Modification of CD43 and other lymphocyte O-glycoproteins by core 2 N-acetylglucosaminyltransferase.

CD43, the major leukocyte sialoglycoprotein, is expressed on T lymphocytes in two predominant glycoforms. CD43 115 kDa is a pan T cell marker and is specifically recognized by the monoclonal antibody S7. CD43 130 kDa is associated with T cell activation and is specifically recognized by the monoclonal antibody 1B11. The thymoma EL-4 has been identified to express mainly CD43 115 kDa and little or no CD43 130 kDa. Transfection of EL-4 cells with core 2 beta 1-->6N-acetylglucosaminyltransferase (C2GnT), an enzyme in the O-glycan biosynthesis pathway, resulted in an enhanced expression of the 1B11 epitope, CD43 130 kDa, and a loss of expression of the S7 epitope, CD43 115 kDa. Analysis of CD43 by SDS-PAGE revealed that CD43 in C2GnT transfected EL-4 cells has a molecular weight of 125 kDa compared to 115 kDa in nontransfected or control transfected EL-4 cells. SDS-PAGE analysis of three other lymphocyte O-glycoproteins, CD44, CD45, and RPTP alpha, revealed that C2GnT expression resulted in a molecular weight increase of approximately 3-5 kDa for each of these three cell surface glycoproteins. Our data indicate that, while CD43 may be a predominant substrate for C2GnT, other lymphocyte O-glycoproteins are also modified by this glycosyltransferase. Increased reactivity of cells with the monoclonal antibody 1B11, which specifically detects the expression of murine CD43 130 kDa, may thus be a marker of increases in branching of O-linked glycans generally.