UDP-GlcNAc:Galβ1→3GalNAc (GlcNac to GalNAc) β1→6N-acetylglucosaminyltransferase holds a key role on the control of CD15s expression in human pre-B lymphoid cell lines

Expression mechanism of CD15s (sialyl-Le(X), sLe(X)) antigen has been investigated using human B lymphoid cell lines. sLeX structures were not expressed in mature B lymphoids but highly expressed in pre-B leukemia and pre-B lymphoma cell lines, The expression site was mainly on the O-linked oligosaccharide chains and E-selectin mediated-cell adhesion capability of sLe(X)-positive cells were significantly suppressed by benzyl-alpha-GalNAc treatment. Subsequently, the bases of the sLeX expression control mechanism were examined at the levels of enzymatic activities and transcripts of glycosyltransferases, (1) The activities of alpha 1-->3fucosyltransferase, alpha 2-->3sialyltransferase, beta 1-->4Gal-transferase, and elongation beta 1-->3GlcNAc-transferase, did not correlate with sLeX expression levels. (2) The transcripts of Fuc-TVII were not parallel with sLeX expression, and those of ST3Gal IV and beta 1-->4Gal-transferase were constitutively detected in all cell lines tested, (3) There was no detectable enzyme activity for core 3 and 4 backbone structure synthesis in human B cell lines. (4) By contrast, the enzyme activities and transcripts of UDP-GlcNAc: Gal beta 1-->3GalNAc (GlcNAc to GalNAc) beta 1-->6N-acetylglucosaminyltransferase (Core2GnT) had significant correlation with the cell surface expression of sLe(X) antigen. (5) Moreover, Western blot analysis revealed the presence of a major similar to 150 kDa glycoprotein that carries O-linked oligosaccharides recognized by anti-sLe(X) monoclonal antibody in sLe(X)-positive pre-B leukemia cell lines. This correlation of Core2GnT with CD15s expression suggests that Core2GnT is a regulator of the cell surface expression of sLe(X) in human pre-B lymphoid cells.