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Blood. 2008 Jun 1;111(11):5390-9. doi: 10.1182/blood-2007-10-119743. Epub 2008 Mar 18.

EPO receptor circuits for primary erythroblast survival.

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  • 1Stem and Progenitor Cell Biology Program, Molecular Medicine Division, Maine Medical Center Research Institute, Scarborough, ME 04074, USA.


EPO functions primarily as an erythroblast survival factor, and its antiapoptotic actions have been proposed to involve predominantly PI3-kinase and BCL-X pathways. Presently, the nature of EPO-regulated survival genes has been investigated through transcriptome analyses of highly responsive, primary bone marrow erythroblasts. Two proapoptotic factors, Bim and FoxO3a, were rapidly repressed not only via the wild-type EPOR, but also by PY-deficient knocked-in EPOR alleles. In parallel, Pim1 and Pim3 kinases and Irs2 were induced. For this survival gene set, induction failed via a PY-null EPOR-HM allele, but was restored upon reconstitution of a PY343 STAT5-binding site within a related EPOR-H allele. Notably, EPOR-HM supports erythropoiesis at steady state but not during anemia, while EPOR-H exhibits near wild-type EPOR activities. EPOR-H and the wild-type EPOR (but not EPOR-HM) also markedly stimulated the expression of Trb3 pseudokinase, and intracellular serpin, Serpina-3G. For SERPINA-3G and TRB3, ectopic expression in EPO-dependent progenitors furthermore significantly inhibited apoptosis due to cytokine withdrawal. BCL-XL and BCL2 also were studied, but in highly responsive Kit(pos)CD71(high)Ter119(neg) erythroblasts, neither was EPO modulated. EPOR survival circuits therefore include the repression of Bim plus FoxO3a, and EPOR/PY343/STAT5-dependent stimulation of Pim1, Pim3, Irs2 plus Serpina-3G, and Trb3 as new antiapoptotic effectors.

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