Differential requirements for the O-linked branching enzyme core 2 β1-6-N-glucosaminyltransferase in biosynthesis of ligands for E-selectin and P-selectin

Selectins are carbohydrate-binding adhesion molecules that play important roles in control of leukocyte traffic. Glycosyltransferases involved in selectin ligand biosynthesis include the alpha1,9-fucosyl-transferases FucT-VII and FucT-IV, one or more sialyltransferases, and at least one O-linked branching enzyme. Previous studies have shown that core 2 beta1-6-N-glucosaminyltransferase (C2GlcNAcT-I; EC 2.4.1.102) is required for functional modification of PSGL-1, the leukocyte P-selectin ligand, but have been ambiguous on whether this enzyme is involved in E-selectin ligand formation. Using an attachment and rolling assay under defined shear flow in vitro, this study shows that C2GlcNAcT-I- lymphoid cells stably transfected with FucT-VII complementary DNA attach and roll well on E-selectin at 1.5 dynes/cm.(2) Further, attachment and rolling on P-selectin of neutrophils is sharply reduced and that of short- term polarized Th1 cells is virtually abolished, with leukocytes from C2GlcNAcT-I-/- mice. In contrast, both neutrophils and Th1 cells from C2GlcNAcT-I-/- mice attach and roll as well as wild-type cells on E-selectin. These results show that C2GlcNAcT-I is selectively required for biosynthesis of ligands for P-selectin, but is not essential for at least some E-selectin ligands, Distinct requirements for C2GlcNAcT-I in the formation of ligands for E-selectin versus P-selectin represents a novel level of regulation of expression of selectin ligands and lymphocyte traffic.