Phospholipid modification retards intracellular transport and secretion of immunoglobulin G1 by mouse MOPC-31c plasmacytoma cells.

The intracellular transport and secretion of immunoglobulin G1(IgG1) by mouse MOPC-31C plasmacytoma cells were analyzed from the viewpoint of the roles of phospholipids. The membrane phospholipids were modified by culturing cells in a medium supplemented with choline analogues, N,N'-dimethylethanolamine or N-monomethylethanolamine, and accordingly the membranes were enriched in phosphatidyl-N,N'-dimethylethanolamine or phosphatidyl-N-monomethylethanolamine (Maeda, M., Tanaka, Y. and Akamatsu, Y. (1980) Biochem. Biophys. Res. Commun. 96, 876-881). The modified cells were pulse-labeled with L-[35S]methionine and the secretion of labeled IgG1 was chased. Half of the IgG1 was exported to the extracellular medium 1-1.5 h and 2-3 h after synthesis by choline- and dimethylethanolamine-supplemented cells, respectively. However, most of the newly synthesized IgG1 was not secreted by monomethylethanolamine-supplemented cells, even after 5 h; it remained within the cells. The sensitivity of intracellular IgG1 to endoglycosidase H was examined for probing the movement of IgG1 from the rough endoplasmic reticulum to the Golgi complex. Half of the newly synthesized IgG1 acquired resistance to endoglycosidase H after 30-45 min, 1-1.5 h and 2-3 h in choline-, dimethylethanolamine- and monomethylethanolamine-supplemented cells, respectively. Thus, the transport of IgG1 was markedly retarded by the modification with choline analogues, dimethylethanolamine or monomethylethanolamine, at least in the following two processes, from the rough endoplasmic reticulum to the Golgi complex and from the Golgi to the outside of cells. Modification with monomethylethanolamine was more effective than that with dimethylethanolamine in slowing down the transport of IgG1 and appeared to cause accumulation of IgG1 within the cells. A morphological study was also carried out for the three kinds of cell. The roles of phospholipids in the processes of membrane flow are discussed.