Differentiation of human trophoblast cells in vitro stimulated by extracellular matrix

Effects of extracellular matrix as a differentiation signal on cytotrophoblast cells isolated from human term placentae were tested in vitro (using: fibronectin, laminin, collagens type I and type IV, the basement membrane-like complex matrix Matrigel, and a complex matrix extracted from human term placenta). Whenever matrix components were presented as three-dimensional structures (gels, ‘g’, or thick layers, ‘d’) as opposed to protein coatings on tissue culture plastic (rigid, ‘r’-substrates) there was a pronounced effect on differentiation markers monitored. The culture morphology changed from monolayers on ‘r’-substrates to rounded colonies on ‘g’/‘d’-matrices, and the secretion of chorionic gonadotropin (hCG) was highly increased. The activity of the placental alkaline phosphatase was lower only on the ‘g’/‘d’-matrices, and the secretion of progesterone was reduced on all ‘r’-substrates but increased on gels of collagen type I. Similarities between the differentiation of trophoblast and BeWo choriocarcinoma cells (Hohn et al., 1992) were observed particularly in culture morphology and the expression of hCG. Some differences between BeWo cells and normal trophoblast were found in phosphatase activity and in progesterone production. The most obvious difference was the lack of fibronectin expression in BeWo, which appeared to cause the differences in adhesion to non-coated tissue culture plastic. While BeWo cells poorly attached to plastic, trophoblast cells adhered very well most probably through fibronectin produced by themselves, and mediated by the α5β1 fibronectin receptor (found in both cell types). Trophoblast cells preferentially bound to Matrigel and fibronectin whereas BeWo cells attached well to all substrates used. As opposed to differentiation, substrate adhesion did not depend on the structure of the substrate in both cell types. The differences observed in responsiveness between normal trophoblast andBeWo cells open interesting opportunities to investigate mechanisms of regulation and malfunctions leading to the malignancy of chroiocarcinoma cells. The lack of fibronectin expression may contribute to the malignant behavior of the BeWo cells.