Human Pathophysiology and Translational Medicine Program, Institute for Translational Sciences, University of Texas Medical Branch, Galveston, Texas 77550, USA.
Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas 77550, USA.
RNA. 2024 Jun 17;30(7):824-838. doi: 10.1261/rna.079933.123.
Forkhead box P3 (FOXP3) is the master fate-determining transcription factor in regulatory T (T) cells and is essential for their development, function, and homeostasis. Mutations in cause immunodysregulation polyendocrinopathy enteropathy X-linked (IPEX) syndrome, and aberrant expression of has been implicated in other diseases such as multiple sclerosis and cancer. We previously demonstrated that pre-mRNA splicing of RNAs is highly sensitive to levels of DExD-box polypeptide 39B (DDX39B), and here we investigate the mechanism of this sensitivity. introns have cytidine (C)-rich/uridine (U)-poor polypyrimidine (py) tracts that are responsible for their inefficient splicing and confer sensitivity to DDX39B. We show that there is a deficiency in the assembly of commitment complexes (CCs) on introns, which is consistent with the lower affinity of U2AF2 for C-rich/U-poor py tracts. Our data indicate an even stronger effect on the conversion of CCs to pre-spliceosomes. We propose that this is due to an altered conformation that U2AF2 adopts when it binds to C-rich/U-poor py tracts and that this conformation has a lower affinity for DDX39B. As a consequence, CCs assembled on introns are defective in recruiting DDX39B, and this leads to the inefficient assembly of pre-spliceosome complexes.
叉头框蛋白 P3（FOXP3）是调节性 T（T）细胞中决定命运的主要转录因子，对于其发育、功能和稳态至关重要。 基因突变导致免疫失调多内分泌腺病肠病伴 X 连锁（IPEX）综合征，而 异常表达与多发性硬化症和癌症等其他疾病有关。我们之前证明了 前体 mRNA 的剪接对 DExD-框多肽 39B（DDX39B）的水平高度敏感，在此我们研究了这种敏感性的机制。 内含子具有富含胞嘧啶（C）/尿嘧啶（U）的嘧啶（py）寡聚体，这导致其剪接效率低下，并赋予对 DDX39B 的敏感性。我们表明， 内含子上的承诺复合物（CC）组装存在缺陷，这与 U2AF2 对富含 C/U 的 py 寡聚体的亲和力较低一致。我们的数据表明，这对 CC 向预剪接体的转化具有更强的影响。我们提出，这是由于 U2AF2 结合富含 C/U 的 py 寡聚体时采用的构象改变，并且这种构象与 DDX39B 的亲和力较低。因此， 内含子上组装的 CC 无法有效募集 DDX39B，这导致预剪接体复合物的组装效率降低。
