Epigenetic inactivation of ERF reactivates γ-globin expression in β-thalassemia

The fetal-to-adult hemoglobin switch is regulated in a developmental stage-specific manner and reactivation of fetal hemoglobin (HbF) has therapeutic implications for treatment of β-thalassemia and sickle cell anemia, two major global health problems. Although significant progress has been made in our understanding of the molecular mechanism of the fetal-to-adult hemoglobin switch, the mechanism of epigenetic regulation of HbF silencing remains to be fully defined. Here, we performed whole-genome bisulfite sequencing and RNA sequencing analysis of the bone marrow-derived GYPA⁺ erythroid cells from β-thalassemia-affected individuals with widely varying levels of HbF groups (HbF ≥ 95th percentile or HbF ≤ 5th percentile) to screen epigenetic modulators of HbF and phenotypic diversity of β-thalassemia. We identified an ETS2 repressor factor encoded by ERF, whose promoter hypermethylation and mRNA downregulation are associated with high HbF levels in β-thalassemia. We further observed that hypermethylation of the ERF promoter mediated by enrichment of DNMT3A leads to demethylation of γ-globin genes and attenuation of binding of ERF on the HBG promoter and eventually re-activation of HbF in β-thalassemia. We demonstrated that ERF depletion markedly increased HbF production in human CD34⁺ erythroid progenitor cells, HUDEP-2 cell lines, and transplanted NCG-Kit-V831M mice. ERF represses γ-globin expression by directly binding to two consensus motifs regulating γ-globin gene expression. Importantly, ERF depletion did not affect maturation of erythroid cells. Identification of alterations in DNA methylation of ERF as a modulator of HbF synthesis opens up therapeutic targets for β-hemoglobinopathies.