Abstract
Sickle cell disease (SCD) and β-thalassemia patients are phenotypically normal if they carry compensatory hereditary persistence of fetal hemoglobin (HPFH) mutations that result in increased levels of fetal hemoglobin (HbF, γ-globin chains) in adulthood. Thus, research has focused on manipulating the reactivation of γ-globin gene expression during adult definitive erythropoiesis as the most promising therapy to treat these hemoglobinopathies. Artificial transcription factors (ATFs) are synthetic proteins designed to bind at a specific DNA sequence and modulate gene expression. The artificial zinc finger gg1-VP64 was designed to target the −117 region of the A γ-globin gene proximal promoter and activate expression of this gene. Previous studies demonstrated that HbF levels were increased in murine chemical inducer of dimerization (CID)-dependent bone marrow cells carrying a human β-globin locus yeast artificial chromosome (β-YAC) transgene and in CD34+ erythroid progenitor cells from normal donors and β-thalassemia patients. Herein, we report that gg1-VP64 increased γ-globin gene expression in vivo, in peripheral blood samples from gg1-VP64 β-YAC double-transgenic (bigenic) mice. Our results demonstrate that ATFs function in an animal model to increase gene expression. Thus, this class of reagent may be an effective gene therapy for treatment of some inherited diseases.
Highlights
Human hemoglobin is a tetrameric molecule composed of two α-like and two β-like chains, located on chromosomes 16 and 11, respectively
In this study we demonstrate that gg1-VP64 increased γ-globin gene expression during adult definitive erythropoiesis in β-globin locus yeast artificial chromosome (β-YAC) transgenic mice
Engineered zinc finger transcription factors in which zinc finger motifs are coupled to an activation domain provide new therapeutic venues to enhance gene expression and treat diseases such as hemoglobinopathies [14, 15, 24,25,26]
Summary
Human hemoglobin is a tetrameric molecule composed of two α-like and two β-like chains, located on chromosomes 16 and 11, respectively. Sickle cell disease (SCD) and β-thalassemia patients are phenotypically normal if they carry compensatory mutations that result in HPFH as well [1, 2] These genetic studies have indicated that increased HbF will help alleviate pathophysiology associated with these hemoglobinopathies, and research has focused on elucidating the pathways involved in the maintenance or activation of γ-globin expression by drug or gene therapy. Enforced expression of TR2/TR4 increased fetal γ-globin gene expression in adult erythroid cells from β-YAC transgenic mice [7] and in adult erythroid cells from the humanized SCD mice [10] These studies clearly demonstrate that manipulation of transcription factors efficiently reactivates γ-globin expression during adult definitive erythropoiesis. In this study we demonstrate that gg1-VP64 increased γ-globin gene expression during adult definitive erythropoiesis in β-YAC transgenic mice
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