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During early pregnancy, cytotrophoblast cells differentiate into extravillous trophoblast (EVT) cells and invade the uterine spiral arteries. This physiological process is essential for the development of maternal-fetal circulation. Because EVT cells are exposed to a low-oxygen environment during this process, we investigated the role of hypoxia in the mechanism that regulates the invasive behavior of EVT cells. Real-time PCR and immunofluorescent analysis were performed to investigate how hypoxia influences the expression of E-cadherin in villous explants cultures and in trophoblast-derived BeWo cells. We determined that hypoxia induced E-cadherin down-regulation through Snail up-regulation in villous explant cultures. The influence of E-cadherin loss was examined by analyzing the expression of alpha(5)-integrin and phosphorylated focal adhesion kinase (FAK) by Western blot and evaluating trophoblast invasion using a matrigel invasion assay. E-cadherin loss induced the up-regulation of alpha(5)-integrin, which leads to the tyrosine phosphorylation of FAK, resulting in an increase in the invasive activity of EVT cells. An alpha(5)-integrin neutralizing antibody inhibited the invasion of EVT cells by attenuating FAK tyrosine phosphorylation. Immunohistochemical analysis using clinical placental bed biopsies revealed that alpha(5)-integrin was up-regulated and FAK tyrosine phosphorylated (Try(861)) as EVT cells invade the uterine myometrium, whereas E-cadherin expression was down-regulated. These results suggest that alpha(5)-integrin up-regulation induced by E-cadherin loss under hypoxia has a crucial role in regulating the migration of EVT cells. This finding should help us reach a better understanding of the pathogenesis of critical gestational diseases, such as preeclampsia.