Targeted Remodeling of Human β-Globin Promoter Chromatin Structure Produces Increased Expression and Decreased Silencing

The chromatin structure of the human β-globin gene locus assumes a transcriptionallyactive conformation in erythroid cells. One feature of this chromatin reorganization is the formation of DNase 1 hypersensitive sites in the regions of active globin gene promoters. This reorganization requires the globin locus control region and is associated with normal expression of the β-like globin genes. To determine whether it is possible to artificially enhance the opening of the chromatin structure of a minimal β-globin promoter, we placed a 101bp, erythroid-specific DNase 1 hypersensitive site-forming element (HSFE) immediately upstream of the β-globin promoter and gene. This element includes binding sites for NF-E2, AP-1, GATA-1 and Sp-1. Constructs were stably transfected into murine erythroleukemia cells and promoter chromatin structure and gene expression were analyzed. The HSFE induced an area of enhanced DNase 1 hypersensitivity extending from the transcriptional start site to -300bp of the artificial promoter and significantly increased the proportion of β-globin promoters in an open chromatin configuration. This remodeling of promoter chromatin structure resulted in 3-fold increases in β-globin gene transcription and induction, and inhibited long-term β-globin gene silencing. These results indicate that a relatively smallcisacting element is able to enhance remodeling of promoter chromatin structure resulting in increased β-globin gene expression.