Purification and identification of proteins that bind to the hereditary persistence of fetal hemoglobin -198 mutation in the gamma-globin gene promoter

A natural DNMT1 mutation elevates the fetal hemoglobin level via epigenetic derepression of the γ-globin gene in β-thalassemia

DNA methyltransferase 1 (DNMT1) is a major epigenetic regulator of the formation of large macromolecular complexes that repress human γ-globin expression by maintaining DNA methylation. However, very little is known about the association of DNMT1 variants with β-thalassemia phenotypes. We systematically investigated associations between variants in DNMT1 and phenotypes in 1142 β-thalassemia subjects and identified a novel missense mutation (c.2633G>A, S878F) in the DNMT1 bromo-adjacent homology-1 (BAH1) domain. We functionally characterized this mutation in CD34+ cells from patients and engineered HuDEP-2 mutant cells. Our results demonstrate that DNMT1 phosphorylation is abrogated by substituting serine with phenylalanine at position 878, resulting in lower stability and catalytic activity loss. S878F mutation also attenuated DNMT1 interactions with BCL11A, GATA1, and HDAC1/2, and reduced recruitment of DNMT1 to the γ-globin (HBG) promoters, leading to epigenetic derepression of γ-globin expression. By analyzing the F-cell pattern, we demonstrated that the effect of DNMT1 mutation on increased fetal hemoglobin (HbF) is heterocellular. Furthermore, introduction of S878F mutation into erythroid cells by clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) recapitulated γ-globin reactivation. Thus, the natural S878F DNMT1 mutation is a novel modulator of HbF synthesis and represents a potential new therapeutic target for β-hemoglobinopathies.

Screening of Transcription Factors Involved in Fetal Hemoglobin Regulation Using Phylogenetic Footprinting

Fetal hemoglobin (Hb F) is an important genetic modulator of the beta-hemoglobinopathies. The regulation of Hb F levels is influenced by transcription factors. We used phylogenetic footprinting to screen transcription factors that have binding sites in HBG1 and HBG2 genes’ noncoding regions in order to know the genetic determinants of the Hb F expression. Our analysis showed 354 conserved motifs in the noncoding regions of HBG1 gene and 231 motifs in the HBG2 gene between the analyzed species. Of these motifs, 13 showed relation to Hb F regulation: cell division cycle-5 (CDC5), myelo-blastosis viral oncogene homolog (c-MYB), transcription factor CP2 (TFCP2), GATA binding protein 1 (GATA-1), GATA binding protein 2 (GATA-2), nuclear factor erythroid 2 (NF-E2), nuclear transcription factor Y (NF-Y), runt-related transcription factor 1 (RUNX-1), T-cell acute lymphocytic leukemia 1 (TAL-1), YY1 transcription factor (YY1), beta protein 1 (BP1), chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII), and paired box 1 (PAX-1). The last three motifs were conserved only in the noncoding regions of the HBG1 gene. The understanding of genetic elements involved in the maintenance of high Hb F levels may provide new efficient therapeutic strategies in the beta-hemoglobinopathies treatment, promoting reduction in clinical complications of these genetic disorders.

Locus-specific proteomics by TChP: targeted chromatin purification

Here, we show that transcription factors bound to regulatory sequences can be identified by purifying these unique sequences directly from mammalian cells in vivo. Using targeted chromatin purification (TChP), a double-pull-down strategy with a tetracycline-sensitive "hook" bound to a specific promoter, we identify transcription factors bound to the repressed γ-globin gene-associated regulatory regions. After validation of the binding, we show that, in human primary erythroid cells, knockdown of a number of these transcription factors induces γ-globin gene expression. Reactivation of γ-globin gene expression ameliorates the symptoms of β-thalassemia and sickle cell disease, and these factors provide potential targets for the development of therapeutics for treating these patients.

What influences Hb fetal production in adulthood?

Human hemoglobin genes are located in α and β globin gene clusters in chromosomes 16 and 11, respectively. Different types of hemoglobin are synthesized according to the stage of development with fetal hemoglobin (α(2)γ(2)) (Hb F) being the main hemoglobin in the fetal period. After birth, there is a reduction (to about 1%) in Hb F levels and adult hemoglobin, Hb A (2α(2)β(2)), increases to more than 96% of total hemoglobin. However, some genetic conditions whether linked to the β-globin gene cluster or not are associated with high Hb F levels in adults. Among those linked to β-globin are hereditary persistence of fetal hemoglobin, delta-beta thalassemia (δβ-Thalassemia) and the XmnI polymorphism (-158 C = T). Other polymorphisms not related to β-globin gene cluster are known to influence the γ-globin gene expression in adulthood. The most relevant polymorphisms that increase concentrations of Hb F are the HMIP locus on chromosome 6, the BCL11A locus on chromosome 2, the Xp22.2 region of the X chromosome and the 8q region on chromosome 8. Findings from our research group studying genetic factors involved in γ-globin gene regulation in adults without anemia in the northwestern region of São Paulo State showed that high Hb F levels are influenced by the presence of hereditary persistence of fetal hemoglobin mutations and the XmnI polymorphism, suggesting that both genetic alterations characterize the molecular basis of the evaluated population.

Transcriptional control of the cell cycle

Cell division is a highly coordinated process. In the last decades, many plant cell cycle regulators have been identified. Strikingly, only a few transcriptional regulators are known, although a significant amount of the genome is transcribed in a cell cycle phase-dependent manner. E2F-DP transcription factors and three repeat MYB proteins are responsible for the expression of genes at the G1-to-S and G2-to-M transition, respectively. However, these two mechanisms cannot explain completely the transcriptional regulation seen during the cell cycle. Correspondingly, several new transcriptional regulators have been characterized, stressing the importance of transcriptional control during the cell cycle.

Laminin-1 induces E-cadherin expression in 3-dimensional cultured breast cancer cells by inhibiting DNA methyltransferase 1 and reversing promoter methylation status

This study determines the role of laminin-1 in promoting metastatic colonization during breast cancer. For this purpose, human mammary epithelial cell lines representing normal (MCF-10A), adenocarcinoma (MCF-7), and malignant carcinoma (MDA-MB-231) were propagated in 3-dimensional cultures composed of laminin-1, collagen I, or mixtures of the two, and analyzed by Western blot, immunocytochemistry, semiquantitative reverse transcription polymerase chain reaction, and methylation-specific PCR. Here we demonstrate that laminin-1 decreases methylation of the E-cadherin promoter, resulting in increased mRNA and protein expression for malignant mammary epithelial cells. This decreased methylation is associated with dramatic changes in the cellular and structural morphology as well as a 70-fold decrease in DNA methyltransferase 1 (DNMT1) and a 6-fold decrease in cadherin 11 protein expression. To control for specificity of laminin-1 interactions, cells were also cultured on 2-dimensional plastic substrata and collagen I hydrogels for analysis, and the MCF-10A and MCF-7 were used as nonmalignant controls. Using a 3-dimensional model, we present evidence that laminin-1 is capable of inducing epigenetic change by inhibiting expression of DNMT1 and preventing methylation of the E-cadherin promoter, resulting in E-cadherin expression and the formation of cell-cell bonds in malignant carcinoma.

Fetal hemoglobin chemical inducers for treatment of hemoglobinopathies

The switch from fetal ((G)gamma and (A)gamma) to adult (beta and delta) globin gene expression occurs at birth, leading to the gradual replacement of HbF with HbA. Genetic regulation of this switch has been studied for decades, and the molecular mechanisms underlying this developmental change in gene expression have been in part elucidated. The understanding of the developmental regulation of gamma-globin gene expression was paralleled by the identification of a series of chemical compounds able to reactivate HbF synthesis in vitro and in vivo in adult erythroid cells. Reactivation of HbF expression is an important therapeutic option in patients with hemoglobin disorders, such as sickle cell anemia and beta-thalassemia. These HbF inducers can be grouped in several classes based on their chemical structures and mechanisms of action. Clinical studies with some of these agents have shown that they were effective, in a part of patients, in ameliorating the clinical condition. The increase in HbF in response to these drugs varies among patients with beta-thalassemia and sickle cell disease due to individual genetic determinants.

Control of beta globin genes

The developmental changes in expression of the beta like genes from embryonic to adult stages of human life are controlled at least partially at the level of the promoter sequences of these genes and their binding factors, and competition for promoter specific interactions with the locus control region (LCR). In recent years, the control of beta globin genes has also been investigated at the level of chromatin structure involving the chemical modification of histones and their remodelling by DNA dependent ATPases (SMARCA) containing protein complexes. The role of intergenic RNA is also being investigated with renewed interest. Although a wealth of information on the structure/function relationship of the LCR and globin promoters has been gathered over more than two decades, the fundamental nature of the control of these genes at the molecular level is still not completely understood. In the following pages, we intend to briefly describe the progress made in the field and discuss future directions.