Altered N-glycosylation in CD45 and regulatory roles of altered N-glycosylation in galectin-1-induced growth inhibition in human diffuse large B cell lymphoma

Abstract

Beta1-6 branching of L-PHA reactive oligosaccharides, one of the N-glycan structures, plays an important role in the biological behavior of various tumor cell lines. We reported previously that the expression of L-PHA reactive oligosaccharides was closely associated with the prognosis of patients with human diffuse large B cell lymphoma (DLBCL). In the present study, by Western blotting, we analyzed the N-glycosylation patterns in CD45 having L-PHA reactive oligosaccharides. In two cases of DLBCL which do and do not express non-sialylated L-PHA reactive oligosaccharides CD45 was found to be about 180-210 kDa and 180-200 kDa, respectively. Furthermore, after endoglycosidase F3 treatment the CD45 in both cases was found to be 190 or 160 kDa. Therefore, the differences in CD45 molecular weight between the two cases is due to differences in the amount of N-glycosylation. To clarify the biological functions of CD45 N-glycans in DLBCL, we analyzed the antiproliferative effects on human lymphoma cells of bovine galectin-1 (beta-galactoside-binding lectin-1), which reacts with CD45 N-glycans. Bovine galectin-1 stimulation of the DLBCL cell line HBL-2 resulted in inhibition of its growth in vitro. Swainsonine (SW) is a potent inhibitor of alpha-mannosidase II, which catalyzes the synthesis of complex type N-linked oligosaccharides. Reduction in expression of N-linked oligosaccharides, including L-PHA reactive oligosaccharides, on the cell surface by SW treatment prevented the growth inhibition of HBL-2 cells by galectin-1. On Western blots one 190 kDa isoform of the three CD45 isoforms which have N-linked oligosaccharide ligands for galectin-1, was detected with a reduction in molecular weight of about 5 kDa after SW treatment. These data suggested that the amount of CD45 N-glycans is reduced by SW treatment, and that this reduction of N-glycans prevents the interaction between CD45 and galectin-1. Alteration in N-glycosylation of CD45 may regulate lymphoma cell growth in DLBCL through the interaction between the N-glycans of CD45 and galectin-1.