Infidelity of Cytosine Methylation and Human Cancer

描述（由申请人提供）：新出现的数据表明，人类癌症的发展是一个多步骤的过程，不仅受到遗传损伤的驱动，而且还受到表观遗传变化的驱动。表观遗传信号的扰动可导致肿瘤抑制基因表达的缺失或癌基因表达的不适当。表观遗传控制的分子基础涉及CpG二核苷酸和选择性结合甲基化DNA序列的蛋白质中胞嘧啶残基的酶甲基化，启动一系列相互作用的蛋白质，改变局部染色质结构和转录活性。虽然人类肿瘤中的表观遗传扰动每天都在增加，但表观遗传信号在肿瘤发展中被打乱的机制在很大程度上尚未被探索。在最初的资助阶段，我们发现炎症损伤引起的氧化损伤和卤化可能导致DNA甲基化的丧失。这种竞争性更新应用的重点是探索机制，即halopy嘧啶可以改变表观遗传信号。

DESCRIPTION (provided by applicant): Emerging data suggests that the development of cancer in man is a multi-step process driven by not only genetic damage but also epigenetic changes. Perturbations in epigenetic signals can result in the loss of tumor suppressor expression or inappropriate oncogene expression. The molecular basis of epigenetic control involves the enzymatic methylation of cytosine residues in CpG dinucleotides and proteins that selectively bind to methylated DNA sequences, initiating a cascade of interacting proteins that alter local chromatin structure and transcriptional activity. While the list of epigenetic perturbations in human tumors grows daily, the mechanisms by which epigenetic signals become scrambled in tumor development are largely unexplored. In the initial funding period, we discovered that oxidative damage and halogenation arising from inflammatory damage could result in loss of DNA methylation. This competing renewal application focuses on exploration of the mechanisms whereby halopyrimidines could alter epigenetic signals. In the five aims of the current application, we propose to 1) further map critical contact points between methyl-binding proteins and their DNA-binding sites with nucleoside analogs and purified methyl-binding proteins in gel electrophoretic mobility shift assays, 2) examine the structure, dynamics and coding potential of 5-chlorocytosine (5CIC) and 5-chlorouracil (5CIU)-containing oligonucleotides using high field isotope edited NMR and polymerase extension assays, 3) examine the reactivity of cytosine residues in a CpG dinucleotide toward chlorination reactions using a recently developed mass-tagging assay, 4) examine the capacity of 5-chlorpyrimidines to direct methylase-mediated methylation or to inhibit methylation, and 5) to examine the capacity of 5CIC residues to inhibit transcription and induce heritable epigenetic changes in mammalian cells. This proposal's results will likely shed important new light on mechanisms by which DNA damage could result in heritable epigenetic alterations critical in the development of many human tumors.