ELAM-1 mediates cell adhesion by recognition of a carbohydrate ligand, sialyl-Lex

Alteration of the serum N-glycome of mice locally exposed to high doses of ionizing radiation

Exposure of the skin to ionizing radiation leads to characteristic reactions that will often turn into a pathophysiological process called the cutaneous radiation syndrome. The study of this disorder is crucial to finding diagnostic and prognostic bioindicators of local radiation exposure or radiation effects. It is known that irradiation alters the serum proteome content and potentially post-translationally modifies serum proteins. In this study, we investigated whether localized irradiation of the skin alters the serum glycome. Two-dimensional differential in-gel electrophoresis of serum proteins from a man and from mice exposed to ionizing radiation showed that potential post-translational modification changes occurred following irradiation. Using a large-scale quantitative mass-spectrometry-based glycomic approach, we performed a global analysis of glycan structures of serum proteins from non-irradiated and locally irradiated mice exposed to high doses of γ-rays (20, 40, and 80 Gy). Non-supervised descriptive statistical analyses (principal component analysis) using quantitative glycan structure data allowed us to discriminate between uninjured/slightly injured animals and animals that developed severe lesions. Decisional statistics showed that several glycan families were down-regulated whereas others increased, and that particular structures were statistically significantly changed in the serum of locally irradiated mice. The observed increases in multiantennary N-glycans and in outer branch fucosylation and sialylation were associated with the up-regulation of genes involved in glycosylation in the liver, which is the main producer of serum proteins, and with an increase in the key proinflammatory serum cytokines IL-1β, IL-6, and TNFα, which can regulate the expression of glycosylation genes. Our results suggest for the first time a role of serum protein glycosylation in response to irradiation. These protein-associated glycan structure changes might signal radiation exposure or effects.

Sialic acid cyclization of human Th homing receptor glycan associated with recurrent exacerbations of atopic dermatitis

BACKGROUND

The molecular pathogenesis underlying recurrent exacerbations of atopic dermatitis (AD) is unclear. Some peripheral CCR4(+) and CCR7(+) helper memory T cells express the specific homing receptor, sialyl 6-sulfo Lewis X (G152 glycan). This glycan loses receptor activity via cyclization of its sialic acid moiety, thus becoming cyclic sialyl 6-sulfo Lewis X (G159 glycan). These findings suggest that the disordered expression of G152 and G159 glycans may be associated with recurrent exacerbations of AD.

OBJECTIVE

To assess the possible association of G152 and G159 glycans, which are expressed on peripheral helper T (Th) cells, with frequency of exacerbations.

METHODS

The percentage of glycan-expressing cells among peripheral blood CD4(+)CD45RO(+) lymphocytes was determined by flow cytometry. The association of glycans with the frequency of exacerbations determined by recurrence scores as well as with current disease activity was statistically tested.

RESULTS

Current disease activity was significantly associated with CCR4(+)CCR7(-) memory Th cells expressing CSLEX-1 glycan, the conventional skin-trafficking receptor without sialic-acid-cyclization activity. In contrast, the frequency of exacerbations was positively and negatively associated with CCR4(+)CCR7(+) memory Th cells expressing G152 and G159 glycans, respectively. Receiver operating characteristics analyses indicated that the ratio of the G152(+)/G159(+) cell percentages discriminated patients with highly recurrent AD with the best accuracy.

CONCLUSION

Flow cytometric determination of G159 and G152 glycans on peripheral helper memory T cells may be clinically useful for identifying patients with highly recurrent AD. Disordered sialic acid cyclization of G152 glycan may underlie highly recurrent AD, which may provide a novel therapeutic approach.

Metabolic inhibition of sialyl-Lewis X biosynthesis by 5-thiofucose remodels the cell surface and impairs selectin-mediated cell adhesion

Sialyl-Lewis X (sLe(X)) is a tetrasaccharide that serves as a ligand for the set of cell adhesion proteins known as selectins. This interaction enables adhesion of leukocytes and cancer cells to endothelial cells within capillaries, resulting in their extravasation into tissues. The last step in sLe(X) biosynthesis is the α1,3-fucosyltrasferase (FUT)-catalyzed transfer of an L-fucose residue to carbohydrate acceptors. Impairing FUT activity compromises leukocyte homing to sites of inflammation and renders cancer cells less malignant. Inhibition of FUTs is, consequently, of great interest, but efforts to generate glycosyltransferase inhibitors, including FUT inhibitors, has proven challenging. Here we describe a metabolic engineering strategy to inhibit the biosynthesis of sLe(X) in cancer cells using peracetylated 5-thio-L-fucose (5T-Fuc). We show that 5T-Fuc is taken up by cancer cells and then converted into a sugar nucleotide analog, GDP-5T-Fuc, that blocks FUT activity and limits sLe(X) presentation on HepG2 cells with an EC(50) in the low micromolar range. GDP-5T-Fuc itself does not get transferred by either FUT3 or FUT7 at a measurable rate. We further demonstrate that treatment of cells with 5T-Fuc impaired their adhesive properties to immobilized adhesion molecules and human endothelial cells. 5T-Fuc, therefore, is a useful probe that can be used to modulate sLe(X) levels in cells to evaluate the consequences of inhibiting FUT-mediated sLe(X) formation. These data also reveal the utility of using sugar analogues that lead to formation of donor substrate analogues within cells as a general approach to blocking glycosyltransferases in cells.

A matter of order: how E-selectin makes sweet contacts

An entropy exclusive: Sialyl Lewis(x) can be thought of as a "preorganized water oligomer". Recent research in the Ernst laboratory shows that the recognition of sialyl Lewis(x) by E-selectin is exclusively entropy driven. This finding has implications for the design of carbohydrate-based drugs in general.

Self-recognition of high-mannose type glycans mediating adhesion of embryonal fibroblasts

High-mannose type N-linked glycan with 6 mannosyl residues, termed "M6Gn2", displayed clear binding to the same M6Gn2, conjugated with ceramide mimetic (cer-m) and incorporated in liposome, or coated on polystyrene plates. However, the conjugate of M6Gn2-cer-m did not interact with complex-type N-linked glycan with various structures having multiple GlcNAc termini, conjugated with cer-m. The following observations indicate that hamster embryonic fibroblast NIL-2 K cells display homotypic autoadhesion, mediated through the self-recognition capability of high-mannose type glycans expressed on these cells: (i) NIL-2 K cells display clear binding to lectins capable of binding to high-mannose type glycans (e.g., ConA), but not to other lectins capable of binding to other carbohydrates (e.g. GS-II). (ii) NIL-2 K cells adhere strongly to plates coated with M6Gn2-cer-m, but not to plates coated with complex-type N-linked glycans having multiple GlcNAc termini, conjugated with cer-m; (iii) degree of NIL-2 K cell adhesion to plates coated with M6Gn2-cer-m showed a clear dose-dependence on the amount of M6Gn2-cer-m; and (iv) the degree of NIL-2 K adhesion to plates coated with M6Gn2-cer-m was inhibited in a dose-dependent manner by α1,4-L-mannonolactone, the specific inhibitor in high-mannose type glycans addition. These data indicate that adhesion of NIL-2 K is mediated by self-aggregation of high mannose type glycan. Further studies are to be addressed on auto-adhesion of other types of cells based on self interaction of high mannose type glycans.

Mechanisms and mediators of inflammation: potential models for skin rejection and targeted therapy in vascularized composite allotransplantation

Vascularized composite allotransplantation (VCA) is an effective treatment option for patients suffering from limb loss or severe disfigurement. However, postoperative courses of VCA recipients have been complicated by skin rejection, and long-term immunosuppression remains a necessity for allograft survival. To widen the scope of this quality-of-life improving procedure minimization of immunosuppression in order to limit risks and side effects is needed. In some aspects, the molecular mechanisms and dynamics of skin allograft rejection seem similar to inflammatory skin conditions. T cells are key players in skin rejection and are recruited to the skin via activation of adhesion molecules, cytokines, and chemokines. Blocking these molecules has not only shown success in the treatment of inflammatory dermatoses, but also prolonged graft survival in various models of solid organ transplantation. In addition to T cell recruitment, ectopic lymphoid structures within the allograft associated with chronic rejection in solid organ transplantation might contribute to the strong alloimmune response towards the skin. Selectively targeting the molecules involved offers exciting novel therapeutic options in the prevention and treatment of skin rejection after VCA.

The Increased Expression of HLA-DR and ICAM-1 Molecules by Human Bronchial Epithelial Cells, Induced by Activated Mononuclear Cells, is Downregulated by Nedocromil Sodium

To test the hypothesis that mononuclear cell products could increase the expression of HLA-DR and ICAM-1 molecules in bronchial epithelial cells (BECs), subconfluent cultures of human BECs, obtained from surgically resected bronchi, were incubated with PHA-activated blood mononuclear cell conditioned media (BCM-CM) or recombinant IFN-gamma. The presence of HLA-DR and ICAM-1 molecules on BECs was then evaluated by specific antibody staining and flow-cytometry analysis. The addition to BEC cultures of different concentrations of PHA-stimulated BMC-CM, or of IFN-gamma induced a dosedependent increase of HIA-DR and ICAM-1 expression, while no effect was observed with unstimulated BMC-CM. The ability of nedocromil sodium and, as control, of dexamethasone, to prevent the upregulation of HLA-DR and ICAM-1 expression on BECs was then tested. Increasing concentrations (10(-7) to 10(-4) M) of nedocromil significandy inhibited HLA-DR and ICAM-1 expression by BECs in a dose-dependent fashion. A similarly dose-dependent inhibitory effect was also observed with dexamethasone, which, however, was less active than nedocromil on HL-ADR expression and more active on ICAM-1 expression. Finally, nedocromil and dexamethasone showed a significant synergistic effect on the expression of both cell surface molecules at the lowest concentrations tested.

Increased E-selectin in hepatic ischemia-reperfusion injury mediates liver metastasis of pancreatic cancer

Several recent studies have reported that selectins are produced during ischemia-reperfusion injury, and that selectin ligands play an important role in cell binding to the endothelium and in liver metastasis. Portal clamping during pancreaticoduodenectomy with vessel resection for pancreatic head cancer causes hepatic ischemia-reperfusion injury, which might promote liver metastasis. We investigated the liver colonization of pancreatic cancer cells under hepatic ischemia-reperfusion and examined the involvement of E-selectin and its ligands. A human pancreatic cancer cell line (Capan-1) was injected into the spleen of mice after hepatic ischemia-reperfusion (I/R group). In addition, to investigate the effect of an anti-E-selectin antibody on liver colonization in the IR group, mice received an intraperitoneal injection of the anti-E-selectin antibody following hepatic ischemia-reperfusion and tumor inoculation (IR+Ab group). Four weeks later, mice were sacrificed and the number of tumor nodules on the liver was compared to mice without hepatic ischemia-reperfusion (control group). The incidence of liver metastasis in the I/R group was significantly higher (16 of 20, 80%) than that in the control group (6 of 20, 30%) (P<0.01). Moreover, mice in the I/R group had significantly more tumor nodules compared to those in the control group (median, 9.9 vs. 2.7 nodules) (P<0.01). In the I/R+Ab group, only 2 of 5 (40%) mice developed liver metastases. RT-PCR and southern blotting of the liver extracts showed that the expression of IL-1 and E-selectin mRNA after hepatic ischemia-reperfusion was significantly higher than the basal levels. Hepatic ischemia-reperfusion increases liver metastases and E-selectin expression in pancreatic cancer. These results suggest that E-selectin produced due to hepatic ischemia-reperfusion is involved in liver metastasis.

Separation of kallikrein 6 glycoprotein subpopulations in biological fluids by anion-exchange chromatography coupled to ELISA and identification by mass spectrometry

Kallikrein 6 (KLK6) has been shown to be aberrantly glycosylated in ovarian cancer. Here, we report a novel HPLC anion exchange method, coupled to a KLK6-specific ELISA, capable of differentiating KLK6 glycoform subgroups in biological fluids. Biological fluids were fractionated using anion exchange and resulting fractions were analyzed for KLK6 content by ELISA producing a four-peak elution profile. Using this assay, the KLK6 elution profile and distribution across peaks of a set (n = 7) of ovarian cancer patient matched serum and ascites fluid samples was found to be different than the profile of serum and cerebrospinal fluid (CSF) of normal individuals (n = 7). Glycosylation patterns of recombinant KLK6 (rKLK6) were characterized using tandem mass spectrometry (MS/MS), and found to consist of a highly heterogeneous KLK6 population. This protein was found to contain all of the four diagnostic KLK6 peaks present in the previously assayed biological fluids. The rKLK6 glycoform composition of each peak was assessed by lectin affinity and MS/MS based glycopeptide quantification by product ion monitoring. The combined results showed an increase in terminal alpha 2-6 linked sialic acid in the N-glycans found on KLK6 from ovarian cancer serum and ascites, as opposed to CSF and serum of normal individuals.

Developing inhibitors of glycan processing enzymes as tools for enabling glycobiology

Glycoconjugates are ubiquitous biomolecules found in all kingdoms of life. These diverse structures are metabolically responsive and occur in a cell line- and protein-specific manner, conferring tissue type-specific properties. Glycans have essential roles in diverse processes, including, for example, intercellular signaling, inflammation, protein quality control, glucohomeostasis and cellular adhesion as well as cell differentiation and proliferation. Many mysteries remain in the field, however, and uncovering the physiological roles of various glycans remains a key pursuit. Realizing this aim necessitates the ability to subtly and selectively manipulate the series of different glycoconjugates both in cells and in vivo. Selective small-molecule inhibitors of glycan processing enzymes hold great potential for such manipulation as well as for determining the function of 'orphan' carbohydrate-processing enzymes. In this review, we discuss recent advances and existing inhibitors, the prospects for small-molecule inhibitors and the challenges associated with generating high-quality chemical probes for these families of enzymes. The coordinated efforts of chemists, biochemists and biologists will be crucial for creating and characterizing inhibitors that are useful tools both for advancing a basic understanding of glycobiology in mammals as well as for validating new potential therapeutic targets within this burgeoning field.

Sialyl Lewis(x): a "pre-organized water oligomer"?

Organized and released: Sialyl Lewis(x) (sLe(x)) represents a "pre-organized water oligomer", that is, a surrogate for clustered water molecules attached to a scaffold. The impetus for sLe(x) binding to E-selectin is shown to be the high degree of pre-organization allowing an array of directed hydrogen bonds, and the entropic benefit of the release of water molecules from the large binding interface to bulk water (see picture).

1,3-1,4-α-L-fucosynthase that specifically introduces Lewis a/x antigens into type-1/2 chains

α-L-fucosyl residues attached at the non-reducing ends of glycoconjugates constitute histo-blood group antigens Lewis (Le) and ABO and play fundamental roles in various biological processes. Therefore, establishing a method for synthesizing the antigens is important for functional glycomics studies. However, regiospecific synthesis of glycosyl linkages, especially α-L-fucosyl linkages, is quite difficult to control both by chemists and enzymologists. Here, we generated an α-L-fucosynthase that specifically introduces Le(a) and Le(x) antigens into the type-1 and type-2 chains, respectively; i.e. the enzyme specifically accepts the disaccharide structures (Galβ1-3/4GlcNAc) at the non-reducing ends and attaches a Fuc residue via an α-(1,4/3)-linkage to the GlcNAc. X-ray crystallographic studies revealed the structural basis of this strict regio- and acceptor specificity, which includes the induced fit movement of the catalytically important residues, and the difference between the active site structures of 1,3-1,4-α-L-fucosidase (EC 3.2.1.111) and α-L-fucosidase (EC 3.2.1.51) in glycoside hydrolase family 29. The glycosynthase developed in this study should serve as a potentially powerful tool to specifically introduce the Le(a/x) epitopes onto labile glycoconjugates including glycoproteins. Mining glycosidases with strict specificity may represent the most efficient route to the specific synthesis of glycosidic bonds.

NEU1 and NEU3 sialidase activity expressed in human lung microvascular endothelia: NEU1 restrains endothelial cell migration, whereas NEU3 does not

The microvascular endothelial surface expresses multiple molecules whose sialylation state regulates multiple aspects of endothelial function. To better regulate these sialoproteins, we asked whether endothelial cells (ECs) might express one or more catalytically active sialidases. Human lung microvascular EC lysates contained heat-labile sialidase activity for a fluorogenic substrate, 2'-(4-methylumbelliferyl)-α-D-N-acetylneuraminic acid (4-MU-NANA), that was dose-dependently inhibited by the competitive sialidase inhibitor, 2,3-dehydro-2-deoxy-N-acetylneuraminic acid but not its negative control. The EC lysates also contained sialidase activity for a ganglioside mixture. Using real time RT-PCR to detect mRNAs for the four known mammalian sialidases, NEU1, -2, -3, and -4, NEU1 mRNA was expressed at levels 2700-fold higher that those found for NEU2, -3, or -4. Western analyses indicated NEU1 and -3 protein expression. Using confocal microscopy and flow cytometry, NEU1 was immunolocalized to both the plasma membrane and the perinuclear region. NEU3 was detected both in the cytosol and nucleus. Prior siRNA-mediated knockdown of NEU1 and NEU3 each decreased EC sialidase activity for 4-MU-NANA by >65 and >17%, respectively, and for the ganglioside mixture by 0 and 40%, respectively. NEU1 overexpression in ECs reduced their migration into a wound by >40%, whereas NEU3 overexpression did not. Immunohistochemical studies of normal human tissues immunolocalized NEU1 and NEU3 proteins to both pulmonary and extrapulmonary vascular endothelia. These combined data indicate that human lung microvascular ECs as well as other endothelia express catalytically active NEU1 and NEU3. NEU1 restrains EC migration, whereas NEU3 does not.

E-selectin ligands as mechanosensitive receptors on neutrophils in health and disease

Application of mechanical force to bonds between selectins and their ligands is a requirement for these adhesion receptors to optimally perform functions that include leukocyte tethering and activation of stable adhesion. Although all three selectins are reported to signal from the outside-in subsequent to ligand binding, E-selectin is unique in its capacity to bind multiple sialyl Lewis x presenting ligands and mediate slow rolling on the order of a micron per second. A diverse set of ligands are recognized by E-selectin in the mouse, including ESL-1, CD44 (HCELL), and PSGL-1 which are critical in transition from slow rolling to arrest and for efficient transendothelial migration. The molecular recognition process is different in humans as L-selectin is a major ligand, which along with glycolipids constitute more than half of the E-selectin receptors on human polymorphonuclear neutrophils (PMN). In addition, E-selectin is most efficient at raising the affinity and avidity of CD18 integrins that supports PMN deceleration and trafficking to sites of acute inflammation. The mechanism is only partially understood but known to involve a rise in cytosolic calcium and tyrosine phosphorylation that activates p38 MAP kinase and Syk kinase, both of which transduce signals from clustered E-selectin ligands. In this review we highlight the molecular recognition and mechanical requirements of this process to reveal how E-selectin confers selectivity and efficiency of signaling for extravasation at sites of inflammation and the mechanism of action of a new glycomimetic antagonist targeted to the lectin domain that has shown efficacy in blocking neutrophil activation and adhesion on inflamed endothelium.

Pre-organization of the core structure of E-selectin antagonists

A new class of N-acetyl-D-glucosamine (GlcNAc) mimics for E-selectin antagonists was designed and synthesized. The mimic consists of a cyclohexane ring substituted with alkyl substituents adjacent to the linking position of the fucose moiety. Incorporation into E-selectin antagonists led to the test compounds 8 and the 2'-benzoylated analogues 21, which exhibit affinities in the low micromolar range. By using saturation transfer difference (STD)-NMR it could be shown that the increase in affinity does not result from an additional hydrophobic contact of the alkyl substituent with the target protein E-selectin, but rather from a steric effect stabilizing the antagonist in its bioactive conformation. The loss of affinity found for antagonists 10 and 35 containing a methyl substituent in a remote position (and therefore unable to support to the stabilization of the core) further supports this hypothesis. Finally, when a GlcNAc mimetic containing two methyl substituents (52 and 53) was used, in which one methyl was positioned adjacent to the fucose linking position and the other was in a remote position, the affinity was regained.

E-selectin as a target for drug delivery and molecular imaging

E-selectin, also known as CD62E, is a cell adhesion molecule expressed on endothelial cells activated by cytokines. Like other selectins, it plays an important part in inflammation and in the adhesion of metastatic cancer cells to the endothelium. E-selectin recognizes and binds to sialylated carbohydrates present on the surface proteins of certain leukocytes. E-selectin has been chosen as a target for several therapeutic and medical imaging applications, based on its expression in the vicinity of inflammation, infection or cancer. These systems for drug delivery and molecular imaging include immunoconjugates, liposomes, nanoparticles, and microparticles prepared from a wide range of starting materials including lipids, synthetic polymers, polypeptides and organo-metallic structures. After a brief introduction presenting the selectin family and their implication in physiology and pathology, this review focuses on the formulation of these new delivery systems targeting E-selectin at a molecular level.

Deletion of L-selectin increases atherosclerosis development in ApoE-/- mice

Atherosclerosis is an inflammatory disease characterized by accumulation of leukocytes in the arterial intima. Members of the selectin family of adhesion molecules are important mediators of leukocyte extravasation. However, it is unclear whether L-selectin (L-sel) is involved in the pathogenesis of atherosclerosis. In the present study, mice deficient in L-selectin (L-sel(-/-)) animals were crossed with mice lacking Apolipoprotein E (ApoE(-/-)). The development of atherosclerosis was analyzed in double-knockout ApoE/L-sel (ApoE(-/-)L-sel(-/-)) mice and the corresponding ApoE(-/-) controls fed either a normal or a high cholesterol diet (HCD). After 6 weeks of HCD, aortic lesions were increased two-fold in ApoE(-/-)L-sel(-/-) mice as compared to ApoE(-/-) controls (2.46%±0.54% vs 1.28%±0.24% of total aortic area; p<0.05). Formation of atherosclerotic lesions was also enhanced in 6-month-old ApoE(-/-)L-sel(-/-) animals fed a normal diet (10.45%±2.58% vs 1.87%±0.37%; p<0.05). In contrast, after 12 weeks of HCD, there was no difference in atheroma formation between ApoE(-/-)L-sel(-/-) and ApoE(-/-) mice. Serum cholesterol levels remained unchanged by L-sel deletion. Atherosclerotic plaques did not exhibit any differences in cellular composition assessed by immunohistochemistry for CD68, CD3, CD4, and CD8 in ApoE(-/-)L-sel(-/-) as compared to ApoE(-/-) mice. Leukocyte rolling on lesions in the aorta was similar in ApoE(-/-)L-sel(-/-) and ApoE(-/-) animals. ApoE(-/-)L-sel(-/-) mice exhibited reduced size and cellularity of peripheral lymph nodes, increased size of spleen, and increased number of peripheral lymphocytes as compared to ApoE(-/-) controls. These data indicate that L-sel does not promote atherosclerotic lesion formation and suggest that it rather protects from early atherosclerosis.

CD40/CD40L interaction induces E-selectin dependent leukocyte adhesion to human endothelial cells and inhibits endothelial cell migration

BACKGROUND

CD40 is a receptor expressed on a wide range of cells such as leukocytes and endothelial cells (EC). As a member of the tumor necrosis factor (TNF) superfamily the activation of CD40 by CD40-ligand (CD40L) plays a crucial role for the development and progression of a variety of inflammatory processes including atherosclerosis. The aim of the present study was to investigate the effect of CD40/CD40L interaction on leukocyte adhesion to the endothelium and on endothelial cell migration.

METHODS AND RESULTS

Human umbilical vein endothelial cells (HUVEC) were stimulated with either stable transfectants of mouse myeloma cells expressing the CD40L or wild type cells (4 h). Subsequently adhesion of leukocytes expressing Sialyl Lewis X, the counterpart for E-selectin (HL60 cells), was measured under shear stress (2-2.6 dyne/cm(2)) using a flow chamber adhesion assay. Stimulation of CD40 led to a significant increase of E-selectin dependent adhesion of leukocytes to the endothelium. Incubation of cells with either the CD40L blocking antibody TRAP-1 or the E-selectin blocking antibody BBA2 during CD40 stimulation completely abolished adhesion of leukocytes to HUVEC. Similar results were found in human cardiac microvasculature endothelial cells (HCMEC). In contrast stimulation of CD40 had no effect on adhesion of L-selectin expressing NALM6-L cells. Furthermore, CD40/CD40L interaction abrogated VEGF-induced migration of HUVEC compared to non-stimulated controls. In comparison experiments, stimulation of endothelial cells with VEGF led to a significant phosphorylation of ERK1/2, Akt, and eNOS. Stimulation of endothelial CD40 had no effect on VEGF-induced phosphorylation of ERK1/2. However, VEGF-induced activation of Akt and eNOS was reduced to baseline levels when endothelial CD40 was stimulated.

CONCLUSION

CD40/CD40L interaction induces E-selectin dependent adhesion of leukocytes to human endothelial cells and reduces endothelial cell migration by inhibiting the Akt/eNOS signaling pathway.

Triphasic force dependence of E-selectin/ligand dissociation governs cell rolling under flow

During inflammation, flowing leukocytes tether to and roll on vascular surfaces through the association and dissociation of selectin/ligand bonds. The interactions of P- and L- selectins with their respective ligands exhibit catch-slip bonds, such that increasing force initially prolongs and then shortens bond lifetimes. In addition, catch-slip bonds have been shown to govern L-selectin-mediated cell rolling. Using a flow chamber and biomembrane force probe, we show a triphasic force dependence of E-selectin/ligand dissociation that initially behaves as slip bonds, then transitions to catch bonds, and finally transitions again to slip bonds as the force increases. These transitions govern the velocities of neutrophils, HL-60 cells, and Colo-205 cells rolling on E-selectin, as evidenced by the fact that their velocities exhibited a triphasic force dependence that inversely matched the triphasic lifetime-force relationship. At low forces, slip bonds may also precede catch bonds for interactions of P- and L-selectin with their ligands.

Cloning and characterization of a viral α2-3-sialyltransferase (vST3Gal-I) for the synthesis of sialyl Lewisx

Sialyl Lewis(x) (SLe(x), Siaα2-3Galβ1-4(Fucα1-3)GlcNAcβOR) is an important sialic acid-containing carbohydrate epitope involved in many biological processes such as inflammation and cancer metastasis. In the biosynthetic process of SLe(x), α2-3-sialyltransferase-catalyzed sialylation generally proceeds prior to α1-3-fucosyltransferase-catalyzed fucosylation. For the chemoenzymatic synthesis of SLe(x) containing different sialic acid forms, however, it would be more efficient if diverse sialic acid forms are transferred in the last step to the fucosylated substrate Lewis(x) (Le(x)). An α2-3-sialyltransferase obtained from myxoma virus-infected European rabbit kidney RK13 cells (viral α2-3-sialyltransferase (vST3Gal-I)) was reported to be able to tolerate fucosylated substrate Le(x). Nevertheless, the substrate specificity of the enzyme was only determined using partially purified protein from extracts of cells infected with myxoma virus. Herein we demonstrate that a previously reported multifunctional bacterial enzyme Pasteurella multocida sialyltransferase 1 (PmST1) can also use Le(x) as an acceptor substrate, although at a much lower efficiency compared to nonfucosylated acceptor. In addition, N-terminal 30-amino-acid truncated vST3Gal-I has been successfully cloned and expressed in Escherichia coli Origami™ B(DE3) cells as a fusion protein with an N-terminal maltose binding protein (MBP) and a C-terminal His(6)-tag (MBP-Δ30vST3Gal-I-His(6)). The viral protein has been purified to homogeneity and characterized biochemically. The enzyme is active in a broad pH range varying from 5.0 to 9.0. It does not require a divalent metal for its α2-3-sialyltransferase activity. It has been used in one-pot multienzyme sialylation of Le(x) for the synthesis of SLe(x) containing different sialic acid forms with good yields.

CSLEX (Sialyl Lewis X) is a useful tumor marker for monitoring of breast cancer patients

BACKGROUND

CSLEX is a type II carbohydrate antigen that interacts with the CSLEX-1 monoclonal antibody. CSLEX in combination with carbohydrate antigen 15-3 may be more useful than Carcinoembryonic Antigen with carbohydrate antigen 15-3 as tumor markers for monitoring of breast cancer.

METHODS

The serum levels of tumor markers, including CSLEX, were measured in 480 consecutive breast cancer patients with or without metastasis who visited the outpatient clinic of the Division of Breast and Endocrine Surgery, Shinshu University Hospital, between April 2007 and September 2007.

RESULTS

Serum levels of each of the tumor markers correlated significantly with the status of metastasis (P < 0.01). Combinations of Carcinoembryonic Antigen and carbohydrate antigen 15-3, Carcinoembryonic Antigen and Nation Cancer Center-Stomach-439, Carcinoembryonic Antigen and CSLEX, carbohydrate antigen 15-3 and Nation Cancer Center-Stomach-439, and carbohydrate antigen 15-3 and CSLEX levels also correlated significantly with the status of metastasis (P < 0.01). The sensitivity, specificity, positive predictive value, negative predictive value and accuracy were almost the same for CSLEX and Nation Cancer Center-Stomach-439, which are both type II carbohydrate antigens. The cutoff indexes of serum CSLEX and Nation Cancer Center-Stomach-439 for detection of breast cancer metastasis were 38.8 ± 52.7-fold and 22.1 ± 27.8-fold, respectively (P = 0.16).

CONCLUSIONS

These data suggest that the diagnostic values of CSLEX and Nation Cancer Center-Stomach-439 are similar in single or combined use. However, the cutoff index of serum CSLEX tended to be higher than that of Nation Cancer Center-Stomach-439, which may make CSLEX more useful for detection of breast cancer metastasis.

Lewis Y promotes growth and adhesion of ovarian carcinoma-derived RMG-I cells by upregulating growth factors

Lewis y (LeY) antigen is a difucosylated oligosaccharide carried by glycoconjugates on the cell surface. Overexpression of LeY is frequently observed in epithelial-derived cancers and has been correlated to the pathological staging and prognosis. However, the effects of LeY on ovarian cancer are not yet clear. Previously, we transfected the ovarian cancer cell line RMG-I with the α1,2-fucosyltransferase gene to obtain stable transfectants, RMG-I-H, that highly express LeY. In the present study, we examined the proliferation, tumorigenesis, adhesion and invasion of the cell lines with treatment of LeY monoclonal antibody (mAb). Additionally, we examined the expression of TGF-β1, VEGF and b-FGF in xenograft tumors. The results showed that the proliferation and adhesion in vitro were significantly inhibited by treatment of RMG-I-H cells with LeY mAb. When subcutaneously inoculated in nude mice, RMG-I-H cells produced large tumors, while mock-transfected cells RMG-I-C and the parental cells RMG-I produced small tumors. Moreover, the tumor formation by RMG-I-H cells was inhibited by preincubating the cells with LeY mAb. Notably, the expression of TGF-β1, VEGF and b-FGF all increased in RMG-I-H cells. In conclusion, LeY plays an important role in promoting cell proliferation, tumorigenecity and adhesion, and these effects may be related to increased levels of growth factors. The LeY antibody shows potential application in the treatment of LeY-positive tumors.

GMI-1070, a novel pan-selectin antagonist, reverses acute vascular occlusions in sickle cell mice

Leukocyte adhesion in the microvasculature influences blood rheology and plays a key role in vaso-occlusive manifestations of sickle cell disease. Notably, polymorphonuclear neutrophils (PMNs) can capture circulating sickle red blood cells (sRBCs) in inflamed venules, leading to critical reduction in blood flow and vaso-occlusion. Recent studies have suggested that E-selectin expression by endothelial cells plays a key role by sending activating signals that lead to the activation of Mac-1 at the leading edge of PMNs, thereby allowing RBC capture. Thus, the inhibition of E-selectin may represent a valuable target in this disease. Here, we have tested the biologic properties of a novel synthetic pan-selectin inhibitor, GMI-1070, with in vitro assays and in a humanized model of sickle cell vaso-occlusion analyzed by intravital microscopy. We have found that GMI-1070 predominantly inhibited E-selectin-mediated adhesion and dramatically inhibited sRBC-leukocyte interactions, leading to improved microcirculatory blood flow and improved survival. These results suggest that GMI-1070 may represent a valuable novel therapeutic intervention for acute sickle cell crises that should be further evaluated in a clinical trial.

Synthesis of an Fmoc-threonine bearing core-2 glycan: a building block for PSGL-1 via Fmoc-assisted solid-phase peptide synthesis

Selectins (L, E, and P) are vascular endothelial molecules that play an important role in the recruitment of leukocytes to inflamed tissue. In this regard, P-Selectin glycoprotein-1 (PSGL-1) has been identified as a ligand for P-Selectin. PSGL-1 binds to P-Selectin through the interaction of core-2 O-glycan expressing sialyl Lewis(x) oligosaccharide and the three tyrosine sulfate residues. Herein, we report the synthesis of threonine-linked core-2 O-glycan as an amino acid building block for the synthesis of PSGL-1. This building block was further incorporated in the Fmoc-assisted solid-phase peptide synthesis to provide a portion of the PSGL-1 glycopeptide.

Computational modeling of carbohydrate-recognition process in E-selectin complex: structural mapping of sialyl Lewis X onto ab initio QM/MM free energy surface

To advance our knowledge of carbohydrate recognition by lectins, we propose a systematic computational modeling strategy to identify complex sugar-chain conformations on the reduced free energy surface (FES). We selected the complex of E-selectin with sialyl Lewis X (denoted E-selectin/SLe(x) complex) as a first target molecule. First, we introduced the reduced 2D-FES that characterizes conformational changes in carbohydrate structure as well as the degree of solvation stability of the carbohydrate ligand, and evaluated the overall free energy profile by classical molecular dynamics simulation combined with ab initio QM/MM energy corrections. Second, we mapped flexible carbohydrate structures onto the reduced QM/MM 2D-FES, and identified the details of molecular interactions between each monosaccharide component and the amino acid residues at the carbohydrate-recognition domain. Finally, we confirmed the validity of our modeling strategy by evaluating the chemical shielding tensor by ab initio QM/MM-GIAO computations for several QM/MM-refined geometries sampled from the minimum free energy region in the 2D-FES, and compared this theoretical averaging data with the experimental 1D-NMR profile. The model clearly shows that the binding geometries of the E-selectin/SLe(x) complex are determined not by one single, rigid carbohydrate structure but rather by the sum of averaged conformations fluctuating around the minimum free energy region. For the E-selectin/SLe(x) complex, the major molecular interactions are hydrogen bonds between Fuc and the Ca(2+) binding site in the carbohydrate-recognition domain, and Gal is important in determining the ligand specificity.

Chemoenzymatic synthesis of the sialyl Lewis X glycan and its derivatives

A combination of recombinant FKP and alpha-(1-->3)-fucosyltransferase allows the facile synthesis of the sialyl Lewis X tetrasaccharide glycan and its derivatives in excellent yield. In this system, the universal fucosyl donor, guanidine 5'-diphosphate-beta-L-fucose (GDP-fucose), or its analogues can be generated in situ by cofactor recycling using pyruvate kinase.

The Effects of Load on E-Selectin Bond Rupture and Bond Formation

Molecular dissociation rates have long been known to be sensitive to applied force. We use a laser trap to provide evidence that rates of association may also be force-dependent. We use the thermal fluctuation assay to study single bonds between E-selectin and sialyl Lewis(a) (sLe(a)), the sugar on PSGL-1 to which the three selectins bind. Briefly, an E-selectin-coated bead is held in a laser trap and pressed with various compressive loads against the vertical surface of a bead coated with sLe(a). The time it takes for a bond to form is used to calculate a specific two-dimensional on-rate, kono. We observe an increase in kono with increasing compressive force, providing single molecule evidence that on-rate, in addition to off-rate, is influenced by load. By measuring bond lifetimes at known tensile loads, we show that E-selectin, like its family members L- and P-selectin, is capable of forming catch bonds. Our data support a reverse Bell model, in which compressive forces lower the activation energy for binding. Load-dependent on-rates may be a general feature of all intermolecular bonds.

Epigenetic silencing of the sulfate transporter gene DTDST induces sialyl Lewisx expression and accelerates proliferation of colon cancer cells

Colon cancer cells express the carbohydrate determinant sialyl Lewis(x), while they exhibit markedly decreased the expression of its sulfated derivative, sialyl 6-sulfo Lewis(x). In contrast, normal colonic epithelial cells strongly express sialyl 6-sulfo Lewis(x), but they virtually do not express sialyl Lewis(x). Impaired sulfation was therefore suggested to occur during the course of malignant transformation of colonic epithelial cells and was assumed to be responsible for the increased sialyl Lewis(x) expression in cancers. To elucidate the molecular biological background of the impaired sulfation in cancers, we studied the expression levels of mRNA for 6-O-sulfotransferase isoenzymes, PAPS synthases and transporters, and a cell membrane sulfate transporter, DTDST, in cancer tissues. The most striking decrease in cancer cells compared with nonmalignant epithelial cells was noted in the transcription of the DTDST gene (P = 0.0000014; n = 20). Most cultured colon cancer cells had a diminished DTDST transcription, which was restored when cultured with histone deacetylase inhibitors. Suppression of DTDST transcription under the control of a tet-off inducible promoter resulted in increased sialyl Lewis(x) expression and reduced sialyl 6-sulfo Lewis(x) expression. Unexpectedly, the growth rate of the cancer cells was markedly enhanced when transcription of DTDST was suppressed. These results show that the decrease in the transcription of the sulfate transporter gene is the major cause of decreased expression of sialyl 6-sulfo Lewis(x) and increased expression of sialyl Lewis(x) in colon cancers. The results also suggest that the diminished DTDST expression is closely related to enhanced proliferation of cancer cells.

Fucosylation and gastrointestinal cancer

Fucose (6-deoxy-L-galactose) is a monosaccharide that is found on glycoproteins and glycolipids in verte-brates, invertebrates, plants, and bacteria. Fucosylation, which comprises the transfer of a fucose residue to oligosaccharides and proteins, is regulated by many kinds of molecules, including fucosyltransferases, GDP-fucose synthetic enzymes, and GDP-fucose transporter(s). Dramatic changes in the expression of fucosylated oligosaccharides have been observed in cancer and inflammation. Thus, monoclonal antibodies and lectins recognizing cancer-associated fucosylated oligosaccharides have been clinically used as tumor markers for the last few decades. Recent advanced glycomic approaches allow us to identify novel fucosylation-related tumor markers. Moreover, a growing body of evidence supports the functional significance of fucosylation at various pathophysiological steps of carcinogenesis and tumor progression. This review highlights the biological and medical significance of fucosylation in gastrointestinal cancer.

Glycan array: a powerful tool for glycomics studies

Glycan arrays have become a powerful tool for the high-throughput elucidation of interactions of different carbohydrate structures with a wide variety of biological targets, including antibodies, proteins, viruses and cells. This technique is especially suitable for glycomics studies, because arrays present carbohydrate ligands in a manner that mimics interactions at cell-cell interfaces. This review assesses the recent advances involving glycan arrays, including new methods for glycan-array fabrication, new platforms for novel biological information, and new perceptions of glycomics for improving the understanding of disease-related glycobiology. Furthermore, this review attempts to forecast trends in the development of glycan arrays and possible solutions for some remaining challenges to improve this new technology.

Protection in rats with heatstroke: hyperbaric oxygen vs activated protein C therapy

The present study was attempted to evaluate the therapeutic effects of activated protein C and/or hyperbaric oxygen in an animal model of heatstroke. Sixty-eight minutes heat stress (43 degrees C) initiated, the anesthetized rats were randomized to several groups and administered: 1) no resuscitation (vehicle solution plus normabaric air, 2) intravenous activated protein C (1mg in 1ml of normal saline per kg of body weight), 3) hyperbaric oxygen (100% oxygen at 202kpa for 17min), and 4) intravenous activated protein C plus hyperbaric oxygen. Another group of rats exposed to room temperature (26 degrees C) was used as normothermic controls. Blood sampling was 0min, 70min, and 85min after heat stress initiated. When the vehicle-treated rats underwent heat exposure, their survival time values found were to be 19-25min. Resuscitation with activated protein C or hyperbaric oxygen significantly and equally improved survival during heatstroke (134-159min). As compared with those of activated protein C or hyperbaric oxygen alone, combined activated protein C and hyperbaric oxygen significantly had higher survival time values (277-347min). All vehicle-treated heatstroke animals displayed systemic response, hypercoagulable state, and hepatic and renal dysfunction. Combined activated protein C and hyperbaric oxygen therapy reduced these heatstroke reactions better than activated protein C or hyperbaric oxygen alone. The results indicate consequently, combined activated protein C and hyperbaric oxygen therapy heightens benefit in combating heatstroke reactions.

Regulation of intracellular signaling by extracellular glycan remodeling

The plasma membrane of eukaryotic cells is coated with carbohydrates. By virtue of their extracellular position and recognizable chemical features, cell surface glycans mediate many receptor-ligand interactions. Recently, mammalian extracellular hydrolytic enzymes have been shown to modify the structure of cell surface glycans and consequently alter their binding properties. These cell surface glycan remodeling events can cause rapid changes in critical signal transduction phenomena. This Review highlights recent studies on the roles of eukaryotic extracellular sialidases, sulfatases, and a deacetylase in regulation of intracellular signaling. We also describe possible therapies that target extracellular glycan remodeling processes and discuss the potential for new discoveries in this area.

Early changes in the apparent diffusion coefficient (ADC) in a mouse model of Sandhoff's disease occur prior to disease symptoms and behavioral deficits

Sandhoff's disease is a lysosomal storage disease in which the ganglioside GM2 accumulates in lysosomes. It has been reported that MRI cannot detect abnormalities in spin echo images in clinically presymptomatic Sandhoff's disease patients. Because one of the results of GM2 accumulation is cell swelling and lysosomal distension, our goal was to determine if changes in the diffusion of water is perturbed. We utilized the MRI imaging modality diffusion-weighted imaging to measure the apparent diffusion coefficient in a mouse models of Sandhoff's disease, the hexb-/- mouse, and determined if diffusion-weighted imaging could be utilized to detect early changes prior to behavioral or overt disease symptom onset. Here we report for the first time a comprehensive behavioral characterization of the hexb-/- mouse in conjunction with the apparent diffusion coefficient measurement. Our data indicate that the apparent diffusion coefficient decreases in the hexb-/- mouse in many but not all brain regions prior to disease symptoms (<3.5 to 4 months of age) and behavioral deficits (3 months of age). The magnitude of the decrease ranged from 4-18%.

Adhesion molecules: potential therapeutic and diagnostic implications

The role of cell adhesion molecules (CAMs) and extracellular matrix (ECM) proteins in various pathological processes, including angiogenesis, thrombosis, inflammation, apoptosis, cell migration, and proliferation is well documented. These processes can lead to both acute and chronic disease states such as ocular diseases, metastasis, unstable angina, myocardial infarction, stroke, osteoporosis, a wide range of inflammatory diseases, vascular remodeling, and neurodegenerative disorders. A key success in this field was identification of the role of platelet glycoprotein (GP)IIb/IIIa in the prevention and diagnosis of various thromboembolic disorders. The use of soluble adhesion molecules as potential diagnostic markers for acute and chronic leukocyte, platelet, and endothelial cell insult is becoming increasingly common. The development of various therapeutic and diagnostic candidates based on the key role of CAMs, with special emphasis on integrins in various diseases, as well as the structure-function aspects of cell adhesion and signaling of the different CAMs and ECM are highlighted.