During implantation, the human embryo invades endometrial stromal tissues, reducing the intercellular connections among epithelial cell layers. Since Eph–ephrin interaction can induce repulsive forces to control cell position and movement, we examined the possible involvement of this system in intercellular dissociation among endometrial epithelial cells.
The expression of Eph A receptor on human endometrial epithelial cells and endometrial carcinoma-derived Ishikawa cells was examined by RT–PCR, immunohistochemistry and western blotting. The effects of recombinant ephrin A1 on Eph A2 phosphorylation in Ishikawa cells were also examined by western blotting. A permeability assay was performed to determine the effects of ephrin A1 on cell-to-cell adhesion.
Eph A1, A2 and A4 mRNAs were detected in human endometrial epithelial cells and Ishikawa cells, and ephrin A1 was present in human blastocysts. Immunohistochemical staining showed that Eph A1, A2 and A4 receptors were expressed on the cell surface region of luminal and glandular epithelial cells in human endometrium in both the proliferative and secretory phase. The presence of Eph A2 protein in the human endometrium was confirmed by western blot analysis. Recombinant ephrin A1 was bound to Ishikawa cells and induced phosphorylation of Eph A2 expressed in Ishikawa cells. In addition, stimulation by ephrin A1 for 20 min increased the permeability of monolayer Ishikawa cells versus control cultures (P < 0.01), without affecting cell viability.
This study demonstrated that the Eph–ephrin A system can promote intercellular dissociation in Ishikawa cells suggesting an important role in the initial step of embryo implantation by opening the endometrial epithelial cell barrier.
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