SINGLE GLYCOSYLTRANSFERASE, CORE 2 BETA-1-]6-N-ACETYLGLUCOSAMINYLTRANSFERASE, REGULATES CELL-SURFACE SIALYL-LE(X) EXPRESSION LEVEL IN HUMANPRE-B LYMPHOCYTIC-LEUKEMIA CELL-LINE KM3 TREATED WITH PHORBOLESTER

Sialyl-Le(x) (sLe(x)) antigen expression recognized by KM93 monoclonal antibody was significantly down-regulated during differentiation indu ced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in human pre-B lymph ocytic leukemia cell line KM3. The sLe(x) determinants were almost exc lusively expressed on O-linked oligosaccharide chains of an O-glycosyl ated 150-kDa glycoprotein (gp150). A low shear force cell adhesion ass ay showed that TPA treatment significantly inhibited E-selectin-mediat ed cell adhesion. Transcript and/or enzyme activity levels of alpha 1- ->3-fucosyltransferase, alpha 2-->3-sialyltransferase, beta 1-->4-gala ctosyltransferase, and elongation beta 1-->3-N-acetylglucosaminyltrans ferase did not correlate with sLe(x) expression levels. However, trans cript and enzyme activity levels of core 2 GlcNAc-transferase (C2GnT) were significantly down-regulated during TPA treatment. Following tran sfection and constitutive expression of full-length exogenous C2GnT tr anscript, 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 trans fected cells, the KM93 reactivity of gp150 was not reduced by TPA trea tment, and the inhibition of cell adhesion by TPA was also blocked. Th ese results suggest that sLe(x) expression is critically regulated by a single glycosyltransferase, C2GnT, during differentiation of KM3 cel ls.