Glycoprotein biosynthesis in quiescent and stimulated thymocytes and a T-cell lymphoma.

Abstract

Quiescent thymocytes, mitogen-stimulated thymocytes and acute-leukaemic lymphoblasts provide a model for the study of protein glycosylation in quiescent cells, mitotically active non-malignant and malignant cells respectively. The biosynthesis of both complex and high-mannose-type oligosaccharides was monitored by metabolic labelling with [6-3]fucose and [2-3H]mannose. Bio-Gel P6 elution profiles of [6-3H]fucose-labelled glycopeptides showed that quiescent thymocytes and stimulated thymocytes synthesized qualitatively and quantitatively similar glycopeptides; however, higher-molecular-weight glycopeptides were synthesized by the acute-leukaemic lymphoblasts. The amount of [2(-3)H]mannose incorporated into glycopeptide by quiescent thymocytes was less than 10% of that incorporated by stimulated thymocytes. The Bio-Gel P6 elution profile of [2(-3)H]mannose-labelled glycopeptides from acute leukaemic lymphoblasts was qualitatively similar to that of stimulated thymocytes, with about 40% of the radioactivity incorporated into one glycopeptide peak. This glycopeptide was characterized by Bio-Gel P6 and concanavalin A affinity chromatography, radioactive-sugar analysis, sensitivity to alpha-mannosidase and endoglycosidase H and resistance to beta-glucosaminidase as containing a high-mannose oligosaccharide, possible of Man7-8GlcNAc2 structure. Pulse/chase experiments indicated that this high-mannose oligosaccharide was an end product and not a biosynthetic intermediate. It is concluded that higher-molecular-weight fucose-labelled glycopeptides are characteristic of the malignant cell type, and the synthesis of high-mannose oligosaccharide, Man7-8GlcNAc2, in stimulated thymocytes and acute-leukaemic lymphoblasts is associated with mitotically active cells.