Glycoconjugates and cell adhesion: the adhesive proteins laminin, thrombospondin and von Willebrand's factor bind specifically to sulfated glycolipids

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.

Mercury leads to abnormal red blood cell adhesion to laminin mediated by membrane sulfatides

Exposure to mercury is associated with numerous health problems, affecting different parts of the human body, including the nervous and cardiovascular systems in adults and children; however, the underlying mechanisms are yet to be fully elucidated. We investigated the role of membrane sulfatide on mercuric ion (Hg²⁺) mediated red blood cell (RBC) adhesion to a sub-endothelial matrix protein, laminin, using a microfluidic system that mimics microphysiological flow conditions. We exposed whole blood to mercury (HgCl₂), at a range of concentrations to mimic acute (high dose) and chronic (low dose) exposure, and examined RBC adhesion to immobilized laminin in microchannels at physiological flow conditions. Exposure of RBCs to both acute and chronic levels of Hg²⁺ resulted in elevated adhesive interactions between RBCs and laminin depending on the concentration of HgCl₂ and exposure duration. BCAM-Lu chimer significantly inhibited the adhesion of RBCs that had been treated with 50 μM of HgCl₂ solution for 1 h at 37 °C, while it did not prevent the adhesion of 3 h and 24 h Hg²⁺-treated RBCs. Sulfatide significantly inhibited the adhesion of RBC that had been treated with 50 μM of HgCl₂ solution for 1 h at 37 °C and 0.5 μM of HgCl₂ solution for 24 h at room temperature (RT). We demonstrated that RBC BCAM-Lu and RBC sulfatides bind to immobilized laminin, following exposure of RBCs to mercuric ions. The results of this study are significant considering the potential associations between sulfatides, red blood cells, mercury exposure, and cardiovascular diseases.

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.

Chemotherapy Response Rates Among Patients With Endometrial Cancer Who Have Elevated Serum Platelets

OBJECTIVE

This retrospective study evaluates the influence of serum platelet count on chemotherapy response rates among women with endometrial cancer.

METHODS

From 3 separate cancer centers, a total of 318 patients with endometrial cancer who received postoperative chemotherapy between June 1999 and October 2009 were retrospectively identified. Endometrioid, serous, clear cell, and carcinosarcoma histologies were included. Patients were classified as having an elevated platelet count if their serum platelet count was greater than 400 × 10⁹/L at the time of initial diagnosis. Primary outcome was chemotherapy response, classified as either complete or partial/refractory. Secondary outcomes were disease-free and disease-specific survival. χ² Test and Student t test were performed as appropriate. Kaplan-Meier curves and Cox proportional hazards models were used to assess serum platelet effect on survival.

RESULTS

There were 125 deaths, 76 recurrences, and 48 disease progressions. Of the total group, 53 (16.7%) were categorized as having an elevated platelet count. An elevated platelet count was associated with a lower chemotherapy response rate in univariate analysis (hazard ratio [HR], 2.8; 95% 95% confidence interval [CI], 1.46-5.38; P < 0.01). Multivariate analysis showed elevated platelets to be independently associated with decreased disease-free survival (HR, 2.24; 95% CI, 1.26-3.98; P < 0.01) but not disease-specific survival (HR, 1.03; 95% CI, 0.56-1.88, P = 0.93).

CONCLUSIONS

Patients with endometrial cancer who have an elevated serum platelet count greater than 400 × 10⁹/L may have lower chemotherapy response rates and are at increased risk for recurrence when compared with patients with a count within the reference range.

Antiproliferative activity of fucoidan was associated with the induction of apoptosis and autophagy in AGS human gastric cancer cells

Fucoidan, a sulfated polysaccharide purified from brown algae, possesses a variety of pharmacologic effects, including antiinflammatory, antioxidant, and anticancer properties; however, the underlying action mechanisms are not completely understood. This study investigated the possible mechanisms through which fucoidan exerts its antiproliferative action in cultured AGS human gastric adenocarcinoma cells. We found that fucoidan effectively inhibits the growth of AGS cells by inducing autophagy, as well as apoptosis. Apoptosis by fucoidan treatment was associated with the downregulation of antiapoptotic Bcl-2 and Bcl-xL expression, loss of mitochondrial membrane potential, activation of caspases, and concomitant degradation of poly-(ADP-ribose) polymerase protein. In addition, the morphological study indicated a characteristic finding of autophagy, such as the formation of autophagosomes in fucoidan-treated AGS cells. Furthermore, markers of autophagy, namely, the conversion of microtubule-associated protein light chain 3 (LC3)-I to LC3-II and increased beclin-1 accumulation, were observed. Overall, the present data suggest that fucoidan induces apoptotic and autophagic cell death, and both apoptotic and autophagic mechanisms contribute to the fucoidan-induced AGS cell death.

Thrombospondin-1 (TSP-1) Stimulates Expression of Integrin alpha6 in Human Breast Carcinoma Cells: A Downstream Modulator of TSP-1-Induced Cellular Adhesion

Thrombospondin-1 (TSP-1) is involved in a variety of different cellular processes including cell adhesion, tumor progression, and angiogenesis. This paper reports the novel finding that TSP-1 upregulates integrin α6 subunit in human keratinocytes and human breast cancer cells resulting in increased cell adhesion and tumor cell invasion. The effect of TSP-1 on α6 subunit expression was examined in human keratinocytes and breast adenocarcinoma cell lines (MDA-MB-231) treated with TSP-1 and in TSP-1 stably transfected breast cancer cells. TSP-1 upregulated α6 message and protein in these cells as revealed by differential display, Northern and Western blot analysis and immunohistochemical localization studies. The increased expression of α6 was shown to mediate adhesion and invasion of these cells to laminin, a major component of the basement membrane and extracellular matrix (ECM). These data suggest that TSP-1 plays an integral role in the attachment of cells to the ECM facilitating cell motility and angiogenesis.

Metabolic responses of sulfatide and related glycolipids in Madin-Darby canine kidney (MDCK) cells under osmotic stresses

Incorporation of (35)S-sulfate into the polar molecular species of sulfoglycolipids (SM4s) in Madin-Darby canine kidney cells increased in a hypertonic medium (500 mOsm/L) supplemented with sodium chloride. The unknown sulfoglycolipid (SX) was identified as GlcCer sulfate based on the results of TLC, GLC, and mass spectra. The synthesis of SX increased in the hypotonic medium unlike that of SM4s and SM3. TLC showed that hypertonic stress induced the accumulation of GalCer as a precursor of SM4s, whereas hypotonic stress increased GlcCer as a precursor of GlcCer sulfate. The level of ceramide as a precursor of both GalCer and GlcCer increased under hypertonic stress and decreased under hypotonic stress. Cerebroside sulfotransferase mRNA was shown to be elevated in the hyperosmotic condition but not in the hypotonic condition. The increase in SM4s under hypertonic stress was induced by the activation of both the ceramide galactosyltransferase and the cerebroside sulfotransferase genes, whereas the increase in GlcCer sulfate under hypotonic stress was caused by the accumulation of GlcCer as the result of activation of ceramide glucosyltransferase.

Sulfatides and arylsulfatase A activity in major salivary glands of hamster (Mesocricetus auratus) after adenocarcinoma induction in oral cavity

A biochemical study of sulfatides and arylsulfatase A (ASA) was carried out in the submandibular and sublingual glands of the male and female hamster Mesocricetus auratus after experimental induction of oral adenocarcinoma by 7,12-dimethylbenzanthracene (DMBA). Hamster experimental groups included control animals, animals treated with beta-carotene, animals treated with DMBA, and animals treated with DMBA plus beta-carotene. Oral cavity treatment with DMBA induced carcinogenesis in the buccal mucosa, but not in the major salivary glands, where nevertheless, the morphology and expression of both parameters examined changed. In fact, sulfatide concentrations and enzyme activity increased significantly, while in control and beta-carotene-treated hamsters they were similar in both glands and sexes. After administration of DMBA plus beta-carotene, sulfatide concentration decreased, as did ASA activity, slightly in the submandibular gland and remarkably so in the sublingual one of female hamsters. Thin-layer chromatography (TLC) analysis of lipid patterns, after DMBA treatment, revealed considerable differences, not only in sulfatides, but also in other lipid fractions, as well as between the two glands and two sexes. These findings show that oral cavity treatment with DMBA is not able to induce carcinogenesis in the major salivary glands examined; however, it does cause considerable metabolic changes.

Molecular analysis of a carbohydrate antigen involved in the structure and function of zona pellucida glycoproteins

A lactosaminoglycan-associated antigen is associated with a carbohydrate moiety of all three zona pellucida (ZP) glycoproteins of pig and rabbit but is absent in the mouse and rat. A monoclonal antibody (PS1) recognizing this determinant was obtained by immunizing mice with a porcine ZP glycoprotein isoform purified by two-dimensional polyacrylamide gel electrophoresis. Conditions known to remove O-linked or sialic acid carbohydrate moieties (alkaline reduction; O-glycanase or neuraminidase enzymatic cleavage) did not remove the carbohydrate epitope. However, treatment with endo-beta-glycosidase, endoglycosidase F, or combinations of neuraminidase plus beta-galactosidase, totally removed the determinant, indicating that it is associated with a poly-N-acetyllactosaminoglycan structure present on an N-linked oligosaccharide. Molecular morphology studies using immunofluorescence and confocal microscopy techniques demonstrate that the PS1 antigen is localized at the surface of the ZP. Confirmation of this localization was obtained through studies that show that this antibody will inhibit homologous sperm binding to the pig ZP. Additional analyses using modular contrast microscopy and immunocytochemistry demonstrate that this carbohydrate-associated antigen is localized in discrete layers throughout the ZP matrix. These studies are the first to demonstrate the presence of a lactosaminoglycan type carbohydrate moiety in all three ZP proteins using a monoclonal antibody that appears to be involved in sperm recognition and structural organization.

Unusual hydration properties of C16:0 sulfatide bilayer membranes

After deacylation of bovine brain sulfatide under mild alkaline conditions and reacylation using palmitoyl chloride (, Chem. Phys. Lipids. 34:41-53), the anionic glycosphingolipid N-palmitoyl galactosulfatide (C16:0-GalSulf) has been synthesized. By differential scanning calorimetry (DSC), anhydrous C16:0-GalSulf exhibits an endothermic transition, T(M) = 93 degrees C (DeltaH = 5. 5 kcal/mol C16:0-GalSulf) on heating. With increasing hydration (50 mM sodium phosphate buffer, pH 7.0; 50 mM NaCl), T(M) decreases, reaching a limiting value of 49 degrees C (DeltaH = 8.2 kcal/mol C16:0-GalSulf) at 20 wt% buffer. X-ray diffraction data have been recorded over the hydration range 0-62% at temperatures below (20 degrees C) and above (60 degrees C) T(M). At 20 degrees C, sharp wide-angle reflections at approximately 1/4.4 A(-1), approximately 1/4.1 A(-1), and approximately 1/3.8 A(-1) indicate the presence of an ordered-chain gel phase, whereas at 60 degrees C a broad reflection at 1/4.5 A(-1) characteristic of a melted-chain phase is observed. Lamellar diffraction patterns consistent with the presence of bilayer phases are observed at both temperatures. At 60 degrees C, in the liquid-crystalline L(alpha) phase, the bilayer periodicity increases with hydration, in both water and 100 mM Na(+) buffer. Interestingly, in the gel phase at 20 degrees C, the bilayer periodicity (d = 64 A) is insensitive to hydration (over the range 30-60 wt%) with either water or buffer. The continuous swelling behavior exhibited by the L(alpha) bilayer phase of C16:0-GalSulf is typical of lipids bearing a net negative charge and confirms that the presence of 100 mM Na(+) is insufficient to shield the charge contributed by the sulfate group. In contrast, the lack of continuous swelling behavior of the bilayer gel phase of C16:0-GalSulf is unusual and resembles that of Na(+) soaps. Thus, presumably, alterations in the surface charge characteristics of the C16:0-GalSulf bilayer occur on hydrocarbon chain melting and lead to major changes in lipid hydration.

High titre anti-sulphatide antibodies in HIV-infected individuals

Plasma samples from 35 individuals with human immunodeficiency virus (HIV) infection but without peripheral neuropathy were screened by enzyme linked immunosorbent assay (ELISA) for IgM and IgG antibodies against sulphatide (GalS). Five of these were shown to contain raised anti-GalS IgM antibody titres, while six had raised IgG titres. All plasma samples screened were compared to an internal neurological disease control which contained raised anti-GalS IgM antibody titres. Anti-GalS IgM antibody titres in the HIV cohort ranged between 200 and 2000 arbitrary units/litre (AU/l), whereas, IgG titres were between 200 and 10,000 AU/l. Two of four plasma samples from HIV-infected individuals with neuropathy (HIV+PN) also showed IgM reactivity with GalS; one also binding to the gangliosides GM1, GD1a, GD1b and GT1b. The other two samples showed IgG reactivity against GalS. These data indicate that antibodies against GalS occur more frequently in HIV infection than in HIV-seronegative individuals with and without neurological disease and may participate in the pathogenesis of neuropathies associated with HIV infection.

Anionic Polysaccharides Inhibit Adhesion of Sickle Erythrocytes to the Vascular Endothelium and Result in Improved Hemodynamic Behavior

The abnormal adherence of sickle red blood cells (SS RBC) to vascular endothelium may play an important role in vasoocclusion in sickle cell anemia. Thrombospondin (TSP), unusually large molecular weight forms of von Willebrand factor, and laminin are known to enhance adhesion of SS RBC. Also, these endothelial proteins bind to sulfated glycolipids and this binding is inhibited by anionic polysaccharides. Reversible sickling may expose normally cryptic membrane sulfatides that could mediate this adhesive interaction. In this study, we have investigated the effect of anionic polysaccharides, in the presence or absence of TSP, on SS RBC adhesion to the endothelium, using cultured human umbilical vein endothelial cells (HUVEC) (for the adhesion assay) and the ex vivo mesocecum of the rat (for hemodynamic evaluation). The baseline adhesion (ie, without added TSP) of SS RBC to HUVEC was most effectively inhibited by high molecular weight dextran sulfate (HDS), whereas low molecular weight dextran sulfate (LDS) and the glycosaminoglycan chondroitin sulfate A (CSA) also had significant inhibitory effects. Heparin was mildly effective whereas other glycosaminoglycans (chondroitin sulfates B and C, heparan sulfate, and fucoidan) were ineffective. Similarly, HDS and CSA resulted in an improved hemodynamic behavior of SS RBC. Soluble TSP caused significant increases in SS RBC adhesion and in the peripheral resistance. Both HDS and CSA prevented TSP-enhanced adhesion and hemodynamic abnormalities. Thus, anionic polysaccharides can inhibit SS RBC-endothelium interaction in the presence or absence of soluble TSP. These agents may interact with RBC membrane component(s) and prevent TSP-mediated adhesion of SS RBC to the endothelium.

Anionic Polysaccharides Inhibit Adhesion of Sickle Erythrocytes to the Vascular Endothelium and Result in Improved Hemodynamic Behavior

The abnormal adherence of sickle red blood cells (SS RBC) to vascular endothelium may play an important role in vasoocclusion in sickle cell anemia. Thrombospondin (TSP), unusually large molecular weight forms of von Willebrand factor, and laminin are known to enhance adhesion of SS RBC. Also, these endothelial proteins bind to sulfated glycolipids and this binding is inhibited by anionic polysaccharides. Reversible sickling may expose normally cryptic membrane sulfatides that could mediate this adhesive interaction. In this study, we have investigated the effect of anionic polysaccharides, in the presence or absence of TSP, on SS RBC adhesion to the endothelium, using cultured human umbilical vein endothelial cells (HUVEC) (for the adhesion assay) and the ex vivo mesocecum of the rat (for hemodynamic evaluation). The baseline adhesion (ie, without added TSP) of SS RBC to HUVEC was most effectively inhibited by high molecular weight dextran sulfate (HDS), whereas low molecular weight dextran sulfate (LDS) and the glycosaminoglycan chondroitin sulfate A (CSA) also had significant inhibitory effects. Heparin was mildly effective whereas other glycosaminoglycans (chondroitin sulfates B and C, heparan sulfate, and fucoidan) were ineffective. Similarly, HDS and CSA resulted in an improved hemodynamic behavior of SS RBC. Soluble TSP caused significant increases in SS RBC adhesion and in the peripheral resistance. Both HDS and CSA prevented TSP-enhanced adhesion and hemodynamic abnormalities. Thus, anionic polysaccharides can inhibit SS RBC-endothelium interaction in the presence or absence of soluble TSP. These agents may interact with RBC membrane component(s) and prevent TSP-mediated adhesion of SS RBC to the endothelium.

Porcine 987P glycolipid receptors on intestinal brush borders and their cognate bacterial ligands

Certain strains of enterotoxigenic Escherichia coli adhere to piglet intestinal epithelial cells by means of the 987P fimbriae. The 987P fimbrial structure consists of a helical arrangement of three fimbrial proteins, namely, the major subunit FasA and two minor subunits, FasF and FasG. FasG, which is located at the fimbrial tip and at various positions along the fimbriae, mediates 987P binding to glycoprotein receptors. In this study, we isolated and analyzed the structure of piglet glycolipid brush border receptors and characterized their cognate ligands on the 987P fimbriae. Two major glycolipid bands recognized by 987P fimbrial probes in thin-layer chromatography overlay assays were further purified by high-performance thin-layer chromatography and shown to comigrate with control galactosylceramide containing hydroxylated fatty acids and with sulfatide. Their structures were confirmed by fast atom bombardment mass spectrometry, which detected homologous series of ceramide monohexoside and sulfatide with hydroxylated fatty acyl chains ranging from h16:0 to h24:0. Assembled 987P fimbriae, pre- and postassembly dissociated fimbrial subunits, and Fab fragments of specific anti-FasG, -FasF, and -FasA were used to inhibit 987P-mediated bacterial binding to the two identified piglet glycolipids and corresponding isoreceptor controls. Only assembled fimbriae and anti-FasG Fab fragments were significantly able to inhibit bacterial binding to sulfatide, indicating that in addition to glycoproteins, FasG recognizes a specific glycolipid of piglet brush borders. In contrast, only anti-FasA Fab fragments were significantly able to inhibit bacterial binding to galactosylceramide with hydroxylated fatty acids and piglet hydroxylated ceramide monohexoside, indicating that FasA may determine a third type of ligand-receptor interaction in the piglet intestines. Since these bacterial adhesins recognize their respective glycolipid receptors only after being assembled in their final fimbrial quaternary structure, adhesin binding may involve cooperative interactions and the subunits by themselves may have very low binding affinities. Alternatively, conformation-sensitive domains of these subunits present in the assembled fimbriae may be required for glycolipid binding.

Intrathecal synthesis of anti-sulfatide IgG is associated with peripheral nerve disease in acquired immunodeficiency syndrome

Peripheral nervous system involvement in the acquired immunodeficiency syndrome (AIDS) can take the form of an acute or chronic inflammatory demyelinating polyneuropathy, polyradiculopathy, mononeuropathy multiplex, or autonomic neuropathy. There is no widely held consensus on the etiology of PNS or other neurological complications associated with HIV infection. We report here that PNS disease in HIV-infected individuals is associated with intrathecal synthesis of an antibody directed against sulfatide, a major component of myelin. The anti-sulfatide antibody is also present nonspecifically in serum. The antibody requires the presence of the 3-O-sulfogalactosyl residue for binding and recognizes preferentially the hydroxy fatty acid-containing form of sulfatide. Anti-sulfatide antibodies are therefore one of the humoral factors responsible for demyelinating diseases in AIDS patients.

Accumulation of sulfoglycolipids in hyperosmosis-resistant clones derived from the renal epithelial cell line MDCK (Madin-Darby canine kidney cell)

1. Two clones (osmR-A and osmR-B) resistant to hyperosmotic media of 700 and 800 mosmol/l, respectively, were selected from Madin-Darby canine kidney (MDCK) cells. 2. When cultured in isosmotic medium (300 mosmol/l), the concentration of galactosyl sulfatide and lactosyl sulfatide in these hyperosmosis-resistant clones was 3.4-5.9 times higher than in the wild-type MDCK. The rate of incorporation of [35S]sulfate into sulfolipids of osmR-A and osmR-B was 1.9-6.7 times higher than MDCK. 3. The stimulation of incorporation into sulfolipids by hyperosmotic culture was completely inhibited by cycloheximide. The pulse-chase studies indicated decreased turnover rate of sulfolipids in osmR-A.

Specific inhibition of endothelial cell proliferation by thrombospondin

Angiogenesis is a multi-step event involving endothelial cell migration, attachment, and proliferation. A thrombospondin (TSP)-like protein has recently been described as a naturally-occurring inhibitor of angiogenesis. We now report that human platelet TSP inhibits the in vitro proliferation of endothelial cells from the rabbit corpus luteum, bovine adrenal cortex and pulmonary artery, and human umbilical vein. The antiproliferative effect of TSP was neutralized by monoclonal antibodies against TSP. The growth arrest seen with TSP was specific for endothelial cells since TSP actually stimulated the growth of vascular smooth muscle cells and human foreskin fibroblasts. These results imply that the angiogenesis-inhibiting effect of TSP is mediated through an inhibition of endothelial cell proliferation. Elucidation of the mechanism of action of TSP on endothelial cell proliferation may lead to potential therapeutic approaches for the control of neovascular diseases.