FISH-mapping and genomic organization of the NAD-dependent histone deacetylase gene, Sirtuin 2 (Sirt2)

Sirtuin 2 (SIRT2) is a nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase, which belongs to the Silent information regulator 2 (Sir2) family of sirtuin histone deacetylases (HDACs). The yeast Sir2 protein and its mammalian derivatives play a central role in epigenetic gene silencing, DNA repair and recombination, cell-cycle, microtubule organization, and in the regulation of aging. We have isolated and characterized the human Sirt2 genomic sequence, which spans a region of 20,960 bp and which has one single genomic locus. Determination of the exon-intron splice junctions found the full-length SIRT2 protein to consist of 16 exons ranging in size from 16 bp (exon 1) to 749 bp (exon 9). The 1,963-bp human Sirt2 mRNA has an open reading frame of 1,167 bp that encodes two isoforms of the SIRT2 protein: isoform 1 encodes a 389-aa protein with a predictive molecular weight of 43.2 kDa and an isoelectric point of 5.22, while isoform 2, which is lacking the first three exons, encodes a 352-aa protein with a predictive molecular weight of 39.5 kDa and an isoelectric point of 6.05. Characterization of the 5' flanking genomic region, which precedes the Sirt2 open reading frame, revealed a TATA- and CCAAT-box less promoter that contains a 0.67-kb CpG island and a number of NFkappaB and GATA transcription factor binding sites. Fluorescence in situ hybridization analysis localized the human Sirt2 gene to chromosome 19q13.1. Human SIRT2 is known to be most predominantly expressed in the brain. Since it is however severely reduced in a large number of human brain tumor cell lines, the absence of SIRT2, a potential tumor suppressor, could play a key role in the regulation of the cell-cycle within a multistep pathway that leads to full cellular transformation and, finally, the development of cellular malignancy.