Recombinant Human PlGF-2 Protein, CF

Placenta growth factor (PlGF) is a member of the PDGF/VEGF family of growth factors that share a conserved pattern of eight cysteines (1 ‑ 3). Alternate splicing results in at least three human mature PlGF forms containing 131 (PlGF‑1), 152 (PlGF‑2), and 203 (PlGF‑3) amino acids (aa) respectively (1 ‑ 3). Only PlGF‑2 contains a highly basic heparin‑binding 21 aa insert at the C‑terminus (1). In the mouse, only one PlGF that is the equivalent of human PlGF‑2 has been identified (3). Human PlGF‑2 shares 60%, 56%, 82%, 95% and 95% aa identity with mouse, rat, canine, equine and porcine PlGF‑2. PlGF is mainly found as a variably glycosylated, secreted, 55 ‑ 60 kDa disulfide linked homodimer (4). Mammalian cells expressing PlGF include villous trophoblasts, decidual cells, erythroblasts, keratinocytes and some endothelial cells (1, 5 ‑ 7). Circulating PlGF increases during pregnancy, reaching a peak in mid‑gestation; this increase is attenuated in preeclampsia (8). However, deletion of PlGF in the mouse does not affect development or reproduction. Postnatally, mice lacking PlGF show impaired angiogenesis in response to ischemia (9). PlGF binds and signals through VEGF R1/Flt‑1, but not VEGF  R2/Flk‑1/KDR, while VEGF binds both, but signals only through the angiogenic receptor, VEGF R2. PlGF and VEGF therefore compete for binding to VEGF R1, resulting in a PlGF inhibition of VEGF/VEGF R1 binding coupled to a subsequent promotion of VEGF/VEGF R2‑mediated angiogenesis (1, 5, 9, 10). However, PlGF (especially PlGF‑1) and some forms of VEGF can form dimers that decrease the angiogenic effect of VEGF on VEGF R2 (4, 5). PlGF‑2, like VEGF_164/165, shows heparin‑dependent binding of neuropilin (Npn)‑1 and Npn‑2, and can inhibit nerve growth cone collapse (11, 12). PlGF induces monocyte activation, migration, and production of inflammatory cytokines and VEGF. These activities facilitate wound and bone fracture healing, and also contribute to inflammation in active sickle cell disease and atherosclerosis (6, 7, 9, 13 ‑ 16). Circulating PlGF often correlates with tumor stage and aggressiveness, and therapeutic PlGF‑2 antibodies are being investigated for their ability to inhibit tumor growth and angiogenesis (5, 13).