A cell stress signaling model of fetal hemoglobin induction: what doesn't kill red blood cells may make them stronger  Rodwell Mabaera, Rachel J. West, Sarah J. Conine, Elizabeth R. Macari, Chelsea D. Boyd, Cocav A. Engman, Christopher H. Lowrey  Experimental Hematology  Volume 36, Issue 9, Pages 1057-1072 (September 2008) DOI: 10.1016/j.exphem.2008.06.014 Copyright © 2008 ISEH - Society for Hematology and Stem Cells Terms and Conditions

Figure 1 β-like globin gene expression during human development. (A) Structure of the human β-globin gene locus including the embryonic (ɛ), fetal (γ), and adult (δ and β) β-like globin genes and the 5 DNase hypersensitive sites that comprise the upstream locus control region. (B) Developmental patterns of β-like globin gene expression. Figure 1B is redrawn from reference [23]. Experimental Hematology 2008 36, 1057-1072DOI: (10.1016/j.exphem.2008.06.014) Copyright © 2008 ISEH - Society for Hematology and Stem Cells Terms and Conditions

Figure 2 β-like globin gene expression during in vitro differentiation of human adult erythroid cells. (A) Expression patterns of the human γ- and β-globin genes during in vitro erythroid differentiation of primary human CD34+ peripheral blood cells. Note that the curves present normalized data to highlight the time course of gene expression. Absolute levels of γ-globin mRNA are roughly 10-fold less than for β-globin. (B) The effect of 5-azacytidine treatment on γ-globin mRNA levels during in vitro erythroid differentiation. Drug was added to 500 nM daily from days 10 to 20 of differentiation. Figures based on data originally published in Blood. Mabaera et al. Neither DNA hypomethylation nor changes in the Kinetics of erythroid differentiation explain 5-azacytidine's ability to induce human fetal hemoglobin. Blood. 2008;111:411–420. © the American Society of Hematology. Experimental Hematology 2008 36, 1057-1072DOI: (10.1016/j.exphem.2008.06.014) Copyright © 2008 ISEH - Society for Hematology and Stem Cells Terms and Conditions

Figure 3 Proposed cell stress signaling model of fetal hemoglobin (HbF) induction. Under this model, many different cellular stresses, including those caused by HbF-inducing drugs activate coordinated stress responses, which include γ-globin gene activation. Potential pathways involved in these responses include the integrated stress response (also known as unfolded protein response), p38 mitogen-activated protein kinase (MAPK) and cyclic adenosine monophosphate (cAMP) signaling pathways. Blue ovals indicate examples of HbF-inducing agents that have been shown to act, at least in part, through the p38 MAPK stress signaling pathway. Solid red ovals indicate pathway members that have been experimentally implicated in HbF induction. Dashed red circles indicate factors that are involved in erythropoiesis but have not been directly linked to HbF induction. See text for details. ATF = activating transcription factor; CHOP = CCAAT/enhancer binding protein homologous protein; CREB = cAMP response element binding protein; EIF2A = eukaryotic translation initiation factor 2α; ELK1 = member of ets oncogene family; ER = endoplasmic reticulum; GADD = growth arrest- and DNA damage-inducible gene; GCN2 = general control nonderepressible-2 (EIF2A kinase 4); HRI = heme-regulated inhibitor (EIF2A kinase 1); HU = hydroxyurea; MAX = MYC-associated factor X; MEF2 = MADS box transcription enhancer factor 2; MKK = mitogen-activated protein kinase kinase; MSK1 = mitogen and stress-activated protein kinase 1; MYC = v-MYC avian myelocytomatosis viral homolog; NRF2 = nuclear factor erythroid 2-like 2; PERK = RNA dependent protein kinase-like ER kinase (EIF2A kinase 3); PKA = protein kinase, cAMP-dependent, regulatory, type I α; PKR = RNA-dependent protein kinase (EIF2A kinase 2); ROS = reactive oxygen species; UV = ultraviolet radiation. Experimental Hematology 2008 36, 1057-1072DOI: (10.1016/j.exphem.2008.06.014) Copyright © 2008 ISEH - Society for Hematology and Stem Cells Terms and Conditions