Description
Human Placenta Growth Factor (PlGF) is a polypeptide growth factor and a member of the Platelet-Derived Growth Factor family but more related to Vascular Endothelial Growth Factor (VEGF). PlGF1 acts only as a very weak mitogen for some endothelial cell types and as a potent chemoattractant for monocytes. The physiological function in vivo is still controversial. In several reports it was shown not to be a potent mitogen for endotehlial cells and not angiogenic in vivo by using different assays. Very recently it was shown by one investigator, that PlGF1 from cell culture supernatants was angiogenic in the CAM assay and in the rabbit cornea assay. At least one high-affinity receptor for PlGF (FLT-1 or VEGF-R1) has been demonstrated in different primary cell types (e.g. human umbilical vein endothelial cells and monocytes), but PlGF does not bind to KDR/flk-1. Two different proteins can be generated by differential splicing of the human PGF gene: PlGF1 (131 aa native chain) and PlGF2 (152 aa native chain). Both mitogens are secreted proteins, but PlGF2 can bind to heparin with high affinity. PlGF1 is a homodimer, but preparations of PlGF show some heterogeneity on SDS gels depending of the varying degrees of glycosylation. All dimeric forms posses a similar biological profile. There is good evidence that heterodimeric molecules between VEGF and PlGF exists and that they are biological active. Different cells and tissues (e.g. placenta) express PlGF1 and PlGF2 at different rates. A very related protein of PlGF is VEGF with about 53% homology and VEGF-B with similar biological activities