Estrogen influences dolichyl phosphate distribution among glycolipid pools in mouse uteri

Prominin-1 glycosylation changes throughout early pregnancy in uterine epithelial cells under the influence of maternal ovarian hormones

In preparation for uterine receptivity, the uterine epithelial cells (UECs) exhibit a loss of microvilli and glycocalyx and a restructuring of the actin cytoskeleton. The prominin-1 protein contains large, heavily glycosylated extracellular loops and is usually restricted to apical plasma membrane (APM) protrusions. The present study examined rat UECs during early pregnancy using immunofluorescence, western blotting and deglycosylation analyses. Ovariectomised rats were injected with oestrogen and progesterone to examine how these hormones affect prominin-1. At the time of fertilisation, prominin-1 was located diffusely in the apical domain of UECs and 147- and 120-kDa glycoforms of prominin-1 were identified, along with the 97-kDa core protein. At the time of implantation, prominin-1 concentrates towards the APM and densitometry revealed that the 120-kDa glycoform decreased (P<0.05), but there was an increase in the 97-kDa core protein (P<0.05). Progesterone treatment of ovariectomised rats resulted in prominin-1 becoming concentrated towards the APM. The 120-kDa glycoform was increased after oestrogen treatment (P<0.0001), whereas the 97-kDa core protein was increased after progesterone treatment (P<0.05). Endoglycosidase H analysis demonstrated that the 120-kDa glycoform is in the endoplasmic reticulum, undergoing protein synthesis. These results indicate that oestrogen stimulates prominin-1 production, whereas progesterone stimulates the deglycosylation and concentration of prominin-1 to the apical region of the UECs. This likely presents the deglycosylated extracellular loops of prominin-1 to the extracellular space, where they may interact with the implanting blastocyst.

Long-term effect of cyclic AMP on N-glycosylation is caused by an increase in the activity of the cis-prenyltransferase

Previously we have shown that long-term pretreatment of JEG-3 choriocarcinoma cells with 8-bromo-cAMP increases the capacity for N-glycosylation that was caused by an 8-10-fold enlargement of the dolichol pyrophosphoryl oligosaccharide (Dol-PP-oligosaccharide) pool [Konrad and Merz (1994) J. Biol. Chem. 269, 8659-8666]. The factors involved in the effect of cAMP on synthesis of Dol-PP-oligosaccharide are investigated here. The GlcNAc transfer to dolichol phosphate (Dol-P) was found to be unaffected by pretreatment with 8-bromo-cAMP. By measuring the uptake of [3H]mevalonate, a 20-fold increase in the incorporation of the label into Dol-P was observed in the cells treated with 8-bromo-cAMP. Under the same conditions, the synthesis of dolichol was enhanced 60-fold. However, the incorporation of the radioactivity into cholesterol was not increased in the JEG-3 cells pretreated with 8-bromo-cAMP, which suggests a specific stimulation of the dolichol/Dol-P pathway by cAMP. The cis-prenyltransferase activity was found to be increased 10-fold in cells pretreated with 8-bromo-cAMP. Dolichol kinase activity was unaffected by stimulation with 8-bromo-cAMP. The present study suggests that the larger glycosylation capacity in JEG-3 cells treated with 8-bromo-cAMP is caused by an increase in the microsomal cis-prenyltransferase activity.

A rapid procedure for the separation and analysis of metabolites of the sterol and dolichol pathways

We have previously shown that of several methods examined, the maximum yield of dolichyl phosphate (Dol-P) from rat liver was achieved by saponification of the tissue and subsequent extraction with diethyl ether (R.K. Keller et al. (1985) Anal. Biochem. 147, 166-173). In the present report, we have developed a rapid procedure using non-toxic solvents which resolves the ether extract on a C18 cartridge column into four major fractions: (1) fatty acids; (2) squalene and sterols; (3) dolichol; (4) Dol-P. The utility of the new procedure was demonstrated by preparing the four fractions from liver slices which had been incubated with [3H]acetate. HPLC analysis of the sterol, dolichol and Dol-P fractions yielded well resolved elution profiles, thereby allowing determination of radioactivity incorporated into the major isoprenoids and their metabolites.

Estrogen induces N-linked glycoprotein expression by immature mouse uterine epithelial cells

Characterization of complex glycoconjugates and the effects of estrogen on their expression in immature mouse uterine epithelial cells are reported. The secreted fraction contained nonanionic, O-linked lactosaminoglycan (LAG)-bearing proteins of Mr 30,000-40,000 as well as anionic, O-linked, LAG-bearing glycoproteins with very high apparent molecular weight (greater than 670K). Heparan sulfate (HS) proteoglycans and HS linked to little or no protein were found in the secreted fraction as well. A very similar array of glycoconjugates was found in the nonhydrophobic fraction of cell-associated macromolecules. In addition, the hydrophobic cell-associated fraction contained nonanionic, LAG-bearing glycoproteins of approximately 250K, anionic LAG-bearing glycoproteins distributing over a wide range of molecular weights, and HS proteoglycans with median molecular weights of approximately 250K. In contrast to the glycoproteins produced by their mature counterparts, virtually all glycoproteins produced by immature cells were O-linked. Estrogen treatment of immature mice caused uterine epithelial cells to secrete anionic, high molecular weight (greater than 670K) N-linked glycoproteins as a major product. These estrogen-responsive glycoproteins did not appear to contain LAGs. Estrogen treatment also markedly decreased the proportion of all hydrophobic glycoconjugates in the cell-associated fraction. Collectively, these observations indicate that one aspect of the estrogen-induced maturation of uterine epithelial cells is the stimulation of N-linked glycoprotein synthesis and secretion. Furthermore, stimulation of N-linked glycoprotein synthesis by itself is insufficient to support N-linked LAG glycoprotein production.

Dolichol-linked oligosaccharide and glycoprotein biosyntheses in glial cells in primary culture: development and enzymatic correlates

Primary cultures of cerebral glia derived from neonatal rat brain were utilized to determine 1) the developmental changes of dolichol-linked oligosaccharide and N-linked glycoprotein biosyntheses, 2) the enzymatic correlates of these developmental changes, and 3) the temporal relations between the biosyntheses of dolichol-oligosaccharide and N-linked glycoproteins and the biochemical expression of astrocytic and oligodendroglial differentiation. Marked, parallel developmental increases in the rates of incorporation of [3H]glucosamine into both dolichol-oligosaccharide and glycoprotein were observed, with maximal rates achieved after 9-10 days in culture and little change occurring over the next 10 days in culture. Concerning the enzymatic correlates, dolichol kinase exhibited a moderate developmental increase with a maximum at 5 days in culture, whereas the activities of the three critical enzymes that utilize dolichyl phosphate in the synthesis of the dolichol-linked oligosaccharide, i.e., N-acetylglucosaminylphosphotransferase (GlcNAc-1-P transferase), mannosylphosphoryldolichol (Man-P-Dol) synthase, and glucosylphosphoryldolichol (Glc-P-Dol) synthase, reached maxima after 6-9 days in culture. Both the activity of Man-P-Dol synthase in vitro and the rate of formation of its product, Man-P-Dol, in intact cells were shown to correlate closely with the rates of oligosaccharide and glycoprotein biosyntheses. An important regulatory role for Man-P-Dol synthase and its product, Man-P-Dol, was suggested further by the demonstration of a maturation-dependent activation by Man-P-Dol of GlcNAc-1-P transferase, the first committed step in the pathway. Two enzymatic markers of astrocytic (glutamine synthetase) and oligodendroglial (2',3'-cyclic nucleotide 3'-phosphohydrolase) differentiation exhibited marked developmental increases in activity with onset at the time of attainment of peak rates of dolichol-oligosaccharide and glycoprotein biosyntheses. Importance of the latter processes for glial differentiation is suggested.