Estrogen regulation of the central enzymes involved in O- and N-linked glycoprotein assembly in the developing and the adult rabbit endocervix.

During cervical differentiation in 1- to 6-month-old rabbits, a marked increase was observed in the titer of serum estradiol, the number of secretory cells in the endocervix, and the granule content of these cells. Because these secretory granules are rich in carbohydrates it seemed likely that hormones regulate glycoconjugate biosynthesis in the endocervix. To investigate this possibility, the synthesis of O- and N-linked glycoproteins was studied in cell-free preparations from endocervical epithelium. The activity of N-acetylgalactosaminyl (GalNAc) transferase, the first enzyme in the pathway for O-linked oligosaccharide chain biosynthesis, measured in microsomes prepared from the developing cervix, was increased 8-fold. Oligosaccharyltransferase, the enzyme that catalyzes the first step in the attachment of N-linked oligosaccharide chains to proteins, was measured in microsomes prepared under the same conditions as those used for GalNAc transferase. The results of two independent assay methods revealed an estrogen-dependent 10- to 15-fold increase in oligosaccharyltransferase during cervical differentiation. Consistent with these developmental effects, ovariectomy of adult rabbits resulted in reduced (P less than 0.01) titers of serum estradiol and a 2-fold reduction in the specific activity of GalNAc transferase. When animals were treated with exogenous estradiol, GalNAc transferase activity returned to estrous control levels. The antagonistic action of progesterone on GalNAc transferase activity was verified using endocervical membranes from pseudopregnant animals. Similarly, oligosaccharyltransferase activity was reduced 2- to 3-fold when estrous animals were ovariectomized or made pseudopregnant. The treatment of ovariectomized animals with estradiol resulted in the restoration of oligosaccharyltransferase to estrous control values. Collectively, these results provide the first definitive evidence that hormones can regulate the activity of the enzymes involved in the attachment of O- and N-linked oligosaccharide chains to proteins in the endocervix.