The use of alternative polyadenylation in the tissue-specific regulation of human SMS1 gene expression.

Sphingomyelin synthase 1 (SMS1) is an essential enzyme that catalyses the synthesis of sphingomyelin and diacylglycerol from phosphatidylcholine and ceramide in eukaryotic cells. We previously studied the structure of the human SMS1 gene in detail, and identified its numerous transcripts. We revealed mRNA isoforms that varied in the 5'-untranslated region (UTR) and encoded the full-length protein as well as transcripts resulting from alternative combinations of the exons in the gene's coding region and the 3'-UTR. In the present work, we used real-time PCR data to determine the expression patterns of SMS1 transcripts encoding the full-length protein and the alternative transcripts whose coding region had been interrupted by their alternative exons, which are the conserved portions of intron VII. Our results indicate that the amount of SMS1 transcripts varies considerably between different human tissues. The mechanisms controlling the level of SMS1 transcripts might include tissue-specific intron polyadenylation causing the appearance of truncated transcripts not involved in the synthesis of the full-length protein SMS1.