FDH: A Novel Determinant of Tumor Suppression

该提案的总体目标是表征新的肿瘤抑制活性， 一种关键的代谢酶，并确定转化代谢效应的机制 来调节增殖。10-甲酰四氢叶酸脱氢酶 不可逆地转化10-甲酰四氢叶酸，一种从头嘌呤的必需底物 生物合成，四氢叶酸。通过消耗这种底物，FDH可以限制 嘌呤生物合成这会干扰DNA/RNA生物合成和DNA修复。 由于这一关键的代谢功能，癌细胞中FDH的下调将 支持生存事实上，我们初步观察到外佣 在肿瘤中通过启动子 超甲基化我们进一步证明了在正常人中适度的FDH表达， FDH缺陷型癌细胞诱导凋亡性细胞死亡。相反，非癌细胞 对高水平的酶不敏感。因此，有人提出，癌细胞 沉默FDH基因以逃避细胞毒性。表型效应的研究 在缺乏FDH的肿瘤细胞中正常FDH表达的再激活进一步 探索JNK 1/2和p53作为FDH诱导的凋亡信号传导的关键组分， 确定DHFR和叶酸补充作为增殖拯救因子。 重要的是，一种新的途径连接FDH，通过细胞内叶酸调节， 控制细胞的运动。目前的建议扩展了以前的研究， FDH和相关叶酸的抗增殖机制直接与p53相互作用 并评价其在小鼠模型中的体内作用。我们的核心假设是， 通过启动子甲基化下调是基因表达调控的重要手段之一。 恶性肿瘤细胞比正常细胞获得促存活优势。我们进一步建议 外佣是透过多种机制发挥其调节作用。具体目标是 探讨这些机制和验证我们的假设是：（1）调查功能 FDH与胞浆中p53抑癌蛋白相互作用(2)确定 使用FDH缺陷小鼠，FDH沉默对肿瘤起始/进展影响 模型研究FDH在癌细胞存活/叶酸诱导中的关键作用 在疾病发作时的压力，将提供重要的洞察恶性 这一过程本身，并将关键代谢途径的失调与癌症疾病联系起来， 为恶性转化的诊断建立新的目标。

The overall goal of this proposal is to characterize the novel tumor suppressor activity of a key metabolic enzyme and determine the mechanisms transforming metabolic effects into regulation of proliferation. FDH (10-formyltetrahydrofolate dehydrogenase) irreversibly converts 10-formyltetrahydrofolate, an essential substrate for de novo purine biosynthesis, to tetrahydrofolate. Through depletion of this substrate, FDH can restrict purine biosynthesis. This interferes with DNA/RNA biosynthesis and DNA repair. Because of this critical metabolic function, down-regulation of FDH in cancer cells would be pro-survival. Indeed, we have initially made the important observation that FDH is strongly and ubiquitously down-regulated in tumors through the promoter hypermethylation. We have further demonstrated that moderate FDH expression in FDH-deficient cancer cells induces apoptotic cell death. In contrast, non-cancer cells are insensitive to high levels of the enzyme. Therefore, it is proposed that cancer cells silence the FDH gene in order to escape cytotoxicity. Studies of phenotypic effects upon reactivation of normal FDH expression in FDH-deficient tumor cells have further explored JNK1/2 and p53 as key components of FDH-induced apoptotic signaling, and determined DHFR and folate supplementation as proliferation rescue factors. Importantly, a novel pathway linking FDH, through intracellular folate regulation, to control of cell motility, was discovered. The current proposal extends previous studies of antiproliferative mechanisms of FDH, and related folates, to direct interaction with p53 and evaluation of its role in vivo in mouse model. Our central hypothesis is that FDH down-regulation through promoter hypermethylation is one of the important means by which malignancies gain pro-survival advantage over normal cells. We further suggest that FDH exerts its regulatory effects through multiple mechanisms. The Specific Aims to probe these mechanisms and test our hypothesis are: (1) Investigate the functional interaction of FDH with p53 tumor suppressor protein in cytoplasm. (2) Determine the impact of FDH silencing on tumor initiation/progression using FDH deficient mouse model. Investigation of the critical role of FDH, in cancer cell survival/induction of folate stress at the onset of the disease, will provide important insight into the malignant process itself and link deregulation of key metabolic pathways to cancer disease, as well as establish new targets for diagnostics of the malignant transformation.