l- and P-selectin are known to require sulfation in their ligand molecules. We investigated the significance of carbohydrate 6-sulfation and tyrosine sulfation in selectin-mediated cell adhesion. COS-7 cells were genetically engineered to express P-selectin glycoprotein ligand-1 (PSGL-1) or its mutant in various combinations with 6-O-sulfotransferase (6-Sul-T) and/or alpha1-->3fucosyltransferase VII (Fuc-T VII). The cells transfected with PSGL-1, 6-Sul-T, and Fuc-T VII cDNAs supported rolling mediated by all three selectins and provided the best experimental system so far to estimate kinetic parameters in selectin-mediated cell adhesion for all three selectins using the identical rolling substrate and to compare the ligand specificity of each selectin. L-selectin-mediated rolling was drastically impaired if the cells lacked carbohydrate 6-sulfation elaborated by 6-Sul-T, but not affected when PSGL-1 was replaced with a mutant lacking three tyrosine residues at its NH(2) terminus. L-selectin-mediated adhesion was also hardly affected by mocarhagin treatment of the cells, which cleaved a short peptide containing sulfated tyrosine residues from PSGL-1. In contrast, P-selectin-mediated rolling was abolished when PSGL-1 was either mutated or cleaved by mocarhagin at its NH(2) terminus, whereas the cells expressing PSGL-1 and Fuc-T VII but not 6-Sul-T showed only a modest decrease in P-selectin-mediated adhesion. These results indicate that L-selectin prefers carbohydrate 6-sulfation much more than tyrosine sulfation, whereas P-selectin favors tyrosine sulfation in the PSGL-1 molecule far more than carbohydrate 6-sulfation. E-selectin-mediated adhesion was sulfation-independent requiring only Fuc-T VII, and thus the three members of the selectin family have distinct requirements for ligand sulfation.