Silencing SEC5 inhibits trophoblast invasion via integrin/Ca2+ signaling

The invasion of maternal decidua by extravillous trophoblast (EVT) is essential for the establishment and maintenance of pregnancy, and abnormal trophoblast invasion could lead to placenta-associated pathologies including early pregnancy loss and preeclampsia. SEC5, a component of the exocyst complex, plays important roles in cell survival and migration, but its role in early pregnancy has not been reported. Thus, the present study was performed to explore the functions of SEC5 in trophoblast cells. The results showed that SEC5 expression in human placental villi at first trimester was significantly higher than it was at the third trimester, and it was abundantly localized in the cytotrophoblast (CTB) and the trophoblastic column. SEC5 knockdown was accompanied by reduced migration and invasion in HTR-8/SVneo cells. In addition, the expression and plasma membrane distribution of integrin β1 was also decreased. Furthermore, shRNA-mediated knockdown of SEC5 inhibited the outgrowth of first trimester placental explants. SEC5 and InsP3R were colocalized in the cytoplasm of HTR-8/SVneo cells, and the cell-permeant calcium chelator BAPTA-AM could significantly inhibit HTR-8/SVneo cell invasion. The Ca2+ imaging results showed that the 10% fetal bovine serum-stimulated cytosolic calcium concentration ([Ca2+]c) was not only reduced by downregulated SEC5 but also was blocked by the InsP3R inhibitor. Furthermore, either the [Ca2+]c was buffered by BAPTA-AM or the knockdown of SEC5 disrupted HTR-8/SVneo cell F-actin stress fibers and caused cytoskeleton derangement. Taken together, our results suggest that SEC5 might be involved in regulating trophoblast cell migration and invasion through the integrin/Ca2+ signal pathway to induce cytoskeletal rearrangement.