The E-selectin ligand-1 is selectively activated in Chinese hamster ovary cells by the alpha(1,3)-fucosyltransferases IV and VII

Distinct human α(1,3)-fucosyltransferases drive Lewis-X/sialyl Lewis-X assembly in human cells

In humans, six α(1,3)-fucosyltransferases (α(1,3)-FTs: FT3/FT4/FT5/FT6/FT7/FT9) reportedly fucosylate terminal lactosaminyl glycans yielding Lewis-X (LeX; CD15) and/or sialyl Lewis-X (sLeX; CD15s), structures that play key functions in cell migration, development, and immunity. Prior studies analyzing α(1,3)-FT specificities utilized either purified and/or recombinant enzymes to modify synthetic substrates under nonphysiological reaction conditions or molecular biology approaches wherein α(1,3)-FTs were expressed in mammalian cell lines, notably excluding investigations using primary human cells. Accordingly, although significant insights into α(1,3)-FT catalytic properties have been obtained, uncertainty persists regarding their human LeX/sLeX biosynthetic range across various glycoconjugates. Here, we undertook a comprehensive evaluation of the lactosaminyl product specificities of intracellularly expressed α(1,3)-FTs using a clinically relevant primary human cell type, mesenchymal stem cells. Cells were transfected with modified mRNA encoding each human α(1,3)-FT, and the resultant α(1,3)-fucosylated lactosaminyl glycoconjugates were analyzed using a combination of flow cytometry and MS. The data show that biosynthesis of sLeX is driven by FTs-3, -5, -6, and -7, with FT6 and FT7 having highest potency. FT4 and FT9 dominantly biosynthesize LeX, and, among all FTs, FT6 holds a unique capacity in creating sLeX and LeX determinants across protein and lipid glycoconjugates. Surprisingly, FT4 does not generate sLeX on glycolipids, and neither FT4, FT6, nor FT9 synthesizes the internally fucosylated sialyllactosamine VIM-2 (CD65s). These results unveil the relevant human lactosaminyl glycans created by human α(1,3)-FTs, providing novel insights on how these isoenzymes stereoselectively shape biosynthesis of vital glycoconjugates, thereby biochemically programming human cell migration and tuning human immunologic and developmental processes.

Soluble Siglec-5 associates to PSGL-1 and displays anti-inflammatory activity

Interactions between endothelial selectins and the leukocyte counter-receptor PSGL1 mediates leukocyte recruitment to inflammation sites. PSGL1 is highly sialylated, making it a potential ligand for Siglec-5, a leukocyte-receptor that recognizes sialic acid structures. Binding assays using soluble Siglec-5 variants (sSiglec-5/C4BP and sSiglec-5/Fc) revealed a dose- and calcium-dependent binding to PSGL1. Pre-treatment of PSGL1 with sialidase reduced Siglec-5 binding by 79 ± 4%. In confocal immune-fluorescence assays, we observed that 50% of Peripheral Blood Mononuclear Cells (PBMCs) simultaneously express PSGL1 and Siglec-5. Duolink-proximity ligation analysis demonstrated that PSGL1 and Siglec-5 are in close proximity (<40 nm) in 31 ± 4% of PBMCs. In vitro perfusion assays revealed that leukocyte-rolling over E- and P-selectin was inhibited by sSiglec-5/Fc or sSiglec-5/C4BP, while adhesion onto VCAM1 was unaffected. When applied to healthy mice (0.8 mg/kg), sSiglec-5/C4BP significantly reduced the number of rolling leukocytes under basal conditions (10.9 ± 3.7 versus 23.5 ± 9.3 leukocytes/field/min for sSiglec-5/C4BP-treated and control mice, respectively; p = 0.0093). Moreover, leukocyte recruitment was inhibited over a 5-h observation period in an in vivo model of TNFalpha-induced inflammation following injection sSiglec-5/C4BP (0.8 mg/kg). Our data identify PSGL1 as a ligand for Siglec-5, and soluble Siglec-5 variants appear efficient in blocking PSGL1-mediated leukocyte rolling and the inflammatory response in general.

Selection for a CEACAM receptor-specific binding phenotype during Neisseria gonorrhoeae infection of the human genital tract

Infections by Neisseria gonorrhoeae are increasingly common, are often caused by antibiotic-resistant strains, and can result in serious and lasting sequelae, prompting the reemergence of gonococcal disease as a leading global health concern. N. gonorrhoeae is a human-restricted pathogen that primarily colonizes urogenital mucosal surfaces. Disease progression varies greatly between the sexes: men usually present with symptomatic infection characterized by a painful purulent urethral discharge, while in women, the infection is often asymptomatic, with the most severe pathology occurring when the bacteria ascend from the lower genital tract into the uterus and fallopian tubes. Classical clinical studies demonstrated that clinically infectious strains uniformly express Opa adhesins; however, their specificities were unknown at the time. While in vitro studies have since identified CEACAM proteins as the primary target of Opa proteins, the gonococcal specificity for this human family of receptors has not been addressed in the context of natural infection. In this study, we characterize a collection of low-passage-number clinical-specimen-derived N. gonorrhoeae isolates for Opa expression and assess their CEACAM-binding profiles. We report marked in vivo selection for expression of phase-variable Opa proteins that bind CEACAM1 and CEACAM5 but selection against expression of Opa variants that bind to the neutrophil-restricted decoy receptor CEACAM3. This is the first study showing phenotypic selection for distinct CEACAM-binding phenotypes in vivo, and it supports the opposing functions of CEACAMs that facilitate infection versus driving inflammation within the genital tract.

Modulation of glycan recognition by clustered saccharide patches

All cells in nature are covered with a dense and complex array of glycan chains. Specific recognition and binding of glycans is a critical aspect of cellular interactions, both within and between species. Glycan-protein interactions tend to be of low affinity but high specificity, typically utilizing multivalency to generate the affinity required for biologically relevant binding. This review focuses on a higher level of glycan organization, the formation of clustered saccharide patches (CSPs), which can constitute unique ligands for highly specific interactions. Due to technical challenges, this aspect of glycan recognition remains poorly understood. We present a wealth of evidence for CSPs-mediated interactions, and discuss recent advances in experimental tools that are beginning to provide new insights into the composition and organization of CSPs. The examples presented here are likely the tip of the iceberg, and much further work is needed to elucidate fully this higher level of glycan organization.

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.

Core 1-derived O-glycans are essential E-selectin ligands on neutrophils

Neutrophils roll on E-selectin in inflamed venules through interactions with cell-surface glycoconjugates. The identification of physiologic E-selectin ligands on neutrophils has been elusive. Current evidence suggests that P-selectin glycoprotein ligand-1 (PSGL-1), E-selectin ligand-1 (ESL-1), and CD44 encompass all glycoprotein ligands for E-selectin; that ESL-1 and CD44 use N-glycans to bind to E-selectin; and that neutrophils lacking core 2 O-glycans have partially defective interactions with E-selectin. These data imply that N-glycans on ESL-1 and CD44 and O-glycans on PSGL-1 constitute all E-selectin ligands, with neither glycan subset having a dominant role. The enzyme T-synthase transfers Gal to GalNAcalpha1-Ser/Thr to form the core 1 structure Galbeta1-3GalNAcalpha1-Ser/Thr, a precursor for core 2 and extended core 1 O-glycans that might serve as selectin ligands. Here, using mice lacking T-synthase in endothelial and hematopoietic cells, we found that E-selectin bound to CD44 and ESL-1 in lysates of T-synthase-deficient neutrophils. However, the cells exhibited markedly impaired rolling on E-selectin in vitro and in vivo, failed to activate beta2 integrins while rolling, and did not emigrate into inflamed tissues. These defects were more severe than those of neutrophils lacking PSGL-1, CD44, and the mucin CD43. Our results demonstrate that core 1-derived O-glycans are essential E-selectin ligands; that some of these O-glycans are on protein(s) other than PSGL-1, CD44, and CD43; and that PSGL-1, CD44, and ESL-1 do not constitute all glycoprotein ligands for E-selectin.

PSGL-1 from the murine leukocytic cell line WEHI-3 is enriched for core 2-based O-glycans with sialyl Lewis x antigen

Leukocyte trafficking involves specific recognition between P-selectin and L-selectin and PSGL-1 containing core 2-based O-glycans expressing sialyl Lewis x (SLe(x)) antigen. However, the structural identity of the glycan component(s) displayed by murine neutrophil PSGL-1 that contributes to its P-selectin counter-receptor activity has been uncertain, since these cells express little if any SLe(x) antigen, and because there have been no direct studies to examine murine PSGL-1 glycosylation. To address this uncertainty, we studied PSGL-1 glycosylation in the murine cell line WEHI-3 using metabolic-radiolabeling with (3)H-monosaccharide precursors to detect low-abundance O-glycan structures. We report that PSGL-1 from WEHI-3 cells expresses a di-sialylated core 2 O-glycan containing the SLe(x) antigen. This fucosylated O-glycan is scarce on PSGL-1 and essentially undetectable in total leukocyte glycoproteins from WEHI-3 cells. These results demonstrate that WEHI-3 cells selectively fucosylate PSGL-1 to generate functionally important core 2-based O-glycans containing the SLe(x) antigen.

Identification of leukocyte E-selectin ligands, P-selectin glycoprotein ligand-1 and E-selectin ligand-1, on human metastatic prostate tumor cells

Prostate tumor cells, which characteristically metastasize to bone, initiate binding interactions with bone marrow endothelium under blood flow conditions through binding interactions with E-selectin. We hypothesized that E-selectin ligands on prostate tumor cells are directly associated with bone-metastatic potential. In this report, we elucidate the identity of E-selectin ligands on human metastatic prostate tumor cells and examine their association with prostate tumor progression and metastasis in vivo. To our surprise, we found that the E-selectin-binding form of P-selectin glycoprotein ligand-1 (PSGL-1) is expressed on the human bone-metastatic prostate tumor MDA PCa 2b cell line. Interestingly, we also found that human prostate tumor cells derived from bone, lymph node, and brain metastases expressed another leukocyte E-selectin ligand, E-selectin ligand-1 (ESL-1). Immunohistochemical analysis of PSGL-1 and ESL-1 in normal prostate tissue and in localized and metastatic prostate tumors revealed that ESL-1 was principally localized to intracellular cell membrane and expressed on all normal and malignant prostate tissue, whereas PSGL-1 was notably detected on the surfaces of bone-metastatic prostate tumor cells. These findings implicate a functional role of PSGL-1 in the bone tropism of prostate tumor cells and establish a new perspective into the molecular mechanism of human prostate tumor metastasis.

Regulation of PSGL-1 interactions with L-selectin, P-selectin, and E-selectin: role of human fucosyltransferase-IV and -VII

P-selectin glycoprotein ligand-1 (PSGL-1) interactions with selectins regulate leukocyte migration in inflammatory lesions. In mice, selectin ligand activity regulating leukocyte recruitment and lymphocyte homing into lymph nodes results from the sum of unequal contributions of fucosyltransferase (FucT)-IV and FucT-VII, with FucT-VII playing a predominant role. Here we have examined the role of human FucT-IV and -VII in conferring L-selectin, P-selectin, and E-selectin binding activities to PSGL-1. Lewis x (Le(x)) carbohydrate was generated at the CHO(dhfr)(-) cell surface by FucT-IV expression, whereas sialyl Le(x) (sLe(x)) was synthesized by FucT-VII. Both human FucT-IV and -VII had the ability to generate carbohydrate ligands that support L-selectin-, P-selectin-, and E-selectin-dependent rolling on PSGL-1, with FucT-VII playing a major role. Cooperation was observed between FucT-IV and -VII in recruiting L-, P-, or E-selectin-expressing cells on PSGL-1 and in regulating cell rolling velocity and stability. Additional rolling adhesion assays were performed to assess the role of Thr-57-linked core-2 O-glycans in supporting L-selectin-, P-selectin-, and E-selectin-dependent rolling on PSGL-1. These studies confirmed that core-2 O-glycans attached to Thr-57 play a critical role in supporting L- and P-selectin-dependent rolling and revealed that additional binding sites support >75% of E-selectin-mediated rolling. The observations presented here indicate that human FucT-IV and -VII both contribute and cooperate in regulating L-selectin-, P-selectin-, and E-selectin-dependent rolling on PSGL-1, with FucT-VII playing a predominant role in conferring selectin binding activity to PSGL-1.

LEC12 and LEC29 Gain-of-Function Chinese Hamster Ovary Mutants Reveal Mechanisms for Regulating VIM-2 Antigen Synthesis and E-selectin Binding

LEC12 and LEC29 are two gain-of-function Chinese hamster ovary glycosylation mutants that express the Fut9 gene encoding alpha(1,3)fucosyltransferase IX (alpha(1,3) Fuc-TIX). Both mutants express the Lewis X (Le(X)) determinant Galbeta(1,4)[Fucalpha(1,3)]GlcNAc, and LEC12, but not LEC29 cells, also express the VIM-2 antigen SAalpha(2,3)-Galbeta(1,4)GlcNAcbeta(1,3)Galbeta(1,4)[Fucalpha(1,3)]GlcNAc. Here we show that LEC29 cells transfected with a Fut9 cDNA express VIM-2, and thus LEC29 cells synthesize appropriate acceptors to generate the VIM-2 epitope. Semiquantitative reverse transcription-PCR showed that LEC12 has 10- to 20-fold less Fut9 gene transcripts than LEC29. However, Western analysis revealed that LEC12 has approximately 20 times more Fut9 protein than LEC29. The latter finding was consistent with our previous observation that LEC12 has approximately 40 times more in vitro alpha(1,3)Fuc-T activity than LEC29. The basis for the difference in Fut9 protein levels was found to lie in sequence differences in the 5'-untranslated regions (5'-UTR) of LEC12 and LEC29 Fut9 gene transcripts. Whereas reporter assays with the respective 5'-UTR regions linked to luciferase did not indicate a reduced translation efficiency caused by the LEC29 5'-UTR, transfected full-length LEC29 Fut9 cDNA or in vitro-synthesized full-length LEC29 Fut9 RNA gave less Fut9 protein than similar constructs with a LEC12 5'-UTR. This difference appears to be largely responsible for the reduced alpha(1,3)Fuc-TIX activity and lack of VIM-2 expression of LEC29 cells. This could be of physiological relevance, because LEC29 and parent Chinese hamster ovary cells transiently expressing a Fut9 cDNA were able to bind mouse E-selectin, although they did not express sialyl-Le(X).

Complement Regulatory Protein C1 Inhibitor Binds to Selectins and Interferes with Endothelial-Leukocyte Adhesion

C1 inhibitor (C1INH), a member of the serine proteinase inhibitor (serpin) family, is an inhibitor of proteases in the complement system, the contact system of kinin generation, and the intrinsic coagulation pathway. It is the most heavily glycosylated plasma protein, containing 13 definitively identified glycosylation sites as well as an additional 7 potential glycosylation sites. C1INH consists of two distinct domains: a serpin domain and an amino-terminal domain. The serpin domain retains all the protease-inhibitory function, while the amino-terminal domain bears most of the glycosylation sites. The present studies test the hypothesis that plasma C1INH bears sialyl Lewis(x)-related moieties and therefore binds to selectin adhesion molecules. We demonstrated that plasma C1INH does express sialyl Lewis(x)-related moieties on its N-glycan as detected using mAb HECA-452 and CSLEX1. The data also show that plasma C1INH can bind to P- and E-selectins by FACS and immunoprecipitation experiments. In a tissue culture model of endothelial-leukocyte adhesion, C1INH showed inhibition in a dose-dependent manner. Significant inhibition (>50%) was achieved at a concentration of 250 micro g/ml or higher. This discovery may suggest that C1INH plays a role in the endothelial-leukocyte interaction during inflammation. It may also provide another example of the multifaceted anti-inflammatory effects of C1INH in various animal models and human diseases.

The alpha (1,3)-fucosyltransferase Fuc-TIV, but not Fuc-TVII, generates sialyl Lewis X-like epitopes preferentially on glycolipids

Fuc-TIV and Fuc-TVII are the two alpha(1, 3)-fucosyltransferases in myeloid cells responsible for the biosynthesis of sialyl Lewis X (sLe(x)), the minimal ligand structure for the selectins. We have compared the ability of Fuc-TIV and Fuc-TVII to generate sLe(x)-like epitopes in transfected Chinese hamster ovary (CHO)-Pro(-)5 cells expressing the P-selectin glycoprotein ligand-1 and the core-2 branching enzyme C2GnT. We found that mouse Fuc-TIV and Fuc-TVII can generate similar levels of cell surface sLe(x). Surprisingly however, Fuc-TIV-generated sLe(x) was resistant to proteinase K and trypsin treatment and could be removed from cells by delipidation with chloroform/methanol, whereas 80-90% of Fuc-TVII-generated sLe(x) was protease-sensitive, and most of it resistant to delipidation. Despite similar levels of sLe(x) on the cell surface, Fuc-TVII transfectants adhered to immobilized E-selectin-IgG under static and flow conditions better than Fuc-TIV transfectants. Binding was mainly protease sensitive, indicating that glycoproteins were more efficient ligands than glycolipids. In summary, we conclude that the two fucosyltransferases differ in their in vivo specificity for acceptor substrates with Fuc-TVII generating sLe(x) preferentially on glycoproteins, whereas most of the Fuc-TIV-generated sLe(x) is found on glycolipids. Interestingly, the non-catalytic portion of Fuc-TIV in a Fuc-TIV/VII chimeric enzyme mediated the specificity for glycolipid substrates.

Immature mouse dendritic cells enter inflamed tissue, a process that requires E- and P-selectin, but not P-selectin glycoprotein ligand 1

Inflammatory processes are associated with the rapid migration of dendritic cells (DCs) to regional lymph nodes and depletion of these potent antigen-presenting cells (APCs) from the inflamed tissue. This study examined whether sites of cutaneous inflammation can be repopulated with DCs from a pool of immature DCs circulating in the blood. In adoptive transfer experiments with ex vivo–generated radioactively labeled primary bone marrow–derived DCs injected into mice challenged by an allergic contact dermatitis reaction, immature DCs were actively recruited from the blood to sites of cutaneous inflammation, whereas mature DCs were not. Immature, but not mature, DCs were able to adhere specifically to immobilized recombinant E- and P-selectin under static as well as under flow conditions. P-selectin–dependent adhesion of immature DCs correlates with their higher level of expression of the carbohydrate epitope cutaneous lymphocyte-associated antigen (CLA) and is blocked by a novel inhibitory antibody against mouse P-selectin glycoprotein ligand 1 (PSGL-1). Surprisingly, however, emigration of immature DCs into inflamed skin is retained in the presence of this anti–PSGL-1 antibody and is also normal when immature DCs are generated from fucosyltransferase (Fuc-T) Fuc-TVII–deficient mice. By contrast, emigration of wild-type immature DCs is reduced by adhesion-blocking anti–E- and P-selectin antibodies, and immature DCs generated ex vivo from Fuc-TVII/Fuc-TIV double-deficient mice emigrate poorly. Thus, fucosylated ligands of the endothelial selectins, determined in part by Fuc-TIV, and independent of PSGL-1, are required for extravasation of DCs into sites of cutaneous inflammation.

Immature mouse dendritic cells enter inflamed tissue, a process that requires E- and P-selectin, but not P-selectin glycoprotein ligand 1

Inflammatory processes are associated with the rapid migration of dendritic cells (DCs) to regional lymph nodes and depletion of these potent antigen-presenting cells (APCs) from the inflamed tissue. This study examined whether sites of cutaneous inflammation can be repopulated with DCs from a pool of immature DCs circulating in the blood. In adoptive transfer experiments with ex vivo-generated radioactively labeled primary bone marrow-derived DCs injected into mice challenged by an allergic contact dermatitis reaction, immature DCs were actively recruited from the blood to sites of cutaneous inflammation, whereas mature DCs were not. Immature, but not mature, DCs were able to adhere specifically to immobilized recombinant E- and P-selectin under static as well as under flow conditions. P-selectin-dependent adhesion of immature DCs correlates with their higher level of expression of the carbohydrate epitope cutaneous lymphocyte-associated antigen (CLA) and is blocked by a novel inhibitory antibody against mouse P-selectin glycoprotein ligand 1 (PSGL-1). Surprisingly, however, emigration of immature DCs into inflamed skin is retained in the presence of this anti-PSGL-1 antibody and is also normal when immature DCs are generated from fucosyltransferase (Fuc-T) Fuc-TVII-deficient mice. By contrast, emigration of wild-type immature DCs is reduced by adhesion-blocking anti-E- and P-selectin antibodies, and immature DCs generated ex vivo from Fuc-TVII/Fuc-TIV double-deficient mice emigrate poorly. Thus, fucosylated ligands of the endothelial selectins, determined in part by Fuc-TIV, and independent of PSGL-1, are required for extravasation of DCs into sites of cutaneous inflammation.

differential L-selectin binding activities of human hematopoietic cell L-selectin ligands, HCELL and PSGL-1

Expression of L-selectin on human hematopoietic cells (HC) is associated with a higher proliferative activity and a more rapid engraftment after hematopoietic stem cell transplantation. Two L-selectin ligands are expressed on human HCs, P-selectin glycoprotein ligand-1 (PSGL-1) and a specialized glycoform of CD44 (hematopoietic cell E- and L-selectin ligand, HCELL). Although the structural biochemistry of HCELL and PSGL-1 is well characterized, the relative capacity of these molecules to mediate L-selectin-dependent adhesion has not been explored. In this study, we examined under shear stress conditions L-selectin-dependent leukocyte adhesive interactions mediated by HCELL and PSGL-1, both as naturally expressed on human HC membranes and as purified molecules. By utilizing both Stamper-Woodruff and parallel-plate flow chamber assays, we found that HCELL displayed a 5-fold greater capacity to support L-selectin-dependent leukocyte adherence across a broad range of shear stresses compared with that of PSGL-1. Moreover, L-selectin-mediated leukocyte binding to immunopurified HCELL was consistently >5-fold higher than leukocyte binding to equivalent amounts of PSGL-1. Taken together, these data indicate that HCELL is a more avid L-selectin ligand than PSGL-1 and may be the preferential mediator of L-selectin-dependent adhesive interactions among human HCs in the bone marrow.

Affinity, kinetics, and thermodynamics of E-selectin binding to E-selectin ligand-1

E-selectin is an endothelial adhesion molecule, which mediates the tethering and rolling of leukocytes on vascular endothelium. It recognizes the glycoprotein E-selectin ligand-1 (ESL-1) as a major binding partner on mouse myeloid cells. Using surface plasmon resonance, we measured the kinetics and affinity of binding of monomeric E-selectin to ESL-1 isolated from mouse bone marrow cells. E-selectin bound to ESL-1 with a fast dissociation rate constant of 4.6 s(-1) and a calculated association rate constant of 7.4 x 10(4) m(-1) s(-1). We determined a dissociation constant (K(d)) of 62 microm, which resembles the affinity of L-selectin binding to glycosylation-dependent cell adhesion molecule-1. The affinity of the E-selectin-ESL-1 interaction did not change significantly when the temperature was varied from 5 degrees C to 37 degrees C, indicating that the enthalpic contribution to the binding is small at physiological temperatures, and that, in contrast to typical protein-carbohydrate interactions, binding is driven primarily by favorable entropic changes. Interestingly, surface plasmon resonance experiments with recombinant ESL-1 from alpha 1,3-fucosyltransferase IV-expressing Chinese hamster ovary cells showed a very similar K(d) of 66 microm, suggesting that this fucosyltransferase is sufficient to produce fully functional recombinant ESL-1. Following the recent description of the affinity and kinetics of the selectin-ligand pairs L-selectin-glycosylation-dependent cell adhesion molecule-1 and P-selectin-P-selectin glycoprotein ligand-1, this is the first determination of the parameters of E-selectin binding to one of its naturally occurring ligands.

Identification of a missense mutation (G329A;Arg(110)--> GLN) in the human FUT7 gene

The human FUT7 gene codes for the alpha1,3-fucosyltransferase VII (Fuc-TVII), which is involved in the biosynthesis of the sialyl Lewis x (SLe(x)) epitope on human leukocytes. The FUT7 gene has so far been considered to be monomorphic. Neutrophils isolated from patients with ulcerative colitis were examined for apparent alterations in protein glycosylation patterns by Western blot analysis using monoclonal antibodies directed against SLe(x) and SLe(x)-related epitopes. One individual showed lower levels of SLe(x) expression and an elevated expression of CD65s compared to controls. The coding regions of the FUT7 gene from this individual were cloned, and a G329A point mutation (Arg(110) --> Gln) was found in one allele, whereas the other FUT7 allele was wild type. No Fuc-TVII enzyme activity was detected in COS-7 cells transiently transfected with the mutated FUT7 construct. The FUT7 Arg(110) is conserved in all previously cloned vertebrate alpha 1,3-fucosyltransferases. Polymerase chain reaction followed by restriction enzyme cleavage was used to screen 364 unselected Caucasians for the G329A mutation, and a frequency of < or =1% for this mutation was found (3 heterozygotes). Genetic characterization of the family members of one of the additional heterozygotes identified one individual carrying the G329A mutation in both FUT7 alleles. Peripheral blood neutrophils of this homozygously mutated individual showed a lowered expression of SLe(x) and an elevated expression of CD65s when analyzed by Western blot and flow cytometry. The homozygous individual was diagnosed with ulcer disease, non-insulin-dependent diabetes, osteoporosis, spondyloarthrosis, and Sjögren's syndrome but had no history of recurrent bacterial infections or leukocytosis.

CD44 is a major E-selectin ligand on human hematopoietic progenitor cells

E-selectin plays a critical role in mediating tissue-specific homing of T cells into skin, and of primitive hematopoietic progenitor cells (HPCs) into bone marrow (BM). Though it is known that a glycoform of PSGL-1 (CLA) functions as the principal E-selectin ligand on human T lymphocytes, the E-selectin ligand(s) of human HPCs has not been identified. We used a shear-based adherence assay to analyze and define the E-selectin ligand activity of membrane proteins from human HPCs. Our data show that PSGL-1 expressed on human HPCs is an E-selectin ligand, and that HPCs also express a previously unrecognized E-selectin ligand, CD44. The E-selectin ligand activity of CD44 is conferred by the elaboration of sialylated, fucosylated binding determinants on N-glycans. This glycoform of CD44 is expressed on primitive CD34+ human HPCs, but not on more mature hematopoietic cells. Under physiologic flow conditions, this molecule mediates E-selectin-dependent rolling interactions over a wider shear range than that of PSGL-1, and promotes human HPC rolling interactions on E-selectin expressed on human BM endothelial cells. These findings offer new insights into the structural biology and physiology of CD44, and into the molecular basis of E-selectin-dependent adhesive interactions that direct homing of human HPC to BM.

The acceptor and site specificity of alpha 3-fucosyltransferase V. High reactivity of the proximal and low of the distal galbeta 1-4GlcNAc unit in i-type polylactosamines

We report here on in vitro acceptor and site specificity of recombinant alpha3-fucosyltransferase V (Fuc-TV) with 40 oligosaccharide acceptors. Galbeta1-4GlcNAc (LN) and GalNAcbeta1-4GlcNAc (LDN) reacted rapidly; Galbeta1-3GlcNAc (LNB) reacted moderately, and GlcNAcbeta1-4GlcNAc (N, N'-diacetyl-chitobiose) reacted slowly yet distinctly. In neutral and terminally alpha3-sialylated polylactosamines of i-type, the reducing end LN unit reacted rapidly and the distal (sialyl)LN group very slowly; the midchain LNs revealed intermediate reactivities. The data suggest that a distal LN neighbor enhances but a proximal LN neighbor reduces the reactivity of the midchain LNs. This implies that Fuc-TV may bind preferably the tetrasaccharide sequence Galbeta1-4GlcNAcbeta1-3Galbeta1-4GlcNAc for transfer at the underlined monosaccharide. Terminal alpha3-sialylation of i-type polylactosamines almost doubled the reactivities of the LN units at all positions of the chains. We conclude that, in comparison with human Fuc-TIV and Fuc-TIX, Fuc-TV reacted with a highly distinct site specificity with i-type polylactosamines. The Fuc-TV reactivity of free LNB resembled that of LNBbeta1-3'R of a polylactosamine, contrasting strongly with the dissimilarity of the reactivities of the analogous pair of LN and LNbeta1-3'R. This observation supports the notion that LN and LNB may be functionally bound at distinct sites on Fuc-TV surface. Our data show that Fuc-TV worked well with a very wide range of LN-glycans, showing weak reactivity only with distal (sialyl)LN units of i-type polylactosamines, biantennary N-glycans, and I branches of polylactosamines.

P-selectin glycoprotein ligand-1 and E-selectin ligand-1 are differentially modified by fucosyltransferases Fuc-TIV and Fuc-TVII in mouse neutrophils

P-selectin glycoprotein ligand-1 (PSGL-1) and E-selectin ligand-1 (ESL-1) are the two major selectin ligands on mouse neutrophils. Transfection experiments demonstrate that each ligand requires alpha1,3-fucosylation for selectin-binding. However, the relative contributions made by the two known myeloid alpha1, 3-fucosyltransferases Fuc-TVII or Fuc-TIV to this alpha1, 3-fucosylation are not yet clear. To address this issue, we have used mice deficient in Fuc-TIV and/or Fuc-TVII to examine how these enzymes generate selectin-binding glycoforms of PSGL-1 and ESL-1 in mouse neutrophils. Selectin binding was analyzed by affinity isolation experiments using recombinant, antibody-like forms of the respective endothelial selectins. We observe essentially normal binding of E- or P-selectin to PSGL-1 expressed by Fuc-TIV-deficient neutrophils but find that PSGL-1 expressed by Fuc-TVII-deficient neutrophils is not bound by E- or P-selectin. By contrast, E-selectin binds with normal efficiency to ESL-1 on Fuc-TVII-deficient neutrophils but exhibits an 80% reduction in its ability to bind ESL-1 isolated from Fuc-TIV-deficient neutrophils. The same specificity with which Fuc-TVII and Fuc-TIV generate selectin-binding forms of PSGL-1 and ESL-1 was found in transfection experiments with CHO-Pro(-)5 cells. In contrast, each fucosyltransferase alone could generate selectin-binding glycoforms of each of the two ligands in CHO-DUKX-B1 cells. Our data imply that in mouse neutrophils and their precursors, Fuc-TVII exclusively directs expression of PSGL-1 glycoforms bound with high affinity by P-selectin. By contrast, Fuc-TIV preferentially directs expression of ESL-1 glycoforms that exhibit high affinity for E-selectin. This substrate specificity can be mimicked in CHO-Pro(-)5 cells.

Cysteine-rich fibroblast growth factor receptor alters secretion and intracellular routing of fibroblast growth factor 3

Expression of the cysteine-rich fibroblast growth factor (FGF) receptor (CFR) in COS-1 cells strongly inhibits the secretion of co-expressed FGF3. By using a column retention assay and affinity chromatography, we demonstrate that at physiological salt concentrations FGF3 binds with strong affinity to CFR in vivo and in vitro. Furthermore, to show that FGF3 binds to CFR in vivo, truncation mutants of CFR with changed subcellular distributions were shown to cause a similar redistribution of FGF3. Although CFR is a 150-kDa integral membrane glycoprotein that is primarily located in the Golgi apparatus, we show here that in COS-1 cells a substantial proportion of CFR is secreted. This is due to a carboxyl-terminal proteolytic cleavage that releases the intraluminal portion of the protein for secretion. However, the apparent size of the integral membrane and secreted CFR appears similar, since the loss of protein mass is balanced by a gain of complex carbohydrates. The released CFR is associated with the extracellular matrix through its affinity for glycosaminoglycans. These findings show that CFR can modulate the secretion of FGF3 and may control its biological activity by regulating its secretion.

alpha(1,2)-fucosylation prevents sialyl Lewis x expression and E-selectin-mediated adhesion of fucosyltransferase VII-transfected cells

E-selectin is a cytokine-inducible, calcium-dependent endothelial cell adhesion molecule that plays a critical role in the leucocyte-endothelium interaction during inflammation and is thought to contribute to the metastatic dissemination of tumour cells. Like the other selectins, E-selectin binds to ligands carrying the tetrasaccharide sialyl-Lewis x (NeuAcalpha2,3Galbeta1,4[Fucalpha1, 3]GlcNAc)1 or its isomer sialyl-Lewis a (NeuAcalpha2, 3Galbeta1, 3[Fucalpha1,4]GlcNAc). We examined the effect of expressing the H-type alpha(1,2)-fucosyltransferase or the alpha(2, 6)-sialyltransferase on the synthesis of sialyl-Lewis x by alpha(1, 3)fucosyltransferase. We found that H-type alpha(1, 2)-fucosyltransferase but not alpha(2,6)-sialyltransferase, strongly inhibited sialyl-Lewis x expression and E-selectin adhesion. We assume that H-type alpha(1,2)-fucosyltransferase competes with the endogenous alpha(2,3)-sialyltransferase for the N-acetyllactosamine structures assigned to further serve as acceptors for alpha(1, 3)fucosyltransferase.

Stromal Derived Factor-1–Induced Chemokinesis of Cord Blood CD34+ Cells (Long-Term Culture-Initiating Cells) Through Endothelial Cells Is Mediated by E-Selectin

Homing of hematopoietic stem cells to the bone marrow (BM) involves sequential interaction with adhesion molecules expressed on BM endothelium (BMEC) and chemokine stromal derived factor-1 (SDF-1). However, the mechanism whereby adhesion molecules regulate the SDF-1–induced transendothelial migration process is not known. E-selectin is an endothelial-specific selectin that is constitutively expressed by the BMEC in vivo. Hence, we hypothesized that E-selectin may mediate SDF-1–induced transendothelial migration of CD34+ cells. We show that CD34+ cells express both E-selectin ligand and fucosyltransferase-VII (FucT-VII). Soluble E-selectin–IgG chimera binds avidly to 75% ± 10% of CD34+ cells composed mostly of progenitors and cells with long-term culture-initiating cell (LTC-IC) potential. To assess the functional capacity of E-selectin to mediate CD34+ cell migration in a transendothelial migration system, CD34+ cells were placed on transwell plates coated with interleukin-1β–activated BMEC. In the absence of SDF-1, there was spontaneous migration of 7.0% ± 1.4% of CD34+ cells and 14.1% ± 2.2% of LTC-IC. SDF-1 induced migration of an additional 23.0% ± 4.4% of CD34+cells and 17.6% ± 3.6% of LTC-IC. Blocking MoAb to E-selectin inhibited SDF-1–induced migration of CD34+ cells by 42.0% ± 2.5% and LTC-IC by 90.9% ± 16.6%. To define the mechanism of constitutive expression of E-selectin by the BMEC in vivo, we have found that vascular endothelial growth factor (VEGF165) induces E-selectin expression by cultured endothelial cells. VEGF-stimulated endothelial cells support transendothelial migration of CD34+ cells that could be blocked by MoAb to E-selectin. These results suggest that trafficking of subsets of CD34+ cells with LTC-IC potential is determined in part by sequential interactions with E-selectin and SDF-1.

Stromal Derived Factor-1–Induced Chemokinesis of Cord Blood CD34+ Cells (Long-Term Culture-Initiating Cells) Through Endothelial Cells Is Mediated by E-Selectin

Homing of hematopoietic stem cells to the bone marrow (BM) involves sequential interaction with adhesion molecules expressed on BM endothelium (BMEC) and chemokine stromal derived factor-1 (SDF-1). However, the mechanism whereby adhesion molecules regulate the SDF-1–induced transendothelial migration process is not known. E-selectin is an endothelial-specific selectin that is constitutively expressed by the BMEC in vivo. Hence, we hypothesized that E-selectin may mediate SDF-1–induced transendothelial migration of CD34+ cells. We show that CD34+ cells express both E-selectin ligand and fucosyltransferase-VII (FucT-VII). Soluble E-selectin–IgG chimera binds avidly to 75% ± 10% of CD34+ cells composed mostly of progenitors and cells with long-term culture-initiating cell (LTC-IC) potential. To assess the functional capacity of E-selectin to mediate CD34+ cell migration in a transendothelial migration system, CD34+ cells were placed on transwell plates coated with interleukin-1β–activated BMEC. In the absence of SDF-1, there was spontaneous migration of 7.0% ± 1.4% of CD34+ cells and 14.1% ± 2.2% of LTC-IC. SDF-1 induced migration of an additional 23.0% ± 4.4% of CD34+cells and 17.6% ± 3.6% of LTC-IC. Blocking MoAb to E-selectin inhibited SDF-1–induced migration of CD34+ cells by 42.0% ± 2.5% and LTC-IC by 90.9% ± 16.6%. To define the mechanism of constitutive expression of E-selectin by the BMEC in vivo, we have found that vascular endothelial growth factor (VEGF165) induces E-selectin expression by cultured endothelial cells. VEGF-stimulated endothelial cells support transendothelial migration of CD34+ cells that could be blocked by MoAb to E-selectin. These results suggest that trafficking of subsets of CD34+ cells with LTC-IC potential is determined in part by sequential interactions with E-selectin and SDF-1.

Fucose in N-glycans: from plant to man

Fucosylated oligosaccharides occur throughout nature and many of them play a variety of roles in biology, especially in a number of recognition processes. As reviewed here, much of the recent emphasis in the study of the oligosaccharides in mammals has been on their potential medical importance, particularly in inflammation and cancer. Indeed, changes in fucosylation patterns due to different levels of expression of various fucosyltransferases can be used for diagnoses of some diseases and monitoring the success of therapies. In contrast, there are generally at present only limited data on fucosylation in non-mammalian organisms. Here, the state of current knowledge on the fucosylation abilities of plants, insects, snails, lower eukaryotes and prokaryotes will be summarised.

PSGL-1-mediated adhesion of human hematopoietic progenitors to P-selectin results in suppression of hematopoiesis

Cellular interactions are critical for the regulation of hematopoiesis. The sialomucin PSGL-1/CD162 mediates the attachment of mature leukocytes to P-selectin. We now show that PSGL-1 also functions as the sole receptor for P-selectin on primitive human CD34+ hematopoietic progenitor cells (HPC). More importantly, ligation of PSGL-1 by immobilized or soluble ligand or anti-PSGL-1 antibody results in a profound suppression of HPC proliferation stimulated by potent combinations of early acting hematopoietic growth factors. These data demonstrate an unanticipated but extremely marked growth-inhibitory effect of P-selectin on hematopoiesis and provide direct evidence that PSGL-1, in addition to its well-documented role as an adhesion molecule on mature leukocytes, is a potent negative regulator of human hematopoietic progenitors.

Memory B lymphocytes from secondary lymphoid organs interact with E-selectin through a novel glycoprotein ligand

Recirculation of B lymphocytes through the secondary lymphoid organs is key for recognition and response to foreign antigen. B lymphocytes within secondary lymphoid organs comprise a heterogeneous population of cells at distinct differentiation stages. To ascribe a particular adhesive behavior to discrete B-cell subsets within secondary lymphoid organs, we investigated their functional interaction with endothelial selectins under flow. We describe herein the characterization of a subset of human tonsillar B cells that interact with E-selectin but not P-selectin. E-selectin-interacting B cells had a phenotype of non-germinal center (CD10(-), CD38(-), CD44(+)), memory (IgD-) cells. Furthermore, FucT-VII was expressed selectively in CD44(+) E-selectin-adherent B lymphocytes. B-cell rolling on E-selectin required sialic acid but was independent of previously described selectin ligands. A novel glycoprotein ligand of 240 kDa carrying N-linked glycans was isolated from B-cell membranes by an E-selectin immunoadhesin. Binding of this protein was strictly Ca2+ dependent, was inhibited by a cell adhesion-blocking mAb against E-selectin, and required the presence of sialic acid but not N-linked carbohydrates. Our results enable us to assign to resident memory B lymphocytes a novel adhesion function, the rolling on E-selectin, that provides insights on the adhesion pathways involved in homing of memory B cells to tertiary sites.

The gain-of-function Chinese hamster ovary mutant LEC11B expresses one of two Chinese hamster FUT6 genes due to the loss of a negative regulatory factor

The LEC11 Chinese hamster ovary (CHO) gain-of-function mutant expresses an alpha(1,3)fucosyltransferase (alpha(1,3)Fuc-T) activity that generates the LeX, sialyl-LeX, and VIM-2 glycan determinants and has been extensively used for studies of E-selectin ligand specificity. In order to identify regulatory mechanisms that control alpha(1,3)Fuc-T expression in mammals, mechanisms of FUT gene expression were investigated in LEC11 cells and two new, independent mutants, LEC11A and LEC11B. Northern and ribonuclease protection analyses, using probes that span the coding region of a cloned CHO FUT gene, detected transcripts in each LEC11 mutant but not in CHO cells or other gain-of-function CHO mutants that express a different alpha(1,3)Fuc-T activity. Coding region sequence analysis and alpha(1,3)Fuc-T acceptor specificity comparisons with recombinant human Fuc-TV and Fuc-TVI showed that the cloned FUT gene is orthologous to the human FUT6 gene. Southern analyses identified two closely related FUT6 genes in the Chinese hamster, whose evolutionary relationships are discussed. The blots showed that rearrangements had occurred in LEC11A and LEC11 genomic DNA, consistent with a cis mechanism of FUT6 gene activation in these mutants. By contrast, somatic cell hybrid analyses revealed that LEC11B cells express FUT6 gene transcripts due to the loss of a trans-acting, negative regulatory factor. Sequencing of reverse transcriptase-polymerase chain reaction products identified unique 5'- and 3'-untranslated region sequences in FUT6 gene transcripts from each LEC11 mutant. Northern and Southern analyses with gene-specific probes showed that LEC11A cells express only the cgFUT6A gene (where cg is Cricetulus griseus), whereas LEC11 and LEC11B cells express only the cgFUT6B gene. In LEC11A x LEC11B hybrid cells, the cgFUT6A gene was predominantly expressed, as predicted if a trans-acting negative regulatory factor functions to suppress cgFUT6B gene expression in CHO cells. This factor is predicted to be a cell type-specific regulator of FUT6 gene expression in mammals.

Mouse C127 cells transfected with fucosyltransferase fuc-TIII express masked Lewisx but not Lewisx antigen

To study human alpha1,3/1,4fucosyltransferase (Fuc-TIII) as an alpha1,3 fucosyltransferase, we constructed two cell clones, C127-FT and C127-T-FT, by transfecting cDNA in parental (C127) or Polyoma T antigen expressing (C127-T) mouse cells, respectively. Both C127-FT and C127-T-FT clones express high levels of a fucosyltransferase activity kinetically similar to Fuc-TIII and an RNA that is amplified by a Fuc-TIII-specific oligonucleotide primer pair after reverse transcription. Clone C127-FT is Lewisxpositive, by flow cytometry, only after alpha-galactosidase or sialidase treatment, and releases [3H]Fuc N-glycans which efficiently bind to immobilized Griffonia simplicifolia I and Sambucus nigra lectins. Immunoblotting confirms that C127-FT glycoproteins acquire Lewisxreactivity only after specific deglycosylation, and shows that a small subset of Griffonia simplicifolia I isolectin B4reactive glycoproteins bears masked Lewisx, suggesting fine substrate recognition by Fuc-TIII. Moreover, transient transfection of H type alpha1, 2fucosyltransferase in clone C127-T-FT directs synthesis of Lewisyantigen, as detected by flow cytometry. Results indicate that Fuc-TIII expressed in C127 cells synthesizes masked Lewisxantigen while Lewisxantigen is not detectable.

Mechanisms that regulate the function of the selectins and their ligands

Selectins are a family of three cell adhesion molecules (L-, E-, and P-selectin) specialized in capturing leukocytes from the bloodstream to the blood vessel wall. This initial cell contact is followed by the selectin-mediated rolling of leukocytes on the endothelial cell surface. This represents the first step in a cascade of molecular interactions that lead to leukocyte extravasation, enabling the processes of lymphocyte recirculation and leukocyte migration into inflamed tissue. The central importance of the selectins in these processes has been well documented in vivo by the use of adhesion-blocking antibodies as well as by studies on selectin gene-deficient mice. This review focuses on the molecular mechanisms that regulate expression and function(s) of the selectins and their ligands. Cell-surface expression of the selectins is regulated by a variety of different mechanisms. The selectins bind to carbohydrate structures on glycoproteins, glycolipids, and proteoglycans. Glycoproteins are the most likely candidates for physiologically relevant ligands. Only a few glycoproteins are appropriately glycosylated to allow strong binding to the selectins. Recently, more knowledge about the structure and the regulated expression of some of the carbohydrates on these ligands necessary for selectin binding has been accumulated. For at least one of these ligands, the physiological function is now well established. A novel and exciting aspect is the signaling function of the selectins and their ligands. Especially in the last two years, convincing data have been published supporting the idea that selectins and glycoprotein ligands of the selectins participate in the activation of leukocyte integrins.

Acceptor specificity of the human leukocyte alpha3 fucosyltransferase: role of FucT-VII in the generation of selectin ligands

The alpha3 fucosyltransferase, FucT-VII, is one of the key glycosyltransferases involved in the biosynthesis of the sialyl Lewis X (sLex) antigen on human leukocytes. The sialyl Lewis X antigen (NeuAcalpha(2-3)Galbeta(1-4)[Fucalpha(1-3)]GlcNAc-R) is an essential component of the recruitment of leukocytes to sites of inflammation, mediating the primary interaction between circulating leukocytes and activated endothelium. In order to characterize the enzymatic properties of the leukocyte alpha3 fucosyltransferase FucT-VII, the enzyme has been expressed in Trichoplusia ni insect cells. The enzyme is capable of synthesizing both sLexand sialyl-dimeric-Lexstructures in vitro , from 3'-sialyl-lacNAc and VIM-2 structures, respectively, with only low levels of fucose transfer observed to neutral or 3'-sulfated acceptors. Studies using fucosylated NeuAcalpha(2-3)-(Galbeta(1-4)GlcNAc)3-Me acceptors demonstrate that FucT-VII is able to synthesize both di-fucosylated and tri-fucosylated structures from mono-fucosylated precursors, but preferentially fucosylates the distal GlcNAc within a polylactosamine chain. Furthermore, the rate of fucosylation of the internal GlcNAc residues is reduced once fucose has been added to the distal GlcNAc. These results indicate that FucT-VII is capable of generating complex selectin ligands, in vitro , however the order of fucose addition to the lactosamine chain affects the rate of selectin ligand synthesis.

Stimulation of P-selectin glycoprotein ligand-1 on mouse neutrophils activates beta 2-integrin mediated cell attachment to ICAM-1

The entry of neutrophils into inflamed tissues is initiated by cell rolling on the blood vessel wall followed by arrest and transendothelial migration. Rolling is mediated by the selectins, while the two subsequent steps require activated beta 2-integrins. We have investigated whether the binding of P-selectin to mouse neutrophils could trigger the activation of beta 2-integrins. We show that cross-linking of P-selectin glycoprotein ligand-1 (PSGL-1) on mouse neutrophils with an antibody-like recombinant form of P-selectin or with monoclonal antibodies stimulated the production of reactive oxygen intermediates and enhanced neutrophil attachment to intercellular adhesion molecule 1 (ICAM-1)-expressing CHO cells. This effect was independent of whether complete antibodies or F(ab')2 fragments were used. The adhesion-stimulating effect of P-selectin could be blocked by monoclonal antibodies against PSGL-1. Increase of cell attachment was dependent on lymphocyte function-associated antigen 1 (LFA-1) and on Mac-1, since it could be blocked with antibodies against both respective integrin alpha-chains. Moreover, cell surface expression of Mac-1 increased upon cross-linking of PSGL-1. In agreement with published data, treatment of human neutrophils with P-selectin-IgG did not enhance attachment to ICAM-1. Our data suggest that ligation of PSGL-1 on mouse neutrophils, but not on human neutrophils, activates beta 2-integrin mediated cell attachment to ICAM-1.

In vitro degradation of endothelial catenins by a neutrophil protease

It has been recently proposed that adhesion of polymorphonuclear cells (PMNs) to human umbilical vein endothelial cells leads to the disorganization of the vascular endothelial cadherin-dependent endothelial adherens junctions. Combined immunofluorescence and biochemical data suggested that after adhesion of PMNs to the endothelial cell surface, beta-catenin, as well as plakoglobin was lost from the cadherin/catenin complex and from total cell lysates. In this study we present data that strongly suggest that the adhesion-dependent disappearance of endothelial catenins is not mediated by a leukocyte to endothelium signaling event, but is due to the activity of a neutrophil protease that is released upon detergent lysis of the cells.

The binding of T cell-expressed P-selectin glycoprotein ligand-1 to E- and P-selectin is differentially regulated

The HECA452 carbohydrate epitope, also termed cutaneous lymphocyte antigen, is known to bind to E-selectin and defines a human T cell subset preferentially found in inflamed skin. Activated T cells can express a functional form of the P-selectin glycoprotein ligand-1 (PSGL-1), the major ligand known for P-selectin. Here we show that PSGL-1 can exist in two forms, of which only one carries the HECA452 epitope and binds to E-selectin, while the other only binds to P-selectin. We have analyzed the glycoprotein ligands for E- and P-selectin on the mouse CD8+ T cell clone 4G3 at 4, 8, and 12 days after antigen-specific activation. Only at day 4 did the cells bind to E-selectin, whereas cells at all three activation stages bound to P-selectin. Expression of the HECA452 epitope correlated with E-selectin binding. In affinity isolation experiments, PSGL-1 was isolated as the major ligand by E-selectin-IgG and by P-selectin-IgG; however, PSGL-1 only bound to E-selectin at day 4, whereas it bound to P-selectin at all three activation stages. Immunoprecipitated PSGL-1 from cells at day 4, but not from cells at days 8 and 12, was recognized in immunoblots by monoclonal antibody HECA452. In immunoblots of total extracts of cells at day 4, HECA452 recognized a 240/140-kDa pair of protein bands as the major antigen. These bands could be completely removed by depletion of cell extracts with anti-PSGL-1 antibodies. Our data suggest that the carbohydrate requirements for binding of PSGL-1 to P-selectin differ from those necessary for binding to E-selectin. Furthermore, we conclude that the major glycoprotein carrier for the HECA452 epitope on activated 4G3 cells is PSGL-1.

L-selectin from human, but not from mouse neutrophils binds directly to E-selectin

L-Selectin on neutrophils as well as inducible E- and P-selectin on endothelium are involved in the recruitment of neutrophils into inflamed tissue. Based on cell attachment assays, L-selectin was suggested to function as a carbohydrate presenting ligand for E- and P-selectin. However, previous affinity isolation experiments with an E-selectin-Ig fusion protein had failed to detect L-selectin among the isolated E-selectin ligands from mouse neutrophils. We show here that L-selectin from human neutrophils, in contrast to mouse neutrophils, can be affinity-isolated as a major ligand from total cell extracts using E-selectin-Ig as affinity probe. Binding of human L-selectin to E-selectin was direct, since purified L-selectin could be reprecipitated with E-selectin-Ig. Recognition of L-selectin was abolished by sialidase-treatment, required Ca2+, and was resistant to treatment with endoglycosidase F. Binding of L-selectin to a P-selectin-Ig fusion protein was not observed. In agreement with the biochemical data, the anti-L-selectin mAb DREG56 inhibited rolling of human neutrophils on immobilized E-selectin-Ig but not on P-selectin-Ig. No such inhibitory effect was seen with the anti-mouse L-selectin mAb MEL14 on mouse neutrophils. Rolling of E-selectin transfectants on purified and immobilized human L-selectin was inhibited by mAb DREG56. We conclude that L-selectin on human neutrophils is a major glycoprotein ligand among very few glycoproteins that can be isolated by an E-selectin affinity matrix. The clear difference between human and mouse L-selectin suggests that E-selectin-binding carbohydrate moieties are attached to different protein scaffolds in different species.