An element upstream from the human delta-globin-encoding gene specifically enhances beta-globin reporter gene expression in murine erythroleukemia cells

We have previously shown that a DNA-binding factor specific to adult hematopoietic cells (polypyrimidine-binding factor; PYBF) binds to a pyrimidine-rich region 1 kb upstream from the human delta-globin-encoding gene (HBD). The developmental stage-specificity of PYBF and the location of its binding site between the fetal and adult beta-globin (HBB)-like genes suggest that PYBF and its binding site may function in fetal-to-adult globin gene switching. Here, we describe the effect of 383-bp (delta 383) and 99-bp (delta 99) sequences containing the PYBF-binding site on transcription from various globin and non-globin promoters, using a transient assay with the cat reporter gene in murine erythroleukemia (MEL) cells, a cell line with abundant PYBF activity. We show that both delta 383 and delta 99 specifically enhance expression of cat for plasmids containing a human adult globin (HBB) promoter, whereas expression of similar constructs using human fetal ((A) gamma-) globin (HBG1) or simian virus 40 (SV40) promoters is not enhanced. The results suggest that PYBF and the pyrimidine-rich region upstream from HBD can specifically enhance HBB transcription in adult erythroid cells.