Quantitative analysis of alternative splicing options of human plasma membrane calcium pump genes

The alternative splicing options and the quantitative tissue distribution of the transcripts of the four currently known human plasma membrane calcium pump (PMCA) genes have been analyzed in seven tissues (cerebral cortex, skeletal and heart muscle, stomach, liver, lung, and kidney) by quantitative polymerase chain reaction on reverse transcribed mRNA with glyceraldehyde-3-phosphate dehydrogenase as the internal standard. The mRNAs of genes 1 and 4 were found to be present in similar amounts in all tissues, whereas the transcripts of genes 2 and 3 were expressed in a tissue-specific manner, i.e. their amounts were highest in fetal skeletal muscle and brain. Alternative splicing was found to occur in the PMCA transcripts at two major regulatory sites (sites A and C), adjacent to the amino-terminal phospholipid-responsive region and within the carboxyl-terminal calmodulin binding domain, respectively. Novel splicing variants not described previously for human genes were detected for hPMCA3 and 4 at site A and for hPMCA1, 2, and 3 at site C. For all genes a common splice variant was found at both splice sites. The common splice variant at site A was characterized by the inclusion of a small exon (hPMCA1, 39 base pairs (bp); hPMCA2, 42 bp; hPMCA3, 42 bp; hPMCA4, 36 bp). In the common splice variant at site C, an exon (hPMCA1, 154 bp; hPMCA2, 227 bp; hPMCA3, 154 bp; hPMCA4, 178 bp) was excluded in the mRNA. All genes normally express these main splice variants in all tissues in which the corresponding isoform is present. The splicing complexity at site C was found to be augmented in the transcripts of PMCA2 and PMCA3 through the use of additional exons, and in PMCA1 and 3 through the use of additional internal splice sites in the single alternatively spliced 154-base pair exon.