MON-025 Activin a Increases Human Trophoblast Invasion by Up-Regulating Integrinb1 Through ALK4

Activin A Increases Human Trophoblast Invasion by Up-regulating Integrin β1 Through ALK4 Following implantation, extravillous trophoblast cells (EVTs) derived from trophectoderm invade into the maternal decidua to a certain extent, which is tightly regulated by a variety of factors. Activin A, a member of the TGF-β superfamily, has been shown to stimulate the invasion of human trophoblasts (1). Integrin β1 has been implicated in cancer cell invasion and is consistently expressed in human preimplantation embryos (2). However, whether integrin β1 is integrated in activin A signaling and mediates activin A increased-human trophoblast invasion remain unknown. The objective of our study was to investigate the possible mediation role of integrin β1 in the pro-invasive effect of activin A on trophoblasts and illustrate the underlying molecular mechanisms. Primary and immortalized (HTR8/SVneo) cultures of human trophoblast cells were employed as study models. Real-time qPCR, Western blot, and small interfering RNA (siRNA)-mediated knockdown approaches were used to investigate the molecular determinants of activin A-mediated functions. The integrin β1 protein levels in poorly invasive BeWo,JAR and JEG-3 human choriocarcinoma cells were lower than that in highly invasive HTR8/SVneo cells and primary human EVTs, suggesting the possible essential role of integrin β1 in mediating human trophoblast invasion. The expression levels of integrin β1 were up-regulated in a time-dependent manner after activin A treatment in HTR8/SVneo cells. Importantly, siRNA-mediated down-regulation of integrin β1 significantly attenuated both basal and activin A-induced cell invasion in HTR8/SVneo cells as measured by transwell invasion assay. Interestingly, the TGF-β type I receptors (ALK4/5/7) inhibitor SB431542 abolished activin A-induced activation of SMAD2/SMAD3 as well as activin A-up-regulated integrin 1 expression. Moreover, siRNA-mediated down-regulation of ALK4 or SMAD4 attenuated activin A-up-regulated integrin β1 in both HTR8/SVneo cells and human primary EVT cells. These results reveal that activin A promotes human trophoblast cell invasion by up-regulating integrin β1 expression through ALK4-activated SMAD2/3-SMAD4 signaling pathway. Reference: (1) Bearfield et al., Eur J Endocrinol 2005;152:909–16. (2) Campbell et al., Hum Reprod 1995;10:1571–8.