HUMAN CHORIONIC-GONADOTROPIN SECRETION AND PROTEIN-PHOSPHORYLATION INCHORIONIC TISSUE

The signal transduction system acts either monodirectionally (synergis tically) or bidirectionally (antagonistically) in different tissues. W e activated the signal transduction system in BeWo human choriocarcino ma cells and studied the effects on human chorionic gonadotropin (hCG) secretion, cell proliferation, and DNA synthesis. Protein phosphoryla tion in the cytosolic fraction was also studied by two-dimensional pol yacrylamide gel electrophoresis. When phorbol 12-myristate 13-acetate (PMA) was added to cultures, hCG secretion was increased dose-dependen tly, but cell proliferation and H-3-thymidine uptake were not affected . When only cholera toxin was added, hCG secretion was also stimulated dose-dependently, but when both PMA and cholera toxin were added ther e was a synergistic potentiation of hCG production. In contrast, Ca io nophore A23187 had almost no effect on hCG secretion. Two-dimensional gel electrophoresis and autoradiography showed that phosphorylation of a 33 kd acidic protein was produced by cholera toxin, while phosphory lation of a 45 kd acidic protein and dephosphorylation of a 14 kd acid ic protein were caused by the phorbol ester. These proteins may be spe cific substrates of protein kinase A and protein kinase C, respectivel y, in BeWo cells.