Transcription factor competition at the γ-globin promoters controls hemoglobin switching.

BCL11A, the major regulator of fetal hemoglobin (HbF, α2γ2) level, represses γ-globin expression through direct promoter binding in adult erythroid cells in a switch to adult hemoglobin (HbA, α2β2). To uncover how BCL11A initiates repression, we used CRISPR-Cas9, dCas9, dCas9-KRAB and dCas9-VP64 screens to dissect the γ-globin promoters and identified an activator element near the BCL11A-binding site. Using CUT&RUN and base editing, we demonstrate that a proximal CCAAT box is occupied by the activator NF-Y. BCL11A competes with NF-Y binding through steric hindrance to initiate repression. Occupancy of NF-Y is rapidly established following BCL11A depletion, and precedes γ-globin derepression and locus control region (LCR)-globin loop formation. Our findings reveal that the switch from fetal to adult globin gene expression within the >50-kb β-globin gene cluster is initiated by competition between a stage-selective repressor and a ubiquitous activating factor within a remarkably discrete region of the γ-globin promoters.

Citation

Nan Liu, Shuqian Xu, Qiuming Yao, Qian Zhu, Yan Kai, Jonathan Y Hsu, Phraew Sakon, Luca Pinello, Guo-Cheng Yuan, Daniel E Bauer, Stuart H Orkin. Transcription factor competition at the γ-globin promoters controls hemoglobin switching. Nature genetics. 2021 Apr;53(4):511-520

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PMID: 33649594

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