Human invasive trophoblasts transformed with simian virus 40 provide a new tool to study the role of PPARγ in cell invasion process

Invasive cytotrophoblasts play a key role in the development of human placenta and is therefore essential for subsequent development of the embryo. Human implantation is characterized by a major trophoblastic invasion that offers a unique model of a controlled and oriented tumor-like process. The ligand-activated nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) modulates cell growth and differentiation and might be therefore considered as a tumor suppressor. We have recently reported that PPARγ, in synergy with its dimerization partner retinoid X receptor (RXR)α, controls the invasion of human primary cytotrophoblasts. Because these cells are unable to replicate in culture, we have, in the present study, transformed these primary cells with the simian virus 40 large T antigen for studying the role of PPARγ in cell invasion process. Our results show that the cell line human invasive proliferative extravillous cytotrophoblast (HIPEC) 65 expressed markers of human invasive primary cytotrophoblast as determined by immunocytochemistry, immunobloting and real-time RT–PCR, and were highly invasive in vitro. We have next studied the role of PPARγ/RXRα heterodimers in cell proliferation and invasion. Our results show that PPARγ and RXRα are co-expressed by HIPEC 65 and that, as commonly observed, activation of PPARγ/RXRα heterodimers with the specific PPARγ agonist rosiglitazone induced lipid droplet accumulation as revealed by oil red O staining. Treatment with rosiglitazone or with the natural PPARγ agonist 15-deoxy-δ-(12,14) PGJ2 did not modify cell growth, but interestingly, activation of PPARγ by this synthetic (rosiglitazone) or natural (15d-PGJ2) ligand markedly inhibited cell invasion in a concentration-dependent manner. Finally, we showed that other potential natural PPARγ ligand such as oxidized—but not native—low-density lipoprotein inhibited cell invasion. This proliferative and invasive human cytotrophoblast cell line from extravillous origin provides a new tool for studying specifically the role of PPARγ in the control of cell invasion.