Characterization of terminal sialic acid linkages on human thymocytes. Correlation between lectin-binding phenotype and sialyltransferase expression.
T cell surface sialylation changes during maturation in the thymus. We have previously demonstrated increased expression of mRNA encoding the Gal beta 1, 3GalNAc alpha 2,3-sialyltransferase in mature medullary human thymocytes, compared with immature cortical thymocytes. For this enzyme, increased expression of transferase mRNA correlated with increased sialylation of O-glycans. We have now examined the pattern of expression in the human thymus of two additional sialyltransferases, the Gal beta 1,4GlcNAc alpha 2,6-sialyltransferase (ST6N) and the Gal beta 1,3/4GlcNAc alpha 2,3-sialyltransferase (ST3N). The patterns of mRNA expression were compared with the pattern of binding of two sialic acid-specific plant lectins, Sambucus nigra agglutinin and Maackia amurensis agglutinin, which preferentially recognize alpha 2,6- and alpha 2,3-linked sialic acids, respectively, on N-glycans. By in situ hybridization, mRNA encoding ST3N was detected uniformly throughout the thymus. All thymocytes bound M. amurensis agglutinin, demonstrating a direct correlation between the level of ST3N mRNA expression and cell-surface glycosylation. In contrast, mRNA encoding ST6N was also expressed uniformly throughout the thymus; however, only mature (CD3hi) medullary thymocytes bound S. nigra agglutinin. On mature thymocytes, S. nigra agglutinin appeared to bind primarily to the cell-surface glycoprotein CD45; since only the mature thymocytes expressed the CD45RA isoform, while both mature and immature populations expressed the CD45R0 isoform, CD45RA may be a preferred substrate for ST6N. These results demonstrate that glycoprotein sialylation is tightly regulated during T cell development and that the developmentally regulated expression of specific oligosaccharide structures on the cell surface may be influenced by expression of both the relevant glycosyltransferase and specific acceptor substrates.
Baum
L G
LG
Department of Pathology, UCLA School of Medicine 90024-1732, USA.
Derbin
K
K
Perillo
N L
NL
Wu
T
T
Pang
M
M
Uittenbogaart
C
C
D002478:Cells, Cultured; D006801:Humans; D007150:Immunohistochemistry; D037102:Lectins / Q000378:metabolism*; D019158:N-Acetylneuraminic Acid; D010641:Phenotype; D012794:Sialic Acids / Q000737:chemistry / Q000378:metabolism*; D012799:Sialyltransferases / Q000235:genetics* / Q000378:metabolism; D013950:Thymus Gland / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase
D037102:Lectins; D012794:Sialic Acids; D012799:Sialyltransferases; C034256:beta-galactosyl(1-3)N-acetylglucosaminide alpha(2-3)-sialyltransferase; D019158:N-Acetylneuraminic Acid; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase