Functional Analysis of an Aγ-Globin Gene Promoter Variant (HBG1: g.-225_-222delAGCA) Underlines Its Role in Increasing Fetal Hemoglobin Levels Under Erythropoietic Stress
Functional Analysis of an Aγ-Globin Gene Promoter Variant (HBG1: g.-225_-222delAGCA) Underlines Its Role in Increasing Fetal Hemoglobin Levels Under Erythropoietic Stress
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DOI：
10.3109/03630269.2015.1107842
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发表时间：
2016-01-02
期刊：
影响因子：
1
通讯作者：
Pavlovic, Sonja
中科院分区：
文献类型：
--
作者：
Ugrin, Milena;Stojiljkovic, Maja;Pavlovic, Sonja
胎儿血红蛋白遗传持续性（HPFH）是一种以持续性β-珠蛋白基因表达和成年期高水平胎儿血红蛋白（Hb F; 22）合成为特征的疾病。它通常是由影响人胎儿珠蛋白（HBG1和HBG2）基因的启动子变异或大缺失引起的。其中一些引起HPFH的变体，如HBG2：g. - 158C> T，仅在红细胞生成应激的条件下发挥作用，这对于β-地中海贫血（β-地中海贫血）患者是典型的。即，HBG2的存在：g. - 158C> T有利于更高的Hb F反应，而它在健康个体中几乎没有影响。我们分析了先前报道的位于HBG1基因启动子区的缺失（HBG1：g. - 225_-222delAGCA），在正常条件下和在红细胞生成应激条件下。我们的研究结果表明，这种缺失是负责降低HBG1基因表达。具体地，与野生型序列相比，该缺失显示导致K562细胞中报告基因表达的急剧降低，但仅在红细胞生成应激的条件下，通过将促红细胞生成素（EPO）引入细胞培养物中来模拟。此外，电泳迁移率变动分析表明，HBG 1：g. - 225_-222delAGCA缺失产生了额外的转录因子结合位点，我们认为这些位点结合转录阻遏物，从而降低了HBG 1基因启动子的活性。这些结果与计算机模拟分析一致，表明该缺失产生了GATA 1的结合位点，已知GATA 1是β-珠蛋白基因表达的阻遏物。这些数据证实了HBG1：g. -的调节作用。225_-222区域，其在红细胞生成应激条件下发挥作用。
Hereditary persistence of fetal hemoglobin (HPFH) is a condition characterized by persistent -globin gene expression and synthesis of high levels of fetal hemoglobin (Hb F; 22) during adult life. It is usually caused by promoter variants or large deletions affecting the human fetal globin (HBG1 and HBG2) genes. Some of these HPFH-causing variants, such as HBG2: g.-158C>T, exert their effect only under conditions of erythropoietic stress, typical for -thalassemia (-thal) patients. Namely, the presence of HBG2: g.-158C>T favors a higher Hb F response, while it has little effect in healthy individuals. We analyzed a previously reported deletion residing in the promoter region of the HBG1 gene (HBG1: g.-225_-222delAGCA), both in normal conditions and under conditions of erythropoietic stress. Our results indicate that this deletion is responsible for decreased HBG1 gene expression. Specifically, this deletion was shown to result in drastically reduced reporter gene expression in K562 cells, compared to the wild-type sequence but only under conditions of erythropoietic stress, mimicked by introduction of erythropoietin (EPO) into the cell culture. Also, electrophoretic mobility shift analysis showed that the HBG1: g.-225_-222delAGCA deletion creates additional transcriptional factors' binding sites, which, we propose, bind a transcriptional repressor, thus decreasing the HBG1 gene promoter activity. These results are consistent with in silico analysis, which indicated that this deletion creates a binding site for GATA1, known to be a repressor of the -globin gene expression. These data confirm the regulatory role of the HBG1: g.-225_-222 region that exerts its effect under conditions of erythropoietic stress characteristic for -thal patients.