Interleukin-3 (IL-3) inhibits erythropoietin-induced differentiation in Ba/F3 cells via the IL-3 receptor alpha subunit.
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 beta-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 beta-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-3RbetaIL-3 chain (EpoR/IL-3RbetaIL-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 alpha 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-3Ralpha chimera, in contrast, was capable of transmitting a weak Epo-induced proliferative signal but failed to stimulate accumulation of beta-globin mRNA. Most significantly, coexpression of the EpoR/IL-3Ralpha chimera with either EpoR/IL-3Rbeta or wild-type EpoRs suppressed Epo-induced beta-globin mRNA accumulation. Taken together, these results suggest an active role for the IL-3Ralpha subunit in inhibiting EpoR-specific differentiating signals.
Terry Fox Laboratory, British Columbia Cancer Agency, Vancouver, British Columbia V5Z 1L3, Canada. keith@terryfox.ubc.ca
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D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002999:Clone Cells; D004921:Erythropoietin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D005822:Genetic Vectors; D005914:Globins / Q000096:biosynthesis; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D007377:Interleukin-3 / Q000494:pharmacology*; D007700:Kinetics; D046911:Macromolecular Substances; D051379:Mice; D016297:Mutagenesis, Site-Directed; D012333:RNA, Messenger / Q000096:biosynthesis; D017467:Receptors, Erythropoietin / Q000096:biosynthesis / Q000502:physiology*; D016185:Receptors, Interleukin-3 / Q000737:chemistry / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism; D012190:Retroviridae; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
D007377:Interleukin-3; D046911:Macromolecular Substances; D012333:RNA, Messenger; D017467:Receptors, Erythropoietin; D016185:Receptors, Interleukin-3; D011993:Recombinant Fusion Proteins; D004921:Erythropoietin; D005914:Globins