Ectopic Production of Pregnancy-Specific β1-Glycoprotein by a Nontrophoblastic Tumor in Vitro*

Abstract

To demonstrate the ectopic production of pregnancy-specific β₁-glycoprotein (PSβG) 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 PSβG measured by a sensitive and specific RIA. The immunoreactive material was shown to cochromatograph with purified PSβG present in normal term pregnancy serum on a Sephadex G-150 column. The tumor PSβG was adsorbed to concanavalin A-Sepharose and eluted with a-D-methyl-glucoside in a manner similar to purified PSβG. The indirect immunoperoxidase method with anti-PSβG sera localized PSβG 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 PSβG production in a fashion quantitatively similar to that seen with hCG. The number of PSβG-staining intracellular vesicles also increased after exposure to butyrate. These studies provide direct evidence for the ectopic production of PSβG by a nontrophoblastic tumor cell line.