Niu Yuxin, Sengupta Mayami, Titov Anton A, Choi Seung-Chul, Morel Laurence
Department of Pathology, Immunology and Laboratory Medicine, University of Florida, Gainesville, FL, 32610-0275, USA.
Department of Pathology, Immunology and Laboratory Medicine, University of Florida, Gainesville, FL, 32610-0275, USA.
Mol Immunol. 2017 May;85:148-154. doi: 10.1016/j.molimm.2017.02.016. Epub 2017 Mar 1.
PBX1-d is novel splice isoform of pre-B-cell leukemia homeobox 1 (PBX1) that lacks its DNA-binding and Hox-binding domains, and functions as a dominant negative. We have shown that PBX1-d expression in CD4 T cells is associated with systemic lupus erythematosus (SLE) in a mouse model as well as in human subjects. More specifically, PBX1-d expression leads to the production of autoreactive activated CD4+ T cells, a reduced frequency and function of Foxp3+ regulatory T (Treg) cells and an expansion of follicular helper T (Tfh) cells. Very little is known about the function of PBX1 in T cells, except that it directly regulates the expression of miRNAs associated with Treg and Tfh homeostasis. In the present study, we show that PBX1 directly regulated the expression of CD44, a marker of T cell activation. Two PBX1 binding sites in the promoter directly regulated CD44 expression, with PBX1-d driving a higher expression than the normal isoform PBX1-b. In addition, mutations in each of the two binding sites had different effects of PBX1-b and PBX1-d. Finally, we showed that an enhanced recruitment of co-factor MEIS by PBX1-d over PBX1-b, while there was no difference for co-factor PREP1 recruitment. Therefore, this study demonstrates that the lupus-associated PBX1-d isoform directly transactivates CD44, a marker of CD44 activation and memory, and that it has different DNA binding and co-factor recruitment relative to the normal isoform. Taken together, these results confirm that PBX1 directly regulates genes related to T cell activation and shows that the lupus-associated isoform PBX1-d has unique molecular functions.
PBX1-d是前B细胞白血病同源框1（PBX1）的一种新型剪接异构体，它缺乏DNA结合域和Hox结合域，并作为显性负性因子发挥作用。我们已经表明，在小鼠模型以及人类受试者中，CD4 T细胞中PBX1-d的表达与系统性红斑狼疮（SLE）相关。更具体地说，PBX1-d的表达导致自身反应性活化CD4+ T细胞的产生、Foxp3+调节性T（Treg）细胞的频率和功能降低以及滤泡辅助性T（Tfh）细胞的扩增。除了它直接调节与Treg和Tfh稳态相关的miRNA的表达外，关于PBX1在T细胞中的功能知之甚少。在本研究中，我们表明PBX1直接调节CD44的表达，CD44是T细胞活化的标志物。启动子中的两个PBX1结合位点直接调节CD44的表达，PBX1-d驱动的表达高于正常异构体PBX1-b。此外，两个结合位点各自的突变对PBX1-b和PBX1-d有不同的影响。最后，我们表明PBX1-d比PBX1-b增强了辅助因子MEIS的募集，而辅助因子PREP1的募集没有差异。因此，本研究表明，狼疮相关的PBX1-d异构体直接反式激活CD44，CD44是CD44活化和记忆的标志物，并且它相对于正常异构体具有不同的DNA结合和辅助因子募集。综上所述，这些结果证实PBX1直接调节与T细胞活化相关的基因，并表明狼疮相关异构体PBX1-d具有独特的分子功能。
