to be accumulated in some variants of sphingolipid storage diseases. Here, we report that lysosphingolipids with naturally occurring stereochemical configurations induce apoptosis in mouse neuroblastoma Neuro2a cells. The intracellular dehydrogenase activity and [3H]thymidine incorporation of Neuro2a cells were strongly suppressed by the addition of lysosphingolipids in a dose-dependent manner, whereas the parental sphingolipids had no effect. Intranucleosomal DNA fragmentation, chromatin condensation, and phosphatidylserine externalization, which are typical features of apoptosis, were observed when the cells were cultured with 40-80 microM of lysosphingolipids for 24-48 h in the presence of 5% fetal calf serum. Activation of caspase-3-like enzyme occurred after addition of lysosphingolipids followed by incubation at 37 degrees C for 24 h. The addition of an inhibitor of caspases, ZVAD-fmk, to the Neuro2a cell culture completely inhibited the elevation of caspase-3 activity but not the DNA fragmentation. These results may indicate that a caspase-3 independent signaling pathway is involved in the lysosphingolipid-induced apoptosis and suggest that accumulation of lysosphingolipids, but not parental sphingolipids, triggers the apoptotic cascade in neuronal cells of patients with sphingolipidoses.

GM2 ganglioside regulates the function of ciliary neurotrophic factor receptor in murine immortalized motor neuron-like cells (NSC-34)

We previously reported that ciliary neurotrophic factor (CNTF) increased the serum-free cell survival of immortalized motor neuron-like cells (NSC-34), and addition of the exogenous ganglioside GalNAc beta4(Neu5Ac alpha3)Gal beta4GlcCer (GM2) facilitated cell survival together with CNTF. Moreover beta 1,4 N-acetylgalactosaminyltransferase (GM2 synthase) activity increased in NSC-34 cells cultured with CNTF. We now have examined whether CNTF-induced cell survival is associated with the collaboration between GM2 and the CNTF receptor (CNTF-R). Despite the presence of CNTF (50 ng/ml), anti-CNTF-R antibody caused cell death and prevented the up-regulation of GM2 synthase expression. The addition of GM2 (1 to 20 microM) abrogated the anti-CNTF-R antibody effect which shortened cell survival and blocked GM2 synthase activation. Use of [125I]CNTF showed the specificity of CNTF binding in NSC-34 cells in situ. GM2 produced a 5-fold increase in the CNTF binding affinity per cell but did not change the binding site number. The study by metabolic labeling with [1-(14)C]N-acetyl-D-galactosamine ([14C]GalNAc) showed that biosynthesized GM2 was involved in the immunoprecipitation of CNTF-R. These findings indicate that up-regulated GM2 synthesis induces functional conversion of CNTF-R to the activated state, in which it has affinity for CNTF. We conclude that GM2 is a bio-regulating molecule of CNTF-R in motor neurons.

High-dose interferon alfa-2b does not diminish antibody response to GM2 vaccination in patients with resected melanoma: results of the Multicenter Eastern Cooperative Oncology Group Phase II Trial E2696

PURPOSE

High-dose interferon alfa-2b (IFNalpha2b) is the only established adjuvant therapy of resectable high-risk melanoma. GM2-KLH/QS-21 (GMK) is a chemically defined vaccine that is one of the best developed of a range of vaccine candidates for melanoma. A single-institution phase III trial conducted at Memorial Hospital served as the impetus for an intergroup adjuvant E1694/S9512/C509801 trial, which recently completed enrollment of 880 patients. To build on the apparent benefit of IFNalpha2b in resectable high-risk American Joint Committee on Cancer (AJCC) stage IIB or III melanoma, this phase II study was designed to evaluate the combination of GMK and IFNalpha2b. The E2696 trial was undertaken to evaluate the toxicity and other effects of the established adjuvant high-dose IFNalpha2b regimen in relation to immune responses to GMK and to evaluate the potential clinical and immunologic effects of the combined therapies.

PATIENTS AND METHODS

This trial enrolled 107 patients with resectable high- or very high-risk melanoma (AJCC stages IIB, III, and IV).

RESULTS

The results demonstrate that IFNalpha2b does not significantly inhibit immunoglobulin M or G serologic responses to the vaccine and that the combination of high-dose IFNalpha2b and GMK is well tolerated in this patient population.

CONCLUSION

Cox analysis of the results of the combination with IFNalpha2b show improvement in the relapse-free survival of patients with very high-risk melanoma (including those with resectable M1 disease).

Enhancement of TNF-alpha production by ganglioside GM2 in human mononuclear cell culture

Some gangliosides have been regarded as autoantigens of immune-mediated neurological disorders such as Guillain-Barré syndrome (GBS), Miller Fisher syndrome and multifocal motor neuropathy. On the other hand, proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), may be important in the pathogenesis of some neuroimmunological disorders. To clarify the interactions between immune cells and gangliosides, we investigated the effects of gangliosides on the production of proinflammatory cytokines in peripheral blood mononuclear cell (PBMC) cultures. We found that ganglioside GM2 markedly enhances the production of TNF-alpha and that TNF-alpha induction by coated GM2 is still more marked. These findings suggest that immune cells, especially monocytes/macrophages, cause inflammation upon encountering GM2.

GM2 promotes ciliary neurotrophic factor-dependent rescue of immortalized motor neuron-like cell (NSC-34)

We have examined whether ciliary neurotrophic factor (CNTF) can alter serum-free cell survival of immortalized motor neuron-like cells, which were established by fusing mouse neuroblastoma N18TG2 with mouse motor neurons. One of the cell lines, NSC-34 exhibited cell survival in the presence of CNTF. NSC-34 preserves the most characteristics of motor neurons, such as the formation of neuromuscular junctions on co-cultured myotube. GM2 ganglioside is characteristic of motor neurons, and expressed highly in NSC-34. When NSC-34 was cultured with exogenous GM2 ganglioside and CNTF, GM2 facilitated the cell survival effect of CNTF. In the addition, beta 1,4 N-acetylgalactosaminyltransferase (GM2 synthase) activity was enhanced up to 3.9-fold by culture in the presence of CNTF. GM2 might be a functional modulator of CNTF in motor neurons. It might be presented to cell surface by its enzyme activation, and become a signal of early stage, when CNTF rescues motor neurons.

Tenascin-C inhibits beta1 integrin-dependent cell adhesion and neurite outgrowth on fibronectin by a disialoganglioside-mediated signaling mechanism

We have previously shown that the extracellular matrix molecule tenascin-C inhibits fibronectin-mediated cell adhesion and neurite outgrowth by an interaction with a cellular RGD-independent receptor which interferes with the adhesion and neurite outgrowth promoting activities of the fibronectin receptor(s). Here we demonstrate that the inhibitory effect of tenascin-C on beta1integrin-dependent cell adhesion and neurite outgrowth is mediated by the interaction of the protein with membrane-associated disialogangliosides, which interferes with protein kinase C-related signaling pathways. First, in substratum mixtures with fibronectin, an RGD sequence-containing fragment of the molecule or synthetic peptide, tenascin-C inhibited cell adhesion and spreading by a disialoganglioside-dependent, sialidase-sensitive mechanism leading to an inhibition of protein kinase C. Second, the interaction of intact or trypsinized, i.e., cell surface glycoprotein-free, cells with immobilized tenascin-C was strongly inhibited by gangliosides or antibodies to gangliosides and tenascin-C. Third, preincubation of immobilized tenascin-C with soluble disialogangliosides resulted in a delayed cell detachment as a function of time. Similar to tenascin-C, immobilized antibody to GD2 (3F8) or sphingosine, a protein kinase C inhibitor, strongly inhibited RGD-dependent cell spreading. Finally, the degree of tenascin-C-induced inhibition of cell adhesion was proportional to the degree of disialoganglioside levels of expression by different cells suggesting the relevance of such mechanism in modulating integrin-mediated cell-matrix interactions during pattern formation or tumor progression.

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 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.

Inhibition of spontaneous immunoglobulin production by ganglioside GM2 in human B cells

The effects of gangliosides on spontaneous immunoglobulin (Ig) production in human B cells were studied. Of the various gangliosides tested, including GM1, GM2, GM3, GD1a, GD1b, GD3, GT1b, and GQ1b, only GM2 inhibited Ig production, but not thymidine uptake, in human B cell lines. Moreover, the GM2-induced inhibition was blocked by anti-GM2 mAb, but not by control IgM. Of various cytokines, IL-10 and TNF-alpha each partially counteracted the GM2-induced inhibition, and addition of both IL-10 and TNF-alpha completely counteracted the inhibition. On the other hand, anti-IL-10 mAb plus anti-TNF-alpha mAb inhibited spontaneous Ig production. GM2 inhibited endogenous production of IL-10 and TNF-alpha without affecting the binding of IL-10 and TNF-alpha in B cell lines. GM2 also specifically inhibited spontaneous production of Ig, IL-10, and TNF-alpha in in vivo activated B cells obtained from normal donors. This inhibition was blocked by anti-GM2 mAb and was counteracted specifically by IL-10 plus TNF-alpha. Collectively, GM2 may inhibit spontaneous Ig production by inhibiting endogenous production of IL-10 and TNF-alpha in B cells.

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.

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.

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.

Effect of gangliosides on binding, internalization and cytotoxic activity of ricin

The only gangliosides in Burkitt's lymphoma EB-3 cells is GM3. Treatment of Burkitt's lymphoma EB-3 cells with gangliosides GM1 or GM3 results in their binding to and partial incorporation into the cell membrane. About 25% of cell-associated ganglioside GM1 can interact with the ricin. However, such an increase in the number of binding sites does not enhance but rather decreases the cytotoxic effect of ricin. A similar protective effect was observed when the cells were pretreated with ganglioside GM3. In contrast, the increase in ricin biding sites caused by pretreatment of the cells with neuraminidase was accompanied by increase in ricin cytotoxicity. These differences may be related to observed differences in the rate of ricin-endocytosis by native and ganglioside-treated cells.

Metabolism of exogenous gangliosides in cerebellar granule cells, differentiated in culture

The metabolism of exogenous gangliosides in the CNS has been investigated using cerebellar granule cells in culture as a model. For this purpose, GM2 and GM1, both isotopically radiolabeled at the level of the terminal sugar residue or of the long chain base moiety, were administered to differentiated cells for a 15-h pulse, and their metabolic fate was followed in a time course protocol. At each time investigated (1, 2, and 4 days after the pulse), several compounds, besides the ones administered, were detected: (a) GM2 (only after GM1 was given), GM3, lactosylceramide, glucosylceramide, and ceramide, all products of ganglioside stepwise catabolism; (b) GM1 (only after GM2 was given), GD1a, GD1b, O-Ac-GT1b, and GT1b, that is, gangliosides more complex than the one administered; and (c) sphingomyelin. The compounds derived from ganglioside catabolism and sphingomyelin were detected only after administration of long chain base-labeled precursors, whereas the others were found regardless of the labeling position of the precursor. In addition, radioactivity was incorporated in the delipidized residue when sugar-labeled gangliosides were given to cells. Besides qualitative differences, quantitative ones were found after administration of the different precursors.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific binding of glycosylated beta-galactosidase to rat clonal pheochromocytoma PC12h cells: effects of nerve growth factor and gangliosides

Rat clonal pheochromocytoma PC12h cells were found to bind beta-galactosidase modified with specific glycosides. The enzyme modified with p-aminophenyl beta-D-glucoside was most effectively bound to the cells, followed by alpha-D-mannoside and alpha-D-glucoside. The binding was dependent on the number of PC12h cells, the incubation interval, and the pH; the maximal binding at 4 degrees C was obtained by incubation with 75 micrograms of cell protein for 15 min at pH 4.0. The binding proved to be a saturable and receptor-mediated process, and the apparent Km value and the maximal binding capacity of the cells with beta-D-glucosylated beta-galactosidase were 1.03 +/- 0.06 microM and 333 +/- 24 pmol/min/mg of protein, respectively. When the cells were cultured in the presence of nerve growth factor (NGF), GM1, GM2, and a ganglioside mixture, marked morphological differentiation was observed in the presence of NGF, and the specificity of the binding was also affected. By supplementation of NGF in the culture medium, the cells lost the selectivity of the glycoside binding, whereas cells cultured with GM1 supplement showed increased binding of the specific glycosides.

Ganglioside GM1 causes expression of type B monoamine oxidase in a rat clonal pheochromocytoma cell line, PC12h

The effects of ganglioside supplementation of culture medium on monoamine oxidase (MAO) type A and B activities in a rat clonal pheochromocytoma cell line, PC12h, were examined. The MAO activity in PC12h cells proved to be mainly due to type A MAO, and type B MAO activity was negligible. After supplementation of the culture medium with ganglioside GM1, the PC12 cells were found to express type B MAO activity after 4 days of culture, and the amount of type B activity increased with the number of days of culture. After 3 weeks of culture in the presence of GM1, type B activity was about 10% of the total, whereas in control cells type B MAO activity was only about 0.6% of the total. By kinetic analyses of type A and B MAO in PC12h cells after 3 weeks of culture, the increase of type B MAO activity was found to be due to the increase in amount of type B MAO; the Km values were almost the same and only the Vmax values were increased in the cells supplemented with GM1. Among gangliosides tested GM1 was the most effective in causing expression of type B MAO activity, whereas nerve growth factor was not effective. These results suggest that GM1 and other gangliosides may be involved in the expression of type B MAO in nerve cells and in the regulation of levels of the biogenic amines in the brain.

The role of gangliosides in the interaction of human chorionic gonadotropin and cholera toxin with murine Leydig tumor cells

A clonal line of murine Leydig tumor cells (MLTC-1) bound both human chorionic gonadotropin (hCG) and cholera toxin (CT) with high affinity and accumulated cyclic AMP in response to either effector. The major cellular ganglioside was GM3 with small amounts of GM2, GM1, and GD1a. The gangliosides became labeled when the cells were grown in medium containing [3H] galactose or were exposed to galactose oxidase or NaIO4 followed by NaB3H4. CT specifically protected GM1 from surface labeling whereas hCG did not protect any gangliosides from being labeled. When the cells were exposed to sialidase, surface GD1a was eliminated, and GM1 increased with a corresponding increase in CT binding. When sialidase-treated cells were first incubated with the B component of CT, binding and action of CT was blocked. The cells, however, retained their ability to bind and respond to hCG. Addition of purified gangliosides to the medium effectively inhibited the binding and action of CT but not hCG. The cells incorporated the exogenous gangliosides and exhibited increased binding of and responsiveness to CT but not hCG. Both hCG- and CT-receptor complexes were extracted from the cells with nonionic detergent and analyzed by sucrose gradient centrifugation. The hCG-receptor complex had an apparent molecular weight of 190,000 whereas the CT-receptor complex sedimented only slightly faster than CT itself. MLTC-1 gangliosides were separated on thin layer chromatograms which were overlayed with either iodinated CT or hCG. The toxin bound to a ganglioside corresponding to GM1 whereas the hormone did not bind to any of the gangliosides. When the cells were incubated overnight with hCG, they lost their hCG receptors but exhibited an increase in CT binding and gangliosides. Our results indicate that GM1 is the specific receptor for CT whereas gangliosides are not involved in the binding and action of hCG.

Exogenous gangliosides enhance the interaction of fibronectin with ganglioside-deficient cells

The major cell-surface glycoprotein fibronectin mediates a variety of cellular adhesive interactions that have been reported to be competitively inhibited by gangliosides. These effects suggest a possible function of gangliosides as receptors for fibronectin. To test this hypothesis more directly, we examined the interaction of endogenous fibronectin with a ganglioside-deficient cell line, NCTC 2071. These cells, which grow in serum-free medium, synthesized fibronectin. The fibronectin did not bind to these cells, but instead bound diffusely to the culture substratum. When the cells were cultured in medium containing ganglioside, the fibronectin became bound to the cell surface in fibrillar strands. The order of effectiveness of purified gangliosides was GT1b greater than GD1a greater than GM1 greater than GM2 greater than GM3. The effect with mixed gangliosides was accompanied by a restoration of cellular capacity to bind and to respond to cholera toxin. Treatment of the cells with several phospholipids did not alter fibronectin binding. Our results support the hypothesis that gangliosides can help mediate the binding of fibronectin to fibroblasts.

Human melanoma antigen AH is an autoantigenic ganglioside related to GD2

AH antigen, initially defined by an antibody present in a melanoma patient, is a cell surface antigen found on approximately 65% of melanoma cell lines. Absorption analysis indicates that AH is a differentiation antigen marking normal and malignant cells of neuroectodermal origin. The AH determinant has been found to be related to GD2 ganglioside.

A ganglioside-dependent cellular binding mechanism in rat macrophages

A rosetting assay was performed with rat alveolar and peritoneal macrophages and sheep red blood cells (SRBC) treated with gangliosides. SRBC incubated with GM2, GD1a, and a mixture of bovine brain gangliosides (BBG) showed binding to rat macrophages. The extent of binding was dependent on the concentration of gangliosides. Binding induced by GM2 was stronger than that induced GD1a and BBG. GM1 and GA2 did not induce rosette formation. Inhibition studies with gangliosides, sialyllactose, lactose, and neuraminic acid suggested that the macrophage binding site recognizes neuraminic acid in conjunction with neighboring carbohydrates showing highest affinity for GM2. Sodium azide, sodium fluoride, ethylenediaminetetraacetate, cytochalasin B, and colchicine did not inhibit rosette formation. The percentage of peritoneal macrophages binding ganglioside-treated SRBC was lower than that of alveolar macrophages. Proteose-peptone-stimulated peritoneal macrophages, however, showed an increase of rosette formation. Around 30% of adherent spleen cells also had binding activity for GM2-treated SRBC. Peripheral blood mononuclear cells did not bind ganglioside-treated SRBC. Phagocytosis of GM2-treated SRBC attached to alveolar macrophages could not be observed. It is suggested that macrophages may express recognition sites for certain gangliosides that might be important in cell-cell interaction.

Immunochemical determination of ganglioside GM2, by inhibition of complement-dependent liposome lysis

Immunochemical quantitative determination of a lipid antigen, ganglioside GM2, has been developed, based on the inhibition of the immune lysis of liposomes containing the antigen in their lipid bilayer. It has been shown that the full expression of the antigenicity of the competing lipid requires its dispersion in accessory lipids. The assay of inhibition of liposome lysis can be used also for the establishment of the antigenic similarity of structurally related lipid antigens.