Biosynthesis of GlyCAM-1, a mucin-like ligand for L-selectin

L-selectin, a member of the selectin family of leukocyte-endothelial adhesion proteins, mediates the initial attachment of lymphocytes to lymph node high endothelial venules during lymphocyte recirculation. One of the endothelial-associated ligands for L-selectin is GlyCAM-1, a mucin-like glycoprotein, which presents novel sulfated, sialylated and fucosylated O-glycans. In order to understand the generation of these glycans, we have examined the biosynthesis of GlyCAM-1 in lymph node organ culture. Using peptide-specific antibodies, lectins, and recombinant L-selectin, we detected the following species of GlyCAM-1: unglycosylated (< 28 kDa); modified with GalNAc only (28-33 kDa); modified with sialic acid, fucose, and sulfate but lacking L-selectin reactivity (40-50 kDa); and mature (L-selectin-reactive) ligand (50-60 kDa). Pulse-chase labeling at 15 degrees C suggested that GalNAc is added in a pre-Golgi compartment. Treatment with brefeldin A almost completely blocked sulfation, indicating that this modification occurs in the trans-Golgi network. Two distinct sialylation events occurred in the presence of brefeldin A, while fucosylation was partially blocked. We conclude that sialylation precedes both fucosylation and sulfation during biosynthesis. This ordering will help to identify the critical acceptor structures recognized by lymph node glycosyltransferases and sulfotransferases.

Structure of the O-glycans in GlyCAM-1, an endothelial-derived ligand for L-selectin

L-selectin, the leukocyte selectin, mediates the carbohydrate-dependent attachment of circulating leukocytes to endothelium, preceding emigration into tissues. It functions in inflammatory leukocyte trafficking and in lymphocyte homing to lymph nodes. From previous work, the binding of L-selectin to endothelial-associated glycoprotein ligands, GlyCAM-1 and CD34, requires oligosaccharide sialylation, sulfation, and probably fucosylation. We have recently identified a major capping group in GlyCAM-1 as 6' sulfated sialyl Lewis x, a novel structure which potentially satisfies all of these requirements. In the present study, we define the complete structure of beta-eliminated chains of GlyCAM-1 using metabolic radiolabeling, plant lectin binding, and glycosidase digestions in conjunction with high pH anion-exchange chromatography. The majority of the O-glycans in GlyCAM-1 contain the T-antigen, i.e. Gal beta 1-->3GalNAc, which is incorporated into the core-2 structure, i.e. Gal beta 1-->3[GlcNAc beta 1-->6]GalNAc or larger core structures with additional GlcNAc residues. The structures of two O-glycans, based on core-2, were determined to be: [sequence: see text] The implications of these structures and more complex O-glycans for binding by L-selectin are discussed.

Sulfation-dependent recognition of high endothelial venules (HEV)-ligands by L-selectin and MECA 79, and adhesion-blocking monoclonal antibody

L-selectin is a lectin-like receptor that mediates the attachment of lymphocytes to high endothelial venules (HEV) of lymph nodes during the process of lymphocyte recirculation. Two sulfated, mucin-like glycoproteins known as Sgp50/GlyCAM-1 and Sgp90/CD34 have previously been identified as HEV-associated ligands for L-selectin. These proteins were originally detected with an L-selectin/Ig chimera called LEC-IgG. GlyCAM-1 and CD34 are also recognized by an antiperipheral node addressin (PNAd) mAb called MECA 79, which blocks L-selectin-dependent adhesion and selectively stains lymph node HEV. The present study compares the requirements for the binding of MECA 79 and LEC-IgG to HEV-ligands. Whereas desialylation of GlyCAM-1 and CD34 drastically reduced binding to LEC-IgG, this treatment enhanced the binding of GlyCAM-1 to MECA 79. In contrast, the binding of both MECA 79 and LEC-IgG to GlyCAM-1 and CD34 was greatly decreased when the sulfation of these ligands was reduced with chlorate, a metabolic inhibitor of sulfation. Because MECA 79 stains HEV-like vessels at various sites of inflammation, recognition by L-selectin of ligands outside of secondary lymphoid organs may depend on sulfation. In addition to their reactivity with GlyCAM-1 and CD34, both MECA 79 and LEC-IgG recognize an independent molecule of approximately 200 kD in a sulfate-dependent manner. Thus, this molecule, which we designate Sgp200, is an additional ligand for L-selectin.

Ly-49A, a receptor for H-2Dd, has a functional carbohydrate recognition domain

Ly-49A+ murine natural killer (NK) cells cannot lyse target cells that express H-2Dd. We demonstrate a functional requirement for carbohydrate recognition by Ly-49A. Treatment of H-2Dd+ target cells with tunicamycin prevents their binding to Ly-49A+ cells and renders them susceptible to lysis by Ly-49A+ NK cells. Fucoidan, a sulfated polysaccharide, binds to Ly-49A in a calcium-dependent manner, and this binding is inhibited by monosaccharides, particularly sulfated hexoses. The inactivation of Ly-49A+ NK cells by H-2Dd+ target cells is reversed in the presence of glucose 6-SO4. These results indicate that Ly-49A has a functional carbohydrate recognition domain and that target expression of carbohydrates alters their susceptibility to natural killing.

Localization of ligands for L-selectin in mouse peripheral lymph node high endothelial cells by colloidal gold conjugates

L-selectin, a Ca(2+)-dependent lectin-like receptor, mediates lymphocyte attachment to high endothelial venules (HEV) of peripheral lymph nodes (PLN) during the process of lymphocyte homing. Two endothelial-derived ligands for L-selectin, known as GlyCAM-1 (Sgp50) and CD34 (Sgp90), have been identified by affinity precipitation of lymph node extracts with a chimeric molecule that combines the extracellular domains of L-selectin with the human IgG1 Fc region (L-selectin-IgG) (J Cell Biol 110:2221, 1990). Here, using a histologic probe based on colloidal gold conjugated to L-selectin-IgG (LS-Ig), we performed morphologic mapping of the HEV ligands in PLN at both the light and electron microscopic levels. With a postembedding labeling method, intense LS-Ig-gold staining of PLN HEV was observed, while the HEV of Peyer's patches (PP) were negative. The specificity of LS-Ig-gold staining was established by pretreatment of sections with sialidase and coincubation of sections with EGTA, fucoidin, or L-selectin-IgG itself. In ultrastructural studies of high endothelial cells(HEC), gold particles were bound to the trans-Golgi network(TGN) and to peripheral vesicles in the cytoplasm. Gold labeling was also detected in a patchy distribution on the entire luminal vascular surface of HEC. Although the perivascular fibroreticular sheath of HEV was frequently labeled limited labeling was observed on the basolateral surfaces of the HEC. In most cases, the HEC membrane surrounding migrating lymphocytes was negative. These results show that L-selectin ligands pass through the Golgi apparatus during their biosynthesis, are stored in secretory granules, and are expressed on the vascular luminal surface of the HEC. A polyclonal antiserum to GlyCAM-1 intensely stained intracellular organelles in the biosynthetic pathway including cytoplasmic vesicles, but failed to stain the cell surface of HEC. Given its presence in serum as a soluble factor, GlyCAM-1 is likely to be a secretory product.

The selectins and their ligands

The selectins are a family of carbohydrate-binding proteins, or lectins, that have stimulated tremendous interest because of their involvement in a wide array of interactions between leukocytes and endothelial cells. Highlights of recent progress include an extension of the list of instances of selectin participation in inflammatory diseases, further definition of selectin carbohydrate specificities, and identification of their carbohydrate-based ligands.

Myelin localization of a central nervous system ligand for L-selectin

L-selectin is a lectin-like receptor involved in lymphocyte attachment to lymph node high endothelial venules (HEV). Previously, we showed that L-selectin also participates in the in vitro attachment of lymphocytes to central nervous system (CNS) white matter. Use of an L-selectin chimera demonstrated ligand sites within CNS white matter but not the peripheral nervous system (PNS). Now employing higher resolution mapping, including EM cytochemistry, we localize the ligands to the actual myelin sheaths of CNS neurons. In the shiverer mouse, which lacks compact myelin, ligands are greatly diminished. Comparison of the myelin-associated ligand with the previously characterized HEV-ligands demonstrates a number of differences.

Central nervous pathways mediating angina pectoris

The central nervous pathways of angina pectoris have never been identified in vivo in man. We used positron emission tomography to examine the changes in regional cerebral blood flow associated with angina pectoris. Dynamic positron emission tomography with 15O-labelled water was used in 12 patients with angina and angiographically proven coronary artery disease to measure regional cerebral blood flow changes during angina induced by intravenous dobutamine. All subjects had typical retrosternal chest pain accompanied by ischaemic electrocardiographic changes during dobutamine infusion. Compared to the resting state, angina was associated with increased regional cerebral blood flow in the hypothalamus (percentage change in regional cerebral blood flow +6.5 and Z score 7.2) periaquaductal grey (+2.6 and 4.0), bilaterally in the thalamus (left: +2.7 and 4.3; right +3.7 and 4.7) and lateral prefrontal cortex (left +11.5 and 7.6; right +8.5 and 7.8) and left inferior anterocaudal cingulate cortex (+9.4 and 6.6). In contrast, it was reduced bilaterally in the mid-rostrocaudal cingulate cortex (left -3.7 and 6.3; right -4.7 and 4.6) and fusiform gyrus (left -3.2 and 4.0; right -3.3 and 3.7), right posterior cingulate (-3.9 and 5.8) and left parietal cortices (-4.8 and 6.3). Several minutes after stopping dobutamine infusion, when the patients no longer experienced angina and the electrocardiographic changes had resolved, thalamic, but not cortical activation could be seen. We propose that the central structures activated constitute the pathways for perception of anginal pain and that the thalamus may act as a gate to afferent pain signals, with cortical activation being necessary for the sensation of pain. This method of investigation may form a basis for research into anomalies of visceral pain perception such as silent myocardial ischaemia.

Coronary vasodilator reserve, pain perception, and sex in patients with syndrome X

BACKGROUND

It remains unclear whether myocardial ischemia due to coronary microvascular dysfunction is the cause of chest pain in syndrome X (chest pain, ischemic-like stress ECG despite angiographically normal coronary arteries). To assess the function of the coronary microcirculation and its relation to pain perception, we measured myocardial blood flow (MBF) and coronary vasodilator reserve (CVR) in 29 patients with syndrome X and 20 matched normal control subjects.

METHODS AND RESULTS

MBF at rest and after intravenous dipyridamole (0.56 mg.kg-1 over 4 minutes) was measured using positron emission tomography with H2(15)O. CVR was calculated as MBFdipyridamole/MBFrest. ECG changes and chest pain after dipyridamole in syndrome X were compared with those in 35 patients with coronary artery disease (CAD). Resting and postdipyridamole MBFs were homogeneous throughout the left ventricle in syndrome X patients and control subjects. MBF was 1.05 (0.25), mean (SD) versus 1.00 (0.22) mL.min-1.g-1 (P = NS) at rest and 2.73 (0.81) versus 3.00 (1.00) mL.min-1.g-1 (P = NS) after dipyridamole in patients and control subjects, respectively. CVRs were 2.66 (0.76) and 3.06 (1.08) (P = NS) and after correction of resting MBF for rate-pressure product were 2.35 (0.83) and 2.34 (0.90) (P = NS) in patients and control subjects, respectively. Female syndrome X patients had higher resting MBF than males, at 1.18 (0.20) versus 0.88 (0.19) mL.min-1.g-1 (P < .001). Chest pain after dipyridamole occurred in syndrome X as frequently as in CAD (21/29 versus 22/35, P = NS).

CONCLUSIONS

When patients with syndrome X are compared with control subjects, no differences are found in MBF either at rest or after dipyridamole, despite syndrome X patients experiencing chest pain after dipyridamole to the same extent as patients with CAD. These findings, together with the absence of any relation among MBF, chest pain, and ECG changes under stress, cast further doubt on ischemia as the basis of the chest pain, at least in the majority of syndrome X patients.

Hyperventilation in Patients Who Have Sustained Myocardial Infarction after a Work Injury

Patients who present with acute myocardial infarction after a work injury (AMI-WI) often report symptoms consistent with chronic hyperventilation which date back as far as the work injury itself, rather than to the AMI. The aim of the study was to test the hypothesis that hyperventilation significantly contributes to the symptoms of AMI-WI patients.

The prevalence of hyperventilation was assessed by clinical capnography in 12 AMI-WI patients, 20 normal controls, 15 AMI patients whose AMI was conventional and not subsequent to a work injury (AMI-C) and 14 patients with post-traumatic stress disorder (PTSD). End-tidal carbon dioxide partial pressure (PetCO2) was measured at rest, after 1 min hyperventilation (FHPT), after recall of the relevant stressor (Think) and when the breathing was felt to be normal (MBIN).

PetCO2 levels after FHPT were: 29.0±1.5 (mean±SD) mmHg for AMI-WI; 26.7±1.9 mmHg for PTSD; 32.1± 4.1mmHg for AMI-C and 33.7±1.4 mmHg for the controls ( P< 0.05 and P< 0.01 for AMI-WI and PTSD, respectively, versus controls). After Think, the levels were 25.8±1.6 mmHg for AMI-WI, 24.6±1.4 mmHg for PTSD, 31.2±4.1mmHg for AMI-C and 31.2± 1.5 mmHg for normals ( P<0.05 and P<0.01 for AMI-WI and PTSD, respectively, versus controls). For MBIN, values of PetCO2 were 26.8±1.7 mmHg and 26.7±1.5mmHg for AMI-WI and PTSD versus 33.8±1.2 mmHg for normals, ( P< 0.01 for both versus controls). Ten AMI-WI and 12 PTSD were positive for hyperventilation versus four AMI-C patients and four controls ( P< 0.01). The implications for rehabilitation, compensation and pathophysiology of AMI-WI are discussed, both from a medical-scientific perspective and in terms of admissible legal evidence.

6'-sulfated sialyl Lewis x is a major capping group of GlyCAM-1

The binding of L-selectin to the HEV-derived ligand GlyCAM-1 bears a strict requirement for oligosaccharide sulfation. In the companion study [Hemmerich, S., Bertozzi, C.R., Leffler, H., & Rosen, S. D. (1994) Biochemistry 33, 4820-4829], we identified the major sulfated mono- and disaccharides of GlyCAM-1 as Gal-6-SO4, GlcNAc-6-SO4, (SO4-6)Gal beta 1-->4GlcNAc, and Gal beta 1-->4(SO4-6)GlcNAc. Sialic acid and fucose are also critical to the recognition determinants on GlyCAM-1. However, the hydrolysis conditions employed in the previous study resulted in cleavage of these moieties, precluding their positional assignment. Here, we employ lectins of defined specificity in conjunction with specific exoglycosidases to identify a major GlyCAM-1 capping structure that includes all three critical elements. The complementary reactivity of Maackia amurensis agglutinin with fully sialylated, undersulfated GlyCAM-1 and Sambucus nigra agglutinin/Trichosanthes japonica agglutinin with desialylated but normally sulfated GlyCAM-1 indicates the presence of terminal 6'-sulfated sialyllactosamine. alpha (1-->3/4)Fucosidase removes fucose almost quantitatively from asialo-GlyCAM-1 while substantially enhancing its binding to Lycopersican esculentum agglutinin (specific for beta 1-->4-linked GlcNAc), indicating the presence of Fuc in an alpha 1-->3 linkage to GlcNAc. The strict requirement for desialylation to achieve defucosylation indicates a proximal location of Fuc with respect to terminal sialic acid. The nature of the capping group was further defined by studying the effects of sulfation, sialylation, and fucosylation on the ability of exo-beta(1-->4)galactosidase to release [3H]Gal from GlyCAM-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of the sulfated monosaccharides of GlyCAM-1, an endothelial-derived ligand for L-selectin

L-Selectin, a receptor bearing a C-type lectin domain, mediates the initial attachment of lymphocytes to high endothelial venules of lymph nodes. One of the endothelial-derived ligands for L-selectin is GlyCAM-1 (previously known as Sgp50), a mucin-like glycoprotein with sulfated, sialylated, and fucosylated O-linked oligosaccharide chains. Sialylation, sulfation, and fucosylation appear to be required for the avid interaction of this ligand with L-selectin, but the exact carbohydrate structures involved in recognition remain undefined. In this study, we examine the nature of the sulfate-modified carbohydrates of GlyCAM-1. GlyCAM-1 was metabolically labeled in lymph node organ culture with 35SO4 and a panel of tritiated carbohydrate precursors. Mild hydrolysis conditions were established that released sulfated oligosaccharides without cleavage of sulfate esters. Low molecular weight and singly charged fragments, obtained by a combination of gel filtration and anion-exchange chromatography, were analyzed. The structural identification of the fragments relied on the use of a variety of radiolabeled sugar precursors, further chemical and enzymatic hydrolysis, and high-pH anion-exchange chromatography analysis. Sulfated constituents of GlyCAM-1 were identified as Gal-6-SO4, GlcNAc-6-SO4, (SO4-6)Gal beta 1-->4GlcNAc, and Gal beta 1-->4(SO4-6)GlcNAc. In the accompanying paper [Hemmerich, S., & Rosen, S.D. (1994) Biochemistry 33, 4830-4835] evidence is presented that (SO4-6)Gal beta 1-->4GlcNAc forms the core of a sulfated sialyl Lewis x structure that may comprise a recognition determinant on GlyCAM-1.

Binding of L-selectin to the vascular sialomucin CD34

The adhesive interactions between leukocyte L-selectin and the endothelium are involved in the migration of lymphocytes through peripheral lymph nodes and of neutrophils to sites of inflammation. A recombinant L-selectin stains high endothelial venules (HEVs) in lymph nodes and recognizes sulfated carbohydrates found on two endothelial glycoproteins, Sgp50 and Sgp90. Amino acid sequencing of purified Sgp90 revealed a protein core identical to that CD34, a sialomucin expressed on hematopoietic stem cells and endothelium. A polyclonal antiserum to recombinant murine CD34 stains peripheral lymph node endothelium and recognizes Sgp90 that is functionally bound by L-selectin. Thus, an HEV glycoform of CD34 can function as a ligand for L-selectin.

Robert Feulgen Lecture 1993. L-selectin and its biological ligands

This review considers the leukocyte adhesive receptor known as L-selectin. This protein, belonging to the selectin family of cell-cell adhesion receptors, mediates adhesion by virtue of a C-type lectin domain at its amino terminus. The protein was discovered as a lymphocyte homing receptor involved in the attachment of lymphocytes to high endothelial venules (HEV) of lymph nodes. Its widespread distribution on all leukocyte populations underlies a more general role in a variety of leukocyte-endothelial interactions. In the HEV interaction, cognate HEV ligands for L-selectin have been identified as two sulfated, sialylated, and fucosylated glycoproteins, known as GlyCAM-1 and Sgp90. These ligands have mucin-like domains which confer important properties for their proposed adhesive function. The carbohydrate features of these ligands, essential for their interaction with L-selectin, are reviewed. The existence of extralymphoid ligands for L-selectin is also discussed.

Cell surface lectins in the immune system

Emerging evidence establishes that the immune system employs carbohydrates as recognition determinants for various cellular interactions. The best understood case is provided by the selectin family (L-, E- and P-selectin), which are found on leukocytes or endothelial cells and mediate a variety of leukocyte-endothelial interactions. By virtue of C-type lectin domains, these receptors mediate adhesion by recognizing specific carbohydrate-based ligands on partner cells. This review will summarize current research on the selectins and their ligands. Additionally, several leukocyte receptors, for which lectin activity has been demonstrated or inferred to exist, will be considered briefly.

Sulphation requirement for GlyCAM-1, an endothelial ligand for L-selectin

L-selectin participates in the initial attachment of leukocytes to the vascular endothelium. On lymphocytes, it mediates binding to high endothelial venules of lymph nodes. As a selectin it functions as a calcium-dependent lectin recognizing carbohydrate-bearing ligands on endothelial cells. Two lymph node ligands for L-selectin have been identified as sulphated glycoproteins of M(r) approximately 50K and approximately 90K, called Sgp50 and Sgp90 (ref. 10). The recently cloned Sgp50 (ref. 12), now designated GlyCAM-1, is a high endothelial venule-associated, mucin-like glycoprotein containing predominantly O-linked carbohydrate chains. Sialylation of GlyCAM-1 is necessary for its ligand activity and a role for fucosylation is suspected. We have used chlorate as a metabolic inhibitor of sulphation, and report here that GlyCAM-1 has an additional requirement for sulphate.

Direct demonstration of heterogeneous, sulfated O-linked carbohydrate chains on an endothelial ligand for L-selectin

We have previously identified endothelial ligands for L-selectin as sialylated, fucosylated and sulfated glycoproteins of approximately 50 kDa and 90 kDa (Sgp50 and Sgp90). In this report, we use the beta elimination reaction to demonstrate directly the presence of sulfated O-linked sugar chains on one of these ligands, after metabolic labeling with radiolabeled sulfate or fucose. All of the sulfated and the majority of the fucosylated O-linked sugar chains were shown to be sialylated by affinity chromatography on a Limax agglutinin column. Analyses by anion exchange and gel permeation chromatography revealed a complexity of sugar chains, which were heterogeneous both in charge and size. Charged groups other than sialic acid appeared to exert a predominant influence on the total charge of the sugar chains. The probable existence of a varying number of sulfate modifications per sugar chain is discussed.