Adhesive interactions of trophoblast cells with endometrium are essential for embryo implantation in the uterus. Choriocarcinoma cells, the malignant counterpart of trophoblast, show pronounced invasiveness and are of interest for model studies. We describe here an in vitro model system for the study of adhesion of human JAR choriocarcinoma multicellular spheroids to different human endometrial epithelial cell lines (RL95-2, HEC-1A, KLE, AN3-CA) grown as monolayers. Cell characterization showed JAR spheroids to s++ecrete the placental hormones human chorionic gonadotropin and progesterone into the culture medium; distinct patterns of keratin, vimentin, and uvomorulin expression were seen in the endometrial cell lines. Spheroid attachment to endometrial monolayers was quantified using a centrifugal force-based adhesion assay, and morphology was examined by light and electron microscopy. Results showed the JAR spheroids to attach to three of the endometrial monolayers (RL95-2, HEC-1A, KLE) progressively over a 24-h period (by which time > or = 80% of the spheroids attached). Significant differences in spheroid attachment were most pronounced at 5 h (RL95-2 > HEC-1A > KLE and poly-D-lysine control, i.e. 90:45:17:17% attached). JAR spheroids did not attach to the endometrial cell line AN3-CA. Morphology revealed choriocarcinoma cells to begin to intrude between the uterine RL95-2 epithelial cells at 5 h. At 24 h, this intrusive type of penetration continued to be seen only with the RL95-2 monolayer. The assay system thus identifies differences in attachment properties between choriocarcinoma cells and various endometrial cell lines and forms the basis for further studies on the molecular interactions involved.

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At the initial phase of embryo implantation, the trophoblast must have acquired competence for adhesion to the uterine epithelium, a condition whose cell biological basis is far from understood. In the present study, trophoblast-type cells (BeWo, JAr, and Jeg-3 choriocarcinoma cell lines) were treated with retinoic acid, methotrexate, dibutyryl-cAMP, or phorbol-12-myristate-13-acetate in order to modulate their ability to adhere to uterine epithelial cells (RL95-2). In an established model, multicellular spheroids of choriocarcinoma cells were transferred onto the surface of monolayer cultures of RL95-2 cells followed by a centrifugal force-based adhesion assay. In controls, about 45% of BeWo and JAr cell spheroids and 75% of Jeg-3 spheroids adhered to uterine monolayers within 30 min. Pretreatment of spheroids with either of the agents stimulated differentiation as indicated by the rate of chorionic gonadotropin secretion, but consistently reduced the adhesion to the endometrial monolayer in all three choriocarcinoma cell lines. While previous investigations had shown that invasiveness of trophoblast cells (into extracellular matrix) does not seem to be linked to the differentiation program in a simple manner, the present data suggest that such an (inverse) link may indeed exist with respect to the ability to initiate an adhesive interaction with the uterine epithelium. These observations support the view that epithelial cell interactions as typical for the initial phase of embryo implantation are regulated in a way that is clearly different from cell-matrix interactions governing later phases of trophoblast invasion into the endometrial stroma.