Molecular Mechanisms of Mammalian SIRT6 Function

 描述（由申请人提供）：我们的研究旨在了解染色质调控机制如何影响核和表观遗传程序，以及这些机制的失调如何导致衰老和疾病。SIRT 6是sirtuin酶家族中的染色质调节因子。小鼠SIRT 6缺陷导致寿命缩短，并导致与衰老、癌症和代谢相关的表型。相反，SIRT 6在小鼠中的过表达可以防止代谢疾病并延长寿命。因此，研究SIRT 6的功能有望阐明健康衰老和长寿的基本机制。以前，我们发现SIRT 6选择性地调节与表观遗传和基因调控功能相关的特定染色质标记。我们将SIRT 6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修复和衰老相关的基因表达变化。在这里，我们专注于SIRT 6在衰老中失调的染色质沉默机制中的新功能。我们提出了分子，基因组和功能研究，研究SIRT 6在维持异染色质沉默的重复DNA元件的作用，并询问如何受损沉默导致与衰老相关的细胞功能障碍。 目的1：研究SIRT 6在异染色质中沉默着丝粒重复卫星DNA元件的分子机制。着丝粒异染色质的缺陷在衰老和癌症的背景下都可以观察到。我们将描述SIRT 6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提供见解，其中SIRT 6损失可能有助于癌症进展，以及为人类体细胞提供见解，其中SIRT 6可以防止细胞衰老或表观遗传可塑性的年龄依赖性下降。在目标2中，我们将描述SIRT 6对细胞稳态的异染色质维持的功能作用。我们将测试的假设，异染色质损失在着丝粒触发异常有丝分裂，染色体分离缺陷，和细胞衰老，并可以促进细胞永生化的致癌过程。我们还将研究SIRT 6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下降，有助于衰老和疾病。 在目标3中，我们将研究SIRT 6在异染色质维持中的作用，该异染色质维持在另一类在衰老和癌症中失调的重复DNA元件-内源性逆转录转座元件。我们将探讨这些元件的沉默受损是否会导致影响细胞功能的基因组不稳定性，或导致衰老相关基因的异常转录。 总之，这些研究应该提供深入了解衰老生物学的基本染色质机制。

 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.