Cooperation of Dex with Epo and SCF to induce renewal divisions of erythroid progenitors. (A) Erythroid progenitor cells can be expanded in vitro in the presence of Epo, SCF, and Dex. In the presence of Epo alone, they undergo terminal differentiation into mature enucleated erythrocytes, while addition of Dex and SCF leads to an expansion of immature erythroid progenitors (renewal). The expression of c-MYB and GATA1 was detected by Northern blot analysis on RNA isolated from erythroid progenitors differentiated from 0 to 72 hours in the presence of Epo (10 U/mL). Hybridization with NF-E2 was taken as a control for differentiation. (B) The I/11 erythroid progenitors were factor deprived for 4 hours (4h starvation) and subsequently restimulated with Epo (2 U/mL), SCF (100 ng/mL), and either Dex (10^–6 M) or the GR antagonist ZK (3 × 10^–6 M). Cells were harvested at the indicated times, and the expression of the indicated genes was analyzed by Northern blot analysis. Hybridization with GAPDH cDNA was performed as a loading control.