Transforming Growth Factor β Regulates Proliferation and Invasion of Rat Trophoblastic Cells.

Abstract

Implantation of embryo in the endometrium is a critical step for continuation of pregnancy and implantation failure is a major cause of infertility. In the rat, the implantation process involves invasion of the endometrial epithelial lining by the trophoblastic cells in order to reach the underneath stromal cells. Transforming Growth factor-β (TGF-β) is a multifunctional cytokine which regulates proliferation, differentiation and invasiveness of multiple cell lineages. One or more TGF-β isoforms (TGF-β1, TGF-β2 and TGF-β3) are secreted by the uterus during pregnancy, including at the time of implantation. Recently, we have showed that exposure to TGF-β3 increased the invasiveness of endometrial cells and the aim of the present study was to determine if TGF-β isoforms might be involved in the regulation of trophoblast invasiveness. We used the rat HRP-1 and RCHO-1 trophoblastic cell lines to perform this study. HRP-1 cells were derived from a normal midgestation chorioallantoic placenta, whereas RCHO-1 cells were established from a choriocarcinoma. MTT proliferation assays revealed that each TGF-β isoform decreased HRP-1 cell growth in a dose-dependent manner, whereas RCHO-1 cells were resistant to the growth-suppressive effect of TGF-β. Matrigel invasion assays showed that both HRP-1 and RCHO-1 cells exhibited intrinsic invasive ability under untreated conditions, and preliminary experiments have demonstrated that the capacity of HRP-1 cells to invade the Matrigel was selectively increased by TGF-β2 and TGF-β3, whereas the three TGF-β isoforms could increase the invasiveness of RCHO-1 cells. Activation of ERK, PI 3-K or Smad pathways is known to increase cellular motility and/or invasiveness, and we found that TGF-β activates these pathways in both HRP-1 and RCHO-1 cells in an isoform-specific manner. We thus recently initiated the characterization of the role of each of these pathways in TGF-β-induced invasiveness of trophoblastic cells. Preliminary studies showed that pharmacological inhibitor LY294002 could block TGF-β2-induced Akt phosphorylation and HRP-1 invasiveness, suggesting a role for PI 3-K activity in TGF-β2-induced invasiveness in this cell line. These important functional studies progressively reveal a key role for TGF-β in regulating the invasiveness of trophoblastic cells. Supported by NSERC (238501-06).