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Blood, 1 June 2008, Vol. 111, No. 11, pp. 5390-5399. Prepublished online as a Blood First Edition Paper on March 18, 2008; DOI 10.1182/blood-2007-10-119743.
Submitted October 23, 2007
Stem & Progenitor Cell Biology Program, Molecular Medicine Division, Maine Medical Center Research Institute, Scarborough, ME, United States * Corresponding author; email: wojchd{at}mmc.org.
EPO functions primarily as an erythroblast survival factor, and its anti-apoptotic actions have been proposed to involve predominantly PI3-kinase and BCL-X pathways. Presently, the nature of EPO-regulated survival genes has been interrogated through transcriptome analyses of highly-responsive, primary bone marrow erythroblasts. Two pro-apoptotic 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 KitposCD71highTer119neg 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 anti-apoptotic effectors.
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