Faculty of Medicine, Department of Medical Microbiology, University of Malaya, Kuala Lumpur, Malaysia; Department of Molecular Immunology, Institute for Development, Aging and Cancer, Tohoku University, Sendai, Japan.
Eur J Immunol. 2014 Mar;44(3):894-904. doi: 10.1002/eji.201343496. Epub 2014 Feb 16.
Runx1 transcription factor is a key player in the development and function of T cells. Runx1 transcripts consist of two closely related isoforms (proximal and distal Runx1) whose expressions are regulated by different promoters. Which Runx1 isoform is expressed appears to be tightly regulated. The regulatory mechanism for differential transcription is, however, not fully understood. In this study, we investigated the regulation of the proximal Runx1 promoter in T cells. We showed that proximal Runx1 was expressed at a low level in naïve T cells from C57BL/6 mice, but its expression was remarkably induced upon T-cell activation. In the promoter of proximal Runx1, a highly conserved region was identified which spans from -412 to the transcription start site and harbors a NFAT binding site. In a luciferase reporter assay, this region was found to be responsive to T-cell activation through Lck and calcineurin pathways. Mutagenesis studies and chromatin immunoprecipitation assay indicated that the NFAT site was essential for NFAT binding and transactivation of the proximal Runx1 promoter. Furthermore, TCR signaling-induced expression of proximal Runx1 was blocked by treatment of cells with cyclosporin A. Together, these results demonstrate that the calcineurin-NFAT pathway regulates proximal Runx1 transcription upon TCR stimulation.
Runx1 转录因子是 T 细胞发育和功能的关键调节因子。Runx1 转录本由两个紧密相关的异构体（近端和远端 Runx1）组成，它们的表达受不同启动子的调控。哪种 Runx1 异构体表达似乎受到严格调控。然而，对于差异转录的调控机制尚不完全清楚。在本研究中，我们研究了 T 细胞中近端 Runx1 启动子的调节。我们表明，C57BL/6 小鼠幼稚 T 细胞中低水平表达近端 Runx1，但 T 细胞活化后其表达显著诱导。在近端 Runx1 启动子中，鉴定出一个高度保守的区域，跨度从-412 到转录起始位点，含有一个 NFAT 结合位点。在荧光素酶报告基因测定中，发现该区域通过 Lck 和钙调神经磷酸酶途径对 T 细胞活化有反应。突变研究和染色质免疫沉淀分析表明，NFAT 位点对于 NFAT 结合和近端 Runx1 启动子的转录激活是必需的。此外，细胞用环孢素 A 处理可阻断 TCR 信号诱导的近端 Runx1 表达。总之，这些结果表明，钙调神经磷酸酶-NFAT 途径在 TCR 刺激时调节近端 Runx1 转录。
