Ectopic production of pregnancy-specific beta 1-glycoprotein by a nontrophoblastic tumor in vitro

To demonstrate the ectopic production of pregnancy-specific beta 1-glycoprotein (PSbetaG) by a nontrophoblastic tumor, the in vitro secretion of this glycoprotein was evaluated in an hCG-producing ovarian cystadenocarcinoma cell line maintained in long term cell culture. Parallelism was demonstrated between the immunoreactive material present in the tissue culture media and highly purified PSbetaG measured by a sensitive and specific RIA. The immunoreactive material was shown to cochromatograph with purified PSbetaG present in normal term pregnancy serum on a Sephadex G-150 column. The tumor PSbetaG was adsorbed to concanavalin A-Sepharose and eluted with alpha-D-methyl-glucoside in a manner similar to purified PSbetaG. The indirect immunoperoxidase method with anti-PSbetaG sera localized PSbetaG in secretory vesicles and in the endoplasmic reticulum of the tumor cells by light and electron microscopy. The addition of sodium butyrate to the tissue culture media stimulated PSbetaG production in a fashion quantitatively similar to that seen with hCG. The number of PSbetaG-staining intracellular vesicles also increased after exposure to butyrate. These studies provide direct evidence for the ectopic production of PSbetaG by a nontrophoblastic tumor cell line.