Division of Hematology, Children's Hospital of Philadelphia, Philadelphia, PA.
Hematology/Oncology Division, Department of Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA.
Blood. 2020 Jun 11;135(24):2121-2132. doi: 10.1182/blood.2020005301.
Reactivation of fetal hemoglobin remains a critical goal in the treatment of patients with sickle cell disease and β-thalassemia. Previously, we discovered that silencing of the fetal γ-globin gene requires the erythroid-specific eIF2α kinase heme-regulated inhibitor (HRI), suggesting that HRI might present a pharmacologic target for raising fetal hemoglobin levels. Here, via a CRISPR-Cas9-guided loss-of-function screen in human erythroblasts, we identify transcription factor ATF4, a known HRI-regulated protein, as a novel γ-globin regulator. ATF4 directly stimulates transcription of BCL11A, a repressor of γ-globin transcription, by binding to its enhancer and fostering enhancer-promoter contacts. Notably, HRI-deficient mice display normal Bcl11a levels, suggesting species-selective regulation, which we explain here by demonstrating that the analogous ATF4 motif at the murine Bcl11a enhancer is largely dispensable. Our studies uncover a linear signaling pathway from HRI to ATF4 to BCL11A to γ-globin and illustrate potential limits of murine models of globin gene regulation.
重新激活胎儿血红蛋白仍然是治疗镰状细胞病和β-地中海贫血患者的一个关键目标。此前，我们发现，γ-珠蛋白基因的沉默需要红细胞特异性的 eIF2α 激酶血红素调节抑制剂 (HRI)，这表明 HRI 可能是提高胎儿血红蛋白水平的一个药物靶点。在这里，我们通过在人类红细胞中进行 CRISPR-Cas9 指导的功能丧失筛选，鉴定出转录因子 ATF4 作为一种新的 γ-珠蛋白调节剂，它是一种已知的 HRI 调节蛋白。ATF4 通过结合其增强子并促进增强子-启动子接触，直接刺激 BCL11A 的转录，BCL11A 是 γ-珠蛋白转录的抑制剂。值得注意的是，缺乏 HRI 的小鼠显示出正常的 Bcl11a 水平，这表明存在物种选择性调节，我们在这里通过证明鼠类 Bcl11a 增强子中的类似 ATF4 基序在很大程度上是可有可无的，解释了这一现象。我们的研究揭示了一条从 HRI 到 ATF4 到 BCL11A 再到 γ-珠蛋白的线性信号通路，并说明了珠蛋白基因调控的鼠类模型的潜在局限性。
