Identification and partial characterization of the unglycosylated peptide of carcinoembryonic antigen synthesized by human tumor cell lines in the presence of tunicamycin.

Unglycosylated peptide backbones of carcinoembryonic antigen (CEA) synthesized by human tumor cell lines in the presence of tunicamycin were identified and analyzed by SDS-polyacrylamide gel electrophoresis. Three tumor cell lines, QGP-1 (pancreas), FCC-1 (colon) and KNS-62 (lung) were found to produce CEA molecules of 180,000-190,000 mol. wts labeled with both [3H]leucine and [14C]glucosamine under conventional culture conditions. In contrast, in the presence of tunicamycin, the native CEA molecules disappeared, and a new component that was precipitated with anti-CEA antibodies and labeled only with [3H]leucine but not with [14C]glucosamine was identified in each cell line. Monoclonal antibodies each directed to different major antigenic determinants on the native CEA molecules also reacted with this unglycosylated peptide. The apparent mol. wts of the naked CEA peptides from QGP-1 and FCC-1 were equally about 78,000, whereas that from KNS-62 was somewhat larger than the other two, suggesting some differences in the peptide structure of the CEA molecules.