Plasma membrane-associated pY397FAK is a marker of cytotrophoblast invasion in vivo and in vitro

During human pregnancy specialized placental cells of fetal origin, termed cytotrophoblasts, invade the uterus and its blood vessels. This tumor-like process anchors the conceptus to the mother and diverts the now of uterine blood to the placenta. Previously, we showed that the expression of molecul es with important functional roles, including a number of extracellular mat rix integrin receptors, is precisely modulated during cytotrophoblast invas ion in situ. Here we exploited this observation to study the role of the fo cal adhesion kinase (FAK), which transduces signals from the extracellular matrix and recruits additional signaling proteins to focal adhesions. Immun olocalization studies on tissue sections showed that FAK is expressed by cy totrophoblasts in all stages of differentiation. Because extracellular matr ix-induced integrin clustering results in FAK (auto)phosphorylation on tyro sine 397 (Y397FAK), we also localized this form of the molecule. Immunoloca lization experiments detected Y397FAK in a subset of cytotrophoblasts near the surface of the uterine wall. To assess the functional relevance of this observation, we used an adenovirus strategy to inhibit cytotrophoblast exp ression of FAK as the cells differentiated along the invasive pathway in vi tro. Compared to control cells transduced with a wild-type virus, cytotroph oblasts that expressed antisense FAK exhibited a striking reduction in thei r ability to invade an extracellular matrix substrate. When cytotrophoblast differentiation was compromised (hypoxia in vitro, preeclampsia in vivo), Y397FAK levels associated with the plasma membrane were strikingly lower, a lthough total FAK levels did not change. Together our results suggest that (auto)phosphorylation of Y397 on FAK is a critical component of the signali ng pathway that mediates cytotrophoblast migration/invasion.