Human chorionic gonadotrophin (HCG) and free alpha subunit secreted by cultured human choriocarcinoma (JEG-3) cells.

The cultured human choriocarcinoma JEG-3 cells secrete biologically active HCG and free HCG alpha-subunit. When compared with the alpha-subunit dissociated from HCG obtained either from pregnancy urine or JEG-3 cells, free alpha-subunit has a larger molecular weight, is more acidic and is non-functional, lacking the property to recombine with the HCG beta-subunit. The understanding of the biochemical differences observed between free alpha-subunit and alpha-subunit found in HCG is important and should help to unravel the biosynthesis of gonadotrophins. Two proteins which bind to the cell membrane, epidermal growth factor and concanavalin A, are capable of stimulating JEG-3 cell secretion. Epidermal growth factor stimulates the secretion of HCG while concanavalin A stimulates both HCG and HCG alpha-subunit secretion. Amphotericin B, an antifungal agent commonly used in tissue cultures, which also affects the cell membrane, was shown to stimulate HCG and HCG alpha-subunit secretions. The use of these agents should contribute to the understanding of membrane-related events which lead to the secretion of HCG and alpha-subunit.