SIRT6 stabilizes DNA-dependent protein kinase at chromatin for DNA double-strand break repair. McCord RA et al. The Sir2 chromatin regulatory factor links maintenance of genomic stability to life span extension in yeast. The mammalian Sir2 family member SIRT6 has been proposed to have analogous functions, because SIRT6-deficiency leads to shortened life span and an aging-like degenerative phenotype in mice, and SIRT6 knockout cells exhibit genomic instability and DNA damage hypersensitivity. However, the molecular mechanisms underlying these defects are not fully understood. Here, we show that SIRT6 forms a macromolecular complex with the DNA double-strand break (DSB) repair factor DNA-PK (DNA-dependent protein kinase) and promotes DNA DSB repair. In response to DSBs, SIRT6 associates dynamically with chromatin and is necessary for an acute decrease in global cellular acetylation levels on histone H3 Lysine 9. Moreover, SIRT6 is required for mobilization of the DNA-PK catalytic subunit (DNA-PKcs) to chromatin in response to DNA damage and stabilizes DNA-PKcs at chromatin adjacent to an induced site-specific DSB. Abrogation of these SIRT6 activities leads to impaired resolution of DSBs. Together, these findings elucidate a mechanism whereby regulation of dynamic interaction of a DNA repair factor with chromatin impacts on the efficiency of repair, and establish a link between chromatin regulation, DNA repair, and a mammalian Sir2 factor.
This gene encodes a member of the sirtuin family of proteins, homologs to the yeast Sir2 protein. Members of the sirtuin family are characterized by a sirtuin core domain and grouped into four classes. The functions of human sirtuins have not yet been determined; however, yeast sirtuin proteins are known to regulate epigenetic gene silencing and suppress recombination of rDNA. Studies suggest that the human sirtuins may function as intracellular regulatory proteins with mono-ADP-ribosyltransferase activity. The protein encoded by this gene is included in class IV of the sirtuin family. Alternative splicing results in multiple transcript variants.
, Epigenetic modifications
Expression regulated by
ournal of Mammalian Ova Research 30(1):24-29. 2013
Effects of Maternal Aging on Expression of Sirtuin Genes in Ovulated Oocyte and Cumulus Cells
Naoki Okamoto 1,3, Kazuhiro Kawamura 1,*, Nanami Kawamura 2, Chie Nishijima 1, Bunpei Ishizuka 2, Nao Suzuki 1 and Kazuaki Hirata 3
1 Department of Obstetrics and Gynecology
2 Department of Advanced Reproductive Medicine
3 Department of Anatomy, St. Marianna University School of Medicine, Kanagawa 216-8512, Japan
* To whom corresponding should be addressed. e-mail: firstname.lastname@example.org
Sirtuins, a family of NAD+-dependent protein deacetylases, regulate important physiological events including aging and cell metabolism, mainly by protecting cells/tissues from oxidative damage. Ovarian aging decreases the quality of oocytes through induction of mitochondrial dysfunction and increases in DNA strand breaks by accumulation of reactive oxygen species. However, involvement of sirtuins in regulating oocyte quality with aging has not been determined. Here, we found the expression of sirtuin genes (Sirt1?7) in mouse ovaries and isolated oocytes and cumulus cells in a cell-specific manner. Based on real-time RT-PCR, all seven sirtuin genes were detected in the ovary with Sirt2 transcript levels showing the highest abundance. Oocyte expressed high levels of Sirt6, whereas the expressions of Sirt1, Sirt2, Sirt4, and Sirt6 were high in cumulus cells. When comparing samples from young and aged mice, oocyte levels of Sirt1?7 mRNA were not different. However, Sirt2 and Sirt6 transcript levels were decreased in cumulus cells of aged mice. Our findings suggest a possible association of Sirt2 and Sirt6 transcript levels in cumulus cells with impaired oocyte quality in aged mice. Further understanding the roles of these sirtuins in cumulus cell and oocyte could provide a better strategy to minimize aging-related decline in oocyte quality.
////////Effects of caloric restriction and a high-fat diet on the ovarian lifespan in rats and the expression of SIRT1 and SIRT6 proteins. Luo LL et al. Background and Aims: Caloric restriction (CR) extends the mammal lifespan and suppresses ovary development. Sirtuins are involved in the mechanisms of lifespan extension of CR. However, whether, as well as to what extent, CR affects ovary lifespan or the ovarian follicle development is largely unknown. We investigated the effects of moderate and severe caloric restriction on the ovarian follicle reserves in rats compared with a high-fat dietary regimen. Methods: Female Sprague-Dawley rats (n=48) were randomly divided into four groups: normal control (NC), 25% caloric restriction (MCR), 45% CR (SCR) and high-fat diet (HF). They were maintained on these regimens for 2 months. Results: Histological analysis showed that both the 25 and 45% CR rats had a significantly higher percentage of primordial follicles and greater number of healthy follicles than the NC rats, whereas the HF rats did not differ significantly from the NC rats. Immunohistochemical analysis revealed that SIRT1 and SIRT6 proteins were present in the nucleus and cytoplasm of the oocyte. The 25% CR diet increased the expression of both SIRT1 and SIRT6 in the ovary, whereas the 45% CR and HF diets caused a decrease in SIRT1 expression. The level of SIRT6 protein did not change with the 45% CR diet, and it appeared slightly lower in the HF than in the NC groups. Conclusions: Thus, caloric restriction may inhibit the transition from primordial to developing follicles and extend the entire growth phase of a follicle to preserve the reserve of germ cells. SIRT1 and SIRT6 are both associated with these effects.
Mutation name: None
type: null mutation fertility: unknown Comment: Genomic instability and aging-like phenotype in the absence of mammalian SIRT6. Mostoslavsky R et al. The Sir2 histone deacetylase functions as a chromatin silencer to regulate recombination, genomic stability, and aging in budding yeast. Seven mammalian Sir2 homologs have been identified (SIRT1-SIRT7), and it has been speculated that some may have similar functions to Sir2. Here, we demonstrate that SIRT6 is a nuclear, chromatin-associated protein that promotes resistance to DNA damage and suppresses genomic instability in mouse cells, in association with a role in base excision repair (BER). SIRT6-deficient mice are small and at 2-3 weeks of age develop abnormalities that include profound lymphopenia, loss of subcutaneous fat, lordokyphosis, and severe metabolic defects, eventually dying at about 4 weeks. We conclude that one function of SIRT6 is to promote normal DNA repair, and that SIRT6 loss leads to abnormalities in mice that overlap with aging-associated degenerative processes.