Induction of glycoprotein biosynthesis in activated B lymphocytes

Resting murine splenic B lymphocytes (B cells) can be stimulated to proliferate by exposure to a variety of polyclonal activators. To investigate changes in glycoprotein synthesis that occur during the activation process, N-glycosylation activity was assessed by following the incorporation of [2-³H]mannose into dolichol-linked oligosaccharide intermediates and glycoprotein after B cells were exposed to anti-immunoglobulin M (anti-μ). Stimulation of B cells by anti-μ resulted in a dramatic induction of N-glycosylation activity. The incorporation of radiolabeled mannose into oligosaccharide-lipid increased 9-fold while the rate of labeling of glycoprotein increased 27-fold between 18 and 38 h after exposure to anti-μ. Maximal stimulation of N-glycosylation activity was observed at an anti-μ concentration of 20-50 μg/ml. Similar results were obtained when B cells were activated by bacterial lipopolysaccharide (LPS), another polyclonal activating agent. The major dolichol-bound oligosaccharide labeled during the induction period was determined to be Glc₃Man₉GlcNAc₂ by HPLC analysis. Nearly full induction of oligosaccharide-lipid synthesis and protein N-glycosylation was also seen when DNA synthesis was suppressed by activating B cells with anti-μ in a serumfree medium, or by activating with anti-μ or LPS in the presence of hydroxyurea. The results suggest that the N-glycosylation pathway is induced during the G₀ to G₁ transition or during the G₁ period, and that entry into S phase is not required. These studies describe a striking developmental increase in N-glycosylation activity and extend the information on biochemical changes occurring during the activation of B cells.