Vascular Endothelial Growth Factor Stimulates Proliferation but Not Migration or Invasiveness in Human Extravillous Trophoblast1

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Abstract
Vascular endothelial growth factor (VEGF) is a homodimeric glycoprotein that promotes angiogenesis and vascular hyperpermeability and interacts with two receptors, fms-like tyrosine kinase (Flt-1) and kinase domain-containing region (KDR). In situ localization in the pregnant human uterus revealed that VEGF mRNA is expressed primarily by the maternal decidua, whereas the receptor Flt-1 is expressed primarily by chorionic vascular endothelium and trophoblast cells—in particular, the extravillous trophoblast (EVT). We examined whether the mRNA and protein of VEGF and its receptors are expressed by invasive human first-trimester EVT cells propagated in culture and whether VEGF influences EVT cell proliferation, migration, and invasiveness. Proliferation was assessed by the uptake of [3H]thymidine. Invasion and migration across transwells were assessed by the degree of cellular transgression of a Millipore membrane coated, respectively, with and without Matrigel. Results of immunocytochemical and reverse transcription-polymerase chain reaction analysis revealed that both protein and mRNA of VEGF, Flt-1, and KDR were expressed by cultured normal EVT cells as well as their premalignant derivative produced by SV-40 Tag-immortalization, and BeWo choriocarcinoma cells. Under serum-free conditions, exogenous VEGF121 (the non-heparin-binding isoform) stimulated proliferation of all three cell lines in a concentration-dependent manner. The effects were abolished with a VEGF-neutralizing antibody. The same stimulatory effects on EVT cells were also seen with exogenous VEGF165 (a heparin-binding isoform), only after a cleaving of the heparin-binding domain with plasmin or a blocking of heparin binding sites with excess soluble heparan sulphate proteoglycans (HSPGs), suggesting a regulatory role of HSPGs. However, VEGF121 and VEGF165 (with and without the HSPG pretreatment) had no effect on normal EVT cell migration or invasiveness. Thus, VEGF may provide a dual role in angiogenesis and EVT cell proliferation during normal placental development.