Cancer Susceptibility and S Phase Initiation Sites

描述（由申请人提供）：基因缺失和序列突变是评估肿瘤病因和进展时通常考虑的机制。在过去的几十年里，这个话题已经被广泛地研究过。同样，以染色体数量和结构改变为表现的遗传不稳定性也是癌症发展的一个典型特征，一直是研究的重点。最近人们认识到，许多癌症表现出与基因突变不一致的基因表达改变。这些变化被认为与这些基因启动子的DNA甲基化改变以及这些启动子位点的组蛋白修饰有关。在确定能够解释后一种癌症相关变化的机制方面所做的努力要少得多。在这个项目中，我们试图了解可以解释癌变过程中非印迹基因等位基因从同步复制到非同步复制的转变机制。虽然我们知道，这种复制时间的变化可以导致在许多类型的癌症中看到的基因表达的改变，但负责复制时间保存的确切机制尚不清楚。其他人和我们发现DNA复制和转录通常在基因启动子和相关CpG岛内或附近启动。在这个项目中，我们试图更好地定义在转录启动子上发现的DNA复制起源功能所需的基本基因组元件。我们还提出了以下问题：起始点激活时间的差异是否对应于起始点激活所需的特定因子结合时间的差异？在正常的人类细胞中是否存在减缓或暂停DNA复制分叉进程的位点？这些位点是否参与了DNA复制相邻起始点激活时间顺序的调控？为了深入了解这些机制并回答这些问题，我们提出以下建议

DESCRIPTION (provided by applicant): Deletions and sequence mutations of genes are the mechanisms typically considered when evaluating the etiology and progression of neoplasia. This topic has been extensively examined over the past several decades. Likewise, genetic instability as manifested by development of numerical and structural alterations of chromosomes is also a typical feature of cancer development that has been the subject of intense study. More recently it has been recognized that many cancers manifest alterations in gene expression that are not coincident with gene mutations. These changes are thought to be associated with alterations of DNA methylation in the promoter of these genes and by histone modifications at the sites of these promoters. There have been far fewer efforts to identify the mechanisms that can explain these latter types of cancer-related changes. In this project we seek to understand mechanisms that can explain the transition of alleles of non-imprinted genes from synchronous to non-synchronous replication timing in carcinogenesis. While it is known that such shifts in replication timing can lead to the alterations in gene expression seen in many types of cancers, the exact mechanisms responsible for the conservation of replication timing are not known. Others and we found that both DNA replication and transcription are often initiated in or near the gene promoter and associated CpG island. In this project we seek to better define the essential genomic elements required for the function of DNA replication origins found at transcriptional promoters. We also pose the following questions: Do differences in origin firing times correspond to differences in the binding time of specific factors necessary for origin activation? Are there sites in normal human cells that slow or pause the progression of DNA replication forks? Are such sites involved in the regulation of the order of activation time of adjacent origins of DNA replication? To gain insights into these mechanisms and answer these questions we propose the following Specific Aims. Specific Aim 1: Characterize genetic elements necessary for activity of the HPRT origin of replication. Specific Aim 2: Analyze binding of the pre-replication complex at the HPRT and G6PD origins of replication on the active and the inactive X chromosome in female human cells. Specific Aim 3: Analyze the architecture of replication and potential fork progression barriers in an early replicated region of the human genome.