School of Life Science, Gwangju Institute of Science and Technology, Gwangju 500-712, Republic of Korea.
Biochem Biophys Res Commun. 2012 Apr 6;420(2):467-72. doi: 10.1016/j.bbrc.2012.03.029. Epub 2012 Mar 13.
Alternative splicing plays an important role in the control of apoptosis. A number of genes related to apoptosis undergo alternative splicing. Among them, the apoptotic regulator Bcl-x produces two major isoforms, Bcl-xL and Bcl-xS, through the alternative splicing of exon 2 in its pre-mRNA. These isoforms have antagonistic function in apoptotic pathway; Bcl-xL is pro-apoptotic, while Bcl-xS is anti-apoptotic. The balanced ratio of two isoforms is important for cell survival. However, regulatory mechanisms of Bcl-x splicing remain poorly understood. Using a mini-gene system, we have found that a 105 nt exonic region (E3b) located within exon 3 affects exon 2 splicing in the Bcl-x gene. Further deletion and mutagenesis studies demonstrate that this 105 nt sequence contains various functional elements which promote skipping of exon 2b. One of these elements forms a stem-loop structure that stimulates skipping of exon 2b. Furthermore our results prove that the stem-loop structure functions as an enhancer in general pre-mRNA splicing. We conclude that we have identified a cis-regulatory element in exon 3 that affects splicing of exon 2 in the Bcl-x gene. This element could be potentially targeted to alter the ratio of Bcl-xL and Bcl-xS for treatment of tumors through an apoptotic pathway.
可变剪接在凋亡的调控中起着重要作用。许多与凋亡相关的基因都经历了可变剪接。其中，凋亡调节因子 Bcl-x 通过其前体 mRNA 中exon2 的可变剪接产生两种主要的异构体，Bcl-xL 和 Bcl-xS。这些异构体在凋亡途径中具有拮抗作用；Bcl-xL 促进凋亡，而 Bcl-xS 抑制凋亡。两种异构体的平衡比例对细胞存活很重要。然而，Bcl-x 剪接的调控机制仍知之甚少。我们使用迷你基因系统发现，位于 exon3 内的 105nt 外显子区域（E3b）影响 Bcl-x 基因中 exon2 的剪接。进一步的缺失和突变研究表明，这个 105nt 序列包含各种促进 exon2b 跳过的功能元件。其中一个元件形成一个发夹环结构，刺激 exon2b 的跳过。此外，我们的结果证明该发夹环结构作为一般前体 mRNA 剪接的增强子发挥作用。我们得出结论，我们已经在 Bcl-x 基因的 exon3 中鉴定出一个影响 exon2 剪接的顺式调控元件。该元件可作为一个潜在靶点，通过凋亡途径改变 Bcl-xL 和 Bcl-xS 的比例，用于治疗肿瘤。
