Human myeloid α3-fucosyltransferase is involved in the expression of the sialyl-Lewisx determinant, a ligand for E- and P-selectin

Abstract

The sialyl-Lex determinant (NeuAcα2→3Galβ1→4[Fucα-1→3]GlcNAc) has been identified as a major ligand in the selectin-mediated adhesion of neutrophils and monocytes to activated endothelium or platelets. This carbohydrate epitope is formed by the sequential action of α3-sialyltransferase and α3-fucosyltransferase on N-acetyllactosamine (Galβ1→4GlcNAc) disaccharide termini of glycoconjugates. We have addressed the role of the human myeloid α3-fucosyltransferase in the expression of this epitope at the leucocyte surface by determining its activity in human-mouse leukemic cell hybrids (WEGLI), normal human granulocytes and chronic myeloid leukemia (CML) cells using sialylated and desialylated glycoproteins and oligosaccharides as acceptor substrates. In contrast to what has been reported for the myeloid-type enzyme, we found that the α3-fucosyltransferase of the cells studied can use sialylated acceptors be it that the activity is several times lower than with asialo-substrates. Characterization of the product obtained with a sialylated oligosaccharide indicated that the enzyme can catalyze the formation of the sialyl-Lex structure. Flow cytometry of the WEGLI cells using a sialyl-Lex-specific monoclonal antibody (MoAb) showed that these cells indeed express sialyl-Lex at their surface, provided that they contain human chromosome 11. Earlier the presence of this chromosome had been correlated with the expression of α3-fucosyltransferase activity. In addition to sialyl-Lex, WEGLI cells containing chromosome 11 showed high-expression levels of related structures recognized by antibodies VIM-2 and VIM-8, suggesting that fucose addition can occur at both distal and proximal GIcNAc residues in poly-N-acetyllactosaminoglycan sequences. Based on the human chromosome contents it could be ruled out that the α3-fucosyltransferase of WEGLI cells is a Lewis-type α3/ 4- or plasma-type α3-fucosyltransferase, the genes of which have been mapped to chromosome 19. It is concluded that the enzyme studied is of the myeloid-type and indeed is involved in the synthesis of sialyl-Lex (and also VIM-2 and VIM-8 structures) in leukocytes provided that its expression is at a sufficiently high level. © 1933 by The American Society of Hematology.