Re-expression of nonglycosylated surface IgA in trypsin-treated MOPC 315 plasmacytoma cells.

The importance of glycosylation for the re-expression of surface immunoglobulin in trypsin-treated MOPC 315 plasmacytoma cells was examined by using tunicamycin, an antibiotic that prevents glycosylation by inhibiting the formation of N-acetylglucosamine-lipid intermediates. Tunicamycin greatly inhibited the secretion of nonglycosylated MOPC 315 IgA in trypsin-treated cells. Two hours after trypsin treatment, there was an 80% inhibition of secretion as measured by immunoprecipitation assays of biosynthetically labeled immunoglobulin. However, tunicamycin had no effect on the time course of re-expression of surface IgA in these cells as measured by TNP-sheep erythrocyte rosette formation and [125I] TNP-albumin binding to the plasmacytoma cells. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of 125I-labeled cell surface IgA re-expressed in the presence of tunicamycin revealed a protein with an apparent m.w. identical to nonglycosylated MOPC 315 alpha-chains, further suggesting that nonglycosylated surface IgA was being inserted into the plasma membrane. This protein did not bind to concanavalin A-Sepharose. These data suggest that in MOPC 315 plasmacytoma cells, glycosylation is necessary for immunoglobulin secretion but not for immunoglobulin expression at the cell surface.