Cultured human syncytiotrophoblasts synthesize pregnancy-specific beta-1-glycoprotein (SP1)

The synthesis of pregnancy-specific beta-1-glycoprotein (SP1) was studied in human syncytiotrophoblast cultures from first trimester placentas. Incorporation of 35S-methionine into SP1 was demonstrated by immunoprecipitation and polyacrylamide gel electrophoresis. In double diffusion the precipitation line of neosynthesized SP1 gave a reaction of complete immunological identity with maternal serum SP1. By indirect immunofluorescence intracellular SP1 was localised in the perinuclear region of the cells. The average rate of SP1 release into culture fluid was 600 ng/mg protein in 24 hours. On a molar basis the release of SP1 was 10 times less than that of human chorionic gonadotrophin (hCG). Our results demonstrate, for the first time, that cultured human syncytiotrophoblasts synthesis SP1 immunologically indistinguishable from placental SP1.