Our work is based on the premise that a detailed, mechanistic understanding of how fetal hemoglobin (HbF) is shut off in adult erythroid cells will provide new opportunities to interfere with the process and reactivate HbF for clinical benefit in patients with b-thalassemia and sickle cell disease. BCL11A, a transcription factor, plays a central role in silencing of g-globin gene expression in development and in adult erythroid cells. Human genetics and experiments in the laboratory indicate that partial reduction of BCL11A function (to about 40% of normal level) would be therapeutic. While the genetic findings are compelling, relatively little is understood regarding the precise mechanisms by which BCL11A represses g-globin gene expression. A current model posits that BCL11A executes its function in large part through binding to the g-globin promoter at a specific site (a distal TGACCA motif) and recruits the NuRD chromatin complex to achieve repression. Key aspects of this model will be tested by focused experiments. First, novel methods for conditional degradation of BCL11A protein in cells will be employed to develop a system in which repression or activation of g-globin gene transcription can be followed in a step-by-step manner. Specific predictions of the current model for BCL11A action will be tested by generation of targeted mutations of BCL11A or subunits of the NuRD complex in an immortal adult human erythroid cell line (HUDEP-2 cells). Findings from these experiments that support or challenge aspects of the current model will drive formulation of a more sophisticated description of how BCL11A acts and identify points at which g-globin gene silencing may be reversed. These studies are essential for creating new opportunities for targeted reactivation of HbF expression with small molecules (drugs). Such novel therapeutic approaches are desperately needed to address the existing and growing global health burden of the hemoglobin disorders.

Public Health Relevance

(PUBLIC) Red cell cells produce hemoglobin, the principal oxygen carrying protein in our entire body. Inherited disorders that affect the synthesis or structure of adult hemoglobin, called b-thalassemia and sickle cell disease, are common throughout the world, and particularly in resource-poor countries in Africa and Asia. These disorders adversely affect well-being and survival of affected individuals, and together constitute a major global health challenge. Our work focuses on the control of expression of the fetal-type hemoglobin (HbF), which is expressed during fetal life and largely silent in the adult. A unique protein, BCL11A, silences expression of HbF and serves as a critical molecular switch. The goal of the project is to determine in detail how BCL11A silences HbF as this knowledge forms the foundation for discovery of new drugs to reactivate HbF in patients with the major hemoglobin disorders.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Molecular and Cellular Hematology Study Section (MCH)
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Qasba, Pankaj
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Boston Children's Hospital
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