DEVELOPMENTAL REGULATION OF A PREGNANCY-SPECIFIC OLIGOSACCHARIDE STRUCTURE, NEUAC-ALPHA-2,6GALNAC-BETA-1,4GLCNAC, ON SELECT MEMBERS OF THE RAT PLACENTAL PROLACTIN FAMILY

Successful pregnancy is dependent upon an array of signaling proteins secreted by the trophoblast cells of the placenta, Among these is a gr oup of proteins related to pituitary prolactin, known as the prolactin /growth hormone family, These proteins are expressed at specific times during gestation and synthesized in distinct trophoblast cell types i n the rat placenta, We report here that select members of this family, prolactin-like protein (PLP-A), PLP-B, PLP-C, decidual/trophoblast PR P, and placental lactogen I variant, only which are expressed in the s pongiotrophoblast, late in rat placental development bear Asn-linked o ligosaccharides terminating with NeuAc alpha 2,6GalNAc beta 1,4GlcNAc beta-R. This reflects the concurrent expression of these prolactin/gro wth hormone family members with the peptide specific beta 1,4GalNAc-tr ansferase and an alpha 2,6-sialyltransferase, which can add sialic aci d to terminal beta 1,4-linked GalNAc, We have determined that at least one of the prolactin like proteins, PLP-A, is recognized by the prote in specific GalNAc-transferase. The presence of NeuAc alpha 2,6GalNAc beta 1,4GlcNAc beta-R on only a limited number of glycoproteins synthe sized by the spongiotrophoblasts between mid gestation and birth refle cts the need for both the GalNAc-transferase and the peptide recogniti on determinant for efficient addition of GalNAc. Thus, expression of t he GalNAc-transferase and specific members of the prolactin/growth hor mone family is developmentally regulated in the rat placenta, suggesti ng a physiological role for the terminal NeuAc alpha 2,6GalNAc beta 1, 4GlcNAc beta-R sequence on Asn-linked oligosaccharides of these protei ns.