Laboratory for Transcriptional Regulation, RIKEN Center for Integrative Medical Sciences (IMS), 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan.
Sci Rep. 2017 Feb 2;7:41351. doi: 10.1038/srep41351.
A TCRβ enhancer, known as the Eβ enhancer, plays a critical role in V(D)J recombination and transcription of the Tcrb gene. However, the coordinated action of trans-acting factors in the activation of Eβ during T cell development remains uncharacterized. Here, we characterized the roles of Runx complexes in the regulation of the Eβ function. A single mutation at one of the two Runx binding motifs within the Eβ severely impaired Tcrb activation at the initiation phase in immature thymocytes. However, TCRβ expression level in mature thymocytes that developed under such a single Runx site mutation was similar to that of the control. In contrast, mutations at two Runx motifs eliminated Eβ activity, demonstrating that Runx complex binding is essential to initiate Eβ activation. In cells expressing Tcrb harboring rearranged V(D)J structure, Runx complexes are dispensable to maintain TCRβ expression, whereas Eβ itself is continuously required for TCRβ expression. These findings imply that Runx complexes are essential for Eβ activation at the initiation phase, but are not necessary for maintaining Eβ activity at later developmental stages. Collectively, our results indicate that the requirements of trans-acting factor for Eβ activity are differentially regulated, depending on the developmental stage and cellular activation status.
一个 TCRβ 增强子，称为 Eβ 增强子，在 V(D)J 重组和 Tcrb 基因的转录中起着关键作用。然而，在 T 细胞发育过程中，反式作用因子在 Eβ 激活中的协调作用仍未被描述。在这里，我们描述了 Runx 复合物在调节 Eβ 功能中的作用。Eβ 内的两个 Runx 结合基序之一的单个突变严重损害了未成熟胸腺细胞中 Tcrb 的起始阶段激活。然而，在这种单个 Runx 位点突变下发育的成熟胸腺细胞中的 TCRβ 表达水平与对照相似。相比之下，两个 Runx 基序的突变消除了 Eβ 活性，表明 Runx 复合物结合对于启动 Eβ 激活是必不可少的。在表达带有重排 V(D)J 结构的 Tcrb 的细胞中，Runx 复合物对于维持 TCRβ 表达是可有可无的，而 Eβ 本身对于 TCRβ 表达是持续需要的。这些发现表明，Runx 复合物对于 Eβ 在起始阶段的激活是必不可少的，但对于在后期发育阶段维持 Eβ 活性不是必需的。总之，我们的结果表明，反式作用因子对 Eβ 活性的要求是根据发育阶段和细胞激活状态而不同调节的。
