Kruppel-Like Transcription Factor KLF1 Is Required for Optimal γ- and β-Globin Expression in Human Fetal Erythroblasts

In human adult erythroid cells, lower than normal levels of Kruppel-like transcription factor 1 (KLF1) are generally associated with decreased adult beta- and increased fetal.-globin gene expression. KLF1 also regulates BCL11A, a known repressor of adult gamma-globin expression. In seeming contrast to the findings in adult cells, lower amounts of KLF1 correlate with both reduced embryonic and reduced fetal beta-like globin mRNA in mouse embryonic erythroid cells. The role of KLF1 in primary human fetal erythroid cells, which express both gamma- and gamma-globin mRNA, is less well understood. Therefore, we studied the role of KLF1 in ex vivo differentiated CD34+ umbilical cord blood cells (UCB erythroblasts), representing the fetal milieu. In UCB erythroblasts, KLF1 binds to the beta-globin locus control region (LCR), and the beta-globin promoter. There is very little KLF1 binding detectable at the.-globin promoter. Correspondingly, when cultured fetal UCB erythroblasts are subjected to lentiviral KLF1 knockdown, the active histone mark H3K4me3 and RNA pol II recruitment are diminished at the beta-but not the.-globin gene. The amount of KLF1 expression strongly positively correlates with gamma-globin mRNA and weakly positively correlates with BCL11AmRNA. With modest KLF1 knockdown, mimicking haplo insufficiency, gamma-globin mRNA is increased in UCB erythroblasts, as is common in adult cells. However, a threshold level of KLF1 is evidently required, or there is no absolute increase in gamma-globinmRNA in UCB erythroblasts. Therefore, the role of KLF1 in.-globin regulation in fetal erythroblasts is complex, with both positive and negative facets. Furthermore, in UCB erythroblasts, diminished BCL11A is not sufficient to induce.-globin in the absence of KLF1. These findings have implications for the manipulation of BCL11A and/or KLF1 to induce gamma-globin for therapy of the beta-hemoglobinopathies.