Selectin ligands

Soluble adhesion molecules E-cadherin, intercellular adhesion molecule-1, and E-selectin as lung cancer biomarkers

BACKGROUND

Altered levels of circulating adhesion molecules found in several carcinomas, including lung cancer, reflect local loss of diffusion barriers and tumor volume and can be potentially used as biomarkers. In the present study, we investigated the role of soluble E-cadherin (sE-cad), soluble intercellular adhesion molecule-1 (sICAM-1), and soluble E-selectin (sE-sel) as biomarkers in lung cancer.

METHODS

Sixty-two patients with recently diagnosed lung cancer, 42 with small cell lung cancer (SCLC), and 20 with non-small cell lung cancer (NSCLC), as well as 29 healthy volunteers were enrolled. Blood samples were collected at the time of diagnosis and measurement of soluble adhesion molecules in the serum samples was performed by enzyme-linked immunoassay using monoclonal antibodies against E-cadherin, E-selectin, and ICAM-1.

RESULTS

Serum levels of sE-cad, sE-sel, and sICAM-1 in both SCLC and NSCLC were significantly elevated compared with control subjects (P < .001). In addition, patients with SCLC or NSCLC with distant metastasis had a marked increase of sE-Cad (P < .001), but no such correlation with sE-sel and sICAM-1 was found.

CONCLUSIONS

Our findings suggest that sE-cad, sE-sel, and sICAM-1 have an adjunctive diagnostic role in lung cancer. Furthermore, sE-cad may also have a prognostic role and could be a useful biomarker in the prediction of lung cancer outcome.

Colloquium paper: uniquely human evolution of sialic acid genetics and biology

Darwinian evolution of humans from our common ancestors with nonhuman primates involved many gene-environment interactions at the population level, and the resulting human-specific genetic changes must contribute to the "Human Condition." Recent data indicate that the biology of sialic acids (which directly involves less than 60 genes) shows more than 10 uniquely human genetic changes in comparison with our closest evolutionary relatives. Known outcomes are tissue-specific changes in abundant cell-surface glycans, changes in specificity and/or expression of multiple proteins that recognize these glycans, and novel pathogen regimes. Specific events include Alu-mediated inactivation of the CMAH gene, resulting in loss of synthesis of the Sia N-glycolylneuraminic acid (Neu5Gc) and increase in expression of the precursor N-acetylneuraminic acid (Neu5Ac); increased expression of alpha2-6-linked Sias (likely because of changed expression of ST6GALI); and multiple changes in SIGLEC genes encoding Sia-recognizing Ig-like lectins (Siglecs). The last includes binding specificity changes (in Siglecs -5, -7, -9, -11, and -12); expression pattern changes (in Siglecs -1, -5, -6, and -11); gene conversion (SIGLEC11); and deletion or pseudogenization (SIGLEC13, SIGLEC14, and SIGLEC16). A nongenetic outcome of the CMAH mutation is human metabolic incorporation of foreign dietary Neu5Gc, in the face of circulating anti-Neu5Gc antibodies, generating a novel "xeno-auto-antigen" situation. Taken together, these data suggest that both the genes associated with Sia biology and the related impacts of the environment comprise a relative "hot spot" of genetic and physiological changes in human evolution, with implications for uniquely human features both in health and disease.

Higher specificity of the activity of low molecular weight fucoidan for thrombin-induced platelet aggregation

Algal fucoidans possess a wide variety of biological activities, including anticoagulation and antithrombosis, making them potential candidates for clinical use. We assessed the antiaggregant, anticoagulant and antithrombotic activities and the underlying mechanism of the low- and high-molecular weight fucoidans from the seaweed Laminaria japonica of Qingdao, China (F-Q and HMWF-Q). In the platelets of rats and humans, HMWF-Q demonstrated a pro-aggregation response, whereas F-Q (like the commercially purchased fucoidan (F-S) and heparin), showed an inhibitory effect on thrombin-induced aggregation with an IC(50) of 8 microg/mL, approximately five times lower than those of F-S and heparin. In the activated partial thromboplastin time test, F-Q (40 microg/mL) demonstrated less potent effect than F-S (40 microg/mL) and heparin (7mug/mL); 162+/-2.4s vs. 250+/-13.2s and >300s, p<0.01, respectively. It was also less effective than F-S on inhibiting thrombin catalyzed fibrinogen cleavage (IC(50) 10 microg/mL vs. 2.8 microg/mL) in vitro and rat thrombosis in vivo at 3mg/kg (i.v.). The inhibitory effects of F-Q and heparin on thrombin activity were strikingly enhanced by either antithrombin (AT) or heparin cofactor II (HCII). A direct interaction of F-S with thrombin, and F-Q or heparin with AT was demonstrated in both fluorescence quenching and PAGE analysis. Additionally, a pro-aggregation effect and an enhancement of thrombin activity were also observed with F-S, but not with F-Q or heparin, treatment. These results indicate that F-Q inhibits thrombin via activation of AT and HCII, whereas F-S mainly interacts directly with thrombin. Importantly, F-Q shows a higher specificity for hypoaggregation and a weaker effect for anticoagulant profiles than heparin and F-S. Therefore, F-Q could be a promising candidate for the treatment of thrombosis-related cardiovascular diseases.

In vivo tumor cell adhesion in the pulmonary microvasculature is exclusively mediated by tumor cell--endothelial cell interaction

BACKGROUND

Metastasis formation is the leading cause of death among colon cancer patients. We established a new in-situ model of in vivo microscopy of the lung to analyse initiating events of metastatic tumor cell adhesion within this typical metastatic target of colon cancer.

METHODS

Anaesthetized CD rats were mechanically ventilated and 106 human HT-29LMM and T84 colon cancer cells were injected intracardially as single cell suspensions. Quantitative in vivo microscopy of the lung was performed in 10 minute intervals for a total of 40 minutes beginning with the time of injection.

RESULTS

After vehicle treatment of HT-29LMM controls 15.2 +/- 5.3; 14.2 +/- 7.5; 11.4 +/- 5.5; and 15.4 +/- 6.5 cells/20 microscopic fields were found adherent within the pulmonary microvasculature in each 10 minute interval. Similar numbers were found after injection of the lung metastasis derived T84 cell line and after treatment of HT-29LMM with unspecific mouse control-IgG. Subsequently, HT-29LMM cells were treated with function blocking antibodies against beta1-, beta4-, and alphav-integrins wich also did not impair tumor cell adhesion in the lung. In contrast, after hydrolization of sialylated glycoproteins on the cells' surface by neuraminidase, we observed impairment of tumor cell adhesion by more than 50% (p < 0.05). The same degree of impairment was achieved by inhibition of P- and L-selectins via animal treatment with fucoidan (p < 0.05) and also by inhibition of the Thomson-Friedenreich (TF)-antigen (p < 0.05).

CONCLUSIONS

These results demonstrate that the initial colon cancer cell adhesion in the capillaries of the lung is predominantly mediated by tumor cell - endothelial cell interactions, possibly supported by platelets. In contrast to reports of earlier studies that metastatic tumor cell adhesion occurs through integrin mediated binding of extracellular matrix proteins in liver, in the lung, the continuously lined endothelium appears to be specifically targeted by circulating tumor cells.

Engineering mammalian cells in bioprocessing - current achievements and future perspectives

Over the past 20 years, we have seen significant improvements in product titres from 50 mg/l to 5-10 g/l, a more than 100-fold increase. The main methods that have been employed to achieve this increase in product titre have been through the manipulation of culture media and process control strategies, such as the optimization of fed-batch processes. An alternative means to increase productivity has been through the engineering of host cells by altering cellular processes. Recombinant DNA technology has been used to over-express or suppress specific genes to endow particular phenotypes. Cellular processes that have been altered in host cells include metabolism, cell cycle, protein secretion and apoptosis. Cell engineering has also been employed to improve post-translational modifications such as glycosylation. In this article, an overview of the main cell engineering strategies previously employed and the impact of these strategies are presented. Many of these strategies focus on engineering cell lines with more efficient carbon metabolism towards reducing waste metabolites, achieving a biphasic production system by engineering cell cycle control, increasing protein secretion by targeting specific endoplasmic reticulum stress chaperones, delaying cell death by targeting anti-apoptosis genes, and engineering glycosylation by enhancing recombinant protein sialylation and antibody glycosylation. Future perspectives for host cell engineering, and possible areas of research, are also discussed in this review.

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.

Advances in the biology and chemistry of sialic acids

Sialic acids are a subset of nonulosonic acids, which are nine-carbon alpha-keto aldonic acids. Natural existing sialic acid-containing structures are presented in different sialic acid forms, various sialyl linkages, and on diverse underlying glycans. They play important roles in biological, pathological, and immunological processes. Sialobiology has been a challenging and yet attractive research area. Recent advances in chemical and chemoenzymatic synthesis, as well as large-scale E. coli cell-based production, have provided a large library of sialoside standards and derivatives in amounts sufficient for structure-activity relationship studies. Sialoglycan microarrays provide an efficient platform for quick identification of preferred ligands for sialic acid-binding proteins. Future research on sialic acid will continue to be at the interface of chemistry and biology. Research efforts not only will lead to a better understanding of the biological and pathological importance of sialic acids and their diversity but also could lead to the development of therapeutics.

Molecular interactions in cancer cell metastasis

Metastasis, the process by which cancer cells leave the primary tumour, disseminate and form secondary tumours at anatomically distant sites, is a serious clinical problem as it is disseminated disease, which is often impossible to eradicate successfully, that causes the death of most cancer patients. Metastasis results from a complex molecular cascade comprising many steps, all of which are interconnected through a series of adhesive interactions and invasive processes as well as responses to chemotactic stimuli. In spite of its clinical significance, it remains incompletely understood. This review provides an overview of some of the molecular interactions that are critical to metastasis. It summarises the principle molecular players in the major steps of the metastatic cascade. These are: (1) tumour angiogenesis, (2) disaggregation of tumour cells from the primary tumour mass, mediated by cadherins and catenins, (3) invasion of, and migration through, the basement membrane (BM) and extracellular matrix (ECM) surrounding the tumour epithelium, and subsequent invasion of the BM of the endothelium of local blood vessels. This is mediated through integrins and proteases, including urokinase form of plasminogen activator (uPA), matrix metalloproteinases (MMPs) and cathepsins, (4) intravasation of the tumour cells into the blood vessels prior to hematogeneous dissemination to distant sites, (5) adhesion of the circulating tumour cells to the endothelial cell lining at the capillary bed of the target organ site. This occurs through adhesive interactions between cancer cells and endothelial cells involving selectins, integrins and members of the immunoglobulin superfamily (IgSF), (6) invasion of the tumour cells through the endothelial cell layer and surrounding BM (extravasation) and target organ tissue and (7) the development of secondary tumour foci at the target organ site.

Glycosynaptic microdomains controlling tumor cell phenotype through alteration of cell growth, adhesion, and motility

Glycosphingolipids (GSLs) GM3 (NeuAcalpha3Galbeta4Glcbeta1Cer) and GM2 (GalNAcbeta4[NeuAcalpha3]Galbeta4Glcbeta1Cer) inhibit (i) cell growth through inhibition of tyrosine kinase associated with growth factor receptor (GFR), (ii) cell adhesion/motility through inhibition of integrin-dependent signaling via Src kinases, or (iii) both cell growth and motility by blocking "cross-talk" between integrins and GFRs. These inhibitory effects are enhanced when GM3 or GM2 are in complex with specific tetraspanins (TSPs) (CD9, CD81, CD82). Processes (i)-(iii) occur through specific organization of GSLs with key molecules (TSPs, caveolins, GFRs, integrins) in the glycosynaptic microdomain. Some of these processes are shared with epithelial-mesenchymal transition induced by TGFbeta or under hypoxia, particularly that associated with cancer progression.

Human umbilical cord blood cells protect against hypothalamic apoptosis and systemic inflammation response during heatstroke in rats

BACKGROUND

Intravenous administration of human umbilical cord blood cells (HUCBC) has been shown to improve heatstroke by reducing arterial hypotension as well as cerebral ischemia and damage in a rat model. To extend these findings, we assessed both hypothalamic neuronal apoptosis and systemic inflammatory responses in the presence of HUCBCs or vehicle medium immediately after initiation of heatstroke.

METHODS

Anesthetized rats, immediately after the initiation of heat stress, were divided into two groups and given either serum-free lymphocyte medium (0.3mL per rat, intravenously) or HUCBCs (5 x 10(6) in 0.3 mL serum-free lymphocyte medium, intravenously). Another group of rats were exposed to room temperature (26 degrees C) and used as normothermic controls. Heatstroke was induced by exposing the anesthetized rats to a high ambient temperature of 43 degrees C for 68 minutes.

RESULTS

After the onset of heatstroke, animals treated with serum-free lymphocyte medium displayed hyperthermia, hypotension, bradycardia, hypothalamic neuronal apoptosis and degeneration, and up-regulation of systemic inflammatory response molecules including serum tumor necrosis factor-alpha, soluble intercellular adhesion molecule-1 and E-selectin. Heatstroke-induced hypotension, bradycardia, hypothalamic neuronal apoptosis and degeneration, and increased systemic inflammatory response molecules were significantly inhibited by HUCBC treatment. Although heatstroke-induced hyperthermia was not affected by HUCBC treatment, the serum levels of the anti-inflammatory cytokine interleukin-10 were significantly increased by HUCBC therapy during hyperthermia.

CONCLUSIONS

These findings suggest that HUCBC transplantation may prevent the occurrence of heatstroke by reducing hypothalamic neuronal damage and the systemic inflammatory responses.

The thrombotic potential of oral pathogens

In recent times the concept of infectious agents playing a role in cardiovascular disease has attracted much attention. Chronic oral disease such as periodontitis, provides a plausible route for entry of bacteria to the circulation. Upon entry to the circulation, the oral bacteria interact with platelets. It has been proposed that their ability to induce platelet aggregation and support platelet adhesion is a critical step in the pathogenesis of the infection process. Many published studies have demonstrated multiple mechanisms through which oral bacteria are able to bind to and activate platelets. This paper will review the various mechanisms oral bacteria use to interact with platelets.

ABO blood group glycans modulate sialic acid recognition on erythrocytes

ABH(O) blood group polymorphisms are based on well-known intraspecies variations in structures of neutral blood cell surface glycans in humans and other primates. Whereas natural antibodies against these glycans can act as barriers to blood transfusion and transplantation, the normal functions of this long-standing evolutionary polymorphism remain largely unknown. Although microbial interactions have been suggested as a selective force, direct binding of lethal pathogens to ABH antigens has not been reported. We show in this study that ABH antigens found on human erythrocytes modulate the specific interactions of 3 sialic acid-recognizing proteins (human Siglec-2, 1918SC influenza hemagglutinin, and Sambucus nigra agglutinin) with sialylated glycans on the same cell surface. Using specific glycosidases that convert A and B glycans to the underlying H(O) structure, we show ABH antigens stabilize sialylated glycan clusters on erythrocyte membranes uniquely for each blood type, generating differential interactions of the 3 sialic acid-binding proteins with erythrocytes from each blood type. We further show that by stabilizing such structures ABH antigens can also modulate sialic acid-mediated interaction of pathogens such as Plasmodium falciparum malarial parasite. Thus, ABH antigens can noncovalently alter the presentation of other cell surface glycans to cognate-binding proteins, without themselves being a direct ligand.

Leukocyte-endothelial interactions in inflammation

At sites of inflammation, infection or vascular injury local proinflammatory or pathogen-derived stimuli render the luminal vascular endothelial surface attractive for leukocytes. This innate immunity response consists of a well-defined and regulated multi-step cascade involving consecutive steps of adhesive interactions between the leukocytes and the endothelium. During the initial contact with the activated endothelium leukocytes roll along the endothelium via a loose bond which is mediated by selectins. Subsequently, leukocytes are activated by chemokines presented on the luminal endothelial surface, which results in the activation of leukocyte integrins and the firm leukocyte arrest on the endothelium. After their firm adhesion, leukocytes make use of two transmigration processes to pass the endothelial barrier, the transcellular route through the endothelial cell body or the paracellular route through the endothelial junctions. In addition, further circulating cells, such as platelets arrive early at sites of inflammation contributing to both coagulation and to the immune response in parts by facilitating leukocyte-endothelial interactions. Platelets have thereby been implicated in several inflammatory pathologies. This review summarizes the major mechanisms and molecules involved in leukocyte-endothelial and leukocyte-platelet interactions in inflammation.

A fucose-containing O-glycoepitope on bovine and human nucleolin

In this paper, we demonstrate the existence and localization of fucosyl-containing O-glycoforms of nucleolin in cultured bovine endothelial cells (CVEC) and malignant cultured human A431 cells. The tool for this discovery was an antibody raised against gp273, a glycoprotein ligand for the sperm-egg interaction in the mollusc bivalve Unio elongatulus. The function and immunological properties of gp273 mainly depend on clustered Lewis-like, fucose-containing O-glycans. Here an anti-gp273 antibody was used to evaluate whether glycoepitopes similar to those of gp273 are part of potential ligands of selectins in endothelial cells. We found that anti-gp273 strongly and exclusively interacted with a 110 kDa protein in CVEC and A431 tumor cells. After partial purification, mass spectrometry identified the protein as nucleolin. This was confirmed by comparing anti-gp273 and anti-nucleolin antibody immunoblotting after nucleolin depletion. We confirmed that anti-gp273 binding to nuclear and extranuclear nucleolin was against a fucose-containing O-glycoepitope by immunoblot analysis of the protein after chemically removing O-glycans and by lectin-blot analysis of control and nucleolin-depleted samples. Using anti-gp273 IgG, we detected nucleolin on the plasma membrane and cytoplasm. O-Glycosylation may regulate the plethora of functions in which nucleolin is involved.

Antiganglioside antibodies and their pathophysiological effects on Guillain-Barré syndrome and related disorders--a review

Guillain-Barré syndrome (GBS) is an acute immune-mediated polyradiculoneuropathy which can cause acute quadriplegia. Infection with micro-organisms, including Campylobacter jejuni (C. jejuni), Haemophilus influenzae, and Cytomegalovirus (CMV), is recognized as a main triggering event for the disease. Lipooligosaccharide (LOS) genes are responsible for the formation of human ganglioside-like LOS structures in infectious micro-organisms that can induce GBS. Molecular mimicry of LOSs on the surface of infectious agents and of ganglioside antigens on neural cells is thought to induce cross-reactive humoral and cellular immune responses. Patients with GBS develop antibodies against those gangliosides, resulting in autoimmune targeting of peripheral nerve sites, leading to neural damage. Heterogeneity of ganglioside expression in the peripheral nervous system (PNS) may underlie the differential clinical manifestation of the GBS variants. Recent studies demonstrate that some GBS sera react with ganglioside complexes consisting of two different gangliosides, such as GD1a and GD1b, or GM1 and GD1a, but not with each constituent ganglioside alone. The discovery of antiganglioside complex antibodies not only improves the detection rate of autoantibodies in GBS, but also provides a new concept in the antibody-antigen interaction through clustered carbohydrate epitopes. Although ganglioside mimicry is one of the possible etiological causes of GBS, unidentified factors may also contribute to the pathogenesis of GBS. While GBS is not considered a genetic disease, host factors, particularly human lymphocyte antigen type, appear to have a role in the pathogenesis of GBS following C. jejuni infection.

Beyond molecular recognition: using a repulsive field to tune interfacial valency and binding specificity between adhesive surfaces

Surface-bound biomolecular fragments enable "smart" materials to recognize cells and other particles in applications ranging from tissue engineering and medical diagnostics to colloidal and nanoparticle assembly. Such smart surfaces are, however, limited in their design to biomolecular selectivity. This feature article demonstrates, using a completely nonbiological model system, how specificity can be achieved for particle (and cell) binding, employing surface designs where immobilized nanoscale adhesion elements are entirely nonselective. Fundamental principles are illustrated by a model experimental system where 11 nm cationic nanoparticles on a planar negative silica surface interact with flowing negative silica microspheres having 1.0 and 0.5 microm diameters. In these systems, the interfacial valency, defined as the number of cross-bonds needed to capture flowing particles, is tunable through ionic strength, which alters the range of the background repulsion and therefore the effective binding strength of the adhesive elements themselves. At high ionic strengths where long-range electrostatic repulsions are screened, single surface-bound nanoparticles capture microspheres, defining the univalent regime. At low ionic strengths, competing repulsions weaken the effective nanoparticle adhesion so that multiple nanoparticles are needed for microparticle capture. This article discusses important features of the univalent regime and then illustrates how multivalency produces interfacial-scale selectivity. The arguments are then generalized, providing a possible explanation for highly specific cell binding in nature, despite the degeneracy of adhesion molecules and cell types. The mechanism for the valency-related selectivity is further developed in the context of selective flocculation in the colloidal literature. Finally, results for multivalent binding are contrasted with the current thinking for interfacial design and the presentation of adhesion moieties on engineered surfaces.

Elevated expression of L-selectin ligand in lymph node-derived human prostate cancer cells correlates with increased tumorigenicity

Human prostate cancer LNCaP cells including C-33 and C-81 cells were originally derived from the lymph nodes of a patient with metastatic prostate cancer. These two cells were employed for characterization of L-selectin ligand and in vitro tumorigenicity, because they mimic the clinical conditions of early and late-stage human prostate cancer. C-81 cells exhibit higher in vitro migratory and invasive properties as compared with C-33 cells. We find that the L-selectin ligand and mucin glycan-associated MECA-79 epitope were elevated in C-81 cells. An increase of these glycotopes positively correlates with elevated tumorigenicity and expression of key glycosyl- and sulfotransferase genes. These results suggest that modulated expression of selective glycogenes correlates with altered tumorigenicity of cancer cells.

Serum-free production of a chimeric E-selectin-IgG protein from 1 to 100 l scale: Repeated batch cultivation versus continuous spin filter perfusion

On inflamed endothelium the cell surface protein E-selectin isexpressed which supports the initial process of attachment -capturing and rolling of leukocytes. A recombinant CHO cell linesecreting a soluble E-selectin-IgG chimera was cultivated competitively under serum free conditions in three different bioreactor systems: a 1 l Super-Spinner, a 2 l stirred tank bioreactor equipped with a spinfilter, and a 100 l stirred tankbioreactor. In the smallest system 25.4 mg E-selectin-IgG wereproduced in 62 days using a repeated batch process whileachieving a maximal viable cell density of 3.7 x 10(6) cells ml(-1). Using continuous perfusion mode a total amount of35.2 mg were produced with a maximal viable cell density of1.65 x 10(7) cells ml(-1) in the 2 l bioreactor within 29 days. Large scale cultivation in a 100 l stirred tankbioreactor yielded 105.6 mg in three batches with a maximal viable cell density of 9.7 x 10(5) cells ml(-1) within 15 days. After removal of the cells by continuous centrifugation and a depth filter clearance step, the supernatants were concentrated via ultra filtration. Purificationwas performed by affinity chromatography with rProtein A. Integrity of the E-selectin-IgG protein was checked with SDS PAGE. Its activity was verified in a cellular adhesion assay performed with HL-60 cells and a recombinant CHO cell line expressing membrane-anchored E-selectin constitutively, and E-selectin expressing HUVECs, respectively. Soluble E-selectin-IgG was used to block adhesion to these cell layerscompetitively. A concentation of 18.8 and 37.5 mug ml(-1)was sufficient to reduce the amount of adhering HL-60 cells to 50% on CHO and HUVEC layers, respectively.

Affinity of low molecular weight fucoidan for P-selectin triggers its binding to activated human platelets

BACKGROUND

P-selectin is an adhesion receptor expressed on activated platelets and endothelial cells. Its natural ligand, P-selectin glycoprotein ligand-1, is expressed on leucocytes and the P-selectin/PSGL-1 interaction is involved in leukocyte rolling. We have compared the interaction of P-selectin with several low molecular weight polysaccharides: fucoidan, heparin and dextran sulfate.

METHODS

Binding assays were obtained from the interaction of the polysaccharides with Sialyl Lewis X and PSGL-1 based constructs onto microtiter plates coated with P-selectin. SELDI TOF mass spectrometry was performed with anionic chips arrays coated with P-selectin in the absence or in the presence of polysaccharides. Kd were obtained from surface plasmon resonance experiments with immobilized P-selectin constructs, polysaccharides being injected in the mobile phase. Human whole blood flow cytometry experiments were performed with fluorescein isothiocyanate labelled polysaccharides with or without platelets activators.

RESULTS

The fucoidan prevented P-selectin binding to Sialyl Lewis X with an IC(50) of 20 nM as compared to 400 nM for heparin and <25000 nM for dextran sulfate. It exhibited the highest affinity for immobilized P-selectin with a KD of 1.2 nM, two orders of magnitude greater than the K(D) of the other polysaccharides. Mass spectrometry evidenced the formation of a complex between P-selectin and fucoidan. The intensity of the fucoidan binding to platelets was dependent on the level of platelet activation. Competition between fucoidan and an anti P-selectin antibody demonstrated the specificity of the interaction.

GENERAL SIGNIFICANCE

Low molecular weight fucoidan is a promising therapeutic agent of natural origin for biomedical applications.

alpha1,3 fucosyltransferase-VII up-regulates the mRNA of alpha5 integrin and its biological function

After transfection of alpha1,3fucosyltransferase (FucT)-VII cDNA into H7721 human hepatocarcinoma cells, the expression of alpha5, but not beta1 integrin was significantly up-regulated. This was evidenced by the increase of alpha5 integrin on cell surface as well as the increase of alpha5 mRNA and protein in the cells. However, the expressions of sialyl Lewis X (SLe(x), the product of alpha1,3FucT-VII) on both alpha5 and beta1 integrin subunits were unchanged. Concomitantly, the tyrosine autophosphorylated FAK and dephosphorylated Src (FAK and Src involve in the signal transduction of integrin alpha5beta1) were up-regulated, while the Tyr-527 phosphorylated Src was down-regulated. The above-mentioned alterations were correlated to the expressions of alpha1,3FucT-VII in different alpha1,3FucT-VII transfected H7721 cell lines. In addition, after alpha1,3FucT-VII transfection, cell adhesion to fibronectin (Fn) and chemotaxic cell migration were obviously promoted. The cell adhesion could be blocked by alpha5 integrin antibody, and cell migration was obviously attenuated by the antibodies to both alpha5 integrin and SLe(x). These findings suggest that the increased surface alpha5 integrin caused by the up-regulation of alpha5 mRNA promotes the cell adhesion to Fn, cell migratiom, and Fn-induced signaling of alpha5beta1 integrin. The up-regulation of surface SLe(x) originated from the over expression of alpha1,3FucT-VII also led to the stimulation of cell migration. This is the first time to report that alpha1,3FucT-VII can regulate the mRNA expression of integrin.

MUC1 and the MUCs: A Family of Human Mucins with Impact in Cancer Biology

Mucins represent a family of glycoproteins characterized by repeat domains and a dense O-glycosylation. During the last two decades, the gene and peptide structures of various mucins as well as their glycosylation states were partly elucidated. Characteristic tumor-associated alterations of the expression patterns and glycosylation profiles were observed in biochemical, immunochemical, and histological studies and are discussed in the light of efforts to use the most prominent member in this family, MUC1, as a tumor target in anti-tumor strategies. Within this context the present review, focusing on MUC1, describes recent work on the regulation of mucin biosynthesis by cytokines and hormones, the role of mucins in cell adhesion, and their interaction with the immune system. Important aspects of clinical diagnostics based on mucin antigens are discussed, including the application of tumor serum assays and the significance of numerous studies revealing correlations between the expression of peptide cores or mucin-associated carbohydrates and clinicopathological parameters like tumor progression and prognosis.

Core saccharide dependence of sialyl Lewis X biosynthesis

The sialyl-Lewis X (SLe(x)) determinant is important in leukocyte extravasation, metastasis and bacterial adhesion. The role of the protein, N-glycan and O-glycan core structures for the biosynthesis of SLe(x) in vivo by fucosyltransferases (FucTs) is not known. Immunoglobulin G (IgG) Fc fusion proteins of alpha(1)-acid glycoprotein (AGP), P-selectin glycoprotein ligand-1 (PSGL-1) or CD43 were used to probe the specificity of FucT-III-VII expressed alone in 293T and COS cells or together with O-glycan core enzymes in Chinese hamster ovary (CHO)-K1 cells. Western blotting with the monoclonal antibodies CSLEX and KM93 showed that FucT-III and V-VII produced SLe(x) on core 2 in CHO cells. Only FucT-V, -VI and, with low activity, -VII worked on core 3 on CD43/IgG, but no SLe(x) was detected with CSLEX on PSGL-1/IgG with core 3. KM93 stained SLe(x) on core 2, but was not reactive with SLe(x) on core 3. FucT-III, V-VII made SLe(x) on N-glycans of AGP/IgG in CHO, but not in COS and 293T cells, even though the same FucTs could make SLe(x) on CD43/IgG and PSGL-1/IgG in these cells. Our results define the specificities of FucT-III-VII in SLe(x) biosynthesis on O-glycans with different core structures and the fine specificity of the widely used anti-SLe(x) monoclonal antibody, KM93.

Chemical preparation of sialyl Lewis x using an enzymatically synthesized sialoside building block

The sialyl Lewis x tetrasaccharide with a propylamine aglycon was assembled by chemoselective glycosylation from a p-tolyl thioglycosyl donor obtained from an enzymatically synthesized sialodisaccharide. Combining the advantages of highly efficient enzymatic synthesis of sialoside building blocks, and diverse chemical glycosylation, this chemoenzymatic approach is practical for obtaining complex sialosides and their analogues.

Leukocyte adhesion molecule and chemokine production through lipoteichoic acid recognition by toll-like receptor 2 in cultured human lymphatic endothelium

We have recently reported that the human lymphatic endothelium has toll-like receptor 4 (TLR4)-mediated lipopolysaccharide recognition mechanisms that induce the expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Although ligand engagement with TLR2 enables activation of the MyD88-dependent pathway similarly to TLR4, whether TLR2 ligands such as lipoteichoic acid (LTA) trigger the activation of lymphatic endothelium remains unclear. This study has been designed to investigate the expression dynamics of LTA-induced leukocyte adhesion molecules and chemokines in cultured human lymphatic endothelium (LEC). Reverse transcription/polymerase chain reaction (RT-PCR) and real-time quantitative PCR analyses have shown that LEC usually expresses TLR2 and increases TLR2 gene expression on LTA treatment. Indeed, LTA-treated LEC increases the expression of E-selectin, ICAM-1, and VCAM-1 but does not alter the gene expression of ICAM-2, ICAM-3, junctional adhesion molecule-1 (JAM-1), JAM-3, or platelet endothelial cell adhesion molecule-1 (PECAM-1). The expression of LTA-induced E-selectin, ICAM-1, and VCAM-1 in LEC is suppressed by anti-TLR2 but not by anti-TLR4 and is also suppressed by TLR2-specific short interfering RNA (siRNA) but not by siRNA for TLR4. The expression of CCL2, CCL5, and CCL20 (Cys-Cys motif chemokines) and of CXCL1, CXCL3, CXCL5, CXCL6, and CXCL8 (Cys-X-Cys motif chemokines) was induced in LEC with LTA. These data suggest that the human lymphatic endothelial phenotype has TLR2-mediated LTA-recognition mechanisms, resulting in increased expression of inflammatory leukocyte adhesion molecules and phagocyte-attractive chemokines. The human lymphatic endothelium may thus function to collect leukocytes from tissues into lymphatic vessels by means of immunologically functional molecules.

The expression of E-selectin and chemokines in the cultured human lymphatic endothelium with lipopolysaccharides

This study investigated the expression of selectins and chemokines in cultured human lymphatic endothelial cells stimulated with lipopolysaccharides. In microarray, vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 gene expressions in the lymphatic endothelium with lipopolysaccharides did not change at 0.5 h but increased two- to three-fold at 12 h, whereas E-selectin increased 10-fold at 0.5 h and 68-fold at 12 h compared with untreated cells. The E-selectin mRNA and protein increased in the lymphatic endothelial cells with lipopolysaccharides at more than two-fold levels compared with human umbilical vein endothelial cells. Induction of Cys-Cys chemokine ligand 2, 3, 5, 7, 8 and 20 mRNAs in the lymphatic endothelial cells with lipopolysaccharides was detected in microarray and real-time PCR. The Cys-Cys chemokine ligand 2, 5 and 20 mRNA amounts in cells with high concentration lipopolysaccharides were larger in the lymphatic endothelial cells than in human umbilical vein endothelial cells. The Cys-Cys chemokine ligand 3 and 8 mRNAs were not detected in human umbilical vein endothelial cells. Induction of Cys-X-Cys chemokine ligand 1, 3, 5, 6 and 8 mRNAs was detected in the lymphatic endothelial cells with lipopolysaccharides. The Cys-X-Cys chemokine ligand 3, 5 and 8 mRNA amounts in cells with high concentration lipopolysaccharides were larger in the lymphatic endothelial cells than in human umbilical vein endothelial cells. In conclusion, it was demonstrated that the cultured human lymphatic endothelial cells express E-selectin and phagocyte-attractive chemokine genes.

Purified polysaccharide from Ginkgo biloba leaves inhibits P-selectin-mediated leucocyte adhesion and inflammation

AIM

To investigate the anti-inflammatory mechanism of the polysaccharides of Ginkgo biloba leaves (PGBL) by inhibiting leucocyte adhesion.

METHODS

The rough PGBL were isolated and purified. The anti-inflammatory effects of purified PGBL (p-PGBL) were assayed by ear edema induced by xylol and the acute peritonitis model in mice. The effect of p-PGBL on inhibiting the interaction between P-selectin and its ligands was investigated by flow cytometry and flow chamber.

RESULTS

p-PGBL could effectively inhibit the acute inflammation in mice and interfere with the adhesion of HL-60 cells, a human leukaemia cell line, or neutrophils to P-selectin in static conditions, as well as the adhesion of neutrophils to Chinese hamster ovary cells expressing human P-selectin and human umbilical vein endothelial cells in flow conditions in a dose-dependant manner.

CONCLUSIONS

p-PGBL can inhibit the inflammatory process through interfering with the interaction between P-selectin and its ligands.

Glycan antagonists and inhibitors: a fount for drug discovery

Glycans, the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids, represent a relatively unexploited area for drug development compared with other macromolecules. This review describes the major classes of glycans synthesized by animal cells, their mode of assembly, and available inhibitors for blocking their biosynthesis and function. Many of these agents have proven useful for studying the biological activities of glycans in isolated cells, during embryological development, and in physiology. Some are being used to develop drugs for treating metabolic disorders, cancer, and infection, suggesting that glycans are excellent targets for future drug development.

Loss of N-glycolylneuraminic acid in humans: Mechanisms, consequences, and implications for hominid evolution

The surface of all mammalian cells is covered with a dense and complex array of sugar chains, which are frequently terminated by members of a family of molecules called sialic acids. One particular sialic acid called N‐glycolylneuraminic acid (Neu5Gc) is widely expressed on most mammalian tissues, but is not easily detectable on human cells. In fact, it provokes an immune response in adult humans. The human deficiency of Neu5Gc is explained by an inactivating mutation in the gene encoding CMP‐N‐acetylneuraminic acid hydroxylase, the rate‐limiting enzyme in generating Neu5Gc in cells of other mammals. This deficiency also results in an excess of the precursor sialic acid N‐acetylneuraminic acid (Neu5Ac) in humans. This mutation appears universal to modern humans, occurred sometime after our last common ancestor with the great apes, and happens to be one of the first known human‐great ape genetic differences with an obvious biochemical readout. While the original selection mechanisms and major biological consequences of this human‐specific mutation remain uncertain, several interesting clues are currently being pursued. First, there is evidence that the human condition can explain differences in susceptibility or resistance to certain microbial pathogens. Second, the functions of some endogenous receptors for sialic acids in the immune system may be altered by this difference. Third, despite the lack of any obvious alternate pathway for synthesis, Neu5Gc has been reported in human tumors and possibly in human fetal tissues, and traces have even been detected in normal human tissues. One possible explanation is that this represents accumulation of Neu5Gc from dietary sources of animal origin. Finally, a markedly reduced expression of hydroxylase in the brains of other mammals raises the possibility that the human‐specific mutation of this enzyme could have played a role in human brain evolution. Yrbk Phys Anthropol 44:54–69, 2001. © 2001 Wiley‐Liss, Inc.

Is adamantane a suitable substituent to pre-organize the acid orientation in E-selectin antagonists?

The selectins play a key role in the inflammatory process, that is, the recruitment of leukocytes from blood vessels into inflamed tissue. Because excessive infiltration of leukocytes can induce acute or chronic reactions, the control of leukocyte extravasation is of great pharmaceutical interest. All physiological ligands of the selectins contain the tetrasaccharide epitope sialyl Lewis(x), which therefore became the lead structure in selectin antagonist research. Previous studies indicated that an important factor for the affinity of sLe(x) is the fact that in solution its pharmacophores are already conformationally pre-organized in the bioactive orientation. In mimics where the GlcNAc- and the NeuNAc-moieties of sLe(x) were replaced by (R,R)-cyclohexane-1,2-diol and (S)-cyclohexyllactic acid, respectively, an optimized pre-organization of the pharmacophores could be realized, leading to antagonists with improved affinities. To further optimize the pre-organization of the carboxylic acid, a pharmacophore essential for binding, the replacement of NeuNAc by bulky (R)- and (S)-adamantyl-lactic acid was studied. Although antagonist (S)-7 showed a slightly reduced affinity, the expected beneficial effect of the (S)-configuration at C-2 of the lactate could be confirmed.

Biological modulation by lectins and their ligands in tumor progression and metastasis

Lectins are a group of specific proteins that preferentially bind to carbohydrates inside and outside cells. To date, an increasing number of animal lectins have been found and categorized into several families in terms of the significant primary structural homology, while the classification is not always straightforward. These lectins can exert immense biological functions mainly through their specific carbohydrate-protein interactions in a variety of situations. In cancer biology, aberrant glycosylation changes on many glycoproteins and glycolipids are often observed and numerous experimental evidences have revealed that these structural changes are related to tumor malignancy. Galectins, which are broadly expressed animal lectins, can play crucial biological roles in tumor cell-cell or cell-matrix interactions through their binding activities to the tumor cell surface carbohydrate determinants. Certain galectin family proteins have also shown to affect tumor cell survival, signal transduction, and proliferation mainly inside the cell. Selectins, which are one of the C-type lectins and expressed leukocytes and/or vascular endothelium, can also play an immense role in tumor cell adhesion and invasion. In addition, certain annexin family proteins, which are originally known as phospholipid binding proteins, have been revealed to possess the carbohydrate binding activity, and these novel functions in tumors are being unveiled. Understanding how carbohydrate-protein interactions function in tumor cells will be one of the important goals in cancer research. This review focuses on the role of these lectins and their ligands in cancer progression and metastasis.

Role of cell adhesion molecules and immune-cell migration in the initiation, onset and development of atherosclerosis

Atherosclerosis is currently the leading factor of death in developed countries. It is now recognized as a chronic immune-inflammatory disease, whose initial stages involve the interaction of leukocytes with the endothelial monolayer. The initial stage of atherosclerosis requires the interplay of various cell adhesion molecules and immune cells to trigger leukocyte and lymphocyte migration from the circulating blood into the arterial intima. Studies have unveiled the role of inflammatory mediators in the initiation, onset and progression of the disease. During the last few years we have gained a greater understanding of the mechanism that modulates monocyte, macrophage and T cell infiltration, the role these cells play in the atherosclerotic lesion, in the formation of the fibrous plaque formation with the consequent narrowing of the arteries, and the mechanisms that lead to plaque rupture and the formation of thrombi and emboli. This review talks about the leukocyte recruitment in early atherosclerosis, the formation of the plaque, and the mechanisms that lead to thrombosis in advanced atherosclerosis. Finally, we discuss the potential for novel therapies to treat this disease.

A new macromolecular paramagnetic MR contrast agent binds to activated human platelets

A new functionalized macromolecular magnetic resonance (MR) contrast agent has been developed from a carboxymethyldextran-Gd(DOTA) devoid of biospecificity. The functionalized contrast agent was synthesized in order to mimic PSGL-1, the main ligand of P-selectin, a glycoprotein mainly expressed on the surface of activated platelets. The starting compound, CM1, was first carboxymethylated by monochloroacetic acid leading to a series of 10 derivatives varying in their carboxymethyl content. CM8 derivative, with a degree of substitution in carboxymethyl of 0.84, was chosen for subsequent fluorolabeling and sulfation to give CM8FS. CM8FS has an average number molecular weight of 27 000 +/- 500 g/mol, a hydrodynamic radius of 5.7 +/- 0.2 nm and a high relaxivity (r(1) = 11.2/mM (Gd)/s at 60 MHz). Flow cytometry experiments on whole human blood or on isolated platelets evidenced in vitro a preferential binding of CM8FS on TRAP-activated human platelets. Interestingly, CM8FS did not bind to other blood cells or to resting platelets. Pellets of TRAP-activated human platelets have also been imaged in tubes with a 1.5 T MR imager. A MR signal was observed for activated platelets incubated with CM8FS. Altogether, these in vitro results evidenced the recognition of activated human platelets by a fluorescent paramagnetic contrast agent grafted with carboxyl and sulfate groups. This biomimetic approach associated with the versatile macromolecular platform appears promising for the development of new contrast agents for molecular imaging of activated platelets in cardiovascular diseases such as atherosclerosis and aneurysms.

New sialyl Lewis(x) mimic containing an alpha-substituted beta(3)-amino acid spacer

A highly convergent and efficient synthesis of a new sialyl Lewis(x) (sLe(x)) mimic, which was predicted by computational studies to fulfil the spacial requirements for a selectin antagonist, has been developed. With a beta(2,3)-amino acid residue l-galactose (bioisostere of the l-fucose moiety present in the natural sLe(x)) and succinate are linked, leading to a mimic of sLe(x) that contains all the required pharmacophores, namely the 3- and 4-hydroxy group of l-fucose, the 4- and 6-hydroxy group of d-galactose and the carboxylic acid of N-acetylneuraminic acid. The key step of the synthesis involves a tandem reaction consisting of a N-deprotection and a suitable O-->N intramolecular acyl migration reaction which is promoted by cerium ammonium nitrate (CAN). Finally, the new sialyl Lewis(x) mimic was biologically evaluated in a competitive binding assay.

Inhibition of L-selectin binding by polyacrylamide-based conjugates under defined flow conditions

Selectins mediate tethering and rolling of leukocytes along the endothelium in a shear force-dependent manner. This key step in the cellular immune response is a target for experimental anti-inflammatory therapies. In the present paper we have examined the inhibitory activity of the minimal selectin ligand sialyl Lewis x (SiaLe(x)), its isomer sialyl Lewis a (SiaLe(a)) and sulfated tyrosine (sTyr) residues under dynamic flow reflecting the rheological conditions in the blood stream. The monomeric ligands were compared to multivalent polyacrylamide (PAA)-based conjugates under defined flow conditions on the molecular level, using surface plasmon resonance (SPR) technology, and on the cellular level, using a parallel-plate flow chamber. SPR measurements showed that a spatial arrangement of binding epitopes mimicking the selectin binding motif of the natural ligand PSGL-1 inhibits L-selectin binding successfully with IC(50) values in the nanomolar range. Using a flow chamber adhesion assay it could be shown that the multivalent inhibitors efficiently blocked rolling and tethering of NALM-6 pre-B cells transfected with human L-selectin to activated endothelium and that the inhibitory activity increased with rising shear stress. While PAA-conjugates were almost not inhibitory at low shear stress, NALM-6 cell rolling was nearly completely inhibited at high shear stress. The results indicate that multimeric conjugates of SiaLe(x), SiaLe(a) and sTyr are highly effective inhibitors of L-selectin-mediated cell adhesion particularly under flow conditions. Consequently, SiaLe(x), SiaLe(a) and/or sTyr on macromolecular carriers may be promising candidates for anti-inflammatory therapy.

Role of Streptococcus gordonii surface proteins SspA/SspB and Hsa in platelet function

Streptococcus gordonii colonization of damaged heart surfaces in infective endocarditis is dependent upon the recognition of host receptors by specific bacterial surface proteins. However, despite several attempts to identify the mechanisms involved in this interaction, the nature of the bacterial proteins required remains poorly understood. This study provides clear evidence that several S. gordonii surface proteins participate in the interaction with platelets to support platelet adhesion and induce platelet aggregation. S. gordonii strains were found to support strong (DL1-Challis, SK12, SK184, and Blackburn) or moderate (UB1545 delta hsa and CH1-Challis) adhesion or failed to support platelet adhesion (M5, M99, and Channon). In addition, under flow conditions, platelets rolled and subsequently adhered to immobilized S. gordonii at low shear (50 s(-1)) in an Hsa-dependent manner but did not interact with S. gordonii DL1 at any shear rate of >50 s(-1). S. gordonii strains either induced (DL1-Challis, SK12, SK184, UB1545 delta hsa, and M99) or failed to induce (M5, CH1-Challis, Channon, and Blackburn) platelet aggregation. Using a proteomic approach to identify differential cell wall protein expression between aggregating (DL1) and nonaggregating (Blackburn) strains, we identified antigen I/antigen II family proteins SspA and SspB. The overexpression of SspA or SspB in platelet-nonreactive Lactococcus lactis induced GPIIb/GPIIIa-dependent platelet aggregation similar to that seen with S. gordonii DL1. However, they failed to support platelet adhesion. Thus, S. gordonii has distinct mechanisms for supporting platelet adhesion and inducing platelet aggregation. Differential protein expression between strains may be important for the pathogenesis of invasive diseases such as infective endocarditis.

Structure and function of glycosphingolipids and sphingolipids: recollections and future trends

Based on development of various methodologies for isolation and characterization of glycosphingolipids (GSLs), we have identified a number of GSLs with globo-series or lacto-series structure. Many of them are tumor-associated or developmentally regulated antigens. The major question arose, what are their functions in cells and tissues? Various approaches to answer this question were undertaken. While the method is different for each approach, we have continuously studied GSL or glycosyl epitope interaction with functional membrane components, which include tetraspanins, growth factor receptors, integrins, and signal transducer molecules. Often, GSLs were found to interact with other carbohydrates within a specific membrane microdomain termed "glycosynapse", which mediates cell adhesion with concurrent signal transduction. Future trends in GSL and glycosyl epitope research are considered, including stem cell biology and epithelial-mesenchymal transition (EMT) process.

Normal cellular prion protein is a ligand of selectins: binding requires Le(X) but is inhibited by sLe(X)

The normal PrP(C) (cellular prion protein) contains sLe(X) [sialyl-Le(X) (Lewis X)] and Le(X). sLe(X) is a ligand of selectins. To examine whether PrP(C) is a ligand of selectins, we generated three human PrP(C)-Ig fusion proteins: one with Le(X), one with sLe(X), and the other with neither Le(X) nor sLe(X). Only Le(X)-PrP(C)-Ig binds E-, L- and P-selectins. Binding is Ca(2+)-dependent and occurs with nanomolar affinity. Removal of sialic acid on sLe(X)-PrP(C)-Ig enables the fusion protein to bind all selectins. These findings were confirmed with brain-derived PrP(C). The selectins precipitated PrP(C) in human brain in a Ca(2+)-dependent manner. Treatment of brain homogenates with neuraminidase increased the amounts of PrP(C) precipitated. Therefore the presence of sialic acid prevents the binding of PrP(C) in human brain to selectins. Hence, human brain PrP(C) interacts with selectins in a manner that is distinct from interactions in peripheral tissues. Alternations in these interactions may have pathological consequences.