Transcriptional regulation of CDKN2A/p16 by sirtuin 7 in senescence

Cell senescence is a state of limited cell prolif- eration during a stress response or as part of a programmed process. When a senescent cell stops dividing, maintaining metabolic activity contributes to cellular homeostasis mainte- nance. In this process, the cell cycle is arrested at the G0/G1 phase. p16^INK4A protein is a key regulator of this process via its cyclin-dependent kinase inhibitor (CDKI) function. CDKI 2A (CDKN2A)/p16 gene expression is regulated by DNA methylation and histone acetylation. Sirtuins (SIRTs) are nicotinamide dinucleotide (NAD⁺)-dependent deacetylases that have properties which prevent diseases and reverse certain aspects of aging (such as immune, metabolic and cardiovas- cular diseases). By performing quantitative PCR, Western blot, ChIP, and siRNAs assays, in this study it was demon- strated that CDKN2A/p16 gene transcriptional activation and repression were accompanied by selective deposition and elimination of histone acetylation during the senescence of MRC5 cells. Specifically, significant H3K9Ac and H3K18Ac enrichment in cells with a senescent phenotype concomitant with CDKN2A/p16 gene overexpression was demonstrated compared with the non-senescent phenotype. Furthermore, the presence of H3K18Ac in deacetyl-transferase SIRT7 knockdown MRC5 cells allowed CDKN2A/p16 promoter activation. These results suggested that SIRT7 served as a critical component of an epigenetic mechanism involved in senescence mediated by the CDKN2A/p16 gene.