Erythroid progenitor cells express functional RCAS1R.

(A) Expression of RCAS1R, glycophorin A, and TfR on ECFCs was determined by flow cytometry at indicated times during erythroid maturation in liquid culture with 15% FCS, 15% human AB serum, 20 ng/mL rhSCF, and 2 U/mL rhEPO. Upper panels show the time profile of the expression of glycophorin A and TfR during erythroid maturation. Middle panels show glycophorin A versus RCAS1R expression by 2-color cytometry. Lower panels show TfR versus RCAS1R expression. Data are representative of 2 independent experiments. (B) Expressions of Fas (■), RCAS1 (○), and RCAS1R (●) on ECFCs were determined by flow cytometry, at indicated times, in liquid culture. The expression of Fas is derived from 3 independent experiments. (C) Effect of nRCAS1 on DNA synthesis of ECFCs was determined by [³H]-thymidine uptake. ECFCs were incubated at 37°C, 5% CO₂ with or without nRCAS1 for 24 hours. For the last 6 hours of the culture period, cells were pulsed with 1 μCi [³H]-thymidine and collected onto glass filters. The incorporated radioactivity was measured using a Beta plate reader. Percentage inhibition was calculated by dividing radioactivity of the cells incubated with nRCAS1 by that without nRCAS1.