Tremblay Mathieu, Herblot Sabine, Lecuyer Eric, Hoang Trang
Clinical Research Institute of Montréal, Montréal, Québec H2W 1R7, Canada.
J Biol Chem. 2003 Apr 11;278(15):12680-7. doi: 10.1074/jbc.M209870200. Epub 2003 Feb 3.
The expression of the pT alpha gene is required for effective selection, proliferation, and survival of beta T-cell receptor (beta TCR)-expressing immature thymocytes. Here, we have identified two phylogenetically conserved E-boxes within the pT alpha enhancer sequence that are required for optimal enhancer activity and for its stage-specific activity in immature T cells. We have shown that the transcription factors E2A and HEB associate with high affinity to these E-boxes. Moreover, we have identified pT alpha as a direct target of E2A-HEB heterodimers in immature thymocytes because they specifically occupy the enhancer in vivo. In these cells, pT alpha mRNA levels are determined by the presence of one or two functional E2A or HEB alleles. Furthermore, E2A/HEB transcriptional activity is repressed by heterodimerization with SCL, a transcription factor that is turned off in differentiating thymocytes exactly at a stage when pT alpha is up-regulated. Taken together, our observations suggest that the dosage of E2A, HEB, and SCL determines pT alpha gene expression in immature T cells.
pTα基因的表达对于表达βT细胞受体（βTCR）的未成熟胸腺细胞的有效选择、增殖和存活是必需的。在此，我们在pTα增强子序列中鉴定出两个系统发育保守的E盒，它们对于最佳增强子活性及其在未成熟T细胞中的阶段特异性活性是必需的。我们已经表明，转录因子E2A和HEB与这些E盒具有高亲和力结合。此外，我们已确定pTα是未成熟胸腺细胞中E2A-HEB异二聚体的直接靶标，因为它们在体内特异性占据增强子。在这些细胞中，pTαmRNA水平由一个或两个功能性E2A或HEB等位基因的存在决定。此外，E2A/HEB转录活性通过与SCL异二聚化而受到抑制，SCL是一种转录因子，在分化中的胸腺细胞中恰好在pTα上调的阶段被关闭。综上所述，我们的观察结果表明，E2A、HEB和SCL的剂量决定了未成熟T细胞中pTα基因的表达。
