Glycosphingolipids and antitumor immunity.
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Animals↗
Biomedical subjects
L D Bergelson
Publications and source records attributed to L D Bergelson.
The molecular organization of the influenza virus surface. Studies using photoreactive and fluorescent labeled phospholipid probes.
The membrane structures of remantadin-sensitive and remantadin-resistant influenza virus strains were studied using a photoreactive fatty acid as well as analogues of phosphatidylcholine, phosphatidylethanolamine and sphingomyelin, carrying a fluorescent or photoreactive reporter group at the end of one of the aliphatic chains. The results obtained demonstrated for the first time that the phospholipids of the viral membrane form lateral domains differing by the fluidity of their hydrocarbon chains and, probably, by the head-group composition of the lipids. The hemagglutinin small subunit (HA2) was shown to protrude into the apolar region of the phospholipid bilayer, whereas the M1 protein makes contact only with the inner surface. In the remantadin-sensitive virions the heavy hemagglutinin chain (HA1) appears not to be in contact with the lipid bilayer, whereas in the remantadin-resistant strain HA1 has a hydrophobic segment that proved to be inserted into the bilayer.
Animals↗
Phospholipid topology and flip-flop in intestinal brush-border membrane.
The topological distribution of the two major phospholipids of brush-border membrane, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), has been investigated using brush-border membrane vesicles from rabbit small intestine. Bee venom phospholipase A2 and phosphatidylcholine exchange protein from bovine liver were used as membrane probes. It is shown that the brush-border membrane retains its integrity under conditions of phospholipase hydrolysis and intermembrane phospholipid exchange. Kinetic analysis of the data of phospholipase hydrolysis and phospholipid exchange at temperatures under 10 degrees C shows that both PC and PE occur in two pools: a minor (about 25%) more readily accessible pool and a major one (about 75%) less readily available. The rate of PC exchange between these two pools is relatively fast. The half-time derived under conditions of phospholipase hydrolysis is of the order of 20 min. Under conditions of phospholipid exchange the exchange rates may be even faster. The difference in exchange kinetics observed with the two methods of probing is probably due to changes in membrane properties such as the bilayer fluidity induced by the probing process itself. It is proposed that the two pools represent the transverse distribution of the phospholipids. The two major phospholipids of brush-border membranes, PC and PE, would be distributed mainly on the inner (cytoplasmic) side of the brush-border membrane. The phospholipid exchange between the brush-border vesicles and unilamellar phosphatidylcholine vesicles in the presence of phosphatidylcholine exchange protein reveals that significant quantities of phospholipid are taken up by brush-border membrane independently, i.e., in a separate process independent of the exchange protein-catalyzed phosphatidylcholine exchange.
Androgen-Binding Protein↗
The binding of the B-chain of ricin to Burkitt lymphoma cells. A new approach to ligand-receptor interaction studies.
It is shown that conformational changes of receptor proteins brought about by binding of a ligand induce changes in the lipid environment of the receptor that can be monitored by fluorescent lipid probes. On this basis a new approach to studies of ligand-receptor binding is proposed. Using the interaction of the ricin B-chain with Burkitt lymphoma cells as an example and fluorescent labelled sphingomyelin as a probe, the ligand-induced changes of fluorescence anisotropy were shown to be concentration-dependent and to permit determination of the binding constant and the number of receptor-binding sites. The method was found to be specific and highly sensitive, allowing detection of the action of one RB molecule per cell. Scatchard analysis of the binding of 125I-RB demonstrated the presence on the cell surface of two binding sites with Kd approximately 10(-10) and approximately 10(-8) M, respectively. Only the high-affinity sites were detected by the fluorescence technique. Saturation of these sites resulted in maximum inhibition of protein synthesis.
Burkitt Lymphoma↗
Monoclonal antibody reveals heterogeneity in human aortic intima: detection of a ganglioside antigen associated with a subpopulation of intimal cells.
The cells of the arterial wall are heterogeneous. To study the functions and peculiarities of various subpopulations of arterial cells the authors have generated an IgM mouse monoclonal antibody, designated 3-Lena, which interacts with human aortic cells (demonstrated by RIA and flow cytofluorometry). The cellular antigens interacting with monoclonal antibody 3-Lena are gangliosides GM3, GD3, GD1a, and GT1b. Presumably, the epitope is represented by the structure -NeuAc alpha 2----3Gal beta 1, a component of the oligosaccharide moiety of the ganglioside molecule. In addition to aortic cells, those dissociated from other large human vessels as well as cells of the myometrium and lung parenchyma interact with 3-Lena. Cells dissociated from the spleen and renal cortex exhibit a substantially weaker interaction, while liver and myocardial cells do not react. Compared with human aortic cells, aortic cells of other mammalian species stain less effectively (dog, swine) or do not stain at all (bovine, ram). Flow cytofluorometric analysis demonstrates that practically all human aorta medial cells interact with antibody 3-Lena, whereas a certain portion of cells in the intimal population do not. In the outer intimal sublayer adjoining the media, the cells reacting with monoclonal antibody 3-Lena make up the bulk of the cell population, and the inner sublayers are characterized by a prevalence of nonreactive cells. After separation of reactive and nonreactive human aortic intimal cells by a cytofluorometer-cell sorter, 3-Lena+ cells were found to have an elongated bipolar shape, whereas most 3-Lena- cells have multiple processes and variable elongated, stellate, or irregular shapes.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Influence of platelet activation factor and prostaglandins on cholesterol esterification in human plasma.
Prostaglandin E1 (PGE1) and platelet activation factor (PAF) were found respectively to activate or to inhibit cholesterol esterification in whole plasma but not in lipoprotein-deficient plasma. It is suggested that these effects are mediated by the interaction of PGE1 and PAF with high-density lipoproteins [(1984) FEBS Lett. 173, 291-294]. Possible physiological implications of these findings are discussed.
Alprostadil↗
Influence of cholesterol and prostaglandin E1 on the molecular organization of phospholipids in the erythrocyte membrane. A fluorescent polarization study with lipid-specific probes.
Anthryl-labeled fluorescent probes closely mimicking phosphatidylcholine and sphingomyelin were applied to study the state of these phospholipids in the rabbit erythrocyte membrane. At normal cholesterol levels both probes exhibited higher fluorescence polarization values in the membranes than in phospholipid vesicles of similar lipid composition, indicating a decreased fluidity of the probe environment in erythrocyte ghosts. In ghosts prepared from normal erythrocytes no evidence of lateral separation of phosphatidylcholine and sphingomyelin was found. At higher cholesterol levels, however, these lipids appear to segregate. Probably the effect of cholesterol on the erythrocyte membrane lipids involves lipid-protein interactions. At physiological concentrations, prostaglandin E1 only weakly affects the state of phosphatidylcholine and sphingomyelin in erythrocyte membranes. Cholesterol enrichment amplifies the effect of prostaglandin E1. Although the prostaglandin E1-induced changes depended much upon whether the ghosts were enriched with cholesterol in vitro or in vivo, with both types of ghosts effects of prostaglandin E1 were seen at extremely low effector concentrations that may have presented a few molecules of prostaglandin per ghost. The structural and functional significance of these findings is discussed.
Alprostadil↗
Determination of total intracellular lipid content by flow cytofluorometry.
It was demonstrated that perylenoyl-labeled triglyceride, rac-1,2-dioleoyl-3-[9(3-perylenoyl)nonanoyl]glycerol (PLTG), specifically stains the intracellular lipids in formalin-fixed and non-fixed cells in situ and in suspension. The fluorescence of labeled cells was registered on a FACS-II cytofluorometer. It was found that the mean intensity of fluorescence in PLTG-labeled cells of various types, both fixed and non-fixed, correlates with their total lipid content. There was no correlation, however, between the mean intensity of fluorescence and intracellular levels of lipids belonging to different classes: phospholipids, triglycerides, cholesterol or cholesteryl esters.
Animals↗
Action of influenza virus neuraminidase on gangliosides. Haemagglutinin inhibits viral neuraminidase.
The action of partly purified neuraminidase (NA) of influenza A virus, a mixture of detergent solubilized NA and haemagglutinin (HA) and of intact virions on gangliosides GT1b, GD1a, GD1b, GM1 was studied. The viral NA transformed GT1b mainly into GD1b with formation of only minor amounts of GM1. HA was found to inhibit the hydrolysis activity of viral NA. At the same time viral NA transformed GD1a quantitatively into GM1 which was not hydrolyzed by the enzyme. These results suggest that the function of NA is to transfer the 'primary' receptor (such as GT1b) into the proper carbohydrate sequence (GD1b-like) which is proposed to serve as the minimal structure required for influenza virus reception.
G(M1) Ganglioside↗
Lipid-specific fluorescent probes in studies of biological membranes.
Lipid-specific fluorescent probes are natural lipids carrying an apolar fluorophore in one of the hydrocarbon chains. Since such probes retain the head groups and resemble the molecular shape of native membrane lipids, they largely mimic the behaviour of their natural prototypes in biological membranes. Information provided by the lipid-specific probes is more differentiated and easier to interpret than that obtained from non-lipid probes. The principles of design of lipid-specific probes are formulated and the relative advantages and disadvantages of various fluorophores are discussed. In order to reduce ambiguities caused by perturbation of the probe environment, it is proposed to use, in a comparative manner, two or more lipid-specific probes resembling each other in all aspects except the polar head groups (the 'two probes' concept). Two types of fluorophores, the anthrylvinyl group and the perylenoyl group, were found to be well suited for the synthesis of lipid-specific probes. Use of both types of probes 'in tandem' opens new possibilities for studying lipid-protein and lipid-lipid interactions in biological membranes. The anthrylvinyl- and perylenoyl-labeled lipids were applied in studies of serum lipoproteins and erythrocyte membranes. A new highly sensitive ligand-receptor binding assay and a new approach to biological signal amplifying based on the use of lipid-specific probes are described.
Animals↗
[Comparative study of gangliosides from murine B- and T-lymphomas].
Gangliosides from murine B-lymphomas (MOPC 21 and MOPC 406) and T-lymphoma EL-4 were studied by thin-layer chromatography, immunoprecipitation with specific antisera to gangliosides and by treatment with neuraminidase. It was found that the gangliosides of all three lymphomas differ in their interaction with antisera and neuraminidase although they are similar in their chromatographic behaviour.
Animals↗
Interaction of prostaglandin E1 with human high density lipoproteins.
Prostaglandin E1 has been shown to interact with serum high density lipoproteins (HDL) in a manner resembling the interaction of a ligand with a high affinity binding site. The presence of 10(-12)-10(-10) M prostaglandin E1 induces a rearrangement of the HDL surface lipids and probably influences the biological functions of the lipoproteins.
Alprostadil↗
Changes of glycolipids dependent on cell density of Ehrlich ascites carcinoma cells.
The glycolipid composition of Ehrlich ascites carcinoma cells was found to depend strongly on the cell density of the suspension. The general trend observed upon dilution of the cell suspension was a reduction of the less complex gangliosides GM3 and GM2 with concomitant increase of the more complex gangliosides, especially GM1. The increase of the content of ganglioside GM1 upon dilution was accompanied by a comparable decrease of the content of its immediate precursor, asialo-GM1, whereas the content of other neutral glycosphingolipids did not change very much. When the cell suspension was diluted with medium conditioned by dense cells the ganglioside profile of the diluted suspension remained similar to that of the dense cell suspension. It is postulated that the medium conditioned with dense cells contains a transferable factor inhibiting sialylation of asialo-GM1.
Animals↗
Lipid-cell interactions. Liposome adsorption and cell-to-liposome lipid transfer are mediated by the same cell-surface sites.
The competitive behavior of solid vs. fluid liposomes in liposome-to-cell adsorption and cell-to-liposome lipid transfer processes was investigated with L cells and FBT epithelial sheets. Binding, transfer and 31P-NMR experiments have demonstrated that: (i) solid liposomes adhere to the cell surface as integral vesicles retaining the entrapped substances; (ii) fluid liposomes are partly disintegrated at the cell surface with concomitant entry of entrapped substances into the cytoplasm, while their lipids remain on the cell surface; (iii) fluid liposomes that escape lysis dissociate from the cell, taking away cell lipid molecules. The latter process underlies the mechanism of cell-to-fluid liposome lipid transfer. In contrast, no lipid transfer occurs between the plasma membrane and solid liposomes. Cell-bound solid liposomes interfere with the transfer of cell lipids to fluid liposomes, while these in turn inhibit the binding of solid liposomes to the cell surface. Moreover, cell-induced aggregation of both fluid and solid freshly added liposomes is also inhibited by preincubation of the cells with either solid or fluid liposomes. Thus, different types of interaction of both fluid and solid liposomes with the cell are mediated by the same (or closely related) sites on the cell surface.
Adsorption↗
Shedding of gangliosides from tumor cells depends on cell density.
The ganglioside composition of mouse ascites hepatoma ( MAH ) cells, the ascites fluid and cell-conditioned media were determined and found to be qualitatively identical, but quantitatively different. The ganglioside content of the ascites fluid and the medium conditioned by MAH -cells at the native cell concentration (10(8) cells/ml) comprised respectively 74.9% and 23% of the cell-associated gangliosides. When incubated at lower cell-density (10(6) cells/ml) the cells were found to be release about three-times higher amounts of ganglioside per cell than during incubation at the native concentration. Centrifugation of the dense-cell-conditioned medium revealed the major part of the released gangliosides to be associated with a 150000 X g pellet that probably contains shed plasma membrane fragments. In the 150000 X g pellet of the extracellular fluids the relative content of the most polar cell ganglioside corresponding chromatographically to GT1b was about ten-times higher than in the cells. The possibility is raised that the more intense shedding of gangliosides from less crowded MAH cells may play a role in the self protection of the tumor from host immune rejection during initial stages of growth.
Animals↗
Regulatory action of cholesterol esters on the eicosanoid metabolism.
The influence of cholesterol esters (CE) on the formation of prostacyclin (PGI2) and thromboxane A2 (TXA2) depends on the concentration of the added CE and the fatty acid, esterified in the CE. Our results demonstrate that the formation of eicosanoids depends on the CE composition in the microenvironment of the enzymes. Therefore we suggest that the influence of elevated CE levels on the development of atherosclerosis may be also mediated by their influence on the eicosanoid metabolism.
Animals↗
Interaction of prostaglandins with phospholipid vesicles, serum lipoproteins and erythrocytes.
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Alprostadil↗
Shedding of gangliosides from calf thymocytes.
In the course of our work on calf thymus gangliosides [Dyatlovitskaya, Zablotskaya, Azizov & Bergelson (1980) Eur. J. Biochem. 110, 475-483] we studied the gangliosides exfoliated from the cell surface of thymocytes. It was shown that calf thymocytes shed gangliosides both in vivo and in vitro. Various gangliosides were found to be present in high amounts both in extracellular plasma membrane vesicles and in the 64000 X g supernatant. The extracellular membrane fragments were comparatively higher in disialosyllactosylceramide and the 64000 X g supernatant was higher in sialosyllactosylceramide than the cells. Comparison of the ganglioside composition of extracellular membrane fragments, thymocytes and lymphocytes led us to suggest that the shedding of gangliosides from the surface of thymocytes may be involved in the transformation of immunologically incompetent cortical thymocytes into immunocompetent virgin T-cells.
Animals↗