Indexed on: 06 Nov '09Published on: 06 Nov '09Published in: Endocrinology
Invasion of human trophoblasts is promoted through activation of wingless (Wnt) signaling, suggesting a role of the pathway in placental development and morphogenesis. However, details on the process such as involvement of canonical and/or noncanonical Wnt signaling cascades as well as their target genes are largely unknown. Hence, signal transduction via canonical Wnt signaling or phosphatidylinositide 3-kinase (PI3K)/AKT and their cross talk as well as trophoblast-specific protease expression were investigated in trophoblastic SGHPL-5 cells and primary extravillous trophoblasts purified from first-trimester placentas. Western blot analyses revealed that the recombinant Wnt ligand Wnt-3A increased phosphorylation of AKT and the downstream kinase glycogen synthase kinase (GSK)-3beta as well as accumulation of activated, nuclear beta-catenin. In accordance, luciferase expression of a canonical Wnt/TCF reporter and cell migration in first-trimester villous explant cultures and of SGHPL-5 cells were stimulated. Chemical inhibition of PI3K abolished Wnt-dependent phosphorylation of AKT and GSK-3beta and trophoblast motility but did not affect appearance of activated beta-catenin or Wnt/TCF reporter activity. In contrast, inhibition of the canonical pathway through soluble Dickkopf-1 did not influence AKT and GSK-3beta phosphorylation but reduced Wnt reporter activity, accumulation of active beta-catenin, and cell migration. Both inhibitors decreased Wnt-3A-induced secretion of pro- and active matrix metalloproteinase-2 from SGHPL-5 cells and pure EVT. The data suggest that Wnt-3A may activate canonical Wnt signaling and PI3K/AKT through distinct receptors. The two signaling cascades act independently in trophoblasts; however, both pathways promote Wnt-dependent migration and the release of matrix metalloproteinase-2, which has been identified as novel Wnt target in invasive trophoblasts.