Interleukin-3 (IL-3) inhibits erythropoietin-induced differentiation in Ba/F3 cells via the IL-3 receptor α subunit

Abstract

Introduction of erythropoietin receptors (EpoRs) into the interleukin-3 (IL-3)-dependent murine hemopoietic cell line, Ba/F3, enables these cells to not only proliferate, after an initial lag in G1, but also to increase β- globin mRNA levels in response to erythropoietin (Epo). With IL-3 and Epo costimulation, IL-3-induced signaling appears to be dominant since no increase in β-globin mRNA occurs. Differentiation and proliferation signals may be uncoupled since EpoRs lacking all eight intracellular tyrosines were compromised in proliferative signaling but retained erythroid differentiation ability. Intriguingly, a chimeric receptor of the extracellular domain of the EpoR and the transmembrane and intracellular domains of IL-3Rβ(IL-3) chain (EpoR/IL-3Rβ(IL-3)) was capable of Epo-induced proliferative and differentiating signaling, suggesting either the existence of a second EpoR subunit responsible for differentiation or that the α subunit of the IL-3 receptor (IL-3R) prevents it. Arguing against the former, a truncated EpoR lacking an intracellular domain was incapable of promoting proliferation or differentiation. An EpoR/IL-3Rα chimera, in contrast, was capable of transmitting a weak Epo-induced proliferative signal but failed to stimulate accumulation of β-globin mRNA. Most significantly, coexpression of the EpoR/IL-3Rα chimera with either EpoR/IL-3Rβ or wild-type EpoRs suppressed Epo-induced β-globin mRNA accumulation. Taken together, these results suggest an active role for the IL-3Rα subunit in inhibiting EpoR-specific differentiating signals.