Sulfatide is expressed in both erythrocytes and platelets of bovine origin

Function of Platelet Glycosphingolipid Microdomains/Lipid Rafts

Lipid rafts are dynamic assemblies of glycosphingolipids, sphingomyelin, cholesterol, and specific proteins which are stabilized into platforms involved in the regulation of vital cellular processes. The rafts at the cell surface play important functions in signal transduction. Recent reports have demonstrated that lipid rafts are spatially and compositionally heterogeneous in the single-cell membrane. In this review, we summarize our recent data on living platelets using two specific probes of raft components: lysenin as a probe of sphingomyelin-rich rafts and BCθ as a probe of cholesterol-rich rafts. Sphingomyelin-rich rafts that are spatially and functionally distinct from the cholesterol-rich rafts were found at spreading platelets. Fibrin is translocated to sphingomyelin-rich rafts and platelet sphingomyelin-rich rafts act as platforms where extracellular fibrin and intracellular actomyosin join to promote clot retraction. On the other hand, the collagen receptor glycoprotein VI is known to be translocated to cholesterol-rich rafts during platelet adhesion to collagen. Furthermore, the functional roles of platelet glycosphingolipids and platelet raft-binding proteins including G protein-coupled receptors, stomatin, prohibitin, flotillin, and HflK/C-domain protein family, tetraspanin family, and calcium channels are discussed.

Annexin A4 inhibits sulfatide-induced activation of coagulation factor XII

BACKGROUND

Factor XII (FXII) is a plasma serine protease that initiates the intrinsic pathway of blood coagulation upon contact with anionic substances, such as the sulfated glycolipid sulfatide. Annexins (ANXs) have been implicated in the regulation of the blood coagulation reaction by binding to anionic surfaces composed of phospholipids and sulfated glycoconjugates, but their physiological importance is only partially understood.

OBJECTIVE

To test the hypothesis that ANXs are involved in suppressing the intrinsic pathway initiated by sulfatide, we examined the effect of eight recombinant ANX proteins on the intrinsic coagulation reaction and their sulfatide binding activities.

METHODS

Recombinant ANXs were prepared in Escherichia coli expression systems and their anticoagulant effects on the intrinsic pathway initiated by sulfatide were examined using plasma clotting assay and chromogenic assay. ANXA4 active sites were identified by alanine scanning and fold deletion in the core domain.

RESULTS AND CONCLUSIONS

We found that ANXA3, ANXA4, and ANXA5 strongly inhibited sulfatide-induced plasma coagulation. Wild-type and mutated ANXA4 were used to clarify the molecular mechanism involved in inhibition. ANXA4 inhibited sulfatide-induced auto-activation of FXII to FXIIa and the conversion of its natural substrate FXI to FXIa but showed no effect on the protease activity of FXIIa or FXIa. Alanine scanning showed that substitution of the Ca2+ -binding amino acid residue in the fourth fold of the core domain of ANXA4 reduced anticoagulant activity, and deletion of the entire fourth fold of the core domain resulted in complete loss of anticoagulant activity.

Peptide Antagonists for P-selectin Discriminate between Sulfatide-Dependent Platelet Aggregation and PSGL-1-Mediated Cell Adhesion

BACKGROUND

Membrane-exposed sulfatides are proposed to contribute to P-selectin-dependent platelet aggregation. Here, we demonstrated that P-selectin-mediated platelet aggregation on a collagen-coated surface under flow indeed depended on sulfatides and that this interaction differed considerably from the interaction of P-selectin with P-selectin Glycoprotein Ligand-1 (PSGL-1), which underlies leukocyte-endothelium adhesion.

METHODS AND RESULTS

Upon platelet activation, sulfatides were translocated to the platelet surface to form focal hot-spots. Interestingly, P-selectin was observed to exclusively interact with liposomes with a sulfatide density higher than 21% (w/w), indicating that the binding profile of P-selectin for sulfatide-rich liposomes was dependent on sulfatide density. Sulfatide-liposome binding to P-selectin and sulfatide/P-selectin-dependent platelet aggregation was blunted by peptide antagonists, carrying the EWVDV motif within N-terminal extensions, such as CDVEWVDVSC (half maximal inhibitory concentration IC₅₀ = 0.2 μM), but not by the EWVDV core motif itself (IC₅₀ > 1000 μM), albeit both being equally potent inhibitors of PSGL-1/P-selectin interaction (IC₅₀= 7-12 μM).

CONCLUSIONS

Our data suggest that the sulfatide/P-selectin interaction implicates multiple binding pockets, which only partly overlap with that of PSGL-1. These observations open ways to selectively interfere with sulfatide/P-selectin-dependent platelet aggregation without affecting PSGL-1-dependent cell adhesion.

Erythrocyte membrane sulfatide plays a crucial role in the adhesion of sickle erythrocytes to endothelium

Enhanced adhesion of sickle erythrocytes to the vascular endothelium and subendothelial matrix is fundamental to the development of vascular occlusion in sickle cell disease. Erythrocyte membrane sulfatide is implicated in the pathogenesis of vasoocclusive crises in sickle cell disease (SCD) patients. Because previous evidence linking sulfatide to cell adhesion has largely been circumstantial due to a lack of reagents that specifically target sulfatide, we used two sulfatide-specific strategies to address the role of erythrocyte membrane sulfatide in sickle cell adhesion to the vascular endothelium: a single-chain fragment variable chain (scFv) antibody against sulfatide as well as cerebroside sulfotransferase-deficient mice incapable of synthesising sulfatide. The sickle erythrocytes from mice and humans adhered at a greater extent and at higher shear stresses to activated endothelium than normal erythrocytes, and approximately 60% of the adhesion was prevented by the anti-sulfatide scFv. Similarly, the extent of adhesion of sulfatide-deficient erythrocytes was lower than normal erythrocytes. These findings suggest an important role for membrane sulfatide in sickle cell disease pathophysiology.

Lipid Membranes Facilitate Conformational Changes Required for Reovirus Cell Entry

Cellular entry of nonenveloped and enveloped viruses is often accompanied by dramatic conformational changes within viral structural proteins. These rearrangements are triggered by a variety of mechanisms, such as low pH, virus-receptor interactions, and virus-host chaperone interactions. Reoviruses, a model system for entry of nonenveloped viruses, undergo a series of disassembly steps within the host endosome. One of these steps, infectious subviral particle (ISVP)-to-ISVP* conversion, is necessary for delivering the genome-containing viral core into host cells, but the physiological trigger that mediates ISVP-to-ISVP* conversion during cell entry is unknown. Structural studies of the reovirus membrane penetration protein, μ1, predict that interactions between μ1 and negatively charged lipid head groups may promote ISVP* formation; however, experimental evidence for this idea is lacking. Here, we show that the presence of polyanions (SO4(2-) and HPO4(2-)) or lipids in the form of liposomes facilitates ISVP-to-ISVP* conversion. The requirement for charged lipids appears to be selective, since phosphatidylcholine and phosphatidylethanolamine promoted ISVP* formation, whereas other lipids, such as sphingomyelin and sulfatide, either did not affect ISVP* formation or prevented ISVP* formation. Thus, our work provides evidence that interactions with membranes can function as a trigger for a nonenveloped virus to gain entry into host cells.

IMPORTANCE

Cell entry, a critical stage in the virus life cycle, concludes with the delivery of the viral genetic material across host membranes. Regulated structural transitions within nonenveloped and enveloped viruses are necessary for accomplishing this step; these conformational changes are predominantly triggered by low pH and/or interactions with host proteins. In this work, we describe a previously unknown trigger, interactions with lipid membranes, which can induce the structural rearrangements required for cell entry. This mechanism operates during entry of mammalian orthoreoviruses. We show that interactions between reovirus entry intermediates and lipid membranes devoid of host proteins promote conformational changes within the viral outer capsid that lead to membrane penetration. Thus, this work illustrates a novel strategy that nonenveloped viruses can use to gain access into cells and how viruses usurp disparate host factors to initiate infection.

Polymorphonuclear leukocyte apoptosis is accelerated by sulfatides or sulfatides-treated Salmonella Typhimurium bacteria

Neutrophils die by apoptosis following activation and uptake of microbes or enter apoptosis spontaneously at the end of their lifespan if they do not encounter a pathogen. Here we report that sulfatides or sulfatides-treated Salmonella Typhimurium bacteria accelerated human neutrophil apoptosis. Neutrophil apoptosis was examined by flow cytometry. Sulfatides caused prominent increase in percentage of apoptotic cells after 2.5 hrs of incubation. Salmonella Typhimurium bacteria by themselves did not affect the basal level of apoptosis in neutrophil population. When neutrophils were added to S. Typhimurium "opsonized" by sulfatides, apoptotic index significantly increased, whereas the number of phagocyting cells was not influenced. Sulfatides' proapoptotic effect was strongly dependent on the activity of β-galactosidase; inhibition of this enzyme impaired its potency to accelerate apoptosis. These data support the mechanism of neutrophil apoptosis triggering based on sulfatides' ability to accumulate in intracellular compartments and mediate successive increase in ceramide content resulting from β-galactosidase activity.

Sulfatides partition disabled-2 in response to platelet activation

BACKGROUND

Platelets contact each other at the site of vascular injury to stop bleeding. One negative regulator of platelet aggregation is Disabled-2 (Dab2), which is released to the extracellular surface upon platelet activation. Dab2 inhibits platelet aggregation through its phosphotyrosine-binding (PTB) domain by competing with fibrinogen for alphaIIbbeta3 integrin receptor binding by an unknown mechanism.

METHODOLOGY/PRINCIPAL FINDINGS

Using protein-lipid overlay and liposome-binding assays, we identified that the N-terminal region of Dab2, including its PTB domain (N-PTB), specifically interacts with sulfatides. Moreover, we determined that such interaction is mediated by two conserved basic motifs with a dissociation constant (K(d)) of 0.6 microM as estimated by surface plasmon resonance (SPR) analysis. In addition, liposome-binding assays combined with mass spectroscopy studies revealed that thrombin, a strong platelet agonist, cleaved N-PTB at a site located between the basic motifs, a region that becomes protected from thrombin cleavage when bound to sulfatides. Sulfatides on the platelet surface interact with coagulation proteins, playing a major role in haemostasis. Our results show that sulfatides recruit N-PTB to the platelet surface, sequestering it from integrin receptor binding during platelet activation. This is a transient recruitment that follows N-PTB internalization by an actin-dependent process.

CONCLUSIONS/SIGNIFICANCE

Our experimental data support a model where two pools of Dab2 co-exist at the platelet surface, in both sulfatide- and integrin receptor-bound states, and their balance controls the extent of the clotting response.

Pharmacological regulation of factor XII activation may be a new target to control pathological coagulation

FXII was identified 50 years ago as a coagulation protein in the intrinsic pathway of blood coagulation as FXII deficient patients had marked prolongation of the in vitro surface-activated coagulation time. However, series of investigations have convincingly shown that FXII has no role in normal hemostasis. Recently, experimentally induced thrombosis in factor XII-knockout mice has provided evidence that factor XII (FXII) deficient mice are protected against ischemic brain injury after obstructive clot formation. Based on these experiments it has, therefore, been suggested, that blocking of FXII could be a unique target to prevent obstructive clot formation in arterial thrombosis without side effect of increased bleeding. FXII deficiency has, however, not convincingly been shown to protect against arterial thrombosis in humans. The target mentioned above may either be an inhibition of FXII activation or an inhibition of its proteolytic activity. FXII is a zymogen of the proteolytic enzyme, FXIIa, the substrates of which are factor XI and prekallikrein. Thus, FXIIa is not only involved in the activation of the coagulation system, but is also associated with the kallikrein/kinin system. The activation of the latter is deeply involved in inflammation and pain sensation. Furthermore, FXIIa binds to endothelial cells and to the extracellular matrix, indicating a role in vascular repair. Therefore, a complete evaluation of all these properties of FXII and FXIIa has to be considered when formulating a strategy for blocking FXII activation.

Quantitative determination of the binding of beta2-glycoprotein I and prothrombin to phosphatidylserine-exposing blood platelets

The plasma protein beta2GPI (beta2-glycoprotein I) has been proposed to mediate phagocytosis of apoptotic cells and to play a role in the antiphospholipid syndrome. This suggestion is based mainly on the presumption that beta2GPI has an appreciable interaction with PS (phosphatidylserine)-exposing cell membranes. However, quantitative data on the binding of beta2GPI to PS-exposing cells under physiologically relevant conditions are scarce and conflicting. Therefore we evaluated the binding of beta2GPI to PS-expressing blood platelets. Flow cytometry showed that binding of beta2GPI is negligible at physiological ionic strength, in contrast with significant binding occurring at low ionic strength. Binding parameters of beta2GPI and (for comparison) prothrombin were quantified by ellipsometric measurement of protein depletion from the supernatant following incubation with platelets. At low ionic strength (20 mM NaCl, no CaCl2), a dissociation constant (K(d)) of 0.2 microM was found for beta2GPI, with 7.4x10(5) binding sites per platelet. Under physiologically relevant conditions (120 mM NaCl and 3 mM CaCl2), binding of beta2GPI was not detectable (extrapolated K(d)>80 microM). Prothrombin binding (at 3 mM CaCl2) was much less affected by ionic strength: K(d) values of 0.5 and 1.4 muM were observed at 20 and 120 mM NaCl respectively. The low affinity and the presence of many lipid-binding proteins in plasma that can compete with the binding of beta2GPI suggest that only a small fraction (<5%) of the binding sites on PS-exposing blood cells are likely to be occupied by beta2GPI. These findings are discussed in relation to the alleged (patho-)physiological functions of beta2GPI.

Regulation of fish gill Na(+)-K(+)-ATPase by selective sulfatide-enriched raft partitioning during seawater adaptation

Na(+)-K(+)-ATPase is arguably the most important enzyme in the animal cell plasma membrane, but the role of the membrane in its regulation is poorly understood. We investigated the relationship between Na(+)-K(+)-ATPase and membrane microdomains or "lipid rafts" enriched in sulfatide (sulfogalactosylceramide/SGC), a glycosphingolipid implicated as a cofactor for this enzyme, in the basolateral membrane of rainbow trout gill epithelium. Our studies demonstrated that when trout adapt to seawater (33 ppt), Na(+)-K(+)-ATPase relocates to these structures. Arylsulfatase-induced desulfation of basolateral membrane SGC prevented this relocation and significantly reduced Na(+)-K(+)-ATPase activity in seawater but not freshwater trout. We contend that Na(+)-K(+)-ATPase partitions into SGC-enriched rafts to help facilitate the up-regulation of its activity during seawater adaptation. We also suggest that differential partitioning of Na(+)-K(+)-ATPase between these novel SGC-enriched regulatory platforms results in two distinct, physiological Na(+) transport modes. In addition, we extend the working definition of cholesterol-dependent raft integrity to structural dependence on the sulfate moiety of SGC in this membrane.

Chemokines bind to sulfatides as revealed by surface plasmon resonance

Chemokines bind to sulfated cell surface glycosaminoglycans and thereby modulate signaling mediated by G-protein-coupled seven-transmembrane domain chemokine receptors. Similar to glycosaminoglycans, sulfated oligosaccharides are also exposed on the cell surface by sulfatides, a class of glycosphingolipids. We have now identified sulfated glycosphingolipids (sulfatides) as novel binding partners for chemokines. Using surface plasmon resonance (SPR), the binding of proinflammatory and homeostatic chemokines to glycosphingolipids, in particular sulfatides, was investigated. Chemokines were immobilized while glycosphingolipids or additional phospholipids incorporated into liposomes were applied as soluble analytes. A specific affinity of the chemokines MCP-1/CCL2, IL-8/CXCL8, SDF-1alpha/CXCL12, MIP-1alpha/CCL3 and MIP-1beta/CCL4 to the sulfatides SM4s, SM3, SM2a and SB2, SB1a was detected. No significant interactions with the chemokines were observed for gangliosides, neutral glycosphingolipids or phospholipids. Chemokine receptors have been associated with the detergent-insoluble fraction supposed to contain 'rafts', i.e., glycosphingolipid enriched microdomains of the cell surface. Accordingly, the data suggest that early chemokine receptor signaling may take place in the vicinity of sulfated glycosphingolipids on the cell surface, whereby these sulfatides could modulate the chemokine receptor-mediated cell activation signal.

Glycosphingolipid structural analysis and glycosphingolipidomics

Sphingosines, or sphingoids, are a family of naturally occurring long-chain hydrocarbon derivatives sharing a common 1,3-dihydroxy-2-amino-backbone motif. The majority of sphingolipids, as their derivatives are collectively known, can be found in cell membranes in the form of amphiphilic conjugates, each composed of a polar head group attached to an N-acylated sphingoid, or ceramide. Glycosphingolipids (GSLs), which are the glycosides of either ceramide or myo-inositol-(1-O)-phosphoryl-(O-1)-ceramide, are a structurally and functionally diverse sphingolipid subclass; GSLs are ubiquitously distributed among all eukaryotic species and are found in some bacteria. Since GSLs are secondary metabolites, direct and comprehensive analysis (metabolomics) must be considered an essential complement to genomic and proteomic approaches for establishing the structural repertoire within an organism and deducing its possible functional roles. The glycosphingolipidome clearly comprises an important and extensive subset of both the glycome and the lipidome, but the complexities of GSL structure, biosynthesis, and function form the outlines of a considerable analytical problem, especially since their structural diversity confers by extension an enormous variability with respect to physicochemical properties. This chapter covers selected developments and applications of techniques in mass spectrometric (MS) that have contributed to GSL structural analysis and glycosphingolipidomics since 1990. Sections are included on basic characteristics of ionization and fragmentation of permethylated GSLs and of lithium-adducted nonderivatized GSLs under positive-ion electrospray ionization mass spectrometry (ESI-MS) and collision-induced mass spectrometry (CID-MS) conditions; on the analysis of sulfatides, mainly using negative-ion techniques; and on selected applications of ESI-MS and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to emerging GSL structural, functional, and analytical issues. The latter section includes a particular focus on evolving techniques for analysis of gangliosides, GSLs containing sialic acid, as well as on characterizations of GSLs from selected nonmammalian eukaryotes, such as dipterans, nematodes, cestodes, and fungi. Additional sections focus on the issue of whether it is better to leave GSLs intact or remove the ceramide; on development and uses of thin-layer chromatography (TLC) blotting and TLC-MS techniques; and on emerging issues of high-throughput analysis, including the use of flow injection, liquid chromatography mass spectrometry (LC-MS), and capillary electrophoresis mass spectrometry (CE-MS).

Sulfatide and Na+-K+-ATPase: A Salinity-sensitive Relationship in the Gill Basolateral Membrane of Rainbow Trout

We investigated the effect of salinity on the relationship between Na(+)-K(+)-ATPase and sulfogalactosyl ceramide (SGC) in the basolateral membrane of rainbow trout (Oncorhynchus mykiss) gill epithelium. SGC has been implicated as a cofactor in Na(+)-K(+)-ATPase activity, especially in Na(+)-K(+)-ATPase rich tissues. However, whole-tissue studies have questioned this role in the fish gill. We re-examined SGC cofactor function from a gill basolateral membrane perspective. Nine SGC fatty acid species were quantified by tandem mass spectrometry (MS/MS) and related to Na(+)-K(+)-ATPase activity in trout acclimated to freshwater or brackish water (20 ppt). While Na(+)-K(+)-ATPase activity increased, the total concentration and relative proportion of SGC isoforms remained constant between salinities. However, we noted a negative correlation between SGC concentration and Na(+)-K(+)-ATPase activity in fish exposed to brackish water, whereas no correlation existed in fish acclimated to freshwater. Differential Na(+)-K(+)-ATPase/SGC sensitivity is discussed in relation to enzyme isoform switching, the SGC cofactor site model and saltwater adaptation.

The role of sulfatide in thrombogenesis and haemostasis

In 1961, Wago et al. reported a potential anticoagulant role for sulfatide using animal experiments. Since then there have been many studies of sulfatide in the field of thrombogenesis/haemostasis, yielding contradictory conclusions. Some report that sulfatide has anti-thrombotic activity because it prolongs clotting time, inhibits platelet adhesion, and prolongs bleeding. Others report that sulfatide induces thrombosis in animal models. This mini-review is a chronologic review of reports examining the role of sulfatide in thrombogenesis/haemostasis together with the introduction of data from our laboratory and a discussion of the possible mechanisms underlying these curious phenomena.

Sulfatides inhibit platelet adhesion to von Willebrand factor in flowing blood

Sulfatides are sulfated glycosphingolipids present on cell surfaces that bind to adhesive proteins such as von Willebrand factor (VWF), P-selectin, laminin and thrombospondin. Previous studies have localized the sulfatide-binding site of VWF to amino acid residues Gln626-Val646 in the A1 domain. The A1 domain also contains the binding site for platelet glycoprotein Ib (GP Ib), a site that has been reported to be distinct from the sulfatide-binding site. In this study, we analyzed the interaction of sulfatides with VWF and its effect on GP Ib-mediated platelet adhesion under flow conditions. Recombinant VWF A1 domain (rVWF-A1) bound specifically and saturably to sulfatides (half-maximal concentration of approximately 12.5 microg mL(-1)), binding that was blocked by dextran sulfate (IC(50) approximately equal to 100 microg mL(-1)) but not by heparin at concentrations up to 100 U mL(-1). Furthermore, sulfatides (125 microg mL(-1)) prevented the adhesion of platelets or glycocalicin-coupled polystyrene beads to a rVWF-A1-coated surface under high shear stress. In addition, plasma VWF prebound to a sulfatide-coated surface failed to support subsequent platelet adhesion. These results provide firm evidence that sulfatides bind the VWF A1 domain at a site overlapping the GP Ib-binding site.

Expression of the myelin and oligodendrocyte progenitor marker sulfatide in neurons and astrocytes of adult rat brain

Sulfatide is a myelin component of the central (CNS) and peripheral nervous system (PNS) and is used extensively to identify oligodendrocyte progenitor cells. We have explored sulfatide expression in CNS gray matter (cerebellum, cerebral cortex, and hippocampus) and the PNS in adult rats using an anti-sulfatide antibody (Sulph I) and confocal microscopy. Biochemical analyses revealed two Sulph I antigens, sulfatide and seminolipid; sulfatide was present at about five times higher concentration, and the affinity of Sulph I for sulfatide was 2.5 times higher than that for seminolipid. Thus sulfatide was considered the dominant antigen. We found Sulph I immunostaining, in addition to that in myelinated areas in subpopulations of astrocytes and neurons. Astrocyte Sulph I staining was localized to the cell bodies and in some cases also to the processes. In the cerebellum, some Sulph I-positive astrocytes corresponded to Golgi epithelial cell bodies. We also found Sulph I staining in neuronal cell bodies, which in some neurons was clearly localized to the cytoplasm and in others to the nuclear membrane. Sulph I immunostaining in the PNS was located in the myelin sheath and paranodal end segments. These results demonstrate the expression of sulfatide in cell types other than oligodendrocytes and Schwann cells, showing that sulfatide is not a selective marker for adult oligodendrocyte progenitor cells. Moreover, these findings show that sulfatide is localized also to intracellular compartments and indicate that other roles of sulfatide in astrocytes and neurons, compared to myelin, might be considered.

Characterization of blood group ABO(H)-active gangliosides in type AB erythrocytes and structural analysis of type A-active ganglioside variants in type A human erythrocytes

Several monosialogangliosides containing the type A-active epitope have been detected in type A erythrocytes on immunological analysis with a monoclonal antibody, and three of them were purified by repeated silica bead column chromatography and by scraping from the TLC plate. Two of these A-active gangliosides were characterized by methylation analysis by GC/MS, negative SIMS, MALDI-TOF/MS, proton nuclear magnetic resonance spectroscopy, and immunological assays, and their structures were concluded to be as follows. A-active ganglioside I:A-active ganglioside II:The reactivity of the purified gangliosides to the anti-A monoclonal antibodies (mAbs) exhibited enhancement after removal of the sialic acid. Therefore, the sialic residue has been shown to inhibit the binding to the terminal A-active epitope through the formation of an immune complex. To confirm the presence of A- (including S-A-I, -II and -III) and B-active gangliosides, the reactivity of anti-A and -B mAbs were investigated using total gangliosides from type A, -B and -AB erythrocytes on TLC plate. The results were that the gangliosides from types A and AB showed positive reaction to anti-A mAbs, whereas in the anti-B mAbs binding the gangliosides from types B and AB were positive. Thus, it revealed that A-active gangliosides were present in type A and -AB, and B-active gangliosides in types B and AB. As there was no difference in respective gangliosides on type AB erythrocytes of 22 individuals, both A- and B-active gangliosides are equally present in type AB erythrocytes. The biological significance of these A- and B-active ganglioside variants remains vague at present. As these molecules exhibit different reactivities to the anti-A mAbs, it is very likely that they can regulate the antigenicity of the A-epitope on the cell surface.

Midkine binds specifically to sulfatide the role of sulfatide in cell attachment to midkine-coated surfaces

Midkine is a heparin-binding polypeptide which is implicated in the control of development and repair of various tissues. Recognition of sulfate groups in glycosaminoglycans is important for its function. To elucidate further its mechanism of action, the interactions of midkine with sulfated glycolipids were studied. Of various glycolipids and lipids examined, midkine bound strongly to sulfatide and cholesterol-3-sulfate (CHO-3-SO4) in a dose-dependent manner but failed to bind to other standard glycolipids and lipids. The properties of midkine binding to sulfatide and to CHO-3-SO4 differed in their sensitivity to inhibition by anionic polysaccharides, salt concentration and unlabeled midkine. Heparin inhibited midkine binding to sulfatide but weakly inhibited its binding to CHO-3-SO4. Liposomes bearing sulfatide carried out significant interactions with immobilized midkine, whereas those bearing CHO-3-SO4 did not. Incorporation of sulfatide into 32D cells and trypsinized COS cells enhanced 125I-labelled midkine binding, whereas incorporation of ganglioside or galactosylceramide had no effect. Furthermore, sulfatide-incorporated cells enhanced cell attachment to midkine-coated coverslips. These results indicate that midkine binds to sulfatide under physiological conditions and the midkine-sulfatide interaction may be important in controlling cell attachment.

Structural analysis and immunohistochemical localization of two acidic glycosphingolipids from the porcine, parasitic nematode, Ascaris suum

The acidic glycolipid fraction (AF) of the porcine, parasitic nematode, Ascaris suum , consisted of two subfractions. The major component AF II reacted with orcinol-sulfuric acid and molybdate, while the minor component AF I gave a positive reaction with azure-A, a cationic dye specific for sulfatides. Sugar constituent analysis, methanolysis, methylation analysis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, liquid secondary-ion mass spectrometry, and gas-liquid chromatography/mass spectrometry specified AF II to be an unusual phosphoinositolglycosphingolipid (Galalpha1-Ins-P-1ceramide) and the minor component AF I to be a 3-sulfogalactosylcerebroside (HSO3-3Galss1-1ceramide). The ceramide moiety of both components consisted of lignoceric (C24:0) and cerebronic (C24h:0) acids and mainly C17 iso-branched sphingosine. Immunohistochemical localization studies of the glycolipid-bound antigenic determinants with a polyclonal antiserum against AF II and an anti-sulfatide monoclonal antibody against AF I revealed the presence of the AF II-epitope in the intestine, whereas the AF I-epitope was found in the hypodermis, contractile zone of somatic muscle cells and the external musculature of the uterus. To our knowledge, this is the first report of the presence of a sulfatide in an invertebrate.