Differentiation- dependent regulation of adhesion molecules in trophoblast cells

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The trophoblast, an important component of the mammalian placenta, has several essential biological roles in the maintenance of pregnancy. First, trophoblasts must attach to the uterine endometrium, and then they must invade to a depth at which the vascular network exists. Here, we investigated the effects of epidermal growth factor (EGF) on a2 integrin expression, adhesiveness to collagen, and invasive activity using human BeWo choriocarcinoma cells. EGF induced the expression of a2 integrin mRNA and protein, as shown by Northern blotting, Western blotting, and flow cytometry. Human chorionic gonadotropin (hCG) secretion was enhanced by the addition of EGF, which suggests that the BeWo cells functionally differentiated similarly to normal trophoblasts. EGF also dose-dependently stimulated the invasiveness of BeWo cells. Antibody against a2 integrin inhibited this effect, suggesting that it may be mediated by an increase of cell surface integrin. EGF had no effect on the adhesiveness o … More f BeWo cells to collagen, whereas it stimulated the chemokinetic activity in a dose-dependent manner. The increase of chemokinetic activity was suppressed by antibody against a2 integrin. These results suggest that EGF may induce a2 integrin expression in trophoblasts, thereby enhancing their invasiveness into the endometrium via an increase of their chemokinetic activity.Transcriptional regulation of a5 integrin, one of the adhesion molecules that are induced in accordance with invasive activity of trophoblast, was also investigated. The following results were obtained.1) Flow cytometry analysis indicated that a5 integrin on BeWo cells were induced by the addition of EGF at 48 hours.2) The 5'-flanking region of the human a5 integrin gene was linked to the luciferase gene to monitor how this gene was regulated by the addition of EGF. EGF increased the transcriptional activity of a5 integrin promoter as high as 5 times compared to the basal level.3) The induction mentioned above was not suppressed by the addition of a MEK inhibitor (PD98059), suggesting that the action of EGF seemed to utilize a signaling pathway other than authentic MAP kinase cascade. Less