Elevation of the activities of glycosyl transferases involved in polylactosaminoglycan biosynthesis in autoimmune MRL lpr/ lpr mouse T cells

Abstract

Lymph node (LN) T cells from autoimmune MRL/MpJ- lpr/ lpr (lpr) mice and control MRL/MpJ- + / + ( + / + ) mice were compared as to glycosyl transferase activities involved in the biosynthesis of polylactosaminoglycans. The N-acetylglucosaminyl transferase (GlcNAc transferase) activity responsible for the extension of polylactosaminoglycans was assayed. The reaction products with this GlcNAc transferase were characterized by sequential glycosidase treatment and methylation analysis, and the enzyme was found to be classifiable as an UDP-GlcNAc: N-acetyllactosamine β1–3 GlcNAc transferase (polylactosamine extension enzyme). The activity of this GlcNAc transferase in T cells from enlarged LN of Ipr mice was 3–6 times higher than that in T cells from + / + mice. On the other hand, activated T cells from + / + mice only showed about a 2-fold increase in the activity of the transferase, compared with that in resting T cells. B cells from + / + mice also showed a significantly higher activity of the transferase than + / + T cells, the enzyme activity being comparable to or slightly lower than that in lpr T cells. Furthermore, when the reaction mixture contained both UDP-GlcNAc and UDP-Gal as donors, extension of the Gal-GlcNAc residue was observed. These results indicated the biosynthetic basis for the abundance of polylactosaminoglycans in lpr T cells and normal B cells. We also found that lpr T cells exhibited significant UDP-GlcNAc:asialo-bovine submaxillary mucin GlcNAc transferase activity. Only weak activity of this enzyme was detected in + / + resting and activated T cells, and B cells. This enzyme activity suggested the potential for polylactosaminoglycan formation on the mucin-type sugar chains on the surface of lpr T cells.