Zacharias D A, Strehler E E
Department of Biochemistry and Molecular Biology, Mayo Graduate School, Mayo Clinic/Foundation, Rochester, Minnesota 55905, USA.
Curr Biol. 1996 Dec 1;6(12):1642-52. doi: 10.1016/s0960-9822(02)70788-4.
Most eukaryotic genes are divided into introns and exons. Upon transcription, the intronic segments are eliminated and the exonic sequences spliced together through a series of complex processing events. Alternative splicing refers to the optional inclusion or exclusion of specific exons in transcripts derived from a single gene, which leads to structural and functional changes in the encoded proteins. Although many components of the machinery directing the physical excision of introns and joining of exons have been elucidated in recent years, the signaling pathways regulating the activity of the machinery remain largely unexplored.
A calcium-mediated signaling pathway regulates alternative splicing at a specific site of human plasma membrane calcium pump-2 transcripts. This site consists of three exons, which are differentially used in a tissue-specific manner. In IMR32 neuroblastoma cells, a transient elevation of intracellular calcium changed the predominant pattern from one in which all three exons are included to the coexpression of a variant including only the third exon. Western-blot analysis demonstrated that the newly expressed mRNAs are faithfully translated. Once induced, the new splicing pattern was maintained over multiple cell divisions. Protein synthesis was not required to induce the alternative splice change, indicating that all components necessary for a rapid cellular response are present in the cells.
Calcium signaling exerts a direct influence on the regulation of alternative splicing. Notably, a calcium-mediated change in the expression of alternatively spliced variants of a calcium regulatory protein was discovered. The change in splicing occurs quickly, is persistent but reversible and leads to a corresponding change in protein expression. The specific nature in which differently spliced protein variants are expressed, and now the fact that their expression can be regulated by distinct intracellular signaling pathways, suggests that the regulation of alternative splicing by physiological stimuli is a widespread regulatory mechanism by which a cell may coordinate its responses to environmental cues.
大多数真核基因被分为内含子和外显子。转录时，内含子片段被去除，外显子序列通过一系列复杂的加工事件拼接在一起。可变剪接是指在源自单个基因的转录本中特定外显子的选择性包含或排除，这会导致编码蛋白的结构和功能发生变化。尽管近年来指导内含子物理切除和外显子连接的许多机制组件已被阐明，但调节该机制活性的信号通路仍 largely 未被探索。
一条钙介导的信号通路在人质膜钙泵 -2 转录本的特定位点调节可变剪接。该位点由三个外显子组成，它们以组织特异性方式被差异使用。在 IMR32 神经母细胞瘤细胞中，细胞内钙的短暂升高改变了主要模式，从包含所有三个外显子的模式变为仅包含第三个外显子的变体的共表达。蛋白质印迹分析表明新表达的 mRNA 被忠实地翻译。一旦诱导，新的剪接模式在多个细胞分裂中得以维持。诱导可变剪接变化不需要蛋白质合成，表明细胞快速反应所需的所有组件都存在于细胞中。
钙信号对可变剪接的调节有直接影响。值得注意的是，发现了钙调节蛋白可变剪接变体表达的钙介导变化。剪接变化发生迅速、持续但可逆，并导致蛋白质表达的相应变化。不同剪接的蛋白质变体表达的特定性质，以及现在它们的表达可由不同细胞内信号通路调节这一事实，表明生理刺激对可变剪接的调节是一种广泛的调节机制，通过该机制细胞可以协调其对环境线索的反应。
