Ectopic and eutopic secretion of chorionic gonadotropin and its subunits in vitro: comparison of clonal strains from carcinomas of lung and placenta

We compared rates of secretion in vitro of human chorionic gonadotropin (HCG) and its subunits α and β by established clonal cell lines of a bronchogenic carcinoma (ChaGo) and a choriocarcinoma (JEG). Clones showing the highest secretion rates of either HCG or its subunits were studied: ChaGo-K1, a new clonal strain, and ChaGo-C5 and JEG-3, two previously reported clonal lines. Cells were grown under identical conditions in the same laboratory. Hormone and subunit concentrations were measured by radioimmunoassays. ChaGo-K1 and ChaGo-C5 secreted only α-subunit whereas JEG-3 secreted only HCG. Average peak secretion rates in picomoles/day/mg protein were: for ChaGo-K1, HCG<0.3, α=290, and β<0.5; for ChaGo-C5, HCG<0.3, α=21, and β<0.5; and for JEG-3, HCG = 18, α<0.7, and β<0.5. The ChaGo-K1 secretion rate of α was greater than that of any of our previously reported ChaGo clones. Significant quantities of estradiol and progesterone accumulated in the media of all three cell lines; however, only JEG-3 secreted detectable quantities of placental lactogen. Thus under identical culture conditions, a bronchogenic carcinoma clonal line secreted only α-subunit, whereas a choriocarcinoma line secreted only HCG; these findings implied major differences in cellular control mechanisms. Moreover, the ectopic secretions of α exceeded the eutopic trophoblastic secretion of HCG, which suggested that in certain cases ectopic protein production may be even more efficient than nonectopic production.