The goal of the project is to increase our understanding of the structure-function relationships and glycobiology of the oligosaccharide moieties on glycoprotein hormones. Currently under investigation are, human chorionic gonadotropin (hCG), gonadotropin beta-core fragment, glycoprotein hormone free alpha subunits associated with pregnancy or malignancy, and pituitary free alpha subunits secreted throughout the normal menstrual cycle. We have shown that the free ` subunit purified from pregnancy urine stimulates secretion of prolactin from primary cultures of human decidual cells in a dose-dependent manner. This finding indicated that free alpha is a glycoprotein hormone with potential functions that are independent of heterodimeric gonadotropins. We further found that free alpha can play a role in recruitment of endometrial stromal cells for decidualization. This observation expands the function of the free alpha subunit into areas of reproductive physiology that occur during the luteal phase of the menstrual cycle and may suggest involvement of free alpha in implantation. Carbohydrate modifications, resulting in a variety of branched glycan structures, occur on all glycoproteins prior to secretion. These modifications can affect virtually every aspect of the molecule's behavior, including receptor binding and signal transduction, yet the underlying regulatory mechanisms remain elusive. We have investigated functional aspects of the glycan moieties on free `, demonstrating that specific types of carbohydrate modifications on free ` can either prevent or facilitate combination with hCG-beta to form intact hormone. We have found that the free alpha subunits that are located in fetal compartments in high concentrations during early pregnancy exhibit physical properties that are similar to those of the free alpha subunit isolated from pregnancy urine. We have shown that the oligosaccharide moieties on this early pregnancy free alpha function to maintain the molecule in an uncombined form in placental compartments that also contain high amounts of combinable free beta-subunit. We have identified differences in the oligosaccharide moieties of free alpha and hCG as a function of gestational development; in particular, the glycosylation of free alpha changes dramatically as pregnancy progresses. In five pregnancies examined thus far, the glycosylation changes were found to begin at week 14-15 of gestation and were completed by week 17, suggesting developmental regulation of glycoprocessing enzymes in the cells that secrete alpha subunit. We plan to examine how the differences observed in glycosylation affect the bioactivity of these molecules.
