Krivega Ivan, Byrnes Colleen, de Vasconcellos Jaira F, Lee Y Terry, Kaushal Megha, Dean Ann, Miller Jeffery L
Laboratory of Cellular and Developmental Biology, and.
Molecular Genomics and Therapeutics Section, Molecular Medicine Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD.
Blood. 2015 Jul 30;126(5):665-72. doi: 10.1182/blood-2015-02-629972. Epub 2015 May 15.
Induction of fetal hemoglobin (HbF) production in adult erythrocytes can reduce the severity of sickle cell disease and β-thalassemia. Transcription of β-globin genes is regulated by the distant locus control region (LCR), which is brought into direct gene contact by the LDB1/GATA-1/TAL1/LMO2-containing complex. Inhibition of G9a H3K9 methyltransferase by the chemical compound UNC0638 activates fetal and represses adult β-globin gene expression in adult human hematopoietic precursor cells, but the underlying mechanisms are unclear. Here we studied UNC0638 effects on β-globin gene expression using ex vivo differentiation of CD34(+) erythroid progenitor cells from peripheral blood of healthy adult donors. UNC0638 inhibition of G9a caused dosed accumulation of HbF up to 30% of total hemoglobin in differentiated cells. Elevation of HbF was associated with significant activation of fetal γ-globin and repression of adult β-globin transcription. Changes in gene expression were associated with widespread loss of H3K9me2 in the locus and gain of LDB1 complex occupancy at the γ-globin promoters as well as de novo formation of LCR/γ-globin contacts. Our findings demonstrate that G9a establishes epigenetic conditions preventing activation of γ-globin genes during differentiation of adult erythroid progenitor cells. In this view, manipulation of G9a represents a promising epigenetic approach for treatment of β-hemoglobinopathies.
诱导成体红细胞中胎儿血红蛋白（HbF）的产生可减轻镰状细胞病和β地中海贫血的严重程度。β珠蛋白基因的转录受远距离基因座控制区（LCR）调控，LCR通过包含LDB1/GATA-1/TAL1/LMO2的复合物与基因直接接触。化合物UNC0638对G9a H3K9甲基转移酶的抑制作用可激活成体人类造血前体细胞中的胎儿β珠蛋白基因并抑制成人β珠蛋白基因的表达，但其潜在机制尚不清楚。在此，我们利用健康成年供体外周血中CD34(+)红系祖细胞的体外分化研究了UNC0638对β珠蛋白基因表达的影响。UNC0638对G9a的抑制作用导致分化细胞中HbF剂量依赖性积累，最高可达总血红蛋白的30%。HbF的升高与胎儿γ珠蛋白的显著激活和成人β珠蛋白转录的抑制相关。基因表达的变化与该基因座H3K9me2的广泛丢失、γ珠蛋白启动子处LDB1复合物占据的增加以及LCR/γ珠蛋白接触的重新形成有关。我们的研究结果表明，G9a建立了表观遗传条件，在成体红系祖细胞分化过程中阻止γ珠蛋白基因的激活。据此，对G9a的调控代表了一种有前景的表观遗传方法，用于治疗β血红蛋白病。
