Role of erythroid Kruppel-like factor in human gamma- to beta-globin gene switching.

Erythroid Kruppel-like factor (EKLF) is an erythroid-specific transcription factor that contains zinc finger domains similar to the Kruppel protein of Drosophila melanogaster. Previous studies demonstrated that EKLF binds to the CACCC box in the human beta-globin gene promoter and activates transcription. CACCC box mutations that cause severe beta-thalassemias in humans inhibit EKLF binding. Results described in this paper suggest that EKLF functions predominately in adult erythroid tissue. The EKLF gene is expressed at a 3-fold higher level in adult erythroid tissue than in fetal erythroid tissue, and the EKLF protein binds to the human beta-globin promoter 8-fold more efficiently than to the human gamma-globin promoter. Co-transfection experiments in the human fetal-like erythroleukemia cell line K562 demonstrate that over-expression of EKLF activates a beta-globin reporter construct 1000-fold; a linked gamma-globin reporter is activated only 3-fold. Mutation of the beta-globin CACCC box severely inhibits activation. These results demonstrate that EKLF is a developmental stage-enriched protein that preferentially activates human beta-globin gene expression. The data strongly suggest that EKLF is an important factor involved in human gamma- to beta-globin gene switching.