Sialidase expression in activated human T lymphocytes influences production of IFN-γ

Abstract

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.

NEU1 Sialidase Expressed in Human Airway Epithelia Regulates Epidermal Growth Factor Receptor (EGFR) and MUC1 Protein Signaling

“…Upon NEU1 Tyr-412 phosphorylation in activated lymphocytes, NEU1 is redistributed to the cell surface (48). In other studies, NEU1 was targeted to the plasma membrane of phorbol 12-myristate 13-acetate-differentiated human monocytes (47) and activated human T lymphocytes (49). In each case, NEU1 was accompanied by cathepsin A. NEU1 activation has been coupled to ligand engagement of TLR4 (36), the elastin receptor complex (37,38), and Trk A (39).…”

“…6). Although the mechanisms through which NEU1 might be translocated to the plasma membrane are poorly understood, it has been detected on the surface of multiple cell types (47)(48)(49). A tyrosine-containing internalization motif in the COOH terminus of NEU1, amino acids 412-415, reportedly targets the enzyme to the lysosome in COS-7 cells, human skin fibroblasts, and lymphocytes (48).…”

NEU1 Sialidase Regulates the Sialylation State of CD31 and Disrupts CD31-driven Capillary-like Tube Formation in Human Lung Microvascular Endothelia

“…Although NEU1 had been considered primarily a lysosomal enzyme (34,35), it is now known to associate with several surface multireceptor signaling complexes, including epidermal growth factor receptor/mucin 1 (MUC1) (37), Toll-like receptor 4 (TLR4)/ CD14/MD2 (38), and the elastin receptor complex (39). Although the mechanisms through which NEU1 might be translocated to the plasma membrane are poorly understood (40), it has been detected on the surface of multiple human cell types, including activated lymphocytes (40,41), phorbol 12-myristate 13-acetate differentiated monocytes (42), fibroblasts (43), and, most recently, erythrocytes (44). NEU1 is also surface-expressed on human lung microvascular endothelia, where it restrains EC migration into a wound (32).…”

Human immunosuppressive protein, galectin-1 emerges as a novel regulatory factor in autoimmune disorders

“…During T-cell activation, the expression of NEU1 on the cell surface is upregulated strikingly although NEU3 expression remains relatively constant [140]. In our experiments, NEU1 expressed at significantly lower level in SLE, RA and SS T-cells compared to control T-cells (Fig 12).…”