Analysis of the involvemetnt of CD9 in the regulation of human trophoblast invasion

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Trophoblast invasion is one of the most important steps of implantation and placentation. Although many elements of trophoblast invasion resemble the events that occur during malignant tumor cell invasion, trophoblast invasion is confined spatially to the uterus and temporally to early pregnancy. However, the regulatory mechanisms which prevent the extravillous trophoblasts from further invasion are not well understood.The CD9 molecule is a 24-27 kDa cell surface glycoprotein, which may be related to Schwann cell migration and adhesion. In this study, we showed that CD9 was expressed on the extravillous trophoblasts in the cell columns of first trimester placentae, which invade into endometrium during implantation and placentation, but not on villous trophoblasts. Moreover, proteins were purified from chorion leave by affinity chromatography with anti-integrin alpha3 and alpha5 monoclonal antibodies and Western blotting, revealed that CD9 was associated with both integrins. In order to estimate the functional role of CD9 on trophoblasts, we used the human trophoblast-like choriocarcinoma cell line BeWo. Anti-CD9 monoclonal antibody (mAb) showed significant stimulatory effect on BeWo cell invasion. On the other hand, mAbs against integrins alpha3 and alpha5 inhibited BeWo cell invasion. Anti-CD9 mAb also showed a stimulatory effect on BeWo cell invasion under the treatment with mAb against integrin alpha3. In contrast, it had no effect under the treatment with mAb against integrin alpha5.These findings indicate that CD9 is deeply related to the invasive properties of BeWo cells and that the role of CD9 in WeBo cell invasion is partially mediated by integrin alpha5, suggesting the involvement of CD9 in trophoblastic invasion.