Lecointe N, Bernard O, Naert K, Joulin V, Larsen C J, Romeo P H, Mathieu-Mahul D
CNRS UMR 9942, Institut de Génétique Moléculaire de Montpellier, France.
Oncogene. 1994 Sep;9(9):2623-32.
The tal-1 gene, which is frequently activated in human T cell acute leukemias (T-ALLs), codes for a protein of the basic helix-loop-helix family (b-HLH) and potentially a transcription factor. In human and murine hematopoiesis tal-1 is expressed during the differentiation of the erythroid, megakaryocytic and mastocytic cell lineages. The expression of tal-1 appears to be comodulated with that of the transcription factor GATA-1 gene, suggesting that the GATA-1 protein may regulate the tal-1 gene activity in these hematopoietic lineages. To get further insights into the molecular mechanisms that control tal-1 expression, we have isolated 5' sequences of the murine gene and compared them to their human counterparts. The 5' flanking sequences from the two genes show several regions of high homology. The alignment of both sequences enabled us to predict that similarly, to the human, the mouse gene contains two alternative first exons (Ia and Ib). Remarkably, in both species, the proximal region of the tissue-specific exon Ia (i.e. gene segment -122 to +1) contains two GATA-motifs (at -65 and -33) and one SP-1 consensus binding site (-59). Mobility shift assays demonstrate that GATA proteins are able to interact with both GATA-motifs in a sequence specific fashion, but with different efficiencies. Moreover transfection studies show that the GATA-1 protein directly mediates tal-1 transcription by interacting with the -122/+1 fragment, defined as a minimal promoter in erythroid cells. Mutagenesis of the promoter establishes that the -33 GATA-binding site present in this fragment is critical for tal-1 expression in erythroid cells, but by itself does not lead to full promoter activity. Indeed, further mutations show that the second -65 GATA-binding site and the binding motif for SP1 (-59) significantly contribute to the overall activity of the proximal tal-1 promoter. Altogether, our data provide evidence that GATA-1 cooperates with the transcription factor SP1 to mediate the erythroid-specific expression of the tal-1 gene.
tal-1基因在人类T细胞急性白血病（T-ALL）中经常被激活，它编码一种属于碱性螺旋-环-螺旋家族（b-HLH）的蛋白质，可能是一种转录因子。在人类和小鼠的造血过程中，tal-1在红系、巨核系和肥大细胞系的分化过程中表达。tal-1的表达似乎与转录因子GATA-1基因的表达共同调节，这表明GATA-1蛋白可能在这些造血谱系中调节tal-1基因的活性。为了进一步深入了解控制tal-1表达的分子机制，我们分离了小鼠基因的5'序列，并将它们与人类的对应序列进行比较。这两个基因的5'侧翼序列显示出几个高度同源的区域。两个序列的比对使我们能够预测，与人类相似，小鼠基因包含两个选择性的第一外显子（Ia和Ib）。值得注意的是，在两个物种中，组织特异性外显子Ia的近端区域（即基因片段-122至+1）包含两个GATA基序（位于-65和-33）和一个SP-1共有结合位点（-59）。凝胶迁移试验表明，GATA蛋白能够以序列特异性的方式与两个GATA基序相互作用，但效率不同。此外，转染研究表明，GATA-1蛋白通过与定义为红系细胞中最小启动子的-122/+1片段相互作用，直接介导tal-1转录。启动子的诱变表明，该片段中存在的-33 GATA结合位点对红系细胞中tal-1的表达至关重要，但它本身并不能导致完全的启动子活性。事实上，进一步的突变表明，第二个-65 GATA结合位点和SP1的结合基序（-59）对近端tal-1启动子的整体活性有显著贡献。总之，我们的数据提供了证据，表明GATA-1与转录因子SP1合作，介导tal-1基因的红系特异性表达。
