Description
Pregnancy-specific beta-1-glycoprotein 1 (PSG1), also called SP1, PSG1 or B1G1 and designated CD66f, is a secreted glycoprotein of the human PSG family within the CEA (carcinoembryonic antigen) superfamily. PSG1 shares 84-91% amino acid (aa) sequence identity with the most similar family members, PSG3, 4, 6, 7, and 8. Mature PSG1 contains a V-type Ig-like domain that is important for adhesion (N1), and three C2-type Ig-like domains (A1, A2 and B2). Three potential isoforms vary at the extreme C-terminus. Although rodents express pregnancy-specific glycoproteins, identity with human PSG proteins is low and limited to the N1 domain. PSG1 is one of the most abundant fetal proteins found in maternal blood during pregnancy. It is secreted by syncytiotrophoblasts and exerts proangiogenic effect by inducing VEGF-A secretion and formation of tubes in endothelial cells. PSG1 also serves an immunomodulatory function through up-regulation of TGF-beta in macrophages, monocytes, and trophoblasts. In addition PSG1 has been shown to induce secretion of anti-inflammatory cytokines IL-10 and IL-6 in human monocytes. PSG1 binds Integrin alpha IIb beta 3 and inhibits platelet-fibrinogen interactions. Recent studies also suggest PSG1's involvement in cancer biology and correlation with chemotherapy resistance in breast cancer