P- and E-Selectins Recognize Sialyl 6-Sulfo Lewis X, the Recently Identified L-Selectin Ligand

Abstract

Recently we identified sialyl 6-sulfo Lex as a major L-selectin ligand on high endothelial venules of human peripheral lymph nodes. In this study we investigated the ligand activity of sialyl 6-sulfo Lex to E- and P-selectins and compared it with the binding activity of conventional sialyl Lex, by using cultured human lymphoid cells expressing both carbohydrate determinants. The results of the recombinant selectin binding studies and the nonstatic monolayer cell adhesion assays indicated that both sialyl 6-sulfo Lex and conventional sialyl Lex served as ligand for E- and P-selectins, while L-selectin was quite specific to sialyl 6-sulfo Lex. Anti-PSGL-1 antibodies as well as O-sialoglycoprotein endopeptidase treatment almost completely abrogated the binding of P-selectin but barely affected the binding of E-selectin, indicating that these carbohydrate determinants carried by O-glycans of PSGL-1 selectively serves as a ligand for P-selectin, while the ligand for E-selectin is not restricted to PSGL-1 nor to O-sialoglycoprotein endopeptidase-sensitive glycans. The binding of L-selectin was markedly reduced by O-sialoglycoprotein endopeptidase treatment but only minimally affected by anti-PSGL-1 antibodies, indicating that O-glycans carrying sialyl 6-sulfo Lex were the major L-selectin ligands, while PSGL-1 was only a minor core protein for L-selectin in these cells. These results indicated that each member of the selectin family has a distinct ligand binding specificity.