Activation Of Gamma-Globin Gene Expression By Gata1 And Nf-Y In Hereditary Persistence Of Fetal Hemoglobin

Hereditary persistence of fetal hemoglobin (HPFH) ameliorates beta-hemoglobinopathies by inhibiting the developmental switch from gamma-globin (HBG1/HBG2) to beta-globin (HBB) gene expression. Some forms of HPFH are associated with gamma-globin promoter variants that either disrupt binding motifs for transcriptional repressors or create new motifs for transcriptional activators. How these variants sustain gamma-globin gene expression postnatally remains undefined. We mapped gamma-globin promoter sequences functionally in erythroid cells harboring different HPFH variants. Those that disrupt a BCL11A repressor binding element induce gamma-globin expression by facilitating the recruitment of nuclear transcription factor Y (NF-Y) to a nearby proximal CCAAT box and GATA1 to an upstream motif. The proximal CCAAT element becomes dispensable for HPFH variants that generate new binding motifs for activators NF-Y or KLF1, but GATA1 recruitment remains essential. Our findings define distinct mechanisms through which transcription factors and their cis-regulatory elements activate gamma-globin expression in different forms of HPFH, some of which are being recreated by therapeutic genome editing.Introduction of hereditary persistence of fetal hemoglobin variants into the gamma-globin promoter by using CRISPR mutagenesis and editing provides insights into transcription factor interplay, with implications for gene therapies targeting this element.