Molecular Mechanisms of Mammalian SIRT6 Function

 描述(由申请人提供)：我们的研究试图了解染色质调节机制如何影响核和表观遗传程序，以及这些机制的解除调节如何导致衰老和疾病。SIRT6是sirtuin酶家族中的一种染色质调节因子。小鼠缺乏SIRT6会导致寿命缩短，并导致与衰老、癌症和新陈代谢相关的表型。相反，在小鼠体内过表达SIRT6可以预防代谢性疾病，延长寿命。因此，研究SIRT6的功能有助于阐明健康衰老和长寿的基本机制。在此之前，我们发现SIRT6选择性地调节与表观遗传和基因调节功能相关的特定染色质标记。我们将SIRT6对染色质的调节与影响衰老和癌症的关键核过程联系起来，包括端粒维持、DNA修复和衰老相关基因表达的变化。在这里，我们关注SIRT6在染色质沉默机制中的新功能，这些机制在衰老过程中被解除调控。我们建议进行分子、基因组和功能研究，以研究SIRT6在维持重复DNA元件的异染色质沉默中的作用，并询问沉默受损如何导致与衰老相关的细胞功能障碍。在目标1中，我们将研究SIRT6在着丝粒重复卫星DNA元件异染色质沉默中的分子机制。着丝粒异染色质的缺陷在衰老和癌症的背景下都能观察到。我们将表征SIRT6在着丝粒染色质上的生化活性，这在有丝分裂过程中是如何调节的，以及它如何影响高阶染色质的变化。我们的研究将为癌细胞生物学和人类体细胞提供见解，在癌细胞生物学中，SIRT6缺失可能导致癌症进展，而在人类体细胞中，SIRT6可能防止细胞衰老或表观遗传可塑性的年龄相关性下降。在目标2中，我们将表征SIRT6维持异染色质对细胞内稳态的功能影响。我们将验证着丝粒异染色质丢失会触发异常有丝分裂、染色体分离缺陷和细胞衰老的假设，并可以促进细胞永生化的致癌过程。我们还将研究SIRT6和其他SIRT酶在这些过程中的功能相互作用。这些研究应该阐明异染色质分解是如何转化为细胞表型或功能衰退的，从而导致衰老和疾病。 在目标3中，我们将研究SIRT6在另一类重复DNA元件中的异染色质维持中的作用，这些重复DNA元件在衰老和癌症内源性逆转座子元件中被解除调控。我们会问，这些元件的沉默受损是否会导致基因组不稳定，从而影响细胞功能，或者导致衰老相关基因的异常转录。总而言之，这些研究应该能为衰老生物学中的基本染色质机制提供见解。

 DESCRIPTION (provided by applicant): Our research seeks to understand how chromatin regulatory mechanisms influence nuclear and epigenetic programs, and how de-regulation of these mechanisms contributes to aging and disease. SIRT6 is a chromatin regulatory factor in the sirtuin family of enzymes. SIRT6-deficiency in mice leads to shortened lifespan and phenotypes associated with aging, cancer, and metabolism. Conversely, SIRT6 over-expression in mice protects against metabolic disease and extends lifespan. Thus, studying SIRT6 function promises to elucidate fundamental mechanisms that underlie healthy aging and longevity. Previously, we showed that SIRT6 selectively regulates specific chromatin marks associated with epigenetic and gene-regulatory functions. We linked chromatin regulation by SIRT6 to key nuclear processes that impact on aging and cancer, including telomere maintenance, DNA repair, and aging-associated gene expression changes. Here, we focus on new functions of SIRT6 in chromatin silencing mechanisms that are deregulated in aging. We propose molecular, genomic, and functional studies to study the role of SIRT6 in maintaining heterochromatin silencing at repetitive DNA elements, and ask how impaired silencing leads to cellular dysfunction associated with aging. In Aim 1, we will study the molecular mechanisms of SIRT6 in heterochromatin silencing of repetitive satellite DNA elements at centromeres. Defects in centromeric heterochromatin are observed in the contexts of both aging and cancer. We will characterize the biochemical activity of SIRT6 at centromeric chromatin, how this is regulated during mitosis, and how it affects higher order chromatin changes. Our studies will provide insights for cancer cell biology, where SIRT6 loss may contribute to cancer progression, and for human somatic cells, where SIRT6 may guard against cellular senescence or age-dependent decline in epigenetic plasticity. In Aim 2, we will characterize the functional effects of heterochromatin maintenance by SIRT6 on cellular homeostasis. We will test the hypotheses that heterochromatin loss at centromeres triggers abnormal mitoses, chromosome segregation defects, and cellular senescence, and can facilitate the oncogenic process of cellular immortalization. We will also examine functional interplay between SIRT6 and other SIRT enzymes in these processes. These studies should elucidate how heterochromatin breakdown is translated into cellular phenotypes or functional decline that contributes to aging and disease. In Aim 3, we will investigate the role of SIRT6 in heterochromatin maintenance at another class of repetitive DNA elements that are deregulated in aging and cancer - endogenous retrotransposable elements. We will ask if impaired silencing of these elements leads to genomic instability that can affect cellular function, or to aberrant transcription of aging- relatd genes. Together, these studies should provide insights into fundamental chromatin mechanisms in aging biology.