The mechanisms by which pharmacologic agents stimulate γ-globin gene expression in β-globin disorders has not been fully established at the molecular level. In studies described here, nucleated erythroblasts were isolated from patients with β-globin disorders before and with butyrate therapy, and globin biosynthesis, mRNA, and protein-DNA interactions were examined. Expression of γ-globin mRNA increased twofold to sixfold above baseline with butyrate therapy in 7 of 8 patients studied. A 15% to 50% increase in γ-globin protein synthetic levels above baseline γ globin ratios and a relative decrease in β-globin biosynthesis were observed in responsive patients. Extensive new in vivo footprints were detected in erythroblasts of responsive patients in four regions of the γ-globin gene promoter, designated butyrate-response elements gamma 1-4 (BRE-G1-4). Electrophoretic mobility shift assays using BRE-G1 sequences as a probe demonstrated that new binding of two erythroid-specific proteins and one ubiquitous protein, αCP2, occurred with treatment in the responsive patients and did not occur in the nonresponder. The BRE-G1 sequence conferred butyrate inducibility in reporter gene assays. These in vivo protein-DNA interactions in human erythroblasts in which γ-globin gene expression is being altered strongly suggest that nuclear protein binding, including αCP2, to the BRE- G1 region of the γ-globin gene promoter mediates butyrate activity on γ- globin gene expression.
ASJC Scopus subject areas
- Cell Biology