Chromatin Regulation by Mammalian SIRT7 in Aging and Disease

描述(由申请人提供)： Sirtuin酶家族的成员是影响人类健康和疾病的基因组稳定性、应激反应和代谢程序的重要调节者。SIRT6和SIRT7是密切相关的哺乳动物sirtuins，调节基本的核过程。这些酶催化染色质上高度选择性的组蛋白去乙酰化反应，从而从特定的赖氨酸残基上去除重要的乙酰基标记。适当地调节组蛋白在染色质上的乙酰化模式对于建立控制基因表达、DNA修复和DNA复制等过程的特殊染色质状态至关重要。因此，当SIRT6或SIRT7失活时，组蛋白乙酰化模式的失调会在细胞和整个生物体水平上产生病理后果。事实上，SIRT6具有许多与衰老、新陈代谢和癌症相关的功能。相比之下，人们对SIRT7的了解要少得多。我们最近发现SIRT7是一种高度选择性的H3K18Ac(乙酰化组蛋白H3赖氨酸18)脱乙酰酶，在调节致癌转化程序和肿瘤形成中发挥关键作用。现在，我们的初步研究为SIRT7在细胞代谢过程中的其他表观遗传功能提供了证据，该过程对癌症和脂肪肝疾病都有影响。本提案旨在阐明SIRT7在这些过程中的作用和机制。此外，我们的初步数据显示，SIRT7的特异性底物H3K18Ac也可以被SIRT6脱乙酰化。我们将询问在特定的基因组和生理环境中，H3K18Ac的脱乙酰基在SIRT6和SIRT7之间是如何协调的，以及这些sirtuins是否提供了补偿机制，以保护缺陷的H3K18Ac脱乙酰基的病理后果。在目标1中，我们将阐明SIRT7在肿瘤转化和肿瘤通路中的新作用和机制。我们将利用遗传和生化策略，研究SIRT7和致癌Myc转录因子之间的新联系，以调控癌细胞的翻译能力，增殖， 和生存。此外，我们还将询问SIRT7是否会影响原代细胞在培养中的致癌转化效率和小鼠的总体肿瘤易感性。在目标2中，我们将描述SIRT7在预防脂肪肝疾病中的作用和机制。在人类中，这种疾病非常普遍，容易导致肝功能衰竭和癌症。然而，人们对其潜在机制知之甚少。我们将结合分子、基因组和细胞方法与SIRT7突变小鼠的研究，以探讨SIRT7影响脂肪肝发病的分子机制。越来越多的证据表明内质网(ER)应激与脂肪肝的发生和发展有关。我们将验证SIRT7通过减弱内质网应激的致病效应以及通过直接调节参与脂质代谢的基因的表达来预防脂肪肝的假设。在目标3中，我们将研究SIRT6和SIRT7在H3K18Ac动态平衡和癌细胞生物学中的功能相互作用和重叠。我们将使用新产生的系统来同时灭活这两种酶，使用双RNAi策略和双突变小鼠，并分析基因组、细胞和整个生物体的表型。总之，这些研究应该阐明人类生理和疾病中的基本染色质机制，以及SIRT6和SIRT7作为治疗靶点的潜力。

DESCRIPTION (provided by applicant): Members of the Sirtuin family of enzymes are important regulators of genomic stability, stress responses, and metabolic programs that impact on human health and disease. SIRT6 and SIRT7 are closely related mammalian sirtuins that regulate fundamental nuclear processes. These enzymes catalyze highly selective histone deacetylation reactions at chromatin, whereby important acetyl marks are removed from specific lysine residues. Proper regulation of histone acetylation patterns at chromatin is essential for establishing specialized chromatin states that control processes such as gene expression, DNA repair, and DNA replication. Dysregulation of histone acetylation patterns, as occurs when SIRT6 or SIRT7 are inactivated, can therefore have pathological consequences at the cellular and whole organism levels. Indeed, SIRT6 has numerous demonstrated functions relevant for aging, metabolism, and cancer. By contrast, much less is understood about SIRT7. We recently showed that SIRT7 is a highly selective H3K18Ac (acetylated histone H3 lysine 18) deacetylase that plays a pivotal role in modulating oncogenic transformation programs and tumor formation. Now, our preliminary studies provide evidence for additional epigenetic functions of SIRT7 in cellular metabolic processes that impact on both cancer and fatty liver disease. This proposal aims to elucidate the role and mechanisms of SIRT7 in these processes. In addition, our preliminary data reveal that the specific substrate of SIRT7, H3K18Ac, can also be deacetylated by SIRT6. We will ask how deacetylation of H3K18Ac is coordinated between SIRT6 and SIRT7 in specific genomic and physiologic settings, and whether these sirtuins provide compensatory mechanisms that protect against pathological consequences of defective H3K18Ac deacetylation. In Aim 1, we will elucidate novel roles and mechanisms of SIRT7 in oncogenic transformation and cancer pathways. We will use genetic and biochemical strategies to study a new link between SIRT7 and the oncogenic Myc transcription factor in regulating cancer cell translational capacity, proliferation, and survival. In addition, we will ask whether SIRT7 influences the efficiency of oncogenic transformation of primary cells in culture and overall tumor susceptibility in mice. In Aim 2, we will characterize the role and mechanisms of SIRT7 in preventing fatty liver disease. In humans, this disease is highly prevalent and predisposes to liver failure and cancer. However, its underlying mechanisms are poorly understood. We will combine molecular, genomic, and cellular approaches with studies of SIRT7 mutant mice to investigate the molecular mechanisms through which SIRT7 influence fatty liver disease pathogenesis. Growing evidence implicates endoplasmic reticulum (ER) stress in the development and progression of fatty liver disease. We will test the hypothesis that SIRT7 prevents fatty liver disease by attenuating the pathogenic effects of ER stress, as well as by directly regulating the expression of genes involved in lipid metabolism. In Aim 3, we will examine the functional interplay and overlap between SIRT6 and SIRT7 in H3K18Ac homeostasis and cancer cell biology. We will employ newly generated systems to inactivate both enzymes simultaneously, using double RNAi strategies and double mutant mice, and assay genomic, cellular and whole organism phenotypes. Together, these studies should elucidate fundamental chromatin mechanisms in human physiology and disease and the potential of SIRT6 and SIRT7 as therapeutic targets.