Sialidase expression in activated human T lymphocytes influences production of IFN-gamma.
Sialidases influence cellular activity by removing terminal sialic acid from glycoproteins and glycolipids. Four genetically distinct sialidases (Neu1-4) have been identified in mammalian cells. In this study, we demonstrate that only lysosomal Neu1 and plasma membrane-associated Neu3 are detected in freshly isolated and activated human T lymphocytes. Activation of lymphocytes by exposure to anti-CD3 and anti-CD28 IgG resulted in a ninefold increase in Neu1-specific activity after growth of cells in culture for 5 days. In contrast, the activity of Neu3 changed minimally in activated lymphocytes. The increase in Neu1 enzyme activity correlated with increased synthesis of Neu1-specific mRNA. Neu1 was present on the surface of freshly isolated and activated CD4 and CD8 T lymphocytes, as determined by staining intact cells with anti-Neu1 IgG and analysis by flow cytometry and by Western blot analysis of biotin-labeled cell surface proteins. Cell surface Neu1 was found tightly associated with a subunit of protective protein/cathepsin A (PPCA). Compared with freshly isolated lymphocytes, activated cells expressed more surface binding sites for galactose-recognizing lectins Erythrina cristagalli (ECA) and Arachis hypogaea. Growth of cells in the presence of sialidase inhibitors 2,3-dehydro-2-deoxy-N-acetylneuraminic acid or 4-guanidino-2-deoxy-2,3-dehydro-N-acetylneuraminic acid resulted in a smaller increase in number of ECA-binding sites and a greater amount of cell surface sialic acid in activated cells. Inhibition of sialidase activity also resulted in reduced expression of IFN-gamma in activated cells. The down-regulation of IFN-gamma occurred at the transcriptional level. Thus, sialidase activity in activated T lymphocytes contributes to the hyposialylation of specific cell surface glycoconjugates and to the production of IFN-gamma.
Nan
Xinli
X
Institute of Human Biology, and Department of Medicine, University of Maryland Medical Center, 725 West Lombard Street, Baltimore, MD 21201, USA.
Carubelli
Ivan
I
Stamatos
Nicholas M
NM
D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D006001:Glycoconjugates / Q000378:metabolism; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism*; D008213:Lymphocyte Activation; D019158:N-Acetylneuraminic Acid; D009439:Neuraminidase / Q000378:metabolism*; D013601:T-Lymphocytes / Q000201:enzymology* / Q000378:metabolism
D016207:Cytokines; D006001:Glycoconjugates; D007371:Interferon-gamma; C486385:NEU1 protein, human; C465436:Neu3 protein, human; D009439:Neuraminidase; D019158:N-Acetylneuraminic Acid