CD9 is expressed on human endometrial epithelial cells in association with integrins alpha(6), alpha(3) and beta(1).

Recently we reported that CD9 is involved in the invasion of a trophoblast-like choriocarcinoma cell line, BeWo, probably through the regulation of integrin functions. Integrins have also been reported to be expressed in the human endometrium and it has been suggested that they play important roles in blastocyst implantation. This study used immunohistochemistry to investigate the expression of CD9 in the endometrium during the menstrual cycle. CD9 was found to be intensely expressed on the cell surface of the glandular epithelium throughout the menstrual cycle without any apparent differences in staining intensity. In addition, Western blotting analysis of the affinity-purified proteins confirmed that CD9 was associated with integrins beta(1), alpha(3) and alpha(6) in the human endometrium. Therefore it can be concluded that CD9, in association with integrins alpha(6), alpha(3) and beta(1), is a constitutive molecule of the endometrial glandular epithelium. These results also suggest that CD9 may be an important regulator of these integrins in the human endometrium.