It was recently demonstrated that erythropoietin combined with stem cell factor and transforming growth factor beta (EST; EPO+SCF+TGF-B) signals a pancellular reversal of gamma-globin gene silencing among ex vivo cultures of CD34+ cells when compared to cultures supplemented with erythropoietin (EPO) alone (

Bhanu et al., Blood. 2005; 105(1):387–93
). This primary human erythroblast culture model is now being utilized to study the molecular basis of globin gene regulation. In this study, we sought to determine whether EST-signaled effects are restricted to the gamma-globin gene(s). For this purpose, quantitative PCR (QPCR) assays were developed for the alpha-globin (zeta, mu, alpha, and theta) and beta-globin (epsilon, gamma, delta, and beta) gene clusters. EPO versus EST matched cultures from a total of 15 donors (3 single donors and two pools, 6 donors each) were investigated using culture day 7 proerythroblasts and day 14 hemoglobinized precursors. The QPCR products were quantified by comparison with plasmid-generated standard curves (20,000,000 to 200 copies). The patterns of mu-, alpha- and theta-globin gene expression were unchanged under all culture conditions. The delta- and beta-globin transcripts showed a significant reduction in levels in response to EST. In contrast, zeta-, epsilon- and gamma-globins all demonstrated significant increases in response to EST. The increases were consistently detected in the individual and pooled samples. The most dramatic increase in the zeta-, epsilon- and gamma-globins occurred at the proerythroblast stage of differentiation. On day 7, zeta-globin levels showed 190-fold increase (EPO: 6.9E+01±5.5E+01;EST: 1.3E+04±7.7E+03; p=0.01), epsilon-globin levels, a 27-fold increase (EPO: 1.0E+03±5.8E+02; EST: 2.7E+04±1.1E+04; p=0.001), and gamma-globin levels, a 13-fold increase (EPO: 9.1E+05±4.1E+05; EST: 1.2E+07±1.8E+06; p=0.001). Consistent with the 3–4 log difference between the levels of zeta- and epsilon-, versus gamma-globin copy numbers and the low sensitivity of HPLC compared with QPCR, no embryonic proteins were detected by reverse-phase HPLC (day 14 samples studied; 9 donors). However, G-gamma and A-gamma globin peaks confirmed EST-signaled activation of both gamma-globins genes (G-gamma/A-gamma= 1.0 in EPO versus 1.9 in EST; (total gamma)/(total gamma + beta-globin) = 3.7±2.4% in EPO versus 42.4 ±5.8% in EST; p=1.6E-08). These novel data suggest that cytokines can reverse the coordinated developmental silencing of human embryonic and fetal genes in both globin loci.

Topics:
embryo, erythroblasts, fetus, genes, globins, gamma-globins, beta-globin, erythropoietin, high pressure liquid chromatography procedure, alpha-globin

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2005, The American Society of Hematology
2005
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