Zfp36l2 is required for self-renewal of early erythroid BFU-E progenitors

Stem cells and progenitors in many lineages undergo self- renewing divisions, but the extracellular and intracellular proteins that regulate this process are largely unknown. Glucocorticoids stimulate red cell formation by promoting self-renewal of early erythroid burst forming unit-erythrocyte (BFU-E) progenitors1-4. Here we show that the RNA binding protein Zfp36l2 is a transcriptional target of the glucocorticoid receptor (GR) in BFU-Es and is required for BFU-E self-renewal. Zfp36l2 is normally downregulated during erythroid differentiation from the BFU-E stage but its expression is maintained by all tested GR agonists that stimulate BFU-E self-renewal, and the GR binds to several potential enhancer regions of Zfp36l2. Knockdown of Zfp36l2 in cultured BFU-E cells did not affect the rate of cell division but disrupted glucocorticoid-induced BFU-E self-renewal, and knockdown of Zfp36l2 in transplanted erythroid progenitors prevented expansion of erythroid lineage progenitors normally seen following induction of anemia by phenylhydrazine treatment. Zfp36l2 preferentially binds to mRNAs that are induced or maintained at high expression levels during terminal erythroid differentiation and negatively regulates their expression levels. Thus Zfp36l2 functions as part of molecular switch promoting BFU-E self-renewal and thus a subsequent increase in the total numbers of CFU-E progenitors and erythroid cells that are generated

Defining the Minimal Factors Required for Erythropoiesis through Direct Lineage Conversion

Erythroid cell commitment and differentiation proceed through activation of a lineage-restricted transcriptional network orchestrated by a group of well characterized genes. However, the minimal set of factors necessary for instructing red blood cell (RBC) development remains undefined. We employed a screen for transcription factors allowing direct lineage reprograming from fibroblasts to induced erythroid progenitors/precursors (iEPs). We show that Gata1, Tal1, Lmo2, and c-Myc (GTLM) can rapidly convert murine and human fibroblasts directly to iEPs. The transcriptional signature of murine iEPs resembled mainly that of primitive erythroid progenitors in the yolk sac, whereas addition of Klf1 or Myb to the GTLM cocktail resulted in iEPs with a more adult-type globin expression pattern. Our results demonstrate that direct lineage conversion is a suitable platform for defining and studying the core factors inducing the different waves of erythroid development

ZFP36L2 is required for self-renewal of early burst-forming unit erythroid progenitors

Stem cells and progenitors in many lineages undergo self-renewing divisions, but the extracellular and intracellular proteins that regulate this process are largely unknown. Glucocorticoids stimulate red blood cell formation by promoting self-renewal of early burst-forming unit–erythroid (BFU–E) progenitors. Here we show that the RNA-binding protein ZFP36L2 is a transcriptional target of the glucocorticoid receptor (GR) in BFU–Es and is required for BFU–E self-renewal. ZFP36L2 is normally downregulated during erythroid differentiation from the BFU–E stage, but its expression is maintained by all tested GR agonists that stimulate BFU–E self-renewal, and the GR binds to several potential enhancer regions of ZFP36L2. Knockdown of ZFP36L2 in cultured BFU–E cells did not affect the rate of cell division but disrupted glucocorticoid-induced BFU–E self-renewal, and knockdown of ZFP36L2 in transplanted erythroid progenitors prevented expansion of erythroid lineage progenitors normally seen following induction of anaemia by phenylhydrazine treatment. ZFP36L2 preferentially binds to messenger RNAs that are induced or maintained at high expression levels during terminal erythroid differentiation and negatively regulates their expression levels. ZFP36L2 therefore functions as part of a molecular switch promoting BFU–E self-renewal and a subsequent increase in the total numbers of colony-forming unit–erythroid (CFU–E) progenitors and erythroid cells that are generated.National Institutes of Health (U.S.) (Grant P01 HL 32262

HIF1α synergizes with glucocorticoids to promote BFU-E progenitor self-renewal

With the aim of finding small molecules that stimulate erythropoiesis earlier than erythropoietin and that enhance erythroid colony-forming unit (CFU-E) production, we studied the mechanism by which glucocorticoids increase CFU-E formation. Using erythroid burst-forming unit (BFU-E) and CFU-E progenitors purified by a new technique, we demonstrate that glucocorticoids stimulate the earliest (BFU-E) progenitors to undergo limited self-renewal, which increases formation of CFU-E cells > 20-fold. Interestingly, glucocorticoids induce expression of genes in BFU-E cells that contain promoter regions highly enriched for hypoxia-induced factor 1α (HIF1α) binding sites. This suggests activation of HIF1α may enhance or replace the effect of glucocorticoids on BFU-E self-renewal. Indeed, HIF1α activation by a prolyl hydroxylase inhibitor (PHI) synergizes with glucocorticoids and enhances production of CFU-Es 170-fold. Because PHIs are able to increase erythroblast production at very low concentrations of glucocorticoids, PHI-induced stimulation of BFU-E progenitors thus represents a conceptually new therapeutic window for treating erythropoietin-resistant anemia