ADENOSINE 3',5' - MONOPHOSPHATE AND PHORBOL ESTER INDUCE TRANSFORMING GROWTH FACTOR-BETA-1 MESSENGER-RIBONUCLEIC-ACID LEVELS IN CHORIOCARCINOMA CELLS

Transforming growth factor-beta-1 (TGF-beta-1), a regulator of growth and differentiation of many cell types, has previously been purified from the human placenta, and the messenger (m) RNA is abundantly expressed there. We found that the approximate 2.5-kilobase TGF-beta-1 mRNA is expressed in JEG-3 human choriocarcinoma cells, which have been widely used as a model system for studying the regulation of trophoblast hormone secretion. Cholera toxin (CT) elevates the cellular levels of the second messenger cAMP and increases the secretion of CG and steroids in these cells, thus being a potent inducer of trophoblast-differentiated functions. We show that CT also stimulates TGF-beta-1 mRNA levels in JEG-3 cells in a concentration- and time-dependent manner as studied by Northern and dot blotting. The maximal effect (about 5-fold increase above basal levels) occurs within 12-48 h of induction with a CT concentration of 1.0 ng/ml. The cell-permeable cAMP-analog 8-bromo-cAMP stimulates the accumulation of TGF-beta-1 mRNA in JEG-3 cells as well. Furthermore, this cAMP analog also induces TGF-beta-1 mRNA levels in normal cultured term placental cytotrophoblasts. 12-O-Tetradecanoyl phorbol-13-acetate, an active phorbol ester protein kinase C regulator and inducer of TGF-beta-1 mRNA in many cells, increases TGF-beta-1 mRNA accumulation in JEG-3 cells with a similar time course as cAMP analogs but to a lesser extent. Human HT-1080 fibrosarcoma and A-549 lung carcinoma cells exhibit up-regulation of TGF-beta-1 mRNA in response to TGF-beta-1 itself, but we show that activation of the cAMP-dependent pathway does not affect TGF-beta-1 mRNA levels in these cells. Cycloheximide, an inhibitor of protein synthesis, prevents the effect of CT and 12-O-tetradecanoyl phorbol-13-acetate on TGF-beta-1 mRNA expression in JEG-3 cells, suggesting that a protein mediator may be involved in the transduction of their effects. Our finding of a cAMP-dependent induction pathway for TGF-beta-1 mRNA expression in JEG-3 cells provides a new mechanism for the regulation of the synthesis of this ubiquitous growth and differentiation factor and suggests that TGF-beta-1 may have a role in trophoblast differentiation.