Lahlil Rachid, Lécuyer Eric, Herblot Sabine, Hoang Trang
Clinical Research Institute of Montreal, Montreal, Quebec H2W 1R7, Canada.
Mol Cell Biol. 2004 Feb;24(4):1439-52. doi: 10.1128/MCB.24.4.1439-1452.2004.
SCL/TAL1 is a hematopoietic-specific transcription factor of the basic helix-loop-helix (bHLH) family that is essential for erythropoiesis. Here we identify the erythroid cell-specific glycophorin A gene (GPA) as a target of SCL in primary hematopoietic cells and show that SCL occupies the GPA locus in vivo. GPA promoter activation is dependent on the assembly of a multifactorial complex containing SCL as well as ubiquitous (E47, Sp1, and Ldb1) and tissue-specific (LMO2 and GATA-1) transcription factors. In addition, our observations suggest functional specialization within this complex, as SCL provides its HLH protein interaction motif, GATA-1 exerts a DNA-tethering function through its binding to a critical GATA element in the GPA promoter, and E47 requires its N-terminal moiety (most likely entailing a transactivation function). Finally, endogenous GPA expression is disrupted in hematopoietic cells through the dominant-inhibitory effect of a truncated form of E47 (E47-bHLH) on E-protein activity or of FOG (Friend of GATA) on GATA activity or when LMO2 or Ldb-1 protein levels are decreased. Together, these observations reveal the functional complementarities of transcription factors within the SCL complex and the essential role of SCL as a nucleation factor within a higher-order complex required to activate gene GPA expression.
SCL/TAL1是一种碱性螺旋-环-螺旋（bHLH）家族的造血特异性转录因子，对红细胞生成至关重要。在此，我们确定红系细胞特异性糖蛋白A基因（GPA）是原代造血细胞中SCL的一个靶点，并表明SCL在体内占据GPA基因座。GPA启动子的激活依赖于一个多因子复合物的组装，该复合物包含SCL以及普遍存在的（E47、Sp1和Ldb1）和组织特异性的（LMO2和GATA-1）转录因子。此外，我们的观察结果表明该复合物内存在功能特化，因为SCL提供其HLH蛋白相互作用基序，GATA-1通过与GPA启动子中的关键GATA元件结合发挥DNA拴系功能，而E47需要其N端部分（很可能具有反式激活功能）。最后，在造血细胞中，通过截短形式的E47（E47-bHLH）对E蛋白活性的显性抑制作用、FOG（GATA之友）对GATA活性的显性抑制作用，或者当LMO2或Ldb-1蛋白水平降低时，内源性GPA表达会受到破坏。总之，这些观察结果揭示了SCL复合物中转录因子的功能互补性，以及SCL作为激活基因GPA表达所需的高阶复合物中的成核因子的重要作用。
