Glycosylation of CD45: carbohydrate composition and its role in acquisition of CD45R0 and CD45RB T cell maturation-related antigen specificities during biosynthesis.
The contribution of oligosaccharides to the biochemical composition and antigen heterogeneity of the phosphotyrosine phosphatase CD45 glycoproteins has been studied on the K-562 erythroleukemic cell line. Treatment of immunoprecipitated CD45 glycoproteins with distinct exo- and endoglycosidases revealed the presence of highly sialylated O- and N-linked complex carbohydrates in the composition of mature CD45 glycoproteins. Incubation of K-562 cells with the N-glycosylation inhibitor tunicamycin blocked carbohydrate processing during biosynthesis of CD45 proteins, generating unglycosylated polypeptides similar in size to those resulting from digestion of CD45 proteins with a mixture of both N- and O-glycanases. Epitopes defining the T cell maturation related CD45R0 and CD45RB antigen specificities were present on the mature 180- and 190-kDa K-562 CD45 proteins, respectively. However, the CD45R0 and CD45RB epitopes were not detected on the high mannose biosynthetic CD45 precursors. Furthermore, treatment of CD45 proteins with O-glycanase or neuraminidase resulted in the loss of both CD45R0 and CD45RB epitopes, although reactivity of the anti-CD45R0 and anti-CD45RB mAb was not affected by mAb preincubation with either sialic acids or sialyllactose in solution. From these results we conclude that the blockade of early steps of N-glycosylation during carbohydrate processing resulted in the inhibition of subsequent incorporation of O-linked sugars on CD45 polypeptides, thus preventing the late acquisition of the CD45R0 and CD45RB determinants on the 180- and 190-kDa CD45 polypeptides.
Servicio de Immunología, Hospital de la Princesa, Universidad Autónoma de Madrid, Spain.
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Pulido
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Sánchez-Madrid
D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000276:immunology / Q000378:metabolism*; D000943:Antigens, Differentiation / Q000276:immunology / Q000378:metabolism*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology / Q000378:metabolism*; D000939:Epitopes; D006031:Glycosylation; D006649:Histocompatibility Antigens / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D017493:Leukocyte Common Antigens; D008970:Molecular Weight; D011233:Precipitin Tests; D011499:Protein Processing, Post-Translational; D012795:Sialoglycoproteins / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000276:immunology; D013950:Thymus Gland / Q000276:immunology
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D000945:Antigens, Differentiation, T-Lymphocyte; D000939:Epitopes; D006649:Histocompatibility Antigens; D012795:Sialoglycoproteins; D017493:Leukocyte Common Antigens