Pecci A, Viegas L R, Baranao J L, Beato M
Institut für Molekularbiologie und Tumorforschung (IMT), Marburg 35033, Germany.
J Biol Chem. 2001 Jun 15;276(24):21062-9. doi: 10.1074/jbc.M008665200. Epub 2001 Mar 26.
Differential splicing from the bcl-X gene generates several isoforms with opposite effects on the apoptotic response. To explore the mechanism controlling the balance between the various isoforms, we have characterized the 5' region of the mouse bcl-X gene. We identified three new promoters in addition to the two previously described (Grillot, D. A., M., G.-G., Ekhterae, D., Duan, L., Inohara, N., Ohta, S., Seldin, M. F., and Núñez, G. (1997) J. Immunol. 158, 4750-4757). These five promoters (P1-P5) would give rise to at least five mRNAs with different 5'-untranslated region, all sharing the same translation initiation site. Except for the product of the most proximal promoter (P1), the other mRNAs are generated by alternative splicing of noncoding exons to a common acceptor site located in the first translated exon. Reverse transcriptase-polymerase chain reaction, primer extension, and RNase protection assays demonstrate a tissue-specific pattern of promoter usage. P1 and P2 are active in all tissues analyzed, whereas the other three promoter show tissue-specific activities. P3 is active in spleen, liver, and kidney, P4 is active in uterus and spleen, and P5 is active in spleen, liver, brain, and thymus. We present evidence suggesting that promoter selection influences the outcome of the splice process. Transcripts from P1 generate mainly the mRNA for the long isoform Bcl-X(L), whereas transcripts from P2 generate mRNAs for the isoforms Bcl-X(L), Bcl-X(S), and Bcl-X(gamma) and transcripts from P3 yield mainly mRNAs for the isoform Bcl-X(gamma). Our results suggest a key role of promoter choice in determining alternative splicing and, thus, the balance of Bcl-X isoforms.
bcl-X基因的差异剪接产生了几种对凋亡反应具有相反作用的异构体。为了探究控制各种异构体之间平衡的机制，我们对小鼠bcl-X基因的5'区域进行了特征分析。除了先前描述的两个启动子外，我们还鉴定出了三个新的启动子（Grillot, D. A., M., G.-G., Ekhterae, D., Duan, L., Inohara, N., Ohta, S., Seldin, M. F., and Núñez, G. (1997) J. Immunol. 158, 4750 - 4757）。这五个启动子（P1 - P5）将产生至少五种具有不同5'-非翻译区的mRNA，它们都共享相同的翻译起始位点。除了最靠近近端的启动子（P1）的产物外，其他mRNA是通过非编码外显子与位于第一个翻译外显子中的共同受体位点的可变剪接产生的。逆转录酶 - 聚合酶链反应、引物延伸和核糖核酸酶保护试验证明了启动子使用的组织特异性模式。P1和P2在所有分析的组织中都有活性，而其他三个启动子表现出组织特异性活性。P3在脾脏、肝脏和肾脏中活跃，P4在子宫和脾脏中活跃，P5在脾脏、肝脏、大脑和胸腺中活跃。我们提供的证据表明启动子选择会影响剪接过程的结果。来自P1的转录本主要产生长异构体Bcl-X(L)的mRNA，而来自P2的转录本产生异构体Bcl-X(L)、Bcl-X(S)和Bcl-X(γ)的mRNA，来自P3的转录本主要产生异构体Bcl-X(γ)的mRNA。我们的结果表明启动子选择在决定可变剪接以及Bcl-X异构体平衡方面起着关键作用。
