Pang Liyan, Xue Hai-Hui, Szalai Gabor, Wang Xun, Wang Yuhuan, Watson Dennis K, Leonard Warren J, Blobel Gerd A, Poncz Mortimer
Children's Hospital of Philadelphia, ARC 316H, 3165 Civic Center Blvd, Philadelphia, PA, USA.
Blood. 2006 Oct 1;108(7):2198-206. doi: 10.1182/blood-2006-04-019760. Epub 2006 Jun 6.
Numerous megakaryocyte-specific genes contain signature Ets-binding sites in their regulatory regions. Fli-1 (friend leukemia integration 1), an Ets transcription factor, is required for the normal maturation of megakaryocytes and controls the expression of multiple megakaryocyte-specific genes. However, in Fli-1-/- mice, early megakaryopoiesis persists, and the expression of the early megakaryocyte-specific genes, alphaIIb and cMpl, is maintained, consistent with functional compensation by a related Ets factor(s). Here we identify the Ets protein GABPalpha (GA-binding protein alpha) as a regulator of early megakaryocyte-specific genes. Notably, GABPalpha preferentially occupies Ets elements of early megakaryocyte-specific genes in vitro and in vivo, whereas Fli-1 binds both early and late megakaryocyte-specific genes. Moreover, the ratio of GABPalpha/Fli-1 expression declines throughout megakaryocyte maturation. Consistent with this expression pattern, primary fetal liver-derived megakaryocytes from Fli-1-deficient murine embryos exhibit reduced expression of genes associated with late stages of maturation (glycoprotein [GP] Ibalpha, GPIX, and platelet factor 4 [PF4]), whereas GABPalpha-deficient megakaryocytes were mostly impaired in the expression of early megakaryocyte-specific genes (alphaIIb and cMpl). Finally, mechanistic experiments revealed that GABPalpha, like Fli-1, can impart transcriptional synergy between the hematopoietic transcription factor GATA-1 and its cofactor FOG-1 (friend of GATA-1). In concert, these data reveal disparate, but overlapping, functions of Ets transcription factors at distinct stages of megakaryocyte maturation.
许多巨核细胞特异性基因在其调控区域含有标志性的Ets结合位点。Ets转录因子Fli-1（友伴白血病整合1）是巨核细胞正常成熟所必需的，并控制多个巨核细胞特异性基因的表达。然而，在Fli-1基因敲除小鼠中，早期巨核细胞生成持续存在，早期巨核细胞特异性基因αIIb和cMpl的表达得以维持，这与相关Ets因子的功能补偿一致。在此，我们确定Ets蛋白GABPα（GA结合蛋白α）是早期巨核细胞特异性基因的调节因子。值得注意的是，GABPα在体外和体内优先占据早期巨核细胞特异性基因的Ets元件，而Fli-1则结合早期和晚期巨核细胞特异性基因。此外，在整个巨核细胞成熟过程中，GABPα/Fli-1表达的比例下降。与这种表达模式一致，来自Fli-1缺陷型小鼠胚胎的原代胎儿肝脏来源的巨核细胞显示出与成熟后期相关基因（糖蛋白[GP]Ibalpha.GPIX和血小板因子4[PF4]）的表达降低，而GABPα缺陷型巨核细胞在早期巨核细胞特异性基因（αIIb和cMpl）的表达上大多受损。最后，机制实验表明，GABPα与Fli-1一样，能够在造血转录因子GATA-1与其辅因子FOG-1（GATA-1的友伴）之间赋予转录协同作用。总之，这些数据揭示了Ets转录因子在巨核细胞成熟不同阶段的不同但重叠的功能。
