STUDIES ON THE EFFECT OF THYROID-HORMONE AND EPIDERMAL GROWTH-FACTOR ON THE CULTURED HUMAN CYTOTROPHOBLAST

We have previously reported that human placental cytotrophoblasts (C-cells) contain nuclear 3,5,3'-triiodo-L-thyronine (T3) receptors. Using a C-cell culture system, the present study was undertaken to clarify some of the effects of T3 ans EGF on trophoblastic cells. C-cells were purified from human term placenta by treatment with trypsin-DNAse and percoll gradient centrifugation aggregated, then fused, differentiating into multinuclear syncytiotrophoblasts (S-cells) with incubation times up to 96 h in vitro. As the incubation time increased, the number of immunocytochemically reactive cells with antibodies to hCG-alpha, hCG-beta and hPL increased. Anti-EGF antibody reacted only with the initial C-cells, while anti-EGF receptor antibody reacted only with fused S-cells. Maximum secretion of hCG and hCG-alpha by the cultured cells was evident only when the cells were cultured in T3 (10(-8) M) or EGF (10 ng/ml) containing medium. When the initial cells were exposed to 10(-8) M T3 from 0 to 48 h of incubation, the secretion in 48-96 h was significantly accelerated. However, exposure from 48 to 96 h had no effect on peptide excretion. Although an exposure of these cells to 10 ng/ml EGF during 48-96 h of incubation stimulated the secretion of hCG and hCG-alpha, 0-48 h exposure did not produce any positive effect regardless of incubation time. These results indicated that the main target cell of T3 is the C-cell, while that of EGF is the S-cell. Furthermore, it is suggested that the interaction between T3 and its receptor facilitated functional cell differentiation. It is possible to propose a paracrine/autocrine control mechanism in which EGF synthesized by C-cells acts on S-cells.