Single glycosyltransferase, core 2 β1→6-N- acetylglucosaminyltransferase, regulates cell surface sialyl-Le(x) expression level in human pre-B lymphocytic leukemia cell line KM3 treated with phorbolester

Abstract

Sialyl-Le(x) (sLe(x)) antigen expression recognized by KM93 monoclonaI antibody was significantly down-regulated during differentiation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in human pre-B lymphocytic leukemia cell line KM3. The sLe(x) determinants were almost exclusively expressed on O-linked oligosaccharide chains of an O-glycosylated 150-kDa glycoprotein (gp150). A low shear force cell adhesion assay showed that TPA treatment significantly inhibited E-selectin-mediated cell adhesion. Transcript and/or enzyme activity levels of α1→3-fucosyltransferase, α2→3-sialyltransferase, β1→4-galactosyltransferase, and elongation β1→3-N-acetylglucosaminyltransferase did not correlate with sLe(X) expression levels. However, transcript and enzyme activity levels of core 2 GlcNAc-transferase (C2GnT) were significantly down-regulated during TPA treatment. Following transfection and constitutive expression of full-length exogenous C2GnT transcript, C2GnT enzyme activities were maintained at high levels even after TPA treatment and down-regulation of cell surface sLe(x) antigen expression by TPA was completely abolished. Furthermore, in the transfected cells, the KM93 reactivity of gp150 was not reduced by TPA treatment, and the inhibition of cell adhesion by TPA was also blocked. These results suggest that sLe(x) expression is critically regulated by a single glycosyltransferase, C2GnT, during differentiation of KM3 cells.