The most well characterized of these are the de novo methylases, DNMT3A, and DNMT3B, which symmetrically methylate cytosines in the dinucleotide Cytosine-phosphate-Guanine

(CpG) on both strands of unmethylated DNA, and DNMT1, a so-called maintenance methylase, that adds a methyl group to the symmetric CpG on the unmethylated strand of DNA after DNA replication. From the time of the discovery that silent embryonic and fetal β-type globin genes are methylated and that the cytidine analog, 5-azacytidine, inhibits the processive methylation of hemimethylated DNA after replication, many studies have focused on DNMT1 as Selleck OSI906 a target for reversing globin gene silencing. Initial studies in animal models42 were followed by clinical interventions that demonstrated increased HbF expression in patients with both sickle cell anemia and β-thalassemia who were treated with 5-azacytidine.43, 44 and 45 The mechanism by which 5-azacytidine actually induces increased human fetal gamma globin gene expression has been debated, and mechanisms such as generalized cytotoxicity and induced erythroid cellular stress have been proposed.13, 46, 47, 48, 49 and 50 Nonetheless selleck compound in well-characterized primate and human β-globin gene locus-bearing transgenic

mouse models, disruption of DNA methylation appears to www.selleck.co.jp/products/azd9291.html be a major mechanism of relieving ɣ-globin gene silencing, although perhaps indirectly in part.51, 52, 53, 54, 55 and 56 Despite the development of more specific inhibitors of DNMT1,

such as decitabine, which, unlike 5-azacytidine, lacks effects on RNA metabolism, concerns about the safety of this class of agents have limited clinical application in β-hemoglobinopathies. However, a recent study of low dose decitabine in β-thalassemia patients reported an increase in HbF without detectable short-term cytotoxicity or genotoxicity.57 The readers of DNA methylation are a group of proteins that preferentially bind to DNA containing symmetrically methylated CpG dinucleotides. The largest family of these are the methylcytosine-binding domain (MBD) proteins, which include MBD1, MBD2, MECP2, and MBD4.58 Of these, the role of MBD2 in regulating embryonic/fetal β-type globin gene silencing in adult erythroid cells is the most well characterized. MBD2 binds preferentially to DNA containing a high density of methylated CpGs. MBD2 has been shown to bind directly to the avian embryonic ρ-globin gene, and knockdown of MBD2 derepresses the gene in adult erythroid cells in culture.59 Knockdown of MBD2 has also been shown to induce a large increase in expression of the silent human ɣ-globin gene in human β-globin locus–bearing transgenic mice53 and in human primary CD34 precursor–derived adult erythroid cells.