Date Published: June 15, 2012
Publisher: Hindawi Publishing Corporation
Author(s): Flávia C. Costa, Halyna Fedosyuk, Renee Neades, Johana Bravo de Los Rios, Carlos F. Barbas, Kenneth R. Peterson.
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 Aγ-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.
Human hemoglobin is a tetrameric molecule composed of two α-like and two β-like chains, located on chromosomes 16 and 11, respectively. The β-like chain is comprised of the product of one of five functional genes (embryonic ε-, fetal Aγ- and Gγ-, and adult δ- and β-globin) which are developmentally expressed in the order that they are arrayed in the locus [1, 2]. As human erythroid development proceeds, the proper β-like globin genes are activated or repressed, giving rise to the different hemoglobin chains expressed throughout development . Hemoglobin switching from fetal γ-globin to adult β-globin gene expression begins shortly before birth and is usually completed within the first 6 months after birth. In some individuals, hemoglobin switching is not completed, resulting in a condition called hereditary persistence of fetal hemoglobin (HPFH), which is characterized by high expression of fetal hemoglobin (HbF, γ-globin) during adult definitive erythropoiesis [1, 2]. 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 thus, research has focused on elucidating the pathways involved in the maintenance or activation of γ-globin expression by drug or gene therapy.
The use of synthetic gene-targeted transcription factors that bind to specific DNA sequences to regulate the expression of endogenous genes is an emerging field. 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, 24–26].