Effect of tunicamycin on release of macromolecules and tumor antigens by human melanoma cells.

Tunicamycin, an inhibitor of glycosylation, was used to examine whether glycosylation is required for shedding of tumor antigens and other macromolecules by human melanoma cells. Cellular proteins were labeled with [35S]methionine, glycoproteins with [14C]glucosamine, and external surface components with 125I by the lactoperoxidase method; 0.5 and 2.5 microgram tunicamycin/ml effectively inhibited glycosylation without significantly reducing protein synthesis. We found that release of labeled macromolecules in the presence or absence of tunicamycin was similar. Tunicamycin-treated cells released 10.2% of [35S]methionine, 29.8% of [14C]glucosamine, and 57.2% of 125I-labeled macromolecules in 24 h compared to 5.5, 14.9, and 50.8%, respectively, for untreated control cells; 62.5% of the radioactivity associated with cell-surface melanoma-associated antigens defined by specific antiserum were released in 24 h as opposed to 50.4% by untreated cells. These results indicate that release of many cellular proteins, including glycoproteins, external surface proteins, and some melanoma-associated antigens, does not require glycosylation.