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.
NCBI Summary:
This gene encodes a member of the sirtuin family of NAD-dependent enzymes that are implicated in cellular stress resistance, genomic stability, aging and energy homeostasis. The encoded protein is localized to the nucleus, exhibits ADP-ribosyl transferase and histone deacetylase activities, and plays a role in DNA repair, maintenance of telomeric chromatin, inflammation, lipid and glucose metabolism. Alternative splicing results in multiple transcript variants encoding different isoforms. [provided by RefSeq, Mar 2016]
General function
, Epigenetic modifications
Comment
Cellular localization
Cytoplasmic, Nuclear
Comment
Ovarian function
Oocyte maturation
Comment
Cumulus cell-derived and maternal SIRT6 differentially regulates porcine oocyte meiotic maturation. Cao Z et al. (2019) SIRT6, a member of the sirtuin family, is a NAD + dependent protein deacetylase and has been implicated in transcriptional regulation of somatic cells and post-transcriptional regulation of oocyte meiosis. However, the function of cumulus cell-derived and maternal SIRT6 in meiotic maturation of porcine oocytes is not yet known. Here, we report that SIRT6 mRNA and protein exists in the oocyte and its surrounding cumulus cells during meiotic maturation. Functional studies using a specific inhibitor in cumulus-enclosed oocytes revealed important roles for SIRT6 in germinal vesicle breakdown (GVBD) and cumulus expansion. Moreover, inhibitor treatment led to a significant reduction in the rate of first polar body (PB1) extrusion and early development of parthenogenetically activated embryos. In contrast, SIRT6 inhibition in cumulus-free oocytes only resulted in a significant reduction in the rate of PB1 extrusion. Furthermore, SIRT6 dysfunction regardless of the origin in both cumulus cells and oocytes severely impaired spindle organization and chromosome alignment at the metaphase stage. Molecularly, SIRT6 inhibition in cumulus cells significantly reduced expression of genes associated with cumulus expansion and gap junctional communication and even expression levels of active phosphorylated CDK1 in oocytes. Importantly, adenylate cyclase inhibition could partially rescue GVBD and PB1 extrusion in SIRT6-inhibited cumulus-enclosed oocytes. Taken together, these results demonstrate that cumulus cell-expressed and maternal SIRT6 differentially regulates porcine oocyte meiotic maturation.//////////////////
Sirt6 depletion causes spindle defects and chromosome misalignment during meiosis of mouse oocyte. Han L et al. (2015) Sirt6, a member of the sirtuin family of NAD-dependent protein deacetylases, has been implicated in multiple biological processes. However, the roles of Sirt6 in meiosis have not been addressed. In the present study, by employing knockdown analysis in mouse oocytes, we evaluated the effects of Sirt6 on meiotic apparatus. We found that specific depletion of Sirt6 results in disruption of spindle morphology and chromosome alignment in oocytes. Consistent with this observation, incidence of aneuploidy is also markedly increased in Sirt6-depleted oocytes. Furthermore, confocal scanning showed that kinetochore-microtubule interaction, an important mechanism controlling chromosome segregation, is severely impaired in metaphase oocytes following Sirt6 knockdown. Unexpectedly, we discovered that Sirt6 modulates the acetylation status of histone H4K16 as their knockdown specifically induces the hyperacetylation of H4K16 in oocytes, which may be associated with the defective phenotypes described above via altering kinetochore function. Altogether, our data reveal a novel function of Sirt6 during oocyte meiosis and indicate a pathway regulating meiotic apparatus.//////////////////
Expression regulated by
Comment
Ovarian localization
Oocyte, Cumulus
Comment
ournal of Mammalian Ova Research 30(1):24-29. 2013
doi: http://dx.doi.org/10.1274/jmor.30.24
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: kawamurak@marianna-u.ac.jp
Abstract:
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.
Follicle stages
Comment
Phenotypes
Mutations
1 mutations
Species: mouse
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.