Effect of tunicamycin on synthesis and secretion of carcinoembryonic antigen by human colonic adenocarcinoma cells.

The effect of the glycosylation inhibitor, tunicamycin, on synthesis and secretion of the membrane-associated glycoprotein carcinoembryonic antigen (CEA), was studied in the LS174T human colon cancer cell line. Tunicamycin treatment inhibited total cellular glycoprotein synthesis but did not affect CEA levels of cellular homogenate, membrane or cytosol fractions as determined by enzyme immunoassay. Control cells metabolically labelled with 3H-glucosamine, 3H-leucine or 35S-cysteine exhibited membranous and extracellular (i.e. secreted) CEA with an MW of 200 kDa as judged by SDS-gel electrophoresis following immunoprecipitation. However, in the tunicamycin-treated cells several forms of CEA with lower MWs and representing molecules with decreased glycosylation could be detected in addition to the original CEA molecule of 200 kDa present in control cells. The rates of synthesis, secretion and turnover of the lower-molecular-weight forms of poorly glycosylated CEA that appear after tunicamycin treatment are similar to those of CEA in control cells. These data suggest that the carbohydrate portion of the CEA molecule is not essential in synthesis, incorporation into the membrane, and secretion of CEA by colon cancer cells in vitro.