THE ROLE OF MATRIX CONTACT AND OF CELL-CELL INTERACTIONS IN CHORIOCARCINOMA CELL-DIFFERENTIATION

Cell differentiation is supported much better by gels of extracellular matrix than by the same matrix provided as a rigid substrate, Many ce ll types including normal and malignant trophoblast cells, however, fo rm multicellular multilayered aggregates on matrix gels with increased cell-to-cell contacts as compared to regular monolayers on rigid matr ix substrates. In such cultures, it remained open, so far, whether sti mulated expression of differentiation markers is caused by enhanced ce ll-to-cell communication or is displayed only by cells in direct conta ct to the gel, Therefore, choriocarcinoma cells (BeWo) were grown as a ggregates: (a) on gels of the basement membrane-like Matrigel, (b) on plastic coated with poly-HEMA, or (c) as aggregates (spheroids) in sus pension culture, Production of the differentiation marker chorionic go nadotropin was stimulated significantly in aggregates attached to gels of Matrigel or to the poly HEMA substrate but not in suspended sphero ids. With respect to cell-cell communications, however, expression of E-cadherin mRNA was not altered in any type of aggregates, as compared to control cultures on plastic, The expression of connexin43 mRNA (no t of connexin26) was increased only in suspended spheroids, while micr oinjection of the fluorescent dye Lucifer Yellow suggested that cell c ommunication via gap junctions was absent from cells grown as monolaye rs and was not induced in any type of aggregate, When cells were grown on gels of Matrigel, the relevance of direct cellular contact to the substrate for differentiation was analyzed by immunohistochemistry Tro phoblastic differentiation markers (chorionic gonadotropin, placental lactogen, placenta-type alkaline phosphatase, and pregnancy-specific g lycoprotein beta 1) as well as the proliferation marker Ki-67 were not preferentially expressed in cells that were in contact with the gel. Similar random distributions of all these markers were also observed i n spheroids cultured in suspension, The distributions of several matri x molecules and of different integrins were comparable between aggrega tes on matrix gels and those in suspension culture. According to these data, cell-cell communication appears to play a subordinate role for cytodifferentiation in cell aggregates on matrix gels, so that substra te anchorage and physical properties of the substrate may be the decis ive factors. Interestingly, however, direct contact to the substrate d oes not seem to be essential for the stimulation of differentiation in cells on matrix gels, The results are discussed in the context of the ''tensegrity''(2))-model for cell-matrix interactions in which proper mechanical properties of the substrate are important for the regulati on of cell differentiation by allowing a balanced integrity of externa l and cell-internal tensile forces.