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

EA-1, a novel adhesion molecule involved in the homing of progenitor T lymphocytes to the thymus

The mouse progenitor T lymphocyte (pro-T) cell line FTF1 binds in vitro to thymus blood vessels, the thymic capsule, and liver from newborn mice. A mAb, EA-1, raised against an embryonic mouse endothelial cell line, blocked adhesion. The antibody also interfered with pro-T cell adhesion to a thymus-derived mouse endothelial cell line; it had no effect on the adhesion of mature T lymphocytes and myeloid cells. The antigen recognized by EA-1 is located on the vascular endothelium of various mouse tissues and absent on pro-T cells. EA-1 antibody precipitates molecules with apparent molecular weights of 110,000, 140,000, 160,000, and 200,000. Immunoclearing and binding-inhibition studies with antibodies against known adhesion molecules suggest that the EA-1 antigen is a novel adhesion molecule involved in colonization of the embryonic thymus by T cell progenitors.

CD62 and endothelial cell-leukocyte adhesion molecule 1 (ELAM-1) recognize the same carbohydrate ligand, sialyl-Lewis x

The leukocyte receptor CD62, which is expressed on activated platelets and endothelial cells, is shown to mediate cell adhesion by binding a sialylated carbohydrate structure, sialyl-Lewis x, found on neutrophils, monocytes, and tumor cells. This structure has previously been identified as the ligand for another member of the LEC-CAM family of cell adhesion molecules, endothelial cell-leukocyte adhesion molecule 1, which also binds neutrophils and monocytes. The results demonstrate that although the two LEC-CAMs differ in their biological activities by their distribution and mode of expression, they are capable of mediating cell adhesion by recognition of the same carbohydrate ligand.

The human peripheral lymph node vascular addressin is a ligand for LECAM-1, the peripheral lymph node homing receptor

The trafficking of lymphocytes from the blood and into lymphoid organs is controlled by tissue-selective lymphocyte interactions with specialized endothelial cells lining post capillary venules, in particular the high endothelial venules (HEV) found in lymphoid tissues and sites of chronic inflammation. Lymphocyte interactions with HEV are mediated in part by lymphocyte homing receptors and tissue-specific HEV determinants, the vascular addressins. A peripheral lymph node addressin (PNAd) has been detected immunohistologically in mouse and man by monoclonal antibody MECA-79, which inhibits lymphocyte homing to lymph nodes and lymphocyte binding to lymph node and tonsillar HEV. The human MECA-79 antigen, PNAd, is molecularly distinct from the 65-kD mucosal vascular addressin. The most abundant iodinated species by SDS-PAGE is 105 kD. When affinity isolated and immobilized on glass slides, MECA-79 immunoisolated material binds human and mouse lymphocytes avidly in a calcium dependent manner. Binding is blocked by mAb MECA-79, by antibodies against mouse or human LECAM-1 (the peripheral lymph node homing receptor, the MEL-14 antigen, LAM-1), and by treatment of PNAd with neuraminidase. Expression of LECAM-1 cDNA confers PNAd binding ability on a transfected B cell line. We conclude that LECAM-1 mediates lymphocyte binding to PNAd, an interaction that involves the lectin activity of LECAM-1 and carbohydrate determinants on the addressin.

Molecular mapping of functional domains of the leukocyte receptor for endothelium, LAM-1

The human lymphocyte homing receptor LAM-1, like its murine counterpart MEL-14, functions as a mammalian lectin, and mediates the binding of leukocytes to specialized high endothelial cells in lymphoid organs (HEV). LAM-1 is a member of a new family of cell adhesion molecules, termed selectins or LEC-CAMs, which also includes ELAM-1 and PAD-GEM (GMP-140/CD62). To localize the regions of LAM-1 that are involved in cell adhesion, we developed chimeric selectins, in which various domains of PAD-GEM were substituted into LAM-1, and used these chimeric proteins to define the domain requirements for carbohydrate binding, and to localize the regions recognized by several mAb which inhibit the adhesion of lymphocytes to lymph node HEV. The binding of PPME or fucoidin, soluble complex carbohydrates that specifically define the lectin activity of LAM-1 and MEL-14, required only the lectin domain of LAM-1. The LAM1-1, LAM1-3, and LAM1-6 mAb each strongly inhibit the binding of lymphocytes to HEV in the in vitro frozen section assay, and defined three independent epitopes on LAM-1. Blocking of PPME or fucoidin binding by LAM1-3 indicated that this site is identical, or in close proximity, to the carbohydrate binding site, and analysis of the binding of LAM1-3 to chimeric selectins showed that the epitope detected by LAM1-3 is located within the lectin domain. Although the LAM1-6 epitope is also located in the lectin domain, LAM1-6 did not affect the binding of PPME or fucoidin. The LAM1-1 epitope was located in, or required, the EGF domain, and, importantly, binding of LAM1-1 significantly enhanced the binding of both PPME and fucoidin. These results suggest that adhesion mediated by LAM-1 may involve cooperativity between functionally and spatially distinct sites, and support previous data suggesting a role for the EGF domain of LAM-1 in lymphocyte adhesion to HEV.

Glycobiology: a growing field for drug design

Recent information on protein-carbohydrate interactions in physiological and pathological situations substantiates the intuitive belief in carbohydrates as candidates for drug design. Most noteworthy, short saccharide sequences have been shown to be specific receptors for adhesion of circulating leukocytes to vascular endothelial cells, a phenomenon induced at local inflammatory sites. There is strong evidence that mammalian sperm cells carry proteins that interact specifically with saccharide receptors on eggs. The influenza virus receptor on animal cells, sialic acid, has been analysed in the crystal conformation as a complex with the viral receptor-binding protein. These and other convincing examples discussed here by Karl-Anders Karlsson will inspire new approaches to the treatment of several important medical conditions where existing methods are insufficient.

A novel cell surface trans-sialidase of Trypanosoma cruzi generates a stage-specific epitope required for invasion of mammalian cells

When trypomastigotes of T. cruzi emerge from cells of the mammalian host, they contain little or no sialic acids on their surfaces. However, rapidly upon entering the circulation, they express a unique cell surface trans-sialidase activity. This enzyme specifically transfers alpha (2-3)-linked sialic acid from extrinsic host-derived macromolecules to parasite surface molecules, leading to the assembly of Ssp-3, a trypomastigote-specific epitope. The T. cruzi trans-sialidase does not utilize cytidine 5' monophospho-N-acetylneuraminic acid as a donor substrate, but readily transfers sialic acid from exogenously supplied alpha (2-3)-sialyllactose. Monoclonal antibodies that recognize sialic acid residues of Ssp-3 inhibit attachment of trypomastigotes to host cells, suggesting that the unusual trans-sialidase provides Ssp-3 with structural features required for target cell recognition.

Involvement of adhesion molecules (CD11a-ICAM-1) in vascular endothelial cell injury elicited by PMA-stimulated neutrophils

Protective effect of anti-CD11a and anti-ICAM-1 antibodies on the cytotoxicity induced by PMA-stimulated neutrophils was studied using cultured endothelial cells isolated from bovine carotid artery. Anti-CD11a antibody and anti-ICAM-1 antibody inhibited the endothelial cell injury induced by the activated neutrophils in a dose dependent manner. On the other hand, both antibodies themselves had no effect on either the luminol chemiluminescence released out of the activated neutrophils or the adhesion of the neutrophils to the endothelial cell monolayer. These data suggest that these adhesion molecules play some important roles in the vascular endothelial cell injury elicited by activated neutrophils.

Identification of a carbohydrate-based endothelial ligand for a lymphocyte homing receptor

Lymphocyte attachment to high endothelial venules within lymph nodes is mediated by the peripheral lymph node homing receptor (pnHR), originally defined on mouse lymphocytes by the MEL-14 mAb. The pnHR is a calcium-dependent lectin-like receptor, a member of the LEC-CAM family of adhesion proteins. Here, using a soluble recombinant form of the homing receptor, we have identified an endothelial ligand for the pnHR as an approximately 50-kD sulfated, fucosylated, and sialylated glycoprotein, which we designate Sgp50 (sulfated glycoprotein of 50 kD). Recombinant receptor binding to this lymph node-specific glycoprotein requires calcium and is inhibitable by specific carbohydrates and by MEL-14 mAb. Sialylation of the component is required for binding. Additionally, the glycoprotein is precipitated by MECA-79, an adhesion-blocking mAb reactive with lymph node HEV. A related glycoprotein of approximately 90 kD (designated as Sgp90) is also identified.

Endothelial-leukocyte adhesion molecule 1 stimulates the adhesive activity of leukocyte integrin CR3 (CD11b/CD18, Mac-1, alpha m beta 2) on human neutrophils

Two classes of adhesion molecules have well-defined roles in the attachment of unstimulated polymorphonuclear leukocytes (PMN) to cytokine-treated endothelial cells. Endothelial-leukocyte adhesion molecule 1 (ELAM-1) on endothelial cells interacts with specific carbohydrate residues on the PMN, and the leukocyte integrins (CD18 antigens) on PMN interact with intracellular adhesion molecule 1 and other structures on endothelium. Here we show that these two classes of molecules can act sequentially in an "adhesion cascade". Interaction of PMN with ELAM-1-bearing endothelial cells causes PMN to express enhanced adhesive activity of the integrin CR3 (CD11b/CD18). Expression of ELAM-1 on the cytokine-treated endothelium appears both necessary and sufficient for the stimulation of CR3 activity since blockade of ELAM-1 with mAbs prevents the activation of CR3 by cytokine-treated endothelium, and immobilized recombinant ELAM-1 activates CR3. The ability to activate CR3 is shared by chemattractants, suggesting that ELAM-1 may serve as a "tethered chemattractant." This hypothesis is strengthened by the observation that recombinant soluble ELAM-1 directs movement of PMN in chemotaxis chambers. These results suggest a mechanism by which multiple adhesive molecules may function together in diapedesis. ELAM-1 serves both as an adhesin and as a trigger that recruits the participation of additional adhesion molecules. Our results also suggest that ligands for adhesion molecules may also be "receptors" capable of generating intracellular signals.

Mammalian glycosylation mutants as tools for the analysis and reconstitution of protein transport

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The major 85-kDa surface antigen of the mammalian-stage forms of Trypanosoma cruzi is a family of sialidases

Trypanosoma cruzi, an intracellular protozoan parasite infecting a wide variety of vertebrates, is the agent responsible for Chagas disease in humans. An estimated 15-20 million people in South and Central America are infected with the parasite. Chagas disease often results in severe autoimmune and inflammatory pathology and is the major cause of heart failure in endemic areas. Nevertheless, little is known about the host-parasite interactions that lead to this pathology. We have previously cloned several members of a large gene family (SA85-1) and shown that these genes encode 85-kDa T. cruzi, mammalian-stage-specific, surface antigens. Here we report that members of the SA85-1 family possess sialidase activity and are shed by the parasite. We suggest that the sialidases may contribute to the pathology during T. cruzi infection by cleaving sialic acid from cells of the immune system.

Metastatic behavior and cell surface properties of HT-29 human colon carcinoma variant cells selected for their differential expression of sialyl-dimeric Le(x)-antigen

Immunochemical studies of human colorectal carcinoma with various monoclonal antibodies against Le(X)-related carbohydrate antigens previously revealed that the amount of sialyl-dimeric Le(X) antigen (NeuAc alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-R: SLX) associated with metastatic lesions was greater than in the primary tumors. To assess whether an experimental model can be used to study the direct relationship between this carbohydrate antigen and the tumor cell's metastatic behavior, we selected variant cells with increased surface SLX from established human colon carcinoma cell line HT-29. The cells in the upper 5% or lower 5% population in fluorescence intensity after reacting with a monoclonal antibody, FH6, were retrieved separately by a fluorescence-activated cell sorter and propagated. After three- or four-times selection, we obtained stable cell lines with low and high cell surface SLX antigens (HT-29 M1 and HT-29 M2, respectively). Binding of monoclonal antibody FH6 was detected to glycolipids extracted from HT-29 M2 cells but not from HT-29 M1 cells. Glycoprotein components having reactivity with monoclonal antibody FH6 were below the detectable level. HT-29 M2 cells injected intrasplenically into nude mice showed a slightly reduced incidence of metastasis to lung, liver and lymph nodes than did HT-29 M1 cells. Subsequently we found that SLX antigen was not detectable by immunohistochemical examination of these tumor cells grown in nude mice. Re-established cell line from nude mice xenografts expressed SLX antigen in vitro.

Endothelial and epithelial cell adhesion molecules

This review will discuss a number of specific cell adhesion molecules present on the surface of endothelial and epithelial cells in the lung. Molecules such as integrins, proteoglycans, and the hyaluronic acid receptor, CD44, are found on the abluminal or basement membrane side of the cell and function as cell-substratum receptors. Cadherins, integrins, and platelet-endothelial cell adhesion molecule-1 (PECAM-1) are present at the cell-cell borders of adjacent endothelial and/or epithelial cells and function to initiate or maintain cell-cell adhesion. Finally, a number of inducible cell adhesion molecules such as endothelial-leukocyte adhesion molecule-1 (ELAM-1), granule-associated membrane protein 140 (GMP140), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) are expressed on the luminal surfaces of these cells during inflammation and function as cell-cell adhesion molecules important in white blood cell, platelet, or tumor cell adhesion. These adhesion molecules likely play important roles in maintaining the normal structure and function of the lung, as well as participating in pulmonary processes such as inflammation, wound healing, and the development and spread of malignant disease.

Carbohydrate ligands for endothelial-leukocyte adhesion molecule 1

The acute inflammatory response requires that circulating leukocytes bind to and penetrate the vascular wall to access the site of injury. Several receptors have been implicated in this interaction, including a family of putative carbohydrate-binding proteins. We report here the identification of an endogenous carbohydrate ligand for one of these receptors, endothelial-leukocyte adhesion molecule 1 (ELAM-1). Radiolabeled COS cells transfected with a plasmid containing the cDNA for ELAM-1 were used as probes to screen glycolipids extracted from human leukocytes. COS cells transfected with this plasmid adhered to a subset of sialylated glycolipids resolved on TLC plates or adsorbed on polyvinyl chloride microtiter wells. Adhesion to these glycolipids required calcium but was not inhibited by heparin, chondroitin sulfate, keratan sulfate, or yeast phosphomannan. Monosaccharide composition, linkage analysis, and fast atom bombardment mass spectrometry of the glycolipids indicate that the ligands for ELAM-1 are terminally sialylated lactosylceramides with a variable number of N-acetyllactosamine repeats and at least one fucosylated N-acetylglucosamine residue.

ELFT: a gene that directs the expression of an ELAM-1 ligand

The LECCAMs are a family of cell adhesion molecules implicated in certain inflammatory processes. ELAM-1, a LECCAM found on the surface of activated endothelial cells, can mediate adhesion of neutrophils, monocytes, and certain cell lines to endothelial cells in vitro. No ligand for any LECCAM has yet been fully characterized. Here we report the cloning of a cDNA, ELFT (ELAM-1 ligand fucosyltransferase), that can confer ELAM-1 binding activity when transfected into nonbinding cell lines. ELFT encodes a 46 kd protein that has alpha(1,3)fucosyltransferase activity, suggesting that a fucosylated carbohydrate structure is an essential component of the ELAM-1 ligand. Furthermore, ELFT is expressed specifically in cell types that bind to ELAM-1, suggesting that this enzyme is an important regulator of inflammatory events in vivo.