CHANGE IN PLASMA-MEMBRANE CA2-ATPASE SPLICE-VARIANT EXPRESSION IN RESPONSE TO A RISE IN INTRACELLULAR CA2+()

Background: Most eukaryotic genes are divided into introns and exons. Upon transcription, the intronic segments are eliminated and the exoni c sequences spliced together through a series of complex processing ev ents. Alternative splicing refers to the optional inclusion or exclusi on of specific exons in transcripts derived from a single gene, which leads to structural and functional changes in the encoded proteins. Al though many components of the machinery directing the physical excisio n of introns and joining of exons have been elucidated in recent years , the signaling pathways regulating the activity of the machinery rema in largely unexplored. Results: A calcium-mediated signaling pathway r egulates alternative splicing at a specific site of human plasma membr ane calcium pump-a transcripts, This site consists of three exons, whi ch are differentially used in a tissue-specific manner. In IMR32 neuro blastoma cells, a transient elevation of intracellular calcium changed the predominant pattern from one in which all three exons are include d to the coexpression of a variant including only the third exon. West ern-blot analysis demonstrated that the newly expressed mRNAs are fait hfully translated. Once induced, the new splicing pattern was maintain ed 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. Conc lusions: Calcium signaling exerts a direct influence on the regulation of alternative splicing. Notably, a calcium-mediated change in the ex pression of alternatively spliced variants of a calcium regulatory pro tein was discovered. The change in splicing occurs quickly, is persist ent but reversible and leads to a corresponding change in protein expr ession. The specific nature in which differently spliced protein varia nts are expressed, and now the fact that their expression can be regul ated by distinct intracellular signaling pathways, suggests that the r egulation of alternative splicing by physiological stimuli is a widesp read regulatory mechanism by which a cell may coordinate its responses to environmental cues.