Exploring strategies for the design of artificial transcription factors: targeting sites proximal to known regulatory regions for the induction of gamma-globin expression and the treatment of sickle cell disease.

Artificial transcription factors can be engineered to interact with specific DNA sequences to modulate endogenous gene expression within cells. A significant hurdle to implementation of this approach is the selection of the appropriate DNA sequence for targeting. We reasoned that a good target site should be located in chromatin, where it is accessible to DNA-binding proteins, and it should be in the close vicinity of known transcriptional regulators of the gene. Here we have explored the efficacy of these criteria to guide our selection of potential regulators of gamma-globin expression. Several zinc finger-based transcriptional activators were designed to target the sites proximal to the -117-position of the gamma-globin promoter. This region is proximal to the binding sites of known and potential natural transcription factors. Design and study of three transcription factors identified the potent transcriptional activator, gg1-VP64-HA. This transcription factor was able to interact directly with the gamma-globin promoter and up-regulate expression of reporter gene constructs as well as the endogenous gene in a selective manner. Transfection of a gg1-VP64-HA expression vector or retroviral delivery of this transcription factor into the erythroleukemia cell line K562 resulted in an increase of fetal hemoglobin. The gamma-globin content of cells expressing gg1-vp64-HA showed up to 16-fold higher levels of fetal hemoglobin than the native K562 cell line. These transcriptional activators constitute a novel class of regulators of the globin locus that may be suitable for treatment of diseases arising from mutations in this locus such as sickle cell disease and thalassemic diseases.