EXPRESSION OF INTEGRIN ALPHA-6-BETA-4 IN HUMAN TROPHOBLAST AND ITS LOSS FROM EXTRAVILLOUS CELLS

Villous trophoblast from first trimester and term placenta expresses the integrin subunits α6 and β4, as monitored by immunohistochemistry. The subunits, which codistribute in all locations, are present at the basal cell surface where cyto- and syncytiotrophoblast make contact with the villous basement membrane and, in addition, in areas of contact between cytotrophoblast or cyto- and syncytiotrophoblast, but both are absent from the apical syncytial surface. This distribution, which together with other evidence suggests that the two subunits are associated in trophoblast as the heterodimer α6β4, differs from other epithelia in which α6β4 is predominantly basally disposed. Anti-cytokeratin antibodies were used to identify cytotrophoblast columns at the tips of anchoring villi and the migratory interstitial extravillous cytotrophoblast population in the placental bed. Cells in the columns showed a level of expression that diminished with distance from the villous basement membrane, and the α6 and β4 subunits were not detected in interstitial cytotrophoblast. In trophoblast of the chorion laeve, both the subunits were expressed in all layers from the pseudobasement membrane to the edge of the parietal decidua, but not in the decidua itself. Integrin α6β4 distribution was also examined in primary cultures of term trophoblast and in the choriocarcinoma cell line BeWo. The α6 and β4 subunits were present at or near cell contact areas, where basement membrane components including laminin were also detected. The results suggest that integrin α6β4 plays a role in anchoring trophoblast to basement membrane and its loss may play a role in enabling cells to migrate into the maternal tissue compartment. © 1993, Baillière Tindall. All rights reserved.