Abstract
The Sir2 histone deacetylase gene family consists of seven mammalian sirtuins (SIRTs) which are NAD-dependent histone/protein deacetylases. Sir2 proteins regulate, for instance, genome stability by chromatin silencing in yeast. In mammals, their function is still largely unknown. Due to the NAD+ dependency, Sir2 might be the link between metabolic activity and histone/protein acetylation. Regulation of gene expression also seems to play an important role in Sir2 functions, since increasing the dosage of Sir2 genes increases genome stability in yeast and Caenorhabditis elegans. We observed that the modification of histone/protein acetylation status by several class I and II histone deacetylase (HDAC) inhibitors induces differential changes in gene expression profiles of seven SIRT mRNAs in cultured neuronal cells. SIRT2, SIRT4 and SIRT7 were upregulated, whereas SIRT1, SIRT5 and SIRT6 were downregulated by trichostatin A (TSA) and n-butyrate. The upregulation of SIRT mRNAs was inhibited by actinomycin D. Interestingly, the regulation of SIRT mRNAs was highly similar both in mouse Neuro-2a neuroblastoma cells and post-mitotic rat primary hippocampal and cerebellar granule neurons. Using a chromatin immunoprecipitation technique, we showed that the upregulation of SIRT2 expression with TSA is related to the hyperacetylation of DNA-bound histone H4 within the first 500 bp upstream of the transcription start site of the SIRT2 gene. Chemically different types of HDAC inhibitors, such as TSA, apicidin, SAHA, M344 and n-butyrate induced remarkably similar responses in SIRT1-7 mRNA expression patterns. Differential responses in SIRT mRNA expression profiles indicate that the expression of the Sir2 family of genes is selectively regulated and dependent on histone/protein acetylation status.