Bockamp E O, McLaughlin F, Murrell A M, Göttgens B, Robb L, Begley C G, Green A R
University of Cambridge, Department of Haematology, MRC Centre, UK.
Blood. 1995 Aug 15;86(4):1502-14.
The SCL/TAL-1 gene encodes a basic helix-loop-helix transcription factor that is expressed in multipotent hematopoietic progenitors before lineage commitment. Its expression is maintained during differentiation along erythroid, mast, and megakaryocytic lineages, but is repressed after commitment to nonexpressing lineages. To begin to address the molecular mechanisms underlying this complex pattern of expression, we have studied the regulation of the murine SCL promoter in erythroid and T-cell lines. Analysis of the methylation and chromatin structure of the SCL promoter region showed that SCL mRNA expression correlated with DNase hypersensitive sites and methylation status of the promoter. Transient reporter assays showed that promoter 1a was active in erythroid cells but not in T cells. Sequences between -187 and +26 were sufficient for lineage-restricted activity of promoter 1a. A joint promoter construct containing both promoter 1a and promoter 1b also exhibited lineage-restricted activity. Conserved GATA (-37), MAZ (+242), and ETS (+264) motifs were all shown to contribute to SCL promoter activity in erythroid cells, but several other motifs were not required for full promoter activity. The pattern of complexes binding to the +242 MAZ and +264 ETS sites were the same in erythroid and T cells. However, GATA-1 bound the -37 GATA site in erythroid cells, whereas in T cells GATA-3 was only able to bind weakly, if at all. Moreover, GATA-1 but not GATA-2 or GATA-3 was able to transactivate SCL promoter 1a in a T-cell environment. These results suggest that inactivity of SCL promoter 1a in T cells reflected the absence of GATA-1 rather than the presence of trans-dominant negative regulators.
SCL/TAL-1基因编码一种碱性螺旋-环-螺旋转录因子，该因子在多能造血祖细胞中于谱系定向之前表达。在沿红系、肥大细胞系和巨核细胞系分化过程中其表达得以维持，但在定向至不表达谱系后受到抑制。为了开始探究这种复杂表达模式背后的分子机制，我们研究了红系和T细胞系中鼠SCL启动子的调控。对SCL启动子区域的甲基化和染色质结构分析表明，SCL mRNA表达与启动子的DNase超敏位点和甲基化状态相关。瞬时报告基因检测显示，启动子1a在红系细胞中具有活性，但在T细胞中无活性。-187至+26之间的序列对于启动子1a的谱系限制性活性而言是足够的。包含启动子1a和启动子1b的联合启动子构建体也表现出谱系限制性活性。保守的GATA（-37）、MAZ（+242）和ETS（+264）基序均显示对红系细胞中的SCL启动子活性有贡献，但其他几个基序对于启动子的完全活性并非必需。与+242 MAZ和+264 ETS位点结合的复合物模式在红系细胞和T细胞中是相同的。然而，GATA-1在红系细胞中结合-37 GATA位点，而在T细胞中，GATA-3即使能结合也只能微弱结合。此外，在T细胞环境中，GATA-1而非GATA-2或GATA-3能够反式激活SCL启动子1a。这些结果表明，SCL启动子1a在T细胞中的无活性反映的是GATA-1的缺失而非反式显性负调控因子的存在。
