Regulation of protein kinase C activity by gangliosides

Novel insights on GM1 and Parkinson's disease: A critical review

GM1 is a crucial component of neuronal membrane residing both in the soma and nerve terminals. As reported in Parkinson’s disease patients, the reduction of GM1 determines the failure of fundamental functional processes leading to cumulative cell distress up to neuron death. This review reports on the role of GM1 in the pathogenesis of the disease, illustrating the current data available but also hypotheses on the additional mechanisms in which GM1 could be involved and which require further study. In the manuscript we discuss these points trying to explain the role of diminished content of brain GM1, particularly in the nigro-striatal system, in Parkinson’s disease etiology and progression.

Heme Oxygenase-1 May Affect Cell Signalling via Modulation of Ganglioside Composition

Heme oxygenase 1 (Hmox1), a ubiquitous enzyme degrading heme to carbon monoxide, iron, and biliverdin, is one of the cytoprotective enzymes induced in response to a variety of stimuli, including cellular oxidative stress. Gangliosides, sialic acid-containing glycosphingolipids expressed in all cells, are involved in cell recognition, signalling, and membrane stabilization. Their expression is often altered under many pathological and physiological conditions including cell death, proliferation, and differentiation. The aim of this study was to assess the possible role of Hmox1 in ganglioside metabolism in relation to oxidative stress. The content of liver and brain gangliosides, their cellular distribution, and mRNA as well as protein expression of key glycosyltransferases were determined in Hmox1 knockout mice as well as their wild-type littermates. To elucidate the possible underlying mechanisms between Hmox1 and ganglioside metabolism, hepatoblastoma HepG2 and neuroblastoma SH-SY5Y cell lines were used for in vitro experiments. Mice lacking Hmox1 exhibited a significant increase in concentrations of liver and brain gangliosides and in mRNA expression of the key enzymes of ganglioside metabolism. A marked shift of GM1 ganglioside from the subsinusoidal part of the intracellular compartment into sinusoidal membranes of hepatocytes was shown in Hmox1 knockout mice. Induction of oxidative stress by chenodeoxycholic acid in vitro resulted in a significant increase in GM3, GM2, and GD1a gangliosides in SH-SY5Y cells and GM3 and GM2 in the HepG2 cell line. These changes were abolished with administration of bilirubin, a potent antioxidant agent. These observations were closely related to oxidative stress-mediated changes in sialyltransferase expression regulated at least partially through the protein kinase C pathway. We conclude that oxidative stress is an important factor modulating synthesis and distribution of gangliosides in vivo and in vitro which might affect ganglioside signalling in higher organisms.

Gangliosides as regulators of cell membrane organization and functions

Gangliosides, characteristic complex lipids present in the external layer of plasma membranes, deeply influence the organization of the membrane as a whole and the function of specific membrane associated proteins due to lipid-lipid and lipid-protein lateral interaction. Here we discuss the basis for the membrane-organizing potential of gangliosides, examples of ganglioside-regulated membrane protein complexes and the mechanisms for the regulation of ganglioside membrane composition.

Gangliosides as components of lipid membrane domains

Cell membrane components are organized as specialized domains involved in membrane-associated events such as cell signaling, cell adhesion, and protein sorting. These membrane domains are enriched in sphingolipids and cholesterol but display a low protein content. Theoretical considerations and experimental data suggest that some properties of gangliosides play an important role in the formation and stabilization of specific cell lipid membrane domains. Gangliosides are glycolipids with strong amphiphilic character and are particularly abundant in the plasma membranes, where they are inserted into the external leaflet with the hydrophobic ceramide moiety and with the oligosaccharide chain protruding into the extracellular medium. The geometry of the monomer inserted into the membrane, largely determined by the very large surface area occupied by the oligosaccharide chain, the ability of the ceramide amide linkage to form a network of hydrogen bonds at the water-lipid interface of cell membranes, the Delta(4) double bond of sphingosine proximal to the water-lipid interface, the capability of the oligosaccharide chain to interact with water, and the absence of double bonds into the double-tailed hydrophobic moiety are the ganglioside features that will be discussed in this review, to show how gangliosides are responsible for the formation of cell lipid membrane domains characterized by a strong positive curvature.

Plasma membrane production of ceramide from ganglioside GM3 in human fibroblasts

Ceramide is a key lipid molecule necessary to regulate some cellular processes, including apoptosis and cell differentiation. In this context, its production has been shown to occur via sphingomyelin hydrolysis or sphingosine acylation. Here, we show that in human fibroblasts, plasma membrane ceramide is also produced from ganglioside GM3 by detachment of sugar units. Membrane-bound glycosylhydrolases have a role in this process. In fact, the production of ceramide from GM3 has been observed even under experimental conditions able to block endocytosis or lysosomal activity, and the overexpression of the plasma membrane ganglioside sialidase Neu3 corresponded to a higher production of ceramide in the plasma membrane. The increased activity of Neu3 was paralleled by an increase of GM3 synthase mRNA and GM3 synthase activity. Neu3-overexpressing fibroblasts were characterized by a reduced proliferation rate and higher basal number of apoptotic cells in comparison with wild-type cells. A similar behavior was observed when normal fibroblasts were treated with exogenous C2-ceramide.

Direct cell-cell communication: a new approach derived from recent data on the nature and self-organisation of ultradian (circahoralian) intracellular rhythms

Recent data concerning ultradian (circahoralian) intracellular rhythms are used to assess the biochemical mechanisms of direct cell-cell communication. New results and theoretical considerations suggest a fractal nature of ultradian rhythms and their self-organisation. The fundamental and innate nature of these rhythms relates to their self-similarity at different levels of cell and tissue organisation. They can be detected in cell-free systems as well as in cells and organs in vivo. Such rhythms are a means of finding an optimal state of cell function rather than achieving a state of absolute stability. As a consequence, oscillations, being irregular and numerous by the set of periods, are resilient to functional overload and injury. Recent data on the maintenance of their fractal structure and, especially on the selection of optimal periods are discussed. The positive role of chaotic dynamics is stressed. The ultradian rhythm of protein synthesis in hepatocytes in vitro was used as a marker of direct cell-cell communication. The system demonstrates cell cooperation and synchronisation throughout the cell population, and suggests that the ultradian rhythms are self-organised. These observations also led to the detection of mechanisms of direct cell-cell communication in which extracellular factors have an essential role. Experimental evidence indicated the involvement of gangliosides and/or catecholamines in this large-scale synchronisation of protein synthesis. The response of all, or a major part, of the cell population is important; after the initial trigger effect, a periodic pattern is retained for some time. The influence of Ca2+-dependent protein kinases on protein phosphorylation can be a final step in the phase modulation of rhythms during cell-cell synchronisation. The intercellular medium plays an important role in self-synchronisation of ultradian rhythms between individual cells. Low cooperative activity of hepatocytes of old rats resulted from altered composition of the intercellular medium rather than direct effects of animal and cellular ageing. Similarly, in the whole body, changes in levels of gangliosides and catecholamines in the blood serum, a natural intercellular medium, can be critical events in age-dependent changes of the serum and accordingly cell-cell synchronisation. Hepatocytes of old rats exhibit some of the properties of young cells following an increase in blood serum ganglioside level, as well as, in in vitro conditions, after the addition of gangliosides to the culture medium. Together with data on ultradian functional and metabolic rhythms, all the material reviewed here allows us to propose a mechanism of direct cell-cell cooperation via the medium in which the cells exist, that supplements the nervous and hormonal central regulation of organ functions. Ultradian intracellular rhythms may thus provide a finer framework within which the integrated dynamics of respiration, heart rate, brain activity, and even behavioural patterns, are brought to an optimal functional pattern. Innate and direct cell-cell cooperation may have been employed as a means of intercellular regulation during the course of metazoan evolution, that preceded nervous regulation and is presently retained in mammals.

A cellular deficiency of gangliosides causes hypersensitivity to Clostridium perfringens phospholipase C

Clostridium perfringens phospholipase C (Cp-PLC), also called alpha-toxin, is the major virulence factor in the pathogenesis of gas gangrene. Previously, a cellular UDP-Glc deficiency was related with a hypersensitivity to the cytotoxic effect of Cp-PLC. Because UDP-Glc is required in the synthesis of proteoglycans, N-linked glycoproteins, and glycosphingolipids, the role of these gly-coconjugates in the cellular sensitivity to Cp-PLC was studied. The cellular sensitivity to Cp-PLC was significantly enhanced by glycosphingolipid synthesis inhibitors, and a mutant cell line deficient in gangliosides was found to be hypersensitive to Cp-PLC. Gangliosides protected hypersensitive cells from the cytotoxic effect of Cp-PLC and prevented its membrane-disrupting effect on artificial membranes. Removal of sialic acids by C. perfringens sialidase increases the sensitivity of cultured cells to Cp-PLC and intramuscular co-injection of C. perfringens sialidase, and Cp-PLC in mice potentiates the myotoxic effect of the latter. This work demonstrated that a reduction in gangliosides renders cells more susceptible to the membrane damage caused by Cp-PLC and revealed a previously unrecognized synergism between Cp-PLC and C. perfringens sialidase, providing new insights toward understanding the pathogenesis of clostridial myonecrosis.

C6 cells express a sodium-calcium exchanger/GM1 complex in the nuclear envelope but have no exchanger in the plasma membrane: comparison to astrocytes

Previous work demonstrated the presence of an isoform of Na(+)/Ca(2+) exchanger in the nuclear envelope of neurons and NG108-15 cells that is tightly associated with GM1 ganglioside and potentiated by the latter. This contrasted with the Na(+)/Ca(2+) exchanger(s) in the plasma membrane, which were suggested to associate more loosely with GM1. To study these aspects of Na(+)/Ca(2+) exchanger expression in nonneuronal neural cells, we have examined nuclear and plasma membrane exchanger patterns in astrocytes and C6 cells, a glia-derived line. We find both cell types contain the tightly associated exchanger/GM1 complex in the nuclear envelope but, surprisingly, only astrocytes possess Na(+)/Ca(2+) exchanger activity in the plasma membrane. This is the first reported example of a cell (C6) with Na(+)/Ca(2+) exchangers in the nuclear envelope but not in the plasma membrane. RT-PCR established the presence of the NCX1 subtype in C6 cells and both NCX1 and NCX2 in astrocytes. Comparison was made with NG108-15 cells, which have Na(+)/Ca(2+) exchangers in both nuclear and plasma membranes, and Jurkat cells, which have no Na(+)/Ca(2+) exchanger in either membrane. Culturing of C6 cells in the presence dibutyryl-cAMP caused upregulation of a high molecular weight isoform of the exchanger together with GM1 in the nuclear envelope, resulting in significant elevation of Na(+)/Ca(2+) exchanger activity in the latter. Application of exogenous GM1 to nuclei from non-treated cells also potentiated exchanger activity, although to a lesser degree. The Na(+)/Ca(2+) exchanger/GM1 complex occurs in the inner membrane of the nuclear envelope, suggesting a functional role in transferring Ca(2+) between nucleoplasm and the envelope lumen.

Ganglioside/calmodulin kinase II signal inducing cdc42-mediated neuronal actin reorganization

Cell surface glycoconjugates are thought to mediate cell-cell recognition and play roles in neuronal development and functions. We demonstrated here that exposure of neuronal cells to nanomolar levels of gangliosides Neu5Acalpha 8Neu5Acalpha 3Galbeta 4GlcCer, Galbeta 3GalNAcbeta 4(Neu5Acalpha 8Neu5Acalpha 3)Galbeta 4GlcCer (GD1b), Neu5Acalpha 3Galbeta 3GalNAcbeta 4(Neu5Acalpha 8Neu5Acalpha 3)Galbeta 4GlcCer (GT1b) or its oligosaccharide portion induced a rapid and transient activation of Ca2+/calmodulin-dependent protein kinase II (CaM-KII) in the subplasmalemma. Galbeta 3GalNAcbeta 4(Neu5Acalpha 3)Galbeta 4GlcCer (GM1), GalNAcbeta 4(Neu5Acalpha 3)Galbeta 4GlcCer, Neu5Acalpha 3Galbeta 4GlcCer, Neu5Acalpha 3Galbeta 3GalNAcbeta 4(Neu5Acalpha 3)Galbeta 4GlcCer (GD1a), and Neu5Acalpha 8Neu5Acalpha 3Galbeta 3GalNAcbeta 4(Neu5Acalpha 8Neu5Acalpha 3)-Galbeta 4GlcCer were ineffective. GT1b and GD1b stimulated transient elevation of bulk cytosolic Ca2+ levels while GM1 slightly elevated the levels and GD1a did not. Thus, the cytosolic Ca2+ elevation by the gangliosides may trigger the CaM-KII activation. The treatment was accompanied by peripheral actin polymerization and filopodia formation in NG108-15 cells and primary hippocampal neurons, but not in glial cells. CaM-KII inhibitors blocked both CaM-KII activation and the subsequent filopodia formation. A small G-protein cdc42 was a potential downstream target of CaM-KII activated by the gangliosides. These results suggest that oligosaccharides of the gangliosides serve as potential regulators of the filopodia formation in neuronal cells by triggering the activation of CaM-KII followed by cdc42 up-regulation via a cell surface receptor-like component. The filopodia formation induced by the gangliosides may have a physiological relevance because long-term exposure of hippocampal neurons to GT1b oligosaccharide induced advanced dendritogenesis. Furthermore, exposure of cerebellar neurons to GT1b oligosaccharide facilitated CaM-KII-dependent dendritic outgrowth and branch formation of cerebellar Purkinje neurons, in which actin isoforms were localized to motile structures in dendrites. Thus, the ganglioside/CaM-KII signal plays a role in modulating dendritic morphogenesis by inducing cdc42-mediated actin reorganization.

Effect of glycosphingolipids purified from Leishmania (Leishmania) amazonensis amastigotes on human peripheral lymphocytes

The effect of purified glycosphingolipids from Leishmania (Leishmania) amazonensis on human lymphoproliferation, on expression of human lymphocyte and monocyte markers (CD3, CD4, CD8, CD14, CD19, and CD45), and on lymphocyte protein kinase C activity was analyzed.

Potentiation of a sodium-calcium exchanger in the nuclear envelope by nuclear GM1 ganglioside

Calcium is recognized as an important intracellular messenger with a pivotal role in the regulation of many cytosolic and nuclear processes. Gangliosides of various types, especially GM1, are known to have a role in some aspects of Ca2+ regulation, operating through a variety of mechanisms that are gradually coming to light. The present study provides evidence for a sodium-calcium exchanger in the nuclear envelope of NG108-15 neuroblastoma cells that is potently and specifically activated by GM1. Immunoblot analysis revealed an unusually tight association of GM1 with the exchanger in the nuclear envelope but not with that in the plasma membrane. Exchanger and associated GM1 were located in the inner membrane of the nuclear envelope, suggesting this system could function to transfer Ca2+ between nucleoplasm and the envelope lumen. The GM1-enhanced exchange was blocked by cholera toxin B subunit while C2-ceramide, a recently discovered inhibitor of the exchanger, blocked all transfer. Exchanger activity was significantly elevated in nuclei isolated from cells that were induced to differentiate by KCl + dibutyryl-cAMP, a treatment previously shown to promote up-regulation of nuclear GM1 in conjunction with axonogenesis. Similar enhancement was achieved by addition of exogenous GM1 to nuclei from undifferentiated cells. These results suggest a prominent role for nuclear GM1 in regulation of nuclear Ca2+ homeostasis.

Ganglioside GM(1) biphasically regulates the activity of protein kinase C by the effects on the structure of the lipid bilayer

Addition of a small amount of ganglioside GM(1) to phosphatidylserine (PS) liposomes, a gradual increase of protein kinase C (PKC) activity was recorded up to about 2 mol% GM(1) where the maximal enzyme activity was obtained. Then the activity of PKC began to decline and even turned to be inhibited with the further increase of GM(1) content. It was also indicated that GM(1)/PS binary liposomes had the highest membrane fluidity and very low spatial density of lipid headgroups which was demonstrated in the MC-540 studies due to the interposition of GM(1) when the liposomes contained about 2 mol% GM(1). Besides, the liposomes containing about 2 mol% GM(1) provided a more hydrophobic environment for PKC than the liposomes containing less or more GM(1) which was indicated in the Acrylodan experiments. These factors commonly induced PKC to be stimulated maximally. Whether at the lower or higher GM(1) content, the membrane structure was not the most suitable to support the activity of PKC, which declined as a consequence.

Ganglioside as an endogenous growth suppressor for glomerular mesangial cells

BACKGROUND

Glomerular mesangial cells potentially secrete many growth-modulating substances that could regulate mesangial cell proliferation. To date, however, the properties of such factors have not been fully evaluated.

METHODS

For that purpose, conditioned medium (CM) from mesangial cells was used for cross-feeding experiments. Cell proliferation was evaluated by 3H-thymidine incorporation assay and direct cell counting. The growth-regulatory molecule was further characterized using biochemical techniques.

RESULTS

Cross-feeding this CM to mesangial cells in vitro, despite stimulation with platelet-derived growth factor (PDGF), effectively suppressed the cells' synthesis of DNA in a dose-dependent manner. The inhibitory substance derived from mesangial cells was less than 3 kD in molecular mass, was heat stable, and was insensitive to proteinase K. After neuraminidase digestion, this inhibitory activity was lost. These data indicated that the inhibiting substance bore the typical features of gangliosides, which are multifunctional glycolipids that reside in cell membrane. Gangliosides were abundant in the CM from mesangial cells, as detected by metabolic radiolabeling and thin-layer chromatography (TLC). This result suggested that mesangial cells constitutively shed gangliosides. The growth suppressive activity in the CM was blunted when mesangial cells were pretreated with the ganglioside synthesis inhibitor d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol-HCl (d-threo-PDMP; 20 micromol/L) in accordance with the decreased ganglioside content in cells. Finally, gangliosides isolated from CM of mesangial cells suppressed PDGF-induced DNA synthesis of mesangial cells.

CONCLUSIONS

These results suggest that mesangial cells constitutively shed gangliosides that then suppress the division of these cells in an autocrine-like manner.

Hyperalgesia induced by peripheral inflammation is mediated by protein kinase C betaII isozyme in the rat spinal cord

We have addressed the molecular mechanism(s) of hyperalgesia, which depends on increased excitability of dorsal horn neurons and on sensitization of primary afferent nociceptors, during peripheral inflammation. Following unilateral adjuvant-induced inflammation in the rat hind paw, time-course changes in behavioral hyperalgesia and functional activities of Ca2+/phospholipid-dependent protein kinase C isozymes were examined. Inflammation was characterized by increase in paw diameter, and behavioral hyperalgesia was quantified as paw withdrawal latency from a radiant heat source. Behavioral hyperalgesia on the injected paw was significantly increased. This was accompanied by a significant increase in total functional membrane-associated protein kinase C activity, whereas total cytosolic protein kinase C activity was unchanged on the sides of the lumbar spinal cord both contralateral and ipsilateral to the inflammation. Importantly, on the side of lumbar cord ipsilateral to the inflamed paw, the activity of membrane-associated protein kinase CbetaII was increased following the same time-course as the paw withdrawal latency decrease, suggesting an increased translocation of protein kinase Cbetall to the membrane related to behavioral hyperalgesia. A defined mixture of purified gangliosides, which inhibits intracellular protein kinase C translocation and activation, decreased inflammation-induced paw withdrawal latency, and specifically decreased the activity of membrane-associated protein kinase Cbetall on the side of the spinal cord ipsilateral to the inflammation. Quantitative immunohistochemical analyses demonstrated intensified protein kinase CbetaII-like immunoreactivity on the side of the spinal cord ipsilateral to the inflammation. Time-course for increases in the activity of membrane-associated protein kinase CbetaII, and in intensity of protein kinase CbetaII-immunoreactivity, paralleled inflammation-mediated changes in paw withdrawal latency and paw diameter. Our findings indicate an apparent involvement of protein kinase CbetaII isozyme specifically in the molecular mechanism(s) of thermal hyperalgesia.

Gangliosides derived from a T cell lymphoma inhibit bone marrow cell proliferation and differentiation

Previously, we have observed a modulation in the bone marrow hematopoiesis and alteration in the repertoire of blood monocytes and lymphocytes in mice bearing a spontaneous T cell lymphoma, designated as Dalton's lymphoma (DL). In the present investigation, we show that in vivo or in vitro treatment of bone marrow cells (BMC) with gangliosides of DL (DLG) results in inhibition of proliferative ability and alteration of colony-forming ability (CFA) of BMC. BMC incubated with DLG also showed a decrease in cell viability in a concentration-dependent manner. BMC colony-forming assays in the presence of macrophage-colony-stimulating factor (M-CSF) showed a dose-dependent decrease in the number of colonies with a concomitant decrease in macrophage- and granulocyte macrophage-colony-forming units (CFU-M and CFU-GM, respectively) and an increase in granulocyte-CFU (CFU-G). Neuraminidase treatment of DLG abrogated their inhibitory action on BMC. Further, antibodies to GD3 and to lesser extent GM2 neutralized the inhibitory effect of DLG on BMC.

Zwitterionic and acidic glycosphingolipids of the Drosophila melanogaster embryo

Defining glycosphingolipid structures in species amenable to genetic manipulation, such as Drosophila melanogaster, provides a foundation for investigating mechanisms that regulate glycolipid expression. Therefore, eight of the 12 major glycosphingolipids, accounting for 64% of lipid-linked carbohydrate in Drosophila embryos, were purified after separation into acidic and zwitterionic pools. The zwitterionic lipids possess phosphoethanolamine (PEtn) linked to one or more GlcNAc residues and comprise a family of serially related structures. The longest characterized glycolipid, an octaosylceramide, designated Nz28, has the structure: GalNAcbeta, 4(PEtn-6)GlcNAcbeta,3Galbeta,3GalNAcalpha,4Ga lNAcbeta, 4(PEtn-6)GlcNAcbeta,3Manbeta,4GlcbetaCer. Heptaosyl (Nz7), hexaosyl (Nz6), pentaosyl (Nz5) and tetraosyl (Nz4) forms of Nz28, sequentially truncated from the nonreducing terminus, possess only one PEtn moiety. The major acidic lipid, designated Az29, possesses two PEtn moieties and a glucuronic acid linked to a Gal-extended Nz28. Two other acidic glycolipids, Az9 and Az6, exhibit one PEtn moiety and the same hexose and N-acetylhexosamine composition as Az29 and Nz6, respectively. The fully extended Drosophila core oligosaccharide differs from that of other dipterans in the linkage at a single glycosidic bond, a distinction with significant structural and biosynthetic consequences. Furthermore, acidic species account for a larger proportion of total glycosphingolipid, and PEtn substitution of GlcNAc is more complete in the Drosophila embryo. Divergent characteristics may reflect interspecies variation or stage-specific glycosphingolipid expression in dipterans.

Ganglioside GD1b supresses immunoglobulin production by human peripheral blood mononuclear cells

Gangliosides are sialic acid-containing glycolipids, that have various immunomodulatory effects. We previously reported that various gangliosides in vitro either inhibited or enhanced spontaneous immunoglobulin (Ig) production by human peripheral blood mononuclear cells (PBMC). GD1b was one of the inhibitory gangliosides. In this study, we further examined the mechanism for the inhibitory effect of GD1b. The inhibitory effect of GD1b was revealed at 0.1 microM, increased dose dependently, and was maximized at 10 microM, which reduced spontaneous IgG, IgM, and IgA production of human PBMC by 50.5%, 52.0%, and 48.3% compared with controls, respectively. GD1b did not affect the proliferation and viability of PBMC. GD1b did not alter Ig production of B cells alone. Interleukin 6 (IL-6) and IL-10 each partially reversed the GD1b-induced inhibition of Ig production by PBMC, and the addition of both cytokines completely reversed the inhibition. When endogenous IL-6 and IL-10 were neutralized by specific antibodies, GD1b did not reveal inhibitory effects on the Ig production. GD1b inhibited IL-6 and IL-10 production of CD4+ T cells, without affecting those of CD8+ T cells, monocytes, or B cells. When CD4+ T cells were preincubated with GD1b and washed and cultured with B cells and monocytes, Ig production was also suppressed. These results suggest that GD1b may indirectly suppress Ig production of B cells in whole PBMC by reducing IL-6 and IL-10 production of CD4+ T cells. GD1b may act as an important inhibitor of human humoral immune responses.

Regulation of transmembrane signaling by ganglioside GM1: interaction of anti-GM1 with Neuro2a cells

Interaction of antibodies to ganglioside GM1 with Neuro2a cells was studied to investigate the role of GM1 in cell signaling. Binding of anti-GM1 to Neuro2a cells induced the formation of 3H-inositol phosphates (3H-IPs) and elevated the intracellular Ca2+ concentration [Ca2+]i. The rise in [Ca2+]i was due to the influx of Ca2+ from the extracellular medium and release from intracellular Ca2+ pools. The Ca2+ influx pathway did not allow the permeation of Na+ or K+. The influx was inhibited by amiloride, a specific blocker of T-type Ca2+ channels, whereas nifedipine and diltiazem, blockers of L-type Ca2+ channels, did not have any effect. Thus, anti-GM1 appears to activate a T-type Ca2+ channel in Neuro2a cells. The intracellular Ca2+ release was inhibited by pretreatment of cells with neomycin sulfate, phorbol dibutyrate, and pertussis toxin (PTx), which also inhibited the 3H-IP formation in Neuro2a cells. Addition of caffeine neither elevated the [Ca2+]i nor affected the anti-GM1-induced [Ca2+]i rise. The data reveal that the binding of anti-GM1 to Neuro2a cells activates phospholipase C via a PTx-sensitive G protein, which leads to formation of IPs and release of Ca2+ from inositol trisphosphate-sensitive pool of endoplasmic reticulum. Anti-GM1 also arrested the differentiation of Neuro2a cells in culture and significantly stimulated their proliferation. This stimulatory effect of anti-GM1 on cell proliferation was blocked by amiloride but not by PTx, suggesting that the influx of Ca2+ was essentially required for cell proliferation. Our data suggest a role for GM1 in the regulation of transmembrane signaling events and cell growth.

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.

Upregulation of nuclear GM1 accompanies axon-like, but not dendrite-like, outgrowth in NG108-15 cells

Recent work has demonstrated that induced neurite outgrowth in neuroblastoma cells and spontaneous differentiation of primary neurons in culture are accompanied by upregulation of GM1 ganglioside in the nuclear envelope. Previous reports have depicted morphological variations in the nature of stimulated neurites resulting from different neuritogenic agents, and a recent study by this laboratory demonstrated that such stimulants could be divided into two categories: those which induce axon-like neurites (group I) as opposed to those that stimulate dendrite-like outgrowths (group II). The former includes KCl, ionomycin, neuraminidase, and cholera toxin B subunit (all agents which elevate intracellular Ca2+), while the latter group is comprised of retinoic acid, dibutyryl cAMP, exogenous GM1, and low serum treatment. The present study was undertaken to determine whether differences in neuritic phenotype could be correlated with upregulation of nuclear GM1. The neuroblastoma x glioma NG108-15 cell line was employed because of its ability to respond robustly to a variety of neuritogenic stimuli. It was found that although both groups of stimulants are capable of inducing stable neurites (terminal differentiation) in this cell line, nuclear GM1 is elevated only in the presence of group I stimulants. Thus, a correlation is indicated between axonogenesis and upregulation of GM1 in the nuclear envelope. Additionally, these two events appear to coincide with elevation of intracellular Ca2+. Conversion of cells to the differentiated phenotype, with or without nuclear GM1 elevation, was found to depend in some cases on concentration of stimulant and duration of treatment.

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.

Cerebrosides A and C, sphingolipid elicitors of hypersensitive cell death and phytoalexin accumulation in rice plants

When plants interact with certain pathogens, they protect themselves by generating various chemical and physical barriers called the hypersensitive response. These barriers are induced by molecules called elicitors that are produced by pathogens. In the present study, the most active elicitors of the hypersensitive response in rice were isolated from the rice pathogenic fungus Magnaporthe grisea, and their structures were identified as cerebrosides A and C, sphingolipids that were previously isolated as inducers of cell differentiation in the fungus Schizophyllum commune. Treatment of rice leaves with cerebroside A induced the accumulation of antimicrobial compounds (phytoalexins), cell death, and increased resistance to subsequent infection by compatible pathogens. The degradation products of cerebroside A (fatty acid methyl ester, sphingoid base, and glucosyl sphingoid base) showed no elicitor activity. Hydrogenation of the 8E-double bond in the sphingoid base moiety or the 3E-double bond in the fatty acid moiety of cerebroside A did not alter the elicitor activity, whereas hydrogenation of the 4E-double bond in the sphingoid base moiety led to a 12-fold decrease in elicitor activity. Furthermore, glucocerebrosides from Gaucher's spleen consisting of (E)-4-sphingenine and cerebrosides from rice bran mainly consisting of (4E,8E)-4,8-sphingadienine and (4E,8Z)-4,8-sphingadienine showed no elicitor activity. These results indicate that the methyl group at C-9 and the 4E-double bond in the sphingoid base moiety of cerebrosides A and C are the key elements determining the elicitor activity of these compounds. This study is the first to show that sphingolipids have elicitor activity in plants.

Effects of endoglycoceramidase or D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol on glucose uptake, glycolysis, and mitochondrial respiration in HL60 cells

The glycosphingolipid content of HL60 cells was reduced by endoglycoceramidase, an enzyme which specifically hydrolyzes glycosphingolipids on the cell surface, or by D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, an inhibitor which specifically reduces the activity of UDP-glucose:ceramide glucosyltransferase. Reduction of the glycosphingolipid content by both reagents resulted in enhancement of glucose uptake and glycolysis. Neither of these effects was observed in the presence of cytochalasin B, an inhibitor of facilitated glucose transport. The uptake of radiolabeled 3-O-methylglucose by the cells was not affected by treatment with either of the reagents, indicating no activation of the glucose transporter. On the other hand, both reagents decreased the level of ATP and CO2 production. The molecule mediating these effects appeared to be ceramide, since both treatments actually increased the intracellular ceramide content, and the cell-permeable short-chain ceramide N-acetylsphingosine, but not sphingosine, sphinganine, or palmitic acid, mimicked the effects of both reagents to comparable extents. Finally, the function of electron transport in isolated mitochondria fractions was found to be reduced by treatment of the cells with N-acetylsphingosine. These results strongly suggest that ceramide may affect mitochondrial respiration.

Immunonutrition: role of biosurfactants, fiber, and probiotic bacteria

Phospholipids constitute an important part of cellular membranes, and membrane fluidity and permeability are dependent on the fatty acid composition of the phospholipid. The composition, which changes with aging and disease is, to a large degree, influenced by nutrient supply. Phospholipids have been effective in protecting cellular membranes such as those of the gastrointestinal tract to an extent not much different from that observed with external supply of established mucosa-protective drugs such as misoprostol and sucralfate. Polar lipids have also been shown to be effective in preventing microbial translocation. The effect is further potentiated by an external supply of probiotic fibers such as pectin, guar gum, and oat gum. These and many other fibers also have documented strong mucosa preventive effects. Prebiotic bacteria such as Lactobacillus plantarum have demonstrated a strong ability to preserve food and prevent spoilage. In addition, L. plantarum seems to not only preserve key nutrients such as omega-3 fatty acids, but also increases its content during storage conditions. L. plantarum alone or in combination with various fibers has demonstrated a strong ability to reduce and eliminate potentially pathogenic microorganisms both in vitro and in vivo. It has recently been shown that L. plantarum possesses the ability to adhere to and colonize intestinal mucosa. It seems unique among the lactobacilli for L. plantarum to use mannose-specific adhesins, uncommon among gram-positive, but common among gram-negative bacteria, which makes it possible that L. plantarum competes with gram-negative other potential pathogens for receptor sites at the mucosal cell surfaces. Additionally, L. plantarum seems to be effective in eliminating nitrate and producing nitric oxide. These functions of L. plantarum are among the reasons why it has been used in combination with various fibers and polar lipids to recondition the gastrointestinal mucosa. For the purpose of a L. plantarum-containing formula being produced and tried, a treatment policy is regarded as an extension of the immunonutrition program and called ecoimmunonutrition.

Expression and regulation of interferon-gamma-induced tryptophan catabolism in cultured skin fibroblasts

Interferon-gamma (IFN-gamma)-induced, indoleamine dioxygenase-catalyzed tryptophan catabolism was studied in cultured human foreskin fibroblasts using the increase in cellular kynurenine synthesis as an index of gene expression. The time courses of the inhibition of IFN-gamma-induced kynurenine synthesis by actinomycin D and cycloheximide showed that the indoleamine dioxygenase gene was transcribed as early as 2 h and translated as early as 5 h after initiation of IFN treatment. Expression was completely inhibited by the Ser/Thr kinase inhibitor, H-7 (66 microM), during the first 2 h after IFN-gamma treatment. Prolonged pretreatment of cells with high concentrations of staurosporine (380 nM) or genestein (610 microM) inhibited expression by 38% and 53%, respectively. Genestein also inhibited expression when it was added to cultures between 8 and 24 h after IFN-gamma treatment. The expression of kynurenine synthesis was inhibited by A23817 during the first 4 h after IFN treatment by mechanisms that were independent of cyclooxygenase, calmodulin, and calcineurin. Exogenous gangliosides (bovine brain gangliosides and purified GM1) inhibited IDO expression throughout the first 24 h after IFN-gamma treatment by mechanisms that did not involve effects on Ca2+ channels. Other biologic response modifiers, including phorbol myristic acetate, arachidonic acid, lipopolysaccharide, analogs of cAMP and cGMP, W-7, and sphingosine, did not induce IDO in the absence of IFN-gamma, nor did they modulate IFN-gamma-induced expression. These results indicate that the expression of kynurenine synthesis is modulated at the transcriptional and posttranscriptional levels by protein tyrosine kinase and by a Ser/Thr kinase with properties distinctly different from those of conventional protein kinase C. The capacity for attenuation of this IFN-gamma-induced response over its entire time course by many effectors and through multiple cellular signaling pathways may represent a mechanism for fine-tuning the level of oxidative tryptophan metabolism to meet the needs of a particular cytostatic or antiproliferative response.

The role of GM1 and other gangliosides in neuronal differentiation. Overview and new finding

The pronounced increases in gangliosides belonging to the gangliotetraose family during the neurite outgrowth phase of neuronal differentiation have suggested a functional requirement for these substances related to process extension, arborization, and possibly synaptogenesis. Support for this hypothesis has come from a variety of experimental paradigms utilizing neuroblastoma cell lines, primary neuronal cultures, and observations on the developing nervous system. We have recently observed that differentiation of both primary neurons and neuroblastoma cells by Ca(2+)-elevating stimulants is characterized by upregulation of GM1 in the nuclear membrane. Immunostaining revealed these Ca(2+)-induced neurites to have axonal characteristics. Recent work has indicated that nuclear GM1 facilitates efflux of nuclear Ca2+, thereby contributing to the reduced level of nuclear Ca2+ that characterizes the differentiated neuron. Thus, while GM1 is generally recognized as a pluripotent molecule with several modulatory roles in the plasma membrane of developing and mature neurons, regulation of Ca2+ flux across the nuclear membrane is proposed as another critical function of this ganglioside in neuronal development, with special relevance to axonogenesis.

Biological water and its role in the effects of alcohol

Alcohol and water compete with each other on target membrane molecules, specifically, lipids and proteins near the membrane surface. The basis for this competition is the hydrogen bonding capability of both compounds. But alcohol's amphiphilic properties give it the capability to be attracted simultaneously to both hydrophobic and hydrophilic targets. Thus, alcohol could bind certain targets preferentially and displace water, leading to conformational consequences. This article reviews the clustering and organized character of biological water, which modulates the conformation of membrane surface molecules, particularly receptor protein. Any alcohol-induced displacement of biological water on or inside of membrane proteins creates the opportunity for allosteric change in membrane receptors. This interaction may also prevail in organelles, such as the Golgi apparatus, which have relatively low concentrations of bulk water. Target molecules of particular interest in neuronal membrane are zwitteronic phospholipids, gangliosides, and membrane proteins, including glycoproteins. FTIR and NMR spectroscopic evidence from model membrane systems shows that alcohol has a nonstereospecific binding capability for membrane surface molecules and that such binding occurs at sites that are otherwise occupied by hydrogen-bonded water. The significance of these effects seems to lie in the need to learn more about biological water as an active participant in biochemical actions. Proposed herein is a new working hypothesis that the molecular targets of ethanol action most deserving of study are those where water is trapped and there is little bulk water. Proteins (enzymes and receptors) certainly differ in this regard, as do organelles.

Diverse aspects of metanephric development

Mammalian nephrogenesis constitutes a series of complex developmental processes in which there is a differentiation and rapid proliferation of pluripotent cells leading to the formation of a defined sculpted tissue mass, and this is followed by a continuum of cell replication and terminal differentiation. Metanephrogenesis ensues with the intercalation of epithelial ureteric bud into loosely organized metanephric mesenchyme. Such an interaction is reciprocal, such that the intercalating ureteric bud induces the conversion of metanephric mesenchyme into an epithelial phenotype, while the mesenchyme stimulates the iterations of the ureteric bud. The induced mesenchyme then undergoes a series of developmental stages to form a mature glomerulus and tubular segments of the kidney. Coincidental with the formation of these nephric elements, the developing kidney is vascularized by the process of vasculogenesis and angiogenesis. Thus, the process of metanephric development is quite complex, and it involves a diverse group of molecules who's biological activities are inter-linked with one another and they regulate, in a concerted manner, the differentiation and maturation of the mammalian kidney. This diverse group of molecules include extracellular matrix (ECM) proteins and their receptors, ECM-degrading enzymes and their inhibitors, growth factors and their receptors, proto-oncogenes and transcription factors. A large body of literature data are available, which suggest a critical role of these molecules in metanephric development, and this review summarizes the recent developments that relate to metanephrogenesis.

The role of ganglioside GM3 in the modulation of conformation and activity of sarcoplasmic reticulum Ca(2+)-ATPase

Rabbit sarcoplasmic reticulum does contain trace amounts of gangliosides, and the main species is GM3. Incorporation of GM3 into the SR vesicles or addition of it to the soybean phospholipid used for reconstitution of proteoliposomes obviously increased ATP hydrolysis, as well as, Ca2+ uptake activity of sarcoplasmic reticulum Ca(2+)-ATPase. Conformation changes of Ca(2+)-ATPase induced by GM3 were also observed by circular dichroism, intrinsic fluorescence and fluorescence quenching measurements.

Effect of sphingosine on rat glial cells: inhibition of prostaglandin E2 and insensitivity of nitric oxide generation

The effect of sphingosine on lipopolysaccharide (LPS)-mediated protein kinase C (PKC) activation and prostaglandin E2 (PGE2) and nitric oxide (NO) production was studied in primary cultures of rat glial cells. Incubation of cells with LPS elicited translocation of PKC from the cytosolic to the membranous compartment, as shown by measuring PKC activity and by immunoblotting. Under these conditions, a sustained increase in both PGE2 and NO production was measured. Thus, PGE2 levels were 259 +/- 28 (n = 8) and 230 +/- 48 (n = 4) (control levels 11.4 +/- 5.2 (n = 5) and 13 +/- 7.5 (n = 3)) pg/ml, at 24 and 48 h, respectively. NO levels were 9.3 +/- 0.9 (n = 10) and 11.6 +/- 0.8 (n = 9) (control levels 0.4 +/- 0.18 and 1.0 +/- 0.44) nmol/ml, at 24 and 48 h, respectively. Sphingosine, a naturally occurring compound, which inhibits PKC activity, elicited a concentration-dependent decrease in LPS-mediated PGE2 production. This inhibition was more pronounced after 48 h than after 24 h of incubation (IC50 = 8 and 20 microg sphingosine, respectively). By contrast, sphingosine did not inhibit NO production under the same conditions. We conclude that sphingosine may be involved in modulation of the local inflammatory response in glial cells, at least in part. We also surmise that LPS-mediated PGE2 production and NO production are probably regulated by different mechanisms, i.e., a PKC-dependent and a PKC-independent mechanism.

Differential effects of synthetic sphingosine derivatives on melanoma cell motility, growth, adhesion and invasion in vitro

Cancer cell surface glycosphingolipids are considered to play a critical role in tumor growth and metastasis. However, the implications of glycoconjugates in the control of cell motility, which is considered to be involved in tumor invasion, are not fully understood. In this study, the effects of a series of synthetic sphingosine derivatives, obtained by the chemical transformation of azidosphingosines, on directional migration of K1735-M2 melanoma cells grown on type I collagen-coated surfaces were investigated. Following the application of 60 microM (2R, 3S, 4E)-2, 3-epimino-4-octadecen-3-ol (S4) the migration rate was 94 +/- 10 microns/day, compared with 377 +/- 22 microns/day in the control experiment. Six other analogues were not as potent. S4 also considerably down-modulated melanoma single cell motility. Inhibition of motile activity was associated with changes in the actin filament organization as well as with changes in the number and distribution of vinculin plaques. Moreover, the compound reduced the attachment abilities of melanoma cells to basement membrane Matrigel. Tumor cell invasion, however, was less affected and proliferation remained unimpaired after treatment with S4. These data suggest at least one intracellular mode of action of this particular synthetic sphingosine derivative by modulation of cytoskeletal organization. Melanoma cell motility and growth may be controlled independently via glycosphingolipids.

Enhancement by ganglioside GT1b of annexin I phosphorylation in bovine mammary gland in the presence of phosphatidylserine and Ca2+

Ganglioside GT1b and, to a lesser extent, GD3, enhanced phosphorylation of a 36 kDa protein (the substrate of protein kinase C) in the particulate fraction from bovine mammary gland. Sialic acids, asialogangliosides, and GM3 were without effect, and GD1a conversely inhibited phosphorylation of the 36 kDa protein. The enhanced phosphorylation by GT1b required the simultaneous presence of phosphatidylserine (PS) and Ca2+. The 36 kDa protein reacted with anti-annexin I in Western blot analysis. Addition of purified annexin I to the reaction mixture containing the particulate fraction increased the extent of phosphorylated 36 kDa protein, and the phosphorylation was further enhanced by GT1b. The enhanced phosphorylation of annexin I by GT1b was also dependent on PS and Ca2+. When annexin I was phosphorylated by purified protein kinase C, GT1b inhibited the annexin I phosphorylation. Addition of epidermal growth factor or insulin to the particulate fraction had little effect on the enhancement. These results suggest that an enzyme or enzymes other than protein kinase C, epidermal growth factor receptor kinase, or insulin receptor kinase is responsible for the GT1b- and GD3-enhanced phosphorylation of annexin I in the presence of PS and Ca2+.

Effect of ganglioside GM3 on the activity and conformation of reconstituted Ca2+-ATPase

Trace amounts of gangliosides were found in rabbit skeletal muscle sarcoplasmic reticulum and their main part was shown, by high performance thin layer chromatography. to be GM3. Addition of GM3 to the soybean phospholipids used for reconstitution of proteoliposomes markedly increased ATP hydrolysis as well as Ca2+ uptake activity of sarcoplasmic reticulum Ca2+-ATPase incorporated into the proteoliposomes. Conformation changes of Ca2+-ATPase induced by GM3 were also observed by intrinsic fluorescence and circular dichroism measurements.

The effect of exogenous gangliosides on matrix metalloproteinase secretion by human glioma cells in vitro

Matrix metalloproteinases (MMPs) are zinc-dependent peptidases and are amongst those enzymes responsible for extracellular matrix (ECM) degradation during tumour-cell migration. Gangliosides are a family of acidic membrane glycolipids thought to play a role during cell development, differentiation and oncogenic transformation. In this descriptive study, we investigated the effects of six exogenous gangliosides (GM1, GM3, GD1a, GD1b, GD3 and GT1b) on the secretion of MMP-2 (72 kDa gelatinase or gelatinase-A) and MMP-9 (92 kDa gelatinase or gelatinase-B). Cell-conditioned media from eight human glioma-derived cell-lines served as the source of MMPs and were investigated using SDS-PAGE zymography. Six of the cell lines showed upregulation of secretion of both enzymes by all six gangliosides. Of the remaining two cell lines, one showed inhibition of MMP secretion by all gangliosides and the other had a small but differential response to the range of gangliosides investigated. These results suggest that gangliosides may stimulate glioma cell invasiveness by promoting MMP expression.

Trophic effect of cholera toxin B subunit in cultured cerebellar granule neurons: modulation of intracellular calcium by GM1 ganglioside

Survival of cerebellar granule cells (CGC) in culture was significantly improved in the presence of cholera toxin B subunit (Ctx B), a ligand which binds to GM1 with specificity and high affinity. This trophic effect was linked to elevation of intracellular calcium ([Ca2+]i), and was additive to that of high K+. Survival was optimized when Ctx B was present for several days during the early culture period. 45Ca2+ and cell survival studies indicated the mechanism to involve enhanced influx of Ca2+ through L-type voltage-sensitive channels, since the trophic effect was blocked by antagonists specific for that channel type. Inhibitors of N-methyl-D-aspartate receptor/channels were without effect. During the early stage of culture Ctx B, together with 25 mM K+, caused [Ca2+]i to rise to 0.2-0.7 microM in a higher proportion of cells than 25 mM K+ alone. A significant change in the nature of GM1 modulation of Ca2+ flux occurred after 7 days in culture, at which time Ctx B ceased to elevate and instead reduced [Ca2+]i below the level attained with 25 mM K+. GM1 thus appears to serve as intrinsic inhibitor of one or more L-type Ca2+ channels during the first 7 days in vitro, and then as intrinsic activator of (possibly other) L-type channels after that period. This is the first demonstration of a modulatory role for GM1 ganglioside affecting Ca2+ homeostasis in cultured neurons of the CNS.

Cholera toxin binds to differentiating neurons in the developing murine basal ganglia

Cell-surface expression of gangliosides in the developing mammalian central nervous system is temporally-regulated in a cell-type and regionally specific fashion. Gangliosides may be involved in cell-cell and cell-matrix interactions, and can act synergystically with several growth factors or growth factor receptors. Thus, a role for gangliosides in the regulation of neuronal stem cell proliferation and differentiation has been suggested. We have previously shown that cholera toxin B subunit (CTB), which binds to the ganglioside GM1, binds heterogeneously to dissociated neuroepithelial cells from the developing mouse telencephalon. We stained fixed sections of the ganglionic eminences (GE) of fetal mouse brains and found that CTB labels regions which contain differentiating neurons, but does not stain the rapidly dividing neuroepithelial cells in the ventricular zone. We dissociated cells from the GE on day 14 of gestation (E14), labeled the cells with CTB-FITC, and separated them by flow cytometry. We found the highest level of CTB binding in postmitotic cells which had begun to express markers of neuronal differentiation. When CTB-sorted cells were placed into short-term (48 h) cell culture, high CTB binding continued to correlate with fewer numbers of proliferating cells and larger numbers of differentiating neurons. CTB binding and fluorescence activated cell sorting appear to be useful for separating populations of differentiating neurons from immature, proliferating cells. These studies further lead us to suggest that GM1 plays a role in the differentiation of neurons in the basal ganglia.

Prosaposin and prosaptide, a peptide from prosaposin, induce an increase in ganglioside content on NS20Y neuroblastoma cells

Prosaposin has been recently identified as a neurotrophic factor eliciting differentiation in neuronal cultured cells (NS20Y). In this paper we investigate whether prosaposin and its active peptide (prosaptide) may modify the ganglioside pattern in neuroblastoma cells. The analysis by high performance thin layer chromatography did not reveal qualitative changes in the ganglioside pattern of NS20Y cells incubated in the presence of prosaposin, compared to control cells, but it did reveal an increase of the content of all three major resorcinol positive bands (GM3, GM2, GD1a). Cytofluorimetric and immunofluorescence microscopic analysis revealed that the increase of the ganglioside content was at the plasma membrane level. These findings suggest that the neurotrophic activity of prosaposin on NS20Y neuroblastoma cells might be mediated in part by the increase of cell surface gangliosides.

Experimental evidence of a temperature-related conformational change of the hydrophilic portion of gangliosides

The present paper reports the experimental observation of an interesting thermodynamic process which could be biologically important: such behaviour, shown by some gangliosides, is likely to be peculiar of these glycosidic compounds as it has never been observed for other membrane-type amphiphilic molecules. In water solution, gangliosides have been found to present a bistable behaviour between two stable states (called A and B) which does not involve any change in the primary structure of the molecule. The interconversion between state A and state B, and vice versa, does not occur spontaneously, but has to be triggered by some external agent, which makes this system a potentially regulated process with important biological correlations. In the present experiments, state B is reached from state A with a temperature rise in the range 30-55 degrees C. The new state is stable regardless of any possible temperature cycle. The initial state A is then regained when the ganglioside solution is dried and the solute is redissolved. The two states are believed to correspond to two different conformations of the hydrophilic portion of the molecule. The bistable behaviour is shown by the gangliosides GM2, GM1, GD1a, GD1b and Fuc-GD1b, GT1b, however, does not show such an effect.

Gangliosides inhibit PDGF-induced signal transduction events in U-1242 MG human glioma cells

In this study we investigated the responses of intracellular calcium ([Ca2+]i) and protein kinase C (PKC) to PDGF in U-1242 MG cells. PDGF-BB stimulated [3H]PDBu binding approximately 2-3 fold. This response was inhibited by preincubating the cells with an inhibitor of phospholipase C (PLC), U73122, suggesting that PLC mediates the induction of PKC translocation by PDGF. PDGF also increased the concentration of [Ca2+]i that was attenuated in a calcium-free medium. This indicates that PDGF-induced elevation of [Ca2+]i is mainly due to influx of extracellular calcium. PDGF-stimulated translocation of PKC was inhibited by the intracellular calcium buffer BAPTA/AM. All gangliosides studied except GM3 inhibited these responses with similar efficacy. Collectively, these results indicate that the signal transduction pathway initiated by PDGF leading to PKC translocation in U-1242 MG cells is intact, and this pathway is inhibited by several gangliosides.