Synthesis and secretion of the ovarian cancer antigen CA 125 by the human cancer cell line NIH:OVCAR-3

To provide further information on the biochemical nature of the cellular and secreted forms of the mucin-like CA 125 ovarian cancer antigen. Pulse-chase experiments were performed in the NIH:OVCAR-3 ovarian cancer cell line with [S-35]Met/Cys radiolabeling. After pulsing the cells with radioisotope for 30 min and analyzing cell lysates by immunoprecipitation with anti-CA 125 antibodies, a doublet species (form B, approximately 400 kD) and a ladder of slower-moving components were detected by SDS-PAGE and autoradiography. After a 4-hour chase period, a much larger species (form A) became evident. With further culture, the B form disappeared and the A form accumulated, suggesting a 'precursor-product' relationship between the two forms. The putative precursor species did not appear in the culture supernatant, but secretion of the mature species (form A) began after about 1 h of synthesis. Lectin-binding experiments demonstrated that the B form is a glycoprotein and not an early apomucin precursor. In contrast to other reports, no smaller species of the mature form of CA 125 were detected in this study. Trypsin digestion severely degraded the antigen but discrete smaller fragments were not formed. CA 125 antigen is synthesized through a glycosylated 400-kD precursor species. The mature form of the antigen appears in the cell after about 1 h of synthesis and in the culture medium after 1-4 h. Copyright (C) 2001 S. Karger AG, Basel.