ATF4 mediates fetal globin upregulation in response to reduced β-globin

Abstract

Fetal development and anemias such as β-hemoglobinopathies trigger rapid production of red blood cells in a process known as stress erythropoiesis. Cellular stress prompts differentiating erythroid precursors to express high levels of fetal γ-globin, which has suggested strategies to treat hemoglobinopathies such as thalassemia and sickle cell disease. However, the mechanisms underlying γ-globin production during cellular stress are still poorly defined. Here we use CRISPR-Cas genome editing and CRISPRi transcriptional repression to model the stress caused by reduced levels of adult β-globin. We find that loss of β-globin is sufficient to induce widespread globin compensation, including robust re-expression of γ-globin. Timecourse RNA-seq of differentiating isogenic erythroid precursors identified the ATF4 transcription factor as a causal regulator of this response. ChIP-seq of multiple erythroid precursor genotypes and differentiation states revealed that β-globin knockout leads to reduced engagement of ATF4 targets involved in the unfolded protein response. This ATF4 program indirectly regulates the levels of BCL11A, a key repressor of γ-globin. Identification of ATF4 as a key regulator of globin compensation adds mechanistic insight to the poorly understood phenomenon of stress-induced globin compensation and could be relevant for proposed gene editing strategies to treat hemoglobinopathies.

The HRI-regulated transcription factor ATF4 activates BCL11A transcription to silence fetal hemoglobin expression

“…This in turn lowered BCL11A and increased g-globin transcription. 38 In that study, ATF4 binding at BCL11A was not detected, and the mechanism of BCL11A reduction remained unclear. Our study strongly suggests that ATF4 directly regulates BCL11A transcription by binding to the BCL11A 155 enhancer, raising the possibility that diverse stress conditions that elevate ATF4 may converge on the same pathway.…”