Effect of Tunicamycin on Release of Macromolecules and Tumor Antigens by Human Melanoma Cells¹

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 µg 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.