The goal of the project is to increase our understanding of the structure-function relationships and glycobiology of the glycan moieties on glycoprotein hormones. Molecules under investigation are, human chorionic gonadotropin (hCG), gonadotropin free alpha subunits associated with pregnancy or malignancy, and pituitary free alpha secreted throughout the normal menstrual cycle. We showed that free alpha stimulated secretion of prolactin and IGFBP-1 from primary cultures of human decidual cells in a dose-dependent manner. This finding indicated that free alpha is a glycoprotein hormone with functions that are independent of heterodimeric gonadotropins. We showed that free alpha demonstrates specific binding to endometrial stromal cells and plays a role in recruitment of cells for decidualization. This observation expands the function of the free alpha to include reproductive physiology associated with the luteal phase of the menstrual cycle and may indicate involvement 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. We have investigated functional aspects of the glycan moieties on free alpha, demonstrating that specific types of carbohydrate modifications on free alpha can either prevent or facilitate combination with hCG-beta to form intact hormone. We have shown that the glycan moieties on 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 glycan moieties of free alpha as a function of gestational development; in particular, the glycosylation of free alpha changes dramatically during the second trimester of pregnancy. Molecules produced in late pregnancy are more highly branched and are more fucosylated than those of early pregnancy. In view of the dramatic changes in glycosylation, it will be important to evaluate their contribution to free alpha bioactivity.
