Regulation of a novel epigenome of protein biosynthesis genes

 描述(由申请人提供)： DNA模板化的细胞过程需要改变染色质结构，以动态地促进对包装DNA的访问。组蛋白的翻译后化学修饰是直接或通过招募效应蛋白改变染色质结构的关键机制之一。我们在酵母中发现了一个新的组蛋白激酶复合体，它含有保守的S相复制起始蛋白CDC7及其激活蛋白Dbf4，以及一些额外的因子。我们发现该复合体将苏氨酸45(H3T45)上的组蛋白H3磷酸化。该位点位于一个关键位置，DNA在这里与核小体入口点和出口点的组蛋白八聚体接触。因此，该位点的修饰有可能极大地改变DNA与组蛋白的接触，为DNA的解缠提供途径。令人惊讶的是，全基因组研究表明，H3T45的磷酸化不仅发生在预期的DNA复制起点，而且还标志着对细胞生长重要的特定基因的启动子。此外，我们发现CDC7在物理上与目标启动子结合，并且是这些位置的RNA聚合酶招募和完全转录所必需的。这个提议的目的是检验我们的假设，即CDC7-Dbf4复合体建立了一种表观基因组状态，在这种状态下，在有利的营养条件下，修改的染色质结构促进了强劲的转录，从而驱动细胞的生长和增殖。此外，我们将测试一个模型，该模型提出，修饰或随后的核小体重塑，通过改变潜在抑制物复合体的染色质结合动力学来调节启动子的活性。如果我们的假设是正确的，我们将确定H3T45残基是核小体的守门人，调节转录目标位置的DNA可及性。重要的是，我们将发现一个新的调控网络，通过它来协调基因表达，以确保伴随细胞增殖而来的必要的细胞生长。尤其重要的是，CDC7和Dbf4在多种癌症中被错误调控，它们的上调表明无复发生存率较低。由于不受控制的细胞生长、分裂和DNA复制与癌细胞的增殖有关，我们预计这种表观基因组标记功能的保存将提供疾病状态的生物标记物，并将为癌症治疗提供一个高度独特的靶点。

 DESCRIPTION (provided by applicant): DNA templated cellular processes require alteration of chromatin structure to dynamically facilitate access to packaged DNA. The post-translational chemical modification of histone proteins is one critical mechanism that alters chromatin structure either directly or via the recruitment of effector proteins. We have identified a novel histone kinase complex in yeast containing the conserved S-phase replication initiation kinase Cdc7, its activating protein Dbf4, and a number of additional factors. We have found that this complex phosphorylates histone H3 on threonine 45 (H3T45). The site lies at a critical location, where DNA contacts the histone octamer at the entry and exit points of the nucleosome. Therefore, modification of this site has the potential to dramatically alter DNA-histone contacts, providing access for the unwrapping of DNA. Surprisingly, genome- wide studies reveal that H3T45 phosphorylation occurs not only at the expected origins of DNA replication, but it also marks the promoters of specific genes important for cell growth. Furthermore, we find that Cdc7 physically associates with target promoters and is required for RNA polymerase recruitment and full transcription at these locations. The goals of this proposal are to test our hypothesis that the Cdc7-Dbf4 complex establishes an epigenomic state, where under favorable nutritional conditions, the modified chromatin architecture facilitates robust transcription that drives cell growth and proliferation. Furthermore, we will test a model that proposes that the modification, or subsequent nucleosome remodeling, regulates promoter activity via altering the chromatin-binding dynamics of a potential repressor complex. If our hypothesis is correct we will have identified the H3T45 residue as a gatekeeper of the nucleosome, regulating DNA accessibility at target locations for transcription. Importantly, we will have uncovered a novel regulatory network by which gene expression is coordinated to ensure the necessary cell growth that accompanies cell proliferation. Of particular importance, Cdc7 and Dbf4 are misregulated in a variety of cancers and their upregulation is indicative of lower relapse-free survival. As uncontrolled cell growth, division and DNA replication are associated with the proliferation of cancer cells we anticipate that conservation of function of this epigenomic mark will provide a biomarker of diseased states and will offer a highly unique target for cancer therapeutics.