Evidence for glucocorticosteroid receptors in the erythroid cell line of fetal rat liver

Comprehensive Proteomic Analysis of Human Erythropoiesis

Mass spectrometry-based proteomics now enables the absolute quantification of thousands of proteins in individual cell types. We used this technology to analyze the dynamic proteome changes occurring during human erythropoiesis. We quantified the absolute expression of 6,130 proteins during erythroid differentiation from late burst-forming units-erythroid (BFU-Es) to orthochromatic erythroblasts. A modest correlation between mRNA and protein expression was observed. We identified several proteins with unexpected expression patterns in erythroid cells, highlighting a breakpoint in the erythroid differentiation process at the basophilic stage. We also quantified the distribution of proteins between reticulocytes and pyrenocytes after enucleation. These analyses identified proteins that are actively sorted either with the reticulocyte or the pyrenocyte. Our study provides the absolute quantification of protein expression during a complex cellular differentiation process in humans, and it establishes a framework for future studies of disordered erythropoiesis.

Developmental regulation of erythropoietin and erythropoiesis

It is well established that erythropoiesis occurs first in the yolk sac, then in the liver, subsequently moving to the bone marrow and, in rodents, the spleen during development. The origin of the erythropoietic precursors and some factors suggested to be important for the changing location of erythropoiesis are discussed in this review. Until recently, the major site of erythropoietin (Epo) production in the fetus was thought to be the liver, but studies have shown now that the Epo gene is expressed strongly in the fetal kidney, even in the temporary mesonephros. The metanephric Epo mRNA is upregulated by anemia, downregulated by glucocorticoids, and contributes substantially to circulating hormone levels in hemorrhaged ovine fetuses. Other sites of Epo and Epo receptor production, likely to have important actions during development, are the placenta and the brain.

Mode of action of erythropoietin and glucocorticoids on the hepatic erythroid precursor cells: role of prostaglandins

The hypothesis that prostaglandins, and especially PGE2, are the second messengers of erythropoietin (Ep) and that glucocorticoids inhibit Ep action by inhibiting PG synthesis was tested on the erythroid cell line from fetal rat liver. The optimal (10(-9) M) stimulatory concentration of PGE2 did not reproduce, by far, the maximal effect of Ep on the growth of CFUE erythroid colonies. Ep did not increase PGE2 release in liquid culture media of cell suspensions made of the whole erythroid line or enriched (over 85%) in precursor cells. Ep did not modify the turnover rate of arachidonate. Nevertheless, indomethacin partially inhibited Ep effect on CFUE development, and this inhibition was abolished by PGE2. These results suggest that PGE2 potentiates Ep action but is not its second messenger. Spontaneous PGE2 release in liquid culture media brought about concentrations of the order of 10(-9) M, and 10(-7) M dexamethasone completely inhibited this release. Part of (but not all) the anti-Ep effects of glucocorticoids might thus be mediated this way. Dexamethasone effects required previous protein synthesis.

Glucocorticoid receptors in murine visceral yolk sac and liver during development

Specific binding of triamcinolone acetonide was analyzed in cytosols from developing mouse visceral yolk sac and fetal, neonatal and adult liver. In the visceral yolk sac, binding capacity increased from 1 X 10(3) sites/cell on day 10 to maximal levels (9 X 10(3) sites/cell) on day 14 of gestation. In fetal liver, binding sites were low (2 X 10(3) sites/cell) from day 14 to 18, increased rapidly after birth to approx. 1.7 X 10(4) sites/cell by day 9 postpartum and were present at approx. 3 X 10(4) sites/cell in adult liver. Scatchard analysis of the data indicated the presence of a single class of cytosolic binding sites of limited capacity and high affinity (Kd = 2-4 nM). The level of specific nuclear binding 2h after injection of [3H]triamcinolone acetonide was proportional to the number of cytosolic binding sites/cell for each tissue tested. The physicochemical characteristics of cytosolic glucocorticoid-receptor complexes were examined by DEAE-Sephadex A-50 column chromatography. "Unactivated" complexes from visceral yolk sac, fetal and adult liver eluted at approx. 0.4 M KCl. Heat "activated" complexes from fetal and adult liver eluted at approx. 0.25 M KCl, whereas those from visceral yolk sac eluted in the prewash fractions (0.02 M potassium phosphate buffer). These results provide evidence that quantitative but not qualitative changes in glucocorticoid receptors occur during liver development and also establish the presence of glucocorticoid receptors in the midgestation mouse visceral yolk sac.

Effect of aminoglutethimide on murine fetal hepatic erythroid colony formation

Pretreatment of pregnant mice with aminoglutethimide phosphate, an inhibitor of glucocorticoid synthesis, increases the content of fetal liver erythroid colony-forming cells (CFU-E), as assessed by the formation of erythroid colonies in vitro by fetal liver cells in plasma clots containing exogenous erythropoietin. In addition, the inability of aminoglutethimide to influence erythroid colony formation in vitro suggests that endogenous glucocorticoids exert a suppressive effect on the number of functional CFU-E in the fetal liver.

Kinetics of dexamethasone binding to the glucocorticoid receptor of intact erythroid cells from rat fetal liver

The erythroid cells from the rat fetal liver have been shown to possess a receptor for glucocorticoids. In the present work, the characteristics of [3H]dexamethasone binding have been studied on intact cells, in order to minimize receptor degradation, and at 4 degrees C, in order to prevent the activation of the hormone-receptor complex. Dissociation kinetics were those of a first-order reaction and the value of the rate constant of dissociation was similar to the values available in the literature. When studied at low concentrations of the ligand and using short-term incubations, association kinetics were apparently those of a simple bimolecular reaction. But at high ligand concentrations and/or using long-term incubations, association kinetics indicated a more complex reaction. Our results were compatible with the model proposed by Pratt W.B., Kaine J.L. and Pratt V.D. (J. Biol. Chem. 250 (1975) 4584-4591) for cytosolic preparations. This model implies the rapid formation of a transient unstable form of the complex, further converted into a stable form with slower kinetics. Equilibrium dissociation constant of the first (rapid) reaction was 80 microM and the rate constant of 'stabilization' was of the order of 70 X 10(-3) min-1. These values agree with the results of Pratt et al. relative to a cytosolic preparation from rat thymocytes.