De facto Target of Histone Deacetylase Inhibitors

总结/摘要 表观遗传重塑越来越被认为是致癌的驱动因素，也是治疗癌症的有希望的药物靶点。 癌症治疗组蛋白去乙酰化酶抑制剂（HDIs）是最突出的表观遗传药物之一， 在500多个针对各种癌症的临床试验中进行了测试，其中两种化合物已经获得批准。尽管他们 抗癌功效普遍，其作用机制尚不清楚。目前认为，通过抑制 组蛋白去乙酰化酶（HDAC），HDIs改变参与细胞生长或存活基因的表达。然而，基因 HDI处理的细胞的表达谱揭示了不同HDI之间的最小变化和不同模式。 许多HDAC，包括HDAC 1、2、3、6及其相关的转录辅调节因子，已被证明是 作为肿瘤抑制剂。关于HDIs如何工作，显然存在知识空白。我们最近的发现 挑战当前对HDIs的看法。我们发现肝脏特异性敲除HDAC 3上调了脂肪生成靶点， 基因和导致肝脂肪变性，这两者都可以通过HDAC 3的酶死亡突变体来拯救。我们 进一步发现HDIs不上调靶基因，尽管引起组蛋白乙酰化过度。等 酶活性和HDAC功能之间的分离质疑HDAC是否是HDI的事实上的靶， 特别是考虑到HDAC 3负责IIa类HDAC（HDAC 4、5、7和10）的酶活性， 9)其不具有固有催化活性。HDACs作为癌基因的观点也与其肿瘤 视网膜母细胞瘤蛋白和雌激素/雄激素受体信号通路的抑制作用。HDIs是 设计用于螯合HDACs催化口袋中的锌离子3，因此可以靶向数百种其他 锌依赖性金属蛋白。我们假设非HDAC蛋白是HDI的事实上的靶点， 抗癌功效我们将通过确定HDAC酶活性是否是 细胞对HDI的反应;表征HDI相互作用的非HDAC蛋白在 HDIs;并确定HDAC酶活性在肝癌发生和肝脏对HDIs的反应中的作用， vivo.我们的假设如果被证明是正确的，将是一个概念上的进步，将彻底改变我们的发展战略 这些很有前途的抗癌药物。我们的研究还直接测试了“组蛋白密码”假说， 在哺乳动物中的规模是前所未有的，并将在表观遗传学和基因转录领域产生广泛的影响 调控

SUMMARY/ABSTRACT Epigenetic remodeling is increasingly recognized as a driver of carcinogenesis and a promising drug target for cancer therapy. Histone deacetylase inhibitors (HDIs) are among the most prominent epigenetic drugs being tested in over 500 clinical trials against a variety of cancers with two compounds already approved. Despite their universal anticancer efficacy, their mechanism of action is not clear. It is currently assumed that, by inhibiting histone deacetylase (HDAC), HDIs alter expression of genes involved in cell growth or survival. However, gene expression profiling of HDI-treated cells revealed minimal changes and distinct patterns among different HDIs. Many HDACs, including HDAC1, 2, 3, 6, and their associated transcriptional coregulators, have been shown to function as tumor suppressors. There is clearly a gap of knowledge on how HDIs work. Our recent findings challenge the current view of HDIs. We found that liver-specific knockout of HDAC3 upregulates lipogenic target genes and causes hepatic steatosis, both of which can be rescued by enzyme-dead mutants of HDAC3. We further found that HDIs do not upregulate target genes despite causing histone hyperacetylation. Such dissociation between enzyme activity and HDAC function questions whether HDAC is de facto target of HDI, especially considering that HDAC3 is responsible for the enzyme activity of class IIa HDACs (HDAC4, 5, 7, and 9) that do not possess intrinsic catalytic activity. The view of HDACs as oncogene is also at odds with their tumor suppressor role in retinoblastoma protein and estrogen/androgen receptor signaling pathways. HDIs are designed to chelate the zinc ion in the catalytic pocket of HDACs3, and therefore could target hundreds of other zinc-dependent metalloproteins. We hypothesize that non-HDAC proteins are de facto targets of HDI for its anticancer efficacy. We will tests the hypothesis by determining whether HDAC enzymatic activity is required for cellular response to HDIs; characterizing the role of HDI-interacting non-HDAC proteins in anticancer effects of HDIs; and determining the role HDAC enzymatic activity in liver carcinogenesis and hepatic response to HDIs in vivo. Our hypothesis, if proven correct, is a conceptual advance that will revolutionize our strategy in development of these promising anticancer drugs. Our study also directly tests the ‘histone code’ hypothesis on an unprecedented scale in mammals, and will have broad impact in the field of epigenetics and gene transcriptional regulation.